To the Editor:—
We read with interest the study reported by Aubrun et al. 1in the June issue of Anesthesiology as well as the accompanying editorial. 2
This study is analysis of routine data collected by nursing staff. The postanesthesia care unit nurses in this study 1followed a routine protocol for the administration of morphine. Most hospitals have standard operating procedures for morphine administration in the PACU. In the study by Auburn et al. , 1nurses were instructed to ask the patients about their pain and helped them perform a visual analog scale (VAS) every 5 min. Then they administered a 2- or 3-mg dose of morphine (depending on body weight) until adequate pain relief occurred (defined as a VAS < 30). It is very hard to perform 5 to 20 consecutive measurements of respiratory rate, oxygen saturation, arterial blood pressure, Ramsay sedation score, and heart rate while administering morphine every 5 min unless one has no other patient care responsibility. The authors 1also mentioned that they had discovered that in approximately 17% of the patients, the VAS was not used but instead a verbal or subjective behavioral scale (not defined) was used to collect pain information. Subjects were excluded from the analysis if their pain was not relieved and they required rescue medication. No information is provided regarding what constituted inadequate analgesia requiring rescue. A major limitation of this study is its retrospective nature; therefore, the data provided should be interpreted cautiously.
The authors state that 3,045 patients were analyzed. An assumption is made that all 3,045 patients had relief of pain (VAS < 30) following treatment with morphine, as no information is provided to the contrary. The overall success rate reported by Aubrun et al. is impressive (> 96%). Their table 1 shows that in 39% of patients, severe pain (VAS > 70) was reduced to mild pain (VAS < 30) with 10 mg or less of morphine (in a 70-kg subject). This appears, on the basis of our experience, to be a rather unexpectedly high success rate in patients with severe postoperative pain. We have been evaluating dose-response of morphine in an ongoing study of patients recovering from total abdominal hysterectomy. In our study, patients are randomized to receive either 12 mg or 21 mg of morphine (3 mg every 3 min) in the PACU, in a double-blind manner. We also defined desired relief as a verbal analog scale of 3 out of 10. We have studied 10 patients so far (unpublished data) and have not achieved the desired relief in any. In another study, we evaluated the analgesic effect of a single 7.5-mg dose of morphine in a double-blind study in patients with lower abdominal procedures and could not measure much analgesia until rescue 10–15 min later. The authors 1evaluated a diverse group of patients. The data, however, were not analyzed on the basis of surgical type to minimize variations in baseline postoperative pain scores. The authors should have provided basic descriptive statistics such as the number of doses of morphine needed to achieve pain relief based on the initial pain score, type of surgery, and percentage of failure and success, as well as the presence of side effects (if any) and the influence of gender and age. It is equally important to measure the effect of morphine on the affective component of pain, as some patients feel relief despite no change in the intensity of pain.
The editorial 2accompanying this manuscript stresses that the difference in various procedures translates into lack of standardization of intraoperative anesthetics. We believe diversity of cases reflects a source of baseline variability in pain scores. Furthermore, the editorial states that “opioids side effects exert a major impact on the course of postoperative recovery and limit effective opioids titration in many cases.” We believe that in the majority of cases it is the fear of side effect that limits effective opioids titration. Indeed, at 2 and 5 min after administration of a single 7.5-mg dose of morphine, we observed no significant hemodynamic change.
Although our European counterparts have reported better success with larger doses, even these doses may not be sufficiently large. Evaluation of higher doses (i.e. , 5 mg) at 3- to 5-min intervals may demonstrate a better relief profile in most patients. The frequency of adverse events should increase with dose; the anticipated occurrence of these side effects, however, may be exaggerated because of our lack of experience. Clinicians are often too concerned about the respiratory effect of rather small doses of morphine (1–2 mg). In some of our patients undergoing abdominal procedures, tachypnea may have represented intentional defense against pain (to avoid deep breaths). We have noticed a significant drop in respiratory rate to a more normal range after relief of pain in some of these patients.
We continue to believe that postoperative pain is undertreated because of the caregiver’s fear and lack of experience. It has been known for quite some time that a VAS of 70 or 80 should be considered severe pain, and that severe pain requires more morphine for treatment than mild or moderate pain. Although postoperative treatment should be individualized, the safety and efficacy of higher doses of morphine must be determined prospectively in patients with moderate-to-severe postoperative pain.
