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     

Hepatic and portal vein blood flow during carbon dioxide pneumoperitoneum for laparoscopic hepatectomy

Background: Laparoscopy under carbon dioxide (CO₂) pneumoperitoneum has many advantages. However, the risks of CO₂ pneumoperitoneum during laparoscopic hepatectomy (LH) have not been defined. Methods: The hemodynamics of the hepatic vein were examined during CO₂ pneumoperitoneum both pre- and posthepatectomy in eight pigs. Portal blood flow was measured with Doppler ultrasound during laparoscopic cholecystectomy in 10 human patients. Results: Experimentally, elevated intraabdominal pressure (IAP) with CO₂ insufflation produced significant increases in CO₂ partial pressure and echogenicity of the hepatic vein in the posthepatectomy group. Clinically, elevated IAP caused significant narrowing of the portal vein and significant decreases in portal blood velocity. The mean portal flow was significantly decreased with elevation of IAP >10 mmHg. Conclusions: LH with CO₂ pneumoperitoneum may lead to embolism caused by CO₂ bubbling through the hepatic vein. Elevated IAP may cause a decrease in hepatic blood flow and induce severe liver damage, especially in patients with poor liver function. Gasless laparoscopy using abdominal wall lifting should be employed in LH to avoid the risks of CO₂ embolism and liver damage. Received: 28 March 1997/Accepted: 12 September 1997     

Hemodynamic changes in the inferior caval vein during pneumoperitoneum

Background: Laparoscopic procedures of increasing difficulty and duration are becoming more and more common. This may cause significant challenges to the circulatory system and possibly influence thrombogenicity. Methods: Experimental study of carbon dioxide pneumoperitoneum in pigs. Results: Inferior caval vein blood flow remained unchanged, whereas inferior caval vein pressure increased during pneumoperitoneum. Inferior caval vein, pulmonary, and systemic vascular resistance increased during pneumoperitoneum and remained increased after exsufflation. Conclusions: Pneumoperitoneum leads to an increased inferior caval vein pressure, which could cause a dilation of peripheral veins. The similar patterns of vascular resistance in the inferior caval vein, pulmonary artery, and systemic arteries (a gradual increase remaining elevated after exsufflation) suggest a common humoral factor or increased sympathetic nerve activity. Received: 2 April 1996/Accepted: 7 June 1996     

Time-related changes in hemodynamic parameters and pressure-derived indices of left ventricular function in a porcine model of prolonged pneumoperitoneum

Background: Advanced laparoscopic procedures require prolonged pneumoperitoneum. Increased intra-abdominal pressure causes a number of hemodynamic changes including a drop in cardiac output, but it is unclear whether there is a direct effect on cardiac contractility. In this experimental study, we sought to determine whether there is a direct impact of pneumoperitoneum on cardiac contractility. We also examined the time-related changes taking place during the insufflation period. Methods: Six young pigs were anesthetized and mechanically ventilated. Pneumoperitoneum was established by insufflating carbon dioxide to a pressure of 15 mmHg and maintained for a period of 180 min. Hemodynamic parameters including left ventricular dP/dT were invasively recorded every 15 min. All hemodynamic changes were statistically evaluated, and parameters were correlated with time. Results: Cardiac output decreased with insufflation from a baseline of 3.37 ± 0.34 lt/min and reached the lowest value at 165 min of pneumoperitoneum (2.86 ± 0.30 l/min; p= 0.023). Systemic vascular resistance (SVR) significantly increased from 2236 ± 227 dyne/s/cm⁵ to a maximum of 3774 ± 324 dyne/s/cm⁵ (p= 0.005). Left ventricular dP/dT maximum did not change significantly with insufflation. The decrease in cardiac output strongly correlated with the increase in SVR (r=−0.949). Time of insufflation correlated with cardiac output (r=−0.762) and dP/dT maximum (r=−0.727). Conclusions: Pneumoperitoneum at 15 mmHg negatively affects cardiac output without significantly affecting cardiac contractility. A significant increase in SVR appears to be the driving event for the decreased cardiac output. Prolonged pneumoperitoneum may have an additional negative effect on hemodynamic parameters. Received: 5 January 2000/Accepted: 4 May 2000/Online publication: 26 July 2000     

Effect of pressure and gas type on intraabdominal, subcutaneous, and blood pH in laparoscopy

Background: According to the literature, the number of port-site metastases in laparoscopic surgery varies considerably depending on the type of gas used for the pneumoperitoneum. In order to investigate this observation we studied the changes in blood, subcutaneous, and intra-abdominal pH during laparoscopy with helium, CO₂ and room air in a rat model. In addition, we looked at the influence of intra-abdominal pressure and duration of pneumoperitoneum on the pH during the laparoscopy. Methods: pH was measured by tonometry, intra-abdominally and subcutaneously. A pH electrode was additionally placed into the subcutaneous tissue and the results compared to those measured by tonometry. Blood samples were taken from a catheter in the carotid artery. The intra-abdominal pressure was 0, 3, 6, 9 mmHg for 30 min in each case. We investigated the effect of pneumoperitoneum with CO₂, helium and air in randomized groups of 5 rats. In an additional series the pressure was held constant at 3 mmHg and the pH was measured every 30 min. Results: Due to the different absorption capacity of the peritoneum, laparoscopy with CO₂ decreases the subcutaneous pH from 7.35 to 6.81. Blood pH is reduced from 7.37 to 7.17 and the intra-abdominal pH from 7.35 to 6.24. Other, less absorbable gases induce smaller changes of blood and subcutaneous pH (only 10% of CO₂). In a variance analysis the p value is less than 0.001. The influence of duration of laparoscopy (30 min vs 90 min) on the subcutaneous pH is less compared to the influence of intra-abdominal pressure (0, 3, 6, 9 mmHg). Conclusions: Depending on the type of gas (CO₂, air, helium) used for laparoscopy blood, subcutaneous and intra-abdominal pH are influenced differently. Because lower pH is known to impair local defense mechanisms, these results may be one explanation for the higher incidence of port-site metastasis in laparoscopy with CO₂ than with other gases, as reported in the literature. Received: 11 June 1998/Accepted: 12 February 1999     

Laparoscopic cholecystectomy and time-course changes in renal function

Background: Recently, the retraction method has been used to reduce intraabdominal pressure (IAP) during laparoscopic surgery. The purpose of this study was to determine the serial changes in renal function during laparoscopic cholecystectomy (LC) using the retraction method. Methods: Urine output, effective renal plasma flow (ERPF), and glomerular filtration rate (GFR) were measured serially in seven patients who underwent LC with 12 mmHg pneumoperitoneum (High-IAP group) and five who underwent LC using the retraction method with 4 mmHg pneumoperitoneum (Low-IAP group). Results: Urine output, ERPF, and GFR were decreased during pneumoperitoneum in the High-IAP group, whereas no significant changes in any of these parameters were observed in the Low-IAP group. Conclusions: Our findings demonstrate that reduction of IAP to 4 mmHg using the retraction method prevents the transient renal dysfunction caused by prolonged 12 mmHg pneumoperitoneum during LC, suggesting that the retraction method reduces the risk of perioperative renal dysfunction during laparoscopic surgery. Received: 26 March 1996/Accepted: 27 July 1996     

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     

Portal venous flow during CO2 pneumoperitoneum in the rat

Backround: CO₂ gas insufflation is routinely used to extend the abdominal wall. The resulting pneumoperitoneum has a number of local and systemic effects on the organism. Portal blood flow, which plays an important role in hepatic function and cell-conveyed immune response, is one of the affected parameters. Methods: An established animal model (rat) of laparoscopic surgery was modified by implanting a perivascular flow probe. Hemodynamics in the portal vein were then measured during increasing intraabdominal pressure generated by carbon dioxide insufflation. Results: Using this technique, an adequate flowmetry of the portal vein was achieved in all animals. The creation of a CO₂ pneumoperitoneum with increasing intraabdominal pressure led to a linear decrease in portal venous flow. Conclusions: Elevated intraabdominal pressure caused by carbon dioxide insufflation may compromise hepatic function and cell-conveyed immune response during laparoscopic surgery. Received: 28 January 1998/Accepted: 22 June 1998     

Lack of neurohumoral response to pneumoperitoneum for laparoscopic cholecystectomy

Background: Pneumoperitoneum (PP) for laparoscopic surgery induces prompt changes in circulatory parameters. The rapid onset of these changes suggests a reflex origin, and the present study was undertaken to evaluate whether release of vasopressor substances could be responsible for these alterations. The influence of two different anesthesia techniques was also evaluated. Methods: American Society of Anesthesiologists (ASA) class I patients, scheduled for laparoscopic cholecystectomy, were investigated. The first group (n= 10) was anesthetized intravenously. The second group (n= 6) had inhalation anesthesia. Plasma vasopressin, catecholamines, and plasma renin activity were investigated as neurohumoral vasopressor markers of circulatory stress. The general stress response to surgery was assessed by analysis of plasma cortisol. Results: Induction of pneumoperitoneum caused no apparent activation of vasopressor substances, although several hemodynamic parameters responded promptly. Conclusion: The hemodynamic alterations, seen at the establishment of PP during stable anesthesia, cannot be explained by elevation of vasopressor substances in circulating blood. Received: 7 April 1997/Accepted: 3 December 1997     

Alterations in hepatic function during laparoscopic surgery

Background: Very few studies have been done on the consequences of pneumoperitoneum on hepatic function. At present, there is no consensus on the physiopathological hepatic implications of pneumoperitoneum. The purpose of this clinical study was to evaluate the effects of pneumoperitoneum on hepatic function in 52 patients treated with laparoscopic procedures. Methods: Thirty-two laparoscopic cholecystectomies and 20 nonhepatobiliary laparoscopic procedures were performed in 52 patients (12 men and 40 women) with a mean age of 44 years (range, 15–74). All patients had normal values on preoperative liver function tests. The anesthesiologic protocol was uniform, with drugs at low hepatic metabolism. The 32 cholecystectomies were randomized into 22 performed with pneumoperitoneum at 14 mmHg and 10 performed at 10 mmHg. All nonhepatobiliary laparoscopic procedures were performed with a pneumoperitoneum of 14 mmHg. The postoperative serologic levels of AST, ALT, bilirubin, and prothrombin time were measured at 6, 24, 48, and 72 h. The serologic changes were related to the procedure, the duration, and the level of pneumoperitoneum. Results: Mortality and morbidity were nil. All 52 patients had a postoperative increase in AST, ALT, bilirubin, and lengthening in prothrombin time. Slow return to normality occurred 48 or 72 h after operation. The increase of AST and ALT was statistically significant and correlated both to the level (10 versus 14 mmHg) and the duration of pneumoperitoneum. Conclusions: The duration and level of intraabdominal pressure are responsible for changes of hepatic function during laparoscopic procedures. Although no symptom appears in patients with normal hepatic function, patients with severe hepatic failure should probably not be subjected to prolonged laparoscopic procedures. Received: 23 May 1997/Accepted: 28 October 1997     

Pneumoperitoneum risk prognosis and correction of venous circulation disturbances in laparoscopic surgery

Background: This study was initiated to find a method of determining the prognosis for possible changes in hemodynamic and respiratory parameters in patients with pneumoperitoneum (PP). Methods: We devised a model for a pseudopneumoperitoneum (PPP), which is created by encircling the wide pneumochamber on the entire abdomen and inflating it to a preset pressure. To verify the prognostic possibilities of the proposed model, we studied the pneumotachygraphy parameters, noninvasive and invasive monitoring parameters of PPP after induction of anaesthesia, and venous circulation disturbances, as well as the medical effect of the intermittent sequential compression device. Results: In healthy patients, the restrictive lung syndrome did not approach the risky limit. In patients ≥60 years old, this syndrome was very close to the limit. In a number of patients with serious cardiovascular and pulmonary pathology, the pressure of >10 mmHg was considered to be intolerable. Lung compliance, which was the parameter most sensitive to the increased intraabdominal pressure, was 47 ± 10 at baseline, and 29 ± 4 (p > 0.05) at both PPP and real PP (14 mmHg). Conclusions: The PPP model is quite similar to the real PP and can be used for preoperative prognosis in laparoscopic surgery. The elevated intraabdominal pressure results in a significant disturbance of venous blood flow in the lower extremities. The use of the device for peristaltic pneumomassage of the lower limbs is effective in correcting negative changes in venous hemodynamics in laparoscopic surgery. Received: 28 July 1997/Accepted: 12 January 1998     

Alterations in hemodynamics and left ventricular contractility during carbon dioxide pneumoperitoneum

Background: Carbon dioxide (CO₂) pneumoperitoneum has been shown to adversely affect hemodynamics in patients. This study specifically examines the potential contribution of altered left ventricular contractility (LVC) to hemodynamic changes observed during CO₂ pneumoperitoneum. Methods: In a canine model, LV volumes, LV pressure, and intrathoracic and central venous pressures were recorded both at basal intra-abdominal pressure (IAP) and after CO₂ insufflation to produce IAPs of 5–25 mmHg. Results: At IAPs greater than 15 mmHg, cardiac output and LV end-diastolic volume decreased. Mean arterial pressure and heart rate were unchanged. LVC, quantified using the linear Frank-Starling relationship, was not affected by increases in IAP. Conclusions: This study is the first to quantify LVC during CO₂ pneumoperitoneum and demonstrates no changes in contractility over IAPs from 5 to 25 mmHg. In the dog model, any hemodynamic alterations induced by CO₂ pneumoperitoneum are secondary to altered LV preload and not alterations in contractility or LV afterload. Received: 8 March 1996/Accepted: 23 April 1996     

Elucidating the relationship between cardiac preload and renal perfusion under pneumoperitoneum

Introduction Pneumoperitoneum is associated with a well-described decrease in renal blood flow, but it remains unclear whether a decrease in cardiac preload is responsible. Our aim was to characterize the relationship between cardiac preload and renal perfusion during pneumoperitoneum. Methods Eleven pigs were submitted to three 30 minute study periods: 1) Baseline (n=11): no interventions, 2) Pneumoperitoneum (n=11): 12 mmHg CO2 pneumoperitoneum, 3) Preload Reduction: pneumoperitoneum and nitroglycerin infusion (n=8); or pneumoperitoneum and hemorrhage to a mean arterial pressure (MAP) of 40 mmHg (n=3). Echocardiographic measurements of left ventricular end-diastolic diameter (LVEDD) were used as an index of preload. Renal cortical perfusion (RCP) was measured using laser doppler flowmetry. Results LVEDD decreased from 4.2 ± 0.5 to 4.1 ± 0.6 cm (p=0.02) with pneumoperitoneum and then to 4.0 ± 0.5 cm (p=0.03) with the addition of nitroglycerin. There was no statistically significant change in RCP with pneumoperitoneum (33.5 ± 8.4 to 28.5 ± 8.4 ml/min/100g tissue, p=0.2), but it decreased to 18.5 ± 11.3 ml/min/100g tissue (p=0.001) with the addition of nitroglycerin. The correlation between RCP and LVEDD was weak (0.35, p=0.003), whereas correlation between RCP and MAP was superior (R=0.59, p<0.0001). Conclusions While decreasing preload under extreme lab conditions also decreases RCP, simply creating a pneumoperitoneum of 12 mmHg does not. The decrease in renal blood flow associated with pneumoperitoneum is likely not solely a function of preload.     

Hemodynamic and arterial blood gas changes during carbon dioxide and helium pneumoperitoneum in pigs

The effects of pneumoperitoneum with carbon dioxide and helium on systemic hemodynamics and arterial blood gases were investigated in pigs in an attempt to clarify the mechanisms by which pneumoperitoneum may induce organ dysfunction. A total of 16 anesthetized female pigs underwent pneumoperitoneum with carbon dioxide or helium (n=8 each) in a stepwise fashion to intraabdominal pressures of 8, 10, 12, 16, and 20 mmHg. Changes in cardiac output; renal and hepatic blood flow; mean arterial, mean pulmonary arterial, mean pulmonary arterial wedge, inferior vena caval, and portal venous pressures; and total peripheral resistance were measured. Arterial blood samples were obtained at the same time the above parameters were determined. Urine volume was measured as an indicator of renal function. Pneumoperitoneum with either carbon dioxide or helium significantly increased venous pressures and simultaneously decreased cardiac output. These changes were associated with decreases in organ blood flow due to increased peripheral resistance. Urinary output was reduced to a similar degree in the two groups. Blood gas analysis revealed pneumoperitoneum-induced metabolic acidosis in both groups, although hypercapnia was observed only in the carbon dioxide group. These findings suggest that pneumoperitoneum-related organ dysfunction may be due to increased intraperitoneal pressure rather than to hypercapnia.     

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Background: Although many aspects of laparoscopic surgery have been determined, the question of which insufflation gas is the best arises repeatedly. The aim of this study was to review the findings on the major gases used today in order to provide information and guidelines for the laparoscopic surgeon. Methods: We reviewed the literature for clinical and laboratory studies on the currently used laparoscopic insufflation gases: carbon dioxide (CO₂), nitrous oxide (N₂O), helium (He), air, nitrogen (N₂), and argon (Ar). The following parameters were evaluated: acid–base changes, hemodynamic and respiratory sequelae, hepatic and renal blood flow changes, increase in intracranial pressure, outcome of venous emboli, and port-site tumor growth. Results: The major advantage of CO₂ is its rapid dissolution in the event of venous emboli. Hemodynamic and acid–base changes with CO₂ insufflation usually are mild and clinically negligible for most patients. Although N₂O is advantageous for procedures requiring local/regional anesthesia, it does not suppress combustion. Findings show that Ar may have unwanted hemodynamic effects, especially on hepatic blood flow. There are almost no hemodynamic or acid-base sequelae with the use of He, air, and N₂, but they dissolve slowly and carry a potential risk of lethal venous emboli. Conclusions: Clearly, CO₂ maintains its role as the primary insufflation gas in laparoscopy, but N₂O has a role in some cases of depressed pulmonary function or in local/regional anesthesia cases. Other gases have no significant advantage over CO₂ or N₂O and should be used only in protocol studies. The relation of port-site metastasis to a specific type of gas requires further research. Received: 16 January 2000/Accepted: 15 March 2000/Online publication: 22 August 2000     

Laparoscopic insufflation of the abdomen reduces portal venous flow

Background: The adverse effects of sustained elevated intraperitoneal pressure (IPP) on cardiovascular, pulmonary and renal systems have been well documented by several reported experimental and clinical studies. Alteration in the splanchnic circulation has also been reported in animal experiments, but details of the exact hemodynamic changes in the flow to solid intraabdominal organs brought on by a raised intraperitoneal pressure in the human are not available. The aim of the present study was to estimate effect of increased IPP on the portal venous flow, using duplex Doppler ultrasonography in patients undergoing laparoscopic cholecystectomy. Methods: The studies were performed using the SSD 2000 Multiview Ultrasound Scanner and the UST 5536 7.0-MHz laparoscopic transducer probe. Details of the measurements were standardized in according to preset protocol. Statistical evaluation of the data was conducted by the two-way analysis of variance (ANOVA). Results: The flow measurement data have demonstrated a significant (p < 0.001) decrease in the portal flow with increase in the intraperitoneal pressure. The mean portal flow fell from 990 ± 100 ml/min to 568 ± 81 ml/min (−37%) at an IPP of 7.0 mmHg and to 440 ± 56 mmHg (−53%) when the IPP reached 14 mmHg. Conclusions: The increased intraperitoneal pressure necessary to perform laparoscopic operations reduces substantially the portal venous flow. The extent of the volume flow reduction is related to the level of intraperitoneal pressure. This reduction of flow may depress the hepatic reticular endothelial function (possibly enhancing tumor cell spread). In contrast, the reduced portal flow may enhance cryo-ablative effect during laparoscopic cryosurgery for metastatic liver disease by diminishing the heat sink effect. These findings suggest the need for a selective policy, low pressure or gas-less techniques to positive-pressure interventions, during laparoscopic surgery in accordance with the disease and the therapeutic intent. Received: 19 March 1996/Accepted: 4 July 1997     

The effect of carbon dioxide pneumoperitoneum on free radicals

Background: Carbon dioxide is usually preferred as the insufflating agent for laparoscopic surgery because it is readily available, noncombustible, and chemically stable. It is still questionable, however, if CO₂ pneumoperitoneum has any effect on free radicals and lipid peroxidation. The purpose of this study was to investigate the possible effects of CO₂ pneumoperitoneum on free radicals and lipid peroxidation in the erythrocytes of rats. Methods: Fifty male Sprague-Dawley rats were divided into five equal groups: controls, a sham-operation group, and three groups of 5, 10, or 15 mmHg pneumoperitoneum with CO₂. At the end of the procedure, blood was collected and the erythrocytes were separated from the plasma. The resultant supernatant fractions of erythrocytes were assayed for superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA). Results: SOD activities of the 5 and 10 mmHg pneumoperitoneum groups were significantly lower than those of the sham operation group. SOD activity was greater in the 15 mmHg pneumoperitoneum group than in any of the other groups, and this activity was significantly different from that seen in the 5 and 10 mmHg pneumoperitoneum groups (p < 0.05). No significant changes were observed in the CAT activities of the study groups (p > 0.05). MDA level was increased in the 5 mmHg pneumoperitoneum group; this result was statistically different from the control and 15 mmHg pneumoperitoneum groups (p < 0.05). No significant differences were found in the CAT activities for the study groups. On the other hand, the SOD activities of the 5 and 10 mmHg pneumoperitoneum groups were significantly lower than those of the sham and the 15 mmHg pneumoperitoneum group (p < 0.05 for all comparisons). Conclusions: These results indicate that CO₂ pneumoperitoneum applied with 5–10 mmHg pressure increases the formation of free oxygen radicals by inhibiting SOD activity and that the accumulation of free radicals elevates the level of MDA, a metabolite of lipid peroxidation. The effect of CO₂ pneumoperitoneum on free radicals and lipid peroxidation is pressure-dependent in rats. The mechanism underlying this pressure dependency is still under investigation. Received: 16 December 1999/Accepted: 14 February 2000/Online publication: 10 May 2000     

Pneumoperitoneum with carbon dioxide enhances liver metastases of cancer cells implanted into the portal vein in rabbits

Background: Little is known about the role of the CO₂ pneumoperitoneum on tumor cells that spread from the portal system into the liver during laparoscopic surgery for gastrointestinal malignancies. Therefore, we designed a study to investigate the effect of CO₂ pneumoperitoneum on cancer cells implanted in the portal vein in a rabbit model. Methods: Immediately after intraportal inoculation of 2.5 × 10⁵ cells of VX₂ cancer, the rabbits received either CO₂ pneumoperitoneum at a pressure of 10 mmHg for 30 min (pneumoperitoneum group, n= 14) or laparotomy alone for 30 min (laparotomy group, n= 14). Results: The number (p < 0.01) and area of cancer nodules (p= 0.045) on the liver surface on day 17 were greater in the pneumoperitoneum group than in the laparotomy group. The frequency of cancer nodules >3.0 mm in diameter was higher in the pneumoperitoneum group than in the laparotomy group (p < 0.001). Conclusions: Compared with laparotomy, CO₂ pneumoperitoneum enhanced the development of liver metastases in this experimental model. Received: 9 December 1998/Accepted: 3 April 1999     

Hemodynamic consequences of high- and low-pressure capnoperitoneum during laparoscopic cholecystectomy

Background: Peritoneal insufflation to 15 mmHg diminishes venous return and reduces cardiac output. Such changes may be dangerous in patients with a poor cardiac reserve. The aim of this study was to investigate the hemodynamic effects of high (15 mmHg) and low (7 mmHg) intraabdominal pressure during laparoscopic cholestectomy (LC) Methods: Twenty patients were randomized to either high- or low-pressure capnoperitoneum. Anesthesia was standardized, and the end-tidal CO₂ was maintained at 4.5 kPa. Arterial blood pressure was measured invasively. Heart rate, stroke volume, and cardiac output were measured by transesophageal doppler. Results: There were 10 patients in each group. In the high-pressure group, heart rate (HR) and mean arterial blood pressure (MABP) increased during insufflation. Stroke volume (SV) and cardiac output were depressed by a maximum of 26% and 28% (SV 0.1 > p > 0.05, cardiac output p > 0.1). In the low-pressure group, insufflation produced a rise in MABP and a peak rise in both stroke volume and cardiac output of 10% and 28%, respectively (p < 0.05). Conclusions: Low-pressure pneumoperitoneum is feasible for LC and minimizes the adverse hemodynamic effects of peritoneal insufflation. Received: 23 May 1997/Accepted: 11 March 1998     

Effect of insufflation gas and intraabdominal pressure on portal venous flow during pneumoperitoneum in the rat

BACKGROUND: Carbon dioxide, the primary gas used to establish a pneumoperitoneum, causes numerous systemic effects related to cardiovascular function and acid-base balance. Therefore, the use of other gases, such as helium, has been proposed. Furthermore, the pneumoperitoneum itself, with the concomitant elevation of intraabdominal pressure, causes local and systemic effects that have been only partly elucidated. Portal blood flow, which plays an important role in hepatic function and cell-conveyed immune response, is one of the affected parameters. METHODS: An established animal model (rat) of laparoscopic surgery was extended by implanting a periportal flow probe. Hemodynamics in the portal vein were then measured by transit-time ultrasonic flowmetry during increasing intraabdominal pressure (2-12 mmHg) caused by gas insufflation (carbon dioxide vs helium). RESULTS: The installation of the pneumoperitoneum with increasing intraperitoneal pressure led to a significant linear decrease in portal venous flow for both carbon dioxide and helium. At higher pressure levels (8-12 mmHg), portal blood flow was significantly lower (1.5-2.5-fold) during carbon dioxide pneumoperitoneum. An intraabdominal pressure of 8 mmHg caused a decrease to 38.2% of the initial flow (helium, 59.7%); whereas at 12 mmHg, portal flow was decreased to 16% (helium, 40.5%). CONCLUSION: Elevated intraabdominal pressure generated by the pneumoperitoneum results in a reduction of portal venous flow. This effect is significantly stronger during carbon dioxide insufflation. Portal flow reduction may compromise hepatic function and cell-conveyed immune response during laparoscopic surgery.