Association between body mass and hypotension in dogs under general anaesthesia

Abstract:
Objectives: To investigate the association between body mass and hypotension during general anaesthesia in dogs undergoing surgical and diagnostic procedures within a referral hospital.
Methods: Retrospective evaluation of the anaesthetic records of 1789 dogs was performed. Data on signalment, anaesthetic protocol and physiological variables, including mean arterial pressure, were collected. A multivariable generalised linear model was used to identify associations between explanatory variables, including body mass, and hypotension.
Results: In the population studied, increasing body mass (per 10 kg) was significantly associated with decreasing odds of hypotension (odds ratio 0.68; 95% confidence interval: 0.60 - 0.77). Additional variables associated with a decreased odds of hypotension were pre16 anaesthetic medication with alpha-2 agonists (odds ratio 0.63; 95% confidence interval 0.48 - 0.82) and increasing body temperature (per 1°C) during general anaesthesia (odds ratio 0.77; 95% confidence interval 0.67 - 0.88). Brachycephaly (odds ratio 1.72; 95% confidence interval
1.25 - 2.38), ASA physical status classification >3 (odds ratio 2.03; 95% confidence interval 1.16 - 3.56), undergoing a surgical procedure (vs diagnostic) (odds ratio 1.57; 95% confidence interval 1.10 - 2.23) and bradycardia (odds ratio 1.37; 95% confidence interval 1.05 - 1.80) were independently associated with increased odds of hypotension.
Clinical significance:
Dogs of lower body mass and brachycephalic breeds may be at higher risk of hypotension during general anaesthesia or alternatively represent subpopulations in which accurate blood pressure measurement presents a greater challenge. Monitoring blood pressure accurately in these groups requires particular attention and provisions for treating hypotension should be readily accessible.