General Systemic Effects

Usually the child’s height and weight are below average. Children with CHD, and especially those with cyanotic CHD, may also demonstrate some developmental delay. The underweight child with CHD, however, has a metabolic rate that is considerably greater than predicted from size or weight. Infants with cyanotic CHD are unable to increase their metabolic rate to meet the demands of physiologic stress (e.g., cooling) and hence tolerate such stress poorly.

Effects on the Respiratory System

CHD can have major effects on pulmonary function. Enlarged vessels or chambers of the heart may compress major airways.

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imbalance. Excess pulmonary blood flow eventually results in irreversible pulmonary hypertension secondary to structural changes in the vessels; these include medial muscle hypertrophy and peripheral extension of the muscular layer into normally nonmuscular arterioles. These vascular changes may be prevented by pulmonary artery (PA) banding or more commonly by total repair during early life.

Children with decreased pulmonary blood flow have less efficient ventilation, requiring increased minute ventilation to eliminate carbon dioxide. The gradient between end-tidal and arterial carbon dioxide levels may be increased. The uptake of inhaled anesthetics into the blood is delayed; however, alveolar (and hence end-tidal) levels may rise rapidly. Cyanosis is associated with a reduced ventilatory response to hypoxemia.

Effects on the Heart

In addition to the special characteristics of the child’s heart (see page 29 ), CHD may impose other changes:

• 1.
  

  Obstructive lesions impose a pressure load on the affected ventricle. This ventricle then hypertrophies (becomes less compliant and less able to increase stroke volume). The thickened ventricle is subject to myocardial ischemia and consequent arrhythmias.

  
  
• 2.
  

  Large shunts or valvular incompetence impose a volume load on the ventricle. This ventricle initially responds with an increased stroke volume but later dilates and fails. The dilated ventricle requires a high wall tension to effect pressure change within the chamber (Laplace’s law); it therefore is vulnerable to myocardial depressants and cannot cope with additional loads.

  
  
• 3.
  

  Myocardial ischemia may result from reduced aortic diastolic pressures and rapid heart rates in some children (i.e., those with a PDA).

Effects on the Blood

Cyanosis induces compensatory changes in the blood: polycythemia and an increased blood volume. The increased hematocrit (Hct) may lead to thrombosis (especially cerebral) and abscess formation. Cyanotic CHD is also commonly accompanied by coagulopathy secondary to thrombocytopenia, impaired platelet function, and decreased vitamin K-dependent factors.

Effects on Hepatic and Renal Function

These functions are impaired in cyanotic CHD and especially in those children with CHF. Splanchnic blood flow is reduced. Clearance of drugs via the liver or kidneys is delayed (i.e., morphine clearance is reduced in many children with CHD).

Preoperative Assessment and Preparation

Review all the medical records, obtain a history from the parents, and perform an independent physical examination, especially of the cardiovascular and respiratory systems, ears, nose, throat, teeth, and veins.

Look for evidence of associated disease or dysmorphic features that might complicate the anesthetic management. Look carefully for signs of cardiac failure: tachypnea, sweating, and hepatomegaly in infants. Carefully determine the respiratory status to exclude acute disease that might compromise the child perioperatively. If the child had a significant lower respiratory infection recently, elective surgery should be postponed for 2 to 3 weeks because of an increased susceptibility to pulmonary complications during this period.

Review the cardiology notes, ECHO, cardiac catheterization, and angiographic data to fully understand the current cardiac pathophysiology. Note salient abnormalities and findings on the anesthesia chart. Review previous anesthesia experience.

Many children with CHD take several medications regularly. β-blockers should be continued up to the day of surgery. With rare exceptions, digitalis and diuretics should be withheld on the day of operation. Calcium channel-blocking drugs are very infrequently used in children but, if they are used, they should be discontinued the day before surgery.

If the child requires O ₂ therapy and/or maintenance of the sitting position during transit to the operating room (OR), order these specifically.

Plan in advance for postoperative pain management. In those whose tracheas may be extubated early, spinal or epidural opioids may be most useful. In most other cases, pain can be managed by an intravenous infusion of an opioid and/or PCA.

Blood Supplies

During any type of cardiac surgery, blood must be immediately available in the OR. In many centers, ordering blood is the responsibility of the surgical service. However, the day before surgery, the anesthesiologist should ensure that adequate supplies of blood and blood products will be available by operation time.

Some children have special requirements. For example:

• 1.
  

  For cyanotic children with an Hb greater than 16 g/dl, plasma should be available.

  
  
• 2.
  

  For all infants, check that the available blood is <3 days old and has been tested for cytomegalovirus. Washed cells should be ordered for small infants to prevent the danger of hyperkalemia. Radiated RBCs or leucocyte poor blood may be indicated for some children (immune deficient or transplant children).

  
  
• 3.
  

  For infants undergoing CPB, ensure that appropriate quantities of packed cells, FFP, and platelets (1 unit/5 kg) and cryoprecipitate have been ordered. Alternatively, fresh whole blood is considered especially advantageous, and is reported to reduce bleeding after CPB, but may be difficult to obtain.

  
  
• 4.
  

  For all children likely to require prolonged CPB (longer than 1.5 hours), ensure that FFP and platelets have been ordered.

  
  
• 5.
  

  Where “relatively minor” surgery is planned for older children and those with an initially high Hct, hemodilution with a clear fluid prime in the pump oxygenator may avert the need for blood transfusion. At the end of CPB, modified ultrafiltration may be used to remove the fluid prime and restore the Hct. Alternatively, the contents of the pump circuit may be collected to be reinfused postoperatively. (Blood should be ordered to be available on a standby basis.)

Premedication

• 1.
  

  Children with CHD require adequate preoperative sedation to reduce excitement, anxiety, and crying (and thus reduce O ₂ consumption). Order a hypnotic to be given the evening before surgery for anxious older children and preoperative sedation for all infants and children greater than 6 months of age.

  
  
• 2.
  

  In recent years, an oral regimen has come to be preferred:

  
  
  
  
  • a.
    

    Midazolam 0.5 to 0.75 mg/kg PO (maximum 20 mg) is very effective; allow 10 to 30 minutes for the peak effect to be achieved. Alternately, oral ketamine (5 mg/kg) or a combination of midazolam (0.25 mg/kg) and ketamine (3 mg/kg) may be effective. (Children given this mixture should be constantly observed and SpO ₂ monitored).

    
    
  • b.
    

    Lorazepam 1 to 2 mg PO is effective for the adolescent patient. This premedication does not usually decrease SaO ₂ , even in cyanotic children. However, the child should be supervised as sedation occurs, and a pulse oximeter may be used as the child becomes settled.

  
  
  
  

  Topical local anesthetic cream should be applied to a predetermined site for intravenous cannulation, covered with an occlusive dressing, and allowed to remain in place until effective and then removed before induction.

  
  
• 3.
  

  For cyanotic children with a high Hct, ensure that oral fluids are regularly offered up to 2 hours before the operation to prevent dehydration. Alternatively, maintenance IV fluids should be administered during the preoperative fasting period.

Routine Anesthesia Management

Open Heart Surgery

• 1.
  

  Follow routine management (see previous discussion). Cerebral function monitoring may be useful during CPB if available, especially for complex lesions. Near infrared spectrometry and transcranial Doppler have been found to be most readily interpreted.

  
  
• 2.
  

  If a TEE probe is to be inserted, monitor ventilation, SaO ₂ , the EtCO ₂ curve, and the BP very carefully. Passage of the probe may compromise ventilation, displace the tracheal tube, and/or compress the major vessels, especially in small infants; it may also trigger autonomic reflexes.

  
  

  The TEE has proved most useful intraoperatively because the exact anatomy and pathophysiology can be defined and the adequacy of repair assessed immediately. Residual shunts can be detected and valve function, ventricular filling, and contractility assessed. The flow in conduits or shunts can also be assessed. TEE probes are available which can be inserted into very small infants.

  
  
• 3.
  

  Maintain anesthesia with:

  
  
  
  
  • a.
    

    N ₂ O/O ₂ in suitable proportions to ensure SaO ₂ at an acceptable level. Use air/O ₂ for children in whom N ₂ O is contraindicated. Very occasionally, it may be necessary to deliver an F i O ₂ <0.21 to maintain pulmonary vasoconstriction and prevent overperfusion of the lungs (single ventricle physiology). In this instance, it is desirable to be able to mix nitrogen with the inspired gases and to monitor the oxygen content of the delivered gases.

    
    
  • b.
    

    If tolerated, isoflurane 0.5% to 0.75% or sevoflurane 2%, depending on the lesion, may be given and supplemented with generous doses of fentanyl.

    
    
  • c.
    

    Children with a history of CHF who may benefit from afterload reduction will probably do well with minimal isoflurane (e.g., VSD with left-to-right shunt). Children with dynamic ventricular outflow obstruction who may benefit from a degree of controlled myocardial depression usually do well with minimal (0.5%) halothane (e.g., tetralogy of Fallot, subaortic stenosis).

  
  
  
  
• 4.
  

  Give incremental doses of muscle relaxants as needed. Administer an additional generous bolus just before bypass to ensure complete immobility.

  
  
• 5.
  

  Give maintenance fluids, such as lactated Ringer’s solution according to body weight to replace the calculated deficit during fasting (if any) and maintain urine output greater than 1 ml/kg/min. Additional “fluid loading” before CPB has not been shown to be advantageous. Avoid dextrose-containing fluids; hyperglycemia may increase neurologic injury in case of cerebral hypoxia/ischemia, but monitor blood glucose concentrations in small infants to detect hypoglycemia.

  
  
• 6.
  

  Blood loss from sponges, suction, drapes, and blood specimens (i.e., blood withdrawn for analysis) must be measured, and the volume replaced. It is seldom necessary to transfuse blood before CPB unless major blood loss occurs during opening of the chest or dissection around the heart (i.e., during repeat operations). In repeat operations, warmed lactated Ringer’s solution should be ready for infusion at the time of sternotomy; blood should also be immediately available in the OR.

  
  
  
  
  • a.
    

    Aim to maintain the Hct near the preoperative level and the intravascular volume at a level to maintain CVP.

    
    
  • b.
    

    If the Hct was markedly increased preoperatively, replace initial losses with plasma, but refrain from hemodilution before CPB. Excess hemodilution may compromise oxygen delivery.

    
    
  • c.
    

    During venous cannulation in small infants, a significant volume of blood may be lost into the cannulae. Ensure that this volume is replaced, usually by transfusion from the pump oxygenator circuit via the aortic cannula.

  
  
  
  
• 7.
  

  Children with cyanotic CHD may benefit from the administration of ε-aminocaproic acid (Amicar), an antifibrinolytic agent, to reduce bleeding. A loading dose of 75 to 100 mg/kg should be infused before skin incision. Alternatively, tranexamic acid, 50 to 100 mg/kg, may be administered.

  
  
• 8.
  

  In children having repeat procedures, administration of ε-aminocaproic acid or tranexamic acid may reduce blood loss.

  
  
• 9.
  

  During dissection around the heart, watch the BP closely; arrhythmias are common, although most are innocuous. If hypotension or arrhythmia persists, ask the surgeon to desist until the condition corrects itself. Continuing hypotension suggests hypovolemia; thus fluid should be infused so that the child can tolerate essential manipulations around the heart.

  
  
• 10.
  

  If N ₂ O is given, discontinue it before cannulation to prevent expanding any potential air embolism.

  
  
• 11.
  

  Before the heart is cannulated, give the initial dose of heparin.

  
  
  
  
  • a.
    

    400 units/kg for neonates

    
    
  • b.
    

    300 units/kg for older children.

  
  
  
  

  Give this dose and recheck the ACT after 2 to 3 minutes; the ACT should be at least 480 seconds before initiation of CPB. Small infants may require more heparin and demonstrate more variation in dose requirements than older children.

  
  

  N.B. There is much discussion in the literature concerning heparin requirements in small infants and in children and whether the ACT is a reliable measure of the adequacy of heparinization during CPB. Current practice in most centers however continues to be as is outlined here. Some centers monitor blood heparin levels ( See previous discussion).

  
  
• 12.
  

  Once CPB is established, the pump flow should be increased to establish a satisfactory perfusion. Indicators of adequate perfusion are the cerebral function monitor, urine output, and the absence of metabolic acidosis on repeated acid-base studies. In children with cyanotic CHD, perfusion pressures may be low during early bypass because of the child’s decreased vascular resistance (children with cyanotic CHD have larger vessels) and the use of a low-viscosity perfusate. Those with tetralogy of Fallot may also have extensive collateral flow into the lungs. High flows may be required initially, but the systemic pressure will increase progressively, especially as cooling progresses. The use of vasoconstrictors is not usually necessary but should be considered if hypotension persists. When the perfusion pressure is low, it is vital that the superior vena cava (SVC) pressure should also be at or near zero. Any increase in jugular venous pressure in these circumstances may have a serious effect on cerebral blood flow. Monitor CVP carefully to detect any compromise of SVC venous return because of obstruction of the cannulae.

  
  
• 13.
  

  During partial bypass, ventilate the lungs with 100% O _2. Never use N ₂ O because of the possibility of expanding an air embolism.

  
  
• 14.
  

  During total bypass:

  
  
  
  
  • a.
    

    Keep the lungs inflated at a low pressure.

    
    
  • b.
    

    Add 0.5% isoflurane to the oxygenator to continue anesthesia and improve perfusion during normothermic bypass, or give additional doses of fentanyl. Remember that fentanyl may bind to the plastic components of the CPB circuit, so blood levels decrease precipitously on bypass. Do not add inhalational agents to the oxygenator during hypothermic bypass; the increased tissue solubility of the agent at low body temperatures may result in residual cardiac depressant effects after rewarming and during weaning from CPB. Discontinue inhalational agents 15 minutes before the end of bypass.

  
  
  
  
• 15.
  

  Hypertension in the adequately anesthetized child may be treated by injection of phentolamine (0.2 mg/kg). During hypothermic CPB, children secrete catecholamines; phentolamine, by its α-adrenergic blocking action, improves perfusion and delays the development of metabolic acidosis.

  
  
• 16.
  

  During bypass (partial and total), repeat the ACT every 30 minutes and give additional doses of heparin as necessary to increase the ACT to more than 480 seconds.

  
  
• 17.
  

  Take blood samples for acid-base, electrolyte, and Hct determinations every 30 minutes and just before CPB is discontinued. Monitor glucose levels in small infants.

  
  
• 18.
  

  Before discontinuing CPB:

  
  
  
  
  • a.
    

    Inflate the lungs, suction the trachea/bronchi, and check ventilation by observing the movement and full reexpansion of both lungs.

    
    
  • b.
    

    Commence pacing if the heart rate is slow or if sinus rhythm is absent; infants and children need an atrial contraction to maintain a good cardiac output at this stage. Atrial pacing can be used for slow heart rates with normal conduction. AV sequential pacing is required if conduction is abnormal. If AV block is present, it is usually possible to sense the atrial contraction and use it to pace the ventricle (AV sequential pacing).

    
    
  • c.
    

    If the cardiac action is impaired, inotropic agents should be commenced at a time well before weaning. A combination of dopamine 5 μg/kg/min, dobutamine 5 μg/kg/min, and milrinone 0.5 µg/kg/min is a common initial routine.

    
    
  • d.
    

    If the myocardial contractility is very severely depressed, start an infusion of epinephrine 0.1 μg/kg/min.

    
    
  • e.
    

    All neonates should have a calcium chloride infusion commenced at 5 mg/kg/hr. Alternatively any hypotension attendant upon the administration of blood or blood products in the intensive care unit (ICU) must be immediately treated by injections of calcium chloride. In our unit we have preferred to use an infusion to prevent delays in administration.

  
  
  
  
• 19.
  

  For children with pulmonary hypertension, the following should be established before weaning:

  
  
  
  
  • a.
    

    A PA line to monitor pressure.

    
    
  • b.
    

    Hyperventilation with oxygen

    
    
  • c.
    

    Correction of any preexisting metabolic acidosis

    
    
  • d.
    

    In some children with mild increase of pulmonary artery pressure, it may be useful to commence an infusion of SNP at 0.5 to 2 μg/kg/min before weaning from bypass.

    
    
  • e.
    

    Add nitric oxide to the inspired gases if necessary to control high PVR.

  
  
  
  
• 20.
  

  As CPB is discontinued:

  
  
  
  
  • a.
    

    Administer calcium chloride (10 mg/kg) to improve cardiac action if necessary. (Calcium should never be given until the heart has resumed a steady regular rhythm).

    
    
  • b.
    

    Request infusion of blood from the pump, and infuse cells until the CVP or left atrial pressure is adequate (8 to 12 mm Hg, depending on the cardiac lesion). The Hct on bypass is usually less, and it is advisable to infuse a mixture of cells to increase the Hct to 30% to 35% as CPB is discontinued. In small infants, fresh whole blood is preferred; otherwise, an appropriate mixture of packed red blood cells and recently thawed FFP may be infused to restore the Hct and administer coagulation factors. Older children, especially those having more minor procedures, may be weaned at a lower Hct, given a diuretic (furosemide), and have the pump contents reinfused over the ensuing period. In this way it may be possible to prevent the need for blood transfusion.

  
  
  
  
• 21.
  

  If the child remains hypotensive despite a good rate and rhythm:

  
  
  
  
  • a.
    

    Adjust the dopamine infusion (5 to 10 μg/kg/min). Larger dopamine doses are often required in infants compared with older children and adults.

    
    
  • b.
    

    Dobutamine 5 to 10 μg/kg/min may be added. This drug also increases inotropy, but it may also increase heart rate and decrease SVR in children.

    
    
  • c.
    

    Calcium infusion may improve performance in some children, especially small infants. It is required in children with DiGeorge syndrome.

    
    
  • d.
    

    If all else fails, an infusion of epinephrine 0.1 to 0.5 μg/kg/min may be indicated.

  
  
  
  
• 22.
  

  Modified ultrafiltration may be employed after CPB has been discontinued. The bypass circuit is modified to withdraw blood from the aortic cannula, pass it through an ultrafiltration unit, and return it to the right atrium. Ultrafiltration removes fluid and filters the blood. This removes excessive intravascular fluid and increases the child’s Hct. In addition, it may remove some inflammatory substances released during CPB. It has been suggested that modified ultrafiltration may reduce bleeding and enhance postoperative cardiopulmonary function.

  
  
• 23.
  

  When the child’s condition is stable and the cannulas have been removed, give protamine slowly, preferably via a peripheral intravenous route. Common practice is to give a dose of protamine (mg/kg) equal to that of the heparin (per 100 U/kg), which was administered before bypass. If hypotension occurs after protamine it usually can be reversed by calcium.

  
  
• 24.
  

  At 20 minutes after CPB, take blood samples for coagulation studies, electrolytes, and blood gases. Repeat ACT and give more protamine if indicated.

  
  
• 25.
  

  If bleeding persists, give platelets (1 unit/5 kg), FFP(20 ml/kg), and/or cryoprecipitate, according to coagulation indices.

  
  

  N.B. Anticipate continued bleeding because of platelet dysfunction and other factor deficiencies:

  
  
  
  
  • a.
    

    After a long pump run

    
    
  • b.
    

    In children with cyanotic CHD

    
    
  • c.
    

    In small infants, in whom the pump-priming volume is very large in relation to blood volume

  
  
  
  

  All bleeding must be well controlled before the chest is closed.

  
  
• 26.
  

  After some complex intracardiac repairs, sternal closure may be delayed, and a plastic membrane sewn in place to cover the heart in the interim. This is appropriate when myocardial edema is present, as leaving the chest open prevents the constricting effects of the closed sternum on cardiopulmonary function and may increase BP and urine output while decreasing CVP. The sternum is closed when myocardial function is improved and it is judged that the child can tolerate this maneuver.

  
  
• 27.
  

  At the end of surgery, the decision must be made whether to extubate the trachea immediately or to continue with ventilatory support. The decision depends on the disease that was present and the intraoperative course.

  
  
• 28.
  

  The trend toward “fast-tracking” some children after cardiac surgery is now well-established; it may be combined with minimally invasive surgical approaches. After simple procedures (i.e., closure of ASD, resection of subaortic membrane), the trachea may be extubated in the OR and the child may be expected to have a very short stay in the ICU. In such cases:

  
  
  
  
  • a.
    

    Employ an anesthesia technique that permits early brisk recovery; avoid large doses of opioids or ultra–long-acting relaxants.

    
    
  • b.
    

    Plan for good postoperative analgesia; a single-shot caudal morphine injection is safe, effective, and easy (see Chapter 5 ).

    
    
  • c.
    

    Ensure that excess pump priming fluid is removed by means of modified ultrafiltration after CPB is discontinued.

  
  
  
  

  It may be more appropriate for some children to be transferred to the ICU for extubation on arrival or soon thereafter, depending on local circumstances.

  
  
• 29.
  

  Many children after CPB require postoperative ventilatory support.

  
  
  
  
  • a.
    

    These include:

    
    
    
    
    • i.
      

      Those with hypoxemia despite a high F i _O2

      
      
    • ii.
      

      Low cardiac output

      
      
    • iii.
      

      Pulmonary hypertension

      
      
    • iv.
      

      Diminished lung compliance

      
      
    • v.
      

      Persistent arrhythmias

      
      
    • vi.
      

      Hypothermia (<34 °C)

      
      
    • vii.
      

      Continuing hemorrhage

    
    
    
    
  • b.
    

    In such children:

    
    
    
    
    • i.
      

      Plan for continuing IPPV and/or CPAP or pressure support ventilation. Controlled ventilation and CPAP are particularly beneficial during the immediate postoperative period; at this stage, the child predictably has a tendency toward reduced lung volumes and increased lung water (especially the infant). IPPV also permits excellent pain control by opioid infusion

      
      
    • ii.
      

      Do not antagonize the muscle relaxants.

      
      
    • iii.
      

      The choice of a nasal versus an oral tracheal tube for postoperative ventilation has varied from unit to unit. Children tolerate nasal tubes extremely well; they are less likely to kink and cannot be occluded by the teeth. They are also easier to secure at a specific depth. It has been suggested that nasal tubes might predispose to middle ear or sinus disease; this has not proved to be a major problem. The continued use of the oral tube removes the need to change the tube and proves quite satisfactory in some units.

    
    

  
  
  
  

  N.B. If nasal intubation is chosen for the ICU, it is preferable to change the tube from an oral to nasal tube at the end of the procedure rather than pass a nasotracheal tube initially: this could cause a nosebleed perioperatively, especially when the child has been heparinized. During some surgeries, blood-stained secretions may accumulate in the tube. The change is then considered advisable to provide the child with a clean tube before transfer to the ICU. Ensure that the nasotracheal tube does not exert pressure on the margins of the nares or the nasal septum; necrosis, ulceration, and scarring can occur. The change to a nasotracheal tube should be made only if the child’s condition is judged to be stable; otherwise, ventilation via the orotracheal tube is advised.

  
  
• 30.
  

  During transport to the ICU (all children):

  
  
  
  
  • a.
    

    Attach a full bag of blood (or other appropriate fluid) to the IV line to ensure immediate replacement volume availability in case of sudden hemorrhage.

    
    
  • b.
    

    Cover the child with warm blankets.

    
    
  • c.
    

    Administer O ₂ by mask or, if the trachea is still intubated, continue controlled ventilation with O _2. Make sure that the tank has an adequate supply of O ₂ for the transfer to ICU.

    
    
  • d.
    

    A battery-powered monitor should provide:

    
    
    
    
    • i.
      

      Pulse oximetry

      
      
    • ii.
      

      ECG

      
      
    • iii.
      

      Intravascular pressures

      
      
    • iv.
      

      EtCO ₂ monitoring is desirable.

    
    
    
    
  • e.
    

    Continue the infusions of inotropic drugs and/or vasodilators using battery-powered syringe pumps. If NO is used, this must be continued during transport and in the ICU. Beware of interruptions to the flow of any of these drugs during transport to the ICU.

  
  

Deep Hypothermia With Circulatory Arrest

Deep hypothermia with circulatory arrest is used for some neonates and infants undergoing cardiac surgery. It is particularly advantageous when surgery involves the aortic root.

Hypothermia is achieved by means of bloodstream cooling on CPB. The debate concerning the safety of profoundly hypothermic circulatory arrest versus continued perfusion is ongoing; many infants managed by DHCA and have shown little evidence of increased cerebral impairment as they grow to adulthood. However, many centers now prefer to limit the duration of DHCA and possibly to use antegrade cerebral perfusion (ACP) during aortic arch reconstruction procedures.