The safety and efficacy of low pneumoperitoneum pressure compared with standard pneumoperitoneum pressure in laparoscopic inguinal hernia repair: a prospective, double-blind, randomized controlled study protocol design

Abstract

Background

Inguinal hernia is a common disease, and laparoscopic tension-free inguinal hernia repair has become the standard procedure for treating inguinal hernia. During surgery, carbon dioxide gas is injected into the patient's abdominal cavity to maintain a specific pneumoperitoneum pressure. Under standard pneumoperitoneum pressure (SPP), we occasionally observe that some patients are prone to subcutaneous emphysema and hypercarbia, especially elderly patients with inguinal hernias, where the occurrence is relatively high. The aim of this study was to analyse whether using lower pneumoperitoneum pressure (LPP) in laparoscopic hernia repair is safer while maintaining surgical success.

Methods

This was a prospective, double-blind, randomized controlled study in which patients were randomly assigned to either the LPP group or the SPP group. The primary outcome measures were the results of patients' arterial blood gas analysis, including partial pressure of carbon dioxide (PaCO2), arterial oxygen partial pressure (PaO2), pH value, arterial oxygen saturation (SaO2), whole blood base excess (ABE), and standard base excess (SBE). The secondary outcome measures included heart rate, blood pressure, cardiac output (CO), stroke volume (SV), end-tidal carbon dioxide pressure (PetCO2), airway pressure (Paw), intraoperative complications, surgical duration, anesthesia recovery time, Length of hospital stay, postoperative pain, and quality of life. The aim of this study was to analyse the differences in these indicators between the two groups of patients.

Discussion

Compared with laparoscopic inguinal hernia repair performed under SPP, the use of LPP in laparoscopic inguinal hernia repair is advantageous for improving patients' blood gas analysis and systemic circulatory indicators. This study demonstrated that LPP for inguinal hernia repair is safe and effective, providing evidence-based support for the selection of pneumoperitoneum pressure values.

Trial registration

Chinese Clinical Trial Registry, ChiCTR2400091218, Registered on October 23, 2024.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-025-09376-7.

Background

Inguinal hernia is a common and recurrent disease, with over 400,000 surgeries performed annually [1]. From 1990 to 2019, the global number of people with hernias reached more than 32.5 million, with the prevalence rate rising to 36%. The prevalence of hernia is projected to increase by 2030, with most affected individuals being male [2]. The lifetime prevalence of inguinal hernia in male patients is 27%−43%, whereas in females, it is 3%−6% [3]. The main treatment for inguinal hernias is surgery, including open surgery and laparoscopic minimally invasive surgery.

Laparoscopic inguinal hernia repair, with its minimal trauma and rapid recovery, has become the primary surgical treatment method for inguinal hernias. Laparoscopic hernia repairs mainly include transabdominal preperitoneal prosthesis (TAPP) and total extraperitoneal prosthesis (TEP). The main goal of any minimally invasive surgery is to minimize disruption of homeostasis and reduce pain, while ensuring the safety and surgical success. Since laparoscopic surgery requires the injection of carbon dioxide (CO2) into the abdominal cavity to maintain continuous pneumoperitoneum pressure, there is concern about potential complications. In laparoscopic hernia surgery, the advantages of operating at a LPP (8–10 mmHg) rather than the SPP (12–15 mmHg) have been noted on multiple occasions. LPP can reduce adverse reactions associated with pneumoperitoneum, including gas embolism and postoperative pain [4, 5]. High pneumoperitoneum pressure(HPP) may affect the patient's respiration, circulation, heart rate, and endocrine system, and even lead to increased intracranial pressure [6, 7]; this is primarily attributed to the upwards displacement of the diaphragm due to increased pneumoperitoneum pressure [8], resulting in reduced lung capacity, increased incidence of atelectasis, impaired gas exchange in the lungs, and ultimately an increased incidence of complications such as patient carbon dioxide retention and acidosis [9]. During the pneumoperitoneum process, reduced lung volume and compliance lead to decreased CO, which can cause severe circulatory disturbances in patients. Under HPP, inferior vena cava return is impaired, CO is reduced, visceral vascular beds constrict, renal blood flow decreases, and the levels of some biochemical indicators transiently increase (1–3 days) [10]. Neudecker et al. confirmed that LPP (7–10 mmHg) has a minimal impact on CO [11], whereas LPP may affect the surgical working space. A recent study suggested that under LPP, the duration under anaesthesia is shorter, and the PetCO2 is lower than that in the SPP group, with no differences in surgical time or postoperative complications [12].

At present, laparoscopic inguinal hernia repair in our country uses SPP (12–15 mmHg), but in clinical practice, surgery can often be successfully completed via LPP, such as 8–10 mmHg. However, the safety and efficacy of LPP in the field of inguinal hernia repair have not been confirmed by any relevant prospective studies. In contrast, in the fields of gynaecology, hepatobiliary surgery, and gastrointestinal surgery, the safety and efficacy of such procedures have been well established, providing numerous benefits to patients [13–16]. The aim of this study was to prospectively demonstrate that LPP laparoscopic inguinal hernia repair is beneficial for improving patients' blood gas analysis results and circulatory indicators and that performing inguinal hernia repair at a LPP is safe and effective.

Methods

Trial design

This was a prospective, double-blind, randomized controlled study in which patients were randomly assigned to either the LPP group or the SPP group. The trial hypothesizes that LPP laparoscopic inguinal hernia repair is beneficial for improving patients' blood gas analysis results and circulatory indicators. This clinical trial protocol and project list are based on the SPIRIT reporting guidelines [17].

Participants

The patients included in this study were from the Zigong Fourth People's Hospital, Sichuan Province, China, totalling 150 cases. The start date for patient enrolment was December 1, 2024. Eligible patients were randomly assigned to either the LPP (10 mmHg) or the SPP (14 mmHg) groups. All patients included in the study were first assessed in the general surgery outpatient clinic. After a clear diagnosis was made by the attending physician and the patient signed the informed consent form, they were included in the study.

Sample size

The sample size was estimated via power analysis and sample size (PASS) software. Assuming a difference in the mean partial pressure of carbon dioxide in blood gas analysis between the two groups, with a two-sided p value < 0.05, power = 0.8, and β = 0.02, and anticipating a 10% patient dropout rate, the total sample size calculated was n = 150, with 75 patients in both the experimental and the control groups. We anticipate enrolling 90 patients per year and expect to complete all patient enrolment by 19 months.

Eligibility criteria

Inclusion criteria

(1). A diagnosis of unilateral inguinal hernia (including indirect, direct, and femoral hernias); (2). No sex restrictions; (3). Age between 18 and 80 years; (4). American Society of Anaesthesiologists (ASA) physical status classification: Classes I to II; (5). BMI between 18.5 kg/m2 and 28 kg/m2.

Exclusion criteria

(1). Bilateral inguinal hernias, irreducible hernias, sliding hernias, incarcerated hernias, recurrent hernias, and other special types of hernias; (2). Patients with concurrent respiratory infection symptoms; (3). Patients with concurrent cardiopulmonary diseases; (4). Those who cannot tolerate general anaesthesia or pneumoperitoneum; (5). Patients with other severe concurrent diseases; (6). Patients who refuse to participate in the study; (7). Patients who require additional surgical procedures during surgery.

Surgeons

The operating surgeons are all experienced surgeons from our hospital, with over 10 years of experience in performing laparoscopic hernia repair surgery.

Surgical method

TAPP involves specific steps, including placing the patient in a supine position, establishing a 10 mm observation port through the umbilicus, and creating 5 mm working ports on either side of the rectus sheath at the level of the umbilicus. Carbon dioxide gas is injected into the abdominal cavity through the observation port to establish pneumoperitoneum, following the ten golden rules of minimally invasive inguinal hernia repair [18]. The intra-abdominal steps include incising the peritoneum, dissecting the preperitoneal space and hernia sac, expanding the space for mesh placement, and suturing the parietal peritoneum. Finally, all the CO2 gas in the abdominal cavity was completely removed. To avoid confounding factors, the same surgical team performed all laparoscopic tension-free inguinal hernia repairs.

Anaesthesia method

All surgeries were performed by two anaesthesiologists with extensive experience (more than 10 years of formal work experience). Both groups of patients received general anaesthesia via inhalation. The steps of anaesthesia included induction, maintenance, and emergence. A uniform anaesthesia plan was used for all patients, with the dosage of anaesthetic drugs calculated based on the patient's weight according to standardized calculations. Additionally, routine perioperative anaesthesia care was provided to patients.

Informed consent

Patients who were diagnosed with inguinal hernia in the outpatient clinic and had indications for surgery were informed by the attending physician about the surgical methods and the research project. Patients have the right to agree or refuse to participate in the study, but they will not be informed about which intraoperative pneumoperitoneum pressure value will be applied to their surgery. Patients who agree to participate in the study will sign an informed consent form for the project (Attachment 1) and an informed consent form for blood collection authorization (Attachment 2).

Intervention

TAPP is a well-established minimally invasive surgery that is used to maintain the operative space during laparoscopy. The method involves injecting CO2 gas at a specific pressure into the abdominal cavity. In the intervention group, a pneumoperitoneum pressure of 10 mmHg was applied, following the standard TAPP surgical procedure for laparoscopic tension-free inguinal hernia repair, and the CO2 gas from the abdominal cavity was completely removed at the end of the procedure.

Control intervention

Patients in the control group underwent TAPP surgery with a pneumoperitoneum pressure of 14 mmHg. At the end of the procedure, all CO2 gas in the abdominal cavity was completely removed. The complete time schedule for enrolment, interventions, and assessments of this clinical trial is shown in Fig. 1.

Fig. 1.

The schedule of enrolment, interventions, and assessments. SPIRIT schedule of enrolment, interventions, and assessments. -t₁: screening period;0: surgery day; t₁:5 min preoperative; t₂:10 min preoperative; t₃:30 min preoperative; t₄:12 h postoperative; t₅: 24 h postoperative; t₆: 48 h Postoperative; t₇:1 month post-discharge; t₈:3 month post-discharge; t₉:6 month post-discharge. Baseline data¹ : Gender, Age, Height, Weight, Inguinal Hernia Classification, Inguinal Hernia Location; Circulation indicators²: Heart rate, Blood pressure, Cardiac output, Stroke volume; Anesthetic monitoring indicators³: End-tidal carbon dioxide pressure, Airway pressure; ABG analysis ⁴: Partial pressure of carbon dioxide, Partial Pressure of Oxygen, Saturation of Peripheral Oxygen, Actual Base Excess, Standard base excess; Postoperative data⁵: Operation Time, Complications, Anesthesia emergence time, Hospital Stay; Postoperative data⁶: Visual Analogue Scale, Intestinal gas expulsion time; Follow-up⁷: Quality of life; Visual Analogue Scale, Seroma, Scrotal swelling, Recurrence. ABG: Arterial blood gas, SE: Subcutaneous emphysema, SEE: Severity of subcutaneous emphysema

Outcomes

Primary outcomes

The arterial blood gas analysis results (including PaCO2, PaO2, pH value, SaO2, ABE, and SBE levels). The blood gas analysis instrument used was the epoc® Blood Analysis System by Siemens Healthineers. The analysis times were after anesthesia induction but before incision, 10 min after pneumoperitoneum establishment, and 30 min after pneumoperitoneum establishment.

Secondary outcomes

1. Circulatory parameters (including intraoperative heart rate, blood pressure, CO and SV), with recording times coinciding with ABG analysis times.

2. PetCO2 and Paw (Monitoring through the Datex-Ohmeda anesthesia machine), with recording times coinciding with ABG analysis times.

3. Intraoperative complications (including bleeding, conversion to open surgery, and incidental injuries).

4. Surgical duration and Surgical smoothness score (using a Likert scale to rate surgical doctors).

5. Anesthesia recovery time (The time from anesthesia to awakening).

6. Length of hospital stay.

7. Postoperative pain (Using the 10-point visual analogue scale to assess patients' pain at 12 h, 24 h, and 48 h postoperatively).

8. Follow-up (1 month, 3 months, and 6 months after discharge).

   • (i)
     Quality of Life (according to the European registry for abdominal wall hernias quality of life scores).
   • (ii)
     The degree of pain (Using the 10-point Visual Analog Scale).
   • (iii)
     Surgery-related complications (seroma).
   • (iv)
     Postoperative recurrence rates.

Randomization and blinding

A random number list was generated via SPSS software, which was then sequentially placed into opaque envelopes. When a patient entered the operating room, the circulating nurse opened the envelope and assigned the patient to a group based on a random number. The circulating nurse, who did not participate in the research project, set the pneumoperitoneum pressure value (14 mmHg or 10 mmHg). Neither the surgeons, anaesthesiologists, nor the outcome analysts were aware of the patient's group assignment.

Unblinding protocol

Unblinding was permitted in the event of severe intraoperative complications or if the surgery could not be completed due to difficulties; the research personnel responsible for the final extraction of results was allowed to be unblinded.

Recording and follow-up

For data collection, staff from the computer centre created electronic forms (Attachment 3) and entered the data into the electronic medical records system. Each patient has a unique hospital identification number, and the electronic form was extracted through this number, facilitating data collectors in gathering patients' research data. Patients were followed up at 1 month, 3 months, and 6 months postoperatively. The methods of follow-up include outpatient visits and telephone calls, with the use of scales to assess patients' quality of life and pain levels. The follow-up also included the assessment of postoperative seroma and hernia recurrence.

Ethics and informed consent

This study was conducted in accordance with the principles of the Declaration of Helsinki [19] and the guidelines for good clinical practice. The research protocol was approved by the Ethics Committee of Zigong Fourth People's Hospital (Date: May 16, 2024, Approval Number: EC-2023–036. Attachment 4.), and the trial was registered with the Chinese Clinical Trial Registry (Registration Number: ChiCTR2400091218). Data monitoring and supervision were conducted through the Zigong Medical Association Comprehensive Management Platform (URL: http://admin2.cmnt.cn/topic/supervise/index?status=01).

Statistics

Data analysis was conducted with SPSS 26.0 software (IBM Corp., Armonk, NY, USA). Data with a normal distribution, as determined by the Shapiro‒Wilk test, are expressed as the means ± standard deviations (means ± SDs) and were analysed via Student's t test. Values that did not conform to a normal distribution are represented by the median and interquartile range (IQR) and were analysed via the nonparametric Mann‒Whitney U test. Categorical variables are expressed as numbers and percentages and were analysed via the chi-square test. Risk ratios (RRs) and 95% confidence intervals (CIs) were calculated via the Wald test.

Confidentiality

This study adheres to data protection laws involving the extraction and analysis of patient personal data. All patient personal information related to the study is stored in an electronic form embedded within the electronic medical record system (EMR V6.0, Goodwill E-Health Info Co. Ltd.). Data access is limited to the hospital's internal local area network and requires password login. All participants in the trial can access the data. Each patient participating in the study has a unique ID, and patient data are linked to this ID without access to personal sensitive information.

Discussion

Inguinal hernia is a common and recurrent disease, with over 400,000 surgeries performed annually [1]. Laparoscopic hernia surgery, owing to its minimal trauma and rapid recovery, has become the main method for treating inguinal hernias. Since this surgery requires general anaesthesia and the injection of CO2 into the abdominal cavity, potential complications, such as hypercarbia, acidosis, and hypoxemia, may arise [15, 20]. Furthermore, CO2 may lead to subcutaneous emphysema and even pneumothorax. Under SPP, the diffusion and accumulation of CO2 in tissues make patients undergoing laparoscopic surgery more prone to acidosis [21]. Intagliata Eva et al. conducted a study comparing patients who underwent laparoscopic cholecystectomy at 12mmHg (Group A) and 8 mmHg (Group B) pneumoperitoneum pressures and reported significant differences in ABG analysis and haemodynamic parameters between the two groups [15]. Liang Chen et al.'s research suggested that, compared with SPP patients, patients who undergo TAPP at a LPP have shorter anaesthesia and postanaesthesia care times and lower peak and trough values of PetCO2, with no statistically significant differences in surgery time, postoperative complications, or recurrence rates between the two groups [12]. The safety of LPP in laparoscopic surgery has been confirmed in various surgical procedures, especially for relatively complex laparoscopic rectal cancer surgeries [16]. Studies by Sung and Prasanna et al. have shown that performing laparoscopic cholecystectomy at a LPP is safe and feasible and can alleviate patient shoulder pain [14, 22]. When performing laparoscopic inguinal hernia repair at the SPP (14 mmHg), anaesthesiologists often request that surgeons reduce pneumoperitoneum pressure during surgery due to excessively high PetCO2 or subcutaneous emphysema. We also observed that reducing the pneumoperitoneum pressure to 10 mmHg during surgery does not affect the smoothness of the operation or the surgery time and improves subcutaneous emphysema in patients. Through a literature review, we found very few comparative studies on LPP versus SPP in laparoscopic hernia repair. Therefore, we designed this study to further confirm that laparoscopic inguinal hernia repair at a LPP can reduce adverse effects on patients compared with SPP and to demonstrate the safety of LPP in laparoscopic inguinal hernia surgery.

Trial status

This approach was approved by the Health Commission of Zigong (2023/12/26). This manuscript was the first version registered in the Chinese Clinical Trial Registry, the protocol version no. is V1.0/2024.10.23. Inclusion has not started.

Abbreviations

TAPP

Transabdominal preperitoneal prosthesis

TEP

Totally extraperitoneal prosthesis

CO2

Carbon dioxide

LPP

Low pneumoperitoneum pressure

SPP

Standard pneumoperitoneum pressure

HPP

High pneumoperitoneum pressure

PASS

Power Analysis and Sample Size

ASA

American Society of Anesthesiologists

PaCO2

Partial pressure of carbon dioxide

PaO2

Partial Pressure of Oxygen

SaO2

Saturation of Peripheral Oxygen

ABE

Actual Base Excess

SBE

Standard base excess

ABG

Arterial blood gas

CO

Cardiac output

SV

Stroke volume

PetCO2

End-tidal carbon dioxide pressure

Paw

Airway pressure

Authors' contributions

KL designed the trial and drafted the trial manuscript. WZh and QL assessed the feasibility of the trial anesthesia and ensured its viability. XlY assessed the feasibility of the laboratory monitoring and ensured its viability. HY and FZh reviewed and revised the manuscript. All authors read and approved the manuscript.

Funding

The trial is a self-funded project with no financial support. The trial is funded by the Zigong Fourth People's Hospital, but the funder has no authority over the study design, collection, management, analysis, and interpretation of data.

Data availability

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.