Assessment of change in end-tidal CO 2 after fluid challenge as a marker of fluid responsiveness as measured by the aortic velocity time integral in healthy anesthetized mechanically ventilated dogs.

Objective: To evaluate if variation in the end-tidal CO ₂ partial pressure (∆Petco 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. Petco 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 ∆Petco 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 ∆Petco ₂ was observed at T10. The AUROC with its 95% confidence interval (CI) for ∆Petco 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, ∆Petco ₂ predicted fluid responsiveness in the dogs studied.
(© Veterinary Emergency and Critical Care Society 2024.)