The effect of race on the incidence of postoperative nausea and vomiting in moderate to high risk patients in South Africa: a prospective study

Date
2014-04-08
Authors
Alli, Ahmad
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Postoperative nausea and vomiting (PONV) is a multifactorial, complex phenomenon that has been widely studied. Little work has been done in assessing the risk of PONV in South African population groups. The aim of the study was to compare the effect of racial background on the incidence of PONV in moderate to high-risk black versus non-black South African patients undergoing general anaesthesia. Methods A prospective, controlled observational study was carried out. After an initial power calculation, 82 patients in each group (164 in total) were required for the study. However, due to researcher availability, time constraints and a readjustment of the power calculation, 95 patients at moderate to high risk for PONV were enrolled onto the study over an extended study period of 20 months (initially the study period was planned to be 6 months). 89 patients fulfilling the inclusion criteria were divided according to race into two cohorts. Ondansetron and dexamethasone were used as PONV prophylaxis after induction of general anaesthesia. Propofol was used as the induction hypnotic with isoflurane to maintain anaesthesia. Nitrous oxide, ketamine and droperidol were avoided. Use of analgesics was unrestricted, but neuraxial and nerve plexus regional anaesthesia were avoided. If a non-depolarising neuromuscular blocking agent was used, a maximum of 2.5mg of neostigmine was given to reverse neuromuscular blockade. Nausea and vomiting were assessed by means of a visual analogue scale in the recovery room and ward. Time intervals to assess degree of PONV were 0 hours (defined by first assessment of a modified Aldrete recovery score of at least 9 out of 10 and Glasgow Coma Scale of at least 14/15), 15 minutes, 90 minutes, 180 minutes, and 24 hours. Reports of incidents of vomiting and complaints of nausea between interviews were obtained from patients through questioning. Results There were 59 black participants and 30 non-black participants. There were 17 males and 72 females. There were no differences in the black and non-black groups with regard to gender, past history of motion sickness, past history of post operative nausea and vomiting, ASA status, smoking and anaesthetic time (p>0.05). There was a significant difference in the distribution of surgical procedures in the black and non-black participants (Mann Whitney U test, p= 0.02), although this did not affect the final result. On univariate analysis there were significant correlations between black South African ethnicity and nausea at all time intervals and also vomiting. Using multivariate regression analysis, non-black South African ethnicity was identified as a risk factor for PONV. It was found that black South African patients were protected against postoperative nausea, with a RR of 0.41 (95% CI, 0.28-0.60). Conclusion In this study we found that black South African ethnicity reduced the risk of PONV as compared with non-black South African ethnicity. We found that non-black South Africans had a similar risk of PONV to that published in international literature and predicted by the Apfel score, whereas the risk of PONV in similar Apfel scored black South African patients was much lower.
Description
A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand , in partial fulfillment of the requirements for the degree of Master of Medicine, Johannesburg, 2013
Keywords
Citation
Collections