Usually the elderly patient experiences a longer duration of narcotic analgesia than the younger patient and thus tends to require less frequent dosage. But is the older patient more susceptible to narcotic drug effects such as confusion, excessive sedation, or respiratory depression? Kaiko's study of patient responses to 947 doses of 8 mg or 16 mg IM morphine found that four hours after IM morphine, 71 percent of patients 70 to 89 years old continued to experience pain relief but only 28 percent of patients 18 to 29 had pain relief. Total pain relief and peak pain relief, however, were not significantly different in older and younger patients(1). Therefore, age seems to be a significant factor in anticipating the duration of morphine analgesia and thus in determining the frequency of administration, but not in determining what the appropriate dosage should be. One likely reason that analgesia lasts longer in older patients is diminished morphine clearance. Kaiko and others found significantly higher plasma morphine levels in older patients (mean 71 years) compared with younger patients (mean 29 years) four hours after receiving IM morphine(2). However, other factors may also be responsible for the extended period of pain relief. There is considerable variation in response to analgesics. Thus dose and frequency must be titrated according to patients' individual responses. Bellville and others studied the relationship between pain relief reports and selected patient characteristics for 712 patients receiving morphine 10 mg IM and/or pentazocine (Talwin) 20 mg IM for postoperative pain. Age was the most significant variable: Pain relief increased with increasing age over 40(3). Thus, the patient over 40 years is likely to require less frequent narcotic doses than a younger patient-but not a lower dose. Height, weight and body surface area were, surprisingly, not found to be accurate guides for determining narcotic requirements. Another unexpected finding was that, despite obtaining better analgesia, patients over the age of 58 were no more sedated than younger patients. The authors emphasized that not all research suggests reduced perception of pain in the aging patient(3). The absorption of IM or sc narcotics may be important in determining the route of administration. One study of 10 patients from 26 to 54 years found that the first postoperative injection of meperidine 100 mg IM provided inadequate analgesia because of poor absorption: Eight patients received no pain relief following the first injection and two patients received total relief for only one hour. Inadequate and unpredictable blood concentrations were found(4). In any elderly patient, but especially in the immediate postoperative period since peripheral circulation may be diminished due to increased circulation to the vital organs, one may anticipate circulatory problems. Then insufficient plasma concentration of drugs may be an even more significant problem. With slower absorption, not only will pain relief be inadequate, but the unpredictability of the absorption rate makes administration of the next dose dangerous since it may be absorbed simultaneously with the first, resulting in sedation and respiratory depression. Safer, more effective postop analgesia may be obtained by the Iv route(4). Consider the Iv route in any elderly patient with questionable peripheral circulation. Keep in mind that the aging process increases susceptibility to effects of all drugs in the following ways: DLess efficient liver and kidney clearance can result in drug accumulation. 0 Since certain organs become more responsive to drugs with age, toxic effects may be observed even when circulating drug levels are within a range that is considered safe for adults.
Read full abstract
Aug 1, 1985
Fabio Facchinetti + 8
Open Access