Venous gas embolism — a comparison of carbon dioxide and helium in pigs

Purpose

The use of helium for insufflation during laparoscopic surgery avoids hypercarbia and acidosis associated with absorbed CO₂, but the effects of helium gas embolism are unknown. We compared the effects of CO₂ with He gas embolism on survival, haemodynamic variables, oxygenation, and ventilation in pigs.

Methods

Anaesthetized juvenile pigs were given progressively larger boluses of either CO₂ (n=5) or He (n=4) into the right atrium. Measurements of haemodynamic vanables, oxygenation, and P_ETCO₂ were made before and after each gas injection.

Results

All animals survived injections of 300 ml CO₂ while no animal survived more than 120 ml He (P < 0.01). Mean arterial pressure decreased more after 60 ml He (99 ±14 to 44 ±20 mmHg) than after 60 ml CO₂ (110 ±12 to 88 ±14 mmHg, P < 0.001). Cardiac output did not change at any injection volume. The P_ETCO₂ decreased more after 60 ml He (30 ±2 to 3 ±6 mmHg) than after 60 ml CO₂ (35 ±3 to 30 ±3 mmHg, P < 0.001). Only the He group showed a decrease in PaO₂ (190 ±51 to 68 ±22 mmHg at 60 ml, P < 0.05).

Conclusion

Helium gas embolism has a greater deleterious effect than CO₂ gas embolism on survival, MAR P_ETCO₂, and PaO₂. These different effects of gas embolism should be recognized when considering the use of helium or other insoluble gases for abdominal laparoscopic insufflation.     

The safety of helium for abdominal insufflation

Background: A search for alternative methods of abdominal insufflation has been prompted by the fact that CO₂ insufflation may cause acidosis, decreased cardiac output, increased systemic vascular resistance, and increased cardiac filling pressures. This study evaluates the safety and the cardiopulmonary effects of helium abdominal insufflation (HAI). Methods: Thirteen ASA class III and IV patients undergoing laparoscopic procedures were studied in a prospective, nonrandomized protocol using HAI. Cardiopulmonary parameters were measured before and after anesthetic induction and every 30 min during HAI. Abdominal insufflation pressure was initially 10 mmHg and was increased to 15 mmHg after 30 min. All measurements were repeated 15 min after deflation of the abdomen. Changes were evaluated by ANOVA. Results: No significant cardiopulmonary complications were observed. No patient developed hypercarbia or acidosis. Peak inspiratory pressure increased with HAI from 20 ± 1 to 34 ± 2 cm H₂O (p < 0.0001). Cardiac index decreased (3.35 ± 0.19 vs 2.37 ± 0.19 l/min/m²; p= 0.0303) and systemic vascular resistance increased (1,123 ± 66 vs 1,406 ± 126 dyne · s/cm⁵; p= 0.0512) while cardiac filling pressures increased with insufflation to 15 mmHg. Conclusions: Minimal cardiac and pulmonary aberrations were observed. Helium was safe for abdominal insufflation and may be the insufflating agent of choice in patients with significant cardiopulmonary disease.     

Alternative methods of exposure minimize cardiopulmonary risk in experimental animals during minimally invasive surgery

Background: Alternative methods of exposure are needed for minimally invasive surgery to avoid hypercarbia and acidosis associated with carbon dioxide (CO₂) abdominal insufflation. The goals of this study were to determine the pulmonary and hemodynamic effects of both helium (HE) abdominal insufflation and placement of a mechanical abdominal wall-lifting device (lifter) during laparoscopy. Methods: Sixteen adult domestic pigs under general endotracheal anesthesia underwent baseline measurements of pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and arterial blood gas. Six pigs underwent standard CO₂ abdominal insufflation, five pigs underwent abdominal insufflation with HE, and a lifter was used for exposure in five other animals. Sequential readings of PCWP, CO, and arterial blood gas were recorded at 20-min intervals for 60 min in all 16 animals. Results: No significant changes from baseline values were noted in arterial pCO₂ or pH in animals who underwent placement of the lifter at any time point. After undergoing HE insufflation, animals experienced modest but significant acidosis and little change in pCO₂. There was a significant rise in arterial pCO₂ and decrease in pH from baseline values at all time points in animals undergoing CO₂ insufflation. Conclusions: This study shows that neither HE abdominal insufflation or the lifter have significant deleterious pulmonary or hemodynamic effects on experimental animals during laparoscopy. Gasless laparoscopy or HE insufflation may provide a safer alternative method of exposure for minimally invasive surgery in patients with pre-existing pulmonary or cardiac dysfunction. By minimizing risk in these patients, costly invasive monitoring may be avoided.Presented at the annual meeting of the Society of American Gastrointestinal Endoscopic Surgeons (SAGES), Orlando, Florida, USA, 11–14 March 1995     

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.     

Hemodynamic effects of helium vs carbon dioxide pneumoperitoneum in an experimental model of acute heart failure

Background  The systemic absorption of carbon dioxide (CO₂) during abdominal insufflation can lead to hypercarbia and acidosis, which contribute to the systemic hemodynamic effects of the pneumoperitoneum (PnP). In several animal and clinical studies, the use of helium (He) as a substitute for CO₂ prevented the development of hypercarbia. One of the common comorbid conditions in which the use of a CO₂ PnP may cause adverse effects is heart failure. The aim of our study was to evaluate and compare the hemodynamic effects of CO₂ and He PnP in an animal model of acute heart failure (AHF). Methods  Hemodynamic and blood gas parameters were measured in 10 domestic pigs during two periods of He and CO₂ insufflation of 30 min duration each, with a 30-min stabilization period between insufflations. The model of AHF was created by sodium pentobarbital injections, and measurements were repeated with both CO₂ and He PnP. The animals were ventilated with constant minute ventilation. Results  Cardiac output had a tendency to decrease during PnP, but these changes were more pronounced with CO₂ PnP in normal the heart (from 2.84±0.65 to 2.18±0.68 L/min, p=0.06) and with He PnP during AHF (from 1.78 ±0.49 to 1.32±0.34 L/min, p=0.016). Systemic vascular resistance increased in every insufflation, but this elevation was not statistically significant. CO₂ and He insufflation caused significant increase of PaCO₂ in the nonfailed heart. During AHF, He insufflation did not elevate PaCO₂. Conclusions  In an experimental model of acute heart failure, insufflation with He did not have any advantage over CO₂. The hemodynamic response to CO₂ and He PnP during normal conditions and under conditions of failed cardiac function support the hypothesis that the hemodynamic response to PnP is a result of a combination of pressure and CO₂ absorption; Furthermore, it appears that increased intraabdominal pressure is the more crucial factor. Online publication: 7 May 2001 Presented in poster format at the annual meeting of the Society of American Gastrointestinal Endoscopic Surgeons (SAGES), San Antonio, TX, USA. 24–27 March 1999     

Laparoscopy without pneumoperitoneum

Laparoscopic surgery with CO₂ insufflation is associated with adverse effects on hemodynamics and gas exchange. The abdominal wall retractor (AWR) is an alternative for pneumoperitoneum. Hemodynamics and gas exchange during the use of an AWR were compared to those of CO₂ pneumoperitoneum.In eight pigs subjected to 1 h of CO₂ pneumoperitoneum or abdominal wall retraction, hemodynamics, gas exchange, and oxygen transport were studied in a randomized cross-over study design.The only change observed during abdominal wall retraction was mild respiratory alkalosis. In contrast, during CO₂ pneumoperitoneum mean arterial blood pressure increased 13%, central filling pressures doubled, and a small increase in cardiac output was observed. Peak airway pressures increased 50%, end-tidal CO₂ increased 20%, and respiratory acidosis was induced (arterial pH from 7.46±0.07 to 7.31±0.06 and pCO₂ from 33±3 mmHg to 53±4 mmHg). Arterial PO₂ decreased but mixed venous oxygen saturation and oxygen consumption were unaffected.In contrast with CO₂ pneumoperitoneum, laparoscopy using abdominal wall retraction was not associated with adverse effects on hemodynamics or gas exchange.     

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.     

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.     

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.     

Signs of reperfusion injury following CO2 pneumoperitoneum: an in vivo microscopy study

Background During laparoscopic surgery, pneumoperitoneum is generally established by means of carbon dioxide (CO₂) insufflation which may disturb hepatic microperfusion. It has been suggested that the desufflation at the end of the procedure creates a model of reperfusion in a previously ischemic liver, thus predisposing it to reperfusion injury. Methods To study the effects of pneumoperitoneum on hepatic microcirculation, Sprague-Dawley rats underwent pneumoperitoneum with an intraabdominal pressure of 8 or 12 mmHg for 90 min. Subsequently, in vivo microscopy was performed to assess intrahepatic microcirculation and transaminases were measured to index liver injury. Results A CO₂ pneumoperitoneum of 8 mmHg did not change serum transaminases; however, further increase of intraperitoneal pressure to 12 mmHg significantly increased AST, ALT, and LDH measured after desufflation to almost 1.5 times as much as control values of 49 ± 5 U/L, 31 ± 3 U/L, and 114 ± 12 U/L. In parallel, in all subacinar zones the permanent adherence of both leukocytes and platelets to the endothelium increased by about sixfold and threefold, respectively. Furthermore, Kupffer cells labeled with latex beads as an index for their activation were significantly increased compared to controls. Conclusion This in vivo observation demonstrated traces of reperfusion injury in liver induced by the insufflation and desufflation of CO₂ pneumoperitoneum. The clinical relevance of this finding and the issue of using hepatoprotective substances to prevent this injury should be further investigated.     

Hemodynamic events in the peritoneal environment during pneumoperitoneum in dogs

Summary The purpose of this experimental study was to determine the hemodynamic conditions of intraperitoneal viscera during pneumoperitoneum by using either CO₂ gas or helium (He) for insufflation.In 16 mongrel dogs (divided into a CO₂ group and an He group) subjected to 14 mmHg pneumoperitoneum for 60 min, the following parameters were assessed at times before and 1, 2, 5, 15, 30, 45, and 60 min thereafter: (1) intestinal mucosal blood flow, by means of a laser-Doppler probe inplanted into a jejunal loop; (2) portal pressure and portal blood pCO₂, through a catheter inserted via a mesenteric jejunal vein; (3) intramural jejunal pH (pHi), by means of a Tonometer, which expresses the degree of tissue ischemia; (4) inferior vena cava pressure and blood pCO₂, through a catheter inserted via a femoral vein; and (5) from the systemic circulation pulse rate, arterial blood pressure, CO, CVP, PVP, SaO₂, pCO₂, and p_aO₂ were measured through a catheter placed into a femoral artery and a Swan-Ganz thermodilution catheter inserted via the external jugular vein: CI and SVR were then calculated.Jejunal mucosal blood flow was found decreased (P<0.0001) and pHi revealed gut mucosal ischemia. Portal and inferior vena cava pressures were found to be elevated (P<0.0001), as was blood pCO₂ of these vessels (P<0.001), in only the CO₂ group. From the systemic circulation, arterial blood pressure, CO, CI, SaO₂, and p_aO₂ revealed a decrease (P<0.001) while arterial pCO₂ (only CO₂ group), CVP, SVR, and PVP revealed an increase (P<0.001).We conclude that severe hemodynamic alterations, not only to the systemic circulation but mainly to the viscera of the peritoneal cavity, are prominent after pneumoperitoneum for laparoscopic surgery. Elevation of portal and inferior vena cava pressures leads to splanchnic blood flow congestion and ischemia, while the use of CO₂ seems to directly influence the pCO₂.     

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     

Microsphere intestinal blood flow analysis during pneumoperitoneum using carbon dioxide and helium

Background Pneumoperitoneum has been associated with a decreased flow in the superior mesenteric artery and portal venous system. Intestinal blood flow was studied during a 2-h pneumoperitoneum with carbon dioxide (CO₂) or helium in a porcine model using colored microspheres.Methods For this study, 12 pigs were divided into two groups (6 CO₂ and 6 helium). Different colored microspheres were injected directly into the left ventricle before, 40, 80, and 120 min after insufflation with either gas at a pressure of 15 mmHg. Microsphere concentration was measured in the mucosa and muscularis/serosa layers of the jejunum, cecum, and sigmoid colon to calculate blood flow.Results Intestinal perfusion initially increases with insufflation and returns to near baseline levels during pneumoperitoneum of 2 h. The effect of helium on tissue perfusion is similar to that of carbon dioxide.Conclusions Intestinal perfusion does not change significantly during prolonged pneumoperitoneum at a pressure of 15 mmHg with CO₂ or helium.Podium presentation at the 2004 meeting of the Society of American Gastrointestinal and Endoscopic Surgeons (SAGES), Denver, Colorado, USA, 31 March-3 April, 2004     

Effects of carbon dioxide vs helium pneumoperitoneum on hepatic blood flow

Background: Elevated intraabdominal pressure due to gas insufflation for laparoscopic surgery may result in regional blood flow changes. Impairments of hepatic, splanchnic, and renal blood flow during peritoneal insufflation have been reported. Therefore we set out to investigate the effects of peritoneal insufflation with helium (He) and carbon dioxide (CO₂) on hepatic blood flow in a porcine model. Methods: Twelve pigs were anesthetized and mechanically ventilated with a fixed tidal volume after the stabilization period. Peritoneal cavity was insufflated with CO₂ (n= 6) or He (n= 6) to a maximum intraabdominal pressure of 15 mmHg. Hemodynamic parameters, gas exchange, and oxygen content were studied at baseline, 90 mm and 150 min after pneumoperitoneum, and 30 min after desufflation. Determination of hepatic blood flow with indocyanine green was made at all measured points by a one-compartment method using hepatic vein catheterization. Results: A similar decrease in cardiac output was observed during insufflation with both gases. Hepatic vein oxygen content decreased with respect to the baseline during He pneumoperitoneum (p < 0.05), but it did not change during CO₂ insufflation. Hepatic blood flow was significantly reduced in both the He and CO₂ pneumoperitoneums at 90 min following insufflation (63% and 24% decrease with respect to the baseline; p < 0.001 and p < 0.05, respectively) being this decrease marker in the He group (p= 0.02). Conclusions: These findings suggest that helium intraperitoneal insufflation results in a greater impairment on hepatic blood flow than CO₂ insufflation. Received: 27 March 1996/Accepted: 19 January 1997     

Metabolic and immunologic consequences of laparoscopy with helium or carbon dioxide insufflation: a randomized clinical study

Background : Previous studies using animal models have demonstrated that carbon dioxide (CO₂) pneumoperitoneum during laparoscopy is associated with adverse physiological, metabolic, immunological and oncological effects, and many of these problems can be avoided by the use of helium insufflation. The present study was performed in patients to compare the effect of helium and CO₂ insufflation on intraperitoneal markers of immunological and metabolic function. Methods : Eighteen patients undergoing elective upper gastrointestinal laparoscopic surgery were randomized to have insufflation achieved by using either helium (n = 8) or CO₂ (n = 10) gas. Intraperitoneal pH was monitored continuously during surgery, and peritoneal macrophage function was determined by harvesting peritoneal macrophages at 5 min and 30 min after commencing laparoscopy, and then assessing their ability to produce tumour necrosis factor‐α (TNF‐α), and their phagocytic function. Results : Carbon dioxide laparoscopy was associated with a lower intraperitoneal pH at the commencement of laparoscopy, although this difference disappeared as surgery progressed. The production of TNF‐α was better preserved by CO₂ laparoscopy, but the insufflation gas used did not affect macrophage phagocytosis. Patients undergoing helium laparoscopy required less postoperative analgesia. Conclusion : The choice of insufflation gas can affect intraperitoneal macrophage function in the clinical setting, and possibly acid–base balance. The present study suggested no immunological advantages for the clinical use of helium as an insufflation gas. The outcomes of the present study, however, are different to those obtained from previous laboratory studies and further research is needed to confirm this outcome.     

Tumour implantation following laparoscopy using different insufflation gases

Background : Because of the possibility of intraperitoneal seeding and port‐site recurrences following laparoscopic surgery, the role of laparoscopy in cancer surgery remains controversial. Previous experimental studies have suggested that chemical, metabolic and immunological changes following carbon dioxide (CO₂) insufflation may be responsible for this phenomenon. Earlier experimental studies done by the University of Adelaide Department of Surgery have also shown that helium insufflation is associated with none of the adverse changes brought about by CO₂ insufflation. Helium insufflation is also associated with lower rates of intra‐abdominal tumour spread. The aim of this study was to determine whether these identified benefits apply to inert gases in general. Methods : Twenty‐four Dark Agouti rats were randomized to undergo laparoscopy with 40 min insufflation using one of the following four gases (six rats in each group); CO₂, helium, argon and nitrogen. A tumour cell suspension was injected into the abdominal cavity at the beginning of laparoscopy. The rats were killed 7 days after surgery, and the peritoneal cavity and port sites were examined for the presence of tumour. Results : Rats undergoing helium insufflation, had the least number of port‐site recurrences and the least amount of intraperitoneal tumour spread. Argon and nitrogen pneumoperitoneum were associated with a large number of port‐site recurrences and widespread tumour seeding. The effect of CO₂ insufflation was intermediate. Conclusion : The choice of insufflation gas influences the incidence of port‐site metastases and the degree of intraperitoneal tumour spread following laparoscopic cancer surgery. The reduced port‐site recurrences and intraperitoneal spread that followed helium pneumoperitoneum is likely to be a unique property of this gas rather than a property of inert gases in general.     

Videoscopic surgery under local and regional anesthesia with helium abdominal insufflation

Background: High-risk patients may not be good candidates for laparoscopic surgery due to the metabolic consequences of transperitoneal absorption of insufflated CO₂ gas and the necessity of general anesthesia because CO₂ insufflation produces pain. Helium gas is metabolically inert and does not produce pain. Thus it permits an alternative approach to performing laparoscopic surgery in high-risk patients. Methods: Laparoscopic cholecystectomy, appendectomy, hernia repair, and peritoneal dialysis catheter procedures were performed under local or regional anesthesia in high-risk patients utilizing helium gas as the insufflation agent. Results: Twenty-one patients underwent laparoscopic procedures under local or regional anesthesia. None of the procedures initiated under local-regional anesthesia required abandonment of the laparoscopic approach or conversion to general anesthesia. There were no operative or perioperative mortalities. Two incidences of pneumothorax occurred with extraperitoneal hernia repair; one required a tube thoracostomy. Conclusions: Helium gas should be considered the agent of choice for intraperitoneal insufflation in high-risk patients not only because helium avoids the metabolic consequences of CO₂ insufflation but also because it permits selected procedures to be performed under local-regional anesthesia. Helium may be contraindicated for laparoscopic procedures involving extraperitoneal insufflation due to the increased risk for pneumothoraces. Received: 15 April 1998/Accepted: 25 August 1998     

Carbon dioxide pneumoperitoneum causes severe peritoneal acidosis,unaltered by heating,humidification, or bicarbonate in a porcine model

Background Carbon dioxide (CO₂) is the most common gas used for insufflation in laparoscopy, but its effects on peritoneal physiology are poorly understood. This study looks at the changes in peritoneal and bowel serosal pH during CO₂ pneumoperitoneum, and whether heating and humidification with or without bicarbonate alters the outcomes.Methods Twenty-one pigs divided into four groups as follows: (1) standard (STD) laparoscopy (n = 5); (2) heated and humidified (HH) laparoscopy (n = 6); (3) heated and humidified with bicarbonate (HHBI) laparoscopy (n = 5); and (4) laparotomy (n = 5). Peritoneal pH, bowel serosal pH, and arterial blood gas (ABG) were obtained at 15-min intervals for 3 h.Results Severe peritoneal acidosis (pH range 6.59–6.74) was observed in all laparoscopy groups, and this was unaltered by heating and humidification or the addition of bicarbonate. Bowel serosal acidosis was observed in all laparoscopy groups with onset of pneumoperitoneum, but it recovered after 45 minutes. No significant changes in peritoneal or bowel serosal pH were observed in the laparotomy group.Conclusion CO₂ pneumoperitoneum resulted in severe peritoneal acidosis that was unaltered by heating and humidification with or without bicarbonate. Alteration in peritoneal pH may conceivably be responsible for providing an environment favorable for tumor-cell implantation during laparoscopy.     

Effect of CO2 Pneumoperitoneum on Growth of Liver Micrometastases in a Rabbit Model

Little is known about the risk of metachronous liver metastases following laparoscopic resection for gastrointestinal malignancies. The effect of CO₂ pneumoperitoneum on the growth of established liver micrometastases was investigated in a rabbit model. Male Japanese white rabbits weighing 2.8 to 3.3 kg were randomized to three groups (n= 15 per group) 3 days following intraportal inoculation of a tumor suspension containing 5 × 10⁴ cells of VX₂ cancer. In the pneumoperitoneum group, insufflation with CO₂ was maintained at a pressure of 10 mmHg for 30 minutes. In the laparotomy group the abdominal cavity remained open through a 45 mm midline incision for 30 minutes; in the control group no treatment other than anesthesia was performed. Cancer nodules on the liver surface were compared among the three groups on day 17. There was no difference in the number of cancer nodules among the groups (p= 0.72). A significant difference in the total area of cancer nodules (mean ± SEM) was found only between the pneumoperitoneum group (696.0 ± 177.0 mm²) and the control group (247.2 ± 60.7 mm²) (p < 0.05). The frequency of cancer nodules larger than 3.0 mm in maximal diameter tended to be highest in the pneumoperitoneum group (p= 0.053). These results suggests that CO₂ pneumoperitoneum may promote the growth of established liver micrometastases in this animal model.