Regional Capnometry with Air-Automated Tonometry Detects Circulatory Failure Earlier Than Conventional Hemodynamics After Cardiac Surgery

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Abstract
Gastrointestinal automated online air tonometry has been proposed for monitoring gastric perfusion in patients at risk of circulatory failure (CF) after cardiopulmonary bypass. In this study, CF was prospectively defined as the requirement for vasoactive support to maintain mean arterial pressure ≥ 70 mm Hg after optimization of preload. Hemodynamic variables—oxygen (O2) delivery (DO2), O2 uptake (VO2), venous-to-arterial [P(v-a)CO2], gastric-to-arterial [P(r-a)CO2], and gastric-to-end-tidal [P(r-et)CO2]PCO2 gap—were retrospectively compared in 14 patients with or without CF during a 12-hr postbypass period (H0–H12). In contrast to patients without CF (n = 7), in patients with CF (n = 7) increased VO2 was not associated with an increase in DO2. P(r-a)CO2 was larger at H0 in CF patients and was the only variable that differed between the two groups. P(v-a)CO2 did not vary significantly in both groups, whereas P(r-a)CO2 increased to a larger extent from H0 to H12 in patients with CF, suggesting selective gastrointestinal hypoperfusion in this group. P(r-et)CO2 provided comparable information to P(r-a)CO2. Hospital length of stay was 4 days longer (P < 0.05) in patients with CF. Increased P(r-a)CO2 and P(r-et)CO2, as monitored with automated air tonometry, were associated with rapid occurrence of CF and prolonged hospital stay after cardiac surgery. Implications Regional and automated capnometry may be used noninvasively to identify patients at risk of circulatory failure after cardiopulmonary bypass earlier than with conventional variables.