Systemic haemodynamics and regional tissue oxygen saturation after bidirectional cavopulmonary shunt: positive pressure ventilation versus spontaneous breathing.

Objectives: Spontaneous breathing has been shown to improve global haemodynamics in patients with bidirectional cavopulmonary shunt. What has not been evaluated, however, is the effect of spontaneous breathing on the distribution of cardiac output after bidirectional cavopulmonary shunt. We investigated the effects of extubation on systemic haemodynamics and regional tissue oxygen saturation, and determined whether redistribution of cardiac output is present after extubation in these patients.

Methods: In 24 patients undergoing bidirectional cavopulmonary shunt, standard haemodynamic variables including heart rate, arterial blood pressure and central venous pressure were monitored continuously. Near-infrared spectroscopy of the brain and mesenteric circulation was monitored and recorded every hour. Cardiac index, derived from ascending aorta flow, was measured by ultrasound at three time points: 30 min before, 30 min after and 12 h after extubation.

Results: The central venous pressure decreased significantly from 19.50 ± 3.65 mmHg before extubation to 16.17 ± 3.41 mmHg 30 min after extubation (P = 0.006) and 13.96 ± 2.49 mmHg 12 h after extubation (P = 0.001). Cardiac index increased significantly from 3.32 ± 0.43 l/min/m(2) before extubation to 3.73 ± 0.51 l/min/m(2) 30 min after extubation (P = 0.012) and 3.98 ± 0.54 l/min/m(2) 12 h after extubation (P = 0.001). Cerebral oxygen saturation increased from 50.83 ± 5.84% before extubation to 56.79 ± 8.64% 30 min after extubation (P = 0.023), then remained unchanged for the following 12 h. Mesenteric oxygen saturation remained unchanged during the early period of extubation, but increased significantly 12 h after extubation (P = 0.002).

Conclusions: The lower values of cerebral oxygen saturation before extubation indicated that the cerebral blood flow was less satisfactory. During the early period of extubation, despite the increase in cardiac index, the mesenteric oxygen saturation is lower than that at 12 h after extubation, suggesting that the obligatory increase in respiratory muscle perfusion and the increase in cerebral oxygen saturation have utilized most of the flow from the increased cardiac index. The increase in mesenteric oxygen saturation 12 h after extubation suggests a gradual improvement in microcirculation and macrocirculation.