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OBSTETRIC ANESTHESIOLOGY

Intraoperative Oxygen Administration Does Not Reduce the Incidence or Severity of Nausea or Vomiting Associated with Neuraxial Anesthesia for Cesarean Delivery

From the Department of Anesthesiology, Ochsner Medical Center, New Orleans, Louisiana.

Address correspondence to Stuart R. Hart, MD, Department of Anesthesiology, Ochsner Medical Center, 1516 Jefferson Highway, New Orleans, LA 70121. Address e-mail to shart{at}ochsner.org.

Abstract

BACKGROUND: Supplemental oxygen may reduce postoperative nausea and vomiting after general anesthesia. We designed this study to evaluate the efficacy of supplemental oxygen administration for reducing nausea and vomiting in women having neuraxial anesthesia for cesarean delivery.

METHODS: We conducted a prospective, randomized, double-blind study of women having standardized neuraxial anesthesia and postoperative analgesia for cesarean delivery. After umbilical cord clamp, women were randomized to receive either 70% or 21% oxygen for surgery. Nausea and vomiting were recorded at three time intervals: induction until delivery, delivery until the end of surgery, and at 24 postoperative hours. ² and Student’s t-tests were used to determine significant differences.

RESULTS: The study groups were similar with respect to demographic and procedural variables. There was no significant difference between groups in the overall incidences of nausea and vomiting. The incidence of severe nausea (rated by mothers) in the oxygen group predelivery, postdelivery, and postoperatively was 3%, 7%, and 9%, respectively, and in the medical air group was 3%, 9%, and 7%, respectively. Severe vomiting (>2 episodes) in both the oxygen and medical air groups were 0%, 2%, and 4% at the corresponding time intervals. These differences were not statistically significant.

CONCLUSION: Administration of supplemental oxygen during cesarean delivery with neuraxial anesthesia does not decrease the incidence or severity of intraoperative or postoperative nausea or vomiting.

There has been controversy concerning whether administration of high concentrations of oxygen during general anesthesia decreases the incidence of postoperative nausea and vomiting (PONV). For instance, in one study, the use of 80% oxygen reduced the incidence of PONV by almost half when compared with a group of patients given an Fio₂ of 0.3 during general anesthesia (1). In fact, the use of a high concentration of oxygen during general anesthesia for women having laparoscopic gynecologic surgery has been shown to be as effective as ondansetron in reducing PONV but at a lesser cost (2). On the other hand, a recent review challenged whether administration of supplemental oxygen is beneficial at all in reducing the incidence of PONV after general anesthesia (3). To our knowledge, there have been no studies on the effect of high concentrations of oxygen in reducing PONV when regional anesthesia is used.

In the United States, many women have a cesarean delivery under neuraxial anesthesia (4). Nausea and vomiting are common occurrences during cesarean delivery and in the immediate postoperative period. Indeed, there are several physiologic changes associated with pregnancy that may predispose the pregnant woman to vomit, such as delayed gastric emptying, increased gastrin secretion by the placenta, lower esophageal sphincter relaxation, and aortocaval compression (supine hypotension syndrome). During cesarean delivery with neuraxial anesthesia, there may also be iatrogenic factors, which result in nausea or vomiting, such as uterine manipulation or exteriorization, hypotension, sympathectomy, and the administration of uterotonic drugs, antibiotics, or opioids (5). Although most anesthesiologists routinely administer supplemental oxygen to the mother before delivery, many discontinue it once the infant is delivered. Accordingly, the hypothesis of this study is that continuing supplemental oxygen during the intraoperative period beyond the delivery of the infant will reduce intra- or postoperative nausea and vomiting in women having a cesarean delivery under neuraxial anesthesia.

METHODS

The study was approved by the Ochsner Clinic Foundation IRB, and informed consent was obtained from all women. To be included in the study, women had to be of ASA physical class 1–3, English-speaking, aged between 18 and 35 yr, and having a cesarean delivery with spinal or epidural anesthesia. Both women scheduled for elective cesarean delivery as well as those in labor requiring a nonurgent cesarean delivery were eligible to participate in the study. However, women were excluded from the study if they experienced vomiting within 1 h prior to cesarean delivery or if they had received an antiemetic in the preceding 24 h. All women were treated under a standardized anesthetic protocol. Before cesarean delivery, metoclopramide 10 mg by IV injection and sodium citrate 30 mL orally were administered. Intravascular fluid administration for women having a scheduled cesarean delivery was accomplished with lactated Ringer’s solution 1000 mL before epidural placement and 2000 mL before spinal anesthesia. If the woman was in labor and required a cesarean delivery, 500–750 mL of crystalloid was used for prehydration. Epidural anesthesia was administered using 20 mL of 2% lidocaine with 1:200,000 epinephrine, fentanyl 100 µg, and preservative-free morphine 3 mg. Spinal anesthesia was established using 1.6 mL hyperbaric 0.75% bupivacaine, fentanyl 10 µg, and morphine 150 µg. Additional IV fluids and left uterine displacement were used to maintain systolic blood pressure more than 100 mm Hg or within 20% of preoperative baseline. Hypotension, if it occurred, was treated with IV injections of ephedrine 5 mg and/or phenylephrine 50 µg at the discretion of the anesthesiologist. After induction of anesthesia, all women were given supplemental oxygen via non-rebreather (NRB) facemask at 10 L/min as is the routine for our practice. After clamping of the umbilical cord, women were randomized by computer-generated allocation in sealed envelopes to receive either medical air (MA group) or oxygen (O group) at 15 L/min via NRB facemask until the end of the procedure. In a pilot study, we had established that these flows through a NRB resulted in an Fio₂ of 0.21 and 0.7, respectively. Both the anesthesiologist and the woman were blinded to the concentration of oxygen administered using a device approved by the Food and Drug Administration for blinding of the inspired gas and not for therapeutic use. This device was created by our biomedical engineering department. After delivery, cefazolin 1–2 g IV and oxytocin 20–40 U in 1000 mL lactated Ringer’s solution were administered. With either the spontaneous complaint of nausea or with emesis, the NRB facemask was removed and ondansetron 4 mg was administered IV for rescue. IV patient-controlled analgesia using morphine was used for rescue if additional postoperative analgesia was required. The incidence and severity of nausea and vomiting were recorded during three time periods: from induction until delivery, from delivery to the end of the procedure, and at 24 postoperative hours. Severity of nausea was rated by the subjects to be mild, moderate, or severe. Vomiting was considered to be mild if it occurred 1–2 times, but severe if more than two emetic episodes occurred during any study period. Women were removed from the study if there was arterial desaturation below 90%, persistent systolic hypotension below 100 mm Hg or 20% of baseline refractory to three attempts at treatment with vasopressor and additional crystalloid administration, conversion to general anesthesia, inability to tolerate the NRB facemask, major changes in operative plan, any violation of study protocol, or at the discretion of the anesthesiologist if deemed to be in the best interest of the patient.

All results are expressed as the mean ± sd or percent. The primary parameter of study was PONV in the interval between delivery of the infant and end of surgery. Power was determined a priori and it was estimated that at least 92 women would be required in each group to detect a meaningful difference of 50% between the two groups with a power of 0.8 and an of 0.05 (P 0.05). ² and Student’s t-tests were used to evaluate differences between the two study groups.

RESULTS

We enrolled 220 women in the study. Five women were excluded from the O group: refusal to wear oxygen mask = 3, supplemental analgesia with inhaled nitrous oxide = 1, and no paperwork = 1. In the MA group, 10 women were excluded: 3 refused to wear the facemask, 2 developed hypoxia and dyspnea, 2 required conversion to general anesthesia, 1 inadvertently received an antiemetic, and no data were found for 2. Therefore, 205 patients completed the trial, 95 in the O group and 110 in the MA group. Women in the two study groups were comparable with respect to demographics (Table 1) and procedure- related variables (Table 2). The use of spinal and epidural anesthesia was also equally distributed between the two study groups (Table 2).

There was no significant difference in the incidence of nausea between the two study groups. For instance, the incidence of nausea from induction to delivery was 8% for the O group and 13% for the MA group. From birth to the end of cesarean delivery, the incidence of nausea in the O and MA groups was 24% and 36%, respectively. Continuing supplemental oxygen administration to the mother beyond the delivery of the infant did not reduce the incidence of nausea in the first 24 h after the procedure. Vomiting occurred with similar frequency in both study groups.

The severity of nausea and vomiting was also similar between the two study groups (Figs. 1 and 2). Rates of severe vomiting were also identical between the two study groups at each time interval.

View larger version (13K): [in this window] [in a new window]   Figure 1. The severity of nausea in mothers given oxygen (O) and medical air (MA) groups from induction to delivery (predelivery), from delivery of the infant to the end of surgery (postdelivery), and during the first 24 h after cesarean delivery (postoperatively).

View larger version (13K): [in this window] [in a new window]   Figure 2. The severity of vomiting in mothers given oxygen (O) and medical air (MA) groups from induction to delivery (predelivery), from delivery of the infant to the end of surgery (postdelivery), and during the first 24 h after cesarean delivery (postoperatively).

DISCUSSION

There has been recent interest in the use of high concentrations of supplemental oxygen to decrease nausea and vomiting. For instance, it has been reported that the incidence of nausea could be halved and vomiting decreased four-fold when supplemental oxygen was administered to patients during ambulance transport (6). The use of high inspired concentrations of supplemental oxygen to decrease PONV has been more controversial (3). For instance, the use of 80% oxygen during general anesthesia resulted in a markedly decreased incidence of vomiting when compared with a lower Fio₂ (1,2). In contrast, others have reported that high inspired concentrations of oxygen during general anesthesia do not decrease the incidence of PONV (7,8). This lack of efficacy is particularly true after procedures at high risk for PONV, such as thyroid, strabismus, and breast surgery (9–11). The mechanism by which high inspired concentrations of oxygen potentially reduces PONV is unknown. However, in earlier studies, it was suggested that oxygen reduced subclinical bowel ischemia during abdominal procedures (12). Alternatively, others have suggested that oxygen may reduce PONV by enhancing the release of dopamine and serotonin from the carotid bodies (13).

There is particular interest in the use of supplemental oxygen to decrease the incidence of PONV in women having cesarean delivery. Short-term oxygen administration can be monitored easily by pulse oximetry and gas analysis. It has little potential for adverse effects or allergy, and may be less costly than other conventional antiemetics. Women having a cesarean delivery are at increased risk for PONV compared with nonpregnant patients having other types of surgeries (5,12). This risk may be related to physiologic changes associated with pregnancy, but it also may be due to other factors coincident with cesarean delivery, such as manipulation and exteriorization of the uterus, aortocaval compression resulting in hypotension during neuraxial anesthesia, and the use of uterotonic drugs (5). Furthermore, women having cesarean delivery, when compared with other surgical procedures, often receive neuraxially administered opioids for postoperative pain relief, which may increase PONV. Other advantages of supplemental oxygen for prevention of PONV are that it will not cause sedation and obtundation, which allows the mother to care for her baby, and there is no concern regarding breastfeeding. Postoperative oxygen supplementation was not found to be an effective treatment for PONV after general anesthesia for cesarean delivery (13). However, in the United States, most women have a cesarean delivery with neuraxial anesthesia (4).

Our data suggest that 70% supplemental oxygen administration beyond the induction to delivery interval during cesarean delivery under neuraxial anesthesia does not reduce the incidence or severity of nausea or vomiting intraoperatively or for the first 24 postpartum hours. To our knowledge, this is the first study to assess the efficacy of supplemental oxygen in reducing PONV during neuraxial anesthesia for cesarean delivery. However, taken together with recent evidence suggesting that indiscriminate supplemental oxygen administration to the mother may result in fetal hyperoxia and the potential for increased fetal free-radical formation, the lack of benefit of supplemental oxygen in reducing PONV joins an increasing body of evidence that oxygen administration should be reserved for clear maternal indications, and not routinely administered to mothers having cesarean delivery with neuraxial anesthesia (14,15).

It is thought that labor itself may increase the incidence of nausea and vomiting. However, in our study, we enrolled women who were in labor as well as those scheduled for cesarean delivery. This mix of women more adequately describes the population of women having a cesarean delivery and adds universality to our findings. It may have been preferable to have a homogenous group of women scheduled for elective cesarean delivery, thus avoiding the potential contribution of labor as a source of nausea and vomiting. However, in contrast to women who are in labor, women who have been fasted overnight may have a greater incidence of hypotension, which, in itself, may contribute to nausea and vomiting (16). Nonetheless, there was no significant difference between the two groups of women regardless of whether or not they were in labor. Furthermore, we know of no study which indicates that laboring women have a greater incidence of nausea and vomiting during cesarean delivery when compared with nonlaboring women. We did not continue administration of the study gases beyond the intraoperative period as had been done in previous studies, because we felt it was not realistic to expect healthy women who should be out of bed and caring for their infants to be tethered to an oxygen administration apparatus.

As stated earlier, neuraxial opioids for relief of postoperative cesarean delivery pain may be associated with nausea and vomiting. For that reason, we standardized the administration of opioids used during regional anesthesia and for postoperative pain relief. In fact, if a woman required adjuvants during the procedure, or if they deviated from the analgesic protocol, they were removed from the study.

In summary, under the conditions of our study, continuing high inspired concentrations of oxygen during the interval between delivery of the infant and the end of cesarean delivery did not reduce the incidence or severity of intraoperative or postoperative (up to 24 h) nausea or vomiting in women having neuraxial anesthesia for cesarean delivery.

ACKNOWLEDGMENTS

We thank the Ochsner Anesthesiology Residents for their tireless work and Drs. Alan Santos and Bobby Nossaman for their critical review of this paper.

Footnotes

Accepted for publication June 8, 2007.

Reprints will not be available from the author.

REFERENCES

1. Greif R, Laciny S, Rapf B, Hickle RS, Sessler DI. Supplemental oxygen reduces the incidence of postoperative nausea and vomiting. Anesthesiology 1999;91:1246–52[Web of Science][Medline]
2. Goll V, Akça O, Greif R, Freitag H, Arkiliç CF, Scheck T, Zoeggeler A, Kurz A, Krieger G, Lenhardt R, Sessler DI. Ondansetron is no more effective than supplemental intraoperative oxygen for prevention of postoperative nausea and vomiting. Anesth Analg 2001;92:112–17[Abstract/Free Full Text]
3. Gan TJ. Risk factors for postoperative nausea and vomiting. Anesth Analg 2006;102:1884–98[Abstract/Free Full Text]
4. Bucklin BA, Hawkins JL, Anderson JR, Ullrich FA. Obstetric anesthesia work force survey: twenty-year update. Anesthesiology 2005;103:645–53[Web of Science][Medline]
5. Balki M, Carvalho JC. Intraoperative nausea and vomiting during cesarean section under regional anesthesia. Int J Obstet Anesth 2005;14:230–41[Web of Science][Medline]
6. Kober A, Fleischackl R, Scheck T, Lieba F, Strasser H, Friedmann A, Sessler DI. A randomized controlled trial of oxygen for reducing nausea and vomiting during emergency transport of patients older than 60 years with minor trauma. Mayo Clin Proc 2002;77:35–8[Abstract/Free Full Text]
7. Apfel CC, Korttila K, Abdalla M, Kerger H, Turan A, Vedder I, Zernak C, Danner K, Jokela R, Pocock SJ, Trenkler S, Kredel M, Biedler A, Sessler DI, Roewer N. A factorial trial of six interventions for the prevention of postoperative nausea and vomiting. N Engl J Med 2004;350:2441–51[Abstract/Free Full Text]
8. Purhonen S, Turunen M, Ruohoaho UM, Niskanen M, Hynynen M. Supplemental oxygen does not reduce the incidence of postoperative nausea and vomiting after ambulatory gynecologic laparoscopy. Anesth Analg 2003;96:91–6[Abstract/Free Full Text]
9. Joris JL, Poth NJ, Djamadar AM, Sessler DI, Hamoir EE, Defêchereux TR, Meurisse MR, Lamy ML. Supplemental oxygen does not reduce postoperative nausea and vomiting after thyroidectomy. Br J Anaesth 2003;91:857–61[Abstract/Free Full Text]
10. Treschan TA, Zimmer C, Nass C, Stegen B, Esser J, Peters J. Inspired oxygen of 0.8 does not attenuate postoperative nausea and vomiting after strabismus surgery. Anesthesiology 2005;103:6–10[Web of Science][Medline]
11. Purhonen S, Niskanen M, Wüstefeld M, Mustonen P, Hynynen M. Supplemental oxygen for prevention of nausea and vomiting after breast surgery. Br J Anaesth 2003;91:284–7[Abstract/Free Full Text]
12. Borgeat A, Ekatodramis G, Schenker CA. Postoperative nausea and vomiting in regional anesthesia. Anesthesiology 2003;98:530–47[Web of Science][Medline]
13. Ghods AA, Soleimani M, Narimani M. Effect of postoperative supplemental oxygen on nausea and vomiting after cesarean birth. J Perianesth Nurs 2005;20:200–5[Medline]
14. Backe SK, Lyons G. Oxygen and elective Caesarean section. Br J Anaesth 2002;88:4–5[Free Full Text]
15. Shaw KS, Wang CC, Ngan Kee WD, Pang CP, Rogers MS. Effects of high inspired oxygen fraction during elective Caesarean section under spinal anaesthesia on maternal and fetal oxygenation and lipid peroxidation. Br J Anaesth 2002;88:18–23[Abstract/Free Full Text]
16. Marx GF, Dourat MF, Costin M. Potential hazards of hypoglycaemia in the parturient. Can J Anaesth 1987;34:400–2[Web of Science][Medline]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Phillips, T. W. Articles by Hart, S. R. Search for Related Content PubMed PubMed Citation Articles by Phillips, T. W., Jr Articles by Hart, S. R. Related Collections Obstetrics Anesthetic Techniques Complications Regional Anesthesia