Comparison of Brody's formula with respiratory gas analysis for estimating oxygen consumption in anaesthetized dogs.

OBJECTIVE

To determine agreement in oxygen consumption (V˙O) values calculated using Sykes' formula V˙O = (FiO - Fe'O) * V˙ (where Fi and Fe are the inspired and end-tidal fractional concentrations of O, respectively, and V˙ is minute volume) with values derived using Brody's formula (V˙O = 10 kg). It was hypothesized that the two methods would not yield statistically significant differences in calculated values.

STUDY DESIGN

Prospective, clinical, pilot study.

ANIMALS

A total of 22 client-owned dogs.

METHODS

Dogs undergoing surgery were anaesthetized with either isoflurane or sevoflurane. The V˙, FiO and Fe'O were measured during mechanical ventilation of the lungs (tidal volume 10 mL kg; respiratory rate: 8-12 breaths minute). Oesophageal temperature was maintained between 37.0 °C and 38.5 °C. Values for V˙O derived by Sykes' and Brody's methods were compared and agreement was determined using Bland-Altman analysis.

RESULTS

Mean V˙O values were 4.67 ± 0.51 mL kg minute and 5.32 ± 1.69 mL kg minute calculated using Brody's formula and Sykes' equation, respectively. There was greater variability in the values obtained from Sykes' equation. The Bland-Altman plot revealed a proportional error with correlation but poor agreement between values.

CONCLUSIONS AND CLINICAL RELEVANCE

Both methods yielded V˙O values of approximately 5 mL kgminute with no statistically significant differences between the two methods.