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From the Department of Anesthesioogy, M.L.N. Medical College and Associated Hospitals, Allahabad, India.
Address correspondence to: Dr. Asok Jayaraj Pullani, 103, New PG Hostel, SRN Hospital, Allahabad, UP, India, PIN 211001. Phone: +91-933-5150468; E-mail: ashokjayaraj{at}yahoo.com
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Abstract |
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Methods: 120 patients of either sex, ASA I–II, undergoing elective middle ear surgeries under general anesthesia were included in this randomized, prospective, double-blinded and placebo-controlled study. The anesthetic technique was standardized. Patients were divided into three groups. Group I was the control group. Capsicum plaster (1 x 1cm) was affixed at the P6 acupoint on both forearms 30 min before induction of anesthesia in patients of Group II. Patients of Groups I and III received an inactive adhesive plaster at the same site. Ondansetron 4 mg iv was given to patients of Group III at the end of surgery and the rest of the patients received a placebo. The plasters were removed six hours after transferring the patients to the postoperative unit. Criteria were fixed for the administration of rescue antiemetics (ondansetron 4 mg iv). PONV and the requirement for rescue antiemetics were recorded by a blinded observer.
Results: The incidence of PONV and the requirement for rescue antiemetics were significantly lower in both the acustimulation and ondansetron groups at six hours. At 24 hr there was a reduction in the requirement for rescue medication in the ondansetron group.
Conclusion: Stimulation of the P6 acupoint with capsicum plaster is an effective method for prevention of PONV after middle ear surgery and its efficacy is comparable to ondansetron for the first six hours after surgery.
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Introduction |
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The antiemetic effect of stimulation of the P6 acupoint by various methods has been established.6 The need of a person trained in acupuncture, costly equipment for electrical stimulation and the availability of acupressure wristbands may limit their use. Recently Kim et al. described the use of a capsicum plaster for the prevention of PONV after abdominal hysterectomy.7 This seems to be a simple, inexpensive and easily available method, but its role has not been fully evaluated. We undertook a study to compare the efficacy of capsicum plaster at P6 acupoint with ondansetron to prevent PONV in patients undergoing middle ear surgeries under general anesthesia.
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Methods |
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All patients received lorazepam 2 mg po the night before surgery and the P6 acupoint was marked out on both forearms. The P6 or "Neiguan" acupoint is located on the anterior aspect of the forearm two body inches proximal to the most distal skin crease of the wrist joint, between the tendons of flexor carpi radialis and palmaris longus. One body inch or "cun" is the width of the patient’s thumb at the interphalangeal joint (Figure
).
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The incidence of PONV was evaluated within six hours and 24 hr after transfer to the postoperative unit by a blinded observer. Nausea and vomiting were recorded separately and an episode of retching was considered as vomiting. A rescue antiemetic (ondansetron 4 mg iv) was given to patients who experienced persisting nausea for more than five minutes, had two or more episodes of vomiting/retching or who demanded treatment for their emetic symptoms.
Statistical analysis
A sample size of 36 patients per group was determined by a priori power analysis8 on the following assumptions: a) more than 50% of the patients not receiving a prophylactic antiemetic would experience PONV,3,9 b) prophylactic acustimulation with capsicum plaster may show a reduction of PONV by 35%,7 c) 
= 0.05 and ß = 0.20. Forty patients were selected in each group to compensate for dropouts. All data were tabulated and analyzed using Microsoft Excel 2000 (Microsoft Corporation, Redmond, WA, USA). Statistical analysis was performed using Fisher’s exact test for categorical data and analysis of variance with Tukey’s multiple comparison test for continuous data. P < 0.05 was considered statistically significant.
Number needed-to-treat (NNT) was calculated by taking the reciprocal of the absolute risk reduction. It shows how many patients receiving the prophylaxis, compared with control, require an intervention before one patient will have an effective response. Confidence intervals for the NNT were calculated and expressed as suggested by Altman.10
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Results |
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).
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).
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Table III compares the NNT of acustimulation and ondansetron for different events with their 95% confidence intervals.
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Discussion |
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The present study was undertaken in a referral centre in North India and most of the subjects were of low socio-economic status. Many of them were ready to accept PONV as a part of their surgery and ignored their symptoms unless specifically questioned. This explains the rationale for inclusion of a placebo group in our study. The present study was randomized, adequately blinded, and employed a standardized anesthetic technique. A willful effort was made to avoid opioids. The patients could not afford propofol-based anesthesia, hence the most accepted practice in this part of the world was employed (thiopental and vecuronium induction; halothane and N2O maintenance). Capsicum plaster was fixed at the P6 points 30 min before giving any anesthetic drug, thereby giving adequate time for onset of action. The plaster was affixed on both forearms to avoid the question of dextrality and sinistrality.13 Ondansetron was administered at the end of surgery, as suggested by recent studies.4,9 We found that the effect of acustimulation with capsicum plaster at the P6 acupoint is comparable to iv ondansetron for the first six hours after surgery.
The subjects in the control group had an incidence of PONV of 50% at six hours after the surgery. This was reduced to 21% by prophylaxis with acustimulation (NNT 4) and 28% by ondansetron (NNT 5). When vomiting alone was considered, the incidence of 25% in the control group was reduced to 8% and 5% by acustimulation (NNT 6) and ondansetron (NNT 5) respectively. The need for rescue antiemetic treatment was reduced by 80% and 72% by acustimulation and ondansetron respectively. All these changes were statistically significant and suggest a comparable efficacy of both methods. The ‘NNT’ indicate that one in four patients given acustimulation and one in five given ondansetron will not experience PONV.
When the incidence of PONV was compared at 24 hr after surgery, none of the groups showed any significant change (Table II
). However there was a significant reduction in the requirement for rescue antiemetics in patients given ondansetron. The requirement was assessed by blinded observers based upon preset criteria, hence this should be taken as a valid outcome of antiemetic prophylaxis.9 This suggests a persisting action of ondansetron even at 24 hr.
Our findings in the ondansetron group correlate well with similar studies in the field.9,14 Although a number of investigations have evaluated acupuncture and different methods of acustimulation for the prevention of PONV, there is a paucity of published material on its role on PONV after middle ear surgery. Dundee et al., the pioneers in this area, reported a 50% reduction of PONV by invasive acupuncture at the P6 point, while non-invasive methods proved to be slightly inferior.13 Lee and Done conducted a meta-analysis on published randomized controlled trials in this field and concluded that nonpharmacologic techniques are effective in preventing PONV in adults in the first six hours, with an NNT of 7.6 In the present study, the efficacy of acustimulation was more marked, suggesting that stimulation of the P6 point specifically inhibits emetic stimuli from the vestibular system, although the mechanism remains obscure. The most probable mechanism of action of acustimulation is attributed to the release of endogenous opioids and modulation of other neurotransmitters in the body.6 Capsaicin, the active ingredient of capsicum plaster when applied to the skin, acts on the peripheral nerves via a mechanism similar to acupuncture. It may also have a direct action on the gastrointestinal tract, thereby inhibiting PONV.7 Acustimulation may have a more potent effect on specific neurotransmitters in the pathways linking the vestibular system to the emetic centre. The evidence that P6 stimulation reduces motion sickness15 supports this hypothesis. Although acustimulation with capsicum plaster was effective in preventing PONV in the first six hours after surgery, it did not show any benefit at 24 hr. This suggests a cessation of action of capsicum plaster before 24 hr, which is contradictory to the report by Kim et al. who demonstrated the persistent effects of capsicum plaster even after 24 hr.7 The reasons for this discrepancy remain unclear.
One of the obvious benefits associated with the use of capsicum plaster is the absence of unpleasant sensation associated with invasive acupuncture.13 Further, one sheet of capsicum plaster costs 9 Indian Rupee [Indian Rupee (INR) = USD $0.20] and, when cut into 1 x 1 cm squares, can be used in at least 25 patients. Thereby, the cost per person approximates INR 0.36, while ondansetron costs INR 28 per 4 mg ampoule. Capsicum plaster is available over the counter as a treatment for musculoskeletal pain and requires no specific training for usage.
Further studies are required to determine the optimal size and duration of action of the capsicum plaster. Changing the plaster at appropriate intervals may prolong its antiemetic efficacy. In summary, the stimulation of the P6 acupoint with a capsicum plaster is a simple, inexpensive and an effective method for the prevention of PONV after middle ear surgery. Its efficacy is comparable to that of ondansetron.
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Footnotes |
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Accepted for publication November 25, 2004. Revision accepted February 18, 2005.
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References |
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2 Honkavaara P, Saarnivaara L, Klemola UM. Prevention of nausea and vomiting with transdermal hyoscine in adults after middle ear surgery during general anaesthesia. Br J Anaesth 1994; 73: 763–6.
3 Honkavaara P. Effect of ondansetron on nausea and vomiting after middle ear surgery during general anaesthesia. Br J Anaesth 1996; 76: 316–8.
4 Gan TJ, Meyer T, Apfel C, et al. Consensus guidelines for managing postoperative nausea and vomiting. Anesth Analg 2003; 97: 62–71.
5 Tramèr MR. Treatment of postoperative nausea and vomiting (Editorial). BMJ 2003; 327: 762–3.
6 Lee A, Done ML. The use of nonpharmacologic techniques to prevent postoperative nausea and vomiting: a meta-analysis. Anesth Analg 1999; 88: 1362–9.
7 Kim KS, Koo MS, Jeon JW, Park HS, Seung IS. Capsicum plaster at the Korean hand acupuncture point reduces postoperative nausea and vomiting after abdominal hysterectomy. Anesth Analg 2002; 95: 1103–7.
8 Campbell MJ, Julious SA, Altman DG. Estimating sample sizes for binary, ordered categorical, and continuous outcomes in two group comparisons. BMJ 1995; 311: 1145–8.
9 Sun R, Klein KW, White PF. The effect of timing of ondansetron administration in outpatients undergoing otolaryngologic surgery. Anesth Analg 1997; 84: 331–6.[Abstract]
10 Altman DG. Confidence intervals for the number needed to treat. BMJ 1998; 317: 1309–12.
11 Andrews PL. Physiology of nausea and vomiting. Br J Anaesth 1992; 69(Suppl. 1): 2S–19S.
12 Gilman A, Hardman JG, Limbird LE. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 10th ed. New York: McGraw-Hill; 2001: 1029.
13 Dundee JW, Ghaly RG, Bill KM, Chestnutt WN, Fitzpatrick KT, Lynas AG. Effect of stimulation of the P6 antiemetic point on postoperative nausea and vomiting. Br J Anaesth 1989; 63: 612–8.
14 Tramèr MR, Reynolds DJ, Moore RA, McQuay HJ. Efficacy, dose-response, and safety of ondansetron in prevention of postoperative nausea and vomiting. A quantitative systematic review of randomized placebo-controlled trials. Anesthesiology 1997; 87: 1277–89.[Medline]
15 Dundee JW, McMillan C. Positive evidence for P6 acupuncture antiemesis. Postgrad Med J 1991; 67: 417–22.[Medline]
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