Lower Belly Pressure During Gallbladder Surgery Fails to Ease Pain in Rigorous Trial

For decades, surgeons performing laparoscopic gallbladder removal have inflated the abdomen with carbon dioxide at pressures around 14 millimeters of mercury, a practice known as standard-pressure pneumoperitoneum. The technique lifts the abdominal wall away from the internal organs, creating the working space that makes keyhole surgery possible. But that insufflation pressure has long been suspected of contributing to the shoulder tip pain, bloating, and general postoperative misery that many patients report in the hours after their operation. A new randomized controlled trial from Tunisia, published in PLOS One, has now put the low-pressure hypothesis to one of its most rigorous tests yet, and the headline finding is a sobering one for advocates of the gentler approach: dropping the pressure to 8 millimeters of mercury did not significantly reduce the pain patients actually felt.

The study, conducted by Amine Ben Safta and colleagues across surgical departments in Tunisia, enrolled 160 consecutive patients scheduled for elective laparoscopic cholecystectomy between November 12, 2024 and December 31, 2025. Participants were randomly assigned to one of two groups in a double-blind design, meaning that neither the patients nor those assessing their outcomes knew which insufflation pressure had been used. One group underwent surgery with the abdominal cavity maintained at 8 millimeters of mercury, the low-pressure arm, while the comparison group received the conventional 14 millimeters of mercury. The trial was registered prospectively at ClinicalTrials.gov under identifier NCT06685250 on November 11, 2024, the day before enrollment began, a detail that matters because prospective registration helps guard against outcome switching and selective reporting, two of the quiet pathologies that have undermined smaller surgical trials in the past.

The researchers chose their primary endpoint with clinical precision: postoperative pain measured on the Visual Analogue Scale, the familiar 0-to-10 ruler on which patients mark the intensity of their discomfort, assessed at six hours after surgery. This early time point was selected because the peritoneal irritation caused by carbon dioxide insufflation is thought to be most pronounced in the immediate recovery period, when the residual gas has not yet been fully absorbed. If lowering the pressure genuinely protects the peritoneum, the argument went, the effect should show up most clearly in those first hours. The analysis followed an intention-to-treat approach, meaning every randomized patient was analyzed in the group to which they were assigned regardless of what actually happened during their operation, the methodologically conservative choice that preserves the randomization’s protection against bias.

The results were unambiguous on the primary outcome. At six hours, the median Visual Analogue Scale score was 3 in the low-pressure group compared with 4 in the standard-pressure group, a difference that failed to reach statistical significance with a p-value of 0.221. At twelve hours the medians were 2 versus 3, with a p-value of 0.074, tantalizingly close to the conventional threshold but still short of it. By twenty-four hours the scores had fallen to 1 versus 2, with a p-value of 0.128. A pattern of small, consistent numerical advantages for the low-pressure group runs through all three time points, and that pattern is worth noting, but in a trial designed to detect a difference in pain scores, none of these comparisons crossed the line separating signal from statistical noise.

Yet the trial was not a complete null result, and the nuance is where the clinical interest lies. During the first twenty-four hours after surgery, patients in the low-pressure group consumed significantly less paracetamol than their standard-pressure counterparts, with mean consumption of 1.04 grams plus or minus 0.906 compared with 1.35 grams plus or minus 0.873, a difference that was statistically significant at p equals 0.014. Paracetamol consumption in this setting functions as an objective, if indirect, proxy for pain: patients and nurses escalate analgesia when discomfort demands it. A measurable reduction in analgesic use alongside non-significant differences in self-reported scores suggests that the low-pressure technique may deliver a modest analgesic benefit that the Visual Analogue Scale, with its coarse granularity and subjectivity, was underpowered to capture cleanly at the chosen sample size.

Equally important for surgical practice is what the trial says about feasibility. A persistent worry with low-pressure pneumoperitoneum has been that a floppier abdomen gives the surgeon less room to work, potentially prolonging operations, compromising exposure of Calot’s triangle, and increasing the risk of bile duct injury. The Tunisian data directly address the first of those concerns: mean operative time was 59.9 minutes plus or minus 27.5 in the low-pressure group versus 58.2 minutes plus or minus 22.4 in the standard-pressure group, a difference so small it rounds to irrelevance with a p-value of 0.880. Experienced teams, in other words, could work at 8 millimeters of mercury without paying a time penalty, at least for elective cholecystectomy in appropriately selected patients.

Safety signals were also reassuring within the limits of the study’s size. No patient required conversion to open laparotomy, and no major morbidities were recorded in either arm. This is a meaningful floor of safety, but the authors are careful about what it cannot establish. Complications such as bile duct injury, vascular injury, and trocar-related trauma are rare events, and a trial of 160 patients has essentially no power to detect differences in their frequency between two insufflation pressures. The researchers explicitly state that larger studies are required to confirm safety equivalence regarding rare surgical complications, a caveat that should temper any rush to change practice based on pain scores and analgesic consumption alone.

The trial’s design strengths deserve emphasis because surgical randomized trials are notoriously vulnerable to bias. The double-blind architecture is unusual and valuable in insufflation studies, since the operating team inevitably knows the pressure setting, but blinding the patients and the outcome assessors removes two major sources of expectancy bias from pain reporting and assessment. The consecutive enrollment of 160 patients reduces selection bias, the prospective registration pins the primary outcome in place before the first data point exists, and the intention-to-treat analysis respects the randomization. The choice of a single, clinically meaningful primary endpoint at a prespecified time point, rather than a battery of exploratory outcomes, gives the negative finding on the Visual Analogue Scale real evidentiary weight.

What, then, should clinicians and patients take away? The study does not support the claim that low-pressure pneumoperitoneum significantly reduces early postoperative pain after laparoscopic cholecystectomy, at least as measured by the Visual Analogue Scale at six hours. But it does suggest that the technique is feasible, does not slow down surgery, and is associated with lower paracetamol use in the first day of recovery, a secondary outcome with genuine patient relevance in an era of opioid-sparing analgesia. For a procedure as common as gallbladder removal, performed hundreds of thousands of times annually worldwide, even modest reductions in analgesic requirements could translate into meaningful cumulative benefits, provided the safety profile holds up under larger scrutiny.

The broader lesson may be about how surgical innovation is evaluated. Low-pressure laparoscopy has accumulated a scattered literature of small trials with mixed results for years, and this study illustrates both the promise and the limits of single-center randomized evidence in resolving that uncertainty. The consistent numerical trend favoring low pressure across all pain time points, combined with the significant analgesic-sparing effect, hints at a real biological phenomenon, peritoneal stretch and chemical irritation from carbon dioxide, that a larger trial with more sensitive pain instruments might confirm. Until such studies arrive, the 8-millimeter approach remains an option rather than a standard, and the trial’s own conclusion stands as the fairest summary: low-pressure pneumoperitoneum is feasible without increasing operative duration, but it did not achieve a statistically significant reduction in pain scores, and only larger studies can settle the safety question that matters most.

Subject of Research: Effect of low-pressure versus standard-pressure pneumoperitoneum on postoperative pain after laparoscopic cholecystectomy

Article Title: Low pressure (8 mmHg) pneumoperitoneum does not significantly reduce postoperative visual analog scale score after laparoscopic cholecystectomy: Randomized trial

Article References: Safta, A. B., Nasri, S., Samaali, I., Dougaz, W., Bousassi, R., Taher, H., Khalfallah, M., Dziri, C., & Nouira, R. (2026). Low pressure (8 mmHg) pneumoperitoneum does not significantly reduce postoperative visual analog scale score after laparoscopic cholecystectomy: Randomized trial. PLOS One, 21(10), e0360476. https://doi.org/10.1371/journal.pone.0360476

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360476

Keywords: laparoscopic cholecystectomy, pneumoperitoneum, postoperative pain, randomized controlled trial, visual analogue scale, low-pressure laparoscopy, paracetamol consumption, surgical outcomes, gallbladder surgery, anesthesia, clinical trial, PLOS One