March 08, 2018

Anesthetic Complications in Dogs with Heart Disease

A recent study set out to determine whether dogs with cardiac conditions had higher rates of complications under anesthesia than healthy dogs.
By Natalie Stilwell, DVM, MS, PhD
Performing anesthetic procedures in geriatric canine patients and those with cardiac disease is a source of anxiety for many pet owners and veterinarians. The overall risk of anesthetic death in dogs, estimated at 0.11% to 0.43%, is shown to increase with age.

To address this statistic, investigators at the North Carolina State University (NCSU) Veterinary Teaching Hospital performed a retrospective study to assess the influence of heart disease on anesthetic complications and mortality. The results were recently published in the Journal of the American Animal Hospital Association.

Study Design
The investigators selected veterinary records for dogs that presented to the NCSU dental service for dental anesthetic procedures between 2006 and 2011. One group consisted of 100 dogs with cardiac disease that were referred to the dental service for surgery due to a perceived high risk of anesthetic complications. While many dogs in the affected group were receiving medical treatment for heart disease at the time of surgery, none had clinical signs of congestive heart failure.

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The control group included 100 dogs that underwent similar dental procedures during the same time period but did not have cardiac or other major diseases. Each dog in the cardiac disease group was matched as closely as possible by breed, age, sex, and type of dental disease with a control case.

Recovered data included signalment, cardiac disease diagnosis, and medications, American Society of Anesthesiologists (ASA) classification, and surgery details. Any anesthetic complications were noted as present or absent, and researchers calculated the percent of total anesthetic time during which tachycardia, bradycardia, or hypotension was present.

Major Findings
The 200 study participants represented 47 dog breeds. Although the disease and control groups were similarly matched by sex and body weight, the mean age of dogs with cardiac disease was significantly higher than the healthy group (11.24 vs. 10.26 years). Also, 57% of dogs with cardiac disease had ASA classifications of 3 or higher (indicating severe systemic disease), compared with 9% of control dogs. 

While maintenance inhalant anesthetic agents and doses were similar between the two groups, midazolam and etomidate were the induction drugs of choice for more dogs with cardiac disease than control dogs. Premedication drug choice and anesthesia duration were similar between groups, and most dogs in both groups were discharged the day of surgery.

Anesthetic complications:
  • The overall frequency of anesthetic complications (marked as 1 or more abnormal reading under anesthesia) was 82.5% in each group.
  • Both groups had similar rates of hypotension (49%), bradycardia (35%-36%), and hypoventilation (21%-24%).
  • Cardiac arrhythmia was infrequent in both groups, and no anesthetic deaths occurred in either group.
  • The percentage of total anesthesia time in which complications were noted was statistically similar between groups.

Take-home Message
Anesthetic complications occurred at similar rates regardless of whether dogs had cardiac disease or not, and none of the 200 dogs experienced anesthetic mortality. The authors hope this study may serve as a helpful resource for veterinarians and pet owners who are considering surgery for the cardiac patient.

 
Dr. Stilwell received her DVM from Auburn University, followed by a MS in Fisheries and Aquatic Sciences and a PhD in Veterinary Medical Sciences from the University of Florida. She provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting. 

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