Exploring the incidence and influencing factors of postoperative nausea and vomiting after laparoscopic bariatric surgery: a protocol for a retrospective observational study

Abstract

Introduction

The global prevalence of obesity and its associated comorbidities is rising, with bariatric surgery emerging as a highly efficacious intervention for obese patients. Postoperative nausea and vomiting (PONV) is a common complication following bariatric surgery, with a standardised protocol for its prevention and management yet to be established. This study aims to determine the incidence and the influencing factors of PONV following various types of bariatric surgeries, thereby facilitating the targeted prevention strategies.

Methods and analysis

This retrospective, single-centre observational study will be conducted at the Third People’s Hospital of Chengdu, with an expected enrolment of 2500 patients who have undergone laparoscopic bariatric surgery from December 2019 to April 2024. The study aims to collect data regarding the incidence of PONV and analyse the potential risk and protective factors associated with its development in this patient population.

Ethics and dissemination

The study has been approved by the ethics committees of the Third People’s Hospital of Chengdu. Given the retrospective nature of the study, informed consent was waived by the ethics committee, and all patient data were anonymised to safeguard privacy prior to the study authors’ visit. The results of this study will be presented at various academic and healthcare conferences, spanning local to international levels and will also be submitted for publication in reputable, peer-reviewed journals.

Trial registration number

This study has been registered with the Chinese Clinical Trial Register (ChiCTR) under registration number ChiCTR2400088738.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This study represents the largest cohort to date in investigating the influencing factors of postoperative nausea and vomiting following various modalities of laparoscopic bariatric surgery.

• Clinically significant factors and those with p values<0.1 in the univariate analysis will be included in the multivariate logistic regression model to adjust for biases.

• The observational nature of the study may have potential unmeasured confounding factors.

Introduction

Obesity, an escalating global health epidemic, poses a profound threat to the well-being of individuals worldwide.¹ As reported by the WHO in 2022, 2.5 billion adults aged 18 years and older were overweight, with 890 million individuals classified as obese. Exceeding 390 million children and adolescents aged 5–19 years were overweight, with 160 million of these individuals being obese.² Obesity is a principal contributor to mortality and leads to a myriad of complications, including, but not limited to cancer, sleep apnoea, respiratory distress, type II diabetes, hypertension and cardiovascular diseases.^{3 4} Traditional interventions, such as lifestyle modifications through exercise and dietary restrictions, have been demonstrated as insufficient in managing severe obesity.⁵ Bariatric surgery is widely acknowledged as the most effective treatment for obesity and its associated complications, with an increasing number of patients opting for this procedure.^{6 7}

Nevertheless, postoperative nausea and vomiting (PONV) is a prevalent issue among patients undergoing bariatric surgery, with an incidence rate ranging from 60% to 90%.^{8 9} Despite the implementation of prophylactic measures, a substantial proportion of patients, approximately 50–70%, still experience PONV.^{10 11} The occurrence of PONV poses a risk for a range of serious complications, including aspiration, suture line disruption, anastomotic leaks, malnutrition, postoperative haemorrhage, subcutaneous emphysema, pneumothorax, increased intragastric pressure, venous hypertension, dehydration and electrolyte imbalances.¹²,¹⁴ These complications can prolong hospital stays and increase healthcare expenditures due to extended recovery periods.⁹ Moreover, PONV significantly affects patients' comfort and satisfaction, emerging as a leading cause of readmission following bariatric surgery.¹⁵ Therefore, identifying the risk and protective factors for PONV following bariatric surgery is of paramount importance to facilitate early and effective prevention strategies for PONV.

Previous studies have identified high-risk factors for PONV following bariatric surgery, which primarily include patient factors (such as female gender, younger age, non-smoking status, history of alcohol abuse, history of motion sickness or PONV, preoperative reflux symptoms, body mass index and complications such as diabetes and sleep apnoea), anaesthesia techniques (including opioids, volatile anaesthetics, neostigmine and prolonged anaesthesia duration), surgical factors (such as surgery duration, induced pneumoperitoneum, antrectomy, increased intragastric pressure, proximal gastric pouch expansion and gastropexy), intraoperative hypotension, postoperative recovery status and pain severity.¹⁶,¹⁹ In recent years, studies have identified several potential measures to reduce the incidence of PONV following bariatric surgery. These measures encompass the use of pharmacological agents (such as dexamethasone, sugammadex, propofol, aprepitant and dexmedetomidine), opioid-free analgesia and multimodal analgesia, total intravenous anaesthesia in lieu of volatile anaesthetics, multimodal antiemetic therapy and goal-directed fluid therapy.⁸¹⁹,²²

The majority of previous studies on PONV in the context of bariatric surgery have focused on patients who have undergone laparoscopic sleeve gastrectomy. However, no study has yet examined the incidence and influencing factors of PONV across all types of laparoscopic bariatric surgeries. Consequently, this study aims to explore the occurrence and associated factors of PONV following all types of laparoscopic bariatric surgeries.

Methods and analysis

Study design and setting

This is a retrospective, single-centre observational study that will be conducted at the Third People’s Hospital of Chengdu. This study will retrospectively include patients who underwent all types of laparoscopic bariatric surgeries at our centre from December 2019 to April 2024. At our centre, all types of bariatric surgeries are performed with laparoscopy. Refer to figure 1 for an overview of data sources and study processes.

Figure 1. Flowchart of the study design.

Inclusion and exclusion criteria

The study will include adult patients who underwent elective laparoscopic bariatric surgery with general anaesthesia at the Third People’s Hospital of Chengdu from December 2019 to April 2024. The exclusion criteria will be as follows: patients under the age of 18 years or over 60 years, patients with a history of drug addiction, patients with inflammatory bowel disease and patients lacking data on PONV.

Primary outcome

The primary outcome is the factors associated with PONV in patients who underwent laparoscopic bariatric surgery under general anaesthesia.

Planned secondary outcomes

The planned secondary outcomes include the correlation between PONV and postoperative recovery parameters, such as postoperative fever, postoperative ICU (Intensive Care Unit) admission, duration of resumption of feeding and length of hospital stay after surgery in patients who underwent laparoscopic bariatric surgery under general anaesthesia.

Outcome measure

Patients will be considered to have PONV if they develop symptoms of nausea and/or vomiting and receive rescue antiemetic measures within 24 hours postsurgery.²³ The rescue antiemetic measures are detailed in table 1.

Table 1. List of remedial antiemetic measures.

Category of remedial antiemetic measures	Concrete measure
5-Hydroxytryptamine (5-HT3) receptor antagonists	Granisetron
	Tropisetron
	Ondansetron
Dopamine receptor antagonists	Metoclopramide
Glucocorticoids	Dexamethasone
H1 receptor antagonists	Promethazine
Traditional Chinese medicine treatment	Acupuncture
	Subcutaneous needle insertion

Potential related factors

Based on the literature review, clinical practice and the available data, we plan to include the following potential factors associated with PONV in our analysis. The planned potential factors are detailed in Box 1.

Box 1. Planned potential factors associated with PONV.

• Factors

• Age (years)

• Sex

• Body mass index (kg/m²)

• ASA (American Society of Anesthesiologists) classification

• Prohibition period (hours)

• Fasting time (hours)

• Apfel risk score

• Reflux oesophagitis

• Hiatal hernia of oesophagus

• Helicobacter pylori infection

• Arrhythmia

• Hypertension

• Cardio dysfunction

• Diabetes

• Impaired glucose tolerance

• Apnoea

• Bronchitis

• Anaemia

• Liver dysfunction

• Renal dysfunction

• Nerve block

• Types of surgery

• Midazolam

• Penehyclidine

• Lidocaine

• Dexmedetomidine

• Venous general analgesia drug

• Total intravenous anaesthesia

• Opioids

• NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)

• Positive inotropic drugs

• Vasoconstrictor drugs

• Neostigmine

• Intraoperative prophylactic medication

• Crystalloid-to-colloid ratio

• Average liquid (mL/kg/hour)

• Blood loss (mL)

• Operative time (min)

• Anaesthesia time (min)

• Analgesic pump usage

• Postoperative moderate-to-severe pain

• Postoperative prophylactic medication

Data collection methods

Data on patients undergoing laparoscopic bariatric surgery from December 2019 to April 2024 will be extracted from the DoCare Anesthesia Clinical Information Management System (Suzhou Medical System Technology, V.5.0), the iPainfree pain management information system software (Jiangsu Apon Medical Technology, V.1.0) and the case information system (Union Digital Medical Record browser, V.2012.4).

Data management

Data from all participants will be available in the electronic medical record database of the Third People’s Hospital of Chengdu and will be simultaneously cross-validated and transcribed into Microsoft Excel by two researchers. These records will be securely stored on a password-protected computer.

Statistical analyses

Sample size

Based on the annual volume of bariatric surgeries performed at the Third People’s Hospital of Chengdu, we conservatively estimate that the final data will include over 2500 patients. This cohort will represent the largest exploration to date of factors contributing to PONV following laparoscopic bariatric surgery.

Statistical method

Categorical covariates will be summarised by frequency and percentage, while continuous covariates will be described by mean and SD, or median (25th–75th percentile) for those not adhering to a normal distribution. Univariate logistic regression will be used to identify potential risk or protective factors associated with PONV. Variables with p values from the univariate logistic regression no more than 0.10, along with those deemed clinically significant, will be incorporated into a multivariate logistic regression model. Factors with p values <0.05 in the multivariate logistic regression analysis will be considered as independent risk or protective factors for PONV. The outcomes of the regression analyses will be expressed as OR and 95% CIs. The variance inflation factor will be computed to evaluate the multicollinearity. All analyses were performed using R (V.4.3.3; R Development Core Team, Vienna, Austria).

Missing data

We will initially attempt to manually fill in the missing data. If data remain absent, variables with a missing rate exceeding 20% will be excluded from the analysis; those with a missing rate of 20% or less will be addressed through five imputations.²⁴ Continuous variables were imputed using predictive mean matching, whereas binary variables were imputed by using logistic regression models. The multiple imputation procedure will be performed by mice package in R (V.4.3.3; R Development Core Team).

Sensitivity analysis

Sensitivity analysis will be conducted by performing the primary analysis—univariate and multivariate logistic regression as mentioned above—on a complete dataset, which was created by excluding patients with missing data. This approach will assess the robustness of our findings and mitigate potential biases that may arise from missing data.

Discussion

The incidence of PONV following bariatric surgery, which ranges from 60% to 90%,¹ is markedly higher than that observed after general surgery, with rates fluctuating between 10% and 40%.^{12 25} Despite this disparity, there are no evidence-based guidelines tailored specifically for the prevention of PONV in patients undergoing bariatric surgery. The identification of risk factors for PONV is crucial, as it empowers anaesthetists to implement targeted preventive strategies. Consequently, we intend to conduct a retrospective observational clinical study to investigate these risk factors and to evaluate the efficacy of various preventive interventions.

This study, which will be the largest of its kind, will undertake a comprehensive analysis of potential risk factors as reported in the previous literature, thereby enhancing the statistical power of our findings. Furthermore, this research will be the first investigation to encompass all types of laparoscopic bariatric surgeries, facilitating a more nuanced understanding of the risks and preventive factors associated with PONV in the laparoscopic bariatric surgery setting.

This study will further validate the controversial factors associated with PONV in previous research, including gender,^{16 26 27} age,^{17 28} obesity,^{17 26} smoking history,^{26 28} opioid medications,^{19 29} surgery duration^{17 30} and anaesthesia duration.^{12 17} Additionally, this research will investigate new potential factors related to PONV, including preoperative comorbidities across various systems, types of bariatric surgeries, neuromuscular blocking agents, vasoactive drugs, and the crystalloid-to-colloid fluid ratio.

The findings of this study could be instrumental in the design of prospective studies and may provide evidence-based support for the development of future PONV guidelines for this patient population.

This retrospective study has several limitations. First, missing data are inevitable and will interfere with the results of such retrospective research. Sensitivity analysis will be conducted to verify the robustness of the results. Second, the observational nature of the study may have potential unmeasured confounding factors, which necessitates a cautious interpretation of the observed associations. Despite these limitations, retrospective studies can provide valuable insights and generate hypotheses for further exploration in prospective studies employing more rigorous methodologies.

Ethics and dissemination

The institutional review board of the Third People’s Hospital of Chengdu approved this study (approval number: 2024 S-252). Informed consent was waived by the ethics committee, and all data were anonymised prior to the study authors’ visit. Registration has already been completed in the Chinese Clinical Trial Register (ChiCTR) under registration number ChiCTR2400088738. The results will be presented at conferences and published in a peer-reviewed journal.

Trial status

Data collection commenced on manuscript submission. The analyses are planned to be completed by the end of 2024.