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

Abstract

Objective: To compare physiologic dead space (VD) and physiologic dead space to tidal volume (VT) ratio (VD/VT) 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 (PĒCO2) 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 (VD and VD/VT) 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 PĒCO2, VD and VD/VT, respectively. Linear regression analysis revealed a correlation coefficient (r2) of 0.79, 0.94, and 0.83 for PĒCO2, VD and VD/VT, respectively. The ICC revealed an excellent consistency for both methods. Conclusions: The single breath test (SBT) can be used for clinical evaluation of VD and VD/VT in anaesthetized ventilated dogs. Clinical relevance: Through measuring VD and VD/VT important information about lung ventilation can be obtained and the SBT is an easy method to use for this purpose. © 2010 The Authors. Journal compilation © 2010 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists.