Laparoscopy is the favoured access to a lot of abdominal operations; for many indications, it is associated with less trauma, faster recovery, reduced costs, similar or better safety, and similar radicality and long-term prognosis in the case of oncologic surgery.
The first step to laparoscopy is to establish a pneumoperitoneum which elevates the abdominal wall and provides for the surgeon’s field of view. This is so natural, that probably most young surgeons do not give a second thought. However, there are reasons for every step of pneumoperitoneum: Why do we use carbon dioxide (CO2)? Why do not we use simple air or some other gas? Will the patient’s body cool down by the gas? Where does it go? How much pressure do we need? Why do we need pressure? Does it do any damage?
Although laparoscopy was invented more than a hundred years ago and has been, depending on the operation, a routine procedure since the 1980s and 1990s, these questions are not trivial and not completely answered, yet. Following a systematic approach, most questions can be summarised within three categories: gas type, temperature, and pressure. This article aims to explain the rationale behind these topics, summarise the current knowledge, and demonstrate open questions. We present the following article in accordance with the PRISMA reporting checklist (available at https://ales.amegroups.com/article/view/10.21037/ales-21-24/rc).
For each topic gas type, temperature, and pressure, we give a rationale, why it is important, and which are the theoretical considerations, we declare the specific search string, summarise the results and discuss them.
Separate systematic literature research on MEDLINE for randomized controlled trials (RCT) was performed for each topic as a double-search by both authors. Trials on adults, published between 2011 and March 2021 were considered. The following data were extracted: author, publishing year, trial registry ID, study type, patients, type of surgery, intervention (gas type, temperature, or pressure), comparator, sample size, primary outcomes, secondary outcomes. If the trial did not declare a primary outcome, all outcomes were considered secondary. For each trial we summarise, which comparator was favoured. Current Cochrane reviews with older data were included in the qualitative analysis.
The ideal gas for a pneumoperitoneum must be cheap, colourless, incombustible, easily removed from the body, non-toxic, and harmless to the patient and the personnel.
Gases that are or have been used, are CO2, nitrous oxide (N2O, laughing gas), air, oxygen, nitrogen (N2), and the inert gases helium (He) and argon (Ar).
CO2 is the most common and fulfills most of the aforementioned criteria. It is absorbed by the peritoneum, delivered to the lungs via blood, and exhaled. Being a soluble acid, it causes hypercarbia and acidosis, which must be compensated by the anaesthetist by hyperventilation. Hypercarbia can directly decrease cardiac contractility and sensitize the myocardium to arrhythmogenic effects of catecholamines, and indirectly lead to sympathetic stimulation with tachycardia (1). Peritoneal irritation with postoperative pain is reported.
N2O is rather inert, cheap, and non-flammable, however, it can support combustion (2). In the early days of colonoscopy, there were explosions when electrocautery was used in an unprepared colon. Later, bowel preparation formulas contained mannitol, a substrate for hydrogen-producing bacteria. The fear of flammable colonic gases (methane and hydrogen) mixing up with N2O during laparoscopy and two case reports of intraoperative explosions from the 1970s lead to the abandonment of N2O and the recommendation to use CO2 (3-8). The assumed hemodynamic advantages of N2O were not evident in the Cochrane reviews. There was low evidence of lower pain scores compared to CO2, as nitrous oxide is an anaesthetic agent.
CO2, and—to a lesser extent—nitrous oxide and helium can increase intracranial pressure (9). There is no information on the other gases.
Helium is the least soluble gas for a pneumoperitoneum, potentially increasing the risk of gas embolism. It requires special insufflators.
Ar is another inert gas, more soluble than N2 and nearly as soluble as air (2).
The generation of trocar metastasis and the influence of the gas are under discussion. Trocar metastases are reported for CO2 and air pneumoperitoneum, again there is insufficient information for other gases (10). As tumour manipulation by the surgeon, aggressivity of the tumour, and a gas spray effect by the intraabdominal pressure are supposed reasons, port-site metastasis cannot be attributed to the gas type (2).
Gas embolism can occur due to misplacement of a Verres needle into a vein, but also by direct absorption of the gas. Therefore, gases with high solubility are safer. In this respect, CO2 is superior to N2O, and both are more soluble than air, oxygen, N2, and the inert gases He and Ar (1).
All gases can affect the cardiocirculatory, respiratory, and neurohumoral systems by their intraabdominal pressure. These effects are less gas-specific and are discussed in the pressure section.
MEDLINE was searched through pubmed.gov with the search string: “(((((((((((((((((laparoscop*) OR (video-assisted surgery)) OR (minimally invasive)) OR (coelioscop*)) OR (celioscop*)) OR (peritoneoscop*)) AND (gas type)) OR (carbon dioxide)) OR (CO2)) OR (nitrous oxide)) OR (laughing gas)) OR (N2O)) OR (nitrogen)) OR (N2)) OR (helium)) OR (argon)) AND (pneumoperitoneum)) OR (peritoneum)”. RCTs on adults, published between 2011 and March 2021 were eligible.
We found nine RCTs, of which six had to be excluded because they did not compare CO2 with another gas, and two because they studied animals or cadavers (Table 1).
|Author||Year||Trial registry||Study type||P||I||C||n||Primary outcome||Secondary outcomes||Favours|
|Han (11)||2012||–||RCT||Women||Gynecologic||CO2/general anaesthesia vs. gasless/general anaesthesia vs. gasless/epidural||75||n.a.||Stress response: serum cortisol, tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, IL-10, and Hsp70 levels at four time points: Before anesthesia (T1), at 30 minutes after the beginning of the operation (T2), at 10 minutes after the end of surgery (T3), and at 8:00 a.m. on the following day (T4)||Gasless/epidural anaesthesia over gasless/general anaesthesia over CO2/general anaesthesia|
The only remaining trial compared CO2 laparoscopy in general anaesthesia (GC group) with gasless laparoscopy in general anaesthesia (GG group) and gasless laparoscopy in epidural anaesthesia (GE group) (11). The gasless laparoscopy was established with an abdominal lift apparatus. The authors focussed on the stress response, measuring plasma levels of cortisol, TNF‑α, IL-6, IL-10, and Hsp70 before, during, and after the operation. Starting with similar baseline levels in all three groups, the cytokine levels increased most in the GC group, followed by the GG and GE groups. The authors assume that CO2-laparoscopy induces a larger stress response than gasless techniques, and that general anaesthesia contributes more to stress response than epidural anaesthesia.
The current Cochrane review identified nine RCTs comparing nitrous oxide, helium, and room air to CO2 with regards to cardiopulmonary complications, surgical morbidity, pneumoperitoneum related serious adverse events (primary endpoints), mortality, quality of life, pain scores, analgesic requirements, costs, and cardiopulmonary changes (secondary outcomes) (12). One trial overlapped with our research. Nitrous oxide was analysed by three trials and exhibited more cardiopulmonary complications (5.7% vs. 2.9%, relative risk ratio 2.0), but the difference was not significant, the trials were heterogeneous and the level of evidence was very low. There were no differences in the other outcomes, either, except for pain levels and analgesia requirements, which were lower with nitrous oxide.
Helium was examined in three trials and exhibited non-significant higher rates of cardiopulmonary complications (4.4% vs. 3.0%) and subcutaneous emphysema (4.9% vs. 0%), and more morphine requirements, but not higher pain scores. The partial blood pressure of CO2 was lower with helium (−13 mmHg). For room air, only one RCT was found, which did not reveal differences regarding complications and mortality. Costs and pain scores were lower with room air. However, the study quality and consequently the level of evidence were very low.
There are many requirements for the ideal gas for a pneumoperitoneum, and none of the gases used are perfect in every aspect. CO2 has become the standard because it is safe, non-combustible, non-explosive, and cheap. It has some effects on hypercapnia, which is not relevant in cardiopulmonary healthy people, and which the anaesthesiologists have broad experience with and know how to treat.
As the first and only reason to take gas is to improve the surgeon’s field of view, one approach is to completely abandon gas and use mechanical abdominal wall lifting techniques. It is unclear, whether the “no-gas”-study of Han et al. should be attributed to the use of air instead of CO2 or to the lower intraabdominal pressure by an abdominal wall lifting technique. The influence of pressure is discussed in the next section. Furthermore, abdominal wall lifting is a quite invasive tool to be combined with minimally invasive surgery.
No recent data is expanding the results of the Cochrane reviews of 2013 and 2017 (12,13). There is a lack of effort in testing inert gases like He or Ar against the standard, especially with regards to safety. One risk is gas embolism. CO2 is safer than oxygen, nitrous oxide, and room air in animal studies, because of its solubility. However, as venous gas embolism is rare, larger scaled meta-analyses will be necessary to provide better safety evidence. Cardiopulmonary changes due to CO2 that we discussed in the rationale are only relevant in patients with pre-existing diseases. As there is broad experience with the properties of CO2 and the handling of its disadvantages, it seems, at first sight, that there is no need for alternatives to CO2. To establish another gas, more high-quality RCTs and meta-analyses are necessary. For which gas should we take these efforts?
For low-income countries, the use of filtered room air promises lower costs. The higher cost-effectiveness of air has been shown (14). However, room air has the narrowest data basis of all gases. From the author’s point of view, perhaps more academic efforts should be directed towards room air.
CO2 is stored in a compressed and liquid state at about −90 °C. When released, it expands rapidly and enters the patient’s body at room temperature with no humidity. Cold CO2 is therefore supposed to cool the body and expose the patient to hypothermia which can cause coagulopathies and alter drug metabolism. However, calorimetric calculations have demonstrated that hundreds of litres of cold dry CO2 will have hardly any impact on the patient’s core temperature (far below 0.5 °C) (15).
Dry CO2 is discussed to damage mesothelial cells (16), leading to peritoneal inflammation, which is assumed to contribute to postoperative pain and the long-time forming of peritoneal adhesions. More adhesions were found in animal models (17).
MEDLINE was searched via pubmed.gov with the search string: “(((((((laparoscop*) OR (coelioscop*)) OR (celioscop*)) OR (peritoneoscop*)) OR (minimally invasive)) OR (video assisted surgery)) AND (temperature OR therm*)) AND (pneumoperitoneum)”. RCTs on adults, published from 2011 to March 2021 were eligible.
We identified only four RCTs, one of which with only the abstract, as the full text was in the Russian language (Table 2). We, therefore, decided to include one RCT on children (age 8–14 years) with appendectomies. All studies compared warm humidified (WH; 37 °C and 95–98% humidity) with cool dry (CD; 20 °C, 0%) CO2.
|Author||Year||Trial registry||Study type||P||I||C||n||Primary outcome||Secondary outcomes||Favours|
|Agaev* (18)||2013||–||RCT (blinding unclear)||n.a.||Cholecystectomy and fundoplication||WH vs. Standard||150||–||WH: less pain scores, less need for analgesics||WH|
|Jiang (19)||2019||ChiCTR-IOR-17010915||RCT (blinding unclear)||Adults 65–75 years||Colorectal||37 °C/98% vs. 20 °C/0%/electric blankets vs. 20 °C/0%/bear hugger||150||Pain: reduced in WH and CB compared to CE||WH and CB are better concerning intraoperative hypothermia, dysfunction of coagulation, early postoperative cough pain, sufentanil consumption, days to first flatus, solid food intake, length of hospital stay, patients’ satisfaction, surgeons’ satisfaction||WH and CB|
|Sammour (20)||2015||NCT00642005||Double-blind RCT||Adults||Colorectal||37 °C/98% vs. 19 °C/0%||82||–||No difference in small bowel obstruction, local recurrence, overall survival, cancer specific survival||–|
|Sutton (21)||2017||–||Single-blind RCT||Adults||Colorectal||36.7 °C/95% vs. room temp./0 °C||101||Cytokines (IL-6, TIMP-1, sVEGF-R1, and HSP-70), no difference||WH needed less narcotics and pain medication, pain scores were similar. No differences in length of stay, complication rates, time of flatus, time of diet. WH had less histological changes in peritoneal biopsies at the start and at the end of operation (n=42, not significant)||WH|
|Yu (22)||2013||NCT01027455||Double-blind RCT||Children 8–14 years||Appendectomy||37 °C/98% vs. 20 °C/0%||190||Opioid consumption: no difference||Pain scores, intraoperative core body temp., postop. recovery and return to normal activities: no difference||–|
*, only abstract available, full text in Russian language. CD, cold dry gas; CE, cold dry gas and electric blankets; CF, cold dry gas and bear hugger; WH, warm humidified gas.
Agaev et al. found fewer pain scores and the need for analgesics in the WH in 150 laparoscopic operations (cholecystectomies and fundoplications); however, we could not access the full text since it was published in the Russian language (18).
Jiang et al. compared WH with two CD-groups; one had external warming with electric (CE) and one with forced heated air blankets (CF). They included only elderly patients with colorectal surgery. Pain scores were similar in WH and CE, but higher in CF. The same constellation was found for intraoperative hypothermia, coagulation dysfunction, early postoperative cough pain, sufentanil consumption, days to first flatus and solid food intake, and length of hospital stay. The authors attribute the differences to insufficient maintenance of normothermia in the group with electric blankets and emphasize the necessity of normothermia. WH and CD with forced heated air blankets were equivalent in this trial (19).
Sammour et al. published a five-year follow-up of a randomized trial of 2010 (23), focussing on the long-term effects of small bowel obstruction as representative of adhesions, local tumour recurrence, overall and cancer-specific survival (20). There were no differences between WH and CD. Small bowel obstruction occurred in 5.6% of WH and 0% of CD patients (P=0.2). One should consider that on one hand, small bowel obstruction is not the only surrogate of adhesions, on the other hand, it can have other reasons than adhesions, for example, anastomotic stenosis.
Sutton et al. combined clinical and experimental outcomes (21). In a subgroup of 42 of 101 patients, they took peritoneal samples at the start and at the end of the operation, which were compared histologically. They found fewer histologic alterations in the end-of-operation specimens in the WH group compared to the CD group, but the difference was not statistically significant. Postoperative plasma levels of cytokines did not differ between WH and CD, either. The WH group needed fewer narcotics and early postoperative analgetic medication, although the pain scores were similar. The authors state not to draw “firm conclusions … regarding the use of pain medications”. There were no differences in clinical outcome parameters length of stay, complication rates, time of flatus, and time of diet.
Yu et al. performed a large-scaled RCT on appendectomies in children, revealing no differences in postoperative opioid consumption, pain scores, intraoperative core body temperature, postoperative recovery, and return to normal activities (22).
A current Cochrane analysis summarises the current knowledge up to 2016 (24): the authors found 22 randomized trials, four of which overlapped with our search. The intraoperative body core temperature was 0.31 °C higher in the warm, humidified CO2 group; however, when studies with a moderate or high risk of bias were excluded, this difference was not statistically significant. Postoperative pain scores did not differ between the warm and cold groups. Morphine use at the first and second postoperative days was similar in the cold and warm, humidified groups, but higher in the warm, not humidified CO2 group. The postoperative recovery time did not differ when the only high risk of bias study was excluded from the analysis. Length of hospital stay and recovery time were similar in all groups.
Since up to several hundred litres of gas flow through the abdomen during the operation, it is reasonable to assume that the gas should have a relevant influence on core body temperature and the body’s moisture homeostasis. However, the clinical studies demonstrate that the body temperature is not impaired by CD in a clinically relevant manner. The clinical trials recording the core temperature found only minimal changes which fit very well to the theoretical calorimetric calculations of Roth et al. (15). The Cochrane analysis did not find significant differences in postoperative pain scores and the need for analgesic medication, and the few recent trials published after the Cochrane review are heterogeneous, not favouring WH gas. Short-time clinical outcomes are not influenced by WH or CD, either.
There is hardly any evidence of the formation of adhesions due to the use of WH or CD gas. It is always difficult to measure the effectiveness of an intervention on the forming of adhesions within a human clinical trial, as the generation of adhesions is multifactorial and difficult to quantify. Even animal autopsy trials do not allow to conclude from the morphologic evidence of adhesions on their clinical relevance. Thus, although there is a clinical long-term follow-up RCT, the data are insufficient to judge the impact of WH and CD on adhesions.
In conclusion, there is no evidence for the use of WH gas. The decision to use WH should be drawn based on the local availability, since warming and humidifying CO2 is related to additional costs.
A pneumoperitoneum, and therefore pressure, is necessary to elevate the abdominal wall from the organs to provide for the surgeon’s field of view. Even abdominal wall lifting techniques which avoid a classic pneumoperitoneum, aim to establish the field of view.
The pressure on the peritoneum, however, reduces the blood flow in the low-pressure vessels, capillaries, and veins, which could contribute to inflammatory or stress response. It also affects the vasopressin and renin-angiotensin-aldosterone-system (25). The pressure on the liver (veins), diaphragm, and lung can reduce the cardiac preload, the lung volume by about one-third, provoke atelectasis, shunt, and ventilation-perfusion-mismatch.
Thus, it seems desirable to reduce the pressure to minimize cardiopulmonary complications, and simultaneously find the balance to still provide a good field of view.
MEDLINE was searched through pubmed.gov with the string: “(((((((laparoscop*) OR (coelioscop*)) OR (celioscop*)) OR (peritoneoscop*)) OR (minimally invasive)) OR (video assisted surgery)) AND (pressure)) AND (pneumoperitoneum)”. The search was limited to randomised clinical trials from 2010 to March 2021. Trials on children, animals, or cadavers were excluded. In contrast to the Cochrane review, all kinds of laparoscopic operations were considered.
Thirty-eight RCTs were identified (Table 3). Nine trials were excluded: three were study protocols, three were not randomised trials, three were trials on children. Most RCTs compared low pressure (LP, about 8 mmHg) with standard (SP, about 12 mmHg) or high pressure (HP, >15 mmHg); these categories were quite homogenous.
|First author||Year||Trial registry||Study type||P||I||C||n||Primary outcome||Secondary outcomes||Favours|
|Aditianingsih (26)||2020||NCT03219398||RCT||Adults 18–65||Living donor nephrectomy||8 vs. 12 mmHg||44||n.a.||LP: lower intra- and postop. HR, intraop. blood levels of IL-6, sVEGFR-2, syndecan-1; higher proximal tubule syndecan-1 expression; intact EM renal tubule and peritubular histology compared to cell damage in SP group||LP|
|Albers (27)||2020||NCT03928171||Observer blinded RCT||Adults||Robot colorectal surgery||8 vs. 12 vs. 16 mmHg||30||Peritoneal perfusion: improved in LP group||LP|
|Ali (28)||2016||–||RCT||Adults||ChE||10 vs. >10 mmHg||160||Shoulder pain: LP with less pain and less administration of analgesics||LP|
|Barrio (29)||2017||–||Blinded RCT||Adults||ChE||8 mmHg/moderate NMB vs. 8 mmHg/deep NMB vs. 12 mmHg||90||n.a.||Surgeon’s reported satisfaction with (I) surgical field exposure, (II) dissection of the gallbladder, (III) extraction/closure: SP was superior to both LP groups.||SP|
|Chang-Sheng (30)||2012||–||RCT||Adults||ChE||9 vs. 12 vs. 15 mmHg||90||Liver enzymes preoperative vs. day 1, 3, and 7 postoperative: significant changes of serum ALT, AST, TBIL and DBIL in SP and HP groups.||LP|
|Díaz-Cambronero (31)||2020||NCT02773173||RCT||Adults||colorectal surgery||Lowest acceptable pressure vs. 12 mmHg||166||Postoperative Quality of Recovery Scale: higher in LP||Emotional and overall recovery, intraoperative complications and lymphocyte-neutrophil ratio on postoperative day 3 lower in LP group; no influence on postoperative complications, duration of hospital stay.||LP|
|Eryılmaz (32)||2012||–||RCT||Adults||ChE||10 vs. 14 mmHg||43||Plasma disappearance rate of indocyanine green intraoperatively: decreased in SP||Blood levels of AST, ALAT and bilirubin 1 and 24 hours after surgery: no differences between LP and SP||LP|
|Gupta (33)||2013||–||RCT||Adults||ChE||8 vs. 14 mmHg||101||n.a.||Total bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase on day 1 and 7 postoperatively: Bilirubin, AST and ALAT were higher in SP on day 1, no differences on day 7.||LP|
|Hsu (34)||2019||–||RCT||Adults||ChE||12 mmHg, low flow rate induction (1 L/min) vs. continuous high flow rate (10L/min)||140||Shoulder pain: less pain in low flow rate group, same incidence in both groups||Length of hospital stay, bradycardia, operative time: no differences||Low flow rate insufflation|
|Hypolito (35)||2014||–||RCT||Adults||12 vs. 20 mmHg||67||n.a.||Mean arterial pressure, pH, HCO3 and base excess differed significantly in HP, but within normal limits||-|
|Ko-Iam (36)||2016||TCTR20140213001||RCT||Adults 18-75||ChE||etoricoxib/7 mmHg vs. placebo/14 mmHg||120||n.a.||Pain and length of hospital stay: less in the treatment group||n.a. (effects may rise from medication)|
|Madsen (37)||2016||–||Double-blind RCT||Adults||ChE||8 mmHg/deep NMB vs. 12 mmHg/moderate NMB||99||Incidence of shoulder pain: less in LP/deep NMB group||No differences in: area under curve VAS scores for shoulder, abdominal, incisional and overall pain during 4 and 14 postoperative days; opioid consumption; incidence of nausea and vomiting; antiemetic consumption; time to recovery of activities of daily living; length of hospital stay; and duration of surgery||LP with deep NMB|
|Madsen (38)||2017||–||RCT||Adults||Hysterectomy||8 mmHg/deep NMB vs. 12 mmHg/moderate NMB||110||n.a.||LP/deep NMB: less sudden abdominal contractions||LP with deep NMB|
|Matsuzaki (39)||2017||NCT01887028||Single-blind RCT||Adults||Hysterectomy||8 mmHg/humidified warm CO2vs. 8 mmHg/standard CO2vs. 12 mmHg/humidified warm CO2vs. 12 mmHg/ standard CO2||82||n.a.||LP and/or warm humidified gas significantly lowered expression of inflammation-related genes in peritoneal tissues and postoperative pain scales||LP +/− warm humidified carbon dioxide|
|Neogi (40)||2020||–||Double-blind RCT||Adults||7 vs. 14 mmHg||82||Surgeon comfort: better in SP; GGT, GPT, GOT and LDH lower in LP||Liver function: LP; surgeon’s comfort: SP|
|Özdemir-van Brunschot (41)||2018||NCT02602964||RCT||Adults||Living donor nephrectomy||Moderate vs. deep NMB with 6 mmHg; surgeon was allowed to increase pressure||34||Surgical conditions (Leiden Surgical Rating Scale): better in deep NMB group||Pain scales: not different; postoperative opiate consumption: less in deep NMB group||Deep NMB|
|Özdemir-van Brunschot (42)||2017||NCT02146417||Living donor nephrectomy||6 mmHg/ deep NMB vs. 12 mmHg/deep NMB||64||Quality of Recovery-40-questionnaire on the first postoperative day: no significant difference||Surgical conditions (Leiden Surgical Rating Scale): no differences||−|
|Schietroma (43)||2013||–||RCT||Adults||Nissen fundoplication||≤8 vs. ≥12 mmHg||68||White blood cells, peripheral lymphocytes subpopulation, human leukocyte antigen-DR, neutrophil elastase, interleukin (IL)-6 and IL-1, and C-reactive protein: reduced postoperative inflammatory response and immunosuppression in the LP group; hospitalization, time of anesthesia, and operation: similar||−|
|Sharma (44)||2016||–||RCT||Adults||ChE||8 vs. 14 mmHg||50||Femoral vein diameter and blood flow: better in LP group||Coagulation profile (prothrombin time, prothrombin index, activated plasma thromboplastin time and international normalized ratio): no significant differences||LP|
|Shoar (45)||2016||IRCT201110072982N5||Double-blind RCT||Adults||ChE||8 vs. 12 mmHg||50||n.a.||Stress response: mean HR, mean arterial pressure, serum levels of cortisol, glucose, adrenaline, C-reactive protein: no significant differences||−|
|Sroussi (46)||2017||–||Single-blind RCT||Adults||Gynecologic laparoscopy for benign disorders||7 vs. 15 mmHg||60||Incidence of shoulder pain: less in LP||Maximal values of peak airway pressure, end tidal CO2 and systolic blood pressure: lower in LP group; length of hospital stay: shorter in LP.||LP|
|Staehr-Rye (47)||2014||NCT01523886||Double-blind RCT||Adults||ChE||8 mmHg/deep NMB vs. 8 mmHg/moderate NMB||48||Surgical space conditions: “marginally better” in deep NMB group||Deep NMB|
|Topal (48)||2011||–||10 vs. 13 vs. 16 mmHg||60||Thrombelastography: impaired in HP group|
|Topçu (49)||2014||–||RCT||Adults||gynecologic laparoscopy||8 vs. 12 vs. 15 mmHg||150||Pain: less in LP||Operation time, hemorrhage: higher in LP|
|Vijayaraghavan (50)||2014||–||RCT||Adults||ChE||8 vs. 12 mmHg||43||n.a.||Postoperative pain and analgetic medication: less in LP; liver function, peak expiration flow rate: no differences; intraoperative surgeon comfort better in LP.||LP|
|Warlé (51)||2013||–||RCT||Adults||Living donor nephrectomy||7 vs. 14 mmHg||20||LP: longer operation time, higher urine output during pneumoperitoneum, lower pain scores; no differences in creatinine levels, complications, SF-36 quality of life domains||LP|
|Yasir (52)||2012||–||RCT||Adults||ChE||8 vs. 14 mmHg||50||Shoulder pain: less in LP||Analgetic medication, length of hospital stay: less in LP||LP|
|Yoo (53)||2015||NCT02109133||RCT||Adults||Robotic radical prostatectomy||Deep vs. moderate NMB, 8 mmHg, surgeon was allowed to increase up to 20 mmHg||67||Intraocular pressure: lower in deep NMB||Surgeon’s comfort: better with deep NMB; lower intraabdominal pressures needed with deep NMB||Deep NMB|
ChE, cholecystectomy; NMB, neuromuscular blockade; RCT, randomized controlled trial; HP, high pressure; LP, low pressure; SP, standard pressure.
Six trials focussed on the effect of deep compared to standard neuromuscular blockade (NMB) to facilitate a lower intraabdominal pressure (37,38,41,47,53,54). The outcomes of these NMB-studies focussed on the surgeon’s conditions (space, field of view, surgeon’s satisfaction) in four trials, all favouring deep NMB (41,47,53,54), intraocular pressure, and intraabdominal contractions (38,53), both favouring deep NMB. General and patient-related outcomes (pain, emesis, opioid consumption, length of stay, etc.) did not differ between deep and normal NMB combined with low-pressure peritoneum.
All eight trials focussing on postoperative pain or analgesic consumption favoured LP (28,34,37,46,49-52). Experimental or biochemical studies revealed an improved peritoneal perfusion in the LP group (27,32), less histological damage in renal tubules (26), partially less elevation of liver enzymes (30,33,40), less inflammatory blood markers (26,31,39). The impact on coagulation was heterogeneous in two studies [(44), no difference; (48), impaired thrombelastography in HP; (49), more haemorrhage in HP]. The femoral vein diameter and blood flow were better in LP group (44).
Only two trials measured respiratory parameters: maximal values of peak airway pressure, end-tidal CO2, and systolic blood pressure were lower in the LP group at Sroussi et al. (46), base excess and bicarbonate were higher with HP, but within normal limits at Hypolito et al. (35). The LP group had higher urine output, but no difference in creatinine serum levels (52).
Quality of recovery as a patient-related outcome was assessed by two RCTs with no landmark results (XX).
The Cochrane review of 2014 identified 21 RCTs comparing low with standard pressure in patients with laparoscopic cholecystectomy. Nineteen of these trials were older than 2011 and did not overlap with our search. Primary outcomes were mortality, serious adverse events, and quality of life, secondary outcomes were conversion to open cholecystectomy, hospital stay, return to normal activity, return to work, operating time. There was no mortality, no differences in serious adverse events. Quality of life and return to work or normal activities were not reported in any of the trials. Length of stay was not significantly different, operating time was 2 minutes longer in the LP group.
The reason to use gas is to form a space between abdominal wall and organs to provide for the surgeon’s field of view and action. This space enables the operation and also ensures the safety of the patient. However, pressure on the organs is inevitable. The potential effects of pressure are numerous: Capillary and venous blood flow, gut motility, autonomous nerve system, etc.
While the Cochrane review focussed on clinical outcomes of one specific, ubiquitous surgical procedure, i.e., cholecystectomy, our search involved all laparoscopic operations and non-clinical outcomes, too. These trials confirmed differences, which have been deducted from the theoretical considerations: peritoneal perfusion and inflammatory responses are better in the LP group because the low pressure impairs the capillary and venous blood flow less. Following the same logic, urine output and liver enzymes are impaired by higher intraabdominal pressure. Unfortunately, the impact on the organs “beyond the diaphragm”, circulation and respiration, is hardly reflected by most of the trials.
However, these statistically significant differences do not translate into clinical relevance, as shown by the Cochrane review. The only clinical difference which has been confirmed is reduced shoulder pain after cholecystectomy. In contrast to this advantage for the patient, there is the surgeon’s discomfort with LP. Although this discomfort did not translate into an increased rate of morbidity for the patient, the surgical field of view should not only be considered as the surgeon’s comfort but also as a relevant factor for the patient’s safety. Furthermore, the low morbidity reported by the Cochrane review corresponds with a rather healthy patient population. Consequently, the authors state that the data do not allow inferences on the impact of LP on a patient with cardiopulmonary comorbidities and that information on the safety of LP is lacking. Recent trials demonstrated that a deeper neuromuscular blockade can facilitate laparoscopy with low pressure. Future trials should focus on patients with comorbidities and high anaesthetical risk and specifically analyse the clinical impact on circulation and respiration.
CO2 is the preferred gas to establish a pneumoperitoneum. Although it has some drawbacks like hypercapnia and acidosis especially in cardiorespiratory diseased patients, there is a broad experience in anaesthesiologic techniques which compensate for its disadvantages. Nitrous oxide has a desirable anaesthetic effect, is also cheap and available, but it does not suffocate combustion. The necessity of this suffocating effect is under discussion. Other gases like He, Ar, N2, and room air are not sufficiently tested for their safety. Room air could be desirable for low-income countries as it is the most cost-effective gas, so more efforts to investigate air for pneumoperitoneum are needed.
The use of warm humidified instead of cold dry CO2 has no benefit but is associated with higher costs.
The potential benefit of low-pressure peritoneum on possible cardiovascular and respiratory complications could not be demonstrated as most trials focus on low-risk patients. It decreases shoulder pain after cholecystectomy. However, low-pressure peritoneum impairs the surgical field of view. At the moment, there is no benefit from using low instead of standard pressure.
Provenance and Peer Review: This article was commissioned by the Guest Editors (Philipp Lingohr and Jonas Dohmen) for the series “Immunologic Implications of Minimal Invasive Surgery” published in Annals of Laparoscopic and Endoscopic Surgery. The article has undergone external peer review.
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Cite this article as: Galetin T, Galetin A. Influence of gas type, pressure, and temperature in laparoscopy—a systematic review. Ann Laparosc Endosc Surg 2022;7:6.