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Anesthesia for Very Old Patients
ANESTHETIC PROTOCOLS FOR SPECIFIC CONDITIONS
467
Anesthesia for Very Old Patients Steve C. Haskins, DVM, MS, and Alan M. Klide, VMD From the Department of Surgery, University of California, Davis, School of Veterinary Medicine, Davis, California (SCH); and the Section of Small Animal Anesthesia, Department of Clinical Studies-Philadelphia, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania (AMK)
Very old animals, without specific organ failures, represent an increased anesthetic risk because of their reduced ability to compensate for the physiologic perturbations caused by general anesthesia and surgery. The precautions and principles of a well-organized anesthetic are especially important in this category of patient. PREOPERATIVE ASSESSMENT AND STABILIZATION
A thorough physical examination and broad laboratory screening are necessary to assess the status of organ functions and to identify problems that become increasingly more common in the aged patient. Identified abnormalities must be normalized, as much as possible under the circumstances, before induction of general anesthesia to maximize the chances of an uneventful anesthetic and recovery. Preoperative sedatives should be used if the animal is n.ervous or outwardly objects to being manipulated for the induction process. We would prefer to use an opioid agonist or agonist-antagonist. Because of their significant cardiovascular effects, phenothiazine tranquilizers and alpha agonists should be avoided. Benzodiazepines are unreliable sedatives. Anticholinergic drugs are not necessarily indicated or contraindicated for the aged patient. Their administration should be guided by the specific indications in the patient. INDUCTION
Anesthetic agents or combinations that are least likely to induce myocardial depression, vasodilation, hypotension, and respiratory depression should be the primary choices for induction of anesthesia. An opioid/diazepam combination may be ideal for dogs because they are least likely to be associated with induction hypotension. Not all opioids are the same in their effects on the cardiovascular system. Opioids least likely to decrease blood pressure are oxymorphone, hydromorphone, and fentanyl. Morphine may cause considerable hypotension, and meperidine causes marked hypotension. The opioids
468
ANESTHETIC PROTOCOLS FOR SPECIFIC CONDITIONS
may induce severe respiratory depression. Patients induced with an opioid should breathe an enriched oxygen mixture and may require positive-pressure ventilation support. Ketamine/diazepam is often recommended as a good choice for induction of either the aged dog or cat. Ketamine may, in some patients, induce hypotension (owing to its direct myocardial depressant effects) and apnea (requiring positivepressure ventilation support). A careful, slow barbiturate titration induction technique may be satisfactory for these patients, even though these agents may induce induction hypotension. The initial dose should be :Y10 to :Yzo of the calculated dose because one can never be sure how an elderly patient might respond. Mask inductions with an inhalational anesthetic may prove satisfactory but are the most likely to induce excessive myocardial depression and hypotension. Therefore inhalational anesthetics are our least favorite choice of the commonly available induction choices. If used for induction, these adverse effects must be monitored carefully. Etomidate is a useful agent for induction of anesthesia because it preserves cardiovascular function. Because it may cause slight twitching or vomiting during induction, etomidate should be preceded by a sedative or opiate, e.g., diazepam and oxymorphone. Propofol may not be indicated because it is a potent vasodilator and usually produces hypotension during induction. This hypotension may be severe and not well tolerated in a patient that cannot compensate.
MAINTENANCE
The considerations for choosing a maintenance drug are the same as those already discussed. Inhalational anesthetics are a common choice, but their cardiovascular consequences must be monitored closely. Isoflurane causes the least myocardial depression of the inhalational anesthetic drugs. If the inhalational agent causes excessive hypotension, it may be necessary to change to an injectable agent. An opioid/diazepam combination would be our first choice for a very old patient, especially if it has severe physiologic dysfunction. Ketamine/diazepam is a second choice for one of the authors. Barbiturates are not a maintenance choice for these patients because of their physiologic and cumulative effects. Monitoring during the anesthetic should be the most complete and the most continuous that your practice has to offer. Anesthetic complications often develop rapidly. The aged patient has a lower threshold to complications and is less able to compensate for them and tolerate them.
ANESTHETIC PROTOCOLS FOR SPECIFIC CONDITIONS
469
RECOVERY
Monitoring and support should continue at the same level of intensity as it did during the operation until the animal is fully recovered from the anesthetic. SUMMARY
Old patients can be safely anesthetized; however, they are less tolerant of the side effects of anesthetic drugs, and so the drugs must be carefully chosen and administered.
Anesthesia for Patients with Stable End-Stage Renal Disease Doris Dyson, DVM, DVSc From the Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada
End-stage renal disease implies that two thirds to three qu'arters of kidney function is impaired. Survival without polysystemic clinical signs results from compensatory mechanisms and limitation of physiologic and pathologic stressors. Anesthesia and surgery can represent a source of stress that is potentially life-threatening in such patients. Patients with renal disease have less tolerance for errors in fluid therapy administration. Dehydration, mild uremia, increased creatinine, potassium abnormalities, and metabolic acidosis may be present on admission. Correction of significant abnormalities should begin preoperatively. Anesthetic protocols must minimize changes in renal blood flow. Recovery should be through metabolism or redistribution rather than excretion, and metabolites should not be harmful to the kidney (e.g., fluoride ions from methoxyflurane). Sympathetic stimulation through general stress and excitement, volume deficiency, or pain can change blood flow distribution and hence must be avoided. Opioid premedication administered at a dose producing mild sedation enables easy handling of the patient (meperidine, 3-5 mg/kg IM, or oxymorphone, 0.025-0.05, mg/kg IM). Because many of these patients are geriatric, it is reasonable to avoid anticholinergics until deemed necessary to treat a bradycardia (<60 beats/min in dogs; <100
467
Anesthesia for Very Old Patients Steve C. Haskins, DVM, MS, and Alan M. Klide, VMD From the Department of Surgery, University of California, Davis, School of Veterinary Medicine, Davis, California (SCH); and the Section of Small Animal Anesthesia, Department of Clinical Studies-Philadelphia, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania (AMK)
Very old animals, without specific organ failures, represent an increased anesthetic risk because of their reduced ability to compensate for the physiologic perturbations caused by general anesthesia and surgery. The precautions and principles of a well-organized anesthetic are especially important in this category of patient. PREOPERATIVE ASSESSMENT AND STABILIZATION
A thorough physical examination and broad laboratory screening are necessary to assess the status of organ functions and to identify problems that become increasingly more common in the aged patient. Identified abnormalities must be normalized, as much as possible under the circumstances, before induction of general anesthesia to maximize the chances of an uneventful anesthetic and recovery. Preoperative sedatives should be used if the animal is n.ervous or outwardly objects to being manipulated for the induction process. We would prefer to use an opioid agonist or agonist-antagonist. Because of their significant cardiovascular effects, phenothiazine tranquilizers and alpha agonists should be avoided. Benzodiazepines are unreliable sedatives. Anticholinergic drugs are not necessarily indicated or contraindicated for the aged patient. Their administration should be guided by the specific indications in the patient. INDUCTION
Anesthetic agents or combinations that are least likely to induce myocardial depression, vasodilation, hypotension, and respiratory depression should be the primary choices for induction of anesthesia. An opioid/diazepam combination may be ideal for dogs because they are least likely to be associated with induction hypotension. Not all opioids are the same in their effects on the cardiovascular system. Opioids least likely to decrease blood pressure are oxymorphone, hydromorphone, and fentanyl. Morphine may cause considerable hypotension, and meperidine causes marked hypotension. The opioids
468
ANESTHETIC PROTOCOLS FOR SPECIFIC CONDITIONS
may induce severe respiratory depression. Patients induced with an opioid should breathe an enriched oxygen mixture and may require positive-pressure ventilation support. Ketamine/diazepam is often recommended as a good choice for induction of either the aged dog or cat. Ketamine may, in some patients, induce hypotension (owing to its direct myocardial depressant effects) and apnea (requiring positivepressure ventilation support). A careful, slow barbiturate titration induction technique may be satisfactory for these patients, even though these agents may induce induction hypotension. The initial dose should be :Y10 to :Yzo of the calculated dose because one can never be sure how an elderly patient might respond. Mask inductions with an inhalational anesthetic may prove satisfactory but are the most likely to induce excessive myocardial depression and hypotension. Therefore inhalational anesthetics are our least favorite choice of the commonly available induction choices. If used for induction, these adverse effects must be monitored carefully. Etomidate is a useful agent for induction of anesthesia because it preserves cardiovascular function. Because it may cause slight twitching or vomiting during induction, etomidate should be preceded by a sedative or opiate, e.g., diazepam and oxymorphone. Propofol may not be indicated because it is a potent vasodilator and usually produces hypotension during induction. This hypotension may be severe and not well tolerated in a patient that cannot compensate.
MAINTENANCE
The considerations for choosing a maintenance drug are the same as those already discussed. Inhalational anesthetics are a common choice, but their cardiovascular consequences must be monitored closely. Isoflurane causes the least myocardial depression of the inhalational anesthetic drugs. If the inhalational agent causes excessive hypotension, it may be necessary to change to an injectable agent. An opioid/diazepam combination would be our first choice for a very old patient, especially if it has severe physiologic dysfunction. Ketamine/diazepam is a second choice for one of the authors. Barbiturates are not a maintenance choice for these patients because of their physiologic and cumulative effects. Monitoring during the anesthetic should be the most complete and the most continuous that your practice has to offer. Anesthetic complications often develop rapidly. The aged patient has a lower threshold to complications and is less able to compensate for them and tolerate them.
ANESTHETIC PROTOCOLS FOR SPECIFIC CONDITIONS
469
RECOVERY
Monitoring and support should continue at the same level of intensity as it did during the operation until the animal is fully recovered from the anesthetic. SUMMARY
Old patients can be safely anesthetized; however, they are less tolerant of the side effects of anesthetic drugs, and so the drugs must be carefully chosen and administered.
Anesthesia for Patients with Stable End-Stage Renal Disease Doris Dyson, DVM, DVSc From the Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada
End-stage renal disease implies that two thirds to three qu'arters of kidney function is impaired. Survival without polysystemic clinical signs results from compensatory mechanisms and limitation of physiologic and pathologic stressors. Anesthesia and surgery can represent a source of stress that is potentially life-threatening in such patients. Patients with renal disease have less tolerance for errors in fluid therapy administration. Dehydration, mild uremia, increased creatinine, potassium abnormalities, and metabolic acidosis may be present on admission. Correction of significant abnormalities should begin preoperatively. Anesthetic protocols must minimize changes in renal blood flow. Recovery should be through metabolism or redistribution rather than excretion, and metabolites should not be harmful to the kidney (e.g., fluoride ions from methoxyflurane). Sympathetic stimulation through general stress and excitement, volume deficiency, or pain can change blood flow distribution and hence must be avoided. Opioid premedication administered at a dose producing mild sedation enables easy handling of the patient (meperidine, 3-5 mg/kg IM, or oxymorphone, 0.025-0.05, mg/kg IM). Because many of these patients are geriatric, it is reasonable to avoid anticholinergics until deemed necessary to treat a bradycardia (<60 beats/min in dogs; <100