ANESTHESIA FOR INTERVENTIONAL OR DIAGNOSTIC CARDIAC PROCEDURES

Advances in interventional and diagnostic cardiac catheterization techniques are significantly changing the operative and nonoperative approach to the patient with a congenital heart defect. Nonoperative interventional techniques are being used instead of procedures requiring surgery and CPB for safe closure of secundum ASDs, VSDs, and PDAs. Stenotic aortic and pulmonic valves, recurrent aortic coarctations, and branch pulmonary artery stenoses can be dilated in the catheterization lab, avoiding surgical intervention.^{[255] [256] [257] [258]} These techniques shorten the hospital stay and are particularly beneficial to patients with recurrent coarctation and muscular or apical VSDs, who are at a higher risk of operative intervention. Many patients with complex cardiac defects are poor operative risks. Innovative interventional procedures improve vascular anatomy, reduce pressure loads on ventricles, and decrease the operative risk for these patients. For example, in tetralogy of Fallot with

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Anesthetic management of interventional or diagnostic procedures in the catheterization laboratory must include the same level of preparation that applies in caring for these patients in the operating room. These patients have the same complex cardiac physiology and, in some cases, greater physiologic complexity and less cardiovascular reserves. Interventional catheterization procedures can impose acute pressure load on the heart during balloon inflation. Large catheters placed across mitral or tricuspid valves create acute valvular regurgitation or, in the case of a small valve orifice, transient valvular stenosis. When catheters are placed across shunts, severe reductions in pulmonary blood flow and marked hypoxemia may occur.^{[258] [259]} The anesthetic plan must consider the specific cardiology objectives of the procedure and the impact of anesthetic management in facilitating or hindering the interventional procedure. In general, there are three distinct periods involved in an interventional catheterization: the data acquisition period, the interventional period, and the post-procedural evaluation period.

During the data acquisition period, the cardiologist performs a hemodynamic catheterization to evaluate the need for and extent of the planned intervention. Catheterization data are obtained under normal physiologic conditions; that is, room air, physiologic PaCO₂ , and spontaneous ventilation are preferred. Increased FIO₂ or changes in PaCO₂ may obscure physiologic data. During the procedural period, the patient is usually intubated and mechanically ventilated. A secured airway allows the anesthesiologist to concentrate on hemodynamic issues. Positive-pressure ventilation also reduces the risk of air embolism. During spontaneous ventilation, a large reduction in intrathoracic pressure can entrain air into vascular sheaths and result in moderate to large pulmonary or systemic air emboli. Precise device placement is also facilitated with muscle relaxants that eliminate patient movements and controlled ventilation, thereby reducing the respiratory shifting of cardiac structures. Substantial blood loss and changes in ventricular function occur commonly during the intervention. Blood volume replacement and inotropic support may be necessary during or immediately after the interventional procedure.

In the postprocedural period, the success and the physiologic impact of the intervention are evaluated. Blood pressure, mixed venous oxygen saturation, ventricular end-diastolic pressure, and cardiac output, when available, are used to assess the impact of the intervention. Persistent severe hemodynamic derangement indicates the need for ICU monitoring and respiratory or cardiovascular support. Because of the hemodynamic variability of many of these patients, as well as changing anesthetic requirements, continuous intravenous infusion with ketamine/midazolam or propofol is appropriate. Potent inhaled anesthetics are generally not used as the primary anesthetic and are reserved for adjunctive anesthesia.

A brief description of some of the interventional procedures and the associated anesthetic implications follows. The success of these interventions will undoubtedly result in widespread availability and use over the next few years.

Transcatheter Technique for Atrial Septal Defect Closures

In the transcatheter technique for ASD closures, a collapsed double-umbrella clamshell device is loaded into a large introducer sheath placed through the femoral vein, advanced to the right atrium, and placed across the ASD into the left atrial chamber. Each side of the device consists of a Dacron mesh patch suspended in six spring-loaded arms that open like an automatic umbrella. Using biplane fluoroscopy and TEE, the catheter is positioned in the left atrium away from the mitral valve. ^[257] The sheath is pulled back to open the six distal arms and its Dacron mesh cover into the left atrium. The sheath and device are then pulled back so the distal arms contact the left atrial septum. Fluoroscopy and TEE are used to confirm that the arms are on the left atrial side and do not interfere with mitral valve motion. Once adequately seated, the sheath is pulled further back to expose the proximal side of the device and the proximal arms, which spring open to engage the right side of the atrial septum. When proper positioning is certain, the device is released.^[257] In a review of 122 children undergoing transcatheter ASD closures, there was a 9% incidence of procedural complications that resulted in hemodynamic complications requiring treatment. ^[258]

Despite nearly a decade of experience, these devices remain under investigational protocol and are therefore available only at a limited number of study centers.