oa Approach to circulation after cardiac surgery in children

Pediatric intensivists are called to patient bedsides in the pediatric cardiac intensive care unit (CICU) after congenital cardiac surgery for low blood pressure (BP) and/or poor perfusion, acute change in heart rate (HR) or rhythm, surgical site bleeding or increased chest tube output, anuria or oliguria, oxygen desaturation less than expected or metabolic acidosis with rising lactic acid and base deficit. Causes of acute circulatory failure after cardiac surgery are divided into four categories which must be considered when approaching the patient in CICU (Table 1).

Assessing cardiac output in CICU remains challenging, hemodynamic parameters are usually monitored, along with physical examination, i.e. HR, BP, right and left atrial pressures. There are surrogate markers i.e., mixed venous saturation, brain and renal NIRS, toe temperature, urine output, and then laboratory workup to determine acidosis due to end-organ dysfunction. Echocardiography can confirm low cardiac output syndrome (LCOS) occurs after cardiac surgery with the following major indicators; abnormal ventricular-vascular interaction after bypass, the functionally univentricular circulation, abnormal diastolic function after surgery to the right heart and residual anatomic lesions.¹

The limited support tools that are available to manage circulatory failure post cardiac surgery in the CICU are the following: Medications: High labile pulmonary vascular tone (PVR) occurs in patients with pulmonary over-circulation i.e., ASD (atrial septal defect), VSD (ventricular septal defect), PDA (patent ductus arteriosus) and AV canal (atrioventricular canal). Pulmonary venous hypertension, i.e. TAPVR with obstruction, HLHS with restrictive atrial communication and in the univentricular heart after Norwood, shunt or PA band has unstable PVR. Functionally univentricular hearts don't tolerate increased SVR and at the same time, decreased SVR may not be desirable for patients who have fixed systemic or pulmonary obstruction. There are a wide variety of medications to use, but essentially two, milrinone^2,3 and epinephrine are very important and widely used. Milrinone is routinely used after cardiac surgery to minimize the LCOS, which works in a receptor independent manner and is synergistic to beta-adrenergic ionotropic effect. Most patients benefit from low dose epinephrine for decreased cardiac function. Nitroprusside is effective where after-load is high, a low dose should always be started titrating to the optimal BP. Generally, there is no role of dopamine in these patients.⁴Ventilation-cardiopulmonary interaction: Ventilation at functional residual capacity needs to be targeted. Managing rhythm: Recognition of rhythm is a crucial aspect of care. It is equally important to pay attention to the appropriate heart rate. Extracorporeal mechanical support: The last resort is to put the patient on extracorporeal membrane oxygenation.

In summary, the past two decades have seen important advances in our understanding of the circulatory physiology of infants and children post cardiac surgery. When approaching the patients with cardiovascular dysfunction, it is essential to approach the cardiopulmonary system in its entirety, rather than consider the heart, lungs, or peripheral circulation as isolated elements. Working towards one common goal of optimizing systemic oxygen delivery and emphasizing anticipatory intensive care tailored to individual patients with the need for early, targeted investigation and intervention is essential when patients are not progressing as expected.