The Extraperitoneal Approach and Subcutaneous Emphysema are Associated with Greater Absorption of Carbon Dioxide During Laparoscopic Renal Surgery

@)22-5347/95/1543-0959$03.00/0

Vol. 154.959-963, September 1995 Printed in U S A .

JOURNAL OF UROLOGY

Copyright 0 1995 by AMEMCANUROLOCICAL ASSOCIATION, hc.

THE EXTRAPERITONEAL APPROACH AND SUBCUTANEOUS EMPHYSEMA ARE ASSOCIATED WITH GREATER ABSORPTION OF CARBON DIOXIDE DURING LAPAROSCOPIC RENAL SURGERY J. STUART WOLF, JR.,*,t TERRI G. MONK, ELSPETH M. McDOUGALL, BRUCE L. McCLENNAN AND RALPH V. CLAYMAN From the Departments of Surgery, Division of Urology, Radiology and Anesthesiology, Washington University School of Medicine, St.Louis, Missouri

ABSTRACT

Purpose: We investigated the association of carbon dioxide absorption with the approach (transperitoneal versus extraperitoneal) and other factors during laparoscopy. Materials and Methods: Carbon dioxide elimination during laparoscopic renal surgery was retrospectively calculated in 63 patients. Results: Carbon dioxide elimination increased with time. Multiple factorial analysis revealed that subcutaneous emphysema and the extraperitoneal approach were independently associated with a greater increase in carbon dioxide elimination. Pneumothorax and pneumomediastinum were more common during extraperitoneal procedures. Conclusions: Carbon dioxide absorption during laparoscopic renal surgery increases with time, and is greatest in patients treated through an extraperitoneal approach and in those with subcutaneous emphysema. Nonetheless, with attentive ventilatory management adverse sequelae of hypercapnia can be avoided. KEY WORDS:laparoscopy, emphysema, carbon dioxide, kidney

The extraperitoneal approach to urological laparoscopy, compared to the transperitoneal approach, has several surgical implications. Advantages of the extraperitoneal approach include direct access to extraperitoneal organs, less need for visceral retraction, elimination of the risk of inhperitoneal contamination with tumor or infection and lack of peritoneal irritation by insufnated carbon dioxide. Disadvantages consist of a smaller working space, and more difficult identificationand exposure of some anatomical structures. Ongoing clinical investigationswill determine the optimal indications for the extraperitonealapproach in urological laparoscopy. Carbon dioxide absorption during laparoscopy represents an important consideration. Experimental and clinical evidence supports an increase and decrease in carbon dioxide absorption during extraperitoneal laparoscopy compared to transperitoneal laparoscopy.13 Circumstances that have been associated with a greater degree of carbon dioxide absorption include prolonged insdilation time,4-8 higher insufflation pressure9-11 and subcutaneous emphysema.1214 The actual value of interest, carbon dioxide absorption,cannot be measured directly. Carbon dioxide elimination, which is the sum of metabolic carbon dioxideproduction and absorption at steady state, is a reasonable measure of carbon dioxide absorption if the partial pressure of arterial carbon dioxide is kept fairly constant. This figure is reported by most investigators.2.1620 In our retrospective study we calculated carbon dioxide elimination based upon data from intraoperative anesthetic records to investigate the associationof carbon dioxide absorption with the laparoscopicapproach and other factors. MATERIALS AND METHODS

Patients undergoing laparoscopic renal surgery from June 1990 through July 1994 a t our university m e d i d center were identified. To obtain a relatively homogeneous patient

population for comparison, only procedures that involved total or near total mobilization of the kidney were included. All procedures were performed with the patient under general anesthesia. Following endotracheal intubation the patients were ventilated with an aidoxygen mixture. Nitrous oxide was not used. Clinical practice at this institution includes adjustment of ventilation during laparoscopy to maintain an end-tidal carbon dioxide pressure of 35 -t 5 mm. Hg. Positive endexpiratory pressure was used at the discretion of the anesthesiologist. The techniques for transperitoneal and extraperitoneal laparoscopic renal surgery have been described previously.21.m Briefly, initial insutllation was usually performed with a Veress needle placed at an abdominal location (for transperitoneal laparoscopy), or at the inferior lumbar triangle or off the tip of the 12th rib (for extraperitoneal laparoscopy). A balloon, usually fashioned from the finger of a large sterile surgical glove tied over the end of a red rubber catheter, was inflated with 11. saline to distend the operative space in all but the initial 2 cases of extraperitoneal laparoacopy. Carbon dioxide was routinely i n s d a t e d a t a pressure limit of 12 to 15 mm. Hg. Retrospective inspection of each operative record allowed for categorization of the lapamscopic approach as extraperitoned, transperitoneal or combined. To be included in the extraperitoneal group all operative manipulation had to be performed solely in the extraperitoneal space without frank entry into the peritoneal cavity. If the procedure started with intraperitoneal insdilation and placement of a single port only for the purpose of observing balloon distension of the retroperitoneal space, after which the peritoneal cavity was desdilated and never again entered while the procedure was performed in the extraperitoneal space, the data were included in the extraperitoneal category. If, however, after operating in the extraperitoneal space, the peritoneal cavity was widely entered either by reflecting the colon or by completing the procedure with transperitoneal pelvic surgery, the data were included in the combined category and excluded from further analysis. The approach in all other cases was considered to be transperitoneal.

Accepted for ublication March 3, 1995. *American poundation for Urologic Disease Resemh Scholar 1994-1996. ?Requests for re rints: 4989 Bamee Hoepital Plaza, weeny Louie, Missouri 63110. Tower, Suite 5101, 959

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960

CARBON DIOXIDE ABSORPTION DURING RENAL LAF'AROSCOPY

In this retrospective study we were unable to measure directly the total amount of carbon dioxide expired by patients during laparoscopy. Instead the carbon dioxide elimination was estimated using routinely recorded parameters. The anesthetic record for each case documented the respiratory rate in breaths per minute, expired tidal volume in ml. per breath and end-tidal carbon dioxide pressure in mm. Hg every 15 minutes from intubation to extubation. For each 15-minute interval carbon dioxide elimination was calculated in ml. per minute per kg. with the equation: carbon dioxide elimination -

end-tidal carbon dioxide pressure X

PB - PWO

expired tidal volume

x respiratory rate x VWt, where Wt is patient weight in kg., P, is barometric pressure (760 mm. Hg) and PHZ0is the partial pressure of water vapor (13 mm. Hg). Others have shown that oxygen consumption and metabolic carbon dioxide production are fairly constant during laparoscopy.2.18.20Thus, any changes in carbon dioxide elimination can be assumed to be due to changes in carbon dioxide absorption. The mean carbon dioxide elimination was calculated for the entire pre-insutnation period and each hour of the first 4 hours of insufflation. For comparisons with time, we used the mean hourly carbon dioxide elimination. We compared the single greatest hourly carbon dioxide elimination in each patient (peak carbon dioxide elimination) for determination of overall between-group differences. Chest radiographs obtained in the recovery room immediately following laparoscopy were reviewed in a blinded fashion by 1 of us (B. L. M.)to determine the presence or absence of subcutaneous emphysema, pneumothorax or pneumome-

groups the Wilcoxon signed rank test was applied. The chisquare test (or Fisher's exact test if an expected value was less than 5) was used to compare proportions of categorical data between patient p u p s . To assess the association of carbon dioxide elimination with continuous variables Spearman's rank correlation was used. A screening model was first applied to identify the most important factors associated with increases in carbon dioxide elimination. After selecting the potentially significant factors, we used a standard least squares model of multiple factorial analysis to determine the

erolysis or ureterectomy, not involving total or near total renal mobilization were not included in the analysis. From June 1990 through July 1994, 75 laparoscopic renal procedures fitting the criteria for our study were performed at our university medical center. All kidneys in this series were in the normal position, such that all laparoscopic procedures were performed in the lumbar and subdiaphragmatic regions of the retroperitoneum. Of the patients 5 were excluded because of incomplete information on the anesthetic record. Of the 70 evaluable patients 7 had a combined extrapentoned transperitoneal approach to laparoscopy, thereby also excluding them from analysis. The procedures in the remaining 63 patients included nephrectomy in 41 (transperitoneal in 28 and extraperitoneal in 13),transperitoneal nephroureterectomy in 6, radical nephrectomy in 4 (transperitoneal in 3 and extraperitoneal in l),nephropexy in 4 (transperitoneal in 3 and extraperitoneal in l),transperitoneal pyeloplasty in 3, extraperitoneal partial nephrectomy in 3 and extraperitoneal wedge resection of a renal lesion in 2. Thus, the transperitoned approach was used in 43 instances and the extraperitoneal approach in 20. The laparoscopic procedure was converted to an open operation during 2 transperitoneal nephrectomies and 1 extraperitoneal partial nephrectomy but sufficient data were accumulated during the laparoscopic portions of the cases for analysis. In 4 patients data for the calculation of the pre-insufflation carbon dioxide elimination were not available, although the carbon dioxide elimination during laparoscopy could be calculated. The median and mean insufflation times in the series were 5.0 hours (range 2.0 to 8.5),with 75% of the procedures exceeding 4 hours. The laparoscopic approach was not statistically associated with patient age, sex, presence of chronic obstructive pulmonary disease, M A class, obesity, use of a pneumo-dissector, total insufflation time, use of positive end-expiratory pressure, arteriallend-tidal carbon dioxide gradient, intraoperative in-

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All Patients

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961

CARBON DIOXIDE ABSORPTION DURING RENAL LAPAROSCOPY

TABLE1. Single factor analysis of variables related to peak increase in carbon dioxide elimination No. PtS.*

Characteristic

Mean Yes No

~

~

~~~~

~

Carbon Dioxide

No, Expiration (mlJmioJ

Difference in Mean Increase Mean at

TABLE2. Subemuos bv aoorwch and subcutaneous ernohvsema

'k$;zbn

Characteristic

%,.

p Valuet

Elimination (ml./min./kg.)

19 40 2.28 0.0004 Extrapentoned 34 10 3.27 <0.0001 Subcutaneous emphysema 7 37 2.16 0.0098 pneumomediastinud pneumothorax 50 6 1.65 0.0500 Not obese* 38 21 0.32 0.7040 Female pts. 5 54 0.65 0.2311 Chronic obstructive pulmonary disease ASA class 1 or I1 46 13 0.57 0.2493 Simple nephrectomy 37 22 0.06 0.8754 29 30 0.90 0.1333 Lt. side pneumo-dissector 8 51 0.47 0.6420 pos. end-expiratory pressure 7 52 2.43 0.3249 postop. cardiopulmonary 4 55 1.46 0.1317 complications 48.0 0.6446 Age (yrs.) Total insufilation time (hrs.) 5.0 0.5673 Intraop. intravenous fluids (cc) 3,934 0.7214 Intraop. urine output (cc) 529 0.8634 ArteriaYend-tidal carbon dioxide 9.32 0.0582 gradient (mm.Hg) * In 4 patients no pre-inadation values were recorded. AU 4 patients had subcutaneous emphysema and 2 had pneumomediastindpneumothorax. t Association between the characteristic and the increase in carbon dioxide expiration at peak. $ No height was recorded in 3 patients, and so we were unable to calculate body mass index.

neal approach and subcuheow emphysema was statistically significant. Although there was a trend for subcutaneous emphysema to develop more oRen during extraperitoneal laparoscopy (94% versus 71% in the tranaperitoneal group), the a m + ciation did not achieve statistical significance (p = 0.0744). Table 2 shows the relationships among carbon dioxide elimination, laparoscopic approach and presence or absence of subcutaneous emphysema. Likewise, figure 2, A illustrates the increase in carbon dioxide elimination with time, comparing the transperitoneal with the extraperitoneal approaches. There was a significant increase in carbon dioxide elimination from 1 hour to the next in the transperitoneal group for all intervals. The same interval changes in carbon dioxide elimination were significant only up to 2 hours in the extraperitoneal group. The 2 groups were significantly different from each other at all points after insufnation except at 4 hours. Figure 2, B reveals the differences in carbon dioxide elimination between patients who did and did not have subcutaneous emphysema, with the difference between the groups being significant at all points. In patients who did and did not have subcutaneous emphysema the interval increases in carbon dioxide elimination were significant during

ks.)

p Value*

Preoo. Peak % Increase ~~

~~

~

~

Extraperitoneal Transperitoneal

19 3.48 8.17 40 3.95 6.35

135 61

Subcutaneousemphysema Nosubcutaneousemphysema

34 3.76 7.99 10 3.62 4.57

113 26

O.OOO4


Extraperitoneal andsubcuta- 15 3.48 8.89 156 neous emphysema Extraperitoneal and no subcu- 1 2.30 4.55 98 taneous emphysema Transperitonealandsubcuta- 19 3.99 7.27 82 neous emphysema Transperitonealandnosubcu- 9 3.77 4.57 21
the first 2 hours and the first hour, respectively. When the approach and presence or absence of subcutaneous emphysema were combined, the 4 groups had widely different carbon dioxide absorptions (table 2). The carbon dioxide elimination increases at peak among the 3 groups with more than 1 subject were all significantly different from each other (Bonferroni-adjustedWilcoxon rank sum test). The effects of the extraperitoneal approach and subcutaneous emphysema were separate and additive, such that patients approached through the extraperitoneal route who also had subcutaneous emphysema experienced more than 7 times greater increases in carbon dioxide elimination (155%) compared to those with intraperitoneal insflation without subcutaneous emphysema (21%). Of the 48 patients who had postoperative chest radiographs 9 with subcutaneous emphysema had a pneumomediastinwn or pneumothorax. Ofthe thoracic gas collections 2 occurred in the transperitoneal group (6%) and 7 in the extraperitoneal group (41%, p = 0.0059). One patient had a pneumothorax without concurrent pneumomediastinum. This patient underwent the first extraperitoneal laparoscopic nephrectomy in December 1990.The pneumothorax was secondary to direct puncture of the pleura with a trocar placed in a supracostal position. Of the remaining 8 patients 2 had pneumomediastinum and pneumothorax, and the rest had pneumomediastinum only (fig. 3). There were 5 patients (8%)with postoperative cardiopulmonary complications. The patient with surgical pleural injury required a tube thoracostomy for 3 days. Congestive heart failure producing pulmonary edema developed in 2 patients early in the series before there was an appreciation

A

FIG.2. Increase in carbon dioxide elimination (VCO2)in atients grouped by lapaxympic approach 64)and [email protected] or absence of subcutaneous emphysema (B). Error bars are standard error of mean. Asterisks indxate sipficant mcrease from reylous interval. Dotted represents increase in carbon dioxide elimination in all patients. +, significant difference between 2 curves. preopemtively.

k,

962

CARBON DIOXIDE ABSORPTION DURING RENAL LAPAROSCOPY

aparoscopic cholecystectomy, Mullett et a1 noted that the ncrease in carbon dioxide elimination at peak was 76%in ;he extraperitoneal group and 25% in the transperitoneal qoup.2 This finding suggests that the extraperitoneal approach may result in greater carbon dioxide absorption than the transperitoneal route. Also included in their report were 10 patients undergoing transperitoneal gynecological laparoscopy who had a mean increase in carbon dioxide elimination at peak of only 15%,implying that the operative site may also have a role in carbon dioxide absorption. Wakizaka et found partial pressure of arterial carbon dioxide to increase with i n s f l a t i o n time greater than 60 minutes and pressure greater than 10 cm. water in patients undergoing laparoscopic cholecystectomy.1l They reported as well that partial pressure of arterial carbon dioxide increased more in obese patients, contrary to our findings. In our series obese patients began with carbon dioxide elimination of 352 ml. per minute compared to 258 ml. per minute in nonobese patients (p = 0.0565). The peak values of carbon dioxide elimination without correction for weight in obese and nonobese patients were 506 and 467 ml. per minute, respectively (p = 0.5379). FIG.3. Chest radiograph in 69-year-old man after extraperitoneal Thus, although absolute peak carbon dioxide elimination valla aroscopic right wedge resection. Subcutaneous emphysema is vis- ues were higher in obese patients, the increase from the ibfe on right side and pneumomediastinum is demonstrated by gas pre-insumation carbon dioxide elimination when corrected density along heart border (arrows). for weight was higher in the nonobese patients (3.10 ml. per minute per kg. in nonobese patients versus 1.45 ml. per minute per kg. in obese patients, p = 0.0500). Smiths and Motew'o e t a1 found carbon dioxide absorption of the decreased urine output and fluid requirement during to increase stepwise with increasing insufflation pressure. laparoscopy. Both patients were administered more than 13 Sosa et a1 studied patients undergoing transperitoneal lapacckg. per hour of intravenous fluid intraoperatively and both roscopic pelvic lymphadenectomy, and reported that the parreceived blood transfusions. In our most recent 40 patients tial pressure of arterial carbon dioxide exceeded 50 mm. Hg the intraoperative intravenous fluid administration aver- in all 7 with and only 1 of 9 without subcutaneous emphyseaged 10.8 cckg. per hour. One patient experienced a small ma.l3 pulmonary embolus postoperatively. Thoracentesis of an ipOur findings confirm that 3 factors (duration of insufllasilateral pleural effusion in this patient produced a n iatro- tion, extraperitoneal approach and development of subcutagenic pneumothorax necessitating a brief course of tube tho- neous emphysema) are important determinants of carbon racostomy drainage. The final pulmonary complication dioxide absorption. Comparison of these patients to a group occurred in a n elderly man with ASA class IV status who died undergoing pelvic laparoscopy at our institution suggests an of the adult respiratory distress syndrome, myocardial in- association with another factor a s well, that is operative farction and cardiac arrhythmia following nephroureterec- site.25 The increase in carbon dioxide elimination a t peak tomy and return to the operating room for hemorrhage. Pul- during pelvic laparoscopy averaged 53%, compared to the monary complications were not associated with the increase 80% increase noted during renal laparoscopy. This effect of in carbon dioxide elimination and no complications were operative site was significant even after controlling for laparelated to hypercapnia. No procedures were aborted because roscopic approach, insufflation time and subcutaneous emof hypercapnia although on a few occasions, predominantly physema, presumably due to the more extensive dissection in the extraperitoneal group, the insufflation pressure briefly performed during renal as opposed to pelvic laparoscopy, was lowered to 8 to 10 mm. Hg to decrease carbon dioxide exposing more tissue surface area to gas with subsequent absorption and allow for more effective ventilation. greater capacity for gas absorption. We were unable to address yet another factor noted in previous studies, that 1s DISCUSSION insumation pressure, because of the routine use of 12 to 15 Several investigators have found that carbon dioxide ab- mm. Hg pressure limit in our series. sorption increases with time during laparoscopy.4-8 Our data The nature of our data collection and calculation predissupport their observations that the rate of increase in ab- poses to several types of error. The data in the anesthetic sorption with time was greatest early in the procedure, with record might have been incorrectly recorded. Periodic data the increase in carbon dioxide absorption leveling off towards collection might not adequately approximate the sum of conthe end of the insufflation period (fig. 1). This is not to be tinuous carbon dioxide elimination. The end-tidal carbon dlconfused with the lack of significant association between oxide pressure might not truly represent expired alveolar the increase in carbon dioxide elimination a t peak and the carbon dioxide pressure because physiological dead space total insufflation time in our series, which is due to the was not calculated, and the equilibrium between arterial and prolonged insufflation time in all of our patients. Paradox- expired carbon dioxide was not assessed in all patients. ically, the carbon dioxide elimination decreased in the Nonetheless, any sources of error would have applied equally extraperitoneal group from hours 3 to 4 of insufflation, to each patient group. During transperitoneal IaparoscoPY? which may be a statistical anomaly. However, it also may increases in carbon dioxide elimination from 7 to 26%)haye represent accumulated leakage of gas into the peritoneal been reported.z>15-2"The greater percent increase noted In cavity through small peritoneotomies, with subsequent our study reflects the prolonged insufflation time in Om change in absorption rate towards that similar t o intra- patients (mean 5 hours in our series, versus mean 22 minutes peritoneal gas. in other reports ) and the extensive operative manipulatio*! In a prospective study comparing carbon dioxide elimi- which included exposure of a large area of upper retropennation between patients undergoing extraperitoneal lapa- toneal tissue regardless of the approach. roscopic pelvic lymphadenectomy and transperitoneal Despite the large increases i n ciirhon dioxide elimination

CARBON DIOXIDE ABSORPTION DURING RENAL LAPAROSCOPY

noted in our study, there were few cardiopulmonary compliations and none was related to hypercapnia. The 5 patients with chronic obstructive pulmonary disease endured laparosCOPYwithout clinical difficulty, although the greater arterial/ end-tidal carbon dioxide gradient in these patients (16.0mm. H g versus 8.6 mm. Hg, p = 0.0159) suggests that they were less able to expire the absorbed carbon dioxide because of the relatively larger dead space-to-tidal volume ratio. Other investigations also have documented greater partial pressure of arterial carbon dioxide and arterialfend-tidal carbon dioxide gradient during carbon dioxide laparoscopy in patients or experimental animals with preoperative pulmonary d y s h c tion.26-28 Multiple factor analysis in our patients revealed that pneumomediastinum, pneumothorax and positive endexpiratory pressure were associated with greater arterial/ end-tidal carbon dioxide gradients, although to a lesser degree than chronic obstructive pulmoniuy disease. In patients with increasing arterialfend-tidal carbon dioxide gradients carbon dioxide elimination might underestimate carbon dioxide absorption. The greater incidence of pneumomediastinum and pneumothorax in patients undergoing extraperitoneal insufflation is not surprising. The potential routes of gas into thoracic spaces are more easily exposed by extraperitoneal gas.= That pneumothorax was noted in our patients only following pneumomediastinum (in the absence of direct surgical injury) suggests that direct passage of gas into the pleural cavity, as noted by some investigators?O is less likely than passage from the mediastinum through the pulmonary hilus.31 As would be expected with pneumothoraces due to carbon dioxide, no patient required thoracostomy in the absence of direct surgical injury. Therefore, chest radiographs after extraperitoned laparoscopy need to be obtained only in cases of a suspected high trocar insertion or pulmonary symptoms, since all other thoracic gas collections appear to be c l i n i d y insignificant. CONCLUSIONS

Subcutaneous emphysema and extraperitoneal insflation are strongly and independently associated with a greater degree of carbon dioxide absorption during laparoscopic renal surgery. The greatest increases in carbon dioxide elimination occur during the first 2 hours of insflation. Laparoscopic renal surgery in general is associated with greater carbon dioxide absorption than is noted during laparoscopic pelvic surgery. Clinically asymptomatic pneumomediastinum and pneumothorax occur more often during extraperitoneal laparoscopy. Despite high levels of carbon dioxide absorption in our series, with careful management of intraoperative ventilation no patient suffered clinical sequelae of hypercapnia. REFERENCES

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