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.
