Comparison of two different methods for physiologic dead space measurements in ventilated dogs in a clinical setting.

摘要

Objective: To compare physiologic dead space (V_D) and physiologic dead space to tidal volume (V_T) ratio (V_D/V_T) obtained by an automated single breath test for carbon dioxide (CO₂) (method SBT) and a manual calculation (method MC) in ventilated healthy dogs. Study design: Prospective clinical study. Animals: Twenty client-owned dogs, ASA I and II undergoing anaesthesia for clinical purposes. Methods: Following pre-medication, induction of anaesthesia, and intubation of the trachea, intermittent positive pressure ventilation was commenced. Mixed expired CO₂ partial pressure (PeCO₂) was measured by two methods: method MC by analysis, using an infrared capnograph, of the expired gas collected in a mixing box and method SBT which calculated it automatically by a device consisting of a mainstream capnograph and a pneumotachograph. At four time points arterial partial pressure of CO₂ (PaCO₂) was measured. Physiologic dead space variables (V_D and V_D/V_T) were calculated manually (method MC) or automatically (method SBT) using the Bohr-Enghoff equation. Method MC and SBT were compared using Bland-Altman plots and linear regression. Intra-class correlation coefficient (ICC) was used to measure consistency of each method. Results: Four measurement pairs were obtained in all 20 dogs for method SBT and MC. The bias was -1.15 mmHg, 7.97 mL and 0.02 for PeCO₂, V_D and V_D/V_T, respectively. Linear regression analysis revealed a correlation coefficient (r2) of 0.79, 0.94, and 0.83 for PeCO₂, V_D and V_D/V_T, respectively. The ICC revealed an excellent consistency for both methods. Conclusions: The single breath test (SBT) can be used for clinical evaluation of V_D and V_D/V_T in anaesthetized ventilated dogs. Clinical relevance: Through measuring V_D and V_D/V_T important information about lung ventilation can be obtained and the SBT is an easy method to use for this purpose.