Nitrous oxide for relief of labor pain: A systematic review

The use of hypnosis to improve pain management during voluntary interruption of pregnancy: an open randomized preliminary study

OBJECTIVE

This report describes an open randomized study that aims to determine whether a brief hypnotic intervention during first-trimester surgical abortion reduces requests for pain medication.

METHODS

Thirty women undergoing first-trimester surgical abortion at the family planning clinics of a large hospital in Quebec City were randomized into a control group that received standard care and a hypnosis group that received, in addition to standard care, an intervention of hypnosis, including analgesia suggestions 20 min before and throughout the surgical procedure. Patients in both groups were given the option to control their pain with nitrous oxide (N(2)O) sedation administered through a nose mask as often and for as long as they wanted during the procedure. N(2)O sedation as the primary outcome was assessed at each step of the procedure. The patient's self-reported anxiety and pain were also assessed during the procedure as secondary outcomes.

RESULTS

Thirty-six percent of patients in the hypnosis group requested N(2)O sedation during the procedure versus 87% in the control group (p<.01). No differences between the groups were found in reports of pain and anxiety during the procedure.

CONCLUSION

These results suggest that hypnosis can be integrated into standard care and reduces the need for N(2)O in patients undergoing first-trimester surgical abortion. This reduction in N(2)O consumption did not lead to significant changes in pain or anxiety, and a larger sample size is required to assess the possible effects of hypnosis on those variables.

A double-blind, randomized controlled trial on the use of a 50:50 mixture of nitrous oxide/oxygen in pain relief during suction evacuation for the first trimester pregnancy termination

BACKGROUND

This prospective study assessed the role of a 50:50 mixture of nitrous oxide (N2O) and oxygen for pain relief during the termination of first trimester pregnancies by suction evacuation under conscious sedation.

METHODS

Ninety women undergoing suction evacuation up to 12 weeks of gestation were randomized by a computer-generated randomization list and allocated using sealed envelopes to receive the N2O/O2 mixture or air during the operation. Pain scores during and after suction evacuation, post-operative side effects and satisfaction level were compared.

RESULTS

No statistically significant differences in pain scores, post-operative side effects and satisfaction levels were found between the two groups.

CONCLUSION

N2O/O2 did not reduce the pain level during suction evacuation for the first trimester pregnancy termination under conscious sedation.

Involvement of brain protein kinase C in nitrous oxide-induced antinociception in mice

Exposure of mice to the anesthetic gas nitrous oxide (N(2)O) produces a marked antinociceptive effect. Protein kinase C is a key regulatory enzyme that may be targeted by general anesthetics. However, a relationship between N(2)O-induced antinociception and protein kinase C has yet to be established. The present study was conducted to identify whether protein kinase C might influence N(2)O-induced antinociception in mice. Regular exposure (11 min) to N(2)O produced concentration-dependent antinociception in mice, as determined using the abdominal constriction test. N(2)O-induced antinociception was attenuated by i.c.v. pretreatment with phorbol 12,13-dibutyrate, a protein kinase C activator. This phorbol 12,13-dibutyrate antagonism of N(2)O-induced antinociception was reversed by i.c.v. pretreatment with calphostin C, a protein kinase C inhibitor. Long-term exposure (41 min in total, including 30 min prior to, and 11 min of analgesic testing) to 70% N(2)O produced reduced analgesic effects, compared with regular exposure to 70% N(2)O, thus indicating acute tolerance to N(2)O-induced antinociception. However, mice pretreated with calphostin C, chelerythrine, which is another protein kinase C inhibitor, and phorbol 12,13-dibutyrate, did not develop acute tolerance. Regarding activation of protein kinase C, regular exposure to 70% N(2)O did not increase protein kinase C within the membrane fraction of brain tissue, as determined by immunoblot analysis, but long-term exposure to 70% N(2)O did. The i.c.v. pretreatment with calphostin C and phorbol 12,13-dibutyrate prevented the increase in protein kinase C observed with long-term exposure to 70% N(2)O. These results suggest that brain protein kinase C negatively regulates the antinociceptive effect of N(2)O, and that activation of brain protein kinase C is related to the development of acute tolerance to N(2)O-induced antinociception in mice.

Alternatives à l'analgésie péridurale au cours du travail

Many systemic techniques, so-called "alternatives" to labor epidural analgesia, have been described: they are all poorly effective and some are associated with significant maternal and neonatal side effects. Nonetheless, these techniques can provide good maternal satisfaction. Accordingly, they are indicated when epidural analgesia is contraindicated or unavailable. Administration of systemic opioids mandates maternal respiratory supervision, oxygen supplementation and/or pulse oxymetry. Systemic opioids may also decrease fetal heart rate variability and produce neonatal respiratory depression; naloxone administration to the neonate is therefore widely indicated. Pethidine should be abandoned because it can produce prolonged neonatal respiratory depression. Nalbuphine produces less nausea/vomiting and less long lasting neonatal respiratory depression. Intravenous PCA fentanyl or sufentanil is presently the method of choice during early labor. Alfentanil seems less effective and may produce more neonatal side effects. Intravenous PCA remifentanil is the most effective technique, but safe administration may be problematic during intermittent supervision usually implemented in labour ward. Nitrous oxide 50% provides little pain relief. Nonetheless, it is associated with few side effects, quite good maternal satisfaction and can be quickly implemented during advanced painful labor. It is not recommended to add it to systemic opioid (except under continuous supervision by the anaesthetic team), because of an increased incidence of maternal desaturation. The use of a subanaesthetic concentration of sevoflurane has been described recently; it is more effective than nitrous oxide. However, guidelines for safe implementation in labor ward remain to be determined.

Nitrous oxide anxiolysis for elective cesarean section

STUDY OBJECTIVE

To determine if inhaled 40% nitrous oxide (N(2)O) via facemask is an effective anxiolytic in women undergoing elective cesarean section under spinal anesthesia.

STUDY DESIGN

Prospective, randomized, double-blinded study.

SETTING

Tertiary-care women's hospital.

PATIENTS

Sixty American Society of Anesthesiologists physical status I and II patients scheduled for elective cesarean section under spinal anesthesia.

INTERVENTIONS

Patients were randomized to 2 groups to receive either 100% O2 via facemask or 40% N2O in O2 via facemask.

MEASUREMENTS

Vital signs (blood pressure, heart rate, and oxygen saturation) and measured variables (visual analog scale [VAS] anxiety, VAS pain, and sedation scores) were obtained at specific periods during the procedure (preoperatively, entering the operating room, spinal injection, skin incision, uterine incision, delivery, and at the conclusion of the surgical procedure). In addition, surgical time and delivery time, mean dose and percentage of patients requiring ephedrine or phenylephrine boluses, the emesis rate, and Apgar scores were measured.

MAIN RESULTS

No differences were noted with respect to maternal mean blood pressure, heart rate, pulse-oximeter oxygen saturation, and sedation or VAS pain scores during the measured periods. No differences were noted in surgical and delivery times, mean dose, or percentage of patients who required ephedrine or phenylephrine to maintain maternal blood pressure, the emesis rate, or 1- and 5-minute Apgar scores. Mean anxiety scores for the N2O group were significantly lower at the time of spinal injection, skin incision, and uterine incision. Multivariate analysis of variance for high-anxiety patients (> or =50 VAS) revealed significantly lower VAS scores in the N2O group, compared with the O2 group again at spinal injection, skin incision, and uterine incision.

CONCLUSIONS

Inhaled 40% N2O via facemask provides effective anxiolysis in women undergoing elective cesarean section under spinal anesthesia in patients with high anxiety (> or =50 VAS) at the time of spinal injection, skin incision, and uterine incision.

General anesthesia improves fetal cerebral oxygenation without evidence of subsequent neuronal injury

Anesthetic exposure during pregnancy is viewed as a relatively routine medical practice. However, recent rodent studies have suggested that common anesthetic agents can damage the developing brain. Here we assessed this claim in a higher order species by exposing previously instrumented near-term pregnant sheep at gestational day 122 (+/-1) to a combination of midazolam, sodium thiopental, and isoflurane at clinically relevant doses and means of anesthetic delivery (i.e., active ventilation). Four hours of maternal general anesthesia produced an initial increase in fetal systemic oxygenation and a sustained increase in fetal cerebral oxygenation, as determined by in utero near-infrared spectroscopy. Postexposure monitoring failed to identify changes in physiologic status that could be injurious to the fetal brain. Finally, through the histologic assessment of noninstrumented sheep at the same gestational time point, we found no evidence for a direct fetal neuro-toxic effect of our triple-drug regimen. Collectively, these results appear to corroborate the presumed safety of inhalational anesthetic use during pregnancy.

Pregnancy and lactation

Pregnancy results in physiologic changes in almost all organ systems in the body mediated mainly by female sex hormones. Physiologic changes of pregnancy influence the dental management of women during pregnancy. Understanding these normal changes is essential for providing quality care for pregnant women. This review article briefly discusses the cardiovascular, respiratory, gastrointestinal, urogenital, endocrine, and oral physiologic changes that occur during normal gestation. A summary of current scientific knowledge of ionizing radiation is presented. Information about the compatibility, complications, and excretion of the common drugs during pregnancy is provided. Drugs and their usage during breast-feeding are also discussed. Guidelines for the management of a pregnant patient in the dental office are summarized.

Effects on the fetus and newborn of maternal analgesia and anesthesia: a review

PURPOSE

To review the effects of maternal anesthesia and analgesia on the fetus and newborn.

METHODS

An on-line computerized search of Medline, Embase, and the Cochrane Collaboration via PubMed was conducted. English language articles were selected. The bibliographies of relevant articles and additional material from other published sources were retrieved and reviewed.

PRINCIPAL FINDINGS

No one test clearly separates the effects on the fetus/newborn, if any, of maternally administered medication during labour and delivery, or during surgery for non-obstetric indications. Supposition in this regard is limited in part by methodology previously used to study the transplacental passage of various drugs. This work needs to be repeated using a human model. Routine maternal supplemental oxygen administration is being questioned in light of research showing that free radical generation and oxidative stress are implicated as the underlying mechanisms in several neonatal conditions. Maternal hypotension is associated with neonatal acidemia and base excess correlates with neonatal outcome. Common postpartum analgesics transfer minimally into breast milk. Maternal or fetal surgery conducted during pregnancy necessitates modification of both anesthetic and surgical approaches. The key to resuscitation of the fetus is resuscitation of the mother: intra-uterine maneuvers, including perimortem Cesarean section, aim to reverse treatable causes of fetal asphyxia, restore fetal oxygenation, and correct fetal acidosis.

CONCLUSIONS

The well-being of the infant is a major criterion for evaluating the anesthetic management of pregnant women. Many tools exist to assist with this determination for the fetus, whereas few are available to evaluate the newborn.

Douleur et analgésie obstétricales

GOAL AND METHODS

Labor pain is of major concern since most parturients experience significant pain of extremely severe intensity for many. The purpose of this review was to provide an overview of the mechanisms and pathways of labor pain (including new insights on integration of the nociceptive signal) and to emphasize the need of effective labor pain relief.

RESULTS

Labor pain can have deleterious effects on the mother, on the fetus and on labor outcome itself. Among the current methods of obstetric analgesia, regional analgesia (the most widespread technique being epidural analgesia) offers the best effectiveness/safety ratio thanks to pharmacological innovations. Systemic analgesia (parenteral opioids, nonopioid painkillers and inhaled anesthetic agents) provides an alternative to regional analgesia but remains less effective and more hazardous. Non-drug approaches (namely psychoprophylaxis and physical methods) may be effective when used with epidural analgesia but are often not potent enough when used alone.

CONCLUSION

Despite its complex pathophysiology, labor pain can be efficiently managed. Thanks to multidisciplinary care, obstetric analgesia (mainly epidural analgesia) prevents deleterious effects of labor pain on the mother and fetus.

Does pain relief during delivery decrease the risk of postnatal depression?

BACKGROUND

To test the hypothesis that sufficient pain relief during delivery decreases the risk of postnatal depression.

METHODS

As part of a prospective follow-up study of the risk factors for postnatal depression and its impact on the mother-infant interaction and child development, 185 parturients filled in the Edinburgh Postnatal Depression Scale (EPDS), first during the first postpartum week and again (n = 162) 4 months later. The incidence and the risk of high EPDS scores was calculated according to the mode of delivery and the mode of pain relief during vaginal delivery, also after adjusting for the length of labor.

RESULTS

Mothers who received epidural/paracervical blockade during their delivery spent less time in the delivery room than mothers in the nitrous oxide/acupuncture group (p = 0.033) or mothers with no pain relief (p = 0.026) and had shorter length of labor than mothers without pain relief (p = 0.04). The adjusted risk of depressive scores at the first postnatal week was decreased in the epidural/paracervical group when compared with no analgesia group (OR: 0.25, 95% CI: 0.09-0.72). This difference was not shown at 4 months postpartum. Elective or emergency cesarean section did not increase the risk of high EPDS scores at the first week or at 4 months postpartum.

CONCLUSION

The mode of pain relief during vaginal delivery seems to be associated with the incidence of postpartum depression, especially immediately after delivery.

Role of nitric-oxide synthase isoforms in nitrous oxide antinociception in mice

Exposure of mice to the anesthetic gas N2O evokes a prominent antinociceptive effect that is sensitive to antagonism by nonselective nitric-oxide synthase (NOS) inhibitors. The present study was conducted to identify whether a specific NOS isoform is implicated in N2O antinociception in mice. In the abdominal constriction test, exposure of mice to 25, 50, and 70% N2O resulted in a concentration-dependent antinociceptive effect that persisted for up to 6 min following removal of the mice from the N2O atmosphere into room air. This N2O antinociceptive effect was antagonized by pretreatment with S-methyl-l-thiocitrulline (SMTC) and higher doses of l-N5-(1-iminoethyl)-ornithine (l-NIO), which reportedly inhibit the neuronal and endothelial isoforms of NOS, respectively. Nevertheless, the N2O-induced antinociception was unaffected by pretreatment with low doses of either SMTC or l-NIO or by pretreatment with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), which selectively inhibits inducible NOS. The s.c. pretreatment with SMTC and l-NIO reduced brain NOS activity in a dose-dependent manner, whereas AMT had no such effect. Moreover, in blood pressure experiments, SMTC increased SBP in dose-unrelated fashion, whereas l-NIO showed an appreciably weaker but dose-related increase in SBP. The i.c.v. pretreatment with SMTC also reduced N2O antinociception and brain NOS activity without increasing of SBP. These results suggest that it is the neuronal isoform of NOS that is involved in mediation of the antinociceptive effect of N2O in the mice.

Sevoflurane analgesia in obstetrics: a pilot study

Continuous and intermittent administration of inhalational anesthetics has been successfully employed for treating pain during labor. We conjectured that intermittent sevoflurane administration would be effective for pain relief during labor without side effects to the mother or fetus. Fifty parturients breathed a mixture of 2-3% sevoflurane, oxygen and air before each uterine contraction began. The patients assessed the quality of analgesia by using a visual analogue scale (0-10) before the administration of sevoflurane and after each uterine contraction. All parturients but one were satisfied, demonstrating a mean visual analogue score before and after sevoflurane administration of 8.7 +/- 1.1 and 3.3 +/- 1.5, respectively. Apgar scores at 1 and 5 min were 9 (range 5-9) and 10 (range 8-10), respectively. Our findings suggest that sevoflurane could be effective for the treatment of labor pain.

The nature and management of labor pain: executive summary

This report describes the background and process for a rigorous project to improve understanding of labor pain and its management, and summarizes the main results and their implications. Labor pain and methods to relieve it are major concerns of childbearing women, with considerable implications for the course, quality, outcome, and cost of intrapartum care. Although these issues affect many women and families and have major consequences for health care systems, both professional and public discourse reveal considerable uncertainty about many questions, including major areas of disagreement. An evidence-based framework, including commissioned papers prepared according to carefully specified scopes and guidelines for systematic review methods, was used to develop more definitive and authoritative answers to many questions in this field. The papers were presented at an invitational symposium jointly sponsored by the Maternity Center Association and the New York Academy of Medicine, were peer-reviewed, and are published in full in this issue of the journal. The results have implications for policy, practice, research, and the education of both health professionals and childbearing women.