Abdominal insufflation with CO2 causes peritoneal acidosis independent of systemic pH.

We have shown that the inflammation-attenuating effects of CO(2) pneumoperitoneum during laparoscopy are not due to changes in systemic pH. However, acidification of peritoneal macrophages in an in vitro CO(2) environment has been shown to reduce LPS-mediated cytokine release. We tested the hypothesis that the peritoneum is locally acidotic during abdominal insufflation with CO(2)--even when systemic pH is corrected. Rats (n = 20) were anesthetized and randomized into two groups: continued spontaneous ventilation (SV) or intubation and mechanical ventilation (MV). All animals were then subjected to abdominal insufflation with CO(2). Mean arterial pH among SV rats decreased significantly from baseline after 15 and 30 minutes of CO(2) pneumoperitoneum (7.329 --> 7.210 --> 7.191, P < 0.05), while arterial pH among MV rats remained relatively constant (7.388 --> 7.245 --> 7.316, P = NS). In contrast, peritoneal pH dropped significantly from baseline and remained low for both groups during CO(2) abdominal insufflation (SV 6.74 --> 6.41 --> 6.40, P < 0.05; MV 6.94 --> 6.45 --> 6.45, P < 0.05). In a second experiment, rats (n = 10) were randomized to receive abdominal insufflation with either CO(2) or helium. Abdominal insufflation with helium did not significantly affect peritoneal pH (7.10 --> 7.02 --> 6.95, P = NS), and the decrease in pH among CO(2)-insufflated animals was significant compared with helium-insufflated animals (P < 0.05). Peritoneal pH returned to baseline levels in all groups within 15 minutes of desufflation in both experiments. A significant local peritoneal acidosis occurs during laparoscopy which is specifically attributable to the use of CO(2) and which is independent of systemic pH. These data provide additional evidence that localized peritoneal acidosis is central to the mechanism of CO(2)-mediated attenuation of the inflammatory response following laparoscopic surgery.     

Effect of CO2 pneumoperitoneum on the systemic and peritoneal cytokine response in a LPS-induced sepsis model

We studied the effect of carbon dioxide (CO2) pneumoperitoneum on the systemic and peritoneal cytokine response in a rat model of intraperitoneal sepsis. After intraperitoneal injection of bacterial lipopolysaccharide (LPS, 10 mg/kg), rats were divided into 3 groups (n = 49 in each group): control (abdominal puncture); CO2 pneumoperitoneum, and laparotomy. Blood and peritoneal lavage fluid (PLF) were sampled at 0, 1, 2, 3, 4, 6, and 8 h after LPS challenge. Blood cell counts, plasma endotoxin level, and the levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interleukin-6 (IL-6) in the plasma and PLF were measured. Blood cell counts did not differ between the 3 groups. Plasma endotoxin levels in the pneumoperitoneum group were significantly increased immediately after the procedure (p < 0.05). Although peak plasma TNF-alpha levels in the pneumoperitoneum group were seen immediately after the procedure, other changes in plasma cytokine levels did not differ significantly between the 3 groups. PLF TNF-alpha and IL-1beta levels in the pneumoperitoneum group were significantly lower than levels in the control and laparotomy groups soon after the procedure (p < 0.05). PLF IL-6 levels in the pneumoperitoneum group tended to be lower than those in the laparotomy group. In conclusion, CO2 pneumoperitoneum might induce different responses between systemic and peritoneal cytokines soon after the procedure in a rat model of intraperitoneal sepsis.     

Mechanism of decreased in vitro murine macrophage cytokine release after exposure to carbon dioxide: relevance to laparoscopic surgery.

OBJECTIVE: The objective of this study was to determine the effect of carbon dioxide (CO2) on the function of peritoneal macrophages. SUMMARY BACKGROUND DATA: Laparoscopic surgery is associated with minimal pain, fever, and low levels of inflammatory cytokines. To understand the mechanisms involved, the authors investigated the effect of different gases on murine peritoneal macrophage intracellular pH and correlated these alterations with alterations in LPS-stimulated inflammatory cytokine release. METHODS: Peritoneal macrophages were incubated for 2 hours in air, helium, or CO2, and the effect of the test gas on immediate or next day lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF) and interleukin-1 release compared. Cytosolic pH of macrophages exposed to test gases was measured using single-cell fluorescent imaging. The in vivo effects of test gases were determined in anesthetized rats during abdominal insufflation. RESULTS: Macrophages incubated in CO2 produced significantly less TNF and interleukin-1 in response to LPS compared to incubation in air or helium. Cytokine production returned to normal 24 hours later. Exposure to CO2, but not air or helium, caused a marked cytosolic acidification. Pharmacologic induction of intracellular acidification to similar levels reproduced the inhibitory effect. In vitro studies showed that CO2 insufflation lowered tissue pH and peritoneal macrophage LPS-stimulated TNF production. CONCLUSIONS: The authors propose that cellular acidification induced by peritoneal CO2 insufflation contributes to blunting of the local inflammatory response during laparoscopic surgery.     

Carbon dioxide pneumoperitoneum prevents mortality from sepsis

Background Carbon dioxide (CO₂) pneumoperitoneum has been shown to attenuate the inflammatory response after laparoscopy. This study tested the hypothesis that abdominal insufflation with CO₂ improves survival in an animal model of sepsis and investigated the associated mechanism. Methods The effect of CO₂, helium, and air pneumoperitoneum on mortality was studied by inducing sepsis in 143 rats via intravenous injection of lipopolysaccharide (LPS). To test the protective effect of CO₂ in the setting of a laparotomy, an additional 65 animals were subjected to CO₂ pneumoperitoneum, helium pneumoperitoneum, or the control condition after laparotomy and intraperitoneal LPS injection. The mechanism of CO₂ protection was investigated in another 84 animals. Statistical significance was determined via Kaplan– Meier analysis for survival and analysis of variance (ANOVA) for serum cytokines. Results Among rats with LPS-induced sepsis, CO₂ pneumoperitoneum increased survival to 78%, as compared with using helium pneumoperitoneum (52%; p < 0.05), air pneumoperitoneum (55%; p = 0.09), anesthesia control (50%; p < 0.05), and LPS-only control (42%; p < 0.01). Carbon dioxide insufflation also significantly increased survival over the control condition (85% vs 25%; p < 0.05) among laparotomized septic animals, whereas helium insufflation did not (65% survival). Carbon dioxide insufflation increased plasma interleukin-10 (IL-10) levels by 35% compared with helium pneumoperitoneum (p < 0.05), and by 34% compared with anesthesia control (p < 0.05) 90 min after LPS stimulation. Carbon dioxide pneumoperitoneum resulted in a threefold reduction in tumor necrosis factor-α (TNF-α) compared with helium pneumoperitoneum (p < 0.05), and a sixfold reduction with anesthesia control (p < 0.001). Conclusion Abdominal insufflation with CO₂, but not helium or air, significantly reduces mortality among animals with LPS-induced sepsis. Furthermore, CO₂ pneumoperitoneum rescues animals from abdominal sepsis after a laparotomy. Because IL-10 is known to downregulate TNF-α, the increase in IL-10 and the decrease in TNF-α found among the CO₂-insufflated animals in our study provide evidence for a mechanism whereby CO₂ pneumoperitoneum reduces mortality via IL-10-mediated downregulation of TNF-α. Supported by R01-GM062899-02, National Institutes of Health, Bethesda, MD. Presented at the annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), Ft. Lauderdale, Florida, 13–16 April 2005     

Effectors of hypercarbia during experimental pneumoperitoneum.

Hypercarbia occurs during laparoscopy with carbon dioxide (CO2) insufflation. This may be due to increased ventilatory dead space after expansion of the peritoneal cavity with impairment of diaphragmatic excursion, or to increased absorption of CO2 from the peritoneum. To separate these effects, the authors examined the consequences of different insufflating gases and of diminished tissue perfusion on hypercarbia and dead space during pneumoperitoneum. Helium was chosen as an alternate insufflating gas because it is both inert and minimally absorbed. Eight swine (18 to 20 kg) were anesthetized, paralyzed, and mechanically ventilated at constant minute volume. Pneumoperitoneum with helium was maintained at 15 mm Hg for 45 minutes. After desufflation and stabilization for 1 hour, pneumoperitoneum was repeated with CO2. The sequence was again repeated after hemorrhagic shock to constant mean arterial pressure of 50 mm Hg. Data was analyzed by analysis of variance; significance levels are P < 0.01 unless otherwise listed. Arterial PCO2 increased significantly with CO2 insufflation within 15 minutes in normotensive animals and within 30 minutes during hypotension. Arterial pH decrease with CO2 pneumoperitoneum was significant in both groups at 30 minutes. Mixed venous PCO2 also increased with CO2 pneumoperitoneum within 30 minutes. Hypotension did not alter these changes. No significant changes were seen with helium pneumoperitoneum. Neither helium nor CO2 pneumoperitoneum significantly altered dead space. The authors make the following conclusions: 1) Absorption of CO2 from the abdomen during CO2 pneumoperitoneum produces respiratory acidosis, which is not seen with helium insufflation; 2) Pneumoperitoneum does not significantly increase dead space with either gas; 3) Transperitoneal absorption of CO2 is only partly related to perfusion because significant hypercarbia occurs during hemorrhagic shock.     

Peritoneal and systemic pH during pneumoperitoneum with CO<Subscript>2</Subscript> and helium in a pig model

Background Local peritoneal effects of laparoscopic gases might be important in peritoneal biology during and after laparoscopic surgery. The most commonly used gas, CO₂, is known to be well tolerated, but also causes changes in acid-base balance. Helium is an alternative gas for laparoscopy. Although safe, it is not widely used. In this study a method for monitoring peritoneal pH during laparoscopy was evaluated and peritoneal pH during CO₂ and helium pneumoperitoneum was studied as well as its systemic reflection in arterial pH. Methods For these experiments 20 pigs were used, with ten exposed to pneumoperitoneum with CO₂, and ten to helium. Peritoneal and sub-peritoneal pH were continuously measured before and during gas insufflation, during a 30-minute period with a pneumoperitoneum and during a 30-minute recovery period. Arterial blood-gases were collected immediately before gas insufflation, at its completion, at 30 minutes of pneumoperitoneum and after the recovery period. Results Peritoneal pH before gas insufflation was in all animals 7.4. An immediate local drop in pH (6.6) occurred in the peritoneum with CO₂ insufflation. During pneumoperitoneum pH declined further, stabilising at 6.4, but was restored after the recovery period (7.3). With helium, tissue pH increased slightly (7.5) during insufflation, followed by a continuous decrease during pneumoperitoneum and recovery, reaching 7.2. Systemic pH decreased significantly with CO₂ insufflation, and increased slightly during helium insufflation. Systemic pH showed co-variation with intra-peritoneal pH at the the end of insufflation and after 30 minutes of pneumoperitoneum. Conclusions Insufflation of CO₂ into the peritoneal cavity seemed to result in an immediate decrease in peritoneal pH, a response that might influence biological events. This peritoneal effect also seems to influence systemic acid-base balance, probably due to trans-peritoneal absorption.     

The influence of CO2 versus helium insufflation or the abdominal wall lifting technique on the systemic immune response

BACKGROUND: Both laparoscopic and conventional surgery result in activation of the systemic immune response; however, the influence of the laparoscopic approach, using CO2 insufflation, is significantly less. Little is known about the influence of alternative methods for performing laparoscopy, such as helium insufflation and the abdominal wall lifting technique (AWLT), and the systemic immune response. METHODS: Thirty-three patients scheduled for elective cholecystectomy were randomly assigned to undergo laparoscopy using either CO2 or helium for abdominal insufflation or laparoscopy using only the AWLT. The postoperative inflammatory response was assessed by measuring the white blood cell count, C-reactive protein (CRP) and interleukin-6 (IL-6). The postoperative immune response was assessed by measuring monocyte HLA-DR expression. RESULTS: CRP levels were significantly higher 1 day after helium insufflation when compared with CO2 insufflation; however, no differences were observed 2 days after surgery. The AWLT resulted in significantly higher levels of CRP both 1 and 2 days after surgery when compared with either CO2 or helium insufflation. A small increase in postoperative IL-6 levels was observed in all groups, but no significant differences were seen between the groups. After both helium insufflation and AWLT a significant decrease in HLA-DR expression was observed, in contrast to the CO2 group. CONCLUSION: Carbon dioxide used for abdominal insufflation seems to limit the postoperative inflammatory response and to preserve parameters reflecting the immune status. These findings may be of importance in determining the preferred method of laparoscopy in oncologic surgery.     

Abdominal insufflation with CO<Subscript>2</Subscript> causes peritoneal acidosis independent of systemic pH

We have shown that the inflammation-attenuating effects of CO₂ pneumoperitoneum during laparoscopy are not due to changes in systemic pH. However, acidification of peritoneal macrophages in an in vitro CO₂ environment has been shown to reduce LPS-mediated cytokine release. We tested the hypothesis that the peritoneum is locally acidotic during abdominal insufflation with CO₂deven when systemic pH is corrected. Rats (n = 20) were anesthetized and randomized into two groups: continued spontaneous ventilation (SV) or intubation and mechanical ventilation (MV). All animals were then subjected to abdominal insufflation with CO₂. Mean arterial pH among SV rats decreased significantly from baseline after 15 and 30 minutes of CO₂ pneumoperitoneum (7.329→7.210→7.191, P < 0.05), while arterial pH among MV rats remained relatively constant (7.388→7.245→7.316, P = NS). In contrast, peritoneal pH dropped significantly from baseline and remained low for both groups during CO₂ abdominal insufflation (SV 6.74 → 6.41 → 6.40, P < 0.05; MV 6.94 → 6.45 → 6.45, P < 0.05). In a second experiment, rats (n = 10) were randomized to receive abdominal insufflation with either CO₂ or helium. Abdominal insufflation with helium did not significantly affect peritoneal pH (7.10 → 7.02 →6.95, P = NS), and the decrease in pH among CO₂-insufflated animals was significant compared with helium-insufflated animals (P < 0.05). Peritoneal pH returned to baseline levels in all groups within 15 minutes of desufflation in both experiments. A significant local peritoneal acidosis occurs during laparoscopy which is specifically attributable to the use of CO₂ and which is independent of systemic pH. These data provide additional evidence that localized peritoneal acidosis is central to the mechanism of CO₂-mediated attenuation of the inflammatory response following laparoscopic surgery. Presented at the Forty-Sixth Annual Meeting of The Society for Surgery of the Alimentary Tract, Chicago, Illinois, May 14–18, 2005 (oral presentation). The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Uniformed Services University, the Department of the Air Force, or the Department of Defense.     

Helium vs carbon dioxide gas Insufflation with or without saline lavage during laparoscopy

BACKGROUND: Helium is an inert gas that, if used for insufflation during laparoscopy, may be followed by less postoperative pain than carbon dioxide (CO2) insufflation, due to a more limited effect on intraabdominal pH and metabolism. Saline lavage has also recently been shown to reduce postoperative pain following laparoscopic surgery. To evaluate these possibilities and to better define the clinical safety of helium insufflation, we undertook a prospective randomized trial comparing CO2 and helium insufflation with or without saline lavage in patients undergoing elective laparoscopic upper abdominal surgery. METHODS: From January to November 2000, 173 patients undergoing elective laparoscopic cholecystectomy or fundoplication were randomized to undergo laparoscopy with either CO2 or helium insufflation. Within each group, patients were further randomized to undergo peritoneal lavage with 2 L of 0.9% saline at the end of the surgical procedure. This yielded the following four patient groups; CO2 (group 1, n = 47), CO2 + saline lavage (group 2, n = 43), helium (group 3, n = 43) and helium + saline lavage (group 4, n = 40). Patients were blinded to their randomization, and post-operative assessment was also performed by a blinded investigator, who applied a standardized scoring system to assess postoperative pain. RESULTS: The study groups were well matched for age, sex, weight, American Society of Anesthesiologists (ASA) status, duration of surgery, and volume of gas utilized, and 81% of patients were discharged within 48 h. There were no differences in the incidence of postoperative complications among the study groups, and postoperative pain scores were not significantly different when all four groups were compared. When helium (groups 3 and 4) was compared with CO2 (groups 1 and 2), no differences in pain score were seen. When no lavage (groups 1 and 3) was compared with lavage (groups 2 and 4), less pain was found in the group undergoing saline peritoneal lavage (mean 4-h pain score, 5.9 vs 5.2; 24-h pain score, 4.8 vs 4.1; p > 0.05). CONCLUSIONS: The use of helium insufflation for laparoscopic surgery, while not associated with any significant adverse sequelae, was not associated with less postoperative pain in this trial. The use of saline peritoneal lavage was associated with less pain in the early postoperative period.     

Acidification during carbon dioxide pneumoperitoneum is restricted to the gas-exposed peritoneal surface: effects of pressure, gas flow, and additional intraperitoneal fluids

BACKGROUND: There are varying data regarding the degree and extent of abdominal acidification during laparoscopy. The aim of this study was to determine the extent of peritoneal acidification during carbon dioxide insufflation and the effects of different pressures, insufflation rates, and free intraperitoneal fluids. MATERIALS AND METHODS: Sixteen male Sprague-Dawley rats weighing 250-300 g were anesthetized and a two-point pH probe was inserted in the abdominal cavity. After closure of the abdominal wall, each group of 4 rats was subjected to one of four insufflation regimens: low pressure (2 mm Hg, no leakage); high pressure (10 mm Hg, no leakage); leakage (2 mm Hg, leakage 0.5 mL/min); and fluid (2 mm Hg, 10 mL intraperitoneal 0.9% NaCl). During insufflation peritoneal pH was continuously measured. RESULTS: Carbon dioxide insufflation significantly decreased the peritoneal pH to <7.0 only in areas exposed to the insufflation gas. Neither changes in pressure nor insufflation rate had major effects on the peritoneal pH. The addition of 10 mL normal saline into the abdominal cavity significantly enhanced the pH change during insufflation. conclusion: Acidification associated with carbon dioxide pneumoperitoneum is limited to the area of inspection and manipulation. The increased acidification following injection of normal saline could offer a useful mechanism to alter the inflammatory response.     

Is helium insufflation superior to carbon dioxide insufflation in bacteremia and bacterial translocation with peritonitis?

PURPOSE: To evaluate the effects of CO2 or helium insufflation on bacteremia and bacterial translocation in rats with peritonitis. MATERIALS and METHODS: Forty male Wistar-Albino rats were divided into four groups, each containing 10 rats. The rats in the first group were injected only with E. coli into their peritoneal cavities with no further manipulation. The second group, following E. coli injection, underwent midline laparotomy without manipulation of the viscera for 1 hour. After the injection of E. coli in the third and fourth groups, CO2 and helium pneumoperitoneum, respectively, were maintained for 1 hour under 14 mm Hg pressure. At the end of the sixth hour, tissue samples were taken from the liver, spleen, lung, and mesenteric lymph nodes in order to evaluate bacterial translocation. During the study, blood samples were taken from each rat at 0, 1, 2, 4, and 6 hours to demonstrate bacteremia. RESULTS: There was a significant increase in bacteremia in the CO2 pneumoperitoneum group compared with the laparotomy-only and helium groups at 1 and 2 hours. Although all the blood samples at the fourth hour were positive for E. coli in every rat of all groups, helium was associated with a lower incidence of bacteremia at the sixth hour compared with other groups (P < 0.05). The CO2 pneumoperitoneum caused bacterial translocation to all organs from which tissue samples were taken. Although there was an insignificant decrease in translocation to the liver, spleen, and lung with helium compared with CO2 insufflation, helium did not increase bacterial translocation to the spleen compared with laparotomy alone, as did CO2 (P < 0.05). CONCLUSION: Helium might be an alternative to CO2 insufflation in patients with peritonitis if these results are confirmed by further experimental and clinical trials.     

The impact of gas laparoscopy on abdominal plasminogen activator activity

Background: The impairment of intestinal perfusion following induction of a pneumoperitoneum may lead to a reduction of peritoneal tissue plasminogen activator (tPA) activity and a concomitant increased risk of adhesion formation. Methods: Pigs were laparotomized to take peritoneal biposy specimens from the cecum, the ileum, and the abdominal wall. A 15 mmHg pneumoperitoneum was established for 3 h by the insufflation of carbon dioxide (group 2, n = 6) or helium (group 3, n = 6). Group 1 (n = 7) received no gas insufflation. After a 2-h recovery period, additional tissue samples were harvested. Specific tPA activity was then determined in the tissue extracts. Results: During surgery, specific tPA activity decreased in all the samples. As compared with the control group (100%), this reduction was strongly aggravated in the cecum (-67.6%, p < 0.05) and the ileum (-70.8%) of the CO2 group but only slightly aggravated in the helium group. The parietal peritoneum was not specifically affected by gas insufflation. Conclusion: The use of a pneumoperitoneum with carbon dioxide significantly affects peritoneal tPA activity and thus may represent a stimulus for adhesion formation. apd: 13 March 2001     

Heated, humidified CO2 gas is unsatisfactory for awake laparoscopy.

BACKGROUND: The necessity for general anesthesia represents an impediment to using a laparoscopic approach for some procedures that are otherwise performed with the patient under local anesthesia using a conventional open technique. Heating and humidifying the insufflation gas reportedly reduces perioperative pain associated with a CO2 pneumoperitoneum, thus enabling awake laparoscopy. METHODS: Two cases are reported herein of laparoscopy performed with the patient under local anesthesia using heated, humidified CO2 gas for the pneumoperitoneum. RESULTS: Both patients experienced pain with insufflation of heated, humidified CO2 gas of sufficient magnitude that the procedure could not be performed. The CO2 gas was washed out and replaced with helium gas insufflation with complete resolution of pain. The laparoscopic procedures were accomplished without further discomfort with local anesthesia and using a helium gas pneumoperitoneum. CONCLUSIONS: Heated, humidified CO2 gas insufflation does not reduce pain sufficiently to permit satisfactory performance of laparoscopy with local anesthesia, especially when full volume insufflation is required. Cold, dry helium gas produces no pain. The theory that cold, dry insufflation gas is a source of peritoneal pain during laparoscopy needs to be reassessed.     

Impact of carbon dioxide and helium insufflation on cardiorespiratory function during prolonged pneumoperitoneum in an experimental rat model

BACKGROUND: Experimental studies on laparoscopic surgery are often performed in rats. However, the hemodynamic and respiratory responses related to the pneumoperitoneum have not been studied extensively in rats. Therefore, the aim of this study was to investigate in spontaneously breathing rats the effects of CO2 and helium, insufflation pressure, and duration of pneumoperitoneum on blood pressure, arterial pH, pCO2, pO2, HCO3-, base excess, and respiratory rate. METHODS: Five groups of 9 Brown Norway rats were anesthetized and underwent CO2 insufflation (6 or 12 mmHg), helium insufflation (6 or 12 mmHg), or abdominal wall lifting (gasless control) for 120 min. Blood pressure was monitored by an indwelling carotid artery catheter. Baseline measurements of mean arterial pressure (MAP), respiratory rate, arterial blood pH, pCO2, pO2, HCO3-, and base excess were recorded. Blood gases were analyzed at 5, 30, 60, 90, and 120 min during pneumoperitoneum, and MAP and respiratory rate were recorded at 5 and 15 min and at 15-min intervals thereafter for 2 h. RESULTS: CO2 insufflation (at both 6 and 12 mmHg) caused a significant decrease in blood pH and increase in arterial pCO2. Respiratory compensation was evident since pCO2 returned to preinsufflation levels during CO2 insufflation at 12 mmHg. There was no significant change in blood pH and pCO2 in rats undergoing either helium insufflation or gasless procedures. Neither insufflation pressure nor the type of insufflation gas had a significant effect on MAP over time. CONCLUSION: The cardiorespiratory changes during prolonged pneumoperitoneum in spontaneously breathing rats are similar to those seen in clinical practice. Therefore, studies conducted in this animal model can provide valuable physiological data relevant to the study of laparoscopic surgery.     

CO2 abdominal insufflation pretreatment increases survival after a lipopolysaccharide-contaminated laparotomy

Carbon dioxide (CO₂)-pneumoperitoneum is known to favorably modify the systemic immune response during laparoscopic surgery. The presented studies were designed to determine whether treating animals with CO₂ abdominal insufflation before undergoing a lipopolysaccharide (LPS)-contaminated laparotomy would serve as “shock prophylaxis” and thus improve survival and attenuate cytokine production. Rats were randomized into five groups: CO₂-pneumoperitoneum, helium-pneumoperitoneum, anesthesia control, laparotomy/LPS control, and LPS only control. Animals in the first four groups all received a laparotomy and a lethal dose of LPS. Immediately preceding their laparotomy, animals in the pneumoperitoneum groups received a 30-minute pretreatment of abdominal insufflation with either CO₂ or helium. The anesthesia control group received a 30-minute pretreatment of isoflurane. Animal mortality was then recorded during the ensuing 72 hours. Subsequently, a similar protocol was repeated for measurements of cytokines. CO₂-pneumoperitoneum increased survival at 48 hours compared with LPS control (P<.05), and decreased interleukin-6 plasma levels at 2 hours (P<.05). Abdominal insufflation with CO₂ before the performance of a laparotomy contaminated with endotoxin increases survival and attenuates interleukin-6. The beneficial immune-modulating effects of CO₂-pneumoperitoneum endure after abdominal insufflation. CO₂-pneumoperitoneum pretreatment may improve outcomes among patients undergoing gastrointestinal surgery who are at high risk for abdominal fecal contamination. Presented at the Forty-Sixth Annual Meeting of The Society for Surgery of the Alimentary Tract, Chicago, Illinois, May 14–18, 2005 (poster presentation). Supported by R01-GM062899-02, National Institutes of Health, Bethesda, Maryland.     

Morphology of the murine peritoneum after pneumoperitoneum vs laparotomy

BACKGROUND: Although there have been studies of the effects of pneumoperitoneum on the peritoneal cavity, we still do not know whether the morphologic changes to the peritoneum are different for pneumoperitoneum vs laparotomy. Using scanning electron microscopy, we examined the murine peritoneum after pneumoperitoneum vs laparotomy and compared the changes. METHODS: Forty-five mice were anesthetized with diethyl ether and divided into seven groups. Pneumoperitoneum was established at 5 mmHg for 30 min with carbon dioxide (CO(2)) (n = 9), helium (n = 9), and air (n = 9). One group underwent laparotomy for 30 min (n = 9), and a control group underwent anesthesia only (n = 3). CO(2) pneumoperitoneum was further established at 10 mmHg for 30 min (n = 3) and at 5 mmHg for 60 min (n = 3). After the procedures, the peritoneum was resected from the mesenterium of the small intestine in each animal and examined by scanning electron microscope for morphologic changes of the mesothelial cells. RESULTS: Bulging up of the mesothelial cells was evident immediately after pneumoperitoneum, whereas detachment of the mesothelial cells was present immediately after laparotomy. Bulging up of the mesothelial cells was reduced at 24 h after CO(2) pneumoperitoneum and fully resolved at 72 h in all pneumoperitoneum groups, whereas the mesothelial cells remained detached at 72 h in the laparotomy group. Intercellular clefts were found immediately after helium pneumoperitoneum and were present at 24 h and 72 h after helium pneumoperitoneum, but they were not seen after air pneumoperitoneum and were only evident after CO(2) pneumoperitoneum at 10 mmHg. Depression of the mesothelial cell surface was observed when pneumoperitoneum lasted 60 min. CONCLUSION: Morphologic peritoneal alterations after pneumoperitoneum differed from those after laparotomy and were influenced by the type of gas, amount of pressure, and duration of insufflation. These peritoneal changes after pneumoperitoneum may be associated with a specific intraperitoneal tumor spread after laparoscopic cancer surgery.     

Impact of laparoscopic gases on peritoneal microenvironment and essential parameters of cell function

Several experimental studies confirm the hypotheses that laparoscopic gases influence the development of tumor metastases [12, 14, 23]. The mechanism for this alteration of malignant tumor growth is still unknown. One reason might be an influence of the in sufflation gas on essential cell function regulating parameters. To investigate the changes of the intra- and extracellular milieu, four parameters—extra- and intracellular pH, intracellular free calcium levels, and tissue oxygen partial pressure—were measured during insufflation with carbon dioxide (CO2), helium (He), or a nonhypoxic gas mixture consistent of 80% CO2 and 20% O2. Study design (In vitro experiments) Intracellular calcium and pH levels were measured in DHD/K12/TRb colon adenocarcinoma cells using fluorescence imaging microscopy. (In vivo experiments) Tissue oxygen partial pressure was measured using a flexible micro catheter (Licox CMP) implanted in the abdominal wall of rats. After establishing the pneumoperitoneum an optical system and an aspirator were inserted to control the position of the micro catheter and to aspirate wound exudates for pH measurements of the wound fluid. Results: Creating of pneumoperitoneum with both CO2 and helium caused a decrease in partial pressure of oxygen in the abdominal wall to about 5 mm Hg whereas insufflation with a nonhypoxic gas mixture (80% CO2 and 20% O2) induced no significant changes. The intra- and extra cellular pH values dramatically decreased during CO2 insufflation (7.4 to 6.2) in vitro. Helium caused a pH increase up to 7.6. Free intracellular calcium was enhanced during CO2 insufflation, whereas helium insufflation did not cause any changes in [Ca2+]i. Nevertheless, a significant decrease of [Ca2+]i was observed during reoxygenation following helium-induced hypoxia. Conclusion: Our study demonstrates that insufflation with either CO2 or He causes significant changes of intra- and extracellular parameters regulating essential cell functions such as oxidative phosphorylation to produce ATP, cell proliferation, or onset of apoptosis.     

Laparoscopic surgery and the parasympathetic nervous system

Background Laparoscopic surgery preserves the immune system and has anti-inflammatory properties. CO₂ pneumoperitoneum attenuates lipopolysaccharide (LPS)-induced cytokine production and increases survival. We tested the hypothesis that CO₂ pneumoperitoneum mediates its immunomodulatory properties via stimulation of the cholinergic pathway. Methods In the first experiment, rats (n = 68) received atropine 1 mg/kg or saline injection 10 min prior to LPS injection and were randomization into four 30-min treatment subgroups: LPS only control, anesthesia control, CO₂ pneumoperitoneum, and helium pneumoperitoneum. In a second experiment, rats (n = 40) received atropine 2 mg/kg or saline 10 min prior to randomization into the same four subgroups described previously. In a third experiment, rats (n = 96) received atropine 2 mg/kg or saline 10 min prior to randomization into eight 30-min treatment subgroups followed by LPS injection: LPS only control; anesthesia control; and CO₂ or helium pneumoperitoneum at 4, 8, and 12 mmHg. In a fourth experiment, rats (n = 58) were subjected to bilateral subdiaphragmatic truncal vagotomy or sham operation. Two weeks postoperatively, animals were randomized into four 30-min treatment subgroups followed by LPS injection: LPS only control, anesthesia control, CO₂ pneumoperitoneum, and helium pneumoperitoneum. Blood samples were collected from all animals 1.5 h after LPS injection, and cytokine levels were determined by enzyme-linked immunosorbent assay. Results Serum tumor necrosis factor-α (TNF-α) levels were consistently suppressed among the saline–CO₂ pneumoperitoneum groups compared to saline–LPS only control groups (p < 0.05 for all four experiments). All chemically vagotomized animals had significantly reduced TNF-α levels compared to their saline-treated counterparts (p < 0.05 for all), except among the CO₂ pneumoperitoneum-treated animals. Increasing insufflation pressure with helium eliminated differences (p < 0.05) in TNF-α production between saline- and atropine-treated groups but had no effect among CO₂ pneumoperitoneum-treated animals. Finally, vagotomy (whether chemical or surgical) independently decreased LPS-stimulated TNF-α production in all four experiments. Conclusion CO₂ pneumoperitoneum modulates the immune system independent of the vagus nerve and the cholinergic pathway. Paper presented at the annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), Fort Lauderdale, Florida, USA, April 2005     

Pneumoperitoneum versus abdominal wall lift: effects on central haemodynamics and intrathoracic pressure during laparoscopic cholecystectomy

BACKGROUND: It has been shown repeatedly that laparoscopic cholecystectomy using pneumoperitoneum (CO2 insufflation) may be associated with increased cardiac filling pressures and an increase in blood pressure and systemic vascular resistance. In the present study, the effects on the central circulation during abdominal wall lift (a gasless method of laparoscopic cholecystectomy) were compared with those during pneumoperitoneum. The study was also aimed at elucidating the relationships between the central filling pressures and the intrathoracic pressure. METHODS: Twenty patients (ASA I), scheduled for laparoscopic cholecystectomy, were randomised into two groups, pneumoperitoneum or abdominal wall lift. Measurements were made by arterial and pulmonary arterial catheterization before and during pneumoperitoneum or abdominal wall lift with the patient in the horizontal position. Measurements were repeated after head-up tilting the patients as well as after 30 min head-up tilt. The intrathoracic pressure was monitored in the horizontal position before and during intervention using an intraesophageal balloon. RESULTS: After pneumoperitoneum or abdominal wall lifting there were significant differences between the two groups regarding MAP, SVR, CVP, CI, and SV. Analogous to previous studies, in the pneumoperitoneum group CVP, PCWP, MPAP, and MAP as well as SVR were increased after CO2 insufflation (P < 0.01), while CI and SV were not affected. In contrast, in the abdominal wall lift group, CI and SV were significantly increased (P < 0.01), as was MAP (P < 0.01), while CVP, PCWP, MPAP, and SVR were not significantly affected. There was a significant difference in intraesophageal pressure between the two groups. In the pneumoperitoneum group, the intraesophageal pressure was increased by insufflation (P < 0.01) while, in the abdominal wall lift group, it was unaffected. In the pneumoperitoneum group the mean increases in cardiac filling pressures were of the same magnitude as the mean increase in the intraesophageal pressure. CONCLUSIONS: In healthy patients, abdominal wall lift increased cardiac index while pneumoperitoneum did not. Cardiac filling pressures and systemic vascular resistance were increased by pneumoperitoneum but unaffected by abdominal wall lift. The recorded elevated cardiac filling pressures during pneumoperitoneum may be only a reflection of the increased intra-abdominal pressure.     

Hyaluronic acid secretion during carbon dioxide pneumoperitoneum and its association with port-site metastasis in a murine model

Background: The mechanism of port-site metastasis after laparoscopic cancer surgery is unclear. This study aimed to determine whether carbon dioxide (CO2) pneumoperitoneum caused an increase in hyaluronic acid, which is secreted from mesothelial cells of the peritoneal cavity, and to assess the risk for port-site metastasis using a murine pneumoperitoneal model. Methods: Sandwich-binding protein assay was used to measure the concentration of hyaluronic acid in the peritoneal cavity at 6, 12, 18, 24, 48, and 72 h after CO2 pneumoperitoneum or laparotomy for 30 min. The concentrations of hyaluronic acid during pneumoperitoneum were compared among different gases (CO2, helium, air), intervals (5, 30, 60 min), and pressures (0-2, 4-6, 8-10 mmHg). To investigate the effects of exogenous hyaluronic acid, the development of port-site metastasis was examined using mouse adenocarcinoma cell-line colon 26 cells. Results: The intraperitoneal concentration of hyaluronic acid after CO2 pneumoperitoneum had increased already at 6 h, had reached the maximum level at 24 h, and had begun to decrease at 72 h. The concentration of hyaluronic acid at 24 h and 48 h in the CO2 pneumoperitoneum group was higher than that in the laparotomy group. This increase in hyaluronic acid also was found during helium and air pneumoperitoneum, and the concentration of hyaluronic acid in the peritoneal cavity was at its maximum when CO2 pneumoperitoneum lasted 30 min at 4 to 6 mmHg. The frequency of port-site metastasis was the highest when hyaluronic acid was injected during CO2 pneumoperitoneum (100%). Conclusions: In a murine model, the intraperitoneal concentration of hyaluronic acid was significantly increased after CO2 pneumoperitoneum, and the increase was more evident than that after laparotomy. Increased hyaluronic acid during pneumoperitoneum may be associated with port-site metastasis after laparoscopic cancer surgery.