The relationship between cerebral and somatic oxygenation and superior and inferior vena cava flow, arterial oxygenation and pressure in infants during cardiopulmonary bypass

We investigated blood flow and regional oxygenation (rSO(2)) during cardiopulmonary bypass (CPB). Twenty infants (mean (SD) age 5 (3) months, weight 5.4 (1.6) kg) were prospectively studied. Total CPB and superior vena cava (SVC) flow were measured using Transonic Bypass Flowmeters, inferior vena cava (IVC) flow derived arithmetically and rSO(2) measured using Near Infra-Red Spectroscopy. Mean SVC flow was 51.3 (14.8) ml.kg(-1).min(-1) and mean IVC flow 62.5 (19.0) ml.kg(-1).min(-1). Mean cerebral rSO(2) was 71 (11)% and somatic rSO(2) 55 (13)%. Cerebral and somatic rSO(2) showed no correlation with SVC and IVC flow. Cerebral rSO(2) showed a positive correlation with P(a)co(2), mean arterial pressure (MAP) and haematocrit (p < 0.0001). Somatic rSO(2) showed a positive correlation with MAP and haematocrit (p = 0.01, p = 0.02). In conclusion, the distribution of blood flow during CPB varies. The most important factor affecting this is P(a)co(2). Cerebral and somatic oxygenation are unaffected by flow but significantly influenced by MAP, haematocrit and P(a)co(2).