- Geriatric patients present changes in physiology and pharmacology that can impact anesthetic management
- These animals can also present co-morbidities that can increase anesthetic risk
- ASA status and increased aging are associated with increased odds of anesthetic-related death in dogs and cats
Geriatric patients present a challenge to the veterinarian based on their unique physiological and pharmacological features. Aging does not necessarily equal disease, however, many of these patients may have co-morbidities that increase their anesthetic risk. For example, some geriatric cats may have advanced kidney disease or hyperthyroidism whereas most of large breed geriatric dogs have osteoarthritis. Old dogs were nearly twice as likely to develop serious peri-anesthetic complications, even when considering their ASA status than middle-aged and young dogs.1,2 Similar findings were observed in other studies with cats and dogs and increasing age was one of the factors associated with increased odds of anesthetic-related death.2-4 It can be hard to define what a senior/geriatric dog is but it is generally accepted that these patients have lived over 75% of their life expectancy. This is particularly true for dogs where different breeds tend to live longer than others. Geriatric patients are those at their life expectancy according to the American Animal Hospital Association guidelines.5 In cats, this is better defined, and senior and geriatric cats have usually between 11–14 and 15 years of age, respectively.6 Specific senior care guidelines have been published and can be of interest.7 More importantly than the age as an “absolute number” it is the healthy status of the patient.
Geriatric patients have limited physiological reserves especially in the presence of coexisting diseases. This can lead to poor nervous, cardiac, renal, respiratory, hepatic and endocrine function. Geriatric patients are notorious for compromised cognitive function due to changes in brain size, loss of neurons and depletion of neurotransmitters. The mature, senior and geriatric patients can present weakening of the respiratory muscles with loss of elastic tissues. Pulmonary fibrosis can be observed which impacts anesthesia by decreasing compliance and elastic recoil of the lungs.
Functional residual capacity is reduced as well as vital capacity. Susceptibility to respiratory infection is increased. In clinical practice, these animals should be preoxygenated using facemask for three minutes to prevent hypoxemia during anesthetic induction and early after extubation in the recovery period.
Monitoring of respiratory function include capnography, pulse oximetry, and blood gas analysis. Regarding the cardiovascular function, there is usually reduced baroreceptor activity, blood volume and cardiac output resulting in overall reduced cardiac reserve. Therefore, geriatric patients have limited means for dealing with hypotension and hemorrhage. This is particularly aggravated by cardiac valve disease or disturbances in the conduction system leading to arrhythmias. Asymptomatic canine degenerative valve disease can be observed in up to 25% of geriatric patients and patients should be screened cautiously.8 A thorough physical examination is recommended. Further diagnostics and extensive cardiac examination including radiographs, ECG and echocardiography are recommended if necessary. Hypertrophic cardiomyopathy is relatively common in cats and anesthetic management can be challenging. Monitoring of the cardiac function is of utmost importance particularly in the geriatric patient. Reduced cardiac output leads to decreased hepatic blood flow. Drug metabolism can be further compromised by diminished microsomal enzyme activity which may result in prolonged anesthetic recoveries especially with injectable anesthetics. If liver function is abnormal, hypoproteinemia and coagulopathies can be present.
Renal function can be also compromised and staging of chronic kidney disease (IRIS staging of CKD) facilitates appropriate treatment and monitoring of the patient in these cases. Staging is based on creatinine levels assessed on at least twice. Sub-staging is based on proteinuria and systemic blood pressure, and appropriate therapy is recommended.9 In these patients, glomerular filtration rate is reduced, acid-base balance and electrolyte concentrations can be affected, and anemia observed. These effects can be exacerbated by general anesthesia and fluid therapy. It is also important to highlight that urea and creatinine levels are increased only when 70% of nephrons have been compromised. Geriatric patients can be affected by several endocrine diseases such as diabetes and anesthetic management will be tailored to the individual patient in all cases.
This lecture discusses a practical approach to anesthetic management of the small animal geriatric patient taking in consideration their specific physiological and pharmacological features.