Objectives Marked minute to minute variability in cerebral oxygenation is observed early in Intensive Care in infants following cardiac surgery1. This study investigates response of cerebral and somatic oxygenation (rSO2i) to changes in ventilation in the PICU following cardiac surgery.

Methods Near-infrared spectroscopy (NIRS) was used to assess changes in rSO2i in 11 infants (mean age 3.6 months) following CPB and biventricular repair. A randomised cross-over design was used to change baseline ventilation by successively increasing or decreasing the minute volume 50% from baseline, 1-hour and 18-hours following ICU admission. Arterial pCO2, rSO2i, Cardiac Index and Systemic Vascular Resistance Index were measured.

Results Mean absolute change in arterial pCO2 from baseline during study periods was 5.76 (SD 3.87) mmHg. Mean baseline CI 1-hour and 18-hours after admission were 3.81 and 4.19 L/min/m2. Both CI and SVRI showed no significant change during study periods. The rate of change for cerebral and somatic regional rSO2i was plotted against the change in arterial pCO2. A positive correlation was observed between changes in arterial pCO2 and cerebral rSO2i in both periods (r2 0.72 and 0.50 respectively). A much weaker relationship was observed between arterial pCO2 and somatic rSO2i over the same study period (r2 0.08 and 0.10 respectively)

Conclusion Changes in ventilation affecting arterial pCO2 levels lead to changes in cerebral but not somatic tissue oxygenation in the first post-operative day in ventilated infants following cardiac surgery. This may have significant implications for the post-operative care of these children and strategies to minimize neurological morbidity.