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Obstetrics & Gynecology 2000;95:704-709
© 2000 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Risk Factors for Hypercarbia, Subcutaneous Emphysema, Pneumothorax, and Pneumomediastinum During Laparoscopy

CYNTHIA M. MURDOCK, MD, ARMAND J. WOLFF, MD and THOMAS VAN GEEM, MD

From the Department of Obstetrics and Gynecology, Creighton University School of Medicine, Omaha, Nebraska; and the Department of Pulmonary and Critical Care Medicine, Georgetown University School of Medicine, Washington, DC.

Address reprint requests to: Cynthia M. Murdock, MD 5999 Harpers Farm Road #W-200 Columbia, MD 21044


   Abstract
Top
Abstract
Materials and Methods
 Results
 Discussion
 References
 
Objective: To determine independent predictors for the development of hypercarbia, subcutaneous emphysema, pneumothorax, and pneumomediastinum during laparoscopy.

Methods: We reviewed 968 laparoscopic cases between January 1, 1997, and December 31, 1998. Patients who had hypercarbia (end-tidal carbon dioxide of 50 mmHg or greater), pneumothorax/pneumomediastinum, and subcutaneous emphysema were compared with controls according to age, operative time, type of surgery, extraperitoneal or intraperitoneal approach, preexisting medical conditions, body mass index, sex, use of Hasson technique, and number of surgical ports. Maximum positive end-tidal CO2 (PETCO2) was added as an independent variable for subcutaneous emphysema, pneumothorax, and pneumomediastinum. Data were analyzed using univariate analysis and then subjected to multivariate analysis using multiple logistic regression analysis.

Results: Incidence rates were 5.5% for hypercarbia, 2.3% for subcutaneous emphysema, and 1.9% for pneumothorax/pneumomediastinum. Independent risk factors for development of hypercarbia were operative time greater than 200 minutes (odds ratio [OR] 2.02), patient age greater than 65 years (OR 2.19), and Nissen fundoplication surgery (OR 3.18). Predictors of the development of subcutaneous emphysema were greater than 50 mmHg (OR 3.49), PETCO2 operative time greater than 200 minutes (OR 5.27), and the use of six or more surgical ports (OR 3.06). Variables that predicted the development of pneumothorax and/or pneumomediastinum were PETCO2 greater than 50 mmHg (OR 4.15) and operative time greater than 200 minutes (OR 20.49).

Conclusion: Longer operative times, higher maximum measured end-tidal CO2, greater number of surgical ports, older patient age, and Nissen fundoplication surgery predispose patients to hypercarbia-related complications during laparoscopy.

During the past 20 years, laparoscopy has become a useful tool in both gynecologic and general surgery. It has evolved from a diagnostic tool to a method of performing complex surgical procedures. Laparoscopic procedures are considered relatively safe and noninvasive; however, there exists a small but important risk of developing complications related to insufflation with carbon dioxide (CO2) gas. These include hypercarbia, subcutaneous emphysema, pneumothorax, and pneumomediastinum. Surgeons and anesthesiologists must be aware of the possibility of these complications and which patients are at higher risk of developing them.

Several case reports in the literature1–5 offer hypotheses on factors that place patients at risk for hypercarbia, subcutaneous emphysema, pneumothorax, and pneumomediastinum. Possible risk factors related to surgical technique include preperitoneal insufflation6–8 and improper trocar placement with leakage of CO2 into subcutaneous tissue.1,4 It has been shown clearly that the increase in arterial CO2 pressure (PaCO2) during laparoscopy primarily results from diffusion of CO2 from the peritoneal cavity.9 Type of surgery6 as well as degree of dissection around the diaphragm and in the retroperitoneal space6 might also be important. Possible patient risk factors include age and concurrent cardiopulmonary disease.10,11 Other authors have suggested that very small congenital defects in the diaphragm could predispose certain patients to pneumothorax and pneumomediastinum.1,12,13 A pleuroperitoneal communication was shown in a patient with ascites.14 Insufflated gas can also reach the pleural space through the vena caval orifice in the diaphragm.15–17

To determine which variables predict the development of hypercarbia, we used the outcome variables subcutaneous emphysema, pneumothorax, and pneumomediastinum, as they have been shown to be indicators of hypercarbia. Capnographic expiratory CO2 levels have evolved as a safety monitor for ventilation problems, cardiac output, distribution of pulmonary blood flow, and metabolic activity during anesthesia. The use of positive end-tidal CO2 (PETCO2) as a marker for hypercarbia during laparoscopy is dependent on the relationship between arterial and alveolar CO2 levels. Any change in CO2 elimination can be assumed to correspond to a change in CO2 absorption since oxygen consumption and metabolic CO2 production are fairly constant during laparoscopy.18 Most studies have been anecdotal case reports that infer risk factors. We studied all laparoscopies performed at our institution during a 2-year period in order to determine objective risk factors for hypercarbia, subcutaneous emphysema, and pneumothorax/pneumomediastinum during laparoscopy.


   Materials and Methods
Top
Abstract
 Materials and Methods
Results
 Discussion
 References
 
We reviewed the records of all patients who had laparoscopy between January 1, 1997, and December 31, 1998, at St. Joseph’s Hospital, Creighton University Medical Center in Omaha, Nebraska. A total of 1064 laparoscopies were done during that time, and 968 charts were available for review. No charts were excluded, although some had missing categoric or numeric data. Patients with pneumothorax, pneumomediastinum, subcutaneous emphysema, or hypercarbia were compared retrospectively with controls according to age, operative time, type of surgery, preperitoneal or intraperitoneal approach, preexisting medical conditions, body mass index (BMI), sex, use of the Hasson technique, PETCO2, and number of surgical ports. Body mass index was calculated from height and weight, which were obtained from the nursing record. Significant medical history, defined as cardiac disease, chronic lung disease, hypertension, and cancer, was obtained from the admission history and physical examination. Type of surgery was categorized into one of the following five groups: all gynecologic procedures, Nissen fundoplication, hernia repair, cholecystectomy, or all other general surgical procedures. Nissen fundoplication consists of a 360° plication of the gastric fundus around the lower esophagus according to the technique described by Hinder et al.19 Number of ports, use of the Hasson cannula, and preperitoneal and intraperitoneal insufflation were obtained from the surgical record. Length of surgery and maximum PETCO2 level were obtained from the anesthesia record. Because the minute ventilation might be increased significantly by the anesthesiologist to overcome an elevated PETCO2, we used a single value to define hypercarbia. Hypercarbia is generally defined as PaCO2 higher than 45 mmHg.18 As the PETCO2-PaCO2 gradient is 3–5 mmHg,20–22 and up to 7 mmHg23 in some studies, we used a PETCO2 of 50 mmHg or greater to represent hypercarbia. The presence of subcutaneous emphysema was confirmed by chest x-ray or physical examination. The presence or absence of pneumothorax or pneumomediastinum was confirmed by chest x-ray. Chest x-rays were done only in cases in which there was clinical suspicion of pneumothorax (ie, cases with abrupt onset of increased PETCO2 levels, increased peak airway pressure accompanied by a decrease in dynamic lung compliance, or diminished breath sounds on auscultation).

Previously studied variables that we did not include were intraabdominal pressure settings and Trendelenburg positioning. Motew et al9 showed that complications do not occur until intraabdominal pressure exceeds 20 mmHg. Maximum pressure settings under 20 mmHg have been used at our institution since 1997. Sufficient data regarding Trendelenburg positioning were not available.

Data were analyzed utilizing SigmaStat statistical software version 2.0 and SPSS 8.0 (SPSS Inc., Chicago, IL). Kruskal-Wallis analysis of variance on ranks was performed on numeric data, with PETCO2 of 50 mmHg or greater, subcutaneous emphysema, pneumothorax, and pneumomediastinum as dependent variables. Positive end-tidal CO2 was also used as an independent variable against the outcome variables subcutaneous emphysema and pneumothorax/pneumomediastinum. {chi}2 testing was used to compare categoric data with the outcome variables PETCO2 of 50 mmHg or greater, subcutaneous emphysema, pneumothorax, and pneumomediastinum. For purposes of analysis, the presence of either pneumothorax or pneumomediastinum was considered a single outcome. Numeric data that showed significance on univariate analysis were categorized for multiple logistic regression analysis. The following binomial categories were created on the basis of clinical utility and outcomes of univariate analysis: PETCO2 of 50 mmHg or greater, operative time more than 200 minutes, age greater than 65 years, and the use of six or more operative ports. Multiple logistic regression analysis was used to identify independent risk factors for hypercarbia, pneumothorax/pneumomediastinum, and subcutaneous emphysema during laparoscopy, with P < .05 considered statistically significant.


   Results
Top
Abstract
 Materials and Methods
 Results
Discussion
 References
 
Of 968 laparoscopies, there were 53 (5.5%) cases of hypercarbia, 22 (2.3%) cases of subcutaneous emphysema, and 19 (1.9%) cases of pneumothorax and/or pneumomediastinum. Table 1Go shows results of univariate analysis for the outcome hypercarbia. Prolonged operative time, increased number of operative ports, older age, and Nissen fundoplication surgery were all significantly associated (P < .001) with hypercarbia. Table 2Go shows results of univariate analysis for the outcome subcutaneous emphysema. Prolonged operative time, older age, increased PETCO2, increased number of operative ports, and Nissen fundoplication were significantly associated (P < .05) with subcutaneous emphysema.


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  		Table 1. Baseline Characteristics and Potential Determinants for Hypercarbia
 

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  		Table 2. Baseline Characteristics and Potential Determinants for Subcutaneous Emphysema
 
Cholecystectomy and Hasson cannula usage were not significantly associated with subcutaneous emphysema. Table 3Go presents univariate analysis for the combined outcome pneumothorax/pneumomediastinum. Increased operative time, greater number of operative ports, older age, increased maximum end-tidal CO2, and Nissen fundoplication surgery were significantly associated (P < .001) with pneumothorax and/or pneumomediastinum. Gynecologic surgery and cholecystectomy were not significantly associated with pneumothorax/pneumomediastinum. Hypercarbia was also evaluated as an independent variable against the outcomes subcutaneous emphysema and pneumothorax/pneumomediastinum and was significantly associated (P < .001) with the development of either (Tables 2Go and 3Go).


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  		Table 3. Baseline Characteristics and Potential Determinants for Pneumothorax/Pneumomediastinum
 
Results of multiple logistic regression analysis are shown in Table 4Go. Operative time greater than 200 minutes was an independent risk factor for hypercarbia, subcutaneous emphysema, and pneumothorax/pneumomediastinum. Maximum PETCO2 of 50 mmHg or greater predicted a greater likelihood of developing subcutaneous emphysema, pneumothorax, and/or pneumomediastinum. The use of six or more operative ports predicted subcutaneous emphysema. Patient age over 65 years and Nissen fundoplication surgery were associated with a higher risk of hypercarbia.


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  		Table 4. Independent Predictors for Hypercarbia, Subcutaneous Emphysema, and Pneumothorax/Pneumomediastinum
 

   Discussion
Top
Abstract
 Materials and Methods
 Results
 Discussion
References
 
We identified several factors that can alert the surgeon and anesthesiologist that a patient undergoing laparoscopic surgery is at risk of hypercarbia, subcutaneous emphysema, pneumothorax, or pneumomediastinum. Although all of those complications are related to insufflation of the abdomen with CO2, the etiology of each has subtle differences, and each has individual identifiable risk factors.

Independent risk factors for the development of hypercarbia (PETCO2 of 50 mmHg or greater) are operative time greater than 200 minutes, patient age over 65 years, and Nissen fundoplication surgery. Other authors have shown that there is a trend toward increased CO2 absorption with increased duration of insufflation.8,24 An increased incidence of hypercarbia was seen in older patients, independent of preexisting medical conditions. This may be partially caused by declining lung function with age.25 Medical conditions such as cardiac disease, pulmonary disease, hypertension, and cancer were not associated with an increase in subcutaneous emphysema, pneumothorax/pneumomediastinum, or hypercarbia. Wittgen et al11 demonstrated an increase in arterial CO2 levels and a decrease in arterial pH in patients with preexisting cardiopulmonary disease who had laparoscopy, but the difference in PETCO2 was not significant. They hypothesized that PETCO2 levels do not accurately reflect PaCO2 results. However, several other studies20–22 have shown the PETCO2-PaCO2 gradient to be only 3–5 mmHg.20–22 The difference found by Wittgen et al11 actually could have been a result of the small number of patients in that study. Previous investigators6 found a relationship between low BMI and increases in CO2 elimination, suggesting that weight might influence the development of hypercarbia, subcutaneous emphysema, or pneumothorax/pneumomediastinum. Our data found no association between BMI and these outcomes.

Risk factors for the development of subcutaneous emphysema were maximum end-tidal CO2 of 50 mmHg or greater, the use of six or more operative ports, and operative time over 200 minutes. Other authors have shown a strong association between high PETCO2 and subcutaneous emphysema.6,8 Subcutaneous emphysema caused by insufflation with CO2 results in increased CO2 absorption through subcutaneous tissues, with a final outcome of hypercarbia and increased PETCO2. The etiology of subcutaneous emphysema is most likely leakage of insufflated gas into the subcutaneous tissue. An increase in the number of surgical ports also increases the number of points of entry of CO2 gas into the subcutaneous tissue. Several authors have established a link between preperitoneal insufflation and extensive retroperitoneal dissection with the development of subcutaneous emphysema and resultant hypercarbia.3,6–8,26 We were unable to show this type of association, most likely because of the small number of procedures performed at our institution using preperitoneal insufflation. Further, no procedures were performed where significant retroperitoneal dissection was involved.

Risk factors for pneumothorax/pneumomediastinum are maximum end-tidal CO2 of 50 mmHg or greater and operative time greater than 200 minutes. A recent review of the literature27 showed that the rate of pneumothorax during laparoscopic Nissen fundoplication was 2%. The prevalence in our study for pneumothorax/pneumomediastinum during Nissen fundoplication was 9.7%. Several mechanisms of CO2 pneumothorax have been suggested. Congenital diaphragmatic defects could allow leakage of CO2 gas into the pleural cavities.15,17 There have also been reports of hydrothorax associated with ascites14 and peritoneal dialysis.28 Regression analysis did not identify Nissen fundoplication surgery as an independent risk factor for pneumothorax/pneumomediastinum. The high association of Nissen fundoplication with pneumothorax might be a result of the length of the surgical procedure rather than extensive diaphragmatic dissection. The average length of Nissen fundoplication in our study was 227 minutes, which would result in a 20-fold increased incidence of pneumothorax/pneumomediastinum based on procedure length alone.

The incidence rates for subcutaneous emphysema during laparoscopy vary from 0.43% to 2.34%.29,30 Incidence rates for pneumothorax and pneumomediastinum have not been reported. Because these complications can go unrecognized intraoperatively, the true incidence might be higher than expected. Wolf et al6 found 34 of 44 (77%) patients who had laparoscopic surgery to have subcutaneous emphysema on postoperative chest x-ray, nine of them with concomitant pneumomediastinum. In laparoscopic cases confined to urologic procedures, Wolf et al8 reported a 9% pneumomediastinum rate, and a 34% rate of subcutaneous emphysema on standard postoperative chest x-ray. McAlister et al31 performed computed tomographic scans within 24 hours of surgery on 27 patients who had laparoscopic cholecystectomy; 56% had subcutaneous emphysema. These data show that the true incidence of subcutaneous emphysema and pneumothorax/pneumomediastinum might be significantly higher, suggesting that many such complications go undetected. However, according to our data, clinically significant cases can be predicted by prolonged operative timeand elevated maximum end-tidal CO2.

Length of operative procedure is the most easily identified risk factor for complication related to CO2 insufflation. Longer operations predispose patients to hypercarbia, subcutaneous emphysema, and pneumothorax/pneumomediastinum. Other authors have found operative time to correlate directly with CO2 absorption.24,32 Wolf et al6 found that the rate of increase appears to be greatest early in the procedure with the increase in CO2 absorption levels leveling off near the end.

We identified several risk factors for the development of hypercarbia, subcutaneous emphysema, and pneumothorax/pneumomediastinum during laparoscopy. Gynecologic surgeons should be aware that patients who have prolonged operative procedures and those with elevated end-tidal CO2 have increased risk of complications. Increasing the number of operative ports increases the risk of subcutaneous emphysema. Hypercarbia-related complications could become more commonplace with the development of longer and more complex laparoscopic procedures. In cases where these risk factors are present, surgeons should have a high index of suspicion for potential complications, and if any signs or symptoms develop immediate treatment with hyperventilation and release of CO2 pneumoperitoneum should be instituted.


   Footnotes
 
PII S0029-7844(00)00781-X

Received June 28, 1999. Received in revised form October 18, 1999. Accepted October 27, 1999.


   References
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Abstract
 Materials and Methods
 Results
 Discussion
 References
 
1. Kalhan SB, Reaney JA, Collins RL. Pneumomediastinum and subcutaneous emphysema during laparoscopy. Cleve Clin J Med 1990;57:639–42.[Medline]

2. Bard PA, Chen L. Subcutaneous emphysema associated with laparoscopy. Anesth Analg 1990;71:101–2.

3. Klopfenstein CE, Gaggero G, Mamie C, Morel P, Forster A. Laparoscopic extraperitoneal inguinal hernia repair complicated by subcutaneous emphysema. Can J Anaesth 1995;42:523–5.[Abstract/Free Full Text]

4. Kent RB. Subcutaneous emphysema and hypercarbia following laparoscopic cholecystectomy. Arch Surg 1991;126:1154–6.[Abstract]

5. Perko G, Fernandes A. Subcutaneous emphysema and pneumothorax during laparoscopy for ectopic pregnancy removal. Acta Anaesthesiol Scand 1997;41:792–4.[Medline]

6. Wolf JS, Monk TG, McDougall EM, McClennan BL, Clayman RV. The extraperitoneal approach and subcutaneous emphysema are associated with greater absorption of carbon dioxide during laparoscopic renal surgery. J Urol 1995;154:959–63.[Medline]

7. Waisbren SJ, Herz BL, Ducheine Y, Yang HK, Karanfilian RG. Iatrogenic respiratory acidosis during laparoscopic preperitoneal hernia repair. J Laparoendosc Surg 1996;6:181–3.[Medline]

8. Wolf JS, Clayman RV, Monk TG, McClennan BL, McDougal EM. Carbon dioxide absorption during laparoscopic pelvic operation. J Am Coll Surg 1995;180:555–60.[Medline]

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10. Lehmann LJ, Lewis MC, Goldman H, Marshall JR. Cardiopulmonary complications during laparoscopy. South Med J 1995;88: 1072–5.[Medline]

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14. Verreault J, Lepage S, Bisson G, Plante A. Ascites and right plueral effusion: Demonstration of a peritoneo-pleural communication. J Nucl Med 1986;27:1706–9.[Abstract/Free Full Text]

15. Woolner DF, Johnson DM. Bilateral pneumothorax and surgical emphysema associated with laparoscopic cholecystectomy. Anaesth Intensive Care 1993;21:108–10.[Medline]

16. Chui PT, Gin T, Chung SCS. Subcutaneous emphysema, pneumomediastinum and pneumothorax complicating laparoscopic vagotomy. Anaesthesia 1993;48:978–81.[Medline]

17. Gabbott DA, Dunkley AB, Roberts FL. Carbon dioxide pneumothorax occurring during laparoscopic cholecystectomy. Anaesthesia 1992;47:587–8.[Medline]

18. Prough DS, Mathru M. Acid-base, fluids and electrolytes. In: Barash PG, Cullen BF, Stoelting RK, eds. Clinical anesthesiology. 3rd ed. Philadelphia: Lippincott-Raven, 1997:161.

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20. Nunn JF, Hill DW. Respiratory dead space and arterial to end-tidal CO2 tension difference in anaesthetized man. J Appl Physiol 1960;15:383–9.[Abstract/Free Full Text]

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