Assessment of change in end‐tidal CO2 after fluid challenge as a marker of fluid responsiveness as measured by the aortic velocity time integral in healthy anesthetized mechanically ventilated dogs

Abstract Objective To evaluate if variation in the end‐tidal CO 2 partial pressure (∆P etco 2 ) after a fluid challenge could predict fluid responsiveness with a sensitivity of 75% and a specificity of 70% in healthy anesthetized and mechanically ventilated dogs. Design Diagnostic accuracy study. Setting University hospital. Animals Twenty‐seven dogs admitted for neutering. Interventions To obtain a balanced sample between fluid responder and nonresponder dogs, a 10‐mL/kg lactated Ringer's solution was administered over 15 minutes to half of the population before the baseline measurements. All animals then received a fluid challenge of 10 mL/kg lactated Ringer's solution in 5 minutes. Measurements and Main Results The velocity–time integral of aortic blood flow (VTI Ao ) was evaluated with Doppler echocardiography before and after a fluid challenge to classify the included dogs as fluid responders or nonresponders. Fluid responsiveness was defined as an increase of ≥15% of the VTI Ao after the fluid challenge. P etco 2 was evaluated at 1, 5, and 10 (T1, T5, T10) minutes after fluid expansion. Area under the receiver operating characteristic curve (AUROC) analysis was used to assess the ability of ∆P etco 2 to predict fluid responsiveness at different time points. A total of 13 dogs were fluid responders, and 14 were nonresponders. The best predictive capacity for ∆P etco 2 was observed at T10. The AUROC with its 95% confidence interval (CI) for ∆P etco 2 at T10 was 0.75 (0.56–0.93), with a sensitivity of 84.62% (95% CI, 54.60–98.10), a specificity of 64.29% (95% CI, 35.10–87.20), a positive predictive value of 68.80% (95% CI, 41.30–89.00), and a negative predictive value of 81.80% (95% CI, 48.20–97.70). The optimal cutoff was 1 mm Hg. Conclusions The current study showed that, although minimal, ∆P etco 2 predicted fluid responsiveness in the dogs studied.