RETROPERITONEOSCOPIC SURGERY IS NOT ASSOCIATED WITH INCREASED CARBON DIOXIDE ABSORPTION

0022-5347/99/1624-1268/0

Val 162, 1268-1272, October 1999 Printed in U S A.

THE JobmvK OF UROLOGY Copyright 0 1999 by AMERICAN UROLOGICAL &SOCL4TIO~., INC.

RETROPERITONEOSCOPIC SURGERY IS NOT ASSOCIATED WITH INCREASED CARBON DIOXIDE ABSORPTION CHRISTOPHER S. NG, INDERBIR S. GILL," GYUNG TAK SUNG, DAVID G. W W L E Y , RUFFIN GRAHAM AND DANA SCHWEIZER From the Section of Laparoscopic and Minimally Inuasive Surgery, Department of Urology, and Departments of Anesthesiology and Radiology, Cleveland Clinic Foundation, Cleueland, Ohio

ABSTRACT

Purpose: Previous studies have suggested that retroperitoneal laparoscopy is associated with greater carbon dioxide absorption and related postoperative morbidity, such a s subcutaneous emphysema and pneumothorax. We prospectively compared the effects of carbon dioxide absorption during transperitoneal and retroperitoneal laparoscopic renal and adrenal surgery at our institution. Materials and Methods: Data were collected prospectively on 5 1 patients who underwent laparoscopic renal (26) or adrenal (25) surgery via the transperitoneal (18) or retroperitoneal(33) approach from September 1997 to February 1998. Results: There was no significant difference in carbon dioxide elimination in patients who underwent transperitoneal laparoscopy compared to retroperitoneoscopy a t any interval. Subcutaneous emphysema occurred in 12.5% of the transperitoneal and 45% of the retroperitoneal group (p = 0.09). Patients with subcutaneous emphysema had greater carbon dioxide elimination during the first 2.5 hours of insufflation compared to those without subcutaneous emphysema and, thereafter, carbon dioxide elimination decreased to baseline. Conclusions: In contrast to previous reports our prospective nonrandomized study suggests that retroperitoneoscopy is not associated with greater carbon dioxide absorption compared to transperitoneal laparoscopy. Patients with subcutaneous emphysema exhibited only transient increases in carbon dioxide absorption above control levels. KEY WORDS:carbon dioxide, absorption, peritoneum, laparoscopy, surgery

through February 1998 at our institution. Laparoscopic procedures selected for inclusion in the study were relatively comparable in the amount of tissue dissection required, and included adrenalectomy, donor nephrectomy, radical nephrectomy, simple nephrectomy and nephroureterectomy. None of these procedures was converted to open surgery. Other laparoscopic procedures performed during this period but excluded from study were renal cyst marsupialization and renal cryoablation, both of which required much less tissue dissection and mobilization than the study procedures. Following routine preoperative evaluation all patients underwent laparoscopic surgery with general endotracheal anesthesia. Nitrous oxide was not used. A steady state of end tidal carbon dioxide pressure was carefully maintained, and positive end expiratory pressure was used at the discretion of the anesthesiologist. The techniques for transperitoneal and retroperitoneal laparoscopy have been previously described. In the transperitoneal group pneumoperitoneum was established by the closed (Veress needle) technique. Then 4 or 5 ports were placed to perform the procedure. Conversely, in the retroperitoneal group access was gained by the open technique through a 1.5 cm. skin incision at the tip of the 12th rib. A stab incision was made in the anterior thoracolumbar fascia and an index finger was used to enter the retroperitoneal space bluntly. Following finger dissection a trocar mounted dilator balloon was used to create atraumatiMATERIALS AND METHODS cally an adequate working space in the retroperitoneum. The Data were collected prospectively on 51 consecutive pa- dilator balloon was removed, and a 10 or 12 mm. Bluntip* tients undergoing transperitoneal or retroperitoneal laparo- cannula was secured as the primary port. This cannula comscopic renal andor adrenal surgery from September 1997 prises an external adjustable foam cuff and internal circular fascial retention balloon. The fascial retention balloon was positioned within the retroperitoneal space and inflated with Accepted for publication May 28, 1999.

The retroperitoneal approach to laparoscopic renal and adrenal surgery has certain advantages compared to transperitoneal laparoscopy.' Intra-abdominal viscera remain untouched, theoretically minimizing postoperative ileus, reducing the risk of injury to bowel, liver, or spleen and obviating peritoneal contamination. The expeditious access to the renal hilum during laparoscopic simple and radical nephrectomy is a major advantage of the retroperitoneoscopic approach. Although there is some evidence that operative time and hospital stay may be decreased with the retroperitoneal approach, prospective comparison with transperitoneal laparoscopy has not been performed to our knowledge. However, retroperitoneoscopy may be technically more challenging due to the smaller operative field and proximity of port sites. Furthermore, prior reports have suggested that patients have greater absorption of carbon dioxide with the retroperitoneal or extraperitoneal approach compared to transperitoneal laparoscopy, and demonstrate an increased incidence of carbon dioxide related morbidities, such as subcutaneous emphysema, pneumomediastinum and pneumothorax.2 We prospectively collected data on nonrandomized patients undergoing retroperitoneal and transperitoneal laparoscopic renal a n d o r adrenal surgery to determine relative carbon dioxide absorption, and the incidence of subcutaneous emphysema, pneumothorax and pneumomediastinum.

Requests for reprints: Section of Laparoscopic and Minimally Invasive Surgery, 9500 Euclid Ave., A-100,Cleveland, Ohio 44195. 1268

* Origin Medsystems, Menlo Park, California.

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RETROPERITONEOSCOPIC SURGERY AND CARBON DIOXIDE ABSORPTION

30 cc air. The external foam cuff was snugly cinched down, effectively sealing the subcutaneous tissues and muscle layers around the primary port site, thus minimizing air leak. Pneumoretroperitoneum was established (15 mm. Hg carbon dioxide) and 2 or 3 secondary ports were placed under laparoscopic visualization. All procedures were performed a t 1 institution by the same surgeon. Carbon dioxide absorption per se cannot be measured directly during the course of surgery. Furthermore, oxygen consumption and metabolic carbon dioxide production are relatively constant during l a p a r o s ~ o p y .Therefore, ~,~ changes in carbon dioxide elimination accurately reflect changes in carbon dioxide absorption. Carbon dioxide elimination (ml./ kg. per minute) can be calculated using the equation

where ETCO, is end tidal carbon dioxide pressure in mm. Hg, TV is expired tidal volume in ml., RR is respiratory rate is per minute, P, is barometric pressure (760 mm. Hg), P,, partial pressure of water vapor (13 mm. Hg) and Wt is patient weight in kilograms. This method has been validated in prior studies.2 The end tidal carbon dioxide pressure, tidal volume and respiratory rate were recorded by the anesthesiologist every 30 minutes from the time of endotracheal intubation until extubation. Carbon dioxide elimination was calculated from the data on the anesthesia record for the entire pre-insufflation and insufflation periods. Time 0 represents the average carbon dioxide elimination before insufflation, 0.5 represents the carbon dioxide elimination during the first half hour of insufflation and so on. At the end of the procedure the surgeon recorded the presence or absence of subcutaneous emphysema by finger palpation in every case. Chest radiographs were obtained immediately postoperatively in the recovery room in all patients, specifically t o evaluate for subcutaneous emphysema, pneumothorax, pneumomediastinum and pleural effusion. All films were reviewed by 1 radiologist (R. G.) in a blinded fashion. Chest radiographs could not be located for 4 patients who, thus, were excluded from the study. Other information used in data analysis, such as age, sex, American Society of Anesthesiologists (ASA) status, body mass index, operative time, history of chronic obstructive pulmonary disease and tobacco use, was obtained prospectively from our patient database. Student’s 2-tailed t test assuming equal variances and Fisher’s exact test were used to compare data in each group with p c0.05 considered significant. Statistical analysis was performed using standardized computer software. RESULTS

TAnm 2. Comparison between the transperitoneal and retroperitoneal approaches Transperitoneal Retroperitoneal p Value*

_____

No. pts. 18 33 Mean age lyrs.) 57.9 60.8 No. men 14 15 Mean ASA status 2.83 2.94 Mean body mass index (kg./m.2) 29.6 29.5 Mean surgical time (mins.) 191.9 213.2 No. chronic obstructive pulmo2 3 nary disease No. smokers 9 11 No. chest radiography findings: Subcutaneous emphysema 2 14 Pneumothorax 0 0 Pneumomediastinum 0 It Mean carbon dioxide elimination 2 SE (ml.Ag./mins.): 0 Hr. 2.9 2 0.2 2.8 2 0.1 0.5 Hr. 3.3 t 0.2 3.3 5 0.2 1.0 Hr. 3.7 i 0.3 3.8 i 0.3 1.5 Hrs. 4.1 i 0.4 4.0 i 0.3 2.0 Hrs. 4.0 2 0.3 4.0 Z 0.3 2.5 Hrs. 4.0 2 0.3 4.0 ? 0.3 3.0 Hrs. 3.9 i 0.3 3.9 5 0.3 * Significant at p <0.05. t Patient was clinically asymptomatic and required no treatment.

0.57 0.04 0.56 0.98 0.29 1.00 0.37 0.09 1.00 1.00 0.30 0.46 0.45 0.45 0.45 0.49 0.46

presence of co-morbidities, such as chronic obstructive pulmonary disease and tobacco use. There were significantly more men in the transperitoneal group (p = 0.04). Carbon dioxide elimination was plotted with time for all patients (fig. 1 and table 3). Irrespective of approach, for our entire study population carbon dioxide elimination increased with time during the first hour of insufflation and then remained at a plateau for the remainder of the procedure. There was a statistically significant increase during the first 30 minutes of insufflation only. Carbon dioxide elimination in the transperitoneal and retroperitoneal groups was calculated and plotted with time (table 2). Figure 2 depicts a similar increase in carbon dioxide elimination with time in each group. In the retroperitoneal group there was a significant increase in carbon dioxide elimination (p = 0.04) during the first 30 minutes of insufflation, as in the entire study population. However, there was no statistically significant difference between the retroperitoneal and transperitoneal groups at any interval. Chest radiography findings are listed in table 2. Subcutaneous emphysema was noted in 12.5%of transperitoneal and 6.0

5.0

Baseline demographics for the transperitoneal and retroperitoneal groups are presented in tables 1 and 2. There were no statistically significant differences between the groups in regard to age, ASA status, body mass index, operative time or ‘3.0

.

O

TABLE1. Procedures performed on the study population Procedure Transperitoneal: Adrenalectomy Donor nephrectomy Nephroureterectomy Totals Retroperitoneal: Adrenalectomy Radical nephrectomy Simple nephrectomy Nephroureterectomy Totals

No. Procedures 15 2 1 18 10 11 4 8 33

*../

1 .o

0.0

‘

0

1

2

3

lasufflatirntime~0

FIG. 1. Carbon dioxide elimination (VC02)in all patients. Aster. isk represents significant increase (p c0.05) from prevlous time.

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RETROPERITONEOSCOPIC SURGERY AND CARBON DIOXIDE ABSORPTION

I

TABLE3. Carbon dioxide elimination in all 51 patients Time (hrs.)

Mean Carbon Dioxide Elimination 2 SE

p Value*

(ml./kgJminS.)

*

*

*

2.8 2 0.1 Not applicable 0.5 3.3 2 0.2 0.01 1.0 3.8 2 0.2 Not sigmficant 1.5 4.0 2 0.2 Not significant 2.0 4.02 0.2 Not significant 2.5 4.0 2 0.2 Not significant 3.0 3.9 2 0.2 Not significant * Each interval was compared to the previous interval, with p ~0.05considered significant. 0

6.0

5.0 "O

0.0

I J

0

2

1

3

4

Insufflation tim (horn)

FIG. 3. Carbon dioxide elimination (VCOZ) in patients with and without subcutaneous (subcut.)emphysema, and all patients. Asterisk represents significant (p <0.05) difference between curves.

=O

TABLE4. Comparison between patients with and without subcutaneous emphysema on immediate postoperative chest radiography

1

Subcutaneous No Subcutaneous Emohvsema EmDhvsema

-.0

1

2

3

Insufflationtim(hours)

FIG.2. Carbon dioxide elimination (VCOZ)in patients who underwent retroperitoneal or transperitoneal laparoscopy. Asterisk represents significant increase (p (0.05) from previous time in retroperitoneal group only.

45% of retroperitoneal cases, which was not significantly different (p = 0.09). Radiographically detected, clinically asymptomatic pneumomediastinum was noted in only 1renal transplant recipient who underwent bilateral retroperitoneoscopic native nephrectomy with an operative time of 330 minutes, and required no treatment. Pneumothorax was not noted in any patient. Carbon dioxide elimination curves in patients with and without subcutaneous emphysema, and in all patients are compared in figure 3. There was a significant increase in carbon dioxide elimination in patients with (16) compared to those without (31) subcutaneous emphysema during the first 150 minutes of insufflation (table 4). However, this effect rapidly tapered to control levels during the next half hour. Baseline parameters of patients with and without subcutaneous emphysema were comparable, except that there were more women (p = 0.01) and lower body mass index (p = 0.02) among the former (table 4).

No. pta. Mean age (yrs.) No. men Mean ASA status Mean body mass index (kgJm.2) Mean surgical time (mins.) No. chronic obstructive pulmonary disease No. smokers Mean carbon dioxide elimination 2 SE (mlJkg./mins.): 0 Hr. 0.5 Hr. 1.0 Hr. 1.5 Hrs. 2.0 H n . 2.5 Hrs. 3.0 Hrs. 3.5 Hrs. 4.0 Hrs. * Significant at >0.05.

16 66.8 5 3.00 26.3 199.6 2 7 3.1 2 0.4 3.62 1.9 4.1 2 1.8 4.5 ? 3.3 4.5 2 3.0 4.6 2 2.7 4.22 1.8 3.7 2 1.2 3.8 2 1.0

31 56.3 22 2.87 31.3 214.2 3 11 2.72 0.6 3.2 2 1.0 3.3 2 1.1 3.5 2 1.6 3.6 2 1.6 3.6 5 1.5 3.7 2 1.3 3.72 1.0 3.7 2 0.7

Value*

0.06 0.01 0.50 0.02 0.48 1.00

0.75 0.15 0.23 0.04 0.03 0.04 0.02 0.23 0.98 0.71

No clinically significant carbon dioxide related sequelae OcCulTed in any patient. Intraoperatively carbon dioxide elimination was similar between the transperitoneal and retroperi-

toned groups at all intervals, including 0,1,2 and 3 hours. On immediate postoperative chest radiography subcutaneous emphysema was noted in 12.5%of the transperitoneal and 45% of the retroperitoneal group (p = 0.09).Irrespective of the laparoscopic approach, patients with had higher carbon dioxide elimination during the initial 2.5 hours of insufflation compared to those without evidence of subcutaneous emphysema. However, DISCUSSION this elevation was transient and resolved spontaneously soon Although we analyzed a nonrandomized comparison be- thereafter. Asymptomatic pneumothorax and/or pneumometween transperitoneal and retroperitoneal laparoscopy, data diastinum occurred in none of the 18 patients in the transregarding carbon dioxide related parameters were obtained peritoneal and in 1 of 33 in the retroperitoneal group (p = prospectively in all 51 patients undergoing major renal and 1.00). adrenal surgery. Baseline demographics were similar beCarbon dioxide elimination was used as an indirect meastween the groups, except that there were more men in the urement of carbon dioxide absorption. As described previtransperitoneal group. Men and women were not signifi- ously this calculated value is a direct function of 2 dynamic cantly different in age, body mass index, operating time or parameters measured by the anesthesiologist during intubaASA status. tion, namely end tidal carbon dioxide pressure and minute

RETROPERITONEOSCOPIC SURGERY AND CARBON DIOXIDE ABSORPTION

1271

ventilation (tidal volume multiplied by respiratory rate). toneal membrane may have a greater absorptive capacity.12 Therefore, changes in any of these parameters will affect the Coupled with the larger space and, therefore, greater absorpamount of carbon dioxide eliminated at any given time. Fur- tive area available in the peritoneal cavity, this finding may thermore, intraoperative adjustments of minute ventilation explain the greater systemic absorption of carbon dioxide and positive end expiratory pressure by the anesthesiologist during intraperitoneal insufflation. serve to keep blood carbon dioxide levels in a steady state, Wolf et a1 retrospectively reviewed 63 patients who underdespite occasional increases in end tidal carbon dioxide pres- went laparoscopic renal surgery during the previous 4 years sure. In turn, when anesthesiologists at our institution rec- and compared the transperitoneal (43) with the extraperitoognize rising end tidal carbon dioxide levels during a trans- neal or retroperitoneal (20) approach.2 Carbon dioxide elimperitoneal or retroperitoneal laparoscopic procedure, tidal ination was calculated using methodology similar to that volume and respiratory rate are immediately adjusted (usu- used in our study. Retroperitoneoscopic access was obtained ally increased) to maintain a steady state level. In this situ- by the Veress needle technique. Mean insuflation time was ation, although end tidal carbon dioxide pressure is relatively 5 hours. Carbon dioxide elimination increased with time in unchanged, carbon dioxide elimination is clearly increased all of their patients and the extraperitoneal approach was since minute ventilation has increased. However, for our associated with greater carbon dioxide elimination than the purposes any such adjustments would impact the transperi- transperitoneal approach. They also reported a higher incitoneal and the retroperitoneal groups in a similar manner, dence of subcutaneous emphysema (94 versus 71%) and thereby maintaining the validity of our comparison. pneumomediastinum or pneumothorax (41 versus 6%) on Carbon dioxide elimination was calculated from meas- postoperative chest radiography in the retroperitoneal group. urements taken every 30 minutes during intubation. Fleet- Furthermore, patients with subcutaneous emphysema exhibing adjustments of respiratory rate and tidal volume by the ited sustained increases in carbon dioxide elimination. In our study retroperitoneoscopic surgery was not associanesthesiologist between measurements may have occurred but we believe that these minor fluctuations would have no ated with increased carbon dioxide elimination or related significant effect on the overall trends in carbon dioxide sequelae. There are significant technical differences between elimination. Furthermore, although we cannot provide data our study and that of Wolf et al. We prefer the open (Hasson) in this regard, we believe that the choice of anesthetic agent technique of obtaining retroperitoneoscopic access followed does not have any significant bearing on the overall carbon by direct placement of a balloon dilator, while they used the closed (Veress) technique followed by random placement. We dioxide absorption during laparoscopic surgery. The majority of clinical studies on the effects of carbon believe that precise placement of the dilator balloon during dioxide insufflation during laparoscopy are based on obser- the initial creation of a retroperitoneal working space may be vations during laparoscopic cholecystectomy,”6 and gyneco- important not only for affording excellent operative exposure, logical and urological transperitoneal and extraperitoneal but also for minimizing the incidence of pneumothorax and pelvic laparoscopy,7 including laparoscopic pelvic lymph node pneumomediastinum. During simple and radical retroperitodissection. Cardiovascular effects of intraperitoneal carbon neoscopic adrenalectomy and nephrectomy we currently dioxide insufflation include decreased cardiac index and place the balloon dilator between Gerota’s fascia (anteriorly) stroke volume, and increased diastolic blood pressure, mean and the psoas fascia (posteriorly). If the balloon is dilated arterial pressure and heart rate. Others have demonstrated posterior to the psoas fascia, thereby denuding the psoas a decrease in lung and chest wall compliance during trans- muscle of its investing fascia, there may be an increased peritoneal laparoscopy.5 Subcutaneous emphysema has been potential for carbon dioxide to track cephalad along the psoas noted after laparoscopic cholecystectomy and gynecological muscle fibers into the thoracic cavity, resulting in pneumolaparoscopy. In a larger series subcutaneous emphysema and mediastinum or pneumothorax. In addition, mean surgical pneumothorax were more common after extraperitoneal pel- (insufflation) time was 5 hours in the series of Wolf et a1 and 3.5 hours in our study. vic laparoscopy.8 A simple fact bears consideration when comparing carbon However, few studies examine the effects of carbon dioxide insufflation during laparoscopic renal andor adrenal sur- dioxide absorption during major renal or adrenal transperigery. Furthermore, direct comparisons between the trans- toneal and retroperitoneal laparoscopic surgery. During peritoneal and retroperitoneal approaches are scarce. Al- transperitoneal laparoscopic radical nephrectomy, for examthough some controversy exists, there is increasing evidence ple, the ipsilateral line of Toldt is incised and the retroperithat the extraperitoneal approach may have some inherent toneum is entered within the initial 30 minutes of the proadvantages from a hemodynamic and cardiorespiratory view- cedure. During the ensuing 3 to 4 hours of laparoscopy point.9-11 Giebler et a1 characterized the cardiovascular ef- surgical dissection and mobilization are performed largely of fects of retroperitoneal and transperitoneal carbon dioxide the retroperitoneal organs, adipose tissue and fascia1 planes. insufflation in mechanically ventilated pigs (9 in each group). Thus, during more than 75% of the procedure the entire They demonstrated greater increases in cardiac output, pul- peritoneal cavity and retroperitoneal areas are exposed to monary artery pressure, iliac venous pressure and inferior carbon dioxide gas at pressures of 10 to 15 mm. Hg. Therefore, the potential region for systemic absorption of carbon vena caval pressure in the transperitoneal g r o ~ pFurther.~ more, transperitoneal carbon dioxide insufflation was asso- dioxide is large, and includes the transperitoneal and retrociated with increased peak airway pressures and decreased peritoneal areas. However, during retroperitoneal laparoscopy carbon dioxide insufflation is performed exclusively in airway compliance. In a randomized comparison Bannenberg et a1 performed the retroperitoneal space, which is a much smaller area for intraperitoneal and extraperitoneal insufflation in 16 pigs for carbon dioxide absorption. Furthermore, no obvious perito1hour at 15 mm. Hg pressure.l* Animals were mechanically neotomies were noted during our 33 retroperitoneoscopic proventilated at a steady rate of 12 breaths per minute without cedures. However, minute undetected peritoneotomies alany adjustments during the study period to determine the most certainly occur during retroperitoneoscopy, and a true differences between the 2 approaches. The extraperito- combined pneumoperitoneum and pneumoretroperitoneum neal approach was associated with a significantly lower in- may result, akin to the transperitoneal approach. Thus, the only additional factor for enhanced systemic crease in central filling pressures, end tidal carbon dioxide, arterial carbon dioxide pressure and respiratory acidosis. carbon dioxide absorption during retroperitoneoscopy is the Wolf et a1 noted that if insufflation is limited to the retroper- increased potential for subcutaneous emphysema. If port site itoneal space, absorption of carbon dioxide appears to be air leak and the resultant subcutaneous air tracking during reduced compared to intraperitoneal insufflation.* The peri- retroperitoneoscopy can be eliminated or minimized, carbon

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RETROPERITONEOSCOPIC SURGERY AND CARBON DIOXIDE ABSORPTION

dioxide absorption during retroperitoneoscopy should logically be no greater than that during a comparable transperitoneal laparoscopic procedure. We attribute our decreased incidence of subcutaneous emphysema during retroperitoneoscopy to the use of the Bluntip cannula as the primary port. The 1.5 cm. primary port incision in the flank abdominal wall is secured in an airtight manner by inflating the internal fascia1 retention balloon a n d cinching down the external adjustable foam cuff of the cannula. Use of this device has significantly decreased air leak during retroperitoneoscopy in our hands. Before we started using this cannula more than 2 years ago, port site a i r leak a n d subcutaneous emphysema were routine occurrences during retroperitoneoscopic procedures. Unfortunately, d a t a from these earlier cases are not available, precluding a n y objective comparison with our current experience. Additional experience at other centers will be necessary t o confirm these impressions. Interestingly, as reported by others,2 we also observed a significantly lower body mass index ( p = 0.02) in patients with subcutaneous emphysema intraoperatively. Whether t h e abundance of subcutaneous adipose tissue i n the markedly obese (body mass index greater than 30 kg./m.') confers a protective effect from carbon dioxide related sequelae during laparoscopy or the voluminous subcutaneous f a t makes it more difficult to diagnose subcutaneous emphysema remains t o be determined. Retroperitoneoscopy is a safe a n d effective approach to laparoscopic renal a n d adrenal surgery. No major cardiopulmonary complications occurred as a result of carbon dioxide related sequelae a n d no postoperative interventions were necessary. CONCLUSIONS

Our prospective nonrandomized study suggests that retroperitoneoscopic renal a n d adrenal surgery i s not associated with greater carbon dioxide absorption compared t o similar transperitoneal laparoscopy. Patients with subcutaneous emphysema exhibited only transient, self-limited increases in carbon dioxide elimination above control levels. Insufflation time w a s less than 4 hours in more than 70% of cases, which may have contributed to the overall low incidence of postoperative carbon dioxide related sequelae. A prospective randomized study is necessary to confirm these findings.

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7. Casati, A., Valentini, G., Gerrari, S., Senatore, R., Zangrillo, A. and Toni, G.: Cardiorespiratory changes during gynecological laparoscopy by abdominal wall elevation: comparison with carbon dioxide pneumoperitoneum. Brit. J. Anesth., 78: 51, 1997. 8. Wolf, J. S., Carrier, S. and Stoller, M. L.: Intraperitoneal versus extraperitoneal insufflation of carbon dioxide gas for laparoscopy. J. Endourol., 9 63, 1995. 9. Giebler, R. M., Kabatnik, M., Stegen, B. H., Scherer, R. U., Thomas, M. and Peters, J.: Retroperitoneal and intraperitoneal C02 insufflation have markedly different cardiovascular effects. J. Surg. Res., 68: 153,1997. 10. Chiu,A. W., Chang, L. S., Birkett, D. H. and Babayan, R. K.: The impact of pneumoperitoneum, pneumoretroperitoneum, and gasless laparoscopy on the systemic and renal hemodynamics. J. Amer. COILSurg., 181: 397, 1955. 11. Bannenberg, J.J.,Rademaker, B. M., Froeling, F. M. and Meijer, D. W.: Hemodynamics during laparoscopic extra- and intraperitoneal insufflation. An experimental study. Surg. Endo., 11: 911,1997. 12. Collins, J.: Inert gas exchange of subcutaneous and intraDeritoneal gas pockets in piglets. Respir. Physiol., 46 391,1981.