Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA
Age is not a disease, therefore, when designing an anesthetic protocol for a geriatric patient, the understanding of the whole physiological status is more important than knowing their actual chronological age. Focus should be given to coexisting diseases that lead to poor functional organ capacity, such as neurological, pulmonary, cardiac, renal, hepatic and endocrine diseases alone or in combination. A complete geriatric pre-op profile includes history, physical examination, thoracic radiography, ECG, blood work and echocardiography. History of CNS depression, polyuria/polydipsia, exercise intolerance, arrhythmias, cyanosis, abnormal pulse quality, cardiac murmurs and/or syncope indicates a need for a more extensive preanesthetic evaluation. Even though the focus should be on the specific organ dysfunction of that specific patient, and each patient is unique, here are some general tips for your geriatric patient that needs sedation or general anesthesia:
1. Supplement oxygen for your patient!
A minimum of 3 minutes of preinduction oxygenation via facemask, followed by intra-op and postanesthetic phases (including after extubation) prevents possible hypoxemia. During anesthesia, manual or mechanical intermittent positive pressure ventilation and oxygen monitoring is recommended (pulse oximetry, capnography and blood gas analysis). Assisted ventilation is often recommended to maintain both normal ventilation (PCO2 between 35–45 mm Hg) and oxygenation (PaO2 higher than 60 mm Hg). This recommendation is based on the common physiological changes observed in geriatric patients. They are: Weakening of the respiratory muscles, loss of elastic tissue, pulmonary fibrosis, increased airway resistance, decreased pulmonary diffusion capacity, decreased capillary blood volume and increased susceptibility to respiratory infections.
These changes combined can lead to decreased chest wall compliance, decreased elastic recoil of the lungs associated with a decreased vital capacity and functional residual capacity, increased predisposition for atelectasis while under anesthesia, reduced efficiency for expiration and gas exchange impairment. All those changes combined can lead to hypoxemia. At the same time, the thermoregulatory center of geriatric patients is weakened and therefore they are more susceptible to anesthesia-induced hypothermia. Hypothermia can be associated with bradyarrhythmias, reduced minimum alveolar concentration of inhalants and shivering. Shivering can increase oxygen consumption by 400%, also leading to hypoxemia. So, warm them up!
2. Provide cardiovascular monitoring and support!
The possible cardiopulmonary disease is always a possibility for the geriatric patient. Anesthesia can induce cardiovascular depression and hypotension. That is not a good combination! Therefore, close cardiovascular monitoring is vital to recognize the possible cardiovascular change as early as possible. The most common physiologic changes in the cardiovascular system of geriatric animals are: ↓ baroreceptor activity, ↑ circulation time, ↓ blood volume, hypotension, ↓ cardiac output and limited renal, hepatic and CNS ability to adapt to hypotension. Most of these common changes in the geriatric heart are primarily related to myocardial fibrosis, valvular fibrocalcification and ventricular thickening. Cardiac conduction system can also get compromised with age, leading to possible cardiac arrhythmias. Therefore, drugs known as negative inotropes and arrhythmogenics should be avoided in the geriatric patient.
Also, be careful with fluids! It is fundamental to ensure adequate venous return and fluid balance to minimize the risk of anesthesia-related hypotension. However, due to the decreased cardiac reserve, fluid overload can lead to congestive heart failure and pulmonary edema. Therefore, fluid rate should be prescribed based on the individual need, hydration and physical status. So, let’s use that multiparametric monitor!
3. Use low-dose and/or short-acting, reversible drugs!
With age, the hepatic, neurological and renal functions deteriorate. All those possible changes can lead to a prolongation of the drug elimination and possible exacerbation of the drug effects on the CNS. Older dogs and cats commonly experience decreased liver mass and hepatic blood flow secondary to reduced cardiac output. Decreased microsomal enzyme activity, and generalized reduction of metabolic activity are also common. These changes are associated with hypoproteinemia, coagulopathies and hypoglycemia. For all the geriatric patients, liver function analysis and coagulation should be requested prior to the beginning of anesthesia or sedation, especially if highly metabolized drugs are used. Hypotension should be avoided during anesthesia of geriatric patients since it leads to a further decrease in hepatic blood flow, exacerbating the possible ischemic hepatic damage that is already present and associated with advanced age. The aged patient may have also compromised cognitive, sensory, motor and autonomic functions and that is usually correlated with decreased requirement for anesthetic drugs (inhalants, benzodiazepines, opioids, barbiturates) and prolonged recovery time.
Other possible problems commonly observed in elderly dogs and cats are chronic kidney disease, urinary incontinence, bladder tumors and prostate problems. Those changes are associated with decreased renal mass, tubular size, weight and glomerular numbers leading to a reduced filtration function. Reabsorption of protein, water and sodium, secretion of aldosterone, secretion and reabsorption of anionic and cationic compounds, formation of vitamin D, renin and elimination and metabolism of protein-bound compounds are all compromised. That can influence the regulation of blood pressure, acid-base, erythropoietin, resulting in hyperphosphatemia, azotemia, dehydration and hypoproteinemia. Now, general anesthesia can lead to a 40% reduction in renal blood flow and glomerular filtration. That is not a good combination! Now, that can be worse if cardiac output is already compromised by any cardiac disease. Consequently, the effects of anesthesia on the kidney can be exacerbated in geriatric patients with preexisting cardiovascular or renal condition. Hypoxemia, hypovolemia, hypotension, and hypercarbia are factors that contribute to renal failure following anesthesia and should be avoided to decrease the chances of worsening organ dysfunction. These factors reinforce the justification for close cardiorespiratory monitoring of older pets under general anesthesia since early recognition and treatment are key to prevent further compromise of the kidney disease.
4. Pay attention to the patient’s history!
Hyperadrenocorticism, diabetes mellitus and hypothyroidism are common conditions in the geriatric patient. Older patients may have decreased adrenal responsiveness to ACTH stimulation when compared with younger dogs. It has been suggested that corticosteroid supplementation in the preanesthetic period may be beneficial for the geriatric animal because of the possibility of adrenal exhaustion in response to stress of anesthesia and surgery. So, knowing the patient history, understanding the physiology of the possible coexisting disease and working hard to stabilize the patient prior to the anesthesia induction will ensure a higher survival rate!
5. Anesthesia recovery is even more important in geriatric patients!
The anesthetist should be ready to provide oxygen, heat and continuous cardiorespiratory monitoring. It is common to see aspiration pneumonia in elderly patients. So, create the habit of aspirating the esophagus and stomach of these patients before endotracheal extubation. Maintain an open airway via intubation until the animal is swallowing, provide proper nursing care for recumbent animals with soft beds and frequent changing of decubitus, add a source of heat, provide human touch, and compassionate verbal encouragement. It is ok to wait for the pet to recover from anesthesia, rushing will not make it better. However, sometimes reversing the effects of drugs that are not analgesics (e.g., benzodiazepines and alpha2- agonists) can help speed up the recovery time. The AAHA senior care guidelines for dogs and cats also recommend that clients should receive postoperative instructions with clear, concise, verbal and written take-home instructions that include information about possible complications, drug effects, nursing care, nutritional management, home monitoring, and after- hours veterinary phone contact.
In conclusion, the anesthesia of geriatric patients is related with higher risks; however, safe anesthesia can be performed if these guidelines are followed.
References are available upon request.