Andersons pediatric cardiology 1826

—limits a full understanding of the nuances of the complex circulation and may negatively affect assessment and management at the bedside In fact, as our understanding of this complex physiology improves, increasingly complex models have recently been proposed (using a combination of local identifiability, Bayesian estimation and maximum a posteriori simplex optimization)46 as well as an e-simulation model.47,48 “Single-Ventricle Physiology” The term “single-ventricle physiology” has occasionally been used interchangeably before and after all three planned stages of surgical management However, the circulatory patterns in the neonate and infant before and after the neonatal palliation, superior cavopulmonary connection (stage II or Glenn procedure) and total cavopulmonary (stage III or Fontan operation) are all extremely different (see later) Using a single term such as single-ventricle physiology across the surgical spectrum in all of these situations is both irrational and inaccurate Instead, we propose using a more precise shorthand nomenclature, such as the (1) multidistribution circulation, (2) the Glenn circulation, and (3) the Fontan circulation The Glenn circulation is a series circulation, albeit with an obligate 40% to 60% right-to-left shunt from the inferior caval vein to the ventricle, and the Fontan circulation is also a series circulation, with the great majority of systemic venous return entering the pulmonary vascular bed in series with the systemic vascular bed However, in contrast to the series circulation in patients with two ventricles, there are unique features of both the Glenn and Fontan circulations, particularly with respect to the central venous pressure, which is discussed later Physiologic Effects of Staged Reconstruction in the Patient With a Functionally Univentricular Heart Undergoing Superior Cavopulmonary Connection and Subsequent Fontan Procedure The general physiologic aims and management strategies of the multidistribution circulation in the neonate and infant detailed in Table 70.2 and Fig 70.2 pertain to postoperative care as well and are discussed in more detail in Chapter 71 During each of the three planned stages of surgical management, there are a number of important physiologic changes that follow surgery, some of which are temporary, whereas others are planned consequences of the surgical procedure itself (Table 70.3) Table 70.2 General Principles of Surgical Palliation in the Newborn and Beyond Fundamental Management Short Term Longer Term Principles Provide unobstructed systemic Preserve systemic oxygen and nutrient Minimize the severity of blood flow delivery ventricular hypertrophy Preserve ventricular function Provide limited/restricted Provide adequate gas exchange Minimize the risk of elevated pulmonary blood flow without pulmonary vascular resistance pulmonary artery distortion Minimize pulmonary stenosis and hypoplasia Ensure unobstructed Minimize risk of hypoxemia Minimize the risk of pulmonary pulmonary venous return Avoid pulmonary edema venous hypertension and elevated pulmonary vascular resistance Ensure unobstructed systemic Minimize risk of central venous Lower central venous pressure venous return hypertension leading to Improve cardiac output chylothorax, effusions, and thrombosis Minimize risk of postoperative low cardiac output Minimize atrial incisions Reduce risk of perioperative Reduce risk of long-term arrhythmias and sinus node supraventricular arrhythmias and dysfunction sinus node dysfunction Minimize the duration and severity of volume and pressure load Reduce risk of ventricular dysfunction and atrioventricular valve regurgitation Minimize severity of ventricular hypertrophy Minimize inefficient circulatory effects of regurgitant fraction Preserve ventricular function Table 70.3 Acute and Chronic Physiologic Changes During Staged Reconstruction Transient physiologic effects of surgery, cardiopulmonary bypass, and anesthesia Expected changes in loading conditions from surgical procedures ■ Rapid changes in intravascular volume due to bleeding ■ Decrease in ventricular output and myocardial function ■ Increase in systemic vascular resistance ■ Increase in pulmonary vascular resistance ■ Fluid retention due to capillary leak and/or renal dysfunction ■ Decrease in surfactant production ■ Pulmonary edema ■ Decrease in pulmonary venous saturation ■ Changes in oxygen-carrying capacity due to anemia and/or hemoglobin affinity for oxygen ■ Changes in oxygen consumption due to temperature, pain, agitation, sedation, and analgesia ■ In the neonate, there are variable changes in preload (combined systemic and pulmonary venous return) that occur from the unoperated to the operated state ■ In general, there is a postoperative decrease in volume loading compared with the preoperative state because the pulmonary blood flow is decreased with most neonatal surgical interventions ■ In the infant following superior cavopulmonary connection, there is: ■ A decrease in pulmonary blood flow ■ A decrease in volume work (preload) ■ Commonly an increase in afterload (postoperative hypertension) ■ A decrease in ventricular function, which typically recovers over 2–6 months ■ An elevated central venous pressure in the upper half of the body ■ Following the total cavopulmonary (Fontan) connection, there is: ■ Decreased ventricular filling and cardiac output ■ Elevated central venous pressure in the upper and lower parts of the body ■ Increased lymph production ■ Following repair of atrioventricular valve regurgitation (at any stage), there is a: ■ Decrease in volume work (preload) ■ Increase in afterload ■ Decrease in ventricular function, which typically recovers over 2–6 months Superior Cavopulmonary Connection (Bidirectional Glenn)