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ORIGINAL RESEARCH |
From the 1Division of General Obstetrics and Gynecology, Department of Obstetrics and Gynecology, East Carolina University Brody School of Medicine; 2Department of Obstetrics and Gynecology, University Health Systems/Pitt County Memorial Hospital, East Carolina University Brody School of Medicine; and 3Department of Biostatistics, East Carolina University, Greenville, North Carolina.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: Patients were randomly assigned to either heated, 95% humidified CO2 (study group) or heated, dry CO2 (control group) during laparoscopy. Pain control was achieved per standard protocols. Pain scales were administered the first 4 hours and 24 and 48 hours postoperatively.
RESULTS: The 89 patients available in the intent-to-treat model revealed a decrease in total morphine equivalents and a decrease in pain scores at 1, 2, and 24 hours in the study group (directional P values < .05). Subgroup analysis in patients without chronic pelvic pain revealed lower mean pain scores at 1, 2, 24, and 48 hours and decreases in postoperative and total morphine equivalents (directional P values < .05) in the study group.
CONCLUSION: At laparoscopy, heated, 95% humidified CO2 effectively decreases postoperative pain and narcotics usage compared with heated, dry CO2.
LEVEL OF EVIDENCE: II-2
In open laparotomy cases, most surgeons attempt to keep tissues moist to avoid damage. This is not routinely done with laparoscopy. The typical amount used during routine laparoscopy is 2,500–3,000 mL to enhance visualization. Conscious patients do not tolerate this well. Demco2 showed in conscious laparoscopy, patients can only tolerate 500–800 mL of dry carbon dioxide (CO2). With cold, dry CO2, patients have problems with hypothermia, postoperative abdominal and shoulder pain theoretically secondary to peritoneal tissue desiccation.3 Previous attempts by Moore et al4 to solve the problem of hypothermia using warmed irrigation have failed. Moore also showed with regression analysis the volume of cold dry gas had no effect on hypothermia, but rather only the length of the case affected core temperature.
A warmed CO2 system was thought to be the solution to help with pain and temperature loss. Our hospital has begun using a warming system in an attempt to solve the heat loss problem caused by the cold dry CO2. Korell et al5 showed significantly decreased shoulder pain with warmed, dry CO2 compared with cold, dry CO2. However, in a study by Jacobs et al,6 warmed, dry CO2 alone was insufficient for keeping patients’ body temperature elevated; other devices were required.
The next step was to warm and humidify the CO2. Whereas patients can only tolerate 500–800 mL of cold, dry CO2, Demco showed 30% of conscious patients were able to tolerate 3,000 mL of warmed, humidified CO2 or when 15 mm Hg of pressure was achieved with warmed, humidified CO2 with no intravenous sedation.2 A randomized, controlled trial by Mouton et al7 showed a decrease in loss of body temperature with warming and humidifying the CO2 compared with cold, dry CO2. With electron microscopy, Mouton was also able to show less structural injury with the warmed, humidified CO2. Prior studies have shown a reduction in postoperative hypothermia, a shortened recovery room stay, and reduced postoperative pain with warmed, humidified CO2.2,8 Although warmed, humidified CO2 has been shown to be superior to cold, dry CO2, the use of warmed, humidified CO2 has not been compared with warmed, dry CO2. Further evaluation of these techniques was necessary to determine whether humidification provides benefit.
Based on the above studies, our hypothesis was that patients will have decreased pain and will decrease narcotic usage with warmed, humidified CO2 compared with warmed, dry CO2. This study compares subjects exposed to warmed, dry CO2 to warmed, 95% humidified CO2 during laparoscopic surgery as measured by postoperative pain control, pain medication usage, and required length of stay postoperatively.
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MATERIALS AND METHODS |
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The patients underwent the laparoscopic procedure determined by the surgeon with either the warmed, dry CO2 or the warmed, humidified CO2 for the entire case. The Insuflow device (Lexion Medical, St. Paul, MN), which is an Food and Drug Administration–approved device, was used to provide warmed, 95% humidified CO2. The cost of this device is approximately $90.00. The decision of which medications to give in both groups was made by the anesthesiologist in the operating room and in the postanesthesia care unit (PACU) for the first hour. The nurses dispensing these medications were blinded as to the patients’ study group. The narcotics given were a combination of fentanyl, hydromorphone, morphine, and meperidine. Pain medications given in the ambulatory surgical unit and at discharge were by surgeon preference. The narcotics given were a combination of morphine, meperidine, oxycodone, and propoxyphene, with acetaminophen as needed. All narcotics given were recorded and converted to morphine equivalents to perform calculations. Ketorolac tromethamine was also given on an as-needed basis. The nurses dispensing the medications and collecting the pain scores were blinded to the patient’s study group. The medications were given on an as-needed basis and based on the nurse’s assessment of patients’ pain levels. After surgery, the patients were given a visual analog scale9 to be filled out at 1, 2, 3, and 4 hours and on postoperative days 1 and 2. The patients were also blinded to study group until all pain scores were recorded.
Using power calculations, with a visual analog pain scale greater than 5 in 50% of patients in the control group compared with 20% in the study group, a study population of 90 patients was required to achieve power of 80% with a significance level of .05. Other data included operating room time, type of procedure, preoperative and postoperative temperatures, estimated blood loss, CO2 volume, pain medications, length of time until the patient is ready for discharge from the PACU and actual time of departure, length of time until the patient is ready for discharge from the hospital and actual time of departure.
Because the variables were not normally distributed (Kolmogorov-Smirnov test), the nonparametric Mann-Whitney U test was used. For proportions, Fisher exact test or the 
2 test was used, depending on whether tables were or were not sparse. Because the research hypothesis was that humidified CO2 would improve outcomes, directional P values from 1-tailed tests were used to compare hypothesis-related outcomes in the 2 treatment groups. Differences were considered statistically significant if P < .05.
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RESULTS |
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Data were available on 89 patients. Subject accrual commenced on August 16, 2002, and concluded on April 29, 2004. Twelve of the patients had surgery for chronic pelvic pain. Because this was an intent-to-treat study, the data were analyzed first with the chronic pelvic pain patients included. Patient demographics, including age, height, weight, body mass index, ethnicity, and operative characteristics, including postoperative temperature, estimated blood loss, carbon dioxide gas used, number of incisions, and times in the operating room, PACU, and ambulatory surgical unit are shown. There were no significant differences between the 2 groups as seen in Table 1.
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There were no significant differences in past surgical history. Diagnoses for the groups were voluntary sterilization, pelvic mass, infertility, and pelvic pain. In each group, 6 patients were operated on for pelvic pain. In the study group, 35 had a bilateral tubal ligation; the other 12 either had a salpingo-oophorectomy, cystectomy, ablation of endometriosis, lysis of adhesions or chromopertubation. In the control group, 34 had a bilateral tubal ligation; the other 8 either had a salpingo-oophorectomy, cystectomy, ablation of endometriosis, lysis of adhesions or chromopertubation. There was no significant difference between the groups as seen in Table 2 (Fisher exact test for diagnosis: P = .46; Fisher exact test for procedure: P = .81).
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Variations in laparoscopic port size were associated with changes in pain scores. Patients who had a 10-mm trocar had significantly higher pain scores at 24 and 48 hours postoperatively (directional P = .024 and .015, respectively). In each group there were 9 patients who had 10-mm ports, as seen in Table 1.
When including all patients who completed the study, there was a statistically significant difference in total morphine equivalents, with a median of 146 in the study group compared with 162 in the control group. Chronic pelvic pain was noted to be a confounder. The data were subsequently analyzed without chronic pelvic pain patients. This further stratified the differences between the groups. The patient demographics and operative characteristics were analyzed and no significant differences were found. In the nonpelvic pain patient group, there were 77 patients, 41 patients in the humidified CO2 group and 36 patients in the dry CO2 group. Because 10 subjects had no pain data for hours 24 and 48, pain scores for hours 1–4 were analyzed with a nonparametric repeated measures analysis, which indicated both a main effect of group (P = .012) and a group-by-hour interaction effect (P = .003). Because this interaction effect suggests that the shapes of the time profiles differ significantly between groups, groups were compared at each hour as shown in Table 3. There was a significant difference at 1, 2, 24, and 48 hours postoperatively, with directional P = .001, .024, .029, and .032, respectively. There was not a significant difference at 3 and 4 hours postoperatively. There was a greater difference in analgesic use in patients undergoing surgery for indications other than pelvic pain than in the total study population as seen in Table 4.
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There was a statistically significant decrease in postoperative (PACU and ambulatory surgical unit) pain medication usage and a decrease in total (intraoperative and postoperative) pain medication usage, with total morphine equivalents of 146 in the study group compared with 162 in the control group. Although the PACU and ambulatory surgical unit pain medication usage differences did not meet the 0.05 threshold, they were close to being statistically significant (P = .053 and P = .064, respectively).
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DISCUSSION |
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A limitation of our study was including chronic pelvic pain patients in the study originally because the primary outcome variables were pain and pain medication usage. These variables are sure to be influenced by the chronic condition. There are at least 2 possibilities which would cause study problems: 1) marked pain relief and 2) no pain relief. In either case, the result would depend on preexisting pain states or surgical outcomes that were unrelated to the type of distension media used during surgery. Either way could produce outliers, making data interpretation more difficult. A study by Kissler et al10 illustrates this. They showed no difference in pain levels comparing humidified, warmed CO2 to dry, warmed CO2 to dry, cold CO2. In their article, they did not specify diagnosis, which could have been chronic pelvic pain in the procedures they describe, leading to difficulty finding pain differences among the groups. In our study, when patients were included with chronic pelvic pain, there was a statistically significant difference between the study and the control groups. However, this difference was emphasized when pelvic pain patients were removed from the analysis. Another recent study by Einarsson et al11 controlled for this by having patients be their own controls, with local injection of bupivacaine. Unless we did a second surgery on the same patient, however, this would not be an option for a distension medium study.
Another limitation in our study was not blinding the surgeons to whether the CO2 was humidified. We tried to minimize the effect of not blinding the surgeons by having standard postoperative orders, similar procedures, and having multiple different surgeons, so as to not allow 1 individual’s surgical style, opinion, or ability to influence the study. The patients were blinded to study group, as were the nurses dispensing the medications and collecting the pain scores, so as to decrease potential bias in reporting pain levels or the administration of pain medications.
Another limitation in our study was that the procedures performed in our study were relatively simple and in general completed in less than 1 hour. Our goal was to pick uncomplicated cases so that the case itself would not greatly influence the pain levels postoperatively. As mentioned above, we wish that we had excluded chronic pelvic pain patients. Otherwise, the procedures were very similar, which accomplished our goal. Certainly another study looking at longer, more technical cases would be beneficial to assess the usefulness of heated, humidified gas in that setting.
A factor that increased pain levels at 24 and 48 hours postoperatively was port size. Patients who had a 10-mm trocar site had higher pain levels than those with 8-mm or 5-mm sites. This may in part be due to our institutional practice of fascial closure in the 10-mm port site. Whether it is wound size or fascial closure, this would suggest surgeons should use smaller ports whenever feasible. Among the non–chronic pelvic pain patients, there were 7 in each group that had 10-mm ports; consequently, port size was not a confounding variable in group comparisons.
A previous study has shown decreased postoperative recovery times for the heated, humidified gas group.8 We did not find a difference in postoperative recovery times between the groups. We were also unable to show a difference in postoperative temperature between the groups. However, as Moore et al4 pointed out, longer cases were the main variable in causing temperature loss, and the cases in this study were of relatively short duration.
An area of concern is the pain levels on postoperative day 1 and 2. Patients are typically seen a few weeks after surgery, at which point they have minimal or no pain. Yet the pain levels given by the subjects are as high on postoperative day 1 as they are at the second hour after surgery, and day 2 is only slightly better. It is unclear why these levels are so high. The standard at our institution is Darvocet (Eli Lilly and Company, Indianapolis, IN) and ibuprofen. It is possible that this is inadequate. It is also possible that pain levels of that magnitude are acceptable to patients, knowing it will get better shortly. Whatever the reason, it seems better pain relief postoperatively does not end when the patient leaves the hospital.
The device used in this study is approved by the Food and Drug Administration and readily available. The cost of the device is approximately $90.00, as compared with the standard insufflation tubing which costs approximately $6.00. A cost comparison would have to include surgeon’s preference, patient satisfaction, additional pain medications, and dispensing those medications postoperatively.
Using warmed, humidified CO2 at laparoscopy reduces pain postoperatively compared with warmed, dry CO2. Total narcotic usage is also lower, which may help in avoiding the adverse effects of narcotics. This is another tool for the surgeon in helping reduce pain after surgery.
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Footnotes |
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doi:10.1097/01.AOG.0000194065.59688.fa
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REFERENCES |
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2. Demco L. Effect of heating and humidifying gas on patients undergoing awake laparoscopy. J Am Assoc Gynecol Laparosc 2001;8:247–51.[Medline]
3. Ott DE. Desertification of the peritoneum by thin-film evaporation during laparoscopy. JSLS 2003;7:189–95.[Medline]
4. Moore SS, Green CR, Wang FL, Pandit SK, Hurd WW. The role of irrigation in the development of hypothermia during laparoscopic surgery. Am J Obstet Gynecol 1997;176:598–602.[Medline]
5. Korell M, Schmaus F, Strowitzki T, Schneeweiss SG, Hepp H. Pain intensity following laparoscopy. Surg Laparosc Endosc 1996;6:375–9.[Medline]
6. Jacobs VR, Morrison JE Jr, Mettler L, Mundhenke C, Jonat W. Measurement of CO(2) hypothermia during laparoscopy and pelviscopy: how cold it gets and how to prevent it. J Am Assoc Gynecol Laparosc 1999;6:289–95.[Medline]
7. Mouton WG, Bessell JR, Millard SH, Baxter PS, Maddern GJ. A randomized controlled trial assessing the benefit of humidified insufflation gas during laparoscopic surgery. Surg Endosc 1999;13:106–8.[Medline]
8. Ott DE, Reich H, Love B, McCorvey R, Toledo A, Liu CY, et al. Reduction of laparoscopic-induced hypothermia, postoperative pain and recovery room length of stay by pre-conditioning gas with the Insuflow device: a prospective randomized controlled multi-center study. JSLS 1998;2:321–9.[Medline]
9. Melzack R, editor. Pain measurement and assessment. New York (NY): Raven Press; 1983.
10. Kissler S, Haas M, Strohmeier R, Schmitt H, Rody A, Kaufmann M, et al. Effect of humidified and heated CO2 during gynecologic laparoscopic surgery on analgesic requirements and postoperative pain. J Am Assoc Gynecol Laparosc 2004;11:473–7.[Medline]
11. Einarsson JI, Sun J, Orav J, Young AE. Local analgesia in laparoscopy: a randomized trial. Obstet Gynecol 2004;104:1335–9.
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