Anesthesia for Noncardiac Surgery in Children with Congenital Heart Disease

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21 Anesthesia for Noncardiac Surgery in Children with Congenital Heart Disease

ADVANCES IN THE PAST SEVERAL DECADES have dramatically altered the natural history of congenital heart disease (CHD). These refinements have resulted in decreased morbidity and mortality for affected children and improvements in quality of life. As life expectancy continues to increase and survival rates further improve, an escalating number of children with CHD will need to undergo noncardiac surgery or other procedures unrelated to their heart disease. Because the trend continues to be for earlier cardiac surgery, children with CHD who have undergone palliative treatment or repair represent the main patient group that an anesthesiologist is likely to encounter during elective or emergent noncardiac surgery. In some cases, children may require noncardiac surgery before undergoing procedures to address their cardiovascular disease. In others, the condition may not require or be amenable to surgical intervention. The care of children with CHD is becoming more common in all diagnostic and surgical settings.

A wide spectrum of extracardiac anomalies has been described in children with CHD.15 A great incidence of chromosomal syndromes and genetic disorders is associated with CHD, and the reported prevalence of associated malformations ranges between 10% and 33%.68 The organ systems most often affected include musculoskeletal, central nervous, renal-urinary, gastrointestinal, and respiratory. Although many extracardiac malformations are relatively minor and have limited or no clinical implications, many children with CHD have significant noncardiac comorbidities.9 These pathologic and disease processes may necessitate surgical intervention. Other routine ailments and conditions may affect these children and require diagnostic procedures and surgical care.

The challenges of caring for children with CHD are magnified by the diversity of structural malformations, each with specific physiologic perturbations, hemodynamic consequences, and severity. This is further complicated by the variety of medical and surgical management strategies available. Most children require an individualized approach to anesthetic care.1012

Clinical outcomes for CHD depend on the nature of the anatomic abnormalities and the possibility of successful palliation or correction.13 The primary goal of palliative surgery is to favorably influence the natural history of the defect and decrease the likelihood of the severe consequences of the disease. However, children continue to have abnormal cardiovascular anatomy and physiology, and their abnormal circulation is associated with an increased risk of perioperative adverse events.1417

Reparative, corrective, or definitive procedures are expected to improve hemodynamics and cardiac function while minimizing long-term ill effects of an abnormal circulation, improving the overall clinical outcome. Although the pathology might have been surgically treated, the cardiovascular system should not be considered normal. True surgical correction may be the exception rather than the rule in CHD, and repair of a congenital cardiac lesion should not be equated to a cure for most children.

Despite these considerations, for children with good hemodynamic results, the risks associated with noncardiac surgery may not be significantly different from those of others without CHD. These children are considered to be doing well clinically, have a good functional status, require few or no medications, have no exercise restrictions, and undergo routine surveillance. They require minimal or no adjustment in perioperative care compared with that provided to children without CHD. In others, however, residual abnormalities exist. In some who are less fortunate, a pathologic process may remain or develop after cardiac surgery that is related to the primary disease or therapy. This may lead to severe cardiovascular or pulmonary impairment. These residua and sequelae may necessitate further medical or surgical interventions and may increase perioperative morbidity during noncardiac surgery.18 Management of these children is influenced by several factors but to a significant extent by the residual problems of the disease and treatment and associated hemodynamic perturbations.19,20

Many publications have examined the implications of anesthesia for children and adults with CHD undergoing noncardiac surgery.10,1933 However, only a limited number of studies have provided data on perioperative outcomes.3438 In contrast to the extensive literature regarding perioperative cardiac assessment and risk stratification during noncardiac surgery in adults with heart disease and the development of guidelines aimed at improving clinical outcomes, the lack of rigorous scientific data on this subject for the pediatric age group has made an equivalent effort challenging.39

In this chapter, general principles of anesthesia practice are reviewed as they pertain to the care of children with CHD undergoing noncardiac surgery. Unique perioperative considerations and issues applicable to high-risk patient groups are described. Anesthesia management for these children is significantly influenced by factors such as structural abnormalities, pathophysiologic consequences of the defects, functional status, potential residua, sequelae, and long-term outcome.

Preoperative Assessment

A detailed preoperative evaluation is indispensable for identifying and anticipating factors that may place a child with CHD at increased risk during anesthesia (Table 21-1).40,41 An important goal of this assessment is to gather information regarding the nature of the cardiovascular disease and prior therapeutic interventions. A determination of functional status is based on clinical data. The history and physical examination, in addition to the laboratory data and ancillary tests, provide complementary information about anatomic or hemodynamic status, enabling an overall risk assessment. Based on this clinical assessment and consideration of the major pathophysiologic consequences of a particular condition, a systematic, detailed, organized plan should be formulated for anesthesia and perioperative management. In some cases, the preoperative evaluation may establish the need to delay or defer elective noncardiac surgery, other interventions, or diagnostic procedures.

TABLE 21-1 Factors That Place Children with Congenital Heart Disease at Increased Risk during Anesthesia for Noncardiac Surgery

History and Physical Examination

As for all children undergoing anesthesia, the history and physical examination results are essential components of a thorough preoperative evaluation. In addition to the specifics regarding the present illness and planned procedure, the history should focus on the status of the cardiovascular system. Relevant information includes the type of cardiovascular disease and comorbid conditions, medications, allergies, prior hospitalizations, surgical procedures, anesthesia experiences, and complications. Symptoms, including tachypnea, dyspnea, tachycardia, rhythm problems, and fatigue, should be sought. Feeding difficulties and diaphoresis may represent significant symptoms in infants, whereas decreased activity level or exercise intolerance may be a concern for older children. Palpitations, chest pain, and syncope should be characterized. The history should include an assessment of growth and development because these may be affected in children with CHD. Failure to thrive suggests ongoing cardiorespiratory compromise. Those with decompensated disease, complex pathologies, associated genetic defects, or other syndromes may be particularly vulnerable. Recent illnesses such as intercurrent respiratory infections or pulmonary disease may increase the potential for perioperative complications and require careful appraisal of the risk/benefit ratio in elective cases.42,43

The physical examination should include the child’s weight and height. Vital signs, including heart rate, respiratory rate, and blood pressure, should be documented. If the child is known or suspected to have or has been treated for any form of aortic arch obstruction or has had any systemic-to-pulmonary shunt, upper and lower extremity and the right and left upper extremity blood pressure recordings and palpation of the quality of pulses should be documented. This assessment provides information about the patency of arterial beds and helps in the selection of blood pressure monitoring sites. The examination should explore suitable sites for venous and arterial access and identify potential difficulties. Emphasis should be given to the airway and cardiovascular system, with particular attention to any changes from previous examination findings.

General assessment should include the child’s level of activity, breathing pattern, level of distress (if any), and presence of cyanosis. Respiratory evaluation should include the quality of the breath sounds and indicate the presence or absence of labored breathing, intercostal retractions, wheezing, rales, or rhonchi. Abnormalities may suggest congestive symptoms or a pneumonic process. Cardiac auscultation should include assessment of heart sounds, pathologic murmurs, and gallop rhythms. The presence of a thrill, representing a palpable murmur, should be documented. The abdomen should be examined for the presence of hepatosplenomegaly. Assessment of the extremities should include examination of pulses, overall perfusion, capillary refill, cyanosis, clubbing, and edema. Noncardiac anomalies or pathology that may affect anesthesia care (e.g., specific syndrome complex, potentially difficult airway, gastroesophageal reflux) should be recorded.

An important objective of the preoperative evaluation is to identify children with functional cardiopulmonary limitations imposed by their cardiovascular disease. Symptoms and signs consistent with congestive heart failure, cyanosis, hypercyanotic episodes, and compromised functional status (i.e., significant exercise intolerance or syncopal episodes) should raise concerns about potential perioperative problems. The pediatric cardiologist should obtain information about the nature and severity of the cardiovascular pathology, describe the child’s overall clinical status, and assess prior complications. The cardiologist should assist in the identification of children at great risk and optimize their preoperative clinical condition. The perioperative care teams should be alerted to any particular concerns that may affect the care of the child. The anesthesiologist should have a detailed understanding of the child’s cardiac defect, pathophysiologic consequences, nature of the medical and surgical therapies applied, functional status, and implications for perioperative management. Although the surgical team may not have an in-depth understanding of the child’s cardiovascular disease, by sharing the details of the surgical plan and likely perioperative issues with the anesthesiologist, problems may be anticipated and proactively addressed.

Ancillary Studies and Laboratory Data

The baseline systemic arterial saturation value should be determined by pulse oximetry (Spo2) when the child is calm and, in most cases, while breathing room air. Acceptable values depend on many factors, including the specific cardiovascular defects, whether the child has a two- or a one-ventricle circulation, the preoperative versus postoperative status with respect to the cardiac pathology, and the stage in the palliative pathway for those undergoing such a strategy. Children who have undergone definitive procedures should be expected to have normal to a near-normal Spo2 value (at least 95%). After palliative interventions, Spo2 values typically range between 75% and 85%.

The extent of preoperative laboratory testing largely depends on the status of the patient and the type, anticipated duration, and complexity of surgery. Studies most commonly obtained include hematocrit, hemoglobin, electrolytes, and coagulation tests. In cyanotic children, a complete blood cell blood count allows determination of polycythemia, microcytic anemia, and thrombocytopenia. Prothrombin time, partial thromboplastin times, and international normalized ratio (INR) provide an indication of clotting ability. Cyanotic children usually have increased red blood cell mass and relatively small plasma volumes. The collection of specimens for coagulation tests requires sampling tubes that adjust the amount or concentration of citrate to prevent artifactual prolongation of the values. For those receiving diuretic therapy, digoxin, or angiotensin-converting enzyme inhibitors, the determination of a basic metabolic panel may be useful. Blood typing and crossmatching should be performed depending on the anticipated need for blood administration.

A recent electrocardiogram (ECG) should be reviewed for any changes from prior studies (particularly regarding criteria consistent with chamber dilation or ventricular hypertrophy), the presence of rhythm abnormalities, and findings suggesting myocardial ischemia. If an arrhythmia is identified, further evaluation is warranted because it may reflect an underlying hemodynamic abnormality that may affect the perioperative course. A continuous ECG recording (i.e., Holter monitor) and further evaluation may be indicated in the child with a history of rhythm disturbance, palpitations, or syncope or with an ECG suggesting significant ectopy or arrhythmia. An exercise tolerance test or treadmill study may be warranted if there is concern about myocardial ischemia, as may be the case for the child with aortic stenosis, coronary artery anomalies, or exercise-induced arrhythmias.

Review of a recent chest radiograph, including a lateral view, provides information regarding cardiac size, chamber enlargement, and pulmonary vascularity. Prior studies such as echocardiograms, cardiac catheterizations, electrophysiologic procedures, and magnetic resonance imaging should be reviewed. In some cases, it may be necessary to obtain further diagnostic information before proceeding with the planned procedure if there are symptoms that merit additional investigations or issues of concern. These evaluations should be coordinated with the child’s cardiologist. It is also important to consider whether the child may benefit from cardiac catheterization for diagnostic or interventional purposes to address significant structural, functional, or hemodynamic abnormalities before the anticipated procedure. In addition to providing potentially helpful information, the clinical status of the child can be substantially improved in many cases by catheter-based interventions. This may be of significant benefit when the anticipated procedure is considered to be major.

One of the goals of the preoperative evaluation is to obtain the most diagnostic information with the fewest tests and the least risk, discomfort, and expense for the child. The anesthesiologist is particularly suited to determine which tests are appropriate for optimal perioperative planning and whether additional data are needed.

Fasting Guidelines

Although the optimal period of fasting for children before surgery has been the subject of some debate, most centers follow established guidelines to reduce the risk of aspiration.4447 The same guidelines are applicable to children with CHD with a few additional considerations. Intake of clear fluids or the intravenous administration of maintenance fluids may be required in some children to ensure adequate hydration if the fasting period is prolonged. This is particularly important in small infants and in patients with obstructive lesions, cyanotic disease, or single-ventricle physiology. Maintenance of adequate hydration and ventricular preload may limit potential detrimental hemodynamic changes associated with anesthesia and surgery.

Intraoperative Management

Anesthesia and surgery impose additional stresses on the cardiovascular system and provoke compensatory mechanisms to maintain homeostasis. It is important to assess the child’s physiology and cardiovascular reserve to anticipate his or her ability to increase cardiac output to meet metabolic demands. This information, along with the nature and complexity of the surgery, can help to decide the extent of monitoring required. This information can be used to choose anesthetic agents and techniques that least affect the child’s cardiovascular system. Prompt intervention is imperative if decompensation occurs. Good communication among the surgeon, cardiologist, anesthesiologist, and nursing teams during the entire perioperative period is essential in treating children with complex disease.

General Considerations

Intravenous Access

Secure intravenous access is mandatory for administration of fluids and medications during anesthesia care. In most children with CHD, intravenous access is established after an inhalational induction. In those considered at great risk, such as children with severe outflow tract obstruction, moderate to severe cardiac dysfunction, pulmonary hypertension, or potential for hemodynamic compromise, consideration should be given for placement of intravenous access before induction of anesthesia or very early in the induction. The size of the intravenous catheter should be determined by the anticipated fluid requirements. If peripheral access is poor, central venous access may be necessary, particularly if there is potential for large intravascular volume shifts and to allow monitoring of central venous pressure. Placement of a central venous catheter may be assisted by audio Doppler or two-dimensional ultrasound guidance (see Chapter 48). In the small infant with single-ventricle physiology, central venous cannulation with catheter placement in the superior vena cava may be undesirable in view of concerns about potential vascular complications that may affect pulmonary blood flow or subsequent surgical palliation. In these children, a small catheter or alternative approach (e.g., femoral venous access) should be considered. In children with an existent or potential right-to-left shunt, all air must be removed from intravenous infusion tubing. Air filters may be difficult to use in the operating room because they may restrict the rate at which intravenous fluids or blood may be administered in emergency situations. They may be more useful in the preoperative and postoperative periods.

Monitoring

A basic principle of intraoperative monitoring is to use techniques or devices that provide useful information to help with clinical decision making and to avoid monitors that are distracting or redundant. Basic monitoring involves observation of the child, including skin color, capillary refill, respiration, pulse palpation, events on the surgical field, and color of shed blood. Standard noninvasive monitors used during most surgical interventions include oscillometric blood pressure assessment, electrocardiography, pulse oximetry, capnography, and temperature monitoring. A precordial stethoscope can be extremely helpful for monitoring changes in heart tones that may suggest early hemodynamic compromise. In the child with CHD, relatively sophisticated and invasive monitoring may be needed.

Capnography

Capnography can confirm proper endotracheal tube placement, help to assess the adequacy of ventilation, and aid recognition of pathologic conditions such as bronchospasm, airway obstruction, and malignant hyperthermia. In spontaneously breathing, sedated children receiving supplemental oxygen through a nasal cannula, capnography monitors the end-tidal or exhaled carbon dioxide (Petco2) concentration. A prospective, observational study in children undergoing cardiac catheterization with sedation administered by nonanesthesiologists found that monitored Petco2 values provided a reasonable estimate of arterial blood CO2 values.58 Although the absolute value for Petco2 may not be as reliable as in the presence of an endotracheal tube, the capnograph waveform confirms the presence or absence of respirations and air exchange. End-tidal CO2 monitoring also provides a gross index of pulmonary blood flow. In children with cyanotic heart disease, Petco2 values may underestimate arterial carbon dioxide tension (Paco2) measurements due to altered pulmonary blood flow and ventilation/perfusion mismatch.59,60

Transesophageal Echocardiography

Numerous publications have documented the utility of transesophageal echocardiography as a monitoring device in high-risk adults undergoing noncardiac procedures.6172 Sporadic reports have demonstrated the utility of this imaging approach in children undergoing noncardiac surgery.7378 However, the contribution or application of this modality in the pediatric age group in this particular setting has not been well defined and requires further investigation.

Selection of Techniques and Agents

Several anesthetic regimens have been used in children with CHD undergoing noncardiac surgery and studies or procedures that require deep sedation or immobility. Although no single formula or recipe is recommended, the anesthetic techniques and agents used for a particular situation should be selected in consideration of the procedure, the child’s disease process and functional status, and the impact of the hemodynamic effects of the anesthetic and procedure on the pathophysiologic process. Factors such as age, physical characteristics, and preferences of the anesthesiologist must be taken into consideration. The primary goals of anesthesia management with respect to the cardiovascular system are to optimize systemic oxygen delivery, maintain myocardial performance within expected parameters for the patient, and ensure the adequacy of cardiac output. A potentially limited cardiovascular reserve, reduced tolerance for perioperative stress, and detrimental alterations of the balance between pulmonary and systemic blood flow during anesthesia and surgery should be considered. A carefully titrated anesthetic, regardless of the specific agent, is optimal.

Anesthesia Technique

General anesthesia has the advantages of wide acceptance, ease of application, and relative certainty of effect. It is the appropriate choice for most children undergoing noncardiac surgery. Disadvantages include a greater potential for wide fluctuations in the hemodynamics and a prolonged recovery period. The intravenous route allows for rapid induction of anesthesia. If intravenous access is not available, inhalational induction may be performed. Inhalational anesthetics dilate vascular beds and reduce sympathetic responsiveness. These are desirable goals for most children, even those with heart disease, because adequate myocardial function and a reactive sympathetic nervous system are usual. However, children with ventricular dysfunction may require an increased resting sympathetic tone to maintain systemic perfusion. Potent inhalational agents in this setting may further impair myocardial function, decrease sympathetic tone, and potentially cause cardiovascular decompensation. These children and others with a relatively fixed cardiac output may require a technique that combines several medications (i.e., balanced technique) to achieve anesthesia while minimizing the risk of hemodynamic compromise. A potent opioid, amnestic agent, and muscle relaxant technique minimizes myocardial depression and tends to leave sympathetic responsiveness intact while providing analgesia, amnesia, and immobility.

Regional anesthesia has been safe and effective in children with CHD (see Chapters 41 and 42).7679 Advantages of regional anesthesia, such as epidural and spinal techniques, include an effect largely limited to the surgical site, decreased number of systemic medications, a potentially brief recovery period, and usually a more pleasant experience for the child. Use of these techniques, however, may not always be effective. Regional anesthesia retains the potential for hemodynamic compromise, particularly in hypovolemic children or those with a fixed cardiac output. It is also contraindicated in those with coagulation defects. The administration of agents such as local anesthetics, opioids, or other adjuvants (e.g., clonidine) into the caudal space may attenuate the sympathetic outflow associated with surgical manipulation and noxious stimuli and facilitate postoperative pain management.

The choice of technique affects termination of the anesthesia and emergence. Anesthesia performed with fewer agents is inherently simpler and usually easier and more predictable to terminate. The availability of ultra-short-acting opioids (e.g., remifentanil) and other agents (e.g., dexmedetomidine) has avoided the need for postoperative ventilation solely related to residual effects of depressant drugs. Ventricular function and the presence of intracardiac shunts can significantly affect uptake and distribution of inhalational anesthetics and the kinetics of intravenous medications (see Chapter 6).

Inhalational Agents

The use of inhalational anesthetics has been at the forefront of pediatric anesthesia practice for many years.80,81 Sevoflurane was introduced in the mid-1990s, replacing halothane for induction of anesthesia in many centers. A study on the safety and efficacy of inhaled agents in infants and children with CHD during cardiac surgery demonstrated twice as many episodes of hypotension, moderate bradycardia, and emergent drug use in those who received halothane compared with those who received sevoflurane.82 These data and those from other studies that demonstrated the potential benefits of sevoflurane on hemodynamic stability and minimal impact on myocardial performance led to sevoflurane becoming the preferred anesthetic agent for children, particularly those with heart disease.8388 Nonetheless, in some jurisdictions and under some conditions, halothane may remain the primary anesthetic for children.

Intravenous Agents

Propofol is one of the most frequently used medications for intravenous sedation and general anesthesia. It has been used in children with CHD in numerous settings.8992 The hemodynamic effects of propofol have been investigated in children with normal hearts and in those with cardiovascular disease. An echocardiographic study in infants with normal hearts undergoing elective surgery demonstrated that propofol did not alter heart rate, shortening fraction, rate-corrected velocity of circumferential fiber shortening, or cardiac index after intravenous induction.93 However, this medication decreased arterial blood pressure to a greater extent than thiopental, an effect attributed to a reduction in afterload. A comparison of propofol and ketamine during cardiac catheterization found that propofol caused a transient decrease in mean arterial pressure and mild arterial oxygen desaturation in some children.94 In view of the significantly faster recovery, it was concluded that propofol was a practical alternative to ketamine for elective cardiac catheterization in children.

Another investigation in 30 children with CHD undergoing cardiac catheterization demonstrated significant decreases in mean arterial blood pressure and systemic vascular resistance during propofol administration.89 No changes in heart rate, mean pulmonary artery pressure, or pulmonary vascular resistance were observed. In children with intracardiac shunts, the net result of propofol was a significant increase in the right-to-left shunt, a decrease in the left-to-right shunt, and decreased pulmonary-to-systemic blood flow ratio, resulting in a statistically significant decrease in the Pao2 and arterial oxygen saturation (Sao2), as well as reversal of the shunt direction from left-to-right to right-to-left in two patients. It was also shown that propofol could lead to further hemoglobin desaturation in children with cyanotic heart disease.

The effects of propofol have been examined in children undergoing electrophysiologic testing and radiofrequency catheter ablation for tachyarrhythmias. The drug has no significant effect on sinoatrial or atrioventricular node function or accessory pathway conduction in Wolff-Parkinson-White syndrome.95,96 However, a study documented that ectopic atrial tachycardia may be suppressed during propofol administration in children.97

Collectively, these data suggest that the judicious use of propofol may be a reasonable option in children with adequate cardiovascular reserve who can tolerate mild decreases in myocardial contractility and heart rate and mild to moderate decreases in systemic vascular resistance. The effects of propofol on the direction and magnitude of intracardiac shunts may be an important consideration in children with cyanotic heart disease and may influence the hemodynamic assessment of those undergoing evaluation of pulmonary-to-systemic blood flow ratios in the cardiac catheterization laboratory.

Thiopental, a rapid-acting barbiturate, was used for many years for induction of anesthesia. Several investigations have documented the cardiovascular responses to this agent in the pediatric age group. In children with normal hearts, the cardiac index remains unchanged, although the shortening fraction decreases and alterations in load-independent parameters of contractility occur.93 The myocardial depressant properties of barbiturates are well established, as are its effects on venodilation and blood pooling in the periphery. These data suggest that a subset of children who receive thiopental may be at risk for hemodynamic instability. It has been suggested that thiopental should be used with caution, particularly in those with limited reserve or increased sympathetic tone. Thiopental is not available for use in the United States.

Etomidate, a carboxylated imidazole derivative, has anesthetic and amnestic properties but no analgesic effects. This agent demonstrates favorable qualities over other intravenous drugs due to its lack of effect on hemodynamics.98,99 This, combined with laboratory and clinical data that support minimal effects on myocardial contractility, makes this drug a particularly desirable agent in critically ill children and in those with limited cardiovascular reserve.100 Despite these benefits, several undesirable adverse effects are associated with etomidate, including pain on intravenous administration, myoclonic movements that may mimic seizure activity, and inhibition of adrenal steroid synthesis perioperatively.101,102 Although used primarily as an induction agent, etomidate has been administered for sedation of children during cardiac catheterization and in other settings.103105 A concentrated form of this medication is available in Europe but not in the United States.

Ketamine is a dissociative anesthetic agent administered by the intravenous, intramuscular, and oral routes. In view of its sympathomimetic effects that result in an increased heart rate, blood pressure, and cardiac output, this drug has been widely used in children with heart disease, particularly in younger children. The effects of this agent on systemic vascular resistance make it a suitable choice in children with right-to-left shunts because pulmonary blood flow is enhanced. This contrasts with inhalational agents, which by causing systemic vasodilation may decrease pulmonary blood flow in the presence of an intracardiac communication and potentially worsen the degree of cyanosis. In clinical use, however, oxygen saturation typically increases with both agents. Additional favorable properties include intense analgesia at subanesthetic doses and a lack of respiratory depressant effects.

Several investigations have addressed the concern of potential detrimental changes in pulmonary vascular tone resulting from ketamine although no significant effects have been reported on pulmonary arterial pressures and pulmonary vascular resistance at the usual clinical doses.106109 Regarding its effect on myocardial performance, in-vitro investigations have shown a direct myocardial depressant effect in animal species and the failing adult human heart. This is considered to be the result of inhibition of L-type voltage-dependent calcium channels in the sarcolemmal membrane and may be a consideration in critically ill infants with severely impaired cardiac reserves. Additional undesirable effects of ketamine include emergence reactions, excessive salivation, vomiting, and increased intracranial pressure.

Dexmedetomidine is a selective α2-adrenergic agonist agent being increasing used in the pediatric age group. Compared with clonidine, the drug exhibits greater specificity for the α2-adrenergic receptor over the α1-adrenergic receptor. Favorable effects of the drug include sedation, anxiolysis, and analgesia. This medication provides hemodynamic stability, although adverse effects have been reported, including bradycardia, hypertension, and hypotension. A study of the hemodynamic effects in children undergoing dexmedetomidine sedation for radiologic imaging demonstrated modest decreases in heart rate and blood pressure. These changes in response to moderate doses were independent of age, required no pharmacologic interventions, and did not result in any adverse events; however, high dose dexmedetomidine can be associated with significant bradycardia.110,110a In addition, treatment of dexmedetomidine-induced bradycardia with glycopyrrolate (5 μg/kg) has been associated with severe persistent hypertension.110b

Dexmedetomidine is used as a premedication agent, during diagnostic studies and procedural sedation, to reduce emergence delirium, in the treatment of symptoms associated with opioid withdrawal, and as an adjuvant agent in the operating room and postoperative settings.111 In children with CHD, its benefits have been reported during monitored anesthesia care, diagnostic and interventional cardiac catheterization, intraoperative sedation, after cardiac and thoracic surgery, as a primary agent during invasive procedures, and in the treatment of perioperative atrial and junctional tachyarrhythmias.112119 This medication has also been used in children with pulmonary hypertension with good results.120,121

The effects of dexmedetomidine on cardiac electrophysiology have been examined in children; the drug significantly depresses sinus and atrioventricular nodal function.122 Other findings included a reduction in the heart rate and increases in arterial blood pressure. Hammer and colleagues concluded that this medication should be considered undesirable for electrophysiologic studies and that it could be associated with adverse effects in patients at risk for bradycardia or atrioventricular block.122 In contrast, another study concluded that dexmedetomidine was not associated with any significant or any atypical ECG interval abnormalities, except for a trend toward a decrease in heart rate in children with CHD.123 Until additional data are available, it may be prudent to exercise caution when considering the use of dexmedetomidine in children with conduction abnormalities.

Although the experience suggests an overall safety profile in children with CHD, fragile patients may not tolerate the heart rate and blood pressure fluctuations associated with dexmedetomidine administration. Significant adverse effects have been described that include severe bradycardia progressing to asystole.124

Opioids and benzodiazepines are widely used medications in pediatric anesthesia practice. Opioids attenuate the neuroendocrine stress response associated with anesthesia and surgery.125,126 After repair of CHD, these medications have been shown to blunt the stress response in the pulmonary circulation elicited by airway manipulations.127 Morphine administration may be associated with histamine release and hypotension. The synthetic opioids are devoid of these effects and provide excellent hemodynamic stability with minimal changes in heart rate and blood pressure in children with CHD.128 The primary concern about opioid administration is their central respiratory depressant effects because their primary cardiovascular manifestations are minimal. Benzodiazepines provide sedation and amnesia during the perioperative period. Midazolam administration may allow a reduction in the inspired concentration of inhalational anesthetic agents, which is a desirable feature in children with labile hemodynamics or in those considered at great risk for the myocardial depressant properties of inhalational anesthetics. Studies of the effects of benzodiazepines in children with CHD are limited.129

Neuromuscular blocking drugs facilitate endotracheal intubation and prevent reflex movement during surgery if the anesthetics alone are insufficient. All inhalational anesthetics potentiate the effects of nondepolarizing muscle relaxants. These medications have various onsets and durations of action and diverse hemodynamic effects. The cardiovascular and autonomic effects of muscle relaxants have been characterized mainly in adults with acquired cardiovascular disease130133 (see also Chapter 6). Drug selection is based on the need to facilitate endotracheal intubation and surgical relaxation, hemodynamic side effects, and the anticipated duration of surgery.

Induction of Anesthesia

Induction of anesthesia in children with CHD most commonly can be accomplished using the inhaled or intravenous route. The intramuscular route (i.e., ketamine administration) may be preferable in some cases, particularly in an uncooperative, developmentally delayed, or combative child. Less common induction techniques include subcutaneous, intranasal, and rectal administration of agents. These various approaches may also be used in combination (see Chapter 4).

An intravenous induction may be preferable in some children in view of its potentially greater safety margin. In addition to the ability to titrate medications and rapidly correct hemodynamic alterations, other benefits include the speed of effect, although this may be slowed in children with large left-to-right shunts due to recirculation of the drug in the lungs. Left-to-right shunting results in a less concentrated amount of anesthetic agent reaching the brain and delayed onset of action. Right-to-left shunts speed intravenous induction because a significant portion of the medication bypasses the lungs (where it is degraded) and directly enters the systemic circulation, reaching the brain more rapidly than an intact circulation.

If intravenous access is not available, an inhalational induction is performed in most cases. A carefully titrated inhalational induction and early placement of an intravenous catheter usually is safe even in children with moderate hemodynamic disturbances, particularly after premedication has been given. This produces loss of consciousness, with acceptable conditions for establishing intravenous access. Inhalational induction may be delayed in cyanotic children and those with right-to-left shunts, particularly for anesthetics with reduced blood solubility, because the decreased pulmonary blood flow limits the rate of increase in the concentration of the anesthetic in the systemic arterial blood. The rapidity of an inhalational induction is increased in the presence of a reduced cardiac output because the anesthetic partial pressure in the alveoli increases more rapidly as less anesthetic is removed by the smaller pulmonary blood flow (see Chapter 6). Left-to-right intracardiac shunts have limited effects on the speed of induction of inhaled anesthetics.

Postoperative Care

The postoperative management of the child with CHD involves many of the same physiologic principles applicable to intraoperative care. The extent of the postoperative care, optimal place for recovery, and need for monitoring and hospitalization depend in large part on the child’s clinical condition and type and extent of the procedure. Immediately after surgery, most children awaken from anesthesia and recover from muscle relaxants, which may impose various stresses and hemodynamic changes. Adequate oxygenation and ventilation along with airway protection must be ensured and may need to be provided if the child cannot manage these functions on his or her own. Significant hypoventilation must be avoided during this time because it may negatively affect pulmonary vascular tone and overall hemodynamics in vulnerable children with CHD. Adequate pain control and, sometimes, sedation are important postoperatively. This may be a challenging issue for the child who requires noncardiac surgery soon after a prolonged hospitalization in view of the increased likelihood for tolerance to analgesic and sedative drugs.

Observation and physical examination provide much information about the child’s respiratory status, cardiac function, and systemic perfusion during the postoperative period. Adequacy of oxygenation and ventilation can also be assessed with noninvasive monitoring and blood gas analysis. Monitoring urine output may be helpful.

Hemoglobin or hematocrit values are monitored as a measure of oxygen-carrying capability in cases in which significant blood loss or the administration of fluids might have occurred. Serum electrolytes are screened if fluid shifts have taken place during the surgical and postoperative periods. Although digoxin is now used less frequently, particular attention should be given to the avoidance of hypokalemia in children receiving this drug. Serum glucose levels should be followed in neonates and small infants and dextrose-containing fluids administered as appropriate. Determination of ionized calcium (iCa2+) levels may be indicated for patients with a history of DiGeorge sequence because of a propensity for hypocalcemia. The required fluid replacement is dictated by the child’s heart defect, type of surgery performed, and volume losses (see Chapters 8 and 10).

Perioperative Problems and Special Considerations

Several potential perioperative problems related to multiple factors may be encountered while caring for children with CHD who require noncardiac interventions. Because it is not feasible to detail all possible problems and potential concerns, this section highlights the more common issues to serve as a framework.

Cyanosis

Cyanosis is a common finding in children with defects characterized by limited pulmonary blood flow or intracardiac mixing. As surgical management strategies evolve to target the youngest of infants, the effects of cyanosis may be limited in these children. However, in those requiring delayed surgery, palliation, or staged correction of their defects, the effects of cyanosis may be long lasting. Chronic hypoxemia affects all major organ systems. Compensatory mechanisms that attempt to provide adequate systemic oxygen delivery in the presence of chronic hypoxemia include polycythemia, increases in blood volume, alterations in oxygen uptake and delivery, and neovascularization. Despite the favorable effects of the adaptive responses, these alterations may be detrimental. Polycythemia, the most significant compensatory response, is associated with increases in blood viscosity and red cell sludging. The common occurrence of iron-deficiency anemia in cyanotic children further enhances hyperviscosity and the unfavorable consequences of this condition. Several hemostatic abnormalities (e.g., thrombocytopenia, altered platelet function, and clotting factor abnormalities) have been documented as a result of hypoxemia and erythrocytosis that may affect the coagulation system and increase perioperative risks.134139 This is compounded by increased tissue vascularity, with a large number of blood vessels per unit of tissue.

The increased blood viscosity in children with cyanosis is associated with stasis and a risk for thrombotic events.140 If the hematocrit exceeds 65% preoperatively, some clinicians advocate phlebotomy to reduce the hematocrit to 60% to 65%. This limits sludging of red blood cells and increases oxygen delivery to tissues. If blood is removed by preoperative phlebotomy, it may be saved for autologous transfusion in the perioperative period.

During the perioperative period, adequate hydration should be maintained in children with cyanotic CHD, and care should be taken to avoid prolonged venous stasis. Cyanotic children are at risk for paradoxical embolic events, mandating meticulous attention to intravenous lines during fluid or drug administration. This is a reasonable routine approach for all children with CHD, regardless of the nature of the structural abnormalities. The addition of air filters to intravenous tubing should not replace vigilance.

Ventricular Dysfunction

Children with CHD may have ventricular dysfunction involving the right heart, left heart, both sides of the heart, regional cardiac tissue, or global cardiac tissue. It may be temporary or permanent. In systolic dysfunction, contractile function is primarily impaired. Diastolic dysfunction is associated with abnormal relaxation or ventricular compliance. Some children have systolic and diastolic dysfunction. Ventricular dysfunction may result from factors such as age at the time of the operation and chronicity of the cardiac workload (pressure or volume); may be caused by the primary disease, myocardial hypertrophy, ischemia, or cyanosis; or may occur as a direct effect of surgery (e.g., ventriculotomy, cardiopulmonary bypass, ischemic time, circulatory arrest). Diseases that affect cardiac muscle (e.g., myocarditis, dilated cardiomyopathy) may be associated with congestive symptoms, whereas others (e.g., restrictive cardiomyopathy) may lead to diastolic heart failure.

In children with cardiomyopathy that was accompanied by severe ventricular dysfunction, general anesthesia for noncardiac procedures was associated with an increased frequency of complications.142 They often required hospital support before and after the procedure that in many cases included intensive care management. Hospital stay was prolonged for children with severe ventricular dysfunction compared with those with a lesser degree of impairment. Based on these findings, early consideration of perioperative intensive care support was recommended for monitoring and optimization of cardiovascular therapy.142

Ventricular Pressure Overload

Pressure overload in the postoperative patient typically results from residual or recurrent muscular, valvar, or distal outflow obstruction or from increased pulmonary artery pressure or vascular resistance. In children with abnormal distal pulmonary arterial beds, for example, the hypoplastic vessels may not be amenable to surgical repair or other intervention, although associated defects may be satisfactorily addressed. This results in increased proximal pulmonary artery and right ventricular pressures and compensatory myocardial hypertrophy. Right ventricular pressure may exceed systemic values and compromise left ventricular function because septal shift may impair left ventricular filling or result in obstruction to systemic outflow. Abnormal pressure loads to the right ventricle may also result from progressive conduit stenosis after procedures that involve outflow tract reconstructions. Because of the anticipated need in children for successive conduit replacements, these surgical interventions are delayed as much as possible. This implies long-standing pressure loads on the myocardium with associated wall hypertrophy and potentially some element of ischemia until the criteria for surgical intervention have been fulfilled.

Whether the altered loading conditions affect the right or left ventricle primarily, the result is an increased demand due to the increased wall tension. This implies an increased susceptibility of the ventricular myocardium to the supply-and-demand relationship, a reduced tolerance for factors that may alter this fine balance, and an increased risk of ischemia.

Pulmonary Hypertension

Pulmonary hypertension is a relatively common feature of unoperated CHD. It usually is the consequence of an increased pulmonary blood flow. One of the benefits of early correction is a reduction in pulmonary artery pressures and the incidence of pulmonary vascular reactivity after cardiac surgery. However, in some cases, pulmonary hypertension may persist or develop after an intervention.

A less common entity is increased pulmonary vascular resistance, which may be reactive or fixed. The diagnosis is formally determined at cardiac catheterization and involves pulmonary vascular reactivity testing. Pulmonary hypertension and increased pulmonary vascular resistance represent risks for major perioperative complications in children, regardless of cause.143,144

Acute increases in pulmonary vascular tone, also known as pulmonary hypertensive crisis, may result in cardiac arrest. In the presence of an intracardiac communication that allows for shunting, acute increases in pulmonary artery pressure may manifest as arterial desaturation, bradycardia, and systemic hypotension. In the absence of an intracardiac communication, the acute increase in right ventricular afterload may lead to unfavorable leftward shifting of the interventricular septum, compromising left ventricular filling and decreasing cardiac output.

Several factors can increase pulmonary vascular tone (Table 21-2). Therapy should be aggressive in the acute setting, aimed at reducing pulmonary artery pressures with interventions such as additional sedation, hyperventilation, hyperoxygenation, and treatment of acidosis. The use of selective pulmonary vasodilators (e.g., inhaled nitric oxide, other agents) and inotropic support of the right ventricle may be indicated. Manipulation of pulmonary hemodynamics is challenged by the difficulty of directly measuring these parameters in children. Management of critical situations requires a thorough understanding of the pathophysiologic process and experienced clinical judgment. Because of the significant morbidity and potential periprocedural mortality for children with a history of severe pulmonary hypertension, an in-depth evaluation of the risk/benefit ratio of the planned procedure and its impact on the overall quality of life is essential.

TABLE 21-2 Factors Associated with Increased Pulmonary Vascular Tone

Anticoagulation

Anticoagulants, antiplatelet drugs, and thrombolytic agents are increasingly being used in children, particularly in those with CHD.146150 Decisions regarding management are primarily influenced by the nature of the procedure, urgency of the intervention, specific drug therapy, and expected effects or laboratory data. The major concern is the potential for bleeding. Recommendations for the management of children taking warfarin (Coumadin) vary widely.151153 The proposed strategies are quite heterogeneous, and the lack of consensus reflects the paucity of randomized trials addressing this issue. The problem is further complicated by the lack of guidelines specific to pediatric practice.154

If the indications for anticoagulation are for native valve disease or atrial arrhythmias, the risk of a major thromboembolic event is considered to be relatively small, and warfarin may be discontinued 1 to 2 weeks before the day of surgery. In those with mechanical prosthetic valves, the risk of thromboembolic events is greater. Many recommend discontinuing the oral anticoagulant a few days before surgery and allowing the prothrombin time to return to within 20% of normal.151 Administration of parenteral vitamin K or clotting factors, including fresh frozen plasma (FFP), may be required to restore the prothrombin time within an acceptable range, especially in those with liver disease and in emergency cases. Some experts advise preoperative hospitalization, particularly in high-risk individuals such as those with mitral or combined valve prostheses, to discontinue warfarin therapy and to initiate a heparin infusion, which is continued up until a few hours before surgery. Others suggest that low-molecular-weight heparin may be the better option instead of unfractionated heparin because the perioperative conversion from warfarin therapy to heparin can be accomplished without the need for hospitalization.152

Anticoagulation is usually reinitiated after 24 hours in children with valvular prostheses, and this may be achieved with a continuous heparin infusion or intermittent subcutaneous injections. The advantage of heparin is the ability to rapidly reverse the drug effect with protamine sulfate if bleeding complications occur. Oral anticoagulants are reinitiated 2 to 3 days after surgery if there are no bleeding concerns and the child is able to swallow oral medications. Although it has been suggested that there is no need to discontinue anticoagulation therapy for minor procedures, such as dental or ophthalmologic surgery in adults, guidelines for children are less clear.

The risk of bleeding from the surgical intervention versus the risk of a thromboembolism from a reduced anticoagulant dose determines to what extent and for what duration the anticoagulant therapy should be reduced. In some cases, the cardiologist and surgeon may decide to temporarily use aspirin therapy before and after surgery. There is disagreement regarding whether antiplatelet therapy is preferable to anticoagulation in children with prosthetic aortic valves or after certain surgical interventions.155158

Pacemakers and Implantable Cardioverter-Defibrillators

An in-depth discussion of perioperative considerations related to implanted pacemakers or defibrillators can be found in Chapter 14. Consultation with a cardiologist or electrophysiologist is essential when caring for children with implanted devices. Unit interrogation and programming are required in most cases. The main goal is to avoid problems with hardware malfunction related to electromagnetic interference (i.e., electrocautery). Chronotropic agents and backup pacing modalities (e.g., transvenous, epicardial, transcutaneous) should be readily available and carefully considered in the event of pacemaker malfunction associated with an inadequate underlying heart rate. A magnet should be accessible to enable asynchronous pacing if required. Perioperative ECG monitoring is essential, as well as the use of modalities that can confirm pulse generation during pacing. Implanted devices should be interrogated and reprogrammed after the procedure.

Eisenmenger Syndrome

Eisenmenger syndrome is characterized by irreversible pulmonary vascular disease and cyanosis related to reversal in the direction of an intracardiac or arterial level shunt.162,163 This is unlikely to occur in the current surgical era, but it may occasionally occur in older children, adolescents, or adults with CHD. Morbidity is linked to problems associated with chronic cyanosis and erythrocytosis. Other problems include hemoptysis, gout, cholelithiasis, hypertrophic osteoarthropathy, and decreased renal function. Variables associated with poor outcome include syncope, increased right ventricular end-diastolic pressure, and significant hypoxemia (i.e., systemic arterial oxygen saturation less than 85%). Life expectancy is significantly reduced.164 Most succumb suddenly, probably from ventricular tachyarrhythmias. Surgical modalities that have been advocated in selected patients include combined heart and lung transplantation165 and lung transplantation alone.166

Despite the overall poor prognosis and the extremely high risk of a bad outcome, several reports have documented successes with a variety of anesthetic techniques and agents.167171 Nevertheless, it is vital that the family and patient, if of appropriate age, understand these risks before undertaking any procedure requiring anesthesia or deep sedation.

Cardiac Transplantation

Cardiac transplantation may be considered the best option in end-stage cardiac pathology as a result of congenital or acquired disease.172,173 A major consideration in the care of these children is the lack of external nerve supply of the transplanted heart. The physiology of the denervated heart implies that the usual autonomic regulatory mechanisms are not operational, increasing the vulnerability of transplanted children to hemodynamic alterations.174 Compensatory responses may be delayed, further increasing the potential for compromise.

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