Myocardial Pain
55. C.P., a 65-year-old man with a history of angina pectoris, is brought to the ED with a suspected acute myocardial infarction (MI). Meperidine 25 mg IV is prescribed for pain control. Would another analgesic be preferred over pentazocine in C.P.?
This dose of meperidine might be effective for analgesia; however, meperidine has variable hemodynamic effects in patients with hemodynamic instability, whereas fentanyl and morphine's effects are more predictable. Butorphanol (Stadol) and pentazocine can increase pulmonary vascular resistance and pulmonary artery pressure.182,183 Furthermore, pentazocine can produce idiosyncratic hypotensive episodes, which could be disastrous in these patients. Therefore, these agents should be avoided after MI.
Morphine does not increase myocardial wall tension or oxygen consumption and does not affect cardiac dimensions. Morphine also can decrease heart rate and induces only minimal orthostatic changes in blood pressures. In postsurgical patients who are volume depleted, the orthostatic effect of morphine can be quite dramatic, however. Sedative and emetic effects of morphine are comparable to methadone, but may be greater than those of meperidine or hydromorphone. Methadone, hydromorphone, buprenorphine, and nalbuphine affect the cardiovascular system in a manner similar to that of morphine.183
In summary, although all the aforementioned agents are effective analgesics, pentazocine and butorphanol cause greater cardiovascular effects and can exacerbate an acute MI by increasing the cardiac workload and oxygen consumption. Therefore, morphine remains the preferred agent. (See Chapter 17, Myocardial Infarction, for further discussion.)
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