Risk factors for hypotension in anaesthetized dogs: a retrospective analysis of 390 cases

Hypotension during anaesthesia is related to potential adverse outcomes in human and veterinary patients. Careful monitoring of arterial blood pressure during anaesthesia is crucial. This retrospective study aimed at identifying risk factors for hypotension in anaesthetized dogs.

Records from general anaesthetics in dogs between October 2023 and April 2024 were reviewed. Data regarding dog signalment, American Society of Anaesthesiologists (ASA) classification, procedure, employed drugs, mechanical ventilation, regional anaesthesia, fluid therapy, duration of anaesthesia, procedures, technique of arterial blood pressure monitoring, were gathered. Primary outcome was the development of hypotension: Mean Arterial Pressure (MAP) ≤ 60 mmHg for at least 3 consecutive measurements 5 min apart. Data were analyzed with descriptive statistics and multivariable logistic regression, the Mann Whitney U test and tests of linearity on continuous variables. Internal validation of the model and power estimation were performed.

Statistical significance was set at p < 0.05. A total of 390 records were analyzed. Hypotension was present in 72/390 cases (18.5%). An increased Odds Ratio (OR) for hypotension was found with abdominal surgery (overall OR 5.56, 95% CI 2.03-16.00, p = 0.001; abdominal versus (vs) diagnostic OR 5.56, 95% CI 1.33-23.2, p = 0.009; abdominal vs. orthopaedic OR 5.28, 95% CI 1.46-19.1, p = 0.004), age <12 months (overall OR 3.12, 95% CI 1.30-7.42, p = 0.010; young vs. adult OR 3.12, 95% CI 1.11-8.81, p = 0.027) and increasing duration of anaesthesia (OR 1.01, 95% CI 1.00-1.01, p < 0.001). OR for hypotension decreased with higher body mass (OR 0.96, 95% CI 0.94-0.98, p = 0.001), use of regional anaesthesia (overall for epidural-spinal OR 0.14, 95% CI 0.02-0.57, p = 0.014; overall for nerve blocks OR 0.24, 95% CI 0.11-0.50, p < 0.001; epidural-spinal vs. no regional anaesthesia OR 0.14, 95% CI 0.02-0.91, p = 0.036; nerve block vs. no regional anaesthesia OR 0.24, 95% CI 0.09-0.60, p < 0.001), and mechanical ventilation (overall OR 0.52, 95% CI 0.27-0.96, p = 0.039; mechanical ventilation vs. no mechanical ventilation OR 0.52, 95% CI 0.27-0.97, p = 0.039).

Identification of risk factors for hypotension in anaesthetized dogs can contribute to developing prevention and treatment strategies to improve outcomes and safety.