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

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Abstract
Objective: To evaluate if variation in the end‐tidal CO2 partial pressure (∆Petco2) 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 (VTIAo) 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 VTIAo after the fluid challenge. Petco2 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 ∆Petco2 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 ∆Petco2 was observed at T10. The AUROC with its 95% confidence interval (CI) for ∆Petco2 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, ∆Petco2 predicted fluid responsiveness in the dogs studied.

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