Incidence of and Factors Associated With Post-operative Nausea and Vomiting Following Surgery Under Regional Anaesthesia
Conditions: PONV, Regional Anaesthesia
Sponsor: Makerere University

STUDY TITLE:  
INCIDENCE OF AND FACTORS ASSOCIATED WITH POST-OPERATIVE NAUSEA 
AND VOMITING FOLLOWING SURGERY UNDER REGIONAL ANAESTHESIA 
 
 
NCT NUMBER:  
NCT03835234 
 
DOCUMENT DATE: 
31/01/2019 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
1.1 STUDY DESIGN 
This was a prospective cohort study. 
1.2 STUDY SETTING 
This was a single center, hospital based study done in Mulago National Referral Hospital. Mulago 
National Referral Hospital is the Makerere University teaching hospital and is located in Kampala. 
It has a 1500 bed capacity but can admit up to 2500 patients. 
This study was carried out in various theatres of Mulago hospital from August 2018 to January 
2019. The theatres that were used for this study were: the main operating theatre, obstetrics and 
gynecology theatres, the orthopedics and ophthalmology theatres. These were a total of eight 
operating tables with an average of fifteen surgeries daily. 
1.3 STUDY POPULATION 
The target population was all patients 18 years of age and above scheduled for an elective or 
emergency surgical procedure under regional anaesthesia at Mulago hospital. The accessible 
population included all patients attending Mulago hospital for elective and emergency surgery 
under regional anaesthesia during the study period from August 2018 to January 2019. 
1.4 ELIGIBILITY CRITERIA 
1.4.1 INCLUSION CRITERIA 
Patients having emergency or elective surgery under regional anaesthesia. 
Patients aged 18 years and above. 
ASA class 1, 2, 3 and 4 patients 
Patients who consented to being a part of the study. 
1.4.2 EXCLUSION CRITERIA 
Patients who were switched to general anaesthesia after planned regional anaesthesia. 
Patients with nausea and vomiting from pre-existing co-morbidities. 

1.5 SAMPLE SIZE CALCULATION 
Objective 1 
Assuming an incidence of PONV in regional anaesthesia of 31.4%(Quinn et al., 1994) with an 
absolute error of 0.05 and 95% CI 
Using Kish Leslie formula: 
N=Z2 P (1-P) 
        D 2 
Where N=sample size required to determine incidence 
            Z is the value corresponding to 95% confidence interval=1.96 
            P is the prevalence of PONV among patients undergoing surgery under regional 
anaesthesia=0.314 from previous studies 
            D is the absolute error=0.05 
             N =1.96 x 1.96 x 0.314 (1- 0.314)  
                      0.05 x 0.05 
             N =331patients 
Adjusting for loss to follow up of 10% 
             N =n (100+10)/100 
                 =331(100+10)/100 
                 =364 patients 
 
 

Objective 2 
 From the comparison of two proportions formula: 
𝑁=
(𝑍�√( 1
𝑞1 + 1
𝑞2) 𝑃(1 −𝑃) + 𝑍�√𝑃1(1 −𝑃1) 1
𝑞1 + 𝑃2(1 −𝑃2) 1
𝑞2)
2
(𝑃1 −𝑃2)2
 
Using the factor of gender for PONV in regional anaesthesia according to a study by AC Quinn et 
al 1994  
q1 is proportion of males in study               =336/606=0.554 
q2 is proportion of females in study            =270/606=0.446 
p1 is proportion of males with PONV        =22/336 =0.065 
p2 is proportion of females with PONV      =47/270 =0.174 
P=p1q1+p2q2= (0.065x0.554+0.174x0.446) =0.03601+0.0776=0.1136~0.114 
  Zα is standard normal corresponding to level of significance. Using a level of significance of 5%, 
Zα= 1.96 
  Zβ corresponds to power of the study. For a power of 80% Zβ = 0.841 
N=272patients  
 Therefore, choosing the larger sample size from the calculation for sample size for the first 
objective; the sample size used was 364 participants  
 
1.6 SAMPLING METHOD 
Consecutive sampling was used until the sample size was attained. 
1.7 SAMPLING PROCEDURE 
Patients 18 years or older that had been admitted for either elective or emergency surgery under 
regional anaesthesia were selected while in the pre-operative waiting area. Screening for eligibility 
was done by the principal investigator or by the research assistants. Patients that met the eligibility 
criteria were then consented and enrolled into the study. Patient data was gathered using a pretested 
questionnaire that included age, sex, medical history, anaesthetic technique used, duration of 
surgery, intraoperative medication and any nausea or vomiting within 24hours of surgery. Patients 
were followed up for up to 24 hours post-operatively. 
 
 

1.8 DATA MANAGEMENT 
1.8.1 DATA COLLECTION 
A standardised questionnaire was completed by the study research assistants or the principal 
investigator during the immediate pre-operative period to assess pre-operative risk of post-
operative nausea and vomiting. The information collected included patient demographics, past 
medical history, information on fasting and co-morbidities. A second questionnaire was used to 
assess the perioperative conduct of anaesthesia and any events occurring within this period. It 
contained the follow up information as well. 
Patients were followed up once at 24 hours to assess for post-operative nausea and vomiting. 
1.8.2 INDEPENDENT VARIABLES: 
 Socio demographic data such as age and sex, the diagnosis and type of procedure, ASA 
classification, history of PONV or motion sickness, non-smokers, peri-operative opioid use, period 
of pre-operative fasting, PONV prophylaxis use, duration of anaesthesia and surgery were studied. 
 
1.8.3 DEPENDENT VARIABLE:  
Post-operative nausea and vomiting measured by any retching, nausea or vomiting within 24 hours 
following surgery under regional anaesthesia. 
1.8.4 DATA ANALYSIS AND SAFETY 
Completeness and accuracy of data was checked daily and organised by the principal investigator 
before storage. Data was double entered into the computer using EPI data version 3.1, and then 
subsequently exported to STATA version 14.0 for analysis. 
Analysis was done using STATA with the help of a statistician. Both raw data and the analysed 
form were   kept both electronically and hardcopy for further reference. 
All questionnaires were stored in a secure, waterproof place to enable confidentiality and were 
only available to the principal investigator.  
Participant characteristics were expressed as categorical and/or continuous variables. 
 

Continuous variables were expressed as means and standard deviations while categorical data was 
expressed as frequencies with their respective proportions. Data presentation is in tabular and 
graphic forms. 
Cumulative incidence was assessed as the proportion of study participants who developed PONV 
within 24 hours of follow up divided by the total number of study participants enrolled into the 
study with complete follow up.  
At the bivariate level, each variable was compared with the outcome variable using cross tabulation 
and the logistic analysis. Variables that had p-value less than 0.200 at bivariate analysis were 
considered for multivariate analysis using logistic regression and variables were considered 
significant if the p-value <0.05. 
1.8.5 QUALITY CONTROL AND ASSURANCE 
Pre-testing of the questionnaires was done on non-study participants and changes made to the 
questions where necessary before final data collection. 
 Translation of the consent form into Luganda, the main local language used in Mulago was done 
prior to the start of data collection. 
Research assistants were trained on how to obtain informed consent, patient approach and proper 
data collection before data collection commenced. 
All questionnaires were safely stored to enable revisiting them when necessary. 
1.9 ETHICAL CONSIDERATIONS 
Ethical approval was sought from the School of Medicine Research and Ethics Committee 
(SOMREC). 
Permission was sought from the Mulago Hospital Ethics committee. 
Informed consent was sought from the study participants.  
Confidentiality was observed throughout the study. 
 
 
 

DATA COLLECTION TOOL 
INCIDENCE OF AND FACTORS ASSOCIATED WITH POST-OPERATIVE NAUSEA 
AND VOMITING AMONG PATIENTS UNDERGOING REGIONAL ANAESTHESIA 
QUESTIONNARE 1 (to be completed by the principal investigator or research assistants)  
Study Number: .............................................................................................. 
Patient’s name: .............................................................................................. 
Patient’s telephone number(s) 1.................................   2.............................. 
Pre-operative assessment 
1. Case details (state) 
1.1 Diagnosis………………………                  1.2 Procedure……………………….. 
2. Urgency of Surgery (Tick one)  
2.1 Elective  
2.2 Emergency 
3. Patient details (preoperative assessment as recorded) 
        3.1 Age (years)         18-30  
          31-50  
         >50
 
        3.2 Sex M   
   F 
         
        3.3 Weight............kg. 
        3.4 ASA classification    1 
       2  
       3  
       4 
        5 
                             
        3.5 Pulse......... /min.                            3.6 BP............   
 
 
 
 

4. Patient experience 
4.1 Have you had nausea or vomiting before?  
 
 
 
                     1=Yes                      2= No 
4.2 How would you describe the experience? 
1=Very unfavorable 
  
2=Unfavorable 
 
 
3=Neutral 
 
 
5 Risk factors for post-operative nausea and vomiting 
 5.1 Does the patient have any of the following?  (Tick appropriately) 
     (Multiple choices apply)  
 
           1=Yes  
        2= No 
              Female                                                                      
                      
 
              History of PONV                        
              History of motion sickness                                       
                     
      
        Alcohol use  
              Smoker 
   5.2 Time since the last feed (tick appropriately) 
                    2hrs                  4hrs                     6hrs                       8hrs                          >8hrs 
    5.3 Type of feeds (tick) …………… 
                      Solids                                semi-solids                       liquids 
 
 

QUESTIONNAIRE 2  
Study Number: .............................................................................................. 
Patient’s name: .............................................................................................. 
1. Anaesthesia provider (Tick) 
1.1 AO student trainee                 1.2 AO            1.3 SHO              1.4Anaesthesiologist                 
         
2. Length of the operation 
2.1 Time surgery i) started…………………. ii) ended (state in 24hour clock) ………. 
 
2.2 Duration of anaesthesia      
30 min 
       30-60min
            60-120min 
           >120min
 
 
2.3  Duration of surgery 
                  30 min 
       30-60min
            60-120min 
           >120min
 
 
 
3. Conduct of anaesthesia and surgery 
3.1.Type of Surgery 
Emergency  
 
 
 
 
Elective 
 
 
 
 
 
3.2.Anaesthetic technique (state) …………………………………. 
Sedation used                          1=Yes       
             2=No     
  
 
 
 

 
3.3.Number of attempts at the block(tick) 1   
   2  
      >2   
 
 
 
3.4.Drugs used during anaesthesia(tick) 
 
 
 
 
 
 
1=Yes  
 
2=No 
Opioids 
 
 
 
 
 
  
 
 
                            If yes, state which opioid ………………. 
                          Anti-emetics  
 
 
 
 
 
 
 
                          If yes, state which anti-emetic ………………. 
Sedatives 
                                                 
                       
 
                            If yes, state which sedative …………………. 
 
3.5.Did any of the following happen during surgery? (Tick appropriately) 
1=Yes  
 
2=No 
 
 
Retching 
 
 
 
 
 
Nausea 
 
 
 
 
 
Vomiting 
 
 
 
 
 
3.6.Lowest BP recorded(tick)                             
SBP  <110       
           <90   
             <50   
 
DBP <90         
            <70   
            <50    
 
 
 
 
 

4. Recovery room 
5.1 Did any of the following happen during recovery? (Tick appropriately) 
                                                                                                           1=Yes                  2=No 
                    Retching 
                    Nausea 
                    Vomiting 
5. At 24 hours (tick) 
                      5.1 Nausea or vomiting                                  1= Yes                    2=No 
                      5.2 If yes, time to occurrence of PONV from time of surgery……hours……min 
                      5.3 Post-operative opioids received                1=Yes      
       2=No   
  
                            If yes, state which opioid ………………. 
      
 6. Pain assessment 
                      6.1Peri-operative pain                                   1=Yes      
       2=No   
 
                      6.2 
Numerical 
Pain 
Rating 
Score: 
................. 
(Out 
of 
ten) 
 
 
 
 

 RISK FACTORS FOR NAUSEA AND VOMITING SCORING SYSTEM (aPFEL) 
Risk Factors 
Points 
Post-operative Opioids 
1 
Non Smoker 
1 
Female Gender 
1 
History of PONV/Motion Sickness 
1 
Risk score = sum 
0 ... 4