Postoperative nausea and vomiting (PONV) is experienced by approximately 30% of all patients following surgery.1 Patients consider PONV to be a serious complication of anaesthesia.2 In addition to causing substantial discomfort, PONV is also known to prolong both the time spent in the postanaesthetic care unit (PACU) and the total hospital stay.3–5
Existing prevention and treatment of PONV is based on a multimodal regimen. This regimen involves identifying high-risk patients for known risk factors (female sex, non-smoker, previous PONV/motion sickness, inhalation anaesthetics, duration of surgery and perioperative/postoperative opioids) and on medical prophylactic treatment with one or more antiemetics.6–8
Stimulation of the P6 acupoint is described as an alternative method for preventing the development of PONV.9–11 The acupoint P6 is located two cuns (approximately 4 cm) proximal to the transverse crease of the wrist between the tendons of flexor carpi radialis and palmaris longus. (A cun is a Chinese inch and is roughly equivalent to the width of the thumb across the interphalangeal joint.12).
A Cochrane review from 2004, updated in 2009, described P6 acupoint stimulation for the prevention of PONV.10,11 This review favoured P6 stimulation, but with reservations concerning methodology, for example, design, allocation concealment and bias.10,13 One way of stimulating the P6 acupoint is by acupressure. Acupressure is a non-invasive variant of acupuncture involving constant pressure on an acupoint without penetrating the skin. Staff members can easily perform acupressure at acupoint P6 without having knowledge about traditional Chinese acupuncture. Acupressure avoids the needle-related complications, for example, transmission of infectious disease, broken needles or adverse events due to inadequate training of the acupuncturist.14
The objective of the present study was to investigate the effect of P6 acupressure using the acupressure wristband Vital-Band – a Danish product – on the incidence of PONV within the first 24 h postoperatively.
Participants and methods
We included 134 women scheduled for breast surgery at Copenhagen University Hospital, Herlev between May 2005 and December 2006. The study was approved by the local Ethics Committee (jr. nr. KA 05021g) and registered at Clinicaltrials.gov (ID: NCT00275483).
All participants gave oral and written informed consent. We included healthy [the American Society of Anesthesiologists (ASA) class I–II], non-smoking women aged 18 years and older. The breast surgical procedures were mastectomies or lumpectomies either with or without axillary clearance. We randomised only women scheduled for total intravenous anaesthesia.
Patients belonging to ASA class at least 3, who smoked, were pregnant or had any diseases that could influence sensibility in wrists and hands (such as diabetes, carpal tunnel syndrome, former axillary clearance or lymphoedema of the arm) were not allowed to participate in the study. We also excluded women who had nausea and/or vomiting within 24 h preoperatively, as well as those with any skin problems at the location of the wristband. The acupressure wristband Vital-Band evaluated in this trial is made of soft plastic with adjustable fasteners. An elliptical pea-sized stud stimulates the P6 acupoint when the acupressure wristband is tightened correctly (Fig. 1).
The study was randomised clinical trial with blinding of both patients and outcome assessors. Before inclusion, patients were randomised using opaque sealed envelopes. Random allocation sequence was generated by drawing one of these sealed envelopes. The patients were randomised to either P6 stimulation group (stud of the Vital-Band placed over the P6 acupoint ventrally at the forearm) or to sham control group (stud of the Vital-Band rotated 180° and thereby placed in a sham position at the dorsum of the forearm). This point has no significance in the prevention or treatment of nausea and vomiting by acupuncture or acupressure. In order to avoid staff members to figure out the randomisation outcome of the last envelopes, we had more sealed randomisation envelopes than needed according to the sample size calculation.
Randomisation took place on the day of surgery as the patient arrived at the operation room. The acupressure wristbands were applied just before induction of anaesthesia. Both randomisation and application of the Vital-Band were carried out by five nursing assistants who were thoroughly educated in this specific procedure by the manufacturer of the Vital-Band. This included manual stimulation of the P6 acupoint/sham control point with brief presses for 30 s immediately after the wristband was applied. Patients were not asked whether they experienced any acupoint sensations due to the potential risk of unblinding. A photomontage showing the correct method to apply the wristband was used in support of the procedure. When correctly applied, the wristband is unlikely to be displaced from its intended position.
The wristband was covered with a dressing in such a way that both the patient and the outcome assessors were blinded and unable to discover in which position the acupressure wristband had been applied. Anaesthesia was standardised to total intravenous anaesthesia based on propofol and fentanyl. There were no protocolled infusion rates; rather propofol and fentanyl were adjusted by the anaesthetist in order to maintain safety and well being of the patient. Airway was maintained with a laryngeal mask if no specific reason for tracheal intubation was present (gastric reflux, regular morphine use, BMI >30). Then the anaesthesia induction consists of propofol, alfentanil and succinylcholine. Intravenous fluids were not protocolled. First choice at our department is crystalloids (isotonic saline, 0.9% sodium chloride). As the arm at the side of the operation field was fully covered as a part of the sterile draping, a vein on the dorsum of the hand at the same side as the wristband was prescribed for the anaesthesia. Total intravenous anaesthesia was administered through a vein distal to the wristband. We, therefore, fastened the wristband so that acupressure was provided without venous congestion occurring. According to the protocol, no prophylactic antiemetic medication was administered to the study patients.
Primary outcomes were any occurrence of nausea or vomiting within 24 h postoperatively. Secondary outcome was rescue antiemetic medication.
Follow-up was carried out three times during the first 24 h postoperatively by nurses from the PACU: the first follow-up was 30 min after the patient arrived at the PACU; second follow-up was when the patients were ready to leave PACU and return to their ward; third and final follow-up was undertaken 24 h postoperatively by a PACU nurse in either the ward, or if the patient had been discharged, by telephone.
Nausea and vomiting were assessed both by the patients themselves and by the PACU nurses. Also analgesic medication given for potential pain was recorded. The acupressure wristband was removed at the third follow-up and any possible side effects (redness, swelling, tenderness and paresthaesias) were observed. Wristbands were removed early if the patient suffered from side effects.
In addition, we collected data on premedication, operative time, anaesthetics, whether or not surgery included axillary clearance, time the patient spent in the PACU and total length of stay in hospital.
No prophylactic antiemetics were administered. If the patients suffered from nausea and/or vomiting postoperatively, they were treated according to current guidelines.8
The overall risk for PONV development in our study population (having at least two risk factors for PONV development: women and non-smoker8) was estimated to be 45%. This is in agreement with other study findings following breast surgery.15,16 With a relative risk reduction of 50%, a power of 80% and a 5% two-sided significance level, 130 patients were needed for the assessment. For hypothesis testing, the Student's t-test or the Mann–Whitney U-test was used for continuous covariates and the χ 2 test was used for dichotomous covariates. Continuous covariates are presented as medians with interquartile range, as mean values with 95% confidence intervals (CIs) or as medians with minimum and maximum ranges. The latter presentation relates to non-parametric data processed by Mann–Whitney U-test. Dichotomous covariates are presented as percentages with 95% CIs. True intention-to-treat analysis was not possible without imputations because of missing outcome data. In a modified intention-to-treat analysis, we excluded only patients who did not receive a minimum amount of the intended intervention. All randomised patients who succeeded were included in the analysis and their data analysed as ‘available case analysis’.
All data were processed in SPSS version 13.0.
We included 134 patients in our study. We randomised 67 patients to each group. The baseline characteristics of the patients, including PONV risk factors are presented in Table 1.
Of the initial 134 patients, 112 completed the study; 22 patients were withdrawn from the study for the following reasons: included an error (eight); re-operation (two); violation of the study protocol by administration of prophylactic antiemetics either before the operation or during anaesthesia (five); or simply because of insufficient follow-up (four). One patient did not wish to continue with the trial and asked to be withdrawn immediately after surgery. Other reasons for withdrawal from the study were a fractured ankle at the day of surgery (one) and Quincke's oedema (one). Due to organisational reasons, only 40% of the possible includable patients were asked to participate in the study (Trial profile, see Fig. 2).
Several patients had some missing values due to extra workload in the normal clinical setting for the outcome-assessing nurses constituted by the study.
Six patients were discharged less than 24 h postoperatively and because of this, their acupressure wristbands were removed prematurely. These patients had the third follow-up by telephone. Three patients had their wristbands removed prematurely because of side effects.
We found no significant differences in the incidence of PONV between the two groups, neither during the PACU stay nor during the first 24 h postoperatively. By the third follow-up, 35.1% (95% CI 22.7–47.5%) of the patients who received P6 stimulation versus 43.1% (95% CI 29.5–56.7%) of the patients receiving sham control had experienced nausea (P = 0.433). For vomiting, the percentages were, respectively, 25.9% (95% CI 14.6–37.2%) and 26.9% (95% CI 14.8–39.0%) in the P6 stimulation group and the sham control group (P = 1.000; Table 2). These data from the third follow-up are the numbers reported by the patients themselves. With regard to the PACU stay, the data shown in Table 2 are an expression of the PONV evaluation done by the PACU nurses. When the patients themselves assessed PONV in the PACU, we found exactly the same incidence for vomiting and almost the same incidence for nausea: one more patient in the P6 stimulation group (data not shown). By chance, more patients in the sham control group than in the P6 stimulation group were prone to develop PONV. This was due to an accidentally higher proportion of patients in the sham control group having a history of previous motion sickness and/or PONV (Table 1). Beyond this, the groups were comparable with regard to age; intraoperative use of fentanyl and propofol; surgical characteristics (including duration of surgery); total morphine requirements postoperatively; and the total number of hours wearing the Vital-Band (Table 1).
We found no significant reduction between the two groups in the need for rescue antiemetics, respectively, 28.6% (95% CI 17.1–40.1%) and 31.6% (95% CI 18.8–44.8%) in the P6 stimulation group and the sham control group (P = 0.834; Table 2), or in length of stay in the PACU or in the total time to discharge (Table 2).
Approximately, one third of all the patients reported side effects such as redness (40 patients), swelling (17 patients) and tenderness (16 patients) in wrist and hand caused by the wristbands. Four patients even reported paresthaesias. The local side effects caused by the acupressure wristband were equally distributed between the P6 stimulation group and the sham control group (Fig. 3).
We found no preventive effect of acupressure at acupoint P6 on PONV with the acupressure wristband Vital-Band nor did the need for rescue antiemetics or length of stay differ between the two groups.
A considerable proportion of patients reported side effects such as redness, swelling and tenderness in wrist and hand caused by the acupressure wristbands (Fig. 3). These side effects caused three patients to remove the Vital-Band before the end of the 24-h follow-up period.
Our study was designed to achieve optimal allocation concealment and blinding. In the Cochrane review from 2004 by Lee and Done,10 updated in 2009,11 the quality of most of the included trials was criticised concerning these factors. The cautiously positive conclusion in the first published Cochrane review was interpreted with some care because of publication bias and a country effect.17 The country effect covers the fact that ‘clinical trials of acupuncture originating in certain countries have an unusually high proportion of positive results’.18 In the revised version of the Cochrane review, there was no evidence of publication bias,11 but still there was moderate heterogeneity among the included studies.
In the recently updated Cochrane review, which includes another 10 studies examining P6 acupoint stimulation versus sham control for PONV, the authors show a significant reduction in nausea, vomiting and need for rescue antiemetics. However, they did not find evidence of publication bias from contour-enhanced funnel plots but still there was moderate heterogeneity among the included studies.11
The Cochrane review from 2009 documented that the effect of P6 acupoint stimulation versus sham control is more prevalent in patients with high baseline risk of PONV. The number needed to treat (NNT) for preventing PONV is 4–5 when the control event rate is 70–80% but declines to an estimate of 11 when the risk for development of PONV is 30%.
In our study, significantly more patients in the sham control group had a former experience of PONV and/or motion sickness than in the P6 acupressure group [35.3% (95% CI 22.2–48.4%) versus 15.5% (95% CI 6.2–24.8%), P = 0.025], despite meticulous randomisation (Table 1). In addition to this, the two groups were fully comparable having 40–80% estimated probability of PONV,19 mirroring the presence of at least two risk factors (women and non-smoker). Furthermore, an equal number of patients in both groups had three risk factors caused by morphine postoperatively and lastly more patients in the sham control group had a fourth risk factor caused by a history of previous motion sickness and/or PONV. More patients in the sham control group, therefore, had a higher baseline risk of developing PONV than patients in the P6 stimulation group. If there were any effects of the acupressure on PONV prophylaxis, we would, therefore, have expected to see a marked difference in the PONV frequencies between the two groups; however, this was not the case (Table 2).
Several different mechanisms have been proposed for the effect of P6 stimulation on PONV, but the exact mechanism by which acupuncture prevents PONV has not yet been established.20 These mechanisms include neurotransmitters, along with mechanisms that affect vagal modulation and cause gastric relaxation.
P6 stimulation increases the release of β-endorphin from the hypothalamus into the cerebrospinal fluid. β-Endorphins are considered to have an antiemetic effect mediated by the μ-receptors.21,22 The release of β-endorphins is postulated to be due to fibre synapses within the dorsal horn where acupoint-activated skin sensory fibre ends.23
Activation of serotonergic and norepinephrinergic systems altering serotonin transmission could also contribute to the antiemetic effect of P6 stimulation seen by some authors.24 Still the exact mechanism of action of P6 stimulation needs to be elucidated.
At the present time, a growing number of studies have been conducted to examine the effect of acupressure stimulation of the acupuncture point P6 in preventing PONV. The results from these studies are conflicting with inconsistent results regarding the efficacy of P6 stimulation as will be described in the following.
The timing of the application of the wristband in relation to the emetic stimulus is thought to be of some importance. It is claimed that acupoint stimulation should be started before any antiemetic stimuli.25 Traditional Chinese acupuncture at the P6 acupoint had significant effect only when it was given before nalbuphine premedication (a synthetic opioid agonist-antagonist), whereas there was no statistically significant effect when it was given during anaesthesia or after operation.12,25 Most of the studies performed to document an effect of P6 stimulation in preventing PONV apply the stimuli prior to induction of anaesthesia and continue the stimulation at least 6–24 h postoperatively. Even though the studies methodologically follow almost the same prescription, the results are still conflicting, with negative studies23,26,27 and studies in favour of P6 stimulation.22,24,28–31 We applied the Vital-Band before induction of anaesthesia and removed the acupressure wristband after 24 h postoperatively. A similar procedure was followed by Klein et al.26 in patients undergoing cardiac surgery. They also failed to prove any effect of acupressure at acupoint P6 on PONV. Neither did Agarwal et al.23 prove any effect on PONV (in patients undergoing endoscopic urologic surgery). They stimulated the P6 acupoint bilaterally but only for 6 h postoperatively. Turgut et al.29 proved acupressure at P6 to be effective in preventing PONV in women undergoing gynaecological surgery. The procedure was almost the same as that used in our study, except that Turgut stimulated the P6 acupoints with wristbands on both forearms.
A recent study by Streitberger et al.32 proved the effect of P6 stimulation through acupuncture in preventing PONV in patients undergoing gynaecological surgery but not in those undergoing breast surgery. Steitberger points out the importance of choosing subgroups with the largest potentials for benefit as an explanation for the conflicting findings.
To date the published studies dealing with the effect of P6 stimulation on the development of PONV have investigated many different subgroups regarding the type of surgery performed. It is well known that some operative procedures (e.g. eye, ear, gynaecological and laparoscopic) as well as extensive operative time make patients more prone to the development of PONV.33
Gan et al.34 found a reduction in the incidence of PONV after P6 electrostimulation in a study on women undergoing breast surgery lasting on average over 3 h. Our patients had an average operation time of approximately 2 h (Table 1).
From the above, it is evidently difficult to draw conclusions with regard to the timing, duration of P6 stimulation or type of surgery performed.
There is a constant ongoing discussion about the importance of unilateral versus bilateral P6 acupoint stimulation for preventing the development of PONV. It is claimed that the effect of the acupoint stimulation is dependent on stimulation of the dominant side.35 Most studies have stimulated bilaterally; however, this has not resulted in harmonisation of the study results,23,24,26,28–31 and it is not clear whether bilateral stimulation offers any advantages compared to unilateral stimulation.36 However, in our study, it was impossible to stimulate bilaterally simply because the wrist of the arm on the side of the operation would not be available to the anaesthetist and, therefore, any possible side effects caused by the acupressure wristbands would not be noticed intraoperatively.
Wristbands for acupressure are not known to be encumbered with side effects. Just one study by Alkaissi et al.31 reports a wristband (the Sea-band) as being uncomfortable causing transient pain, swelling and itching in 45 patients (study group: 410 patients). Other reports of side effects from acupressure wristbands are only case reports37 in which the participants only wore the wristbands for less than an hour. However, one participant still complained of swelling of the hands and another two participants felt the band was uncomfortable and tight.
As mentioned above, the Vital-Band, which is investigated in the present study, caused several local side effects, which made it unacceptable to some patients and inconvenient for approximately one third of the patients.
Limitations of the study
This present study is influenced by the fact that many staff members were involved in the practical conduction of the study. Doctors from the anaesthesia department were responsible for the inclusion of patients and PACU nurses assessed the outcomes. It was difficult to keep some staff members motivated and loyal to the study throughout the whole study period. This negatively affected the inclusion rate. Postoperative outcome assessment was insufficiently performed on some patients. For four patients (two in each group), the postoperative assessment was not performed at all, which resulted in their exclusion from the trial.
Data collections by clinical nurses have possibly given variations in the assessment of PONV because we did not use standardised questions. Asking the patients whether they suffered from nausea and vomiting was performed as simple yes or no questions. In addition to this, the PACU nurses themselves made a subjective assessment – again yes or no – whether the patients have had any nausea or have been vomiting, and whether the patient should be treated with rescue antiemetics. No data on interrater reliability between the outcome assessing nurses were collected, which theoretically could have affected the true PONV incidence either negatively or positively.
Blinding in reporting adverse skin reactions after removal of the wristband is not absolute because the wristbands were removed by the PACU nurses who at the same time were outcome assessors. This could have led to an underestimation versus overestimation of the adverse skin reactions depending on which randomisation group the patient belongs to. The Vital-Band caused inconvenience to many patients regardless of randomisation and hence positioning of the wristband.
Patients were not told whether the wristbands were applied with the stud placed at the P6 acupoint or with the stud placed in a sham position. Only patients who had knowledge about the P6 acupoint would be able to figure out if they were having P6 acupressure or sham control. We did not have the impression that in general patients in the Danish heathcare system knew about acupoints and their placement. Neither have we received any reports in this study indicating that the patients were aware which treatment group they were randomised to. We would, therefore, claim that there are no objections regarding bias from either the blinding of the outcome assessors or the blinding of the patients.
It is a potential limitation that we only included non-smokers in the study in light of the fact that surgical populations consist of smokers and non-smokers. However, it has previously been shown that NNT decreases when patient's risk factors for PONV development increase.11 As this study shows no effect of P6 acupoint stimulation by acupressure, we believe that inclusion of smokers would not have changed the overall conclusion.
One plausible explanation for the conflicting results among the published studies could be that the cause of PONV is multifactorial having an extremely complex physiology. It seems unlikely that all the causative factors for PONV development could be counteracted by a single-mode therapy such as P6 acupressure. A multimodal approach in PONV prevention is widely accepted as the correct way to handle the problem of PONV.1,7,8
In this study, we investigated the effect of P6 acupoint stimulation with the acupressure wristband Vital-Band for prevention of PONV in women undergoing breast surgery. We did not find that the Vital-Band was effective in preventing PONV in women undergoing breast surgery nor did we find any reduction in the use of rescue antiemetics.
On the basis of the existing knowledge, we would not recommend the use of the acupressure wristband Vital-Band for prevention of PONV in women undergoing breast surgery.
The Company Akura ApS, Heinesgade 5. st., DK-2200 Copenhagen N, has paid 48.000 DKR (approximately 9.000 US$) for testing of their device the Vital-Band (no registered trademark).
The work should be attributed to Trial Unit, Department of Anaesthesiology, Copenhagen University Hospital Herlev, Herlev Ringvej 75, DK-2739 Herlev, Denmark.
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