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     

The role of the spleen in laparoscopy-associated inflammatory response

Background: Carbon dioxide (CO₂) pneumoperitoneum alters the inflammatory response in animal models of sepsis. The spleen is a key organ in inflammation and its removal was predicted to modify this effect. Methods: The acute phase inflammatory response to lipopolysaccharide (LPS) challenge in male rats was examined for the effects of splenectomy (spx) and the technique of removal (open or laparpscopic). A series of experiments compared LPS-only controls with LPS injection 2 or 9 days following open spx, lap CO₂ spx, open sham, or lap CO₂ sham. The method of splenectomy was studied by randomization to control, open spx, lap CO₂ spx, lap helium (He) spx, or lap air spx with LPS challenge on postoperative day 2. Serum levels of tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ) and, interleutin (IL) 10 were collected at multiple time points, assayed by commercial enzyme-linked immunosorbent assay, analyzed by analysis of variance. Results: Levels of TNF-α at 1.5 were significantly lower following open sham than following lap sham (p < 0.05). Splenectomy drastically reduced INF-γ and TNF-α levels compared to controls (p < 0.05) on postoperative day 2. No method of spx preserved TNF-α or INF-γ responses. Recovery of TNF-α response on day 9 was delayed in the spx groups. Conclusions: Splenectomy dramatically reduces TNF-α and INF-γ responses to LPS challenge, although by different mechanisms. Pneumoperitoneum-mediated modulation of the septic inflammatory response is partially dependent on the spleen.     

The effect of timing of pneumoperitoneum on the inflammatory response

Background We examined the effects of an identical period of pneumoperitoneum applied at three different time points after lipopolysaccharide (LPS) challenge. Two different insufflation gases were also compared. Methods Male rats (n = 70) were injected intravenously with 1 mg/kg of LPS (time 0). The time relationship between a 1.5-h period of insufflation and initial LPS stimulation was the experimental variable. All rats were killed 6 h after injection. CO₂ and helium insufflation were investigated. Ten control rats received LPS only. Serum interleukin-6 (IL-6) levels were determined by enzyme-linked immunosorbent assay (ELISA). Hepatic expression of α₂-macroglobulin, β-fibrinogen, and metallothionein were measured by Northern blot analysis. Statistical analysis was performed using one-way analysis of variance (ANOVA). Results Expression of α₂-macroglobulin mRNA was lower in CO₂ groups compared to the control group (p < 0.05 at time 120 and 270). β-Fibrinogen message was diminished in CO₂ 0 and 120 groups compared to control. Serum levels of IL-6 and expression of metallothionein mRNA did not show significant differences between groups. Conclusions These findings suggest that CO₂ pneumoperitoneum downregulates the inflammatory response to LPS challenge. Start time of CO₂ insufflation does not appear to alter hepatic expression of acute phase genes. The mechanism of α₂-macroglobulin downregulation does not appear to be due to IL-6.     

Liver metastasis and ICAM-1 mRNA expression in the liver after carbon dioxide pneumoperitoneum in a murine model

Background Liver metastasis of colorectal malignancies is an important prognostic factor. Several studies have demonstrated that carbon dioxide (CO₂) pneumoperitoneum enhances liver metastasis in animal models. Little is known about intercellular adhesion molecule-1 (ICAM-1) and tumor necrosis factor-alpha (TNF-(α) mRNA expression in the liver after CO₂ pneumoperitoneum. Methods Forty-five male BALB/c mice were randomly divided into three groups after intra-splenic tumor cell (colon 26) inoculation and the following procedures were performed: CO₂ pneumoperitoneum (n = 15), open laparotomy (n = 15), and anesthesia alone (n = 15). On day 7 after each procedure, the livers were excised and the number and diameter of the tumor nodules and the cancer index score were determined. Another 90 male BALB/c mice were randomly divided into three groups as described above, and they underwent each procedure (n = 30 each). After each procedure, the livers were excised on days 0, 1, 3, and ICAM-1 and TNF-α mRNA expression were examined by real-time RT-PCR using SYBR Green I. Results The number of tumor nodules and the cancer index score were larger in the CO₂ pneumoperitoneum group than in the control group (p < 0.05). The mean diameter of the tumor nodules was not different among the three groups. The expression of ICAM-1 in the CO₂ pneumoperitoneum group was higher than that in the other groups on day 1 (p < 0.05), and the TNF-α mRNA was higher than that in the control group on day 1 (p < 0.05). Conclusions CO₂ pneumoperitoneum enhances liver metastasis compared with anesthesia alone, and ICAM-1 expression in the liver after the pneumoperitoneum plays an important role in establishing liver metastasis in a murine model.     

Morphology of the rat peritoneum after carbon dioxide and helium pneumoperitoneum: a scanning electron microscopic study

Background Laparoscopic surgery for patients with cancer has been debated because of the susceptibility that laparoscopic incisions have shown for metastatic tumor growth. Structural damage of the mesothelial layer attributable to the pneumoperitoneum may facilitate intraabdominal tumor cell adhesion and growth. The influence of carbon dioxide (CO₂) and helium pneumoperitoneum on the morphology of the peritoneum was examined.Methods A total of 50 rats received colon carcinoma (DHB/TRb) cells intraperitoneally and CO₂ (n = 25) or helium (n = 25) pneumoperitoneum at 15 mmHg for 15 min. After different periods (2, 12, 24, 48, and 96 h), the rats were killed, and the peritoneum was examined by scanning electron microscopy. Control animals (n = 5) were without pneumoperitoneum.Results The control animals and most of the rats with pneumoperitoneum showed no peritoneal alterations. In four animals of each group, inflammatory alterations of the peritoneum such as bulging and retraction of mesothelial cells were observed at different time points. Tumor cells adherent to the peritoneum were found in a total of six animals. Peritoneal carcinomatosis, tumor nodules, or infiltration of the peritoneum by tumor cells was not observed.Conclusions The study demonstrated that the morphologic integrity of the rat peritoneum is not disturbed when CO₂ or helium is used for insufflation combined with the intraperitoneal injection of carcinoma cells. Pneumoperitoneum therefore probably is not the condition causing peritoneal changes that favor intraperitoneal tumor growth.     

Gas-related impact of pneumoperitoneum on systemic wound healing

Introduction The aim of the present study was to investigate the gas-dependent effects of pneumoperitoneum on wound healing distant from the abdomen. Materials and methods Dorsal skin incisions were performed in 54 male Sprague–Dawley rats. A CO₂ or a helium pneumoperitoneum of 3 mmHg was maintained before, with an overall duration of 30 min (each n = 18). Rats in the control group received laparotomy only (n = 18). Animals were killed after 5 and 10 days. The infiltration of macrophages (CD 68), expression of matrix metalloproteinase 13 (MMP-13) and collagen I/III ratios were analysed in the dorsal skin wounds. Results Both after 5 and 10 days, infiltration of macrophages and expression of MMP-13 were greatest after helium pneumoperitoneum. After 5 days, collagen I/III ratio was significantly increased in the helium group. After 10 days, collagen I/III ratio was lowest in the CO₂ group. Conclusion Our results suggest beneficial effects on systemic wound healing for helium pneumoperitoneum as compared to CO₂.     

Influence of nitrous oxide anesthesia on venous gas embolism with carbon dioxide and helium during pneumoperitoneum

Background: Gas embolism is a potential hazard during laparoscopic procedures. The aim of this study was to evaluate the effects of nitrous oxide (N₂O) inhalation in the case of gas embolism with carbon dioxide (CO₂) and helium during pneumoperitoneum. Methods: For this study, 20 anesthetized pigs were ventilated with N₂O (67% inspired) in O₂ (n= 10) or with halothane (0.7–1.5 inspired) in O₂ (n= 10). In each group, CO₂ (n= 5) or helium (n= 5) pneumoperitoneum was established and gas embolism induced at different rates (CO₂ at 0.5, 1, or 2 ml/kg/min; helium at 0.025, 0.05, or 0.1 ml/kg/min) through the left femoral vein a maximum of 10 min while all hemodynamic parameters were continuously monitored. Results: In the CO₂ group without N₂O, all the animals tolerated rates of 0.5 and 1 ml/kg/min over the 10 min, whereas only 3 of 4 animals in the CO₂ group with N₂O tolerated a rate of 0.5 ml/kg/min, and 2 of 4 animals a rate of 1 ml/kg/min. In the helium group without N₂O, all the animals tolerated gas embolism at all rates, whereas in the helium group with N₂O, 4 of 5 animals needed to be resuscitated at a rate of 0.1 ml/kg/min and one death occurred. Conclusions: Inhalation of N₂O worsens the negative cardiovascular effects of venous CO₂ or helium gas emboli and increases the risk of emboli-induced death when CO₂ or helium are used to establish pneumoperitoneum. The volume of venous venous helium gas emboli causing such effects is substantially smaller than that for venous CO₂ gas emboli. Received: 20 September 1999/Accepted: 1 October 2000/Online publication: 4 August 2000     

Influence of different gases used for laparoscopy (helium, carbon dioxide, room air, and xenon) on tumor volume, histomorphology, and leukocyte–tumor–endothelium interaction in intravital microscopy

Background Previouse studies indicate that helium pneumoperitoneum used for laparoscopic surgery suppresses whereas carbon dioxide pneumoperitoneum increases postoperative tumor growth. The pathomechanisms of decreased tumor growth by helium are unknown. This study was designed to examine the effect of the gases helium, carbon dioxide (CO₂), and air, and xenon, which can be used to induce pneumoperitoneum in laparoscopy on tumor volume, histomorphology, and leukocyte–endothelium interaction measured by intravital microscopy in rats with implanted liver malignoma (Morris hepatoma 3924A).Methods In 46 rats, Morris hepatoma 3294A cells were implanted intrahepatically. After implantation, rats were randomized into two main groups. In the first main group, 10 animals were prepared for examination of leukocyte–endothelium interaction by intravital video microscopy and were randomized into two groups. Five days after implantation they underwent laparoscopy using either helium (n = 5) or CO₂ (n = 5). Ten days after implantation the rats underwent intravital video microscopy to assess leukocyte–endothelium interaction in the tumor and liver vessels. In the second main group 36 rats were prepared for examination of tumor volume arid histomorphology. They were randomized into five groups. Five days after implantation they underwent laparoscopy using helium (n = 7), carbon dioxide (n = 7), room air (n = 7), or xenon (n = 8). The control group (n = 7) received anesthesia only. Rats were killed 10 days after tumor implantation to assess tumor volume and histomorphology.Results Compared to the control group or groups that received CO₂, room air, or xenon for pneumoperitoneum, the establishment of helium pneumoperitoneum caused a significantly smaller tumor volume (Kruskal-Wallis test, p = 0.001; median tumor-volume: control group, 44 mm³; helium 19 mm³). There was no significant difference in histomorphology between the groups. There was only a statistically significant difference in the development of central tumor necrosis in accordance to tumor volume (Mann-Whitney test, p = 0.03). In the tumor samples, roller counts were statistically significantly higher in the helium group compared to the CO₂ group (p = 0.04). For sticker counts, no statistically significant effects due to liver/tumor (p = 0.13) or treatment (p = 0.48) were observed.Conclusions There was a significant decrease in tumor volume using helium pneumoperitoneum for laparoscopy compared to the other gases. Here, we demonstrate that suppression of tumor growth is not due to variation of histomorphology. It seems that helium pneumoperitoneum effects a higher leukocyte–endothelium interaction and thereby a higher immune activation. This could be one explanation for the statistically significantly smaller tumor volume after laparoscopy with helium compared to laparoscopy with CO₂.     

Increased transperitoneal bacterial translocation in laparoscopic surgery

Background: The indications for laparoscopic surgery have expanded to include diseases possibly associated with peritonitis such as appendicitis, perforated peptic ulcers, and diverticulitis. The safety of carbon dioxide (CO₂) pneumoperitoneum in the presence of peritonitis has not been proved. Our previous investigations demonstrated increased bacteremia associated with CO₂ insufflation. In effort to clarify the relative effects of intraabdominal pressure and type of gas, this study was designed to measure bacterial translocation with different gases at different pressures of pneumoperitoneum. Methods: For this study, 110 rats were given intraperitoneal bacterial innoculations with Escherichia coli and equally divided into five groups of 20 animals each. The study groups included a control group with no pneumoperitoneum administered (n = 30), insufflation at a commonly used pressure of 14 mmHg with helium (n = 20) and CO₂ (n = 20), and low insufflation at 3 mmHg with helium (n = 20) and CO₂ (n = 20) in an effort to minimize influences related to pressure. Blood cultures were checked at 15-min intervals for the first 45 min, then hourly thereafter for a total of 165 min after peritoneal inoculation with 2 × 10⁷ E. coli. Results: There is increased risk of bacterial translocation in comparing groups that underwent pneumoperitoneum with those that did not in the rat peritonitis model. Furthermore, these findings are dependent on the presence or absence of gas, but not necessarily on the type of gas used for insufflation. In the low-pressure groups of both gases (helium and CO₂), bacterial translocation was significantly increased, as compared with the control group. Low pressure also was associated with increased bacterial translocation, as compared with high pressure, but beyond 30 min of insufflation, no significant differences were apparent. Conclusions: The risk of bacterial translocation in the E. coli rat peritonitis model is increased with insufflation using CO₂ or helium, and this effect is more significant at lower pressures (3 mmHg) than at higher pressures (14 mmHg). However, no clinically applicable conclusions regarding the relative effects from type of gas or insufflation pressures could be confirmed.     

Inflammatory response and bacterial dissemination afterlaparotomy and abdominal CO2 insufflation in a murine model of peritonitis

Background The immunologic repercussions due to cavity insufflation are the focus of great discussion. The aim of this study was to compare the inflammatory response and bacterial dissemination after laparotomy and abdominal CO₂ insufflation in a murine model of peritonitis. Methods Swiss mice were inoculated intraperitoneally with 0.5 ml of a solution containing 1 × 10⁸ colony-forming units (CFU)/ml of Escherichia coli and were divided into three groups as follow: control (anesthesia for 30 min), laparotomy (2.5-cm midline incision for 30 min), and CO₂ pneumoperitoneum (CO₂ cavity insufflation for 30 min). The number of leukocytes, CFU/ml counting, and the levels of interleukin (IL)-6, tumor necrosis factor-α (TNF-α), and IL-10 were evaluated in blood, peritoneal, and pleural fluid samples obtained at 90 min and 18 h after the procedures. Results The laparotomy group showed a greater bacterial dissemination to the blood, peritoneum, and pleural cavity and also greater neutrophil migration to the peritoneal cavity compared to the CO₂ insufflated and control groups. The 24-h mortality was also significantly higher in the laparotomy group. The IL-6 levels showed a precocious rise in all groups submitted to bacterial inoculation at the 90-min time point. At the 18-h time point, IL-6 levels in the peritoneum were significantly higher in the laparotomy group than in the control or CO₂ insufflated groups. At the same time, TNF-α levels were higher in the laparotomy and CO₂ insufflated groups than in controls; IL-10 levels showed no differences among the groups. Conclusions Our results suggest that cavity insufflation with CO₂ is a more effective method of access, inducing less bacterial dissemination and also a less intense inflammatory response. Cavity insufflation with CO₂ may present a good option for the surgical treatment of patients with bacterial peritonitis.     

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.     

Early peritoneal macrophage function after laparoscopic surgery compared with laparotomy in a mouse mode

Background The authors previously demonstrated postoperative preservation of the immune function measured by delayed-type skin reaction and tumor growth after laparoscopic surgery, as compared with laparotomy. For further elucidation of the origin of the demonstrated immune preservation, peritoneal macrophage (PMo) function was investigated 1 h after different surgical procedures. Methods Female NMRI mice were divided into five groups: anesthesia only, abdominal skin incision, laparotomy, peritoneal carbon dioxide (CO₂) insufflation, and peritoneal air insufflation. Escherichia Coli phagocytosis, tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), and interleukin-10 (IL-10) release of isolated PMo were investigated. Results All invasive interventions reduced the PMo phagocytosis by factors of approximately 2 to 4.7, as compared with the sham control group. Spontaneous ex vivo TNF-α release was significantly increased whenever the abdominal cavity was exposed to ambient air. The macrophage’s ability to release TNF-α after E. coli exposure was diminished in the abdominal air exposure groups, as compared with the CO₂ insufflation group. Conclusion Reduced phagocytosis 1 h after surgical interventions suggests a contribution of PMo to the altered immune function. When exposed to CO₂, PMo show a decreased basal TNF-α release. However, PMo also show an increased TNF-α release after a second immune stimulation (E. coli), suggesting a greater competency of interaction in an immune defense reaction after CO₂ exposure. Both authors contributed equally to the work. An erratum to this article is available at .     

Low-level laser therapy can reduce lipopolysaccharide-induced contractile force dysfunction and TNF-α levels in rat diaphragm muscle

Our objective was to investigate if low-level laser therapy (LLLT) could improve respiratory function and inhibit tumor necrosis factor (TNF-α) release into the diaphragm muscle of rats after an intravenous injection of lipopolysaccharide (LPS) (5 mg/kg). We randomly divided Wistar rats in a control group without LPS injection, and LPS groups receiving either (a) no therapy, (b) four sessions in 24 h with diode Ga–AsI–Al laser of 650 nm and a total dose of 5.2 J/cm², or (c) an intravenous injection (1.25 mg/kg) of the TNF-α inhibitor chlorpromazine (CPZ). LPS injection reduced maximal force by electrical stimulation of diaphragm muscle from 24.15 ± 0.87 N in controls, but the addition of LLLT partly inhibited this reduction (LPS only: 15.01 ± 1.1 N vs LPS + LLLT: 18.84 ± 0.73 N, P < 0.05). In addition, this dose of LLLT and CPZ significantly (P < 0.05 and P < 0.01, respectively) reduced TNF-α concentrations in diaphragm muscle when compared to the untreated control group.     

Immunologic parameters during NOTES compared with laparoscopy in a randomized blinded porcine trial

Background  It remains unclear if the natural orifice translumenal endoscopic surgery (NOTES) technique is less invasive than laparoscopy. Serum interleukins and peritoneal cellular response have been utilized to support the immunologic difference between open and laparoscopic surgery. We hypothesized that there would be no difference between cytokine levels during NOTES or laparoscopic peritoneoscopy. Methods  Twelve pigs were assigned to NOTES or standard laparoscopy with permuted block randomization. Each group underwent 90 min of diagnostic peritoneoscopy using CO₂ for laparoscopy and air for NOTES pneumoperitoneum. Blood draws were obtained at baseline, at procedure end, and on postoperative days (POD) 1, 2, and 7. Quantification of cytokines (IL-1b and TNF-α) was performed with a Duo Set Porcine enzyme-linked immunosorbent assay (ELISA). Laboratory results were captured by a technician blinded to the research question, and data analysis was performed by an investigator blinded to the procedure using t-test and repeated measures linear model. The study was approved by the institutional animal care and use committee (IACUC). Results  All procedures were successfully completed. One NOTES animal succumbed to hemorrhagic gastritis (day 3). All other animals thrived to POD 14, with no gross infections at necropsy. Animals undergoing laparoscopy had lower mean arterial pH than NOTES animals (p < 0.001). Serum and intraperitoneal white blood cell (WBC) counts were similar between the groups. Mean interleukin-1b levels at baseline, at the end of the procedure and at 48 h did not differ (0.50 and 0.31; p = 0.65). TNF-α levels did not differ at baseline or procedure end but increased in the NOTES group on POD 1, persisting to POD 7. Tumor necrosis factor-α (TNF-α) decreased in the laparoscopy group (p = 0.005). Conclusion  Cytokines and WBC did not differ between laparoscopic and NOTES groups during the initial 24 h. These findings do not currently support the assumption that NOTES is less invasive than laparoscopy. The late TNF-α elevation contradicts other studies and requires further examination. Presented at the 27th annual meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), April 9–12th, Philadelphia, PA.     

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.     

Influence of Gases on Intraperitoneal Immunity during Laparoscopy in Tumor-bearing Rats

Laparoscopy has been associated with metastases to abdominal wall wounds. In addition, many recent experimental studies suggest that laparoscopy is associated with increased tumor dissemination. It is possible that immune or metabolic disturbances due to the use of a pneumoperitoneum could contribute to this problem. To investigate this possibility, we studied the effect of two insufflation gases and gasless laparoscopy on in vivo peritoneal macrophage function and intraperitoneal pH in an experimental model. A carcinoma was implanted into the flank of 32 experimental rats that underwent laparoscopic surgery in one of four treatment groups: anesthesia alone, gasless laparoscopy, helium insufflation, and CO₂ insufflation. Intraperitoneal pH was monitored during surgery, and peritoneal macrophage function was determined 3 days after surgery by harvesting peritoneal macrophages and then examining their ability to produce tumour necrosis factor-α (TNF-α). CO₂ insufflation was associated with a consistent fall in intraperitoneal pH and a significant reduction in TNFα production. These findings did not occur in the other study groups. The results of this study demonstrate that CO₂ insufflation results in depressed intraperitoneal macrophage activity. It is possible that it is mediated by pH changes. In addition, it could be a contributing factor to the development of port-site metastases. Further studies are needed to determine whether the factors identified act during clinical surgery.     

Impact of pressure and gas type on anastomotic wound healing in rats

Background Laparoscopic techniques in the treatment of various bowel diseases have become more and more popular in todays clinical routine. However, knowledge about the impact of a carbon dioxide (CO₂) pneumoperitoneum on the quality of healing of the intra-abdominal wound is rare. We therefore investigated the effects of pressure and gas type on anastomosis healing in a rat model.Methods Laparotomy and twofold ileo-ileal anastomosis was performed in 78 male Sprague Dawley rats. A CO₂ or a helium pneumoperitoneum of 3 mmHg (each, n=18) or of 6 mmHg (each, n=12) was maintained before and after ileo-ileostomy. Rats in the control group (n=18) received no pneumoperitoneum. Animals were killed after 5 and 10 days. As indicator of bowel function, mean body weights were compared between the groups. One region of the anastomosis was subjected to computerised bursting-pressure measurements, while the second was explanted for subsequent histopathological examinations: collagen synthesis and degradation was determined by the ratio of collagen type I to type III and by the matrix metalloproteinase MMP-13. The extent of new mucosal layer formation was measured in haematoxylin and eosin (H&E)-stained sections.Results Alteration in mean body weight and the mean anastomosis bursting pressures did not differ between the groups. Likewise, histological examination revealed no statistically significant differences, either in the values for collagen I/III ratios or in the extent of mucosal proliferation. After 10 days, 6 mmHg helium pneumoperitoneum was associated with a more pronounced expression of MMP-13 than that of controls.Conclusions A CO₂ pneumoperitoneum with pressures of 3 mmHg and 6 mmHg was found to have no significant impact upon the healing of anastomosis wounds in rats. Helium pneumoperitoneum offers no advantages over CO₂.     

Influence of different gases used for laparoscopy (helium,carbon dioxide,room air,xenon) on tumor volume,proliferation, and apoptosis

Background: Previous reports suggest that helium pneumoperitoneum used for laparoscopic surgery suppresses postoperative tumor growth. The present study was designed to determine the effects of gases used in laparoscopy on tumor volume, proliferation, and apoptosis in rats with implanted malignoma. Methods: In 36 rats Morris hepatoma 3294A cells were implanted intrahepatically. Then, after 5 days, they underwent laparoscopy using helium (n = 7), CO₂ (n = 7), room air (n = 7), or xenon (n = 8). One group received anesthesia only (n = 7). Rats were killed 10 days after implantation to assess tumor volume, proliferation, and apoptosis. Results: Helium pneumoperitoneum caused a significant smaller tumor volume compared to other groups (Kruskal-Wallis test: p = 0.001; median tumor volume: control: 44 mm³; helium: 19 mm³). There was no significant difference in tumor cell proliferation (PCNA) and apoptosis (TUNEL reaction) between the groups. Conclusions: There was a significant decrease of tumor volume using helium pneumoperitoneum compared to the other gases, but no decreased tumor cell proliferation or increased tumor cell apoptosis. The first two authors contributed to this paper equally.     

Hemodynamic and tissue blood flow responses to long-term pneumoperitoneum and hypercapnia in the pig

Background Increased peritoneal blood flow may influence the ability of cancer cells to adhere to and survive on the peritoneal surface during and after laparoscopic cancer surgery. Carbon dioxide (CO₂) pneumoperitoneum is associated with a marked blood flow increase in the peritoneum. However, it is not clear whether the vasodilatory effect in the peritoneum is related to a local or systemic effect of CO_2. Methods In this study, 21 pigs were exposed to pneumoperitoneum produced with either CO₂ (n = 7) or helium (He) (n = 7) insufflation at 10 mmHg for 4 h, or to two consecutive levels of hypercapnia (7 and 11 kPa) (n = 7) produced by the addition of CO₂ to the inhalational gas mixture. Tissue blood flow measurements were performed using the colored microsphere technique. Results Blood flow in peritoneal tissue increased during CO₂, but not He, pneumoperitoneum, whereas it did not change at any level of hypercapnia alone. There was no change in blood flow in most organs at the partial pressure of CO₂ (PaCO₂) level of 7 kPa. However, at a PaCO₂ of 11 kPa, blood flow was increased in the central nervous system, myocardium, and some gastrointestinal organs. The blood flow decreased markedly in all striated muscular tissues during both levels of hypercapnia. Conclusion The effect of CO₂ on peritoneal blood flow during laparoscopic surgery is a local effect, and not attributable to central hemodynamic effects of CO₂ pneumoperitoneum or high systemic levels of CO₂.     

Evaluation of risk of splenosis during laparoscopic splenectomy in rat model

Laparoscopic splenectomy (LS) is an alternative to open surgery. However, there is a theoretic risk of splenosis and abdominal cavity dissemination of splenic cells if the splenic capsule is broken, as seen by experimental evidence of tumoral cell mobilization by the pneumoperitoneum. We evaluated the features of splenosis after splenectomy operated via an open approach or under laparoscopic control in an experimental model in the rat. A total of 65 Sprague-Dawley rats were distributed in seven groups that included the open approach, CO₂ pneumoperitoneum LS, or wall lift LS with or without a splenic graft. Splenic function was evaluated 90 day later through (1) scintigraphy with Tc-labeled heat-damaged erythrocytes; (2) determination of circulating “pitted” cells; and (3) analysis of the distribution of splenic pulp in the peritoneal cavity. Scintigraphy did not show viable residual tissue in any group after splenectomy; splenic activity in the splenic fossa was observed in 40% of the animals with grafts. Splenectomy increased the “pit” cell count, but it was reduced to normal values with a splenic graft. Necropsy showed normal splenic tissue in the splenic fossa in 100% of animals with a graft. Abdominal implants were observed significantly more frequently after CO₂ LS than after the open surgery or a wall lift LS (80% vs. 20% vs. 30%; p < 0.05). In addition, trocar site implants were observed with CO₂ LS (n= 3) or wall lift LS (n= 2), whereas there were no implants in the wound in the open group. We conclude that in an experimental rat model the pneumoperitoneum may facilitate abdominal splenosis after LS if the splenic capsule is ruptured or if splenic tissue spills compared with surgery without gas (open or laparoscopic).