Anesthesia for the geriatric patient (Proceedings)

What is a geriatric patient? Geriatric patients are pets that have attained 75% of that species or breeds expected life span. Therefore, a 6 year old Yorkshire terrier would not be considered geriatric, but a 6 year old Irish wolfhound would fall under this definition. We can have healthy geriatric patients, but we must take into account how age can affect various mechanical and physiological functions. There are issues that are specific to the geriatric patient.

Cardiovascular system

Geriatric patients have a decrease in cardiac functional reserve so they have a decreased ability to compensate for changes while under anesthesia or sedation. A disease free, older heart will usually have myocardial fibrosis as well as valvular and ventricular wall thickening. This can result in a decreased cardiac output (CO). Geriatrics increase stroke volume (SV), not heart rate (HR), to compensate for decreased CO. The increase in SV is accomplished by increasing preload and atrial contraction (to increase ventricular filling), so geriatric patients can benefit from be preloaded if they are heart healthy. Mitral valve disease (MVD), tricuspid valve disease (TVD) or both are common in geriatric patients. Valvular disease can also cause or may have associated with it left atrial and ventricular enlargement, dilated cardiomyopathy or hypertrophic cardiomyopathy. Geriatrics are more susceptible to arrhythmias (or dysrhythmias) because of cardiac fiber atrophy and age related conduction issues. Avoid anesthetic or sedation drugs that can increase the possibility of dysrhythmias e.g. alpha-2 agonists or ketamine. Anticholinergics should be avoided if being used as part of a standard premed. They can always be given later, if needed. Preloading should be avoided during the preoperative period if moderate to severe cardiac disease is present. Reduction in fluid rates for cardiac patients during the anesthetic period is 5mls/kg/hr.

Pulmonary System

Tidal volume (TV) and respiration rate (RR) decrease with age, so geriatric patients will have an overall increase in PaCO2 (ETCO2). Mechanical problems encountered by this group of patients include thoracic rigidity and loss of thoracic wall compliance. Also, intercostal and diaphragmatic muscles will atrophy and alveoli (lungs) lose their elasticity. This will result in a decreased PaO2 and increased PaCO2 when anesthetic & sedation drugs are administered.

Renal system

Older patients may have a 50% decrease in the number of functional nephrons and have greater difficulty in retaining Na and H20. If possible, preload geriatric renal patients, but not to the point of fluid overloading. Older kidneys have decreased renal blood flow (RBF) and glomerular filtration rates (GFR) so anesthetic or sedation drugs excreted via this route will have longer elimination times (e.g. ketamine in felines). Managing aggressive fluid therapy in the geriatric patient maybe more difficult. Fluid overloading can result in over hydration which leads to edema or heart failure. Geriatric patients are less tolerant of hypovolemia, hypotension, dehydration and blood loss which can result in increased morbidity.

Hepatic system

Anesthetic and sedation drugs that are cleared by the liver are slower to be metabolized as hepatic mass decreases. Liver mass may decrease as much as 50% in geriatric patients. As liver mass decreases, hepatic blood flow decreases as well. Less hepatic enzymes are available to metabolize anesthetic drugs - especially lipid soluble drugs. Combined with decreased RBF and GFR, anesthetic drugs dependent on hepatic and renal clearance may have their ½ life increased as well as their duration of effect. Decreases in clotting function, hypoglycemia and hypoabluminemia may also occur in the geriatric patient.

Nervous system

Brain tissue decreases in geriatric patients due to loss of neurons. The sensory and cognitive areas of the nervous system are altered with increasing age. Neurotransmitters such as dopamine and norepinephrine decrease as well. Cerebral blood flow (CBF), oxygen demand and the sympathetic nervous system (SNS) response to stress are also diminished. Decreases in thermoregulatory function occur as well e.g. production of body heat. Geriatrics patients are more prone to hypothermia than younger patients and rewarm at a slower rate. Shivering can increase O2 demand by 300% which may result in a severe strain on an already comprised cardiopulmonary systemASA Levels: ASA levels were established by the American Society of Anesthesiologists. An ASA level is assigned to a patient after reviewing the patient's medical history. This ASA level designates the patient's anesthetic risk with regard to its medical history. There are 5 ASA levels that range from 1 (healthy, young) – 5 (morbid, will probably not survive next 24 hours with or without surgery). An ASA Level with an "E" after it denotes an emergency surgical procedure. Healthy geriatrics are considered an ASA 2, but if a greater disease process is present than these patients may be classified as an ASA 3 or 4.

Anesthetic preparation

Physical exam including history and CURRENT medications should be performed and noted. Laboratory workup in older patients should include a CBC, chemistries and urinalysis. (This should be done 1-2 days prior to the anesthetic procedure). If cardiac disease is present an ECG should be performed as well as thoracic radiographs and/or echocardiogram. Fluids can be given preoperatively IF cardiac disease is NOT present. Remember: Geriatrics increase CO by increasing preload, but don't overload. Correct any physiological abnormalities prior to anesthesia as these abnormalities can become life threatening during the anesthetic period. An ASA level should be assigned and an anesthetic protocol developed based on the patient's medical history and test performed. Generally food is withheld for a minimum of 8 hours prior to anesthesia, but H20 can be given up until the morning of anesthesia.

Premedications

Anticholinergics are commonly used in veterinary medicine. These drugs should be used carefully in older patients because they may cause tachycardia which increases myocardial work and O2 demand. Geriatric patients have minimal cardiac reserve so tachycardia may lead to cardiac hypoxia and arrhythmias. If the patient has cardiac disease an anticholinergic may increase the possibility of acute cardiac failure. Glycopyrrolate may be a better choice than atropine when treating anesthetic induced bradycardia. Human studies have shown that glycopyrrolate decreases the incidence of tachycardia, seems better able to target heart rate and doesn't cross the blood-brain barrier thereby avoiding CNS effects. Uptake of glycopyrrolate is almost as rapid as atropine when given IV (approximately 1 minute).

Opioids

Mu-agonists such as methadone, morphine, hydromorphone and fentanyl provide the best analgesia and sedation. They have minimal cardiovascular side effects, but respiratory depression can occur so preoxygenation is highly recommended. Respiratory depression is usually dose dependent. Mu opioids can cause bradycardia, but this is easily treated with an anticholinergic. They should be used cautiously if hepatic disease is present. Dosage and frequency should be decreased if warranted. Mu opioids can be reversed with naloxone or butorphanol if the situation arises. Partial mu-agonist (buprenorphine) and mu-antagonist/kappa-agonist (butorphanol) have minimal cardiac and respiratory depression, but provide limited analgesia. Buprenorphine can take as long as 45 minutes (IM) or 20-30 minutes (IV) to take effect. Higher doses decrease dosing frequency. Butorphanol provides inadequate analgesia for most surgical procedures and it will reverse a mu-agonist (methadone, morphine, fentanyl etc). Premedication with buprenorphine and butorphanol will limit the effectiveness of fentanyl CRIs (or any mu opioid) when fentanyl is required to reduce MAC or to control perioperative pain so the use of another full mu agonist is recommended if these situations are likely to occur.

Benzodiazepines

Benzodiazepines cause minimal cardiac and respiratory depression and have a short duration of action. Midazolam can be given IM because it is H20 soluble. Benzodiazepines are metabolized by the liver so limit dosing in patients with hepatic insufficiency. This class of drugs is a more predictable sedative in geriatric patients, but can still cause excitability in some older patients.

Ace & Alpha 2s

Acepromazine should be used with caution in geriatric patients. Ace is a potent vasodilator so it can cause hypotension and hypothermia. It has no analgesic properties and is metabolized by the liver so doses should be decreased for geriatric patients. It is not reversible and has a long duration of effect. Monitor blood pressure (BP) and give fluid support during the anesthetic period when using acepromazine on older patients. Alpha-2s should be used with extreme caution if at all in geriatric patients. Alpha-2s cause profound cardiovascular effects, however these effects are dose dependent. This class of drugs increases the risk of AV block and causes peripheral vasoconstriction resulting in reflective bradycardia. Micro doses are often utilized, but even at these low doses (1-2mcg/kg) perfusion is still controversial. Alpha -2s are reversible and metabolized by the liver.

Induction

Etomidate has rapid onset and elimination It is a hypnotic and not dependent on a single route for elimination. Etomidate causes minimal changes in HR and BP, but will cause some mild respiratory depression. This drug is an excellent choice for cardiac patients. Etomidate will inhibit adrenocortical function. Myoclonus, retching or excitation may occur upon induction and recovery. These side effects are minimized with the use of a benzodiazepine prior to etomidate induction.

Propofol

Propofol has rapid onset and elimination. It is a hypnotic and not dependent on a single route for elimination. It will cause cardiac and respiratory depression upon induction as well as vasodilation. Apnea and cyanosis are common. Preoxygenation is highly recommended prior to induction. Use of a benzodiazepine with propofol will smooth induction and reduce unwanted side effects. The benzodiazepine should be administered after a ¼ of the dose of propofol is delivered. This will reduce the possibility of excitement that can occur with benzodiazepines

Ketamine/benzodiazepine

Induction with this combination is acceptable when used on healthy geriatrics. Ketamine is a sympathomimetic and may not be a good choice in cardiac, renal (felines) or hepatic (canines) compromised patients. Avoid mask induction. Alfaxalone is not yet available in the US, but provides good cardiac stability and minimal respiratory depression. It is rapidly metabolized via the hepatic route.

Maintenance

Inhalant = Poisonous Gas. All inhalants cause dose dependent cardiac and respiratory depression, hypotension and hypothermia. All current inhalants require minimal hepatic metabolization and renal elimination. The best inhalant is one that has low blood solubility, rapid uptake and elimination. Sevoflurane is probably a better anesthetic choice for compromised geriatrics (rapid changes in anesthetic depth), but isoflurane is acceptable for healthy geriatrics.

Monitoring

Minimal equipment should be an ECG, pulse ox, ETCO2, non invasive BP and temperature for all geriatrics whenever possible. Placement of IV catheters in all geriatrics is recommended for emergency and fluid purposes. Oxygen loading is HIGHLY recommended to prevent hypoxemia from developing during induction. Preload if possible (cardiac exception), but don't OVERLOAD. Hypothermia can lead to decreased anesthetic requirements, delayed healing, increased infection rates and cardiac arrhythmias so use external heat sources when possible (Bair Huggers, warm towels etc) Additional monitoring can include invasive BP, CVP, arterial blood gas, blood glucose and urine output (1-2mls/kg/hr).

Common anesthetic problems & treatments

     1. If hypotension develops, decrease the patient's depth of anesthesia. Adding a fentanyl CRI (2-10 mcg/kg/hr or sometimes more) may be needed to further decrease the vaporizer setting (MAC). Give glycopyrrolate if bradycardia develops from the fentanyl CRI.

     2. Fluid bolusing (5-10mls/kg) ×2 is advisable as long as the patient is heart healthy. This will help rule out hypovolemia.

     3. Inotrope support maybe needed. Dopamine or dobutamine are usually best started at a rate of 5-10mcg/kg/min, however patients must be normovolemic when utilizing these drugs. Decrease the CRI if BP becomes too high, but NEVER STOP it. These drugs will increase demand on the heart so titrate to the effective dose.

     4. If bradycardia develops, decrease the plane of anesthesia if possible. Use of an anticholinergic may be needed, but titrate to effect as these drugs will increase workload and O2 demand of heart. If the patient's temperature drops below 91°F the body's baroreceptors may not respond and HR may continue to be low.

     5. Hypoxemia due to mechanical problems will usually be caused by an anesthetic machine malfunction (occluded inspiratory flow, fresh gas flow or ET tube). Hypoxemia due to physiological issues can be due to a patient not ventilating. Provide IPPV which should not exceed a peak inspiratory pressure of 10-15cm of H20 and auscultate chest to rule out bronchial intubation, pulmonary edema, pneumothorax, atelectasis etc. Reduce inhalant anesthetic %.

Recovery

Provide heat post op if necessary. Remember shivering will cause O2 consumption to increase by 300%. Patients may need supplemental O2 until they are able to maintain adequate oxygenation on room air. Continued IV fluid support may be needed until the patient is able to consume food and H2O. Analgesia should never be withheld from a geriatric patient. Remember to titrate or reduce doses. Dysphoria is common in geriatric patients so once pain is ruled out LOW doses of ace (0.01 – 0.02 mg/kg) can be used to reduce anxiety levels. Use local anesthetics whenever possible. NSAIDS can be used cautiously.