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AMBULATORY ANESTHESIA

Supplemental Oxygen Does Not Reduce the Incidence of Postoperative Nausea and Vomiting After Ambulatory Gynecologic Laparoscopy

Sinikka Purhonen, MD^*, Matti Turunen, MD^*, Ulla-Maija Ruohoaho, MD^*, Minna Niskanen, MD, PhD^*, and Markku Hynynen, MD, PhD

*Department of Anesthesiology and Intensive Care, Kuopio University Hospital, Kuopio, Finland; and Department of Anesthesia and Intensive Care, Helsinki University Central Hospital, Jorvi Hospital, Espoo, Finland

Address correspondence and reprint requests to Sinikka Purhonen, MD, Department of Anesthesiology and Intensive Care, Kuopio University Hospital, PO Box 1777, FIN-70211 Kuopio, Finland. Address e-mail to sinikka.purhonen{at}kuh.fi

	Abstract

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Supplemental 80% oxygen administration halves the incidence of postoperative nausea and vomiting (PONV) in inpatients. Whether it prevents PONV after ambulatory surgery is unknown. We tested the efficacy of supplemental 80% oxygen in decreasing the incidence of PONV after ambulatory gynecologic laparoscopy. One hundred patients were given a standardized sevoflurane anesthetic. They were randomly assigned to two groups: routine oxygen administration with 30% oxygen, balance nitrogen (Group A); and supplemental oxygen with 80% oxygen, balance nitrogen (Group B). Oxygen was administered during surgery and up to 1 h after surgery. The incidence of nausea and vomiting and the need for rescue antiemetics did not differ between the groups in the postanesthesia care unit, in the Phase II unit, or during the 24-h follow-up. The overall incidence of nausea and vomiting during the first postoperative 24 h was 62% in Group A and 55% in Group B (P = 0.486). There were no differences in the recovery profiles and patient satisfaction between the groups. In this study, supplemental oxygen did not prevent PONV in patients undergoing ambulatory gynecologic laparoscopy.

IMPLICATIONS: Supplemental 80% oxygen administration during surgery and until 1 h after surgery compared with 30% oxygen administration did not prevent postoperative nausea and vomiting after ambulatory gynecologic laparoscopy.

	Introduction

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Postoperative nausea and vomiting (PONV) is a frequent and distressing sequela of general anesthesia that may increase morbidity, prolong hospital stay (1,2), compromise patient satisfaction (3), and strain resources (4). The optimal strategy for prevention and management of PONV is still controversial (5). Even though many drugs have been studied for the prevention of PONV, prophylaxis is not very effective, may be costly, and has a potential risk of adverse drug reactions (6).

Cost-effectiveness is an important aspect in the management of PONV (5). Supplemental oxygen is inexpensive and is a potential alternative in the prophylaxis of PONV. In one study, the incidence of PONV was halved in patients who received 80% inspired oxygen during laparotomy and for 2 h after surgery, compared with those who received 30% inspired oxygen (7). In another study from the same group, the antiemetic efficacy of intraoperative 80% inspired oxygen was comparable to that of ondansetron after gynecologic laparoscopy (8). Because there are only two previous studies about the efficacy of supplemental oxygen administration in the prevention of PONV and no studies about its benefits in ambulatory surgery, we designed a prospective randomized study to test the hypothesis whether perioperative supplemental 80% oxygen administration reduces the incidence of PONV after ambulatory gynecologic laparoscopy.

	Methods

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After obtaining IRB approval and written, informed consent, we studied 100 consecutive female patients (ASA physical status I–II) scheduled to undergo ambulatory gynecologic laparoscopy. Patients were asked to provide a detailed medical history, including any history of PONV or motion sickness, smoking habits, and the date of the last menstrual period. Exclusion criteria were contraindications to the anesthetics used, nausea or vomiting within 24 h before the scheduled anesthesia, antiemetic drugs within the preceding 24 h, pregnancy or breast-feeding, obesity (body mass index >30 kg/m²), and any pulmonary disease.

All patients received oral paracetamol 2 g 1 h before surgery. Anesthesia was induced with midazolam 20 µg/kg IV, fentanyl 2 µg/kg IV, propofol 2–2.5 mg/kg IV, and glycopyrrolate 0.2 mg IV. Patients were ventilated with 100% oxygen by mask until tracheal intubation, which was facilitated with rocuronium 0.5 mg/kg IV. After induction, each patient received ketoprofen 100 mg (in 20 mL of saline) as a slow bolus IV, and an additional 100 mg of ketoprofen was infused over 30 min. Anesthesia was maintained with sevoflurane (end-tidal sevoflurane concentration 1 minimum alveolar anesthetic concentration [MAC]) in the carrier gas, as described below.

Patients were randomly assigned to two groups by using a computer-generated random number table: patients in Group A breathed routine 30% oxygen, balance nitrogen (not nitrous oxide); whereas patients in Group B breathed supplemental 80% oxygen, balance nitrogen. Normoventilation (end-tidal PCO₂, 32–38 mm Hg) was maintained (V710 ventilator; Siemens-Elema AB, Solna, Sweden) by allowing partial rebreathing with a fresh gas flow of 3 L/min and a positive end-expiratory pressure (PEEP) of 6 mm Hg. Fentanyl 1 µg/kg was given before the skin incision. If there were clinical signs (sweating, lacrimation, or swallowing) or hemodynamic responses (heart rate or blood pressure >30% above the baseline value) suggesting inadequate anesthesia, the sevoflurane concentration was increased in steps of 0.3 MAC. Fifteen minutes after stabilization had been achieved, as judged by the anesthesiologist, the end-tidal concentration was decreased to 1 MAC. Crystalloids were administered at a rate of 15 mL · kg^-1 · h^-1 throughout surgery. Forced-air warming was used to keep the distal esophageal temperature near 36°C. Hemodynamic responses, oxygen saturation, inspired oxygen concentration, end-tidal carbon dioxide concentration, and esophageal temperature were measured throughout surgery (Cardiocap/5; Datex-Ohmeda, Louisville, CO). When the last suture was inserted, the administration of sevoflurane was discontinued, muscle relaxation was reversed with neostigmine 2.5 mg and glycopyrrolate 0.5 mg IV, and the stomach was emptied by suction. Patients were ventilated with 100% oxygen 6 L/min until tracheal extubation.

After extubation, all patients were immediately transported to the postanesthesia care unit (PACU), where 30% or 80% oxygen, according to the randomization, was given to patients until 1 h from the end of surgery. The specified oxygen concentration was mixed with the oxygen blender of the ventilator (Servo, Siemens-Elema AB) and was given at a rate of 20 L/min. To prevent a dilution of gas composition with air, patients breathed through an adhesive continuous positive air pressure mask (Vital Signs, Totowa, NJ) without a PEEP valve. The place of the valve was covered with impermeable tape. A 40-cm piece of breathing tube was joined with a Y-connector to the mask to form the oxygen reserve. To make sure the inspired oxygen concentration was as specified, the fraction of inspired oxygen was measured under the mask (Cardiocap/5) at the beginning of postoperative oxygen administration. Additional oxygen was provided, as necessary, to maintain an oxygen saturation of at least 92% for all patients. The anesthesiologists were aware of the administered oxygen concentration. Patients, surgeons, and the nurses reporting PONV were blinded as to group assignments. The inspired oxygen concentration was postoperatively blinded by shielding the oxygen blender.

After surgery in the PACU, and in the step-down (Phase II) unit, patients were monitored by specifically trained nurses blinded to the group assignment and the actual inspired oxygen concentration. Patients were admitted to the Phase II unit when oxygen administration was discontinued and when their Aldrete score (9) was 9 or 10 out of 10. Rescue medications were administered for nausea lasting >15 min, for the second emetic episode (retching or vomiting), and at patients’ request. Ondansetron 1 mg IV was given as the initial rescue treatment. If two doses of ondansetron 1 mg failed to control PONV, droperidol 10 µg/kg IV was administered once. Pain was treated with fentanyl 1 µg/kg IV in the hospital and with oral ibuprofen or paracetamol after discharge from the hospital. The times at which the patient followed commands (e.g., opened her eyes as requested) and was oriented to her name and date of birth were evaluated at 1-min intervals. PONV (nausea, retching, or vomiting) assessments during the 24-h study period were performed at 30 and 60 min after surgery in the PACU, before admission to the Phase II unit, when the patient was discharged from the hospital, and 24 h after surgery. Nausea and pain were scored by using a linear scale from 0 to 10, with 0 representing no nausea or no pain and 10 representing nausea or pain "as bad as it can be." Each episode of emesis, defined as expulsion of gastric contents or an unsuccessful attempt to expel gastric contents (i.e., retching), was recorded. Patients experiencing retching were included in the vomiting category. The times from the end of surgery to oral intake, readiness for discharge, discharge from the hospital, and all adverse events and medications required were recorded. The data at the hospital were collected by specifically trained nurses.

A research nurse who was blinded to the study group assignments contacted the patients by telephone to obtain the data 24 h after surgery. In addition to the above-mentioned PONV assessment, they asked patients whether PONV had prevented their normal activities. Patients were asked to rate their level of satisfaction with oxygen administration by using a scale from 0 to 10, with 0 representing totally dissatisfied and 10 representing totally satisfied. The anesthetic management was evaluated by asking whether patients would choose the same anesthesia for a future surgery. Patients were also asked about the occurrence of dyspnea, cough, or any other adverse events. If patients were admitted to the hospital overnight, the assessments were made on the ward 24 h after surgery.

Our primary defined outcome was the incidence of nausea, vomiting, or both over the initial 24 postoperative hours. The sample size of the study (49 patients in each group) was estimated by using a 2-sided level of 0.05 and a power of 0.80. The incidence of PONV was assumed to be 60% after 30% oxygen administration and 30% after 80% oxygen administration during the first 24 h after surgery. Comparisons between Groups A and B were performed with the unpaired Student’s t-test, ² test, and Mann-Whitney U-test, where appropriate. The nausea and pain scores were analyzed by using the Mann-Whitney U-test with a Bonferroni correction, and the highest scores in the PACU were used in the analysis. To confirm that the risk for postoperative vomiting was not different in the study groups, we calculated risk scores for each patient according to Apfel et al. (10). We used these risk scores for group comparison because the effect of several nonsignificant risk factors may add up to a clinically significant different baseline risk (11). All tests were performed with SPSS 10.0 for Windows software (SPSS, Inc., Chicago, IL). The level of significance was P < 0.05.

	Results

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We recruited 50 patients into both study groups, but the data of one patient randomized to Group B were excluded because she received hydrocortisone 100 mg IV for an allergic skin reaction in the PACU. The patients in the study groups were different only in oxygen saturation at the end of surgery (Table 1). There were no differences in the study groups with respect to the calculated risk scores for postoperative vomiting. No patient in either group needed additional oxygen to maintain an oxygen saturation of at least 92%.

	Discussion

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In this study, supplemental perioperative 80% oxygen could not be shown to reduce PONV as compared with 30% oxygen in patients undergoing ambulatory gynecologic laparoscopy. The overall incidences of PONV within the first 24 hours after surgery that we report here (55% after 80% oxygen and 62% after routine 30% oxygen) do not differ from the figures reported in previous studies in this patient group (1,12).

Our findings are not in accordance with those of two previous studies (7,8). Greif et al. (7) found that 80% oxygen, as administered during colorectal surgery and for 2 hours after surgery, decreased the incidence of PONV from 30% to 17% as compared with 30% oxygen. However, it is of note that in that study (7), rescue antiemetic therapy was not standardized. Also, the distribution of risk factors for PONV between the groups, such as a history of motion sickness, was not specified. In addition to the different operative procedures, different equipment for postoperative oxygen administration may be one reason for our contradictory results compared with those of Greif et al. In this study, we measured inspired oxygen concentration continuously during surgery and at the beginning of postoperative oxygen therapy.

In another recent study, Goll et al. (8) demonstrated that supplemental 80% oxygen, when administered only during surgery, halved the incidence of PONV from 44% to 22% as compared with 30% oxygen. Even though the baseline incidence of PONV after 30% oxygen administration in our study was more frequent (62%) than that reported by Goll et al., we could not find any antiemetic effect for supplemental oxygen. Although the previous study (8) was also performed in patients undergoing gynecologic laparoscopy, the mean durations of operation and anesthesia were more than twice as long as in our study. Thus, if intraoperative supplemental oxygen were more important than postoperative supplemental oxygen in preventing PONV (8), our patients would have received potentially effective treatment for a shorter time period than patients of the previous study (8). In addition, in contrast to our study, the patients in the study by Goll et al. were not ambulated on the same day. Therefore, they may have experienced less vestibulocochlear stimulation than our patients. Although there was already a strong tendency for less PONV after 80% oxygen during the first six-hour period in the study by Goll et al. (8), we found no difference. Actually, we even noticed a tendency in the incidence of PONV in favor of supplemental oxygen before discharge from the hospital. The incidence of PONV in the PACU was more frequent in our supplemental oxygen group, albeit not significantly. In line with this, the first symptoms of PONV in our patients occurred earlier after 80% oxygen than after 30% oxygen.

In the study by Goll et al. (8), there was less pain in the 80% oxygen group compared with the 30% oxygen group. There also tended to be fewer other risk factors for PONV (more alcohol intake, more current smokers, fewer patients with a history of PONV or motion sickness, and less use of postoperative opioids) in the 80% oxygen group. Although none of these risk factors was alone significant, they may together add up to a different baseline risk that is clinically significant (11). In our study groups, the calculated risk scores for postoperative vomiting were not different. In the studies that showed a beneficial effect of oxygen to prevent PONV, the authors speculated that supplemental oxygen administration might reduce the incidence of PONV by ameliorating regional intestinal hypoxia (7,8). However, there was no attempt to measure tissue oxygenation in these studies. We did not measure tissue oxygenation, either. Thus, it remains unclear whether the reason for discrepancy between our results and those of Greif et al. (7) and Goll et al. (8) is a difference in tissue oxygen concentration. Also, the reason why patients who received a fraction of inspired oxygen of 0.8 in this study had a significantly earlier onset of PONV remains unclear.

There were no adverse events related to 80% oxygen administration. Large concentrations of oxygen during surgery may cause undesirable side events, such as an increased risk of surgical fires (13) and atelectasis formation in the lung (14–18). However, the evidence for the clinical significance of small atelectasis in healthy patients is contradictory (7,14–18). In our study, obese patients and those with any pulmonary disease were excluded. In addition, we used a small PEEP during surgery to prevent atelectasis (18).

In conclusion, this study calls into question the efficacy of supplemental oxygen in preventing PONV in patients undergoing outpatient gynecologic laparoscopy. More studies are required to determine whether there is a place for supplemental oxygen in the management of PONV.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999