Standards of care for PONV
Editor—I congratulate Drs Dolin and Cashman on the completion of the comprehensive review of the acute postoperative pain management.1 I would like to express a few comments on their findings and interpretations. In comparison with i.m, they found nausea and pruritus to be more frequent in patients receiving PCA, and both techniques have similar effects on sedation and vomiting. Therefore, it is logical to conclude that the overall tolerability of PCA is inferior to i.m. technique. A simple explanation of this conclusion could be that the patient with PCA received more narcotic. For that reason, as compared with i.m., PCA was found to be superior in effectiveness2 but with inferior tolerability.1However, this evidence may not reflect reality. Similar to pain, nausea and pruritus are subjective phenomena, necessarily expressed by the patient and recorded by the nurse. Although narcotic side-effect monitoring is widely used, it may not always truly reflect what has actually been perceived by the patient. Milder forms of nausea and pruritus may not have been complained about by the patient and milder complaints from patients may not have been documented by the nurse. An audit of more than 10 000 patients (mostly post-Caesarean section) reported a low incidence of PONV, and discussed factors responsible for under-reporting of narcotic side-effects.3
Less frequent monitoring and patient's voluntary reporting of narcotic side-effects probably under-report the incidence of side-effects. More frequent observations and specific enquiry regarding nausea and pruritus (as commonly occur with PCA) may have found more patients with these undesirable effects. The incidence of nausea and pruritus was probably under-reported in studies (such as the study by Flisberg and colleagues4) where the primary objective was to study the effectiveness of postoperative analgesia or where i.m. technique was used.
Finally, narcotic analgesic technique is an important factor but not the only one causing PONV. The risk of PONV depends on many other factors such as the patient, anaesthesia, surgery, medications, etc. Therefore the standard of care based on only one factor is of limited value. The overall risk of PONV depends on a combined effect of all risk factors. Patients should be categorized as low, moderate and high risk for PONV and for each category, the standard of care should be separately defined.
J. S. Anwari
Riyadh, Saudi Arabia
E-mail: Janwari{at}hotmail.com
Editor—We appreciate Dr Anwari's comments on our reviews of the effectiveness2 and tolerability1 of acute postoperative pain management and are grateful for the opportunity to reply. As Dr Anwari points out, the findings of our two reviews indicate that PCA opioid administration is more effective than i.m. administration, seemingly at the expense of a higher incidence of side-effects. Dr Anwari proposes that patients may receive more opioid with PCA administration compared with i.m. administration as an explanation for this finding.
In our reviews, we simply reported the incidences of pain and side-effects and refrained from formal statistical comparisons between analgesic techniques. However, it is obvious from a scrutiny of the 95% confidence intervals (reproduced from both reviews and outlined in Table 1) that PCA opioid administration is indeed more effective than i.m. opioid administration. It is equally obvious that, with the exception of pruritus (which is more common with PCA), there are no clear cut differences in side-effects between the two analgesic techniques. Therefore we do not agree with Dr Anwari that our findings support the contention that PCA opioid administration is more effective than i.m. opioid administration at the expense of a higher incidence of side-effects.
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Although we did not obtain details of the relative doses of opioid administered using the two techniques we agree that this information may have been instructive. However, given the absence of any major difference in side-effects one might not consider it necessary to speculate whether one technique was associated with a greater opioid dose than the other. Nevertheless, there is Level I evidence which confirms our finding that i.v. opioid PCA provides better analgesia than i.m. opioid analgesia but with no difference in opioid consumption.5
Dr Anwari also suggests that, as a result of under-reporting, side-effects may be even more common than we observed but in the absence of any supportive evidence this remains a speculation. Our review extracted data from a large number of published studies representing the experience of a huge number of patients who had undergone a variety of surgical procedures. We feel that our figures, which are not dissimilar to figures reported by Werner and colleagues,6 accurately represent the likely incidences of the various side-effects reported.
Finally we agree wholeheartedly with Dr Anwari that PONV depends on a multitude of factors including analgesic technique. The overall incidences that we reported reflect the interplay of all of these factors. An Acute Pain Service should expect to manage PONV whatever its cause.
London and Chichester, UK
*E-mail: Jeremy.cashman{at}stgeorges.nhs.uk
References
1 Dolin SJ and Cashman JN. Tolerability of acute postoperative pain management: nausea, vomiting, sedation, pruritus, and urinary retention. Evidence from published data. Br J Anaesth 2005; 95:584–91
2 Dolin SJ, Cashman JN, Bland JM. Effectiveness of acute postoperative pain management: 1. Evidence from published data. Br J Anaesth 2002; 89:409–23
3 Anwari JS, Ahmed F, Mustafa T. An audit of acute pain service in Central, Saudi Arabia. Saudi Med J 2005; 26:298–305[Medline]
4 Flisberg P, Rudin A, Linner R, Lundberg CJF. Pain relief and safety after major surgery. A prospective study of epidural and intravenous analgesia in 2896 patients. Acta Anaesthesiol Scand 2003; 47:457–65[CrossRef][Web of Science][Medline]
5 Walder B, Schafer M, Heinzi H, et al. Efficacy and safety of patient-controlled opioid analgesia for acute postoperative pain. Acta Anaesthesiol Scand 2001; 45:795–804[Web of Science][Medline]
6 Werner MU, Soholm L, Rotboll-Nielsen P, Kehlet H. Does an acute pain service improve postoperative outcome? Anesth Analg 2002; 95:1361–72
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