Use of Alfaxan in Geriatric Patients

General Anesthesia in Geriatric Patients

Dogs and cats are living longer than ever before, in part due to improved availability and options for veterinary care. With increasing age, however, there is often an increased requirement to perform anesthesia. By understanding the physiological changes that occur in geriatric patients and planning appropriately, anesthesia may be performed with confidence. 

As animals age, they undergo progressive and irreversible changes leading to a reduction in physiological reserve capacity. Along with age-related degeneration there may be undetected disease that can further complicate anesthesia. Developing a suitable anesthetic protocol for the geriatric patient involves a thorough physical assessment of the patient, appropriate drug selection, and vigilant, responsive monitoring.

Alfaxan® Multidose is a short-acting induction agent which offers good cardiopulmonary stability in older cats and dogs.

Physiological Considerations

Cardiovascular system

Geriatric patients develop structural cardiac changes resulting in decreased pump efficiency, increased heart rate and reduced ability to respond to hemodynamic changes. Increases in cardiac work load result in higher myocardial oxygen requirements.
If oxygen demands are not met, the muscle may fail, causing life-threatening arrhythmias. It is important to avoid dramatic changes in heart rate and blood pressure, and drugs that may potentially be arrhythmogenic, such as α2-adrenergic receptor agonists, should be used with caution.

Intravenous fluid therapy is essential to support the cardiovascular system during anesthesia, however, fluid overloading may precipitate congestive heart failure and pulmonary edema. It is essential that any evidence of heart disease be investigated prior to anesthesia and that fluid rates be calculated accurately for each patient.

Respiratory system

Decreased lung elasticity and thoracic compliance, high closing volume and easily fatigued ventilatory muscles make geriatric patients prone to ventilation-perfusion mismatching, hypoxemia and hypercapnia. Risk for hypoxemia and hypercapnia increase with the use of drugs that cause respiratory depression. 

Central nervous system

Older animals have decreased brain mass, neurotransmitter availability and cerebral blood flow. This can result in greater sensitivity to anesthetic medications, less response to variations of homeostasis, especially hypothermia, and increased anxiety. Titrating anesthetic drugs to effect is especially important in geriatric patients as the doses required may be significantly lower than in younger animals. Management of anxiety is also essential to ensure a smooth anesthetic and avoid the dangerous effects of excessive stress, including cardiovascular failure.[1]

Urinary system 

Geriatric patients have reduced renal function and mass, with a 50% decrease in functional nephrons sometimes observed.[2] The kidneys’ ability to cope with decreased blood perfusion, correct electrolyte imbalances or excrete excess fluid is often impaired. Urinalysis should be performed to identify any renal insufficiency, which has been estimated to occur in 15-20% of geriatric dogs and cats.[3] 

Anesthetic considerations for geriatric patients

Thorough pre-anesthetic evaluation of geriatric patients is essential to identify any co-morbidities that require management. Clinicians should aim to stabilize the patient and choose drugs with a short duration of action or with reversal agents available, as well as using the lowest effective dose of anesthetic drug(s). 

History and Physical Examination

Ensure any pre-existing diseases are identified prior to anesthesia, especially cardiovascular or respiratory abnormalities. Assigning patients to an ASA category[4], a system for describing physical status of the patient and risk in anesthesia, may assist in determining which further assessments (such as hematology, serum biochemistry, urinalysis or other diagnostic tests) are indicated. Many older pets are already on medication and potential interactions or side effects with anesthetic drugs should be considered when making an anesthetic plan.

Stabilization and supportive care

Correcting hydration, electrolyte and acid base disturbances in the patient may prevent issues during anesthesia. Thermal support and intravenous fluid administration should be provided to the patient as appropriate throughout anesthesia and recovery.

Pre-medication

The aim of pre-medication is to produce and maintain a quiet, fear free, comfortable patient prior to anesthetic induction. Benzodiazepines provide anxiolysis and more consistent sedation in geriatric animals than younger adults. However, their effects may be prolonged with liver dysfunction or concurrent administration of drugs that use the same metabolic pathways, such as H2-receptor antagonists. Very low doses of acepromazine may be appropriate for sedation. Opioid medications are recommended for their potent analgesia, mild sedation and options for reversal if cardiopulmonary depression occurs. Consider administering local or regional anesthesia for further analgesia during surgery.

Anesthetic Induction

Pre-oxygenation for three minutes immediately prior to induction will increase the respiratory reserve of geriatric animals.[5] The use of a short acting intravenous agent, such as Alfaxan® Multidose is recommended. It is especially important to induce slowly to effect in geriatric animals as they often require lower induction doses than younger animals and their increased circulation time can slow the onset of effect of intravenous anesthetics. 

Maintenance

Lower amounts of inhaled anesthetics are also likely to be required in geriatric animals. Patients should be monitored and treated for hypotension, hypoventilation and hypothermia.  

Recovery

Fluid therapy, oxygen supplementation and warming of the patient are likely to be required in the post-anesthetic period. Shivering in hypothermic patients increases oxygen consumption by 200-300% and this extra demand on the cardiopulmonary systems may have severe consequences.[1] Care should be taken to avoid pain, stress and overstimulation. Appropriate analgesia, comfortable bedding and a quiet environment will assist with a smooth recovery.

References

  1. Pettifer, G, Grubb, T 2007, ‘Neonatal and Geriatric Patients’, in W Tranquilli, J Thurmon, K Grimm (eds), Lumb & Jones’ Veterinary Anesthesia and Analgesia, 4th edn, Blackwell Publishing, Ames, Iowa.
  2. Harvey, R, Paddleford, R 1999, ‘Management of geriatric patients’, Vet Clin N Am Small Anim Pract, Vol. 29, pp. 683-699.
  3. Burkholder, W 2000, ‘Dietary considerations for dogs and cats with renal disease’, J Am Vet Med Assoc, Vol. 216, pp. 1730-1734.
  4. ASA Physical Status Classification System, Amer Soc Anaesth. http://www.asahq.org/resources/clinical-information/asa-physical-status-classification-system.
  5. McNally, E, Robertson, S 2009, ‘Comparison of time to desaturation between preoxygenated and nonpreoxygenated dogs following sedation with acepromazine maleate and morphine and induction of anesthesia with propofol’, Am J Vet Res, Vol. 70, pp. 1333-1338.
  6. Ferre, P, Pasloske, K, Whittem, T, Ranasinghe, M, Li, Q, Lefebvre, H 2006, ‘Plasma pharmacokinetics of alfaxalone in dogs after an intravenous bolus of Alfaxan-CD RTU’, Veterinary Anaesthesia and Analgesia, Vol. 33, pp. 229-236.
  7. Pasloske, K, Gazzard B, Perkins, N, Dunlop, C, Whittem, T 2005, ‘A multicentre clinical trial evaluating the efficacy and safety of Alfaxan®-CD RTU administered to dogs for induction and maintenance of anaesthesia’, In British Small Animal Veterinary Association Congress, Birmingham, UK.