Updates on Anesthetic Care of Aging Patients

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Over the past decade, the life expectancy of dogs and cats has increased, leading veterinarians to anesthetize an increasing number of aging patients.1 Owners often ask: “Is my pet too old for anesthesia?” and it is our duty to know the risks and how to mitigate them. Aging is often defined as a gradual accumulation of changes that make animals vulnerable to disease and death.2 In both dogs and cats, morbidity and mortality associated with anesthesia are correlated with age, independently of health status, but how old does “old” mean?

The term “senior” describes the last 25% of an animal’s estimated lifespan until the end of its life. Significant physiological deficits are present during this period, even if the animal shows no overt illness. In many cases, there may be substantial decreases in renal and hepatic function that are not detected by routine hematologic and chemical tests. In cats, “senior” generally refers to animals over 10 years old. The lifespan of dogs varies greatly depending on breed and size, and only with the use of life expectancy charts can we assign different breeds and sizes of dogs to this stage of the life.1

There are 2 categories of older animals: those who appear healthy but have age-related deficits, and those who have these deficits worsened by disease. Specific diseases such as chronic kidney disease and heart failure require modifications to anesthesia protocols that are beyond the scope of this commentary.

The key to caring for older animals under anesthesia is to understand that there is a decrease in functional reserve in all major systems of the body, leaving the animal less able to maintain homeostasis in the face of stressors ( loss of robustness) or return to its basic function. after disruption by external stressors (loss of resilience).3 There are also changes in body composition, such as loss of muscle mass and decreased blood volume that alter drug distribution, metabolism and excretion, requiring us to adjust doses to prevent events. unwanted.

In humans, a diagnosis of frailty is a strong predictor of postoperative outcomes, including morbidity, length of hospital stay, and mortality.4 Frailty is distinct from comorbidity and disability and is not synonymous with aging. Diagnosing frailty allows the clinician to identify patients who are significantly more vulnerable than others of the same age. Tools for assessing frailty in dogs and cats are in their infancy. In dogs, a described frailty phenotype includes chronic undernutrition, poor mobility, exhaustion, low level of physical activity, and weakness.5 A frailty index that counts the number of clinical conditions present (“deficit accumulation”) has also been developed.6 In fragile people, the risks of anesthesia can be reduced by optimizing nutrition and ensuring good management of comorbidities, while “pre-education” (supervised physical exercise) can improve functional reserve; the veterinary profession has the skills to do the same.

For aging patients under anesthesia, here’s what matters:

  • Choice of anesthetic drugs: Choose drugs whose effect can be titrated, which have a high therapeutic index and which are reversible (if possible).
  • Monitoring: Older patients require less inhaled agent; therefore, the vaporizer setting should be adjusted based on an assessment of anesthetic depth.
  • Gastroesophageal reflux, regurgitation, vomiting and aspiration pneumonia: The incidence of these events increases with age. Fasting times of less than 5 hours and administration of maropitant and famotidine are recommended.
  • Environmental stressors: Older patients may have some degree of cognitive decline and hearing and vision problems, which can be confusing during a hospital stay. Limiting external stimuli (noise, light) can help create a more relaxing environment, and limiting the number of people interacting with the patient can reduce confusion. Encourage owners to bring familiar items from home to take their pet with them. If possible, schedule this population as outpatient so they can return home to a familiar environment to recover.
  • Thermoregulation: Older patients are at high risk of developing hypothermia, which can significantly delay healing. During recovery, cold animals will shiver to generate heat but this ability is limited in older patients. Shivering is unpleasant and increases oxygen consumption, which is detrimental in patients with limited cardiac reserves. Maintaining a high ambient temperature (75ºF) in preparation and recovery areas and using warming devices will mitigate heat loss.
  • Positioning during surgery: Many elderly veterinary patients suffer from pain related to osteoarthritis and care should be taken to place them in neutral positions, with padding, to avoid exacerbation of joint and muscle pain postoperatively.

Sheilah Robertson, BVMS (Hons), PhD, DACVAA, DECVAA, DACAW, DECAWBM (AWSEL), CVA, MRCVS, is certified in anesthesia and animal welfare by the respective American and European colleges and holds a certificate in small animal acupuncture. She is the senior medical director of Lap of Love Veterinary Hospice and a professor of hospice at the University of Florida.

The references

  1. Montoya M, Morrison JA, Arrignon F et al. Life expectancy tables for dogs and cats based on clinical data. Veterinarian before Sci. 2023;10:1082102.
  2. McKenzie BA, Chen FL. Assessment and management of decline in physical function in aging dogs. Best Anim Med Companion. 2022;51:100732.
  3. McKenzie BA, Chen FL, Gruen ME, Olby NJ. Canine geriatric syndrome: a framework for advancing research in veterinary geroscience. Veterinarian before Sci. 2022;9:853743. doi:10.3389/fvets.2022.85374
  4. McIsaac DI, MacDonald DB, Aucoin SD. Frailty for perioperative clinicians: a narrative review. Anesth Analg. 2020;130(6):1450-60. doi:10.1213/ANE.0000000000004602
  5. Hua J, Hoummady S, Muller C et al. Assessment of frailty in elderly dogs. Am J Vet Res. 2016;77(12):1357-1365. doi:10.2460/ajvr.77.12.1357
  6. Banzato T, Franzo G, Di Maggio R et al. A frailty index based on clinical data to quantify the risk of mortality in dogs. Scientific representative. 2019;9(1):16749. doi:10.1038/s41598-019-52585-9

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