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

Abstract Objective To determine agreement in oxygen consumption ( V ˙ O 2 ) values calculated using Sykes’ formula V ˙ O 2 = (F i O 2 – F e ′O 2 ) * V ˙ E (where F i and F e are the inspired and end-tidal fractional concentrations of O 2 , respectively, and V ˙ E is minute volume) with values derived using Brody’s formula ( V ˙ O 2 = 10 kg 3/4 ). 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 ˙ E , F i O 2 and F e ′O 2 were measured during mechanical ventilation of the lungs (tidal volume 10 mL kg –1 ; respiratory rate: 8–12 breaths minute –1 ). Oesophageal temperature was maintained between 37.0 °C and 38.5 °C. Values for V ˙ O 2 derived by Sykes’ and Brody’s methods were compared and agreement was determined using Bland–Altman analysis. Results Mean V ˙ O 2 values were 4.67 ± 0.51 mL kg –1 minute –1 and 5.32 ± 1.69 mL kg –1 minute –1 calculated using Brody’s formula and Sykes’ equation, respectively. There was greater variability in the values obtained from Sykes’ equation. The Bland–Altman plotrevealed a proportional error with correlation but poor agreement between values. Conclusions and clinical relevance Both methods yielded V ˙ O 2 values of approximately 5 mL kg –1 minute –1 with no statistically significant differences between the two methods.