Perioperative and Intensive Care Management
Parallel circulation is the whole exam
After stage I palliation the single ventricle ejects into both the aorta and the pulmonary arteries, so the distribution of flow is set by the ratio of systemic to pulmonary vascular resistance. Everything done at the bedside changes that ratio. Supplemental oxygen and hyperventilation lower pulmonary vascular resistance, steal flow from the systemic circulation, and produce metabolic acidosis with a narrow pulse pressure. Mild hypoventilation, sedation, and avoidance of lung overdistension raise pulmonary vascular resistance and restore systemic perfusion. Target saturations are typically 75–85%, not 100%.
Postoperative low cardiac output syndrome peaks at 6–12 hours and is managed with milrinone, careful volume, and avoidance of tachycardia. Delayed sternal closure, chylothorax after Glenn or Fontan, and anticoagulation are routine considerations: aspirin or heparin after shunt placement, warfarin after Fontan in many centers. Near-infrared spectroscopy and lactate trends are more informative than a single saturation.
Traps
Treating the saturation number rather than the patient is the classic error. Aggressively weaning FiO2 to raise a saturation in a child with a shunt can cause profound hypoxemia. Conversely, accepting a saturation of 95% with a rising lactate and cool extremities misses pulmonary overcirculation. High mean airway pressure and aggressive PEEP can raise pulmonary vascular resistance and reduce pulmonary blood flow after a cavopulmonary connection.
Rule of thumb
A saturation of 80% with warm extremities, normal lactate, and good urine output beats a saturation of 95% with acidosis every time.