Cerebrovascular reactivity to carbon dioxide in sepsis syndrome

Cerebral dysfunction in sepsis is common in critically ill adults. However, little is known of the effects of sepsis on cerebral haemodynamics. We studied 12 sedated and ventilated patients in whom sepsis had been established for > 24 h. Transcranial Doppler measurements of the middle cerebral artery flow velocity were made at normocapnia, then hypocapnia (-1 kPa) and hypercapnia (+1 kPa). From these data, cerebrovascular reactivity to carbon dioxide was calculated. Variables indicating disease severity, systemic cardiovascular status and outcome were also recorded. We found significant changes in cerebrovascular reactivity to carbon dioxide. Only three of 12 patients had a cerebrovascular reactivity to carbon dioxide in the normal range; seven patients had a reduced cerebrovascular reactivity to carbon dioxide, whereas in two patients it was raised. In this small sample, we could not find any trend of association between altered cerebrovascular reactivity to carbon dioxide and severity of illness, cardiovascular status or outcome. This study suggests that established sepsis profoundly affects the vascular tone and reactivity, not only of the systemic circulation, but also of the cerebral vasculature.