Postoperative nausea and vomiting (PONV) evokes substantial patient discomfort and may prolong hospital stay . PONV is thought to be of multifactorial origin, including patient-related, anaesthetic and surgical factors . Although the incidence of PONV after intraocular surgery is not so high compared with strabismus surgery , retching and vomiting can cause complications, such as wound dehiscence, iris prolapse, intraocular bleeding and prolonged hospital stay. However, the risk factors for PONV in patients undergoing vitrectomy have not been addressed. It is necessary to clarify factors that influence PONV after vitrectomy before devising anaesthetic strategies to minimize these complications. The aim of this study was to identify the potential risk factors for PONV after vitreous surgery in adults.
Data were collected from the medical records of adult patients undergoing vitrectomy under general anaesthesia at the Fukuoka University Hospital, Japan, between 1 January and 31 December 2003. The study was approved by the local institutional ethics committee. The data collection was limited to elective procedures, patients aged 18–65 yr, and ASA class I–III. All patients received general but no local anaesthesia in the perioperative period. Patients who experienced nausea and/or vomiting were identified retrospectively. The occurrence of PONV during the first 48 h after surgery was noted. PONV during the first 2 h after surgery was analysed separately to identify the risk factors for early PONV. Nausea and vomiting were considered present if noted as such in the medical records. During the postoperative period, in our hospital, patients were routinely asked whether they had nausea by the nursing staff at arrival and every 15–20 min in the postanaesthesia care unit (PACU) and vomiting was recorded as either present or absent by direct observation. On the surgical ward, this process was repeated every 15–30 min for 2 h and every 4–6 h except during the night, i.e. from 21:00 to 06:00 within 48 h after surgery. All the patients who underwent vitrectomy were hospitalized for at least 3 days in our hospital.
Factors we examined were age, gender, body mass index (BMI), smoking status, premedication with H2-blockers, anaesthetic maintenance (inhalation or intravenous (i.v.)), duration of surgery, and intraoperative fentanyl dose. In all cases, anaesthesia was induced with propofol and maintained with sevoflurane/nitrous oxide or propofol. All patients were intubated with the aid of vecuronium and given neostigmine as a reversal agent before tracheal extubation. If PONV were present, the patients received 0.5–1 mg droperidol in the PACU and 5–10 mg metoclopramide in the surgical ward.
Statistical comparisons of eight factors between the patients with and without PONV were performed by means of the t and χ2 tests, where appropriate. Significant factors derived from univariate analysis were then included in the multivariate analysis by means of logistic regression models. P < 0.05 was taken as significant. Statistical analysis was performed using a commercially available software program (StatView software for Windows; SAS Institute, Cary, NC, USA).
Two hundred and forty-seven patients met the inclusion criteria and their preoperative characteristics are summarized in Table 1. Fifty-seven (23%) and 37 patients (15%) reported one or more episodes of nausea and vomiting, respectively, during the study period.
By univariate analysis, gender (P < 0.01), BMI (P < 0.01) and type of anaesthesia (P = 0.01) were significantly related to nausea during the first 2 h after surgery. Female gender was significantly associated with nausea and vomiting throughout the study period (P < 0.01). Other factors did not alter the risk for nausea and/or vomiting (Table 2).
By multivariate analysis with logistic regression models, female gender (P < 0.01, odds ratio (OR) = 5.8, confidence interval (CI) = 2.2−14.9), BMI (P = 0.03, OR = 0.9, CI = 0.7–1.0), general anaesthesia with inhalational anaesthetics (P = 0.04, OR = 2.8, CI = 1.0–7.3) were associated with nausea during the first 2 h after surgery. Female gender was a predictive factor for nausea (P < 0.01, OR = 4.7, CI = 2.4–9.0) and vomiting (P < 0.01, OR = 3.6, CI = 1.7–7.8) throughout the study period (Table 3).
In this study of adult vitrectomy patients, the overall incidence of PONV was 23% and 15%, respectively. This is in accordance with the reported incidences of PONV after intraocular surgery ranging from 18% to 56% [3,4].
Limited information is available regarding the risk factors for PONV after ophthalmic surgery, especially vitrectomy. Iwamoto and colleagues reported, for various types of ophthalmic surgery, including retinal detachment surgery, that female patients showed a greater tendency toward nausea and vomiting, and that droperidol was a useful antiemetic supplement for this complication . Eberhart and colleagues evaluated the prophylactic effect of droperidol and dolasetron in a placebo-controlled study of patients undergoing vitrectomy . These two studies were performed mainly to evaluate the prophylactic effects of antiemetics. Therefore the patient- and anaesthesia-related risk factors for PONV were not extensively evaluated. van den Berg and colleagues studied 607 patients undergoing various types of ophthalmic surgery, including intraocular surgery, and showed that strabismus surgery predisposed particularly to emesis, and was associated with a high incidence of both early and delayed vomiting . In that study, however, the effects of only age and gender were evaluated in intraocular surgery, and only the incidence of vomiting was noted. No report has been found which evaluated the multiple perioperative risk factors for PONV in patients undergoing vitrectomy.
A limitation of our study was the potential for under-reporting PONV by the nurses in the PACU or surgical ward. Prospective interview and chart review study have shown that nausea recording by nurses under-represents the patients' actual experience . However, in our study, patients were asked whether they had nausea by the nursing staff on arrival and every 15–20 min in the PACU, and this process was repeated every 15–30 min for 2 h, and every 4–6 h for 48 h on the surgical ward.
Several factors significantly influenced the occurrence of PONV in a similar manner to that previously reported after various type of surgery, e.g. female gender and maintenance of general anaesthesia with an inhalational agent increased the incidence of PONV. The importance of female gender is well established and appears as the most important predictor of PONV [7–10]. Also, in our study, females had a 3.1–5.8 times higher risk for PONV than males and this sex difference was the only factor which influenced the incidence of both nausea and vomiting throughout the study period.
In our study, maintenance of general anaesthesia with propofol resulted in a reduction of PONV in the early postoperative period compared with sevoflurane– nitrous oxide. This is in accordance with the results of a meta-analysis performed by Tramér and colleagues , who analysed 84 randomized controlled studies involving 6069 patients and found that i.v. induction and maintenance of anaesthesia with propofol had a clinically beneficial effect on PONV in the early postoperative period. Apfel and colleagues  also demonstrated that use of volatile anaesthetics was identified as the main risk factor for PONV in the early postoperative period (0–2 h), with adjusted OR of 19.8, 16.1 and 14.5 for isoflurane, enflurane and sevoflurane, respectively.
The influence of age on PONV is controversial. We did not detect any effect of age on the incidence of PONV. Younger age has been shown to be a risk factor for PONV in the studies by Apfel and colleagues  and Sinclair and colleagues . However, no significant correlation was found by Larson and colleagues  or Koivuranta and colleagues . Koivuranta and colleagues , using the forward procedure of logistic regression, did not find age to be a predictive factor for nausea. The role of age as a risk factor for PONV is unclear. We could not find a relationship between surgery time and the occurrence of PONV. More PONV has been reported after longer operations [8–10,12]. However, these studies all included various type of surgery and the duration of surgery varied greatly. In our study, the type of surgery was limited to vitrectomy and the operation duration did not vary very much. This may be the reason for the negative correlation between surgery time and incidence of PONV.
In our study, other factors such as BMI and smoking did not affect the occurrence of PONV in the same way as previously reported. Several authors have demonstrated that the incidence of PONV is increased or unchanged in obese patients [2,9,14]. Watcha and colleagues suggested that incidence of PONV is increased in obese patients and that the larger volume of adipose tissue, larger residual gastric volume and difficulties in mask ventilation are possible causative factors . However, Apfel and colleagues , and Kranke and colleagues  did not find a relationship between BMI and the incidence of PONV. The reason for the decreased incidence of PONV with higher BMI patients in the early postoperative period in our study is not clear. Only 4 of our 247 patients (1.6%) were obese (BMI > 30), whereas 10.1% of patients had a BMI > 30 in the systemic review of Kranke and colleagues . The small number of obese patients in our study may partly explain the discrepancy between ours and the former studies. BMI did not affect the overall incidence of occurrence of PONV in our study.
Although some authors have suggested that the incidence of PONV is decreased in patients who smoke [6,7,15,16], our study pointed out that smoking status had no predictive value for the occurrence of PONV.
The discrepancies of the results between our study and others may be explained by race-related differences in enzyme activity. So far, no study has been carried out in East Asians to identify the incidence of PONV or risk factors for PONV. The activity of P450 (CYP) isoenzymes, which are responsible for the metabolism of volatile and i.v. anaesthetics, is subject to genetic polymorphism, being dependent on factors such as racial differences . For example, the activity of CYP2D6 which is responsible for the metabolism of many drugs, including some opiates which are known to cause PONV, varies widely among racial groups. The occurrence of CYP2D6 poor metabolizers is higher in Caucasians (5–10%) than in East Asians (<1%) . Chimbira and Sweeney  suggested that induction of CYP isoenzymes by nicotine might play an important role in the prevention of PONV in smokers. The breakdown of nicotine is determined by the level of CYP2A6, the activity of which is also subject, to some extent, to racial differences .
In conclusion, in adult vitrectomy patients, female gender, lower BMI and inhalation anaesthesia are significant risk factors for PONV. Smoking status did not reduce the incidence of these complications.
Support was provided solely from institutional and departmental sources.
1. Pavlin DJ, Rapp SE, Polissar NL et al
. Factors affecting discharge time in adult outpatients. Anesth Analg
2. Watcha MF, White PF. Postoperative nausea and vomiting
: its etiology, treatment, and prevention. Anesthesiology
3. van den Berg AA, Lambourne A, Clyburn PA. The oculo-emetic reflex. Anaesthesia
4. Eberhart LHJ, Morin AM, Hoerle S et al
. Droperidol and doasetron alone or in combination for prevention of postoperative nausea and vomiting
5. Iwamoto K, Schwartz H. Antiemetic effect of droperidol after ophthalmic surgery. Arch Ophthalmol
6. Cohen MM, Duncan PG, DeBoer DP, Tweed WA. The postoperative interview: assessing risk factors for nausea and vomiting. Anesth Analg
7. Quinn AC, Brown JH, Wallace PG, Asbury AJ. Studies in postoperative sequelae: nausea and vomiting – still a problem. Anaesthesia
8. Koivuranta M, Laara E, Snare L, Alahunta S. A survey of postoperative nausea and vomiting
9. Apfel CC, Greim CA, Haubitz GI et al
. A risk score to predict the probability of postoperative vomiting in adults. Acta Anaesth Scand
10. Sinclair DR, Chung F, Mezei G. Can postoperative nausea and vomiting
be predicted? Anesthesiology
11. Tramer M, Moore A, McQuay H. Propofol anaesthesia and postoperative nausea and vomiting
: quantitative systematic review of randomized controlled studies. Br J Anaesth
12. Apfel CC, Kranke P, Katz MH et al
. Volatile anaesthetics may be the main cause of early but not delayed postoperative vomiting: a randomized controlled trial of factorial design. Br J Anaesth
13. Larsson S, Lundberg D. A prospective survey of postoperative nausea and vomiting
with special regard to incidence and relations to patient characteristics, anaesthetic routines and surgical procedures. Acta Anaesth Scand
14. Kranke P, Apfel CC, Papenfuss T et al
. An increased body mass index is no risk factor for postoperative nausea and vomiting
. A systematic review and results of original data. Acta Anaesth Scand
15. Chimbira W, Sweeney BP. The effect of smoking on postoperative nausea and vomiting
16. Stadler M, Bardiau F, Seidel L et al
. Difference in risk factors for postoperative nausea and vomiting
17. Kim K, Johnson JA, Deredorf H. Differences in drug pharmacokinetics between east Asians and Caucasians and the role of genetic polymorphisms. J Clin Pharmacol
18. Inoue K, Yamazaki H, Shimada T. CYP2A6 genetic polymorphism and liver microsomal coumarin and nicotine oxidation activities in Japanese and Caucasians. Arch Toxicol