Incidence of Bradycardia, Hypotension, Bradycardia with Hypotension and Their Risk Factors in Dogs Undergoing General Anesthesia

2019-10-16T16:06:58Z (GMT) by Hung-Chun Lin
Background: Bradycardia and hypotension are complications commonly occurring during general anesthesia in small animals. Intraoperative hypotension has been found to be associated with adverse postoperative consequences.

Objectives: The objectives of his study were first, to determine the incidence of bradycardia, hypotension, and bradycardia with hypotension in dogs undergoing general anesthesia, and second, to identify the risk factors associated with these three complications. The third objective was to evaluate the relationship between these three intraoperative complications and the recovery quality in these dogs.

Methods and Materials: A retrospective cohort study was performed using anesthetic records from 250 dogs undergoing general anesthesia between May 23, 2018 and October 1, 2018 at the Purdue University Veterinary Teaching Hospital. Intraoperative bradycardia was defined as heart rate < 60 beats/min for at least two consecutive readings at 5 minutes apart. Hypotension was defined as mean arterial pressure (MAP) < 60 mmHg or a systolic arterial pressure (SAP) < 80 mmHg for at least two consecutive readings. A univariate analysis followed by multiple logistic regression was performed to build the model for bradycardia, hypotension, and bradycardia with hypotension. The relationships between the three complications and the recovery quality were analyzed using the Pearson’s chi-square test.

Results: The study found that out of the 250 dogs, 114 (45.6%) developed bradycardia, 113 (45.2%) developed hypotension, and 32 (12.8%) dogs developed bradycardia with hypotension. The use of dexmedetomidine-based tranquilizers/sedatives, longer duration of anesthesia, and subjection to orthopedic and neurologic surgical procedures were all identified as risk factors for the dogs to develop bradycardia. The use of acepromazine-based tranquilizers/sedatives, young and old age dogs, and dogs subjected to neurologic surgery were associated with the development of intraoperative hypotension. When the length of the anesthesia increased, the chance for developing bradycardia with hypotension increased. There was no significant association between these intraoperative complications and the recovery quality.

Conclusions: We found a high incidence of bradycardia or hypotension while a much lower incidence of bradycardia with hypotension in the anesthetized dogs. The risk factors for bradycardia were the use of dexmedetomidine-based tranquilizers/sedatives, the longer duration of anesthesia, and the performance of orthopedic surgery and neurosurgery. The risk factors for hypotension included the use of acepromazine-based tranquilizers/sedatives, the older or younger age of dogs, and the performance of neurosurgery. The risk factor for bradycardia with hypotension was the longer duration of anesthesia. While these adverse events developed intraoperatively, we could not identify a direct influence of these complications on the recovery quality.