Cardiovascular Surgery and Cardiologic Procedures




Heart surgery in children is performed almost exclusively for congenital heart disease (CHD). The incidence of CHD is approximately 6 per 1000 live births. The lesions listed in Table 14-1 account for more than 90% of all congenital heart defects. There are various classifications of CHD, but that given in the table is most useful for the anesthesiologist.



TABLE 14-1

Incidence of Congenital Heart Disease

















































Type of Lesion Frequency (%) *
Lesions With Increased Pulmonary Blood Flow
Ventricular septal defect (VSD) 16.6
Patent ductus arteriosus (PDA) 6.5
Endocardial cushion defect (AV canal) 5.3
Atrial septal defect (ASD) 3.1
Truncus arteriosus 1.5
Cyanotic Lesions
Hypoplastic left ventricle 7.9
Tetralogy of Fallot 3.5
Transposition of great arteries 2.5
Tricuspid atresia 1.5
Obstructive Lesions
Coarctation of the aorta 8.0
Pulmonary stenosis 3.5
Aortic stenosis 2.0

(From Fyler DC, Buckley LP, Hellenbrand WE et al: Report of the New England Regional Infant Cardiac Program. Pediatrics 65(Suppl):388, 1980, with permission.)

* Frequency of lesions symptomatic in the first year of life.



The Child with Congenital Heart Disease


Infants with CHD usually present early with respiratory distress and/or cyanosis and difficulty with feeding, or later with failure to thrive. Some malformations cause severe congestive cardiac failure during the neonatal period, evidenced by marked hepatomegaly. Cardiac failure results from the high pressures needed to compensate for obstruction to blood flow (valve stenosis or coarctation) or from high-volume flow through intracardiac or extracardiac shunts (i.e., ventricular septal defect [VSD] or patent ductus arteriosus [PDA]). Dyspnea may result from cardiac failure and/or changes in pulmonary blood flow.


The diagnosis of CHD in infants may be difficult; innocent murmurs are common, and serious lesions may be present with a deceptively soft murmur (see page 460 ). The physiology of the neonatal cardiovascular system may obscure significant lesions; for example, increased PVR may limit left-to-right shunts, and a PDA may mask coarctation of the aorta. An ECHO is essential to make a definitive diagnosis and should be requested whenever CHD is suspected.


Older infants and children with CHD may have reduced exercise tolerance, chest pain, or syncope. Alternatively, a murmur may be discovered on routine medical examination. Children with CHD often experience repeated respiratory infections.


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.


Increased pulmonary blood flow results in small airway obstruction, decreased compliance, increased resistance, and ventilation-perfusion <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='V./Q.’>V./Q.V./Q.
V . / Q .
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).


GENERAL PRINCIPLES OF ANESTHESIA MANAGEMENT




  • 1.

    Children with CHD and their parents are often very apprehensive and deserve careful and considerate attention. Older children and their families may have had to endure repeated surgery.


  • 2.

    The techniques used must minimize demands on the cardiovascular system.



    • a.

      Give adequate premedication to reduce anxiety, activity, and O 2 requirements.


    • b.

      A rapid, smooth induction of anesthesia, with no crying or struggling, is very desirable.


    • c.

      Give adequate doses of analgesics and general anesthetics perioperatively. Prevent tachycardia and/or hypertension. High-dose opioid anesthesia combined with good postoperative analgesia may favorably influence the neuroendocrine and metabolic responses to surgery and improve survival.


    • d.

      Control ventilation but maintain normocarbia unless there is a specific indication to adjust the CO 2 tension. Avoid hypocarbia, which may:



      • i.

        Reduce cardiac output.


      • ii.

        Cause vasoconstriction and increase systemic resistance.


      • iii.

        Decrease PVR and increase left-to-right shunts.


      • iv.

        Shift the hemoglobin/oxygen (Hb/O 2 ) dissociation curve to the left and limit O 2 transfer.


      • v.

        Decrease myocardial blood flow.


      • vi.

        Decrease the serum K level, resulting in arrhythmias.


      • vii.

        Decrease cerebral blood flow.



      Decide on an optimal level of ventilation for each child and maintain this level.


    • e.

      Give adequate doses of muscle relaxants to prevent movement or ventilatory efforts, especially when the heart is open (danger of air emboli).


    • f.

      Maintain body temperature and prevent cold stress except when induced hypothermia is indicated.


    • g.

      When appropriate, consider left ventricular (LV) afterload reduction and/or measures to reduce PVR (see later discussion).



  • 3.

    Optimal myocardial function and cardiac output must be maintained during surgery:



    • a.

      Do not give agents that cause excessive myocardial depression.


    • b.

      Adjust the fluid balance to maintain optimal cardiac filling pressures.



  • 4.

    Prevent detrimental changes in cardiac shunts.



    • a.

      Use anesthetic drugs that have minimal effects on SVR.


    • b.

      Be aware of the possible effects of intermittent positive-pressure ventilation (IPPV) on shunts; avoid high intrathoracic pressures, but maintain the lung volume as necessary by the use of optimal positive end-expiratory pressure (PEEP). PVR is minimal at an optimal lung volume and increases at greater or lesser degrees of lung inflation.


    • c.

      Drugs that produce a controllable degree of myocardial depression (e.g., halothane) may be useful when hyperdynamic ventricular muscle causes obstruction to blood flow and increased shunting (e.g., Tetralogy of Fallot).


    • d.

      Children who depend on systemic-to-pulmonary shunts will desaturate if the systemic arterial pressure decreases.


    • e.

      Anemia may increase left-to-right shunts. Conversely left-to-right shunting may be reduced by increasing Hct. Changes in blood viscosity have a greater effect on PVR than on SVR.


    • f.

      Be prepared to use drugs or other methods to manipulate PVR or SVR.



  • 5.

    Conditions that favor optimal myocardial perfusion must be maintained throughout surgery to prevent ischemic myocardial damage and subsequent impairment of cardiac function postoperatively.



    • a.

      The duration of diastole and the diastolic pressure are important factors in maintaining perfusion of the myocardium, which is especially vulnerable if left-to-right shunting (causing low aortic root diastolic pressure) and ventricular hypertrophy are present. Inadequate anesthesia and analgesia produces tachycardia, which shortens diastole and therefore may impair myocardial perfusion. Replace blood and give adequate fluids to maintain the diastolic pressure.


    • b.

      Maintain an optimal Hct to preserve oxygen transport to the myocardium. Significant anemia may compromise subendocardial blood flow.


    • c.

      During CPB, it is preferable to maintain a regular rhythm until the aorta is cross-clamped and cardioplegia is induced; this preserves myocardial perfusion. If ventricular fibrillation occurs, greater perfusion pressures and an LV vent are needed to ensure adequate myocardial perfusion.



  • 6.

    The cardiac workload must be minimized:



    • a.

      Prevent hypertension and tachycardia during anesthesia by ensuring adequate analgesia and the use of vasodilators and/or β-adrenergic blocking drugs when appropriate.


    • b.

      Avoid excessive doses of drugs that may produce hypertension (e.g., phenylephrine).


    • c.

      Pulmonary hypertension must be controlled.



  • 7.

    Heparin has a larger volume of distribution and a more rapid plasma clearance in infants than in adults. Therefore larger doses may be required initially, an activated clotting time (ACT) of 480 seconds or more is required before CPB, and the level of heparinization should be checked frequently (every 30 minutes). An ACT of 480 seconds is the commonly used threshold value to attain before and during CPB. However, some have questioned whether this is adequate to prevent thrombin formation in the hemodiluted, hypothermic infant, and suggest that a higher ACT is more appropriate (i.e., 600 seconds). Kaolin-activated ACT appears to produce more reproducible ACT results than Celite activated ACT. The determination of blood heparin levels *


    * Hepcon, Medtronic, Minneapolis.

    may provide a better means to monitor heparinization and is being performed in some units.


  • 8.

    During CPB, the myocardium may be protected by:



    • a.

      Cardioplegic solutions that are infused at a pressure of 100 to 150 mm Hg into the coronary circulation after aortic clamping. Controversy still exists concerning the most advantageous type of solution, and this may differ in infants and adults. Most solutions contain increased concentrations of potassium with added dextrose and pH buffers. The addition of free radical scavenger agents and calcium ion channel blockers has been suggested. The ideal cardioplegic solution:



      • i.

        Produces immediate arrest and prevents energy depletion.


      • ii.

        Provides substrate for anaerobic metabolism.


      • iii.

        Buffers metabolic acidosis in the tissue.


      • iv.

        Minimizes tissue edema by its osmolar effects.


      • v.

        Stabilizes cell membranes.


      • vi.

        Minimizes reperfusion injury.



      Blood cardioplegia is preferred by many institutions. Repeated doses of cardioplegic solution are normally given at 15- to 20-minute intervals.


    • b.

      Hypothermia. Remember that the heart has a great tendency to rewarm because of surgical manipulation and heat from operating room lights. Therefore, during prolonged surgery, cold cardioplegic solutions should be repeatedly applied, and a pericardial cooling bath should be used.


    • c.

      Pre-CPB systemic corticosteroids may help preserve myocardial tissue during periods of ischemic arrest, but this is controversial.


    • d.

      An optimal reperfusate solution may be used after a period of ischemic arrest. This may flush out metabolites and prevent reperfusion injury. This solution should be warmed and alkaline and should contain a minimal concentration of ionized calcium and a slightly increased potassium concentration. In practice, a repeat dose of warmed cardioplegic solution is often given just before reperfusion.



  • 9.

    After CPB, small infants and children may bleed excessively owing to dilutional thrombocytopenia and reduced concentrations of coagulation factors. This is primarily a result of the large pump-priming volume in relation to the child’s blood volume. Be prepared to administer platelets and other factors as required. Fresh whole blood, if available, may be particularly advantageous in small infants. Make sure that infants do not cool after weaning from CPB; coagulopathy may result.



SPECIAL PROBLEMS


Large shunts may be present.



  • 1.

    Right-to-left shunts result in:



    • a.

      Reduced PaO 2 . This is often only minimally improved by increasing the F i O 2 .


    • b.

      Delayed uptake of inhaled anesthetics into the blood.


    • c.

      Extreme danger of systemic emboli from venous air embolism. Make certain all IV solutions are bubble free.


    • d.

      Short arm-brain circulation time, with no pulmonary transit; therefore there is a danger of overdose with intravenous drugs.


    • e.

      Less efficient ventilation and gas exchange; increased ventilation is necessary to maintain a normal PaCO 2 , whether the child is awake or anesthetized.


    • f.

      An increased arterial to EtCO 2 gradient; EtCO 2 levels underestimate arterial levels.



  • 2.

    Left-to-right shunts result in:



    • a.

      Pulmonary vascular overperfusion but good ventilatory efficiency and gas exchange initially.


    • b.

      Later, pulmonary hypertension develops and progresses to irreversible increased PVR, which may limit the operability of associated cardiac lesions.


    • c.

      Eventual CHF.



  • 3.

    Obstructive lesions may result in:



    • a.

      Fixed cardiac output, and therefore very limited ability to compensate for changes in metabolic demand or a decrease in SVR.


    • b.

      Myocardial hypertrophy, with possible inadequacy of myocardial perfusion, especially to the subendocardium. Reduced ventricular compliance results in dependence on a high cardiac filling pressure.


    • c.

      CHF.


    • d.

      Sudden serious arrhythmias.



  • 4.

    Heart failure is common in infants with CHD and is worsened by drugs that depress the myocardium (e.g., inhalational anesthetics).


  • 5.

    Electrolyte disturbance



    • a.

      Serum electrolyte (especially K + ) concentrations may be reduced, particularly after prolonged diuretic therapy. (Hypokalemia predisposes to cardiac arrhythmias, particularly with digitalis therapy and during hypothermia.)


    • b.

      Neonates with CHD may have reduced blood Ca ++ and glucose concentrations.


    • c.

      Reduced serum magnesium concentrations may occur and predispose to arrhythmias.



  • 6.

    Drugs essential for CHD therapy can cause problems:



    • a.

      Digitalis: the therapeutic index is low, and toxicity is an ever-present hazard, especially in young children. Check a recent serum digitalis level (therapeutic range, 0.8 to 2 ng/ml). Hypothermia and hyperventilation increase the risk of digitalis toxicity because the serum K + concentration decreases.


    • b.

      Diuretics: may deplete K + , further increasing the risk of digitalis toxicity.


    • c.

      β-Adrenergic blocking agents: they may impair cardiac contractility; however, this is not usually a problem with therapeutic doses. If being used in the treatment of cyanotic spells, these drugs should be continued until the day of surgery.


    • d.

      Calcium channel-blocking agents: these are not commonly used in children. If used in infants, they may cause severe, persistent myocardial depression. The combination of β-blocking agents with calcium channel blockers is very dangerous and should be avoided.



  • 7.

    Polycythemia. A high Hct (greater than 55% in cyanotic lesions) results in:



    • a.

      Increased viscosity of the blood and therefore increased cardiac work


    • b.

      Increased tendency to thrombosis


    • c.

      Further increased risk of thrombosis if dehydration or venous stasis develops


    • d.

      Coagulopathy


    • e.

      Predisposition to cerebral abscess



    Despite the dangers of polycythemia, these children depend on a high Hct to ensure adequate O 2 transport. Hemodilution to normal Hct levels may be followed by severe cardiovascular collapse. Hemodilution before surgery, if indicated, must be very carefully controlled and the Hct not reduced below 40% to 45%.


  • 8.

    Some infants with large left-to-right shunts are at extreme risk of pulmonary hypertensive crises during and after surgery (e.g., truncus arteriosus, arteriovenous [AV] canal). It is important to prevent such crises because they are difficult to reverse. The measures taken may include:



    • a.

      Adequate anesthesia/analgesia during surgery, and minimal handling of the child postoperatively.


    • b.

      Controlled hyperventilation (PaCO 2 = 25 to 30).


    • c.

      Fentanyl infusion (e.g., 25 μg/kg loading dose plus 2 μg/kg/hr).


    • d.

      Sodium nitroprusside (SNP) infusion 0.5 to 5 μg/kg/min.


    • e.

      Inhalation of nitric oxide (NO). NO has specific pulmonary vasodilating properties and is a very useful drug to control PVR. It does require special equipment for its administration. It must be mixed in the inspired gases delivered to the child in a concentration of 20 to 80 ppm; this requires equipment to monitor its final concentration in the mixture. It cannot be premixed in oxygen containing mixtures of gases because nitrogen dioxide (NO 2 ) will be formed, which is damaging to the lungs. It should be mixed with the lowest F i O 2 that ensures adequate Hb saturation to minimize NO 2 formation. NO must not be suddenly withdrawn because severe rebound pulmonary hypertension may result. Large doses may result in the formation of methemoglobin.



  • 9.

    Some infants depend on the patency of the ductus arteriosus as a route for shunting of blood until surgery can be performed (e.g., TGA with intact septum, interrupted aortic arch). Prostaglandin E 1 (PGE 1 ) is used to keep the ductus open in such infants. An infusion of 0.05 to 0.1 μg/kg/min should be continued until the appropriate surgical procedure is completed.


  • 10.

    Associated malformations. Many children with CHD have additional defects (e.g., cleft palate, Down syndrome, subglottic stenosis) that may complicate anesthesia and require special considerations.


  • 11.

    Induction of anesthesia. Different induction methods may be used, but if well conducted, all increase SaO 2 , even in cyanotic children; therefore, the anesthesiologist may choose whichever seems best and most appropriate for a given child. In our practice, an intravenous induction using an opioid analgesic, a very small dose of barbiturate or propofol, and an intubating dose of a nondepolarizing relaxant are usually preferred; this allows for good ventilation, rapid airway control, and very stable conditions. Use of a topical local anesthetic cream and suitable sedation facilitate the ease of venous cannulation. Skillfully applied, the advantage of inserting venous access outweighs the potential for upsetting the child. Beware of using halothane or other myocardial depressant vapors in other than very small concentrations. Ketamine has been commonly used, but an intramuscular injection always upsets the child and leads to stress and crying.


  • 12.

    Muscle relaxants. Nondepolarizing agents take a longer time to reach maximum effect in children with CHD; a more prolonged period of mask ventilation may be needed before intubation.


  • 13.

    Temperature control. Temperature control may be especially poor in neonates with cyanotic CHD; body temperature decreases rapidly if they are exposed to a cool environment. Vasoconstriction in the cold child impairs efforts at insertion of intravenous lines and may result in metabolic acidosis. Keep the child warm.


  • 14.

    Sepsis. This is a major threat to the success of cardiac surgery; great care must be taken to observe strict asepsis when invasive monitoring or infusion lines are being inserted. This is especially important in children undergoing transplantation.


  • 15.

    Repeated surgery. Some children need repeated surgery, which imposes a severe psychological stress on them and their parents. A very considerate, careful approach by the anesthesiologist is essential.



ROUTINE PREOPERATIVE, PERIOPERATIVE, AND POSTOPERATIVE CARE


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.



Suggested Reading


  • Doshi R.R., Qu J.Z.: Preoperative and postoperative anesthetic assessment for pediatric cardiac surgery patients. Int Anesth Clin 2004; 42: pp. 1-13.



  • Anesthesia Management


    Routine Anesthesia Management


    Preoperative




    • 1.

      Check all anesthesia and monitoring equipment before the child enters the OR


    • 2.

      Have the following available in case of emergency:



      • a.

        Sodium bicarbonate, 8.4% solution 20 ml volume


      • b.

        Atropine (0.4 mg/ml) diluted in 4 ml N saline (0.1 mg/ml solution).


      • c.

        Calcium chloride, 10% solution: 10 ml volume


      • d.

        Epinephrine, 1:10,000 preparation: 10 ml volume


      • e.

        Phenylephrine, 0.1 mg/ml: 10 ml volume



      Solutions of inotropic drugs should be prepared, loaded on appropriate infusion pumps with appropriate initial settings and primed. These should be made in a concentration that will permit their infusion at a therapeutic rate without adding an excessive fluid load and set up in such a manner that a carrier infusion of balanced salt solution assures timely delivery. In practice, for small infants and children, it is useful to use a dilution that will deliver the required dose when infused at 1 to 2 ml/hr (see Appendix 3 ).


    • 3.

      Check that preoperative medication has been given as ordered and is effective.


    • 4.

      On arrival in the OR, gently apply basic monitors: pulse oximeters (one probe to a finger, thumb, or ear and one probe to a toe), precordial stethoscope, BP cuff, and ECG electrodes. Record HR and rhythm and BP. Do not prolong this process, especially if the child is apprehensive, but proceed carefully and rapidly.



    Perioperative




    • 1.

      Administer O 2 by mask. Often the child will be happier if the mask is held slightly away from the face. Use a high flow.


    • 2.

      Induce anesthesia, preferably intravenously, particularly in children with right-to-left shunts, which slow inhalation inductions. For most children, fentanyl 2 to 5 μg/kg followed by propofol (3 to 5 mg/kg) or thiopental (2 to 4 mg/kg) given slowly produces a smooth induction with minimal cardiovascular effects. In small infants, precede the fentanyl by a small dose of atropine (0.01 mg/kg) or an appropriate dose of pancuronium to prevent bradycardia. For the very unstable child, omit thiopental but give incremental IV doses of fentanyl slowly up to a total of 30 μg/kg with midazolam up to 0.2 mg/kg for induction.


    • 3.

      Drugs given intravenously should be administered in small doses, slowly. (If a right-to-left shunt is present, they act very rapidly; but if the circulation time is slow, their effect may be less rapid.) Be patient and wait for the desired effect. Beware of overdose.


    • 4.

      For tracheal intubation: give an initial dose of nondepolarizing relaxant and ventilate the lungs until relaxation is adequate; pancuronium 0.1 mg/kg, rocuronium 1 mg/kg, or vecuronium 0.1 mg/kg produce good intubating conditions within 3 minutes (see also item 9 in this list).


      NB: Be aware of the possibility of subglottic stenosis in children with CHD, be prepared to use a smaller diameter tube.


    • 5.

      Use a cuffed endotracheal tube to ensure ability to ventilate well. The tube should pass easily through the glottis and subglottic space; otherwise use a smaller diameter tube. Carefully position the tube and check bilateral ventilation. The cuff does not usually need to be inflated in infants to prevent leaks at normal ventilator pressures.


    • 6.

      Maintain anesthesia with a suitable mixture of N 2 O/O 2 or air/O 2. (It is rare to require >50% O 2 . If a large right-to-left shunt is present, an increase in the F i O 2 has very little effect on the PaO 2 .) It is probably advisable to avoid N 2 O in the child with pulmonary hypertension, although the effect on PVR is small.


    • 7.

      If myocardial function is good, for simple lesions, low concentrations of inhaled agents may be used. Otherwise, for all complex lesions, add opioids in adequate doses.


    • 8.

      Control ventilation to produce desired carbon dioxide tension. Note that EtCO 2 is a satisfactory means to monitor PaCO 2 in acyanotic children but may underestimate the PaCO 2 in those with cyanotic CHD. Always compare the EtCO 2 against the PaCO 2 ; the EtCO 2 can then be used to follow trends.


    • 9.

      The choice of muscle relaxant during maintenance of anesthesia should be influenced by the following:



      • a.

        Rocuronium and vecuronium have very little effect on cardiovascular parameters, have an intermediate duration of action, and, if properly dosed, can readily be reversed for early extubation. They are probably the agents of choice for many infants and children.


      • b.

        Pancuronium (to offset the bradycardic effects of high-dose fentanyl) combined with fentanyl is useful for the very unstable small infant with a complex lesion.



    • 10.

      Insert a nasopharyngeal and rectal or bladder thermometer. An esophageal stethoscope cannot be inserted if a TEE probe will be used.


    • 11.

      Insert adequate-bore intravenous routes, an arterial line, a double-lumen central venous line (see Chapter 4 ), and a urinary catheter. In older children who may be extubated early, it is preferred if possible to place the arterial line and the intravenous line in the same upper limb (usually the left). The other hand can then be used to operate a PCA pump.


    • 12.

      Give maintenance fluids as outlined in Chapter 4 . All fluid administration should be regulated by infusion pumps. If the child was polycythemic preoperatively, plasma may be preferable to blood as replacement fluid, especially if a systemic-pulmonary shunt is being performed. In these children, an Hct of at least 35% to 40% by the end of surgery is usually desirable. Use a fluid warmer for all infusions.


    • 13.

      For those whose trachea may be extubated early after surgery, consider the use of epidural or spinal opioids (see Chapter 5 ).



    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.




    Postoperative Management in the Intensive Care Unit




    • 1.

      Auscultate the chest to ensure that ventilation is adequate when the ICU ventilator is used. Order a suitable F i O 2 concentration, and confirm ventilation and oxygenation by blood gas determination as soon as possible.


    • 2.

      Ensure good analgesia; if regional analgesia has not been provided, order suitable opioids and sedative drugs:



      • a.

        Morphine may be given intravenously as a continuous infusion (10 to 30 μg/kg/hr for children, 5 to 15 μg/kg/hr for infants) or less desirably, every 2 hours.


      • b.

        Midazolam infusion 1 to 2 μg/kg/min or 0.1 mg/kg IV every 2 hours as needed.



    • 3.

      Continue balanced salt solution for maintenance (with added KCL 2 mEq/kg/24 hr provided that urine output is 1 ml/kg/hr or more; otherwise withhold the KCL).


    • 4.

      Check blood loss via the drainage tubes and instruct the nurses to replace this and further losses with reconstituted whole blood.


    • 5.

      A chest radiograph should be obtained. Examine it carefully for pneumothorax, hemothorax, and atelectasis, and to ensure that the tip of the endotracheal tube is well above the carina. Check placement of all other indwelling lines; ensure that the tip of the CVP line is positioned at the level of the junction of the SVC and right atrium. (Cardiac perforation may complicate CVP line advanced to within the atrium.)


    • 6.

      If bleeding persists order coagulation studies. Based on results, administer fresh frozen plasma or platelet concentrates as indicated.



    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.


    Anesthesia Management


    Anesthesia management is as described previously, with the following modifications:



    • 1.

      No dextrose-containing solutions should routinely be given because hyperglycemia may increase the risk of cerebral damage during total circulatory arrest. However, the blood glucose level should be monitored to detect and treat hypoglycemia should it occur. Large doses of fentanyl (more than 50 μg/kg) should be given and may limit the increase in blood glucose concentration that occurs as a metabolic response during hypothermic CPB.


    • 2.

      Give methylprednisolone (Solu-Medrol) 15 to 25 mg/kg IV slowly, before cooling on CPB. Ensure that the child is given adequate doses of relaxant drugs. (Once circulatory arrest has occurred, no additional drugs can be given.)


    • 3.

      Phenytoin (Dilantin) 5 mg/kg may be added to the CPB prime solution as a neuroprotective agent.


    • 4.

      After CPB is begun, ensure that the difference between the esophageal temperature and the temperature of the pump’s output does not exceed 10 °C. Set cooling mattresses to 10 °C. Turn the room temperature down. Pack the head in ice bags.


    • 5.

      The optimal management of blood gas tensions and acid-base balance during profound hypothermia has been the subject of much debate.



      • a.

        The “alpha stat” approach measures blood gases at 37 °C whatever the child’s body temperature (i.e., pH alkalotic when corrected for the actual body temperature) has been widely used in adults. Blood gas analysis shows a normal or low PaCO 2 during cooling.


      • b.

        The “pH stat” approach corrects the blood gases for the child’s body temperature and requires that CO 2 be added to the oxygenator gases during cooling. This has the advantages of increasing CBF and improving oxygen delivery and improves neurologic outcome in infants. It is now the recommended strategy for pediatric patients.



    • 6.

      Administer phentolamine 0.2 mg/kg to improve tissue perfusion, ensure rapid even cooling, and minimize acidosis on rewarming.


    • 7.

      When the esophageal temperature is 16 °C and the rectal temperature is <20 °C, CPB is discontinued, blood is drained to the oxygenator, and the venous cannulas are removed.


    • 8.

      Record the duration of circulatory arrest. The duration of safe circulatory arrest at a given temperature is unknown, but it is generally preferred to limit it to 60 minutes at 15 °C to 18 °C core temperature.


    • 9.

      Keep the lungs slightly inflated at 5 cm H 2 O with an air/O 2 mixture.


    • 10.

      When the repair is complete, the venous cannulas are replaced and the child is rewarmed until the esophageal temperature reaches 37 °C. The temperature of the blood from the pump should never exceed 39 °C, and the child’s temperature should not exceed 37 °C.


    • 11.

      Do not correct the metabolic acidosis often seen during rewarming. It will spontaneously correct as the child’s metabolism resumes. Administration of sodium bicarbonate usually results in postoperative metabolic alkalosis.


    • 12.

      It is suggested that the use of Hct levels of 30% during CPB cooling and rewarming may preserve neurologic functions better than with a reduced Hct.



    Further Reading


  • Schlunt M.L., Brauer S.D.: Anesthetic management for the pediatric patient undergoing deep hypothermic circulatory arrest. Semin Cardiothoracic Vasc Anesth 2007; 11: pp. 16-22.
  • Nelson D.P., Andropoulos D.B., Fraser C.D.: Perioperative neuroprotective strategies. Semin Thorac Cardiovasc Surg (Pediatr Cardiac Surg Annual) 2008; pp. 49-56.
  • Only gold members can continue reading. Log In or Register to continue

    Mar 27, 2019 | Posted by in ANESTHESIA | Comments Off on Cardiovascular Surgery and Cardiologic Procedures
    Premium Wordpress Themes by UFO Themes