Introduction

It seems that the increase in human life span observed during the last decades was accompanied by increase in the life span of pets. As a result, performing anesthetic and surgical procedures in geriatric dogs and cats has become increasingly more frequent.

Currently, definition of "geriatric" does not take into account the age in years, but the percentage of life span for each individual. Thus, dogs and cats that have achieved 75% of their expected life span are considered geriatric.¹

Advanced age was associated with increased anesthetic-related mortality. Dogs and cats ≥12 years were respectively 7 times and 2 times more likely to die during anesthesia than young adults.^2,3 Increased age is associated with decreases in functional organ reserve, which makes geriatric patients less able to compensate for the adverse effects of anesthetics and anesthetic adjuncts. Furthermore, old age is often accompanied with co-existing diseases that may result in poor physical status and be aggravated by anesthesia and surgery. The anesthesia practitioner must be aware of such peculiarities when choosing the anesthetic plan for each particular individual.

Physiological Particularities in Geriatrics

The aging process is accompanied by several changes in the cardiovascular system: myocardial fibrosis, ventricular wall thickening, decreased ventricular compliance, valvular fibrocalcification, decreased baroreceptor activity and conduction abnormalities. As a result, many aged dogs and cats may present with variable degrees of cardiovascular disease. Clinically, these changes result in decreased ability to respond to reductions in cardiac output and blood pressure induced by anesthetics. Geriatric patients are also less tolerable to volume depletion or fluid overload.^1,4,5

In the respiratory system, chest wall and pulmonary compliances are decreased, whereas anatomic dead space and ventilation-perfusion mismatch are increased. Co-existing diseases that may result in pneumonia, pulmonary fibrosis and edema further collaborate for deterioration of pulmonary function. As a result, geriatric patients may have lower arterial partial pressure of oxygen and are more prone to develop hypoxemia during anesthesia.¹

It is expected that liver mass and the number of functional nephrons decrease. Impaired liver function may result in increased half-life of drugs, coagulopathies, hypoproteinemia, and hypoglycemia. Increased half-life of drugs may also result from impaired renal function. Moreover, patients with renal disease are less capable of maintaining fluid, electrolyte and acid-base balance. Anesthesia and hemorrhage associated with surgery may decrease liver and renal blood flow and exacerbate preexisting diseases.^1,4,5 Post-anesthetic renal failure in geriatric patients should be of particular concern.

Anesthetic Management

Preoperative evaluation should include a complete history and thorough physical examination. Details about preexisting diseases and current medications should be provided by the owner and the anesthetist must evaluate their possible influence on anesthesia. A minimum of CBC, urinalysis, serum chemistry and electrolytes is recommended. An ECG, echocardiogram, thoracic radiographs and other diagnostic exams may be requested based on the findings of history and physical examination. Prior to anesthesia, every effort should be made to correct preexisting abnormalities such as fluid deficits and electrolyte or acid-base disorders.^1,4,5

Before anesthetic induction, venous access is mandatory for every patient to deal with emergencies and to administer fluids. The latter will contribute to support of venous return, cardiac output and blood pressure. However, excessive volumes should be avoided because geriatric patients are more susceptible to fluid overload.^1,4

In general, geriatric patients do not require heavy sedation. Therefore, adequate restraint may be achieved by administration of an opioid alone such as morphine, methadone, meperidine, hydromorphone, buprenorphine and butorphanol. Low-dose acepromazine may be combined with the opioid in more agitated animals. However, acepromazine induces vasodilation, decreases blood pressure and intensifies heat loss, these effects not being reversible. Alpha-2 adrenoceptor agonists (xylazine, medetomidine, dexmedetomidine) may be used in combination with an opioid in very aggressive animals, especially in cats, because these are poorly sedated after administration of opioids and phenothiazines. However, the benefits of heavy sedation should be weighed against the profound cardiovascular effects caused by alpha-2 agonists: bradycardia, vasoconstriction, and increased afterload. Acepromazine and alpha-2 agonists should not be administered in patients with hemodynamic instability such as in decompensated heart disease.

All injectable anesthetics can induce respiratory and cardiovascular depression. The incidence and intensity of these effects are dependent on the dose and rate of administration. Therefore, regardless of drug choice, induction of anesthesia should be performed slowly, to effect. Preoxygenation with 100% oxygen is recommended to minimize the risk of hypoxemia during anesthetic induction. Recommended intraoperative monitoring includes ECG, pulse oximetry, blood pressure, capnography, blood glucose levels, body temperature and urine output. Drugs for emergency situations (anticholinergics, inotropes, vasopressors, antiarrhythmics) should be easily available.

Propofol may be considered the first choice for anesthetic induction in most geriatric dogs and cats. However, propofol is known to reduce blood pressure and cardiac output.⁶ The concurrent use of midazolam reduced the propofol dose for induction of anesthesia but did not result in less cardiovascular depression.⁷ Alfaxalone was found to decrease blood pressure of dogs in a similar fashion to propofol.⁸ Thus, in patients with decompensated heart disease or others with hemodynamic instability, etomidate may be a safer choice than propofol or alfaxalone. Dissociative agents (ketamine, tiletamine) are metabolized in liver producing active metabolites that are excreted unchanged in the urine (mostly in cats). In addition, these drugs increase heart rate and myocardial oxygen consumption.⁶ These effects of dissociative agents may be of concern in geriatric patients with variable degrees of liver, kidney and heart disease.

Maintenance of anesthesia is preferably performed with an inhalation anesthetic such as isoflurane or sevoflurane. All patients should have the trachea intubated to allow positive pressure ventilation as required. The minimum alveolar concentration (MAC) of inhalation anesthetics is progressively decreased with increasing age.⁹ Therefore, anesthetic concentrations for maintenance of anesthesia in geriatric patients are expected to be lower than in adults. Intraoperatively, administration of constant rate infusion of analgesics (opioids, lidocaine, ketamine) and use of locoregional anesthetic techniques will further reduce MAC. It is important to use low doses of inhalation anesthetics because these agents induce dose-related cardiovascular depression.¹⁰

Vigilant monitoring should continue during the recovery period. Heat sources should be provided to avoid hypothermia and prolonged recovery. Some geriatric patients may require oxygen supplementation post-extubation due to residual respiratory depression by anesthetics. Postoperative pain can be controlled by administration of opioid analgesics. Nonsteroidal anti-inflammatory drugs may be combined with opioids to improve postoperative pain control, but should be avoided in patients with any sign of preexisting kidney disease.

Final Considerations

There is no anesthetic plan that is considered ideal for every patient and surgical procedure. The same applies to geriatric patients. The choice of anesthetics and anesthetic adjuncts should be tailored to each particular situation. The anesthetic protocol should be based on the physical condition of the patient, the degree of preexisting organ dysfunction and the anticipated levels of nociception and pain originated from the surgical procedure to be performed. Vigilant monitoring throughout the anesthetic period can anticipate and allow effective treatment of anesthetic-related complications.

References

1.  Carpenter RE, Pettifer GR, Tranquilli WJ. Anesthesia for geriatric patients. Vet Clin North Am Small Anim Pract. 2005;35(3):571–80.

2.  Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Risk factors for anaesthetic-related death in cats: results from the confidential enquiry into perioperative small animal fatalities (CEPSAF). Br J Anaesth. 2007;99(5):617–23.

3.  Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Results of the confidential enquiry into perioperative small animal fatalities regarding risk factors for anesthetic-related death in dogs. J Am Vet Med Assoc. 2008;233(7):1096–104.

4.  Baetge CL, Matthews NS. Anesthesia and analgesia for geriatric veterinary patients. Vet Clin North Am Small Anim Pract. 2012;42(4):643–53.

5.  Cunha AF. Neonatal, pediatric, and geriatric concerns. In: Snyder LBC, Johnson RA, eds. Canine and Feline Anesthesia and Co-Existing Disease. Ames, IA: Wiley Blackwell; 2015:310–319.

6.  Berry SH. Injectable anesthetics. In: Grimm KA, Lamont LA, Tranquilli WJ, Greene SA, Robertson SA, eds. Veterinary Anesthesia and Analgesia. Ames, IA: Wiley Blackwell; 2015:277–296.

7.  Covey-Crump GL, Murison PJ. Fentanyl or midazolam for co-induction of anaesthesia with propofol in dogs. Vet Anaesth Analg. 2008;35(6):463–72.

8.  Maney JK, Shepard MK, Braun C, Cremer J, Hofmeister EH. A comparison of cardiopulmonary and anesthetic effects of an induction dose of alfaxalone or propofol in dogs. Vet Anaesth Analg. 2013;40(3):237–44.

9.  Nickalls RW, Mapleson WW. Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane in man. Br J Anaesth. 2003;91(2):170–74.

10. Mutoh T, Nishimura R, Kim HY, Matsunaga S, Sasaki N. Cardiopulmonary effects of sevoflurane, compared with halothane, enflurane, and isoflurane, in dogs. Am J Vet Res. 1997;58(8):885–90.