Anaesthesia for the geriatric dog and cat

Abstract

When anaesthetised, the geriatric patient is at increased risk from: • Hypoxaemia and hypercapnia • Dehydration, hypovolemia, hypotension and poor tissue perfusion • Cardiac arrhythmias • Hypothermia • Prolonged drug action and delayed recovery from anaesthesia • Adverse drug reactions • Stress The following recommendations should reduce the incidence of these complications for the elderly patient and improve the prognosis following general anaesthesia: • Carry out adequate pre-anaesthetic examination and tests to discover the extent of underlying diseases. • Stablilise and / or optimise the patient's condition prior to anaesthesia. • Keep anaesthetic time to a minimum. For example, if the patient does not have a painful condition and is not stressed, consider clipping the hair etc. once the animal is sedated. • Reduce doses of all drugs because of the lower blood volume, increased plasma levels of active drug and the reduced requirement for all anaesthetic drugs. Dose all drugs according to lean body mass. • Use drugs that: - result in minimal cardiac depression, e.g., benzodiazepines - can be antagonised, e.g., benzodiazepines and opioids - have a short duration of action, e.g., propofol. • Avoid very heavy sedation in elderly animals. • Try to avoid alpha-two agonists as their cardiovascular effects are too detrimental in the elderly patient. If you have to use them, use very low doses, combine them with an opioid and reverse them as soon as possible • Maintain normal hydration, blood pressure and renal function by providing adequate IV fluids. • Use oxygen pre-, intra- and post-operatviely because geriatric patients are at increased risk from hypoxaemia. • Monitor the patient closely and keep all physiological parameters within the normal range. Use a veterinary nurse dedicated to recording heart and pulse rate, respiratory rate, depth of anaesthesia, mucous membrane colour and capillary refill time, and anything else that you have the equipment to measure. Suggested minimum monitoring equipment for the geriatric patient should include an oesophageal stethoscope, pulse oximeter and non-invasive blood pressure, e.g., Doppler flow detector. ECG, capnography and body temperature are also recommended: - Maintain mean blood pressure above 70 mmHg or systolic blood pressure greater than 90-100 mmHg - Haemoglobin saturation should at least 95% - Normal values for end-tidal carbon dioxide are 5.3 ± 0.5 kPa (40 ± 5 mmHg) - In the high risk patient, monitor urine output and maintain at 1-2 ml/kg/hr • Be prepared to support respiration with manual or automatic ventilation. • Use adequate analgesia, especially opioids. • Do not use NSAIDs without checking renal and hepatic function and never use them concurrently with steroids. Consider alternative analgesic techniques, e.g., local anaesthetics. • Keep the patient warm. Age itself is not a contra-indication for anaesthesia; however, age-related diseases make anaesthesia more challenging. Thorough pre-operative assessment, careful choice of anaesthetic and analgesic techniques, vigilant monitoring and attentive supportive care will improve the probability of a successful outcome for the elderly patient.