Cardiovascular Physiology, Monitoring, and Hemodynamic Support
Transition and ductal-dependent lesions
Fetal shunts close over hours to days. Lesions dependent on the ductus (critical coarctation, pulmonary atresia, transposition, interrupted aortic arch) present with shock or cyanosis as it closes. Start prostaglandin E1 while anticipating apnea and preparing for intubation. Cyanosis unresponsive to oxygen suggests a fixed intracardiac shunt; a hyperoxia test and four-limb blood pressures are useful screening adjuncts.
Recognizing and treating shock
Classify shock as hypovolemic, cardiogenic, distributive, or obstructive because therapy differs: fluid for hypovolemia, small cautious boluses plus inotropes for cardiogenic, epinephrine and volume for septic shock. Monitor heart rate, blood pressure, capillary refill, mental status, urine output, lactate, and central venous oxygen saturation. The arrest dose of epinephrine is 0.01 mg/kg (0.1 mL/kg of 1:10,000) IV/IO; adenosine 0.1 mg/kg rapid IV push treats stable SVT after vagal maneuvers.
Traps
Repeated 20 mL/kg boluses in cardiogenic shock or myocarditis worsen pulmonary edema. Neonatal hypotension is often judged against gestational age - mean arterial pressure roughly equal to gestational age in weeks is a common rule of thumb, not a universal threshold. Do not delay PGE1 while awaiting echocardiography when ductal-dependent anatomy is suspected.
Rule of thumb
Neonates receive 10 mL/kg boluses over 10–20 minutes; infants and children 20 mL/kg over about 20 minutes, with reassessment after every bolus.