Cerebral oximetry monitors an arterial/venous ratio of 16:84, similar in normoxia, hypoxia, and hypocapnia. Because of biologic variation in cerebral arterial/venous ratios, use of a fixed ratio is not a good method to validate the technology.

The Norwood procedure is currently being applied to a heterogeneous group of patients. Operative and 1-year survival are equivalent for patients with HLHS and those with other cardiac defects. The presence of additional cardiac or extra-cardiac anomalies are predictors of poor outcome.

In a contemporary series of Fontan operations performed largely in patients with hypoplastic left heart syndrome or variants, systemic ventricle morphology had no effect on mortality. Some patient characteristics, however, continue to influence outcome. The decrease in mortality and morbidity in the current era is attributed to changes in management strategies, specifically the use of modified ultrafiltration and baffle fenestration.