Anesthetic risk management (Proceedings)
Anesthetic related mortality would appear to be an easily quantifiable statistic that could be used to measure the outcome of the profession's current anesthetic practices. However, to rely solely on death rate as the measure of the quality of anesthetic care provided is inadequate. The anesthetist's goal should be to minimize the risks to the patient's health while reducing pain and stress.
Anesthetic mortality statistics
Veterinary studiesStatistics for veterinary medicine are difficult to compile. There are no systematic methods for reporting anesthetic complications and objective independent assessment of the clinical course of events leading to anesthetic morbidity and mortality are virtually non-existent. However, several retrospective studies have been published which provide insight into the perioperative death rate and provide some guidance to identification of risk factors. Many of these studies have been summarized in a review by Dr. R.S. Jones.
Equine anesthesia has been associated with greater risk due to the size, physiology, and innate behavior of horses. Overall, the death rate is approximately 1.9%. However, when colic surgery is excluded the rate falls to near 0.9%. For horses undergoing anesthesia for colic surgery, the rate is considerably higher (7.9%). The most common causes of death are cardiac arrest, fractures during recovery, and ischemic myopathy. Anesthesia on an emergency basis carries a significantly greater risk. It is important to note that the anesthetic period was defined as being up to seven days following surgery and the records that were reviewed were primarily in referral hospitals.
Small animal patients
Several retrospective studies have been performed over the last 50 years documenting the anesthetic death rate in dogs and cats. In 1955, one study reported that at a single institution the death rate was 1.1% in dogs and 1.8% in cats. The same institution was re-evaluated in 1979 and the death rate decreased to 0.43% in dogs and 0.25% in cats. The main causes of death were human error leading to overdosage and hypoxia. Equipment malfunctions, hypothermia, and cardiovascular failure were also prevalent. In a similar study of 10,000 feline anesthetics, the death rate was similar (0.3%). In this study the main risk factors identified were failure to obtain accurate body weights, failure to utilize premedications, and failure to intubate patients.
A 1990 study in the UK reported mortality rates in dogs and cats of 0.23% and 0.29% respectively. This study stratified patients based on the presence of preexisting pathology and when analysis was complete the death rate increased to 3.12% for dogs with preexisting disease (0.11% for healthy dogs). Cats also had increased risk with pathology (3.33%) and decreased risk when healthy. Subsequent studies have provided similar results.
The most recent study published was an examination of anesthetic related mortality in feline patients in the United Kingdom. The results indicated the overall risk of death is 0.24%. Interestingly they also examined the risk of sedation and general anesthesia and found no increase in risk of death with anesthesia vs. sedation, including sedation with medetomidine. This is contrary to most veterinarians' perceptions. Unexpectedly, an increase risk of death was found with endotracheal intubation and fluid therapy. This confirms earlier reports that endotracheal intubation should be done carefully to avoid tracheal lacerations in cats, but may also be due to the fact that usually older or ill animals are anesthetized with inhalants and given fluids. These studies suggest that as the patient population ages, and more animals with concurrent diseases are anesthetized, anesthetic care must improve in order to reduce or even maintain current mortality rates.