Indications

IO infusion is indicated for conditions requiring the rapid acquisition of intravenous (IV) access, where the establishment of conventional peripheral access is difficult or impossible: cardiopulmonary arrest, shock, burns, and status epilepticus. In these situations, limited attempts at standard peripheral access are usually made prior to placing an IO needle. In addition to its use in the hospital, IO access has been used successfully in the prehospital setting as well as in critical care transport.

The success rate for acquiring IO access is high—greater than 95% with experienced practitioners. Similar success rates and equivalent pharmacokinetics have been demonstrated when mechanical IO devices are used. ^, Most fluids and medications that can be given through a conventional IV line can be administered as an IO infusion with comparable results. In the setting of cardiac arrest or severe shock, IO access is as effective as peripheral venous access in providing volume resuscitation and antibiotics to the central circulation. However, three antibiotics—chloramphenicol, vancomycin, and tobramycin—achieve subtherapeutic levels when administered via an IO line at standard IV doses.

Additional details regarding laboratory studies obtained from IO versus IV samples are discussed on ExpertConsult.com .

Comparison of laboratory studies obtained from intraosseous versus intravenous samples

IO access can be used for certain clinical laboratory studies. Specimens should be collected promptly after access is established—ideally, after aspirating 1 to 2 mL of waste blood and prior to any medications being given. Bicarbonate, partial pressure of carbon dioxide (P co ₂ ), and partial pressure of oxygen (P o ₂ ) can differ significantly between IO and venous specimens, whereas pH and base excess correlate well, as well as lactic acid. Ionized calcium levels may correlate, but the data are inconsistent. ^, No significant differences were found with glucose, blood urea nitrogen, creatinine, hemoglobin, and hematocrit when comparing IO specimens and venous blood samples. IO sodium concentrations are lower; however, the difference does not appear clinically relevant. IO potassium levels are significantly higher than venous specimens and are invalid; treating these levels poses the risk of inducing iatrogenic hypokalemia. ^, Leukocytes and platelet counts are unreliable from IO specimens. In general, when comparing IO and venous or arterial sources, there are correlations and clinical similarities in laboratory values. However, caution should be exercised with their interpretation, as the evidence is relatively weak. In contrast, a marrow specimen can be cultured in lieu of a blood culture and can be used for blood type and crossmatching. ^,

Contraindications

IO infusion has few absolute contraindications. A fractured or previously punctured bone should not be used, as infusing fluid will extravasate and potentially cause compartment syndrome. Therefore, if an IO needle penetrates the cortex but is nonfunctional, alternative bone sites must be used for subsequent attempts. Bone diseases such as osteogenesis imperfecta and osteopetrosis have been suggested as contraindications to IO infusion. Placing the needle into an area of cellulitis or burn risks seeding infection and causing osteomyelitis. This is a relative contraindication, as limited sites may be available, making these less desirable locations acceptable for use.

Supplies and equipment

The bone marrow space is accessed with the use of one of several different types of needles. Conventional bone marrow needles (e.g., the Jamshidi needle, Becton Dickinson) and IO infusion needles (e.g., the Cook intraosseous infusion needle, Cook Medical) can be used by manual insertion. Usually, a 15- or 18-gauge needle is chosen, with the latter being used in infants. If these are not available, lumbar puncture needles can be used; however, they bend easily. ^, In neonates, a 19- or 21-gauge butterfly needle can be used. Needles with a stylet are preferred to prevent clogging of the needle with bony particulate.

Three mechanical devices appropriate for pediatric patients have been introduced: the Bone Injection Gun (BIG, PerSys Medical), New Intraosseous (NIO, PerSys Medical), and the EZ-IO (Teleflex; Fig. 14.1 ). The BIG and NIO are spring-loaded devices, whereas the EZ-IO is a small, battery-powered drill. These devices penetrate the bone marrow more quickly and are used more frequently than the manual method in many settings, including prehospital. ^, Finally, the FASTResponder (Pyng Medical), a specialized sternal injection gun, is used primarily in the adult population but has been cleared for use in adolescents who are 12 years of age and older in the United States, Canada, and most of Europe.

EZ-IO battery-powered drill.

(Courtesy Vidacare Corporation.)

Other equipment required for IO needle placement and infusion include antiseptic solution (chlorhexidine or povidone-iodine), sterile gloves and drapes, a syringe with saline or heparinized saline flush, a T-connector or stopcock, IV fluid and tubing, and IO dressing components (gauze and tape) and/or securement device. Optional supplies include a syringe for laboratory specimen collection, towel or IV bag for extremity stabilization, pressure bag, and materials for local anesthesia (syringe with 25-gauge needle and 1% lidocaine).

Technique

The IO needle can be placed into the bone marrow at one of several sites: the proximal tibia, distal femur, distal tibia, proximal humerus, iliac crest, and sternum. In preparation for IO insertion, the selected body site needs to be stabilized. In an extremity, this can be achieved by placing a towel or IV bag underneath it. Additionally, the operator’s nondominant hand is used to stabilize the extremity. However, it is essential to ensure that the hand is clear of the area behind the insertion site to minimize the risk of needlestick injury. The anatomic landmarks and intended insertion site should be identified, and the overlying skin prepped with an antiseptic solution. If the patient is conscious, topical anesthesia is indicated.

The proximal tibia is the most commonly used location for IO access. In children, the insertion site is located on the tibial plateau, approximately 1 cm medial and 1 to 2 cm distal to the tibial tuberosity. In young children, this location offers the thinnest cortex while having the highest vascular content in the area and avoids injury to the proximal epiphyseal plate. For adolescents and adults, the insertion site is 2 cm medial and 1 cm proximal to the tibial tuberosity ( Fig. 14.2 ). Accessing the midshaft increases the risk for fracture.

Insertion of the intraosseous needle into the anterior tibia.

To obtain IO access in the distal femur, the needle should be positioned in the midline, approximately 2 to 3 cm proximal to the patella. In the distal tibia, the needle is placed 1 cm proximal to the medial malleolus, midway between the anterior and posterior surfaces. The distal tibia may be easier to access in older children (>6 years), as the proximal tibial cortex has become thicker. Although it is less preferred, the distal fibula can also be accessed 1 cm above the lateral malleolus. For the proximal humerus, the patient’s hand is positioned on the abdomen with the elbow adducted; the insertion site is the greater tubercle, 1 to 2 cm proximal to the surgical neck of the humerus. The anterior superior iliac spine is the insertion site for IO access on the iliac crest.

The sternum has historically been an access point used by the military in combat. More recently, sternal IOs have been developed for use in civilians, including adolescents and adults. A needle is injected a set depth into the manubrium using an injection gun. It can provide effective access, even while cardiopulmonary resuscitation (CPR) is in progress. However, CPR must be paused for placement—ideally, during a pulse and rhythm check. Sternal IO lines should be avoided in infants and children due to the risk for cardiac or major vessel puncture as well as inadequate drug delivery due to the small sternal marrow cavity.

IO needles can be placed manually or using mechanical devices. With manual needles, the needle insertion angle is controversial: some suggest inserting the needle at a 60- to 75-degree angle away from the epiphyseal plate of long bones, while others recommend using a 90-degree angle to prevent the needle from sliding along the bone. The needle is advanced using firm pressure and a twisting motion until a “give” (loss of resistance) is felt, indicating entry into the marrow space. The bony cortex, which thickens with age, requires considerable force to penetrate. The stylet is removed, and a syringe is attached to the needle in an attempt to aspirate marrow.

Correct placement of the needle should always be confirmed to avoid complications such as extravasation. There are several ways to confirm that the needle is correctly placed: (1) aspiration of bloody fluid; (2) observation that the needle stands upright in the bone without support; (3) lack of resistance when saline solution is infused; and (4) absence of noticeable swelling of the soft tissues or extravasation of fluid. Sometimes marrow cannot be aspirated even if the needle is correctly placed; in that case, one must rely on the other means of confirmation.

Placement of IO needles with mechanical devices has success rates equal to or higher than manual methods, with the added benefit of ease of use and less risk to the user. ^, However, the high cost of this equipment may be a limitation, especially in small facilities or resource-limited settings. In children, prehospital providers prefer the IO drill to the spring-loaded injection gun. ^, The appropriate mechanical device is selected based on age/weight of the patient and the intended IO insertion site. The EZ-IO is approved for use in patients who weigh greater than or equal to 3 kg; the appropriate needle length is chosen based on weight, site, and presence of excessive tissue. Operators should ensure that at least 5 mm of the catheter remain visible outside of the skin. Longer needles may be considered in obese patients. where the tibial tuberosity is not palpable and body mass index exceeds 43. This device is approved for pediatric use in the proximal tibia, distal femur, distal tibia, and proximal humerus. In contrast, the BIG Pediatric and NIO-Pediatric (NIO-P) are intended for use only in the proximal tibia, with the former cleared for use in term neonates to children 12 years of age and the latter in children 3 to 12 years of age. Respective adult versions can be used for patients older than 12 years.

Detailed instructions for use of mechanical IO insertion devices are discussed on ExpertConsult.com .

Maintenance

Once correct placement of the needle is confirmed and secured, fluids and medication can be administered with a syringe via a stopcock or T-connector, or a standard IV infusion set can be connected to the needle. The site should be observed visually and by palpation for signs of extravasation immediately after placement and every 5 to 10 minutes during use. If evidence of extravasation is observed, the needle should be removed to avoid compartment syndrome. To remove, while holding the hub of the catheter (or needle) itself or attaching a Luer-Lok syringe, traction is applied while rotating the catheter clockwise, pulling it out of the bone without bending or rocking. Following pressure hemostasis, a dressing is applied using aseptic technique.

IO access is intended only for short-term use in emergency resuscitative situations; long-term use increases the risk of extravasation, compartment syndrome, and infection. ^, Therefore, once IO access is secured, efforts should be directed toward obtaining definitive IV access. Once alternative access is obtained, the IO needle should be removed.

Complications

Significant complications of IO insertion and infusion are rare. The most common complication is extravasation of fluid. The causes of extravasation include incomplete penetration of the bony cortex, movement of the needle such that the hole is larger than the needle, dislodgment of the needle, penetration of the posterior cortex, and leakage of fluid through another hole in the bone, such as a previous IO site or fracture. Extravasation of a small amount of fluid is usually not problematic. However, with larger volumes, compartment syndrome can develop, which may require fasciotomy and even amputation. Use of the IO line for prolonged periods or with pressure bags increases the risk for this complication. If extravasation occurs, the needle should be removed and the extremity diligently observed for signs of compartment syndrome. Experience to date suggests that the complications of the new mechanical insertion devices are similar to manual IO needle use.

Other rare complications include infection and bone fracture. Osteomyelitis, cellulitis, and sepsis have been reported in conjunction with IO infusion. ^, Risk for infection is increased when IO access is prolonged, and these devices are used in patients with bacteremia.

Summary

IO infusion is a valuable means of obtaining temporary emergency vascular access in the critically ill infant or child, as it has a high success rate. Using appropriate technique and vigilantly monitoring the insertion site for extravasation can usually prevent complications.

Indications

There are several indications for an arterial catheter:

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  Need for continuous invasive blood pressure measurements to assess the patient’s hemodynamic status and allow for timely assessment of interventions aimed at improving hemodynamics, such as fluid administration and titration of vasoactive infusions.

  
  
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  Need for frequent sampling of arterial blood for laboratory analysis. Access to arterial blood through an indwelling catheter eases the task of obtaining blood samples painlessly. Catheter-derived arterial samples also eliminate skewing of results caused by physiologic changes related to the stress and discomfort of vascular puncture. Most notably, an indwelling arterial catheter allows for frequent assessment of arterial blood gas measurements, thereby providing the most accurate information on a patient’s acid-base status as well as measurement of partial pressure of arterial oxygen.

  
  
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  Need for continuous monitoring of cerebral perfusion pressure in patients with traumatic brain injury or other causes of increased intracranial pressure (see Chapter 60 ).

  
  
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  Need for arterial access to facilitate therapeutic procedures, such as exchange transfusions and continuous arteriovenous hemodiafiltration.

Contraindications

Few absolute contraindications for placement of arterial catheters exist. The skin at the site of arterial access must be intact prior to insertion of a catheter. Evidence of infection of the skin or underlying structures is a contraindication to catheter placement at that site. Other disruptions in skin integrity, such as burns, are relative contraindications. Severe coagulopathy and systemic anticoagulation increase the risk of hemorrhage from unsuccessful arterial punctures during attempted arterial catheter placement and from the site of arterial catheter insertion. These risks must be weighed against the potential benefits of improved monitoring when facing the decision of whether to place an arterial catheter in this patient population.

A catheter should not be placed in an extremity with compromised perfusion. Evidence of adequate collateral circulation is desirable prior to placement of an arterial catheter. The traditional means of assessing collateral circulation to the hand is the Allen test. The radial and ulnar arteries are compressed until the distal extremity is blanched. Pressure over one artery is then released; capillary refill should return to the distal extremity within 5 seconds. The test is repeated, releasing pressure from the other contributing artery. A normal Allen test does not guarantee adequate collateral circulation, and an abnormal test does not necessarily indicate that complications will occur. Additionally, the Allen test is considered less reliable for patients in shock. It is common for arterial catheters to be placed without assessing collateral circulation in emergent circumstances.

Procedure

Supplies and equipment required for arterial catheterization are listed in eBox 14.1 .

Technique

The initial step in placing an arterial catheter is site selection. The radial, posterior tibial, and dorsalis pedis arteries are optimal sites owing to easy accessibility and typically good collateral circulation. Placement of the catheter in distal arteries of the extremities also allows for ease of site observation and hemorrhage control with direct pressure. Preductal placement in the right radial artery is preferred in infants with ductal-dependent cardiac lesions.

Catheters also can be placed in the axillary or femoral arteries if no peripheral sites are suitable. Insertion of a catheter into the axillary artery is more difficult technically than the other sites mentioned and is associated with a risk of brachial plexus injury due to hematoma compressing the neurovascular bundle. Many physicians have been reluctant to place arterial catheters for long-term use into the femoral artery—particularly in infants and young children—for fear of complications, most notably severe ischemia of the limb. A retrospective study of 234 pediatric burn patients who underwent 745 femoral artery catheterizations revealed a 1.1% rate of loss of distal pulse; limb ischemia was associated with younger age, smaller patient size, and increased severity of the burn injury. Patients who suffered limb ischemia were managed with immediate catheter removal and systemic heparinization. Three underwent thrombectomy, with one requiring amputation of a digit. Traditionally, it is taught that the brachial arteries should not be used for arterial catheters because of the lack of collateral blood flow and risk of distal extremity ischemia. In a review of arterial catheter placements performed at a pediatric cardiac surgical center, 386 brachial artery catheters were placed in infants weighing 20 kg or less with no report of permanent ischemic damage and only three with temporary perfusion loss. Despite these results, the complete lack of collateral circulation at the brachial artery requires careful consideration of risks and benefits before placement of a brachial artery catheter. Additionally, the superficial temporal arteries should not be used owing to poor collateral flow and the potential for retrograde flow, which could result in showering of emboli into the cerebral circulation.

Next, the selected site must be properly immobilized prior to placement of the indwelling catheter. If placing a radial artery catheter, the wrist is hyperextended 30 degrees to develop a straighter course and more superficial position of the radial artery. Typically, the radial pulse is best palpated in a position just proximal to the wrist crease. The technique for radial arterial catheter placement has been summarized in the “Videos in Clinical Medicine” series in the New England Journal of Medicine .

The intended site for arterial catheter placement requires preparation with an aseptic solution and draping of sterile towels. Infiltration of lidocaine (1% without epinephrine) should be considered in most patients unless infiltration will obscure landmarks or the patient is deeply sedated. Alternatively, a topical anesthetic cream can be used for local anesthesia. Systemic narcotics or anxiolytics may be administered but demands caution in patients who are not receiving mechanical ventilation.

Percutaneous placement of the catheter can be accomplished using one of several techniques. In the over-the-needle technique, similar to placement of a peripheral IV catheter, the needle is inserted through the skin at a 30-degree angle. When a flash of blood is obtained in the hub, advance the needle another 1 to 2 mm. Holding the needle steadily, the catheter is advanced over the needle into the lumen of the vessel. Blood should flow continuously into the catheter hub prior to attempting to advance the catheter. Once the catheter is inserted through the skin to the hub, pressure is applied over the artery proximal to the catheter and a flushed Luer-Lok connector is attached to the hub. Correct placement of the catheter is verified by easily aspirating arterial blood into a syringe. The catheter is then flushed and secured with suture or tape. A chlorhexidine-impregnated patch is usually placed at the site of catheter insertion (to decrease catheter-associated bloodstream infections), and an occlusive dressing with a transparent adhesive film is applied over the catheter as a protective barrier.

The second percutaneous technique, transfixation, involves using the over-the-needle technique; however, when a flash of blood is seen in the hub, the needle and catheter are advanced further, through the posterior wall of the artery transfixing the vessel to the underlying structures. The needle is removed, leaving the catheter in place. The catheter is then slowly withdrawn until the tip is again intraluminal with blood flowing into the hub. The catheter is then advanced into the artery to its hub. Catheter advancement can be facilitated by attaching a Luer-Lok connecter with a heparinized flush-filled syringe on it and gently flushing as the catheter is advanced.

The final and most successful percutaneous method for catheter placement in critically ill patients involves the use of the Seldinger technique. A needle is used to pierce the anterior wall of the artery. When arterial blood return is seen, a guidewire is placed through the introducer needle. The wire should meet little to no resistance. If resistance is met, the wire is retracted and pulsatile blood flow is assured at the hub of the needle. The depth or angle of the needle may need to be adjusted if blood is not flowing. If the guidewire glides in easily on insertion, it is advanced into the lumen of the vessel, the needle removed, and the catheter threaded over the guidewire into the arterial lumen. This method can also be used with the over-the-needle catheter technique. Improved success rates and shorter time to insertion characterize pediatric arterial catheters placed using a guidewire compared with no wire guide. However, an adult study found no difference in success rate or insertion times between the two groups.

Ultrasound-assisted placement of arterial catheters is becoming increasingly popular (see Chapter 15 ). Ultrasound guidance significantly increases the first attempt success rate of radial arterial cannulation and decreases hematoma complication rates compared with the palpation or Doppler technique. Studies have also demonstrated decreased time to insertion and decreased number of attempts at catheter placement using ultrasound-guided techniques. However, in the hands of physicians who are inexperienced in performing arterial cannulations via ultrasound guidance (yet proficient in traditional methods), no difference in success rates was observed between the ultrasound-assisted and palpation-based techniques. The study shed light on the importance of experience and frequent practice in the use of ultrasound-guided arterial cannulation to develop competency.

A cutdown approach serves as an alternative if percutaneous attempts are unsuccessful. A superficial incision of the skin is made perpendicular to the artery. The subcutaneous tissues are bluntly dissected parallel to the vessel using a hemostat. When the artery is identified, the posterior wall is gently dissected away from the adjacent structures. Two loops are placed around the vessel, one proximal and one distal. These loops are used to elevate the artery during cannulation; they should never be used to tie off the vessel. The artery is then cannulated under direct visualization using the over-the-needle technique. The catheter is secured with a suture through the skin, and the wound is closed with interrupted sutures. If excessive bleeding persists, gentle traction can be applied to the proximal loop in an attempt to control the hemorrhage.

Maintenance of an arterial catheter

To prolong the patency of an arterial catheter, heparinized fluid is most commonly infused through the catheter. A common practice is to infuse 0.9% sodium chloride containing heparin 1 U/mL at 3 mL/h; slower infusion rates may be used in small infants requiring fluid restriction. There is conflicting literature supporting the use of heparin to positively impact patency and mitigate the risk of thrombus formation in peripheral arterial catheters. ^, More recent adult studies call into question the benefit of heparin and spotlight the need for more rigorous clinical investigation. ^, However, these studies do not take into account the smaller vessel size and prolonged monitoring common in critically ill children. A randomized controlled trial demonstrated that the addition of papaverine (120 mg/L) to routine arterial catheter fluids significantly lowered the rate of catheter failure. This study recommended avoiding the use of papaverine in neonates owing to a perceived increase in risk of intraventricular hemorrhage. However, a more recent study of neonates 25 to 36 weeks’ gestational age did not confirm this concern. Despite these results, some institutions routinely avoid the use of papaverine in arterial catheter fluids in preterm neonates and patients with traumatic brain injury or other preexisting intracranial hemorrhage.

Arterial catheters should always be visible so that any bleeding around the catheter site or inadvertent disconnection of the tubing from the catheter can be immediately identified to avoid significant hemorrhage. Securing the catheter with suture and using Luer-Lok connectors decrease the possibility of accidental detachment. The site of catheter insertion should be closely monitored for signs of infection or compromised perfusion. Mottling of the skin proximal or distal to the catheter may be indicative of intraarterial thrombus formation, and discoloration of fingers or toes distal to a catheter may result from emboli. If these complications occur, the catheter must be removed. Children with femoral artery catheters are at a higher risk of thrombus formation, particularly newborns and children with low body weight, low cardiac output, and elevated hematocrit.

Transducing an arterial catheter is performed by placing the transducer at the level of the right atrium and zeroing to atmospheric pressure for accurate measurements. Studies in animal models have demonstrated that positioning the transducer to be level with the aortic root results in accurate measurement of mean arterial pressure (MAP) regardless of position or catheter site. This is in contrast to the significant error in MAP measurement that occurs when the transducer is level with the catheter tip. Arterial fluids and tubing are currently recommended to be changed every 96 hours. The overlying dressing is also changed on a scheduled basis and any time it becomes soiled or nonocclusive.

Inability to draw blood from a catheter or flattening of the waveform on the monitor is suggestive of either a kinked catheter or thrombus formation at the end of the catheter. If no evidence of compromised perfusion is present distal to the catheter, the catheter may be exchanged over a guidewire. However, strong consideration should be given to removing the existing catheter and placing a new arterial catheter at a different site, as exchanging a catheter over a guidewire has been associated with an increased risk of catheter-related bloodstream infection (CRBSI) in central venous catheters.

Complications

Complications related to arterial catheters include hemorrhage, thrombus formation, emboli, distal ischemia, and infection. Permanent ischemic complications related to radial artery catheters in adult patients are rare. A multi-institutional diagnostic code database study demonstrated that 10.3% of patients with arterial catheters also had a code associated with infection or inflammation, and 7.5% had a thrombotic- or embolic-associated complication code. These complications were more common in younger children and longer hospitalizations. An uncommon but well-recognized complication of arterial catheter placement is growth arrest due to physeal injury from extravasation, aneurysm formation, or ischemia.

Catheter-related infections can be local or systemic. The risk of catheter-related infection was previously thought to be lower for arterial catheters than for central venous catheters. However, a meta-analysis indicated that arterial catheters are an underrecognized source of CRBSI. Risks for an arterial catheter infection are related to the duration of catheter use and catheter placement in the femoral artery. The presence of an arterial catheter has been noted to be a risk for CRBSI, but it has been suggested that a positive culture is more likely to be a surrogate marker for greater illness severity. Nevertheless, an arterial catheter should be considered a potential source of sepsis, and strong consideration should be given to removing an arterial catheter when it is no longer needed for optimal care.

Summary

Arterial catheters are an important way to monitor hemodynamics and gain valuable laboratory data in order to proactively provide interventions and manage critically ill children. The potential risks and benefits of arterial catheter placement should be weighed carefully prior to performing the procedure. Rigorous studies investigating the complications associated with arterial catheterization are lacking for critically ill children; thus, further study is needed.

Indications and contraindications

Indications for CVCs include the following:

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  Need for reliable and durable venous access

  
  
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  Lack of or inadequate peripheral venous access

  
  
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  Administration of vasoactive infusions, total parenteral nutrition, and medications that require central venous delivery

  
  
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  Need for frequent blood sampling

  
  
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  Monitoring of central venous pressure and central venous oxygen saturation

  
  
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  Provision of access for extracorporeal support modalities, such as continuous renal replacement therapy and apheresis

Contraindications to central access are not absolute and are primarily related to specific CVC placement sites. In the presence of coagulopathy or systemic anticoagulation, operators should consider avoiding sites where bleeding may be difficult to control (e.g., subclavian vein). Generally, CVC insertion sites with intravascular hardware (e.g., pacemaker, ventriculoatrial shunt, hemodialysis catheter) or adjacent to permanent hardware (e.g., cerebral ventricular shunt catheters subcutaneously tunneled along the neck) should be avoided owing to risks of infection, hardware puncture, and venous stasis. CVCs placed at a time of bacteremia will likely become colonized with the pathogen. Catheters should not be inserted through overtly infected skin. In traumatic brain injury management, it is reasonable to abstain from CVC placement in the neck vessels to avoid obstruction of jugular venous drainage from the brain and exacerbating intracranial hypertension. The relative risks and benefits of CVC placement should be carefully weighed prior to each procedure.

Technique

Critically ill pediatric patients range greatly in size. Being aware of vessel dimensions as well as the proximity and anatomic relation of the respective artery to the vein are important in central vein cannulation. Central vein diameters vary across the pediatric age groups ( eTable 14.1 ); based on this measurement, an appropriately sized catheter should be selected for CVC placement. These catheters are commonly made of a plastic polymer and available in a variety of diameters, lengths, and number of lumens. CVCs are often packaged with the introducer needle, guidewire, and tissue dilator that correspond to the selected catheter diameter and length.

Maximal sterile barrier precautions should be used whenever a CVC is placed in the pediatric intensive care unit (PICU). This includes mask, cap, sterile gown and gloves, and sterile full-body drape. ^, Additionally, the following should be performed: thorough hand hygiene (which may involve the use of surgical antiseptic handwash or scrub brush), skin preparation at the insertion site using chlorhexidine antiseptic solution (covering an extensive area and allowing adequate dry time), and creation of a large sterile field with sterile drapes and towels to cover the patient’s entire body and bed (in order to minimize the risk of inadvertent contamination of sterile equipment and surfaces). Chlorhexidine is superior to povidone-iodine for skin disinfection. ^, Adequate sedation and analgesia along with local anesthesia should be used to provide patient comfort during the procedure. Patient movement will also be minimized, diminishing the risk of sterile field disruption and allowing the procedure to be performed more easily and safely. Adherence to CVC insertion and maintenance bundles will minimize the risk of CRBSI.

Most CVCs employed in the PICU are placed using the Seldinger technique, in which the clinician places an introducer needle into the desired vein while aspirating with a slip tip syringe. When the lumen of the needle is fully within the vein lumen, blood freely flows into the syringe. The needle is held in place with the nondominant hand while the syringe is disconnected with the other hand. Blood should continue to passively flow from the needle hub but not be pulsatile. A J-tipped guidewire is inserted into the open hub of the needle and advanced into the vein with little to no resistance ( Fig. 14.3 ). If resistance is felt, further advancement of the wire should be avoided. Adjusting the needle position by slightly altering its depth or changing the angle of entry may facilitate guidewire insertion. If there continues to be resistance, the wire is carefully withdrawn, and the syringe is reattached to the needle in order to reidentify the vein’s lumen. If the wire is not easily retracted, the needle and wire should be removed as a unit, reducing the risk of breaking the wire.

Seldinger technique. (A) Guidewire is placed through the introducer needle into the lumen of the vein. (B) Catheter is advanced into the vein lumen along the guidewire. (C) Wings of the catheter are secured to the skin with suture.

Once the guidewire is well within the lumen of the vein, a small nick in the skin adjacent to the needle is made using a No. 11-blade scalpel, enlarging the puncture site to more easily accommodate the dilator and catheter. The introducer needle is carefully withdrawn along the wire, maintaining control of the wire at all times either by holding it directly or intermittently using a sterile hemostat to clamp the end of the wire to ensure that it is not lost into the patient or onto the floor. A dilator is advanced along the wire and then twisted through the puncture site, dilating the tissue planes that lead to the lumen of the vessel; the vein itself should not be dilated. Following withdrawal of the dilator, the catheter is advanced into position over the wire (see Fig. 14.3 ). The guidewire is removed, leaving the catheter in place. Blood should be easily aspirated from each lumen; then, the lumens should be completely cleared of blood by flushing with sterile heparinized saline to reduce the chance of clot formation.

Several systems for securing the catheter are commercially available, but it may also be secured with suture. A large loop of suture is placed in the skin, attached through the wings of the catheter, and tied down. The suture should be taut, preventing catheter movement without causing skin necrosis within the loop of suture. A chlorhexidine-impregnated patch can be applied and a transparent adhesive film placed over the catheter, creating an occlusive dressing.

Internal jugular vein cannulation

Multiple approaches can be used to cannulate the internal jugular vein. The patient is placed supine in slight Trendelenburg position. A roll of bed linen is placed under the shoulders to extend the neck, and the face is turned to the contralateral side. Most commonly, the middle approach is used, in which the introducer needle enters the skin at a 30-degree angle at the apex of the triangle formed by the clavicle and the heads of the sternocleidomastoid muscle and is directed toward the ipsilateral nipple ( Fig. 14.4 A). For the anterior approach, the introducer needle enters the skin along the anterior margin of the sternocleidomastoid halfway between the mastoid process and the sternum and is directed at the ipsilateral nipple ( Fig. 14.4 B). Using the posterior approach, the needle enters the skin along the posterior border of the sternocleidomastoid halfway between the mastoid process and the clavicle and is directed toward the suprasternal notch ( Fig. 14.4 C).

Approaches to the internal jugular vein. The patient is supine, in slight Trendelenburg position, with the neck extended over a shoulder roll and the head rotated to the contralateral side. (A) Middle approach: The introducer needle enters the skin at a 30-degree angle at the apex of the triangle formed by the heads of the sternocleidomastoid muscle and clavicle, directing it toward the ipsilateral nipple. (B) Anterior approach: The carotid pulse is palpated and may be slightly retracted medially. The introducer needle enters along the anterior margin of the sternocleidomastoid, about halfway between the suprasternal notch and mastoid process, while being directed toward the ipsilateral nipple. (C) Posterior approach: The introducer needle enters at the posterior margin of the sternocleidomastoid, just superior to where the external jugular vein crosses, and is directed under its heads toward the suprasternal notch.

Subclavian vein cannulation

Following Trendelenburg positioning of the supine patient, a narrow cloth roll is placed beneath the patient, between the scapulae. The introducer needle enters the skin inferior to the junction of the middle and lateral thirds of the clavicle and is directed toward the suprasternal notch. The needle passes along the inferior surface of the clavicle until it enters the subclavian vein ( Fig. 14.5 ).

Approach to the subclavian vein. The patient is supine, in slight Trendelenburg position, with a small roll along the spine between the shoulders. The needle enters the skin at the junction of the lateral and middle thirds of the inferior clavicle and is directed toward the suprasternal notch, passing along the inferior edge of the clavicle.

Femoral vein cannulation

Following flat or slight reverse Trendelenburg positioning of the supine patient, a towel is placed under the hips to slightly raise them, to enhance exposure of the inguinal crease insertion site. The leg is abducted and externally rotated. The arterial pulse is palpated just distal to the inguinal ligament, halfway between the anterior iliac crest and the pubic symphysis. The femoral vein is approximately 5 mm medial to the artery in infants and toddlers and 1 cm in adolescents and adults. The introducer needle enters the skin 1 to 2 cm distal to the inguinal ligament at a 30-degree angle in line with the course of the vein and parallel to the axis of the thigh ( Fig. 14.6 ).

Approach to the femoral vein. The patient is flat and supine, with the thigh slightly abducted and externally rotated. The introducer needle enters the skin 1 to 2 cm distal to the inguinal ligament and 0.5 to 1 cm medial to the pulse of the femoral artery.

Use of ultrasound for central venous line placement

Ultrasonography has been increasingly used to facilitate the placement of CVCs in the PICU. Anatomic variation of the central veins is not uncommon, reported in 7% to 18% of pediatric patients, and can make cannulation more difficult using landmarks alone. ^, Bedside ultrasonography offers direct visualization of the vessel before and during the intervention. Use of ultrasound reduces insertion-related complications in children and CVC placement success rates are improved with the use of ultrasound. As familiarity with real-time ultrasound guidance is improving, novel techniques, including subclavian access, are successfully being implemented in pediatrics. Routine use of real-time ultrasound guidance for CVC placement is recommended and reflects best practice, particularly for internal jugular catheterization (see Chapter 15 ).

Complications

CRBSI is the most common complication related to CVCs (see Chapter 109 ). In children, the location of the insertion site is not related to infection risk. The risk of infection is decreased by the use of a bundle of practices during insertion and ongoing maintenance of the CVC. The insertion bundle includes strict maximal sterile barrier precautions and aseptic technique. Dressing changes with chlorhexidine skin prep, minimizing catheter access, and daily assessment of the need of the catheter are all recommended as a part of CVC maintenance. Antimicrobial-impregnated catheters may decrease the risk of catheter-related infection, but more pediatric studies are needed.

Pneumothorax may result if the lung is punctured during jugular or subclavian vein CVC placement. This complication is less likely with careful patient positioning, attention to anatomic landmarks, and real-time use of ultrasonography as the introducer needle is advanced. Chest radiography should be performed after these approaches are attempted to document absence of pneumothorax and verify CVC position.

Thrombosis may occur in the vessel surrounding the catheter and is associated with malignancies and diabetic ketoacidosis. ^, Ectopy may ensue when the guidewire or catheter, positioned too deeply, stimulates the right heart. Prompt retraction of the guidewire or catheter typically resolves the ectopic arrhythmia.

Bleeding at the skin puncture site from an inadvertent arterial puncture is usually controlled by direct pressure. However, hemorrhage can be difficult to control and may be potentially life-threatening if there is injury to deeper vascular structures or when coagulopathy is present. Veins and arteries may be perforated far from the intended puncture site by the introducer needle, guidewire, dilator, or catheter. Injury to the femoral or iliac vessels may result in pelvic or retroperitoneal bleeding. Lacerations of the jugular, subclavian, or innominate veins or superior vena cava may result in hemothorax. Bleeding complications are more severe in the presence of a coagulopathy or thrombocytopenia. If possible, these should be treated before and/or during central vein access attempts. ^,

A CVC positioned where it applies pressure to the wall of a vessel or the heart increases the risk of perforation, which can lead to acute blood loss. Cardiac tamponade can occur when the catheter perforates within the pericardial reflection. Undesirable positioning of a central venous line can be detected radiographically and should be corrected as soon as possible. ^,

Ultrasound-assisted peripheral venous access

Ultrasound-assisted peripheral venous access is increasingly used for challenging venous access situations given the availability of point-of-care ultrasound in critical care settings. Ultrasound facilitates visualization of deeper veins that may not be readily found using inspection and palpation and can be used as a dynamic technique to guide catheter placement in real time. This technique requires operator training and experience—like most procedures, its success improves with increasing operator experience. Studies comparing the success of this technique to conventional peripheral venous access have yielded mixed results.

Venous cutdown

With the widespread use of central venous access and IO access during emergencies, venous cutdown is rarely performed. Venous cutdown is indicated when percutaneous access is not achievable and the need for IV access warrants a more invasive approach. Materials needed depend on the technique used for vein cannulation. As with percutaneous CVC placement, the skin should be prepped and draped, and aseptic technique should be used. A skin incision is made perpendicular to the vein. The tissue surrounding the vein is bluntly dissected to completely expose the vein. Ligatures are passed around the vein, distal and proximal to the intended site of cannulation. A small venotomy is created; using the ligatures to control the vein, a catheter is directly passed into the lumen of the vein. The distal ligature can be tightened to control bleeding, while the proximal ligature helps secure the catheter ( Fig. 14.7 ). Alternatively, an over-the-needle IV catheter can be directly introduced into the exposed vein without venotomy. Finally, the Seldinger technique can be used, in which an introducer needle and guidewire are inserted into the lumen of the exposed vein, followed by catheter placement over the wire. This approach is particularly useful for femoral venous cutdown. After the catheter is in place, it is secured with suture, and the wound is closed around the catheter.

Venous cutdown.

The complications of venous cutdown are similar to those seen in other venous access techniques. There is a risk of bleeding from the open wound, especially in patients with coagulopathy or systemic anticoagulation. The open wound also increases the risk of infection. Injury to adjacent structures, such as arteries and nerves, during incision and blunt dissection is another risk with cutdown. ^{, ,}

Supplies and equipment

Prepackaged umbilical catheter insertion trays are commercially available and contain different sizes of catheters. The 3.5 Fr and 5 Fr are the most frequently used catheters. ^, Umbilical catheters are typically made of polyvinylchloride and have a single end hole, as side hole catheters have been linked with higher incidence of thrombosis. ^, Umbilical catheters are available as single or multiple lumens. A single lumen can be used in either vessel, whereas a double- or triple-lumen catheter is used exclusively in the umbilical vein. More than one lumen allows the administration of incompatible fluids. A 3.5 Fr catheter is used for infants weighing <1500 g, and a 5 Fr catheter is used for larger infants. ^,

Technique

The infant is kept in a supine position by using soft restraints of the arms and legs or via a swaddling technique. A catheter is prepared for insertion by connecting to a Luer-Lok stopcock and flushing with saline, with or without heparin. The umbilical stump and surrounding skin are thoroughly cleansed with 2% chlorhexidine or povidone-iodine. ^, The antiseptic agent is allowed to dry and is then removed with sterile saline. The area is draped, sparing the head and chest to allow for appropriate patient monitoring. A cord tie is applied around the umbilical stump. Using a scalpel, the cord is horizontally cut 1 to 2 cm above the umbilical ring. The larger, single thin-walled umbilical vein is typically located at the 12 o’clock position, whereas the two thick-walled generally constricted umbilical arteries are identified at the 5 and 7 o’clock positions. A single umbilical artery is sometimes isolated and can be a normal variation. ^,

Umbilical arterial cannulation

Once the umbilical artery is identified, the iris forceps is used to gently dilate the arterial lumen by first inserting the forceps in the closed position and subsequently allowing both prongs to spring open and dilate the lumen. ^, The catheter is introduced 0.5 cm in the lumen of the vessel. ^, Thereafter, the umbilical cord is pulled toward the infant’s head before further advancing the catheter. The direction of the catheter advancement is caudal. The catheter enters the umbilical artery, passes through the right internal iliac artery, the right common iliac artery, and, finally, the descending aorta. Resistance to catheter advancement is occasionally encountered secondary to vasospasm, at the junction of the umbilical artery and fascial plane, or at the level of the bladder. Gentle pressure can be applied. Sometimes, the catheter can cross the wall of the umbilical artery, creating a false lumen. A double-catheter technique can then be attempted. The first misdirected catheter follows a path of least resistance. A second catheter is also used to bypass this pathway and then enters the aorta. If this technique fails, the second umbilical artery is cannulated. The patency of the catheter is verified by easy blood aspiration and flushing. The catheter is sutured in place, using a purse string stitch cinched tightly to provide hemostasis and wrapping both ends of the suture around the catheter before tying a square knot. The line is further secured using a tape bridge or other available stabilization device. The umbilical tie is loosened and kept in place for any needed hemostasis. A transducer can be attached for continuous blood pressure monitoring while still allowing blood sampling.

Two lengths of UAC insertion are described in the literature. Low or high placement of the catheter is based on the vertebral level at which the catheter tip resides in the aorta. ^, Low placement is defined as the catheter tip caudal to the origins of the renal arteries, whereas a high placement is described as the catheter tip in the descending aorta above the diaphragm and below the left subclavian artery. ^, A Cochrane review evaluated the effects of the position of UACs and concluded that high-placed catheters led to fewer clinical vascular complications. Although reference charts based on patient morphometrics are available, there are simple formulas that predict the depth of insertion of arterial catheter. Shukla’s regression equation based on birth weight (BW) predicts UAC insertion length (cm) as (3 × BW (kg) + 9) for infants weighing 1500 g or more, whereas Wright’s formula (4 × BW [kg] + 7) results in more accurate UAC placement (cm) for infants weighing less than 1500 g. ^,

Umbilical venous cannulation

Once the umbilical vein is identified, a catheter is introduced carefully in the lumen. The umbilical vein does not always require routine dilation prior to the introduction of the catheter. ^{, ,} The umbilical cord is gently pulled toward the feet during placement to straighten the course of the vein. The direction of the catheter advancement is cephalad. A properly placed UVC resides at the inferior vena cava–right atrial junction via the umbilical vein and the ductus venosus. Sometimes, the catheter is misdirected into the portal, splenic, or mesenteric vein. If there is resistance to insertion or poor blood return, inappropriate position of the catheter should be suspected. The double-catheter technique, described in the UAC section, can also be used in UVC placement. The patency of the catheter is then verified by adequate blood return and flushing. The line is secured using the same technique described for UACs.

The length of inserted catheter is determined by the size of the infant and indication for placement. ^{, ,} In emergency situations, the catheter is advanced to a depth where rapid blood return is achieved (2–4 cm in most infants). A long-term UVC resides at the junction of the inferior vena cava and right atrium. The two most commonly used methods to predict accurate depth of UVC are nomograms based on the measurement of the shoulder-umbilicus length and regressions equations based on BW. ^, Shukla’s formula, ([3 × BW (kg) + 9]/2) + 1, is widely used to estimate the length of UVC insertion (cm). Verheij suggested that Shukla’s formula leads to overinsertion of catheters and recommended a revised formula, (3 × BW [kg] + 9)/2.

Proper placement of umbilical arterial and venous catheters

Anteroposterior and lateral views of a thoracoabdominal radiograph are required to confirm proper placement of the catheters. Low UAC placement correlates with the third and fourth lumbar vertebrae on chest film, whereas a high placement correlates with the sixth and tenth thoracic vertebrae. UVC tip should be positioned at or just above the diaphragm or between the eighth to tenth vertebrae. Several studies have questioned the optimal diagnostic approach to determine the correct position of the umbilical catheters. Questions were raised on the difficulty of relating anatomic structures to the projection of vertebral bodies on radiographs secondary to the variability of these structures in relation to bony landmarks. Bedside ultrasonography is suggested as a better modality for verifying the position of the umbilical catheters. However, the disadvantage of this technique is the constant need for qualified personnel to perform the study at the time of the catheter’s placement. Owing to this limitation, most centers still rely on radiography to assess catheter position.

Maintenance

Infants are typically placed in the supine position or on their sides. A dressing should not be applied to the umbilicus so that the catheter insertion site can be easily inspected. ^{, ,} The UVC is maintained as part of a closed system to prevent air embolism. A continuous infusion is needed to keep the lumen of the UAC clear, and the catheter is flushed after blood draws to minimize clot formation. Continuous fluid infusion containing heparin is needed in the arterial line. The composition of the heparin-containing fluid varies by institution and is influenced by gestational age and electrolyte status. A typical infusion includes 38 to 77 mEq/L sodium chloride or sodium acetate or an isotonic amino acid solution with heparin 1 U/mL. ^,

Removal

Umbilical catheters are removed one at a time. Each catheter is pulled to approximately 5 cm, then the catheter is slowly withdrawn in increments of 1 cm/min. This process is especially important during the removal of UACs because it allows the artery to spasm and provide hemostasis. If bleeding occurs, pressure is applied by elevating and pinching the skin just above the cord for venous bleeding or below the cord for arterial bleeding. A hemostat can also be used to pinch the lumen of the vessel for persistent bleeding. ^,

Complications

Umbilical venous and arterial cannulations are associated with potential complications. These complications are related to placement and malposition of the catheters or prolonged catheter placement in the umbilical vessel.

Summary

Umbilical lines are commonly used in the care of severely ill neonates. The use of UACs for blood collection and blood pressure monitoring and the use of UVCs for nutrition or medications have become commonplace in NICUs and can also be used in the PICU. Although there are several benefits to their use, umbilical catheters are associated with potential problems. An awareness of the possible complications is important to minimize serious consequences and provide timely interventions.

Pulmonary artery catheterization

Pulmonary artery catheter (PAC) monitoring was introduced into practice in 1970 by Swan and Ganz (see Chapters 26 , 27 , and 30 ). However, because of the invasiveness of the procedure and lack of a proven survival benefit for patient management, other less invasive surrogate techniques have significantly decreased the use of the PAC.

Placement of the catheter can be performed at the bedside, but skill and experience in the placement, management, and data acquisition are required to avoid complications and for proper interpretation of the hemodynamic data. Most catheters are balloon tipped and flow directed. They are able to measure right atrial, pulmonary artery, and pulmonary capillary wedge pressures as well as determine cardiac output and oxygen saturations in the right heart chambers. Single-lumen catheters may be placed directly into the pulmonary artery at the time of cardiac surgery. Both techniques are used in pediatric patients, but the single-lumen catheter is most frequently employed because of the frequency of pulmonary hypertension complicating the postoperative management of pediatric cardiac patients. The flow-directed, balloon-tipped catheter is usually placed in the ICU to assist in determining the etiology of shock, pulmonary edema, and pulmonary hypertension, as well as to help guide fluid and vasoactive-inotropic therapy over time.

The PAC should not be used for the routine care of ICU patients, but it may be useful in heart failure patients with persistent symptoms despite standard measures, in patients undergoing heart transplantation evaluation, and for patients with pulmonary hypertension. ^, Pulmonary hypertension may either be primary or secondary, the latter including pulmonary hypertension in postoperative congenital cardiac patients. These patients are prone to wide swings in pulmonary artery (PA) pressures associated with variations in oxygenation, ventilation, and sedation level. When inhaled nitric oxide is used to manage postoperative pulmonary hypertension, direct measurement of PA pressure helps guide titration of therapy. In patients with severe respiratory failure requiring high positive airway pressure with associated hemodynamic compromise, PACs may facilitate diagnosis of low cardiac output and direct therapy. When D o ₂ in such patients is significantly limited because of hypoxemia, low cardiac output, or both, measurement of D o ₂ using variables derived from information provided by the catheter may be useful. In children with severe shock unresponsive to fluid resuscitation and requiring vasoactive-inotropic infusions, the PAC may better define the hemodynamic profile, thus directing more specific therapy.

Significant controversy exists regarding the benefits and potential harms caused by this invasive form of hemodynamic monitoring. An older multicenter observational study reported increased mortality with PACs. Subsequently, several randomized clinical trials failed to demonstrate a benefit to PAC-guided therapy. Some studies reported an association with increased morbidity and mortality, whereas others did not find differences with or without PACs. No studies in children have demonstrated better outcomes with the use of the PAC monitoring.

Multiple barriers exist to PAC use, including patient risk with placement, the ability to measure similar variables via less invasive measures, increased cost, inaccurate measurement leading to misuse of PAC-derived variables, and incorrect interpretation and clinical application. Additionally, with the decreased use of this technology, the skill required to maintain competency in placement and interpretation of the data provided presents a significant challenge to many institutions.

Contraindications

There are no specific contraindications to placement of a PAC, but there are several relative contraindications, including bleeding diathesis, which increases the risk for percutaneous access, and severe tricuspid or pulmonary insufficiency, which can make bedside catheter placement prohibitively difficult. Unstable cardiac arrhythmias that are easily triggered by catheter manipulation are also a relative contraindication. Catheter placement for measurement of cardiac output using the thermodilution technique is contraindicated in the presence of intracardiac shunts, tricuspid insufficiency, or pulmonary insufficiency, as the thermodilution measurement will be inaccurate.

Procedure and equipment

Balloon-tipped, flow-directed catheters are available with two diameters, 5 Fr and 7 Fr. The 5 Fr diameter catheter is most appropriate for patients weighing less than 15 kg; the 7 Fr diameter catheter is best for patients weighing more than 15 kg. Some PACs employ fiberoptic spectrophotometry for continuous measurement of mixed venous oxygen saturation. Single-lumen PACs are most commonly placed in the operating room at the time of heart surgery.

The standard PAC is 1 m long. The PAC is equipped with proximal and distal ports facilitating measurement of intravascular pressures, infusion of vasoactive agents, fluids, and blood sampling. The distance between the proximal and distal lumen ports varies depending on the catheter: standards are 10, 15, 20, and 30 cm. Choosing the catheter with the correct lumen distances is crucial in order to monitor the appropriate pressure. At the tip are a thermistor used to calculate cardiac output and a balloon that may be inflated and deflated as necessary. Some catheters have an additional right ventricular port for temporary pacemaker insertion, and some have the fiberoptic oxygen saturation sensor for continuous measurement of mixed venous oxygen saturation. Other necessary pieces of equipment are a monitor with cardiac output capability or a computer to determine cardiac output using thermodilution and compatible pressure transducers. Carbon dioxide is used in some centers to inflate the balloon to minimize the risk of air embolization, although room air is most commonly used. The catheters are placed through a percutaneous introducer sheath, which is placed with the same technique as described for CVCs.

Before placement, the catheter should be flushed and filled with fluid through which intravascular pressures are transmitted to a transducer. The equipment is then zeroed to atmospheric pressure at the level of the patient’s left atrium (midaxillary line, fourth intercostal space) and calibrated. If all air bubbles are not removed from the tubing, they may result in damping of the waveform tracing and, consequently, erroneously low systolic pressure. Thrombus at the tip of the catheter may also alter the waveform (see also Chapter 26 ).

The insertion site is prepared in sterile fashion with chlorhexidine solution and draped with sterile towels. It is important to drape a wide area with sterile sheets (full field barrier drape) in order to avoid exposure of the catheter, because of the length of the PAC. The PAC is inserted through the introducer sheath. A sterile sleeve is placed on the end of the sheath, and the catheter is passed through the sleeve, then through the introducer diaphragm and into the sheath.

Anatomically, the preferred sites of insertion are the right internal jugular, left subclavian, right subclavian, and left internal jugular veins. Usually, the placement of the catheter is guided by pressure waveform monitoring, but fluoroscopic visualization will occasionally be needed, particularly if the PAC is placed from a femoral site. Once the catheter tip enters the venous circulation, the balloon is inflated with air. From this point, the catheter should be advanced with the balloon inflated to prevent damage to the myocardium, cardiac valves, or pulmonary artery branches. If the catheter is withdrawn, the balloon must first be deflated to avoid valvular injury.

The catheter is advanced to the right atrium (RA), then across the tricuspid valve into the right ventricle (RV), and across the pulmonary valve into the PA. As the catheter continues to float with the balloon inflated, it will wedge in a branch PA, occluding the blood flow. The pulmonary artery occlusion pressure (PAOP), or pulmonary artery wedge pressure (PAWP), will be recorded from the distal lumen. If the balloon is deflated, a PA pressure tracing will be recorded. If the waveforms are not obtained, the balloon should be deflated, and the catheter pulled back to the RA before attempting placement again.

After insertion, a chest radiograph is obtained to ensure proper catheter placement and rule out pneumothorax. The catheter tip should be visualized within West zone III of the lung ideally (see Chapters 26 , 42 , and 43 ).

The pressure waveforms are characteristic; when the catheter is advanced to the RA, the atrial trace has a respiratory variation that helps to confirm that the catheter is in the thorax. Once in the atrium, the balloon is inflated and advanced to the RV, where the trace is characterized by a rapid upstroke in early systole with an equally rapid downstroke at the end of systole and diastolic pressure near zero. Turning the catheter with a clockwise motion usually helps in advancing the PAC. The catheter is advanced to the PA. The PA trace has the same peak systolic pressure of the RV, but as systole ends, the trace shows a slower fall that continues through diastole, because the diastolic pressure in the PA is higher than the RV diastolic pressure. Once in the PA, the catheter is advanced slightly until a pulmonary wedge trace is seen. This trace is similar to the RA trace, although usually with a higher pressure. PAWP is obtained when the balloon is inflated and the catheter floats into the wedge position. Because the catheter floats to an area of greatest blood flow in the lung, it most likely will be in an area consistent with West zone III, where arterial pressure is higher than both venous and alveolar pressures.

Measurement of PAWP is best done at end expiration to minimize the effect of changes in pleural pressure. Once the wedge is measured and the balloon is deflated, the PA trace should return. If the trace does not change, the catheter should be retracted until the PA trace is seen. The catheter should not be left inflated in the wedge position because of the risk of pulmonary infarction. The catheter is appropriately positioned when the PA pressure trace is present when the balloon is not inflated and the pulmonary capillary wedge trace is present when the balloon is inflated. Once it has been confirmed that the PAC is in good position by pressure trace and radiography, the catheter should be secured in the sleeve and taped to the patient.

PAC information acquisition and interpretation is detailed on ExpertConsult.com and in Chapter 26 .

Pulmonary artery catheter information acquisition and interpretation

Much hemodynamic and D o ₂ information can be obtained from the Swan-Ganz–type PAC. Multiple hemodynamic pressures can be obtained, including RA, RV PA, and PAWP. RA pressure is useful for determining preload of the RV. Pulmonary artery pressure is useful for determining the presence of pulmonary hypertension both at baseline and with manipulation of oxygenation, ventilation, ventilator pressures, inhaled nitric oxide, and other procedures. PAWP reflects left ventricular preload. In most patients with normal cardiac function and anatomy, right atrial or central venous pressure adequately reflects LV preload as well. However, in the presence of certain congenital heart defects, with significant ventricular dysfunction, or with high mechanical ventilatory pressures, a significant discrepancy may exist between right and left ventricular preload. In such circumstances, measurement of PAWP may be useful for guiding fluid and inotropic therapy.

Mixed venous oxygen saturation (Sv o ₂ ) can be determined directly and continuously with a catheter containing the fiberoptic oximeter. In the absence of the oximeter, intermittent blood sampling from the distal port when in place in the PA allows for Sv o ₂ measurement.

The thermistor at the tip of the catheter allows for measurement of cardiac output using the thermodilution method. This method uses the Fick principle, based on the law of conservation of thermal energy. A specific amount of known temperature fluid is injected in the proximal port (upstream), and the temperature change downstream (at the thermistor) is recorded. The change in temperature over time allows for measurement of blood flow—in this case, cardiac output. According to Jansen, this measure of cardiac output is accurate if the following conditions are met: (1) no loss of cold occurs between the injection site and the thermistor, (2) mixing of the cold injectate (indicator using Fick terms) and the blood is complete, and (3) the temperature change caused by the injection of cold fluid is sufficient to be detected by the thermistor.

To perform thermodilution cardiac output measurements, the catheter must be connected to the thermodilution computer, which is either freestanding or part of the cardiac monitor. A specific volume of injectate, either room temperature or iced, is injected rapidly into the proximal port of the catheter. The temperature difference over time that is detected at the thermistor is recorded as a curve. The computer then integrates the area under the curve, which is inversely proportional to the cardiac output. The cardiac output is calculated and projected. For children, this number should be divided by their body surface area in square meters, deriving the cardiac index. The injectate can be either iced or room temperature. Although a greater signal-to-noise measurement is obtained, the disadvantages of iced injectate include risk of hypothermia in pediatric patients requiring frequent cardiac output measurements and the poor accuracy of the first injection because of warmer fluid in the catheter. In conditions of high or low cardiac output, less variance occurs with iced injectate compared with room-temperature injectate. However, for convenience and the safety of pediatric patients, room-temperature injectate is generally recommended.

Usually, three to five injections yield adequate results. Some error can be introduced by faulty technique. Injecting variable volumes or injecting with variable rates can result in inaccurate measures. Multiple injections and averaging of the results can overcome these problems. The presence of tricuspid or pulmonary insufficiency can lead to an overestimation of cardiac output. Echocardiography may be necessary to rule out the presence of valvular insufficiency. Intracardiac shunts, such as a ventricular septal defect, result in false values for cardiac output. Mechanical ventilation has been shown to alter stroke volume, which can result in a variability of cardiac output measurements. Therefore, one should perform the injection at the same time in the ventilator cycle to standardize the cardiac output measurements.

Maintenance

Care of the PAC is similar to that for any CVC. The catheter and sheath should be dressed sterilely at all times, and the dressing changed according to protocol. The catheter is housed in a sterile sleeve that allows for aseptic technique if further manipulation is necessary. Pressure transduction of the distal (PA) and proximal (RA) ports and continuous electrocardiographic (ECG) monitoring are mandatory. This setup continually confirms proper placement of the catheter. Whenever the balloon is inflated to determine PAWP, the balloon is allowed to deflate passively by opening the balloon port and removing the syringe. This step helps prevent balloon rupture. Balloon rupture should be suspected if blood is obtained when aspirating the balloon port. In this situation, remove and then replace the catheter if it is still clinically indicated. As noted earlier, arrhythmias can occur, particularly if the catheter becomes dislodged. A chest radiograph should be taken daily to assess for catheter position.

The hemodynamic data obtained or calculated with the PAC should be interpreted to make therapeutic decisions. There are not isolated “good” or “bad” cardiac output values, but appropriate cardiac output is that which permits an adequate D o ₂ . As a global index of adequacy between consumption and D o ₂ , Sv o ₂ is the target of choice for therapeutic decisions. Sv o ₂ should be kept above a threshold value between 65% and 70%, and all other PAC parameters should be used to choose how to maintain Sv o ₂ above this value. This Sv o ₂ goal can be achieved by fluid administration, blood transfusion, increasing or decreasing inotropic support, or vasopressors. ^,

Complications

PA catheterization is a significantly invasive procedure. Complications can occur during the Seldinger procedure to access the vein, during the passage of the PAC (across two heart valves), or during catheter use. Bleeding, infection, and pneumothorax may occur during venous access. Arrhythmias can be encountered during placement of the PAC or due to dislodgment of the catheter. Arrhythmias include supraventricular tachycardia while the PAC tip is in the RA to premature ventricular beats or even ventricular tachycardia while the PAC tip is in the RV. Usually, the arrhythmias cease when the PAC tip reaches the pulmonary artery. Lidocaine, amiodarone, and defibrillation may be needed on occasion for ventricular arrhythmias; thus, these drugs should be readily available. Once the catheter is in place, pulmonary infarction or hemorrhage is a risk. Rupture of the distal PA, endothelial damage, and valvular damage have been reported, as well as knotting of the catheter requiring fluoroscopic retrieval. The PAC should be removed as soon as possible to minimize the risk of complications.

Summary

Since the introduction of the PAC, controversy has surrounded the technology regarding the benefits and potential harms caused by this invasive form of hemodynamic monitoring. In adult clinical trials, the usefulness of the PAC has been challenged because no benefit in patient outcome has been observed, and some retrospective studies have described worse outcomes. Accurate acquisition and interpretation of PAC data are paramount for making appropriate therapeutic decisions.