Changes in central venous-to-arterial carbon dioxide tension induced by fluid bolus in critically ill patients

BACKGROUND: In this prospective observational study, we evaluated the effects of fluid bolus (FB) on venous-to-arterial carbon dioxide tension (P(va)CO(2)) in 42 adult critically ill patients with pre-infusion P(va)CO(2) > 6 mmHg. RESULTS: FB caused a decrease in P(va)CO(2), from 8.7 [7.6−10.9] mmHg to 6.9 [5.8−8.6] mmHg (p < 0.01). P(va)CO(2) decreased independently of pre-infusion cardiac index and P(va)CO(2) changes during FB were not correlated with changes in central venous oxygen saturation (S(cv)O(2)) whatever pre-infusion CI. Pre-infusion levels of P(va)CO(2) were inversely correlated with decreases in P(va)CO(2) during FB and a pre-infusion P(va)CO(2) value < 7.7 mmHg could exclude a decrease in P(va)CO(2) during FB (AUC: 0.79, 95%CI 0.64–0.93; Sensitivity, 91%; Specificity, 55%; p < 0.01). CONCLUSIONS: Fluid bolus decreased abnormal P(va)CO(2) levels independently of pre-infusion CI. Low baseline P(va)CO(2) values suggest that a positive response to FB is unlikely.