A knowledge of the natural history of postoperative pain is of importance in at least two respects. It will help the clinician, who finds its treatment is at present unsatisfactory. There is a pressing need for greater efficiency in meeting this problem (Editorial, 1953; Leading articles, 1964; Simpson and Parkhouse, 1961). In the field of research, the extent of the relief of postoperative pain has been much used in clinical trials designed to assay the efficacy of analgesic agents (Lee, 1942; Denton and Beecher, 1949; Masson, 1962; Parkhouse, 1967). To be meaningful, the design of such trials must take into consideration the various factors influencing the degree and course of postoperative pain. Although incidence and severity are obviously closely related, these two facets of pain after operation will be dealt with separately.
In a retrospective analysis of data which evaluates the influence of various factors on the outcome of a clinical assessment of potent analgesie drugs, (1) the method of assaying success of treatment, (2) the influence of different observers in the results obtained, (3) the influence of other factors, viz., age, sex, and weight of the patient, site and duration of operation, and initial severity of pain, were considered. It was concluded that methods based on the subjective assessments of either the patient or observer were valid and sensitive. Changes in spirometrie measurements following treatment were not in themselves valid indices of pain relief, but may be of value in certain circumstances. There was good correlation between the different observers' estimates of pain relief. Low pain severity before treatment was associated with a high er rate of placebo response than was severe pain. Age, sex, body weight, and duration of operation were without significant effect.
Using Ridit analysis, a comparison was made of the overall effects of what are generally considered to be equianalgesic doses of sixteen opiates, with respect to their desired and toxic effects when given as premedication to a standard population. Four mixtures of opiates, the non-opiate diazepam and saline were also included in the analysis. Results with all individual drugs have been previously reported in detail. Under the conditions of this study, pethidine 100 mg, papaveretum 20 mg and even morphine 10 mg are too toxic to warrant their present popularity. More attention should be paid to the use of levorphanol 2 mg, diamorphine 5 mg, methadone 10 mg and oxycodone 10 mg for premedication. These findings may be modified by the concomitant use of atropine or hyoscine. Papaveretum-hyoscine fully justifies its popularity, but its greater efficacy can be explained by its high morphine content and the action of hyoscine. Under appropriate conditions diazepam may be superior to any of the opiates for use in premedication.
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