60: Perioperative Critical Care of the Pediatric Cardiac Surgical Patient

Introduction

Perioperative care of the pediatric cardiac surgical patient requires a multidisciplinary team that includes cardiologists, cardiothoracic surgeons, anesthesiologists, and intensivists as well as multiple other support staff. A well-functioning system requires coordinated effort and communication. This chapter focuses on common perioperative critical care challenges encountered in the care of pediatric cardiac surgical patients, with emphasis on physiologic basis, diagnosis, and treatment.

Pediatric Cardiopulmonary Physiology

Management of children with congenital heart disease (CHD) requires an understanding of neonatal/pediatric cardiopulmonary physiology and how this differs from the adult. First, neonatal and pediatric cardiac output (CO) is significantly more reliant on heart rate (vs stroke volume) than in the adult patient. As such, these patients will maintain a “normal” blood pressure despite impending shock by increasing heart rate to maintain CO. The neonatal and pediatric myocardium is less compliant (compared to an older child or adult) and is less tolerant of changes in preload and afterload. Oxygen consumption is also increased compared with adult patients, and lung volumes are obviously smaller. In order to maintain oxygen supply in the face of increased consumption with smaller lung volumes, minute ventilation is increased with higher respiratory rates. In addition, infants breathe below their functional residual capacity (FRC), and lung units are collapsed and reopened with each breath. This unique physiology results in low tolerance to apnea and very rapid desaturation.

Neonates also have potential for labile pulmonary vascular resistance (PVR) as they transition from fetal to newborn circulation in the first few days of life. Furthermore, neonatal pulmonary physiology differs from that of an older child because of the increased chest wall compliance, reliance on the diaphragm for optimal mechanics, and increased propensity for atelectasis. The preoperative management of neonates with significant unrepaired CHD requires an understanding of both general neonatal cardiopulmonary physiology as well as the specific impact of the particular lesion(s).

Preoperative Care

Although the majority of preoperative care of the pediatric patient with CHD is in the outpatient setting, the neonate with significant unrepaired CHD may require intensive care assessment and monitoring. Goals of preoperative care include optimization of hemodynamics to ensure adequate CO and normal end-organ function while awaiting corrective or palliative neonatal surgery.

In general, infants requiring neonatal surgery can usually be classified into three preoperative “states”: single ventricle (SV) physiology, transposition physiology, and ductal-dependent pulmonary or systemic blood flow.

1. Many complex congenital heart lesions have SV physiology, where there is complete mixing of systemic and pulmonary venous return and thus aortic (AO) saturation equals pulmonary artery (PA) saturation. The total ventricular output is divided between two competing parallel circuits whose flow (pulmonary/systemic) is determined by the resistances of each system. Hypoplastic left heart syndrome (HLHS) typifies SV physiology. Acceptable balance between pulmonary and systemic outputs will provide enough pulmonary blood flow for adequate oxygen delivery ...