Single Ventricle

Balanced circulation is the target - Qp:Qs of 1:1 gives the best trade between oxygenation and systemic perfusion. SaO2 of 75 to 80% (PaO2 roughly 40 to 50 mmHg) is the bedside surrogate. Higher sats mean the lungs are stealing from the body; lower means pulmonary under-circulation.

FiO2 and PaCO2 are your fastest levers - Both a drop in FiO2 and a rise in PaCO2 cut pulmonary blood flow. Mild hypercapnia, PaCO2 45 to 55 mmHg via hypoventilation, is generally preferred when the patient over-circulates.

Preoxygenation is a compromise - High FiO2 drives excess pulmonary blood flow; too low leaves no apnea reserve and risks hypoxemia and hypercarbia. 40 to 60% oxygen is the usual middle ground.

Induction drug choice - Fentanyl, etomidate, and dexmedetomidine barely touch contractility, PVR, or SVR. Ketamine suits patients with good ventricular function — it raises SVR and leaves PVR alone. Propofol drops SVR and depresses the myocardium, and the fall in output steals from pulmonary blood flow. IV induction is usually preferred, but inhalational induction is reasonable when the stress of placing an IV would itself destabilize.

Volatiles and nitrous - All volatiles cut cardiac output dose-dependently, mostly by dropping SVR; sevoflurane does it least. Nitrous oxide markedly raises PVR — leave it off.

Ventilation settings - Tidal volume 8 to 12 mL/kg with PEEP of 3 to 5 keeps oxygenation up and atelectasis down. Positive pressure raises intrathoracic pressure with real hemodynamic cost, so weigh early extubation against the stress and hypercarbia of a marginal wake-up.

Protect coronary perfusion - Hold diastolic pressure up, since pulmonary runoff steals from the coronaries in diastole, and avoid tachycardia to keep myocardial demand down.

Arterial line site matters - A Blalock-Taussig shunt causes runoff from the subclavian artery on the shunted side, so an ipsilateral upper-extremity line reads unreliably. A PDA gives a pre- versus post-ductal discrepancy — know which limb you cannulated.

Shunt thrombosis is the disaster - If pulmonary blood flow falls far enough, a central or BT shunt can thrombose from stasis. That means no pulmonary blood flow at all, with rapid catastrophic collapse needing VA ECMO until shunt flow is re-established.

Debubble every line - Mixing lesions let a venous bubble cross to the arterial side as a paradoxical embolism. Filter and purge everything.

Preoperative picture - Echo and cath data give ventricular function, shunt patency and gradient, estimated pulmonary and systemic blood flow, and aortopulmonary collaterals. On exam, crackles or pulmonary edema mean the lungs are over-circulated.

Hematocrit and fasting - A hematocrit around 40% helps peripheral oxygen delivery. Output is preload dependent, so keep fasting short and continue maintenance fluids where you can.

Anxiety and pain move resistance - Both swing PVR and SVR unpredictably in a ventricle with no reserve. Premedicate and treat pain early. Fentanyl and dexmedetomidine ease emergence without unbalancing the circulation.

After Fontan completion the rules change - Once the staged path is finished, the physiology is no longer a mixing problem — see the Fontan Circulation entry.

Single ventricle is a family of congenital defects in which only one chamber does the pumping — either one ventricle is hypoplastic, or both are well formed but one is almost completely obstructed at its inflow or outflow. Systemic and pulmonary venous blood mix, usually at the atrial level, and that mixed blood is distributed to both circulations from the one functional ventricle.

Survival after birth takes two things: unrestricted mixing, and a patent conduit carrying blood to the lungs — which is why prostaglandin E1, ductal stenting, and Blalock-Taussig shunts show up so early. The single ventricle carries both pressure and volume overload with reduced compliance, so it tolerates swings in preload and afterload badly, and pulmonary diastolic runoff can steal from the coronaries. With outflow unrestricted, the relative resistance of the two circuits decides where blood goes. Staged repair runs Norwood, then bidirectional Glenn, then Fontan.