Anaesthetic Management of Patients with Congenital

REVIEW ARTICLES

Annals of Cardiac Anaesthesia 2002; 7: 00–00

Anaesthetic Management of Patients with Congenital Heart Disease Presenting for Non-Cardiac Surgery Rachna Mohindra, MD, David S. Beebe, MD, Kumar G. Belani, MD Department of Anesthesiology, University of Minnesota Medical School, Minneapolis, Minnesota

The incidence of congenital heart disease is about one percent of all live births in the United States. Treatment is being performed at a younger age and these children are showing improved survival. It is not unusual for children with congenital heart disease to present for non-cardiac surgery. Their management depends on their age, type of lesion, extent of corrective procedure, the presence of complications and other congenital anomalies. Each patient needs a detailed pre-operative evaluation to understand the abnormal anatomy and physiology, and related anaesthetic implications. No anaesthetic agent is an absolute contraindication, although drugs beneficial for one lesion may be detrimental for another. Regional anaesthesia has also been safely used in children with congenital heart disease. However the anaesthesiologist must have a detailed understanding of the pathophysiology of the lesion and the pharmacology of drugs being used to be able to provide safe anaesthesia for children with congenital heart disease. (Annals of Cardiac Anaesthesia 2002; 5: 15–24) Key words: – Anaesthetic management, Non cardiac surgery, Congenital heart disease

Introduction

T

he incidence of congenital heart disease is 8:1000 of all live births in the United States. This results in approximately 32,000 babies born each year with congenital heart disease.1 Palliative and corrective surgery is now being done commonly at a younger age and the survival of such patients has improved. Currently there are over 640,000 children with congential heart disease surviving in the United States. Many of these children survive to adulthood. Although coronary disease is most prevalent in adults (7 million adults in the United States), 1 million adults have or have had repaired congential heart disease. The general anaesthesiologist will therefore frequently encounter patients with congenital cardiac problems presenting for noncardiac surgery.2 The care of such patients is far from routine. The presence of congenital heart disease increases the Address for correspondence: Dr. Beebe, MMC 294, 420 Delaware Street SE, Minneapolis, MN 55455; e mail: [email protected]

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risk for non-cardiac surgery. For example, the mortality for repair of a diaphragmatic hernia is twice as high in a baby with congenital heart disease compared to one without. Anaesthesia related cardiac arrest is also more common in infants with cardiac disease.3 Therefore a detailed understanding of the existing anatomy and pathophysiology is needed along with an organised plan to effectively care for these children. Each patient’s anaesthetic plan needs to be tailored according to the age, cardiac lesion, extent of palliative and corrective surgery if any, the presence of cardiac complications or other congenital abnormalities. In this manuscript we will: 1) Discuss how best to evaluate these patients preoperatively. 2) Describe the current perioperative regimen to prevent subacute bacterial endocarditis. 3) Review the types of congenital cardiac lesions, their correction, potential complications resulting from their correction and the impact on anaesthetic management. 4) Review induction and maintenance of anaesthesia, and 5) discuss management of the pulmonary vascular resistance

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Mohindra et al. Anaesthetic Management of Patients with CHD

and how to maintain physiological balance in children with congenital heart disease undergoing non-cardiac surgery. Finally we will describe the anaesthetic management of an infant with a hypoplastic left heart requiring a Nissen fundoplication. Pre-operative Evaluation A thorough pre-operative evaluation is imperative to formulate a systematic plan for anaesthesia and perioperative care. The anaesthesiologist should focus on understanding the cardiac lesion, the altered physiology and related implications. Cardiology consultation should be obtained in all patients with complex congenital heart disease, and the results of the electrocardiogram, echocardiogram and cardiac catheterisation made available. With a proper assessment the anaesthesiologist can obtain detailed information about the lesion. Knowledge of the lesion can help the anaesthesiologist make adjustments to optimise the patient’s haemodynamic status. For example, in a patient with a ventricular septal defect with right ventricular hypertrophy and a left to right shunt, hypovolaemia, tachycardia and drugs or manipulations that cause increased contractility should be avoided.4,5 The anaesthesiologist must pay particular attention to the presence of other congenital lesions in the preoperative assessment of patients with congenital heart disease. Often, infants and children with congenital heart disease are presenting for correction of these defects. Approximately 25 percent of all infants with congenital heart disease have some other congenital abnormality. Twenty percent of patients with congenital heart disease will have multiple deformities, and 8.5 percent will have abnormalities as part of a syndrome such as Down’s syndrome. Abnormalities are more common in patients with endocardial cushion defects (atrial-ventricular canals), ventriculoseptal defects, or those with tetralogy of Fallot. Approximately 8.8 percent of patients with congenital heart disease have musculo-skeletal abnormalities, 6.9 percent have neurological

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defects and 5.3 percent have genital-urinary irregularities.6 One congenital skeletal abnormality that is of particular concern to anaesthesiologists is atlantooccipital subluxation. This occurs in approximately 20 percent children suffering from Down’s syndrome. Children between age 5 and 6 years are at the highest risk. Subluxation from laryngoscopy and tracheal intubation may result in permanent quadriplegia.6 The current clinical status can be evaluated by inquiring about the child’s exercise tolerance or the infant’s feeding habits. Reduced activity with increasing fatigue and dyspnoea or feeding associated with irritability, dyspnoea or cyanosis indicate poor cardiorespiratory compensation. In babies, poor feeding and failure to gain weight properly may indicate congestive heart failure. Other routine questions like previous anaesthetic experience, allergies and medications should also be asked. History of prolonged intubation following cardiac surgery is of special concern because the patient may have developed subglottic stenosis.4,5 The physical examination should emphasise the airway, heart and lungs. Many syndromes with congenital heart disease have airway abnormalities. For example, patients with Down’s Syndrome often have macroglossia and are at risk for atlanto-occipital joint subluxation.6 The preoperative height and weight should be compared with standard numbers. Baseline values of heart rate, respiratory rate, oxygen saturation and blood pressure should also be noted. Patients should be examined for signs of congestive heart failure such as pedal edema, jugular venous distension, shortness of breath, enlarged liver and rales. Common signs of respiratory distress include increased respiratory rate, diaphoresis, chest retractions, nasal flaring and use of accessory muscles of respiration. Other physical signs such as cyanosis, clubbing, squatting and hypertension should be noted. Differences in blood pressure between each upper extremity may be present because of coarctation of the aorta or harvesting of the subclavian artery in a previous cardiac surgery,

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and determination of where to obtain the proper blood pressure should be made.4,5 In many patients who have had a simple repair of a congenital or cardiac defect and are doing well without medication, only the laboratory values that one would obtain prior to surgery in a normal patient will be necessary. However, children who have received blood transfusion for previous cardiac surgeries might develop serum antibodies. If blood loss is anticipated, blood typing and cross matching should be done preoperatively to ensure availability of compatible blood. In patients who are not corrected, partially corrected or still symptomatic, a more extensive preoperative laboratory evaluation is required. The Important pre-operative investigations include haemoglobin (Hb), haematocrit, coagulation studies and electrolytes. Hb results should be interpreted on the basis of age, disease process and procedure. Normal Hb level for a full term neonate is between 15 and 20 gm/dL. Physiological anaemia is encountered between 2 and 3 months of age when Hb falls to 9 to 11gm/dL. This is a normal condition and does not warrant blood transfusion. Patients with cyanotic congenital heart disease may not show physiological anaemia due to abnormally high levels of erythropoietin in response to low oxygen saturation since birth. Chronic hypoxaemia in these patients can lead to a Hb higher than 20 gm/dL.4,5 Hb levels greater than 20 gm/dL or haematocrits greater than 65% can be associated with hyperviscosity, red blood cell sludging and reduced oxygen delivery to tissues. Thromboembolism may also develop from sludging and poor venous blood flow if the viscosity of the blood is excessive. Red blood cell sludging from hyperviscosity is increased in the dehydrated fasting patient or one who develops hypothermia in the operating room. At Hb levels beyond 20 gm/dL, phlebotomy should be considered to decrease the risk of hyperviscosity and thromboembolism.4,5 Secondary polycythaemia may also be associated with a coagulopathy. Thrombocytopenia, hypofibrinogenaemia and low levels of vitamin K dependant clotting factors may be present in

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Anaesthetic Management of Patients with CHD

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patients with polycythaemia and cyanosis. Hepatic congestion from elevated central venous pressures resulting from surgical corrections of congenital heart disease such as a Fontan procedure or from congestive heart failure may also result in the poor production of clotting factors. Essential coagulation studies include the prothrombin time, partial thromboplastin time, platelet count and fibrinogen level.4,5 Serum electrolytes should also be determined in many patients with congenital heart disease if they are on diuretics, digoxin or have a history of arrhythmias. Arterial blood gases should be measured depending on the presence of cyanosis or respiratory distress.4,5 Prevention of Subacute Bacterial Endocarditis Subacute bacterial endocarditis can develop after non-cardiac surgery in patients with congenital heart disease if bacteria from a mucosal penetrating procedure seeds the abnormal or prosthetic endocardium. Prophylaxis is therefore recommended for most children or adults who have congenital heart disease. One exception is infants who have had a patent ductus arteriosus ligated more than 6 months prior to the procedure. Similarly patients with mitral valve prolapse without regurgitation do not require prophylaxis. Theoretically atrial and ventriculoseptal defects that have been closed primarily without a synthetic patch should not require prophylaxis. However, it is often difficult to determine this, and thus it is safer to administer perioperative antibiotics in most cases.7 Often it is problematic to determine which procedures other than standard surgical incisions may result in transient bacteraemia and risk causing subacute bacterial endocarditis in patients with congenital heart disease. When in doubt, antibiotics should be administered. Procedures requiring prophylaxis include tonsillectomy and adenoidectomy, rigid bronchoscopy, cystoscopy, dental procedures, and urethral and oesophageal stricture dilatation. Standard tracheal intubation, flexible bronchoscopy, pressure equalisation tube insertion and shedding of the primary teeth do not

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require prophylaxis. Table 1 lists the American Heart Association recommendations for antibiotic prophylaxis of patients at high risk for subacute bacterial endocarditis.7 Table 1. American Heart Association Recommendations for Patients at High Risk for Subacute Bacterial Endocarditis Procedure

Antibiotic

Antibiotic for Penicillin Resistant Patient

Oral, Dental, Oesophageal, Upper respiratory tract

Ampicillin 2.0 gm IV or IM, 50 mg/Kg IV or IM in children 30 min before procedure

Clindamycin 600 mg IV, 20 mg/Kg IV in children 30 min before procedure; or Cefazolin 1gm IV, 25 mg/Kg IV 30 min prior to procedure

Genital urinary or Gastrointestinal procedure

Ampicillin 2.0 gm IV or IM plus Gentamycin 1.5 mg/Kg IV or IM 30 min prior to procedure followed by Ampicillin or Amoxycillin 1 gm orally after initial dose, 50 mg/Kg IV or IM plus Gentamycin 1.5 mg/Kg 30 min prior to procedure followed by Amoxycillin or Ampicillin 25 mg/Kg orally in children

Vancomycin 1 gm IV administered 1 hour prior to procedure plus Gentamycin 1,5 mg/Kg IV or IM, Vancomycin 20 mg/ Kg IV 1 hour prior to procedure plus Gentamycin 1.5 mg/ Kg IV or IM in children

Pathophysiology of Congenital Heart Disease The types of defects and their repair often seem confusing and difficult to visualise. However, the pathophysiology of concern to the anaesthesiologist in congenital heart disease is relatively straightforward. The physiology of importance to the anaesthesiologist primarily concerns the pulmonary blood flow. Some lesions such as ventriculoseptal defects, atrial septal defects, and patent ductus arteriosus result in excessive blood flow to the lungs. These babies generally oxygenate well, but may develop symptoms from congestive heart failure due to excessive blood flow to the lungs. Prolonged exposure to high blood flow in the pulmonary circulation can result in pulmonary hypertension. Therefore most of these lesions, if discovered, are repaired at an early age. Following repair, other than requiring subacute bacterial endocarditis prophylaxis, most patients with these conditions

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can be treated like normal patients in terms of their anaesthetic management.4,5,7 On the other hand some lesions result in reduced blood flow to the lungs. In infants with tetralogy of Fallot the pulmonary artery is partially obstructed. Since there is also a large ventriculoseptal defect in this syndrome, blood can then be diverted from the pulmonary circulation to the systemic circulation, resulting in cyanosis. Events that cause an increase in the pulmonary vascular resistance such as stress, hypoxia, high ventilatory pressures or hypercarbia can result in shunting of blood away from the lungs and cyanosis. Increasing the systemic vascular resistance can restore blood flow to the lungs and lessen the degree of hypoxia. Unlike patients who have had simple ventricular or atrial septal defects repaired, patients with tetralogy of Fallot often have some residual defects and alteration in physical status. In a 60 month follow-up study of patients with repaired tetralogy of Fallot by Murphy et al, 30 percent had a residual ventriculoseptal defect, 17 percent had some residual outflow tract obstruction, 89 percent had pulmonary regurgitation, 3 percent had atrialventricular heart block and up to 34 percent had premature ventricular contractions with exercise.8 Some congenital cardiac defects have, at least initially, normal pulmonary blood flow. Coarctation of the aorta is an obstructive lesion to the aorta resulting in hypertension but without altering pulmonary blood flow unless congestive heart failure develops. Of significance for anaesthesiologists caring for these patients for noncardiac surgery is that repair of a coarctation does not always cure the hypertension. Stenosis can redevelop at the site, and many patients require long-term treatment for hypertension.4,5 Finally some cardiac defects present with mixing of the pulmonary and systemic blood in one chamber. Patients with transposition of great vessels initially require this mixing in what is essentially a single ventricle to survive. Current repair restores the separation of the pulmonary and systemic circulations (arterial switch procedure) to create relatively normal anatomy and physiology.

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However residual defects and complications from chronic hypoxia and congestive heart failure may persist.4,5 Infants with hypoplastic right or left ventricles truly have single ventricle physiology. To allow patients to survive with a hypoplastic or inadequate right ventricle, surgeons perform a series of operations, the end result of which is that the systemic venous drainage is bypassed directly to the pulmonary artery (Fontan procedure). These patients no longer have a right ventricle to pump blood through the lungs. Systemic venous pressure must therefore drive the blood through the lungs to provide oxygenation. Adequate hydration is essential in these patients to maintain oxygenation and circulation. On the other hand, chronic venous congestion is always present in patients who have had Fontan procedures. This can result in hepatic dysfunction and coagulopathy.4,5 Patients with a hypoplastic left heart present even a more severe challenge. The repair is complex, has a high mortality and occurs over several stages (Norwood Procedure). The end result is to bypass the right heart with a Fontan procedure, widen the hypoplastic aorta and have the right ventricle provide the systemic circulation like the left ventricle normally does.4,5


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these patients by preventing hypoxia, ventilating adequately to prevent hypercarbia, using agents to prevent excessive sympathetic stimulation and not using excessive airway pressures.4,5 Induction and Maintenance of Anaesthesia: The risk of aspiration in children with congenital heart disease is the same as for healthy children, and the same fasting guidelines can be used. Currently we allow solids and formula until 6 hours before and operation, breast milk until 4 hours prior to surgery, and clear fluids until 2 hours prior to surgery. This regimen allows children to be well hydrated, helps prevent hypoglycemia and feel more comfortable. However children with conditions like prolonged gastric emptying or gastroesophageal reflux should fast for 6-8 hours prior to surgery.4,5 All pre-operative medications except diuretics and anticoagulants should be continued until the morning of surgery. Any drug interactions with anaesthetic agents should be clearly understood and reviewed, if necessary.4,5

Anaesthesiologists also must deal with the injuries caused by the congenital defect prior to the cardiac surgical repair. Uncorrected cyanotic heart disease results in repeated episodes of myocardial ischemia. Subsequent myocardial fibrosis and congestive heart failure develops. Myocardial fibrosis is irreversible if cyanosis persists beyond 7 years of age.9

Premedication should be given to decrease anxiety and fear of the procedure, for easy separation from family and for smooth induction. It can be useful for patients with tetralogy of Fallot where agitation and increased catecholamine release can trigger a “tet” spell. On the other hand over medication can lead to hypercarbia and hypoventilation and even loss of airway. In patients with severe pulmonary hypertension, even a slight increase in carbon dioxide levels can raise pulmonary pressures to greater than systemic levels.4,5

Excessive blood flow to the lungs from, for example, an uncorrected ventricular septal defect damages the pulmonary vasculature and results in pulmonary hypertension. In extreme cases (Eisenmenger’s syndrome) the pulmonary artery pressure can be as high as the systemic pressure. Even in lesser degrees, pulmonary hypertension can increase the risk for general anaesthesia. Anaesthesiologists must be careful to avoid increasing the pulmonary vascular resistance in

DeBock et al studied the effect of standard premedication i.e. morphine 0.1mg/Kg, scopolamine 13 µg/Kg and secobarbital 2.5 mg/ Kg on arterial oxygen saturation in 33 patients. In 16 patients with non-cyanotic congenital heart disease, pulse oximeter readings decreased from 98.1±1.5 to 96.5±1.5% after premedication, considered clinically insignificant. In 17 patients with cyanotic congenital heart disease the pulse oximeter readings increased slightly from 73.5±11.8

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to 74.7±10.2% following the premedication. In 6 patients there was a decrease in the saturation readings but the correlation with the type of cardiac lesion was not considered. The author recommended pulse oximeter monitoring and supplemental oxygen as needed for patients with congenital heart disease after premedication.10 Currently we premedicate most infants and children with congenital heart disease undergoing noncardiac surgery with oral midazolam 0.5 mg/ Kg. This dose has been shown to ease anxiety from separation of the child from the parents and reduce the fright and agitation occasionally associated with anaesthetic induction. Midazolam can also be administered rectally in patients who cannot take the oral medication. Ketamine 3 mg/Kg administered with midazolam rectally can increase the level of sedation.11 No anaesthetic agent is an absolute contraindication to use in children with congenital heart disease. An agent beneficial for one lesion may be detrimental for another. By knowing the pharmacology of the agents and the physiology of the existing lesion adverse situations can be anticipated and dealt with accordingly. In a study by Laishley on the effect of anaesthetic induction regimens on oxygen saturation, 50 infants with cyanotic congenital heart disease were divided into 5 groups each receiving either ketamine, halothane, thiopental, fentanyl and thiopental or fentanyl alone. Oxygen saturation, heart rate and systolic blood pressure were measured at 5-minute intervals at room air, following preoxygenation, laryngoscopy and post intubation. All 5 regimens in this study were found to be equally effective in maintaining the oxygen saturation, heart rate and blood pressure. Halothane did cause a small drop in blood pressure but no change in oxygen saturation. Thiopental alone and with fentanyl in small incremental doses did not cause any detrimental effect on the vital signs. The authors concluded that all 5 induction agents were safe to use in infants with cyanotic congenital heart disease.12 The effects of inhalational and intravenous anaesthetic agents on speed of induction in

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children with left to right shunts or right to left shunts have been extensively studied and the subject of many articles. However the effects of shunts on the speed of induction in children are rarely of clinical significance. In general, the speed of inhaled induction in patients with a left to right shunt and excessive blood flow to the lungs is either faster or unchanged. That is because more blood than normal passes through the lungs with each heartbeat where it equilibrates rapidly with the anaesthetic agent. More agent is therefore delivered to the brain with each heartbeat than normal and the unconsciousness occurs quicker than usual. On the other hand an inhaled induction of anaesthesia will be slower than usual if blood is being diverted away from the lungs as in a right to left shunt.4,5 The opposite occurs with an intravenous induction of general anaesthesia. An intravenous induction will be slower in a left to right shunt because the blood going to the brain from the lungs containing the intravenous agent gets diluted with the systemic blood. It may be faster in a right to left shunt because the blood containing the drug partially bypasses the lung and goes directly to the brain. Therefore the drug reaches the brain quicker than normal. However along with speed of induction, the potential for overdose is also increased.4,5 Maintenance of general anaesthesia in patients with congenital heart disease undergoing noncardiac surgery is usually with an inhaled agent such as isoflurane, a short acting narcotic like fentanyl and a skeletal muscle relaxant such as cisatracurium.4,5 Nitrous oxide may be used in patients with congenital heart disease who have been totally corrected and are physiologically normal, such as those who have undergone an uncomplicated atrial septal defect repair. However, in those patients who have a left to right or right to left shunt, nitrous oxide should not be used. Nitrous oxide can rapidly expand air bubbles that may be inadvertently injected in an intravenous catheter. If a shunt is present air bubble may travel to the brain and cause a stroke. By expanding the air bubble nitrous oxide

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can result in a greater injury. Nitrous oxide also decreases the inspired oxygen concentration and can increase the pulmonary vascular resistance. This can be detrimental in patients with pulmonary hypertension.4,5

temperature, airway pressure, oxygen analyser and precordial stethoscope. Additional monitors like an arterial line or central venous catheter can be placed if necessary, but are not routinely used.4,5

Ketamine is a useful anaesthetic agent in paediatric patients with congenital heart disease because it causes minimal myocardial depression and maintains the systemic vascular resistance. On the other hand some studies have shown ketamine also increases the pulmonary vascular resistance and may worsen a right to left shunt. This may not be significant, however. Hickey administered ketamine to 14 intubated infants with congenital heart disease sedated with diazepam breathing spontaneously with minimum ventilatory support. Seven of the infants had normal pulmonary vascular resistance and 7 had elevated values. No significant changes were observed in cardiac index, pulmonary vascular resistance index and systemic vascular resistance index. The author concluded that in mildly sedated infants with congenital heart disease and controlled ventilation, ketamine had little effect on pulmonary vascular resistance. The increase in pulmonary vascular resistance observed in other studies with ketamine may be due to hypoventilation and related sympathomimetic effects.13

One should be aware that capnography often is inaccurate in patients with congenital heart disease due to altered pulmonary blood flow and ventilation/perfusion mismatch. In a right to left shunt decreased pulmonary blood flow through the lungs increases dead space ventilation. The end-tidal carbondioxide (CO 2) in these cases underestimates arterial carbondioxide tension (PaCO2). The larger the shunt greater the disparity between end-tidal CO 2 and PaCO 2 . 14 Anaesthesiologists should also be aware that a pulse oximeter placed on an extremity with decreased blood flow due to a shunt or a vascular anomaly would underestimate the true level of oxygenation. For example in a patient with Blalock–Taussig shunt with right subclavian artery diverted to pulmonary artery the pulse on the right side may be reduced or absent. Hence the blood pressure cuff, pulse oximeter and arterial line should be placed on the opposite side.4,5

All patients with congenital heart disease should have an intravenous catheter placed even if the procedure is a minor one, to rapidly administer drugs, if necessary. Intravenous access may be obtained post induction if the patient is haemodynamically stable. Care should be taken to avoid air bubbles from entering systemic circulation through the intravenous catheter. This is especially important for patients with right to left shunt because the air bubbles may bypass the lungs and pass directly to the brain. Even in left to right shunts the direction of shunt can be reversed during positive pressure ventilation or the cardiac cycle creating a risk for systemic air embolism.4,5 Monitoring for patients with congenital heart disease undergoing non-cardiac surgery should include a continuous ECG, pulse-oximeter, noninvasive blood pressure device, capnography,

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All children are at risk for hypothermia due to their large body surface area to body weight and decreased subcutaneous tissue. Hypothermia is of particular concern for infants with congenital heart disease because many of them may have polycythaemia. In polycythaemia, hypothermia can lead to red blood cell sludging, metabolic acidosis, decreased oxygen delivery, and organ infarct. Cold shifts the oxyhaemoglobin dissociation curve to the left reducing the availability of oxygen. Hypothermia can also reduce platelet function and contribute to surgical bleeding. Duration of action of certain drugs like vecuronium and atracurium may be prolonged. Forced air surface warming can effectively prevent hypothermia in paediatric patients.4,5 Criteria for extubation in healthy kids with corrected congenital heart defects are the same as for normal children. The anaesthesiologist should be aware that despite reparative procedures, residual defects and altered physiology might

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persist. In patients with uncorrected lesions, persistent cyanosis or congestive heart failure, it is usually safer to awaken and extubate the patients following a short period of ventilation in the intensive care unit. Following extubation all children with congenital heart disease should be closely monitored for adequacy of oxygenation and ventilation. Need for supplemental oxygen is individualised.4,5 Regional anaesthesia can be utilised in many children with congenital heart disease undergoing noncardiac surgery as a primary anaesthetic, or more often to provide postoperative analgesia. Regional anaesthesia improves peripheral blood flow and oxygen delivery, decreases the incidence of deep vein thrombosis and reduces perioperative blood loss, and there have been many successful case reports of the use of epidural anaesthesia in children with congenital heart disease. 15 Anaesthesiologists need to consider the type of cardiac lesion and its systemic effects prior to initiating a regional anaesthetic technique, however. For example, a patient with tetralogy of Fallot will have difficulty oxygenating if his systemic vascular resistance is acutely lowered. The sympathectomy resulting from an epidural or spinal anaesthetic may be harmful in such patients. Children with coarctation of aorta develop dilated intercostal arteries and may be at risk for accidental injection of local anaesthetic into the arteries during an intercostal block. Also those with polycythaemia should have coagulation abnormalities ruled out prior to initiation of spinal or epidural anaesthesia.4-5 Management of The Pulmonary Vascular Resistance In adult patients or children without cardiac disease, anaesthesiologists rarely have to consider the effect of the anaesthetic or ventilatory management on the pulmonary blood flow. In children with congenital heart disease, management of the pulmonary circulation becomes important. In babies the pulmonary vasculature is quite responsive compared to adults. This responsiveness often persists in older children with uncorrected congenital heart disease and

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those partially corrected or who have received only palliative procedures. Anaesthesiologists must decide for each patient whether there is excessive or inadequate blood flow to the lungs and plan the management accordingly. The potent inhaled agents such as isoflurane, desflurane and sevoflurane mildly decrease the pulmonary vascular resistance and may increase the blood flow to the lungs. On the other hand the agents also decrease the systemic vascular resistance and depress the myocardium. The blood flow to the lungs may therefore be unchanged or reduced in a mixing lesion. Nitrous oxide however increases the pulmonary vascular resistance. Ventilation and oxygenation have a much more profound effect on the pulmonary vascular resistance than anaesthetic agents. Table 2 lists what anaesthesiologists can do to alter pulmonary blood flow. Table 2. Management of Pulmonary Blood Flow Increase Pulmonary Blood Flow

Decrease Pulmonary Blood Flow

Oxygen Hypocapnia Alkalosis Normal Functional-Residual Capacity Blocking Sympathetics

Hypoxia Hypercarbia Acidosis Atelectasis/Hyperinflation Sympathetic Stimulation

Knowledge of the child’s cardiac lesion and its effect on pulmonary blood flow can help determine how to manage the patient to help maintain physiological balance. For example, in a child with a left to right shunt such as a ventriculoseptal defect, there usually is good cardiac function but too much blood flow to the lungs. The goal then is to keep the pulmonary vascular resistance elevated and the systemic vascular resistance low while maintaining contractility. This can be achieved by not hyperventilating the patient and not using excessively high oxygen concentration. On the other hand a baby with uncorrected or partially corrected tetralogy of Fallot has too little blood flow to the lungs, especially if he is having a “tet” spell. The goal is to maintain the systemic vascular

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resistance to deliver blood to the lungs. Since patients with tetralogy of Fallot also have an obstruction to the outflow of the right ventricle that worsens with tachycardia, dehydration and sympathetic stimulation, adequate volume maintenance and excessive sympathetic stimulation must be avoided. However, pure mixing lesions without obstruction may be benefited by sympathetic stimulation. Table 3 lists the physiological goals and suggestions to achieve these goals in children with congenital heart disease. Table 3: Physiological Goals for Children with Cardiac Lesions Undergoing Non-Cardiac Surgery Systemic Pulmonary Vascular Vascular Resistance Resistance

Contractility

Heart Rate

Left to Right Shunt (VSD)

↓

↑

Normal

Normal

Right to Left Shunt (TOF)

↑

↓

↓

↓

↓

↑

↑

↑

↓

Normal

Normal

↓

Mixing Lesions

Obstructive (coarct of aorta)

Suggestions Use ↓ FiO2 Avoid ↑ ventilation Maintain blood pressure, Avoid dehydration Maintain SpO2