This is Frank's thesis. It is written for other nurse anesthetists or anesthesiologists -- it is not written in layman's terms. If you have specific questions regarding Frank's thesis, you can contact him at FAjaworski@aol.com . We hope this paper is helpful to you as an added resource, but remember this is NOT medical advice. Please consult with your child's doctors if you have any concern about anesthesia for any kind of surgery for your heart child.

Contents

I. Introduction ............................................................1
II. Analysis ..................................................................3
III. Evaluation ..............................................................9
IV. Conclusions ............................................................9
V. References .............................................................11

I. Introduction

Congenital heart defects occur in 4-8 per 1,000 live births, with hypoplastic left heart syndrome occurring in 0.5 - 2.4 per 10,000 live births, ranking HLHS as high as 5th in frequency of CHDs in some studies. Hypoplastic left heart syndrome is a common and severe malformation.(6.; 5) Hypoplastic left heart syndrome is one of the last forms of congenital heart disease to undergo effective surgical treatment. It is a complex defect which requires either a three-stage surgical reconstruction or transplantation for survival. (10.; 1) Even when these patients have been surgically “repaired” the physiologic consequences of their congenital heart disease and its surgical therapy affect respiratory compliance, heart rate and potential for arrhthymias, pulmonary and systemic vascular pressures, the need for adrenergic agonists and antagonists, the uptake of anesthetic agents, and coagulability. (8.;2) Congenital heart defects were among the first cardiac pathologies repaired surgically, as with the closed heart procedure for ligation of patent ductus arteriosus and the early work of Lillehei in the repair of atrial and ventricular septal defects. (4.; 47-64) This work predates the now more commonly known coronary artery bypass graft. One of the complex lesions that has evaded effective surgical intervention until relatively recently is hypoplastic left heart syndrome. (10.;1)

The primary criteria for defining HLHS are hypoplastic or absent morphologic left ventricle, aortic valve hypoplasia, stenosis or atresia and mitral valve hypoplasia, stenosis or atresia. Secondary criteria are ductus dependent systemic circulation (with the exception of critical aortic stenosis with hypoplastic left ventricle), ascending aorta hypoplasia and aortic arch hypoplasia. It may also include double outlet right ventricle, interrupted aortic arch, atrioventricular septal defect (canal), anomalous pulmonary venous connection and atrial isomerism. (5.; 30) Because of the overwhelming effect of these multiple lesions these patients, when not diagnosed in utero by stage II ultrasound, are usually diagnosed with the onset of congestive heart failure within hours or days of birth. Prior to the development of effective surgical intervention this syndrome was uniformly fatal before three months of age. (1.;91)

Although no therapy presently exists to directly treat severe ventricular hypoplasia, surgical strategies are used that involve abandonment of the native left ventricle as the systemic pump. One approach to hypoplastic left heart syndrome is the strategy pioneered by Norwood in which staged surgical reconstruction is undertaken.(9.;688-695) The right ventricle is recruited for systemic perfusion via a pulmonary artery to aorta anastomosis with arch reconstruction and an atrial septectomy. Pulmonary blood flow is provided by an aortopulmonary shunt. This approach ultimately leads to a Fontan-type procedure with the right ventricle permanently assigned to support the systemic circulation. Growing experience with the Norwood procedure, as well as better understanding of how to manage these patients after surgery, have resulted in satisfactory and improving outcomes. An alternative treatment for infants with severe LV hypoplasia involves replacement of the heart with two normal sized ventricles through cardiac allotransplantation. However, because of the limited supply of donor hearts, many patients die waiting for a suitable heart. Because of this, the majority of centers treating these patients have now concentrated on developing improved techniques for staged reconstruction with hopes of providing satisfactory long-term survival. (7.; 189 and 10.; 1)

The anesthetic management of patients status post orthotopic transplantation has been adequately addressed in the literature. The purpose of this paper is to present the pathophysiology and anesthetic management considerations for the pediatric patient with hypoplastic left heart syndrome after three-stage surgical reconstruction, undergoing a non-cardiac procedure. This will be accomplished through a review of current literature.

II. Analysis

One important element of anesthetic care for these patients is coordination and communication with their cardiologist. These patients are frequently on antiarrhythmic medications, diuretics and blood thinners. Blood thinners should be stopped sufficiently early to allow recovery of normal platelet function before surgery. The patient can be heparinized post-operatively until oral medications are resumed. Prophylaxis against endocarditis should also be discussed with the patient’s cardiologist. Patients in good general conditon need not be admitted to the hospital preoperatively but should undergo pre-anesthetic evaluation before the day of surgery, to allow for changes in medications and acquiring necessary lab results. One important goal of the preop interview is to establish good rapport with the patient and, if the patient is a child, with the parents. (17.; 104)

Preoperative sedation is highly recommended. Rectal midazolam (0.4 mg/kg to a maximum of 10 mg) is recommended for infants. Nasal ketamine (5 mg/kg) with midazolam (0.2 mg/kg) produced no significant cardiac or respiratory effects in a study of heart-healthy children. Although the nasal administration route is usually poorly tolerated, similar cardiorespiratory stability has been observed with intravenous ketamine with benzodiazepenes for sedation and for cardiac catheterization of pediatric cardiac patients. (17.; 105)

Careful preoperative evaluation of these patients should include all aspects of their development. There is a relatively high incidence of serious noncardiac defects in children with congenital heart disease. (19.; 1) Growth retardation is common in unrepaired congenital heart disease, related to congestive heart failure, hypoxemia, poor feeding, associated syndromes, and increased energy expenditure. A study in Belfast, Northern Ireland of 26 patients with univentricular hearts palliated either with a PA band or a shunt only 3 out of the 26 had heights greater than 50th percentile, and taken as a group they were shorter, lighter and had less subcutaneous fat than controls. A study at Boston Children’s Hospital of 500 consecutive Fontan patients showed a mean height Z-score of -0.6 at 5-year followup, and 14% of the group had a height Z-score greater than 2 STD below normal. Growth retardation is a common problem in children with single ventricle palliated with a Fontan procedure. (14.; 1-2)

Compared with other patients with CHD, patients with HLHS are at increased risk for adverse neurodevelopmental sequelae, due to congenital CNS abnormalities, hypoxic-ischemic injury at presentation, multiple periods of CBP and episodes of CHF and cyanosis during infancy. CNS abnormalities not apparent in infancy may only become evident in preschool or school-age children. These include speech and language abnormalities. problems with higher reasoning and mathematics, learning disabilities and attention span and behavioral abnormalities. A neurological examination of 23 HLHS patients post-Fontan produced these diagnoses:

Microcephaly 17.3%
Cerebral palsy 17.3%
Seizure disorder 8.7%
Gross motor abnormalities 39.1%
Fine motor abnormalities 47.8%
ADHD 69.5% (15.; 11)

Because of this all patients should get a thorough neurologic exam preoperatively to avoid confusion on postoperative assessment.

Induction

If platelet function is normalized regional block is appropriate and may be advantageous. In unstable patients general anesthesia with endotrachial intubation for positive airway control is preferred. (17.; 105)

If at all possible, an intravenous line should be started before induction, both to insure a route for medication administration and to allow for judicious preoperative hydration. Hypoplastic left heart syndrome patients, due to their chronic hypoxemia, almost always present with a secondary erythrocytosis, with a hematocrit of greater than 50 being common. (2.; 368) Appropriate replacement of NPO fluid deficit prior to induction can offset their hypercoagulability and prevent microemboli formation. (18.; 4) Use of topical anesthetics such as EMLA®, which contains lidocaine and prilocaine, for preinduction I.V. starts is highly recommended.

If the patient is to be intubated, IV access (if not already in place) should be obtained after the patient is lightly anesthetized to allow administration of hypnotics and muscle relaxants. (17.; 105) IV induction should be accomplished as with non-cardiac patients, carefully titrating agents to their observed effects. Propofol has been shown to cause a significant decrease in systemic vascular resistance in children with congenital heart defects. In HLHS patients with a right-to-left shunt this results in a decrease in the ratio of pulmonary to systemic blood flow, which can lead to arterial desaturation. Assessing and correcting changes in this ratio, the Qp:Qs ratio, will be addressed in the next section.

Mask induction is appropriate in these patients with adequate preop sedation to prevent struggling by the anxious patient which can dangerously increase pulmonary pressures. Theoretically, mask induction will be slowed in these patients due to the right-to-left shunt, and at least one study has shown a measurable delay in rise of arterial blood levels of inhaled agent. Not all researchers feel that this is clinically significant.

In patients with very marginal reserves, as in those with dilated cardiomyopathy, it may be prudent to start a low dose dobutamine infusion (3-5 mcg/kg/min) a few minutes before induction. Once the patient is asleep and arterial blood pressure monitoring has been established the drug can usually be decreased or discontinued.

Airway & Pulmonary

There has been shown to be a 5% incidence of tracheobronchial anomaly in children with diagnosed congenital heart defect, with as high as 50% perioperative morbidity due to the underlying airway anomaly in some defects. (16.; 82) This dictates a high degree of suspicion for potential airway complications, a careful review of prior anesthetic records for evidence of difficulties in airway management, and preparation for alternate airway management or intubation techniques.

These patients also have the potential for restrictive lung disease due to multiple previous thoracotomies, prolonged ventilator support, recurrent pleural effusions with resultant pleural thickening, and the possibility of hypoplastic lungs. (13.; 7) All surgical procedures should be expedited as these patients are not well suited to long anesthesia and surgical times. (8.; 2)

Hypoplastic left heart syndrome patients have the potential for long term communication between pulmonary and systemic circulation due to patency of the fenestration in the interatrial baffle. As previously mentioned, this makes intentional control of the Qp:Qs ratio (ratio of pulmonary to systemic perfusion) of primary importance.

In normal patients, the pulmonary and systemic circulations are in series, and the ratio of blood flow to the two systems is 1:1 or 1.0 at all times. (3.; 229) Hypoplastic left heart syndrome patients with a fenestrated baffle can change this ratio by changes in either the pulmonary or systemic resistance. Decreased pulmonary vascular resistance (PVR) can drive the Qp:Qs ratio up resulting in shock due to hypoperfusion of tissues; at ratios above 2.0 the blood is oxygenated but does not reach the systemic circulation in sufficient volume for adequate perfusion. Decreased systemic vascular resistance (SVR) shunts blood away from the lungs and causes hypoxemia and cyanosis. A Qp:Qs below 0.5 is a risk for serious hypoxemia. (3.; 236-237)

Control of this potential perfusion complication is through vigilant monitoring of metabolic indicators, especially the patient’s color, and manipulation of arterial CO2 tension. Increased ventilation drives CO2 down with the primary effect of decreasing PVR and raising the Qp:Qs ratio; hypoventilation has the opposite effect. In event of very low Qp:Qs, as evidenced by severe cyanosis progressing to shock, a dobutamine infusion starting at 3-5 mcg/kg/min may be necessary. Optimal Qp:Qs ratio appears to be 0.7 to 1.0, but intraoperative management is based on cliniacal signs. (2.; 369)

Metabolism and body temperature are closely linked and decreases in metabolism decrease CO2 production. Maintaining body temperature is key and the practitioner should be prepared for fall in CO2 and a decreased PVR as a normal consequence of induction. Some studies advocate adding CO2 to the circuit to maintain PVR, although this has had differing degrees of success. (8.; 2)

Cardiovascular

Patients post-Fontan have several altered responses to exercise and physical stress that affect response to anesthetic interventions. Heart rate response is blunted, with slower increases and lower maximal heart rates, in the range of 80% of controls. This may be exacerbated by anti-arrhythmics. Ability to increase stroke volume is impaired, due to impaired function of the single ventricle (caused by preoperative chronic volume load, preoperative chronic hypoxia and possibly by the natural history of ventricular hypoplasia) and due to diminished venous vascular capacitance due to increased resting venous tone, which can be further limited with diuretic use. (13.; 6)

Little is known about the myocardial effects of inhaled anesthetics in chronic hypoxemia. Circulatory depressant effects are dose dependent; low to moderate concentrations of inhaled agents are usually well tolerated.

Cardiac arrhythmias are more common in patients with congenital heart disease. Atrial flutter is a frequent sequela of the Fontan operation with a reported prevalence of 12.5% to 26% at intermediate and late follow-up. Atrial flutter in a patient with Fontan circulation can cause significant hemodynamic compromise and is potentially fatal. The high prevalence of atrial arrhythmias may be a result of extensive atrial surgical procedures, elevated atrial pressures and atrial enlargement. Atrial flutter is the single most common atrial arrhythmia in this patient population; however, risk factors asociated with this complication remain ill-defined. (11.; 80-81)

Many patients who are candidates for a Fontan operation, particularly those with L-looped ventricles (AV discordance) develop complete heart block, resulting in placement of a pacemaker. Furthermore, frequent sequelae after a Fontan operation include atrial tachyarrhythmias and sinus node dysfunction. Pacemaker implantation is often beneficial as primary or adjunctive therapy. (12; 887)

Emergence

The most important considerations during emergence are lack of airway stimulation and prevention of nausea and vomiting. Coughing and vomiting will both increase intrathoracic pressure and PVR. To prevent a perfusion crisis this late in the procedure early extubation is advocated (although no significant studies have been undertaken) with minimal suctioning with soft tip catheters. Also, administration of antiemetic medications such as ondansetron or metoclopramide is indicated even without history of prior postoperative nausea and vomiting, as well as nonpharmacologic measures such as adequate hydration, body temperature maintenance and avoidance of potential irritants like nitrous oxide.

There is no specific reason why these patients cannot undergo minor procedures on an outpatient basis, at the discretion of the surgeon and barring any significant intraoperative events.

III. Evaluation

Specific considerations for HLHS are also explored in the research, such as response to induction agents, fluid management, and management of Qp/Qs ratio.

Research referenced for this paper seems to touch on all important elements of anesthetic care, from pre-operative evaluation through emergence. Howevver, there appears to be a need for response to specific agents and techniques, such as relative risks and complications of regional techniques.

Research in these areas appears to be ongoing, with two recent conferences in the southeast, U. S. region alone directly addressing all phases of care of these patiens, including anesthesia. As more survivors of the three-stage Norwood procedure move into the general population, the variables available for study will grow naturally along with the affected patient groups.

IV. Conclusions

Specific considerations should also be taken for especially careful pre-operative evaluation and planning, and aggressive management of Qp/Qs ratio in those patients with existing pulmonray/systemic communication.

Anesthesia providers in a facility serving the general population have a small but growing chance of caring for one of these patients. Those practicing at a pediatric hospital will more likely see these patients, possibly on a recurrent basis. Awareness of current research in this area will allow them to provide the safest possible anesthetic care. In addition, one should include among their consultants anesthesiologists with special expertise in managing patients with ccongenital heart disease. These specialists can serve as attending staff or consultants and resource individuals to the anesthetist. (21.; 261)

Anesthetic management of these patients for non-cardiac surgery is summed up much like that for cardiac surgery: Be mindful of the differences in physiology, anticipate pitfalls, analyze signs, act judiciously and avoid catastrophe. (8.; 2)

V. References

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21. Baum, V. The Adult Patient with Congenital Heart Disease. Journal of Cardiothoracic Vascular Anesthesia 1996 Feb; 10(2):261-82.
22. Bove, E. The Norwood Procedure for HLHS sponsored by The Cardiovascular Institute and Rondal McDonald Children’s Hospital of Loyola University Medical Center during Hypoplastic Left Heart Syndrome Symposiumm; 1999 November 20; Chicago.