Pediatric Cardiac Catheterization

Anesthetic management for cardiac catheterization in pediatric patients can be uniquely challenging. These patients range in age from premature neonates to the upper limits of the pediatric age group. Cardiac anomalies vary from relatively simple atrial septal defects to complex congenital cardiac anomalies such as hypoplastic left heart syndrome. Shunts may be present at multiple levels, and patients may be profoundly cyanotic. Ventricular dysfunction may be severe. Patients may also have coexisting noncardiac congenital abnormalities. In addition, these young patients may be uncooperative, and their parents may be severely stressed and thus of limited assistance. Neonatal studies are frequently performed on an emergency basis, and these patients are often deeply cyanotic and critically ill. Diagnosis of the cardiac anomaly is usually made before cardiac catheterization by echocardiography, but determination of surgical treatment or possible catheter-based intervention is dependent on the results of cardiac catheterization.

Anesthetic techniques used in these cases range from sedation and analgesia to general anesthesia. Again, it must be remembered that a "steady state" must be maintained for diagnostic accuracy. In general, older, cooperative patients are readily managed with intravenous sedation and analgesia. Even in cyanotic patients, supplemental oxygen is not administered unless oxygen saturation falls below baseline levels. Care must be taken to maintain ventilation and PaCO₂ within normal physiologic limits to avoid alterations in pulmonary vascular resistance. ^[113] Medications administered for sedation include fentanyl, midazolam, propofol, and ketamine. Premedication with midazolam, 0.5 mg/kg orally, can be particularly helpful. Some evidence has indicated that ketamine can increase oxygen consumption, so care must be taken to ensure that it does not impair diagnostic accuracy.^[114] Even small infants have been sedated in this manner for these procedures.

That said, infants and small children frequently cannot tolerate the procedure under intravenous sedation and are more readily managed with general anesthesia. As with intravenous sedation for these procedures, premedication with oral midazolam, 0.5 mg/kg, can be very helpful. If intravenous access is not present, inhalation induction with nitrous oxide, oxygen, and a volatile anesthetic such as sevoflurane is performed, and intravenous access is obtained after the patient is anesthetized. Alternatively, intravenous induction with thiopental, ketamine, etomidate, or propofol is performed. A nondepolarizing neuromuscular relaxant is administered, and endotracheal intubation is carried out when the patient is fully relaxed. Correct endotracheal tube position is confirmed by end-tidal CO₂ measurement, and position above the carina is readily confirmed with fluoroscopy. Anesthesia is maintained with volatile anesthetics and controlled ventilation with room air, as long as oxygen saturation does not fall below baseline levels. Controlled ventilation avoids the increases in PaCO₂ frequently seen with levels of intravenous sedation adequate to allow performance of this invasive procedure in pediatric patients. Controlled ventilation has not been found to affect the diagnostic accuracy of cardiac catheterization.^[111] Minute ventilation and the respiratory rate are adjusted to maintain normal PaCO₂ based on analysis of arterial gases from blood drawn by the cardiologist from the arterial catheter. The end-tidal CO₂ determination can be used to subsequently adjust ventilation, but it must be remembered that physiologic dead space is highly variable in such patients. Infiltration of local anesthetic at vascular access sites limits postprocedural discomfort. Small amounts of an opioid such as fentanyl (i.e., 1 to 2 µg/kg intravenously) may be administered to provide postprocedure sedation, thus allowing the patient to remain still and avoid bleeding

2652

Close monitoring of these patients is required. Especially in neonates, deterioration can be rapid. These patients may be very sensitive to anesthetics, and hemodynamic instability may ensue. Repeated blood gas analysis is necessary because metabolic acidosis may be the initial sign of a low-cardiac output state. Even mild degrees of metabolic acidosis should be treated in critically ill patients, and inotropic therapy may be necessary. Hypocalcemia and hypoglycemia may develop in neonates and require treatment. Hypothermia can be a problem in young patients, especially those under general anesthesia. The room may need to be warmed. In addition, inspired gases may need to be warmed and humidified, and a warming blanket or forced air warming system should be available. Rectal temperature may need to be monitored in small patients because an esophageal or axillary probe may intrude into the cardiologist's imaging area. Blood loss during the procedure is less well tolerated than in larger patients because the loss may represent a significant fraction of a smaller patient's blood volume. Hematocrit must be monitored carefully and anemia treated appropriately. Deeply cyanotic patients tend toward polycythemia as they age, and sufficient fluids must be administered to balance the osmotic effects of contrast media, which could result in hemoconcentration and microembolic events.

Complications of cardiac catheterization include arrhythmias, bleeding at vascular access sites, perforation of cardiac chambers or great vessels by catheters, vascular dissection or hematoma, and embolic phenomena. Arrhythmias are the most frequent complication.^[91] Supraventricular tachycardias are the most common and are often related to catheter tip placement, in which case the arrhythmias usually resolve on withdrawal of the catheter. Occasionally, vagal maneuvers, intravenous medication, or cardioversion may be necessary to terminate the arrhythmia. Second- or third-degree heart block may also be seen. Sinus bradycardia may require treatment with atropine. Profound bradycardia may necessitate temporary ventricular pacing if hemodynamic instability results.

Pericardial tamponade can be detected by characteristic hemodynamic alterations, as well as by a widened mediastinum and reduced cardiac motion on fluoroscopy. A definitive diagnosis of tamponade is best made by echocardiography, which is readily available and can be used to guide emergency pericardiocentesis. The pericardiocentesis catheter can cause arrhythmias by mechanical irritation. These arrhythmias can be either supraventricular or ventricular, and they may be poorly tolerated in critically ill patients. As with coronary angiography, emergency surgical procedures may be necessary, and hospital systems must allow rapid, safe transport of these patients to the operating suite.