Update on nitrous oxide and its use in anesthesia practice

Association Between Intrapartum Nitrous Oxide for Labor Analgesia and Short-Term Neonatal Outcomes

OBJECTIVE

To evaluate the association between intrapartum nitrous oxide use and adverse short-term neonatal outcomes.

METHODS

This was a retrospective cohort study of individuals with singleton gestations at 35 or more weeks who attempted labor and delivered at an academic hospital between June 1, 2015, and February 28, 2020. Data were extracted from the electronic medical record using billing and diagnostic codes. Patients were classified based on whether they received no intrapartum analgesia or received nitrous oxide only. Those who received other analgesia types were excluded. The primary outcome was neonatal intensive care unit (NICU) admission. Secondary outcomes included Apgar score less than 7 at 1 minute and 5 minutes, respiratory composite outcome (including meconium aspiration syndrome, neonatal bronchopulmonary disorders, neonatal transient tachypnea, and other neonatal respiratory distress that required NICU admission), hypoglycemia, and hyperbilirubinemia. Univariable and multivariable analyses were used to estimate the association between nitrous oxide exposure intrapartum and the selected outcomes.

RESULTS

Of 6,047 included, 4,153 (68.7%) received no analgesia, and 1,894 (31.3%) received nitrous oxide only. In comparison with individuals who received no analgesia, those who received nitrous oxide were more likely to be nulliparous, be of Black racial identity, have noncommercial insurance, and be less likely to deliver by intrapartum cesarean. The reception of nitrous oxide, compared with the reception of no analgesia, was associated with a lower likelihood of NICU admission (6.4% vs 8.1%; adjusted odds ratio [aOR] 0.77, 95% CI, 0.62-0.96) and an increased likelihood of neonatal hyperbilirubinemia (aOR 1.23, 95% CI, 1.08-1.41). Inhaled nitrous oxide exposure, in comparison with the reception of no analgesia, was not associated with the other secondary outcomes, including Apgar score less than 7 at 1 minute (odds ratio [OR] 0.74, 95% CI, 0.50-1.10) or 5 minutes (OR 0.91, 95% CI, 0.32-2.60), respiratory composite outcome (OR 0.91, 95% CI, 0.70-1.17), and hypoglycemia (OR 0.82, 95% CI, 0.64-1.05).

CONCLUSION

In this single-center retrospective cohort of low-risk patients, intrapartum inhaled nitrous oxide, compared with the reception of no analgesia, was associated with a decreased risk for NICU admission but with an increased risk for hyperbilirubinemia; other outcomes did not differ. These findings may be used to counsel patients when considering nitrous oxide for labor analgesia.

[Inhalation anesthesia in the cat: Development of cuff pressure when using nitrous oxide]

OBJECTIVE

During inhalation anesthesia with nitrous oxide in oxygen the pressure in the cuff of the endotracheal tube may increase due to diffusion of nitrous oxide into the cuff. The aim of the study was to investigate the development of cuff pressure during nitrous oxide anesthesia under clinical conditions in feline patients and to identify possible influencing factors such as tube size and gas flow rate.

MATERIAL AND METHODS

The prospective study included cats scheduled for inhalation anesthesia with nitrous oxide for a minimum duration of 60 minutes at the Department for Small Animals of the University of Leipzig. Cuff pressure was adjusted with a cuff manometer and its development was recorded.

RESULTS

In total, the cuff pressure values of 24 cats were recorded. Animals were allocated into groups by tube size (ID 4.0 mm and ID 4.5 mm) and by fresh gas flow rate: low flow rate (0.6 l/min) and high flow rate (3 l/min). During anesthesia, cuff pressure increased over time, with statistical significance occurring from 45 minutes onwards in comparison to the initial cuff pressure (p=0.005). After 60 minutes, there was a mean cuff pressure increase of 3 cmH2O. Despite this moderate mean increase, highly variable pressure values up to 48 cmH2O in individual animals were recorded. No cat reached the termination criterion of 60 cmH2O cuff pressure. Effects of tube size (p=0.63) and flow rate (p=0.334) on the cuff pressure were not evident.

CONCLUSION

After a period of 45 minutes of nitrous oxide administration, a significant increase in cuff pressure occurs in the cat. However, tube size and total gas flow rate do not seem to influence the cuff pressure development.

CLINICAL RELEVANCE

When using nitrous oxide during inhalation anesthesia, regular cuff pressure evaluation and correction are necessary and hence recommended in feline patients. As individual pressure changes may be highly variable, no fixed recommendations for optimal management are possible.

Protective Effect of Oxygen and Isoflurane in Rodent Model of Intestinal Ischemia-Reperfusion Injury

Animal research in intestinal ischemia-reperfusion injury (IRI) is mainly performed in rodent models. Previously, intraperitoneal (I.P.) injections with ketamine-xylazine mixtures were used. Nowadays, volatile anesthetics (isoflurane) are more common. However, the impact of the anesthetic method on intestinal IRI has not been investigated. We aim to analyze the different anesthetic methods and their influence on the extent of intestinal IRI in a rat model. Male Sprague-Dawley rats were used to investigate the effect of I.P. anesthesia on 60 min of intestinal ischemia and 60 min of reperfusion in comparison to hyperoxygenation (100% O₂) and volatile isoflurane anesthesia. In comparison to I.P. anesthesia with room air (21% O₂), supplying 100% O₂ improved 7-day survival by cardiovascular stabilization, reducing lactic acidosis and preventing vascular leakage. However, this had no effect on the intestinal epithelial damage, permeability, and inflammatory response observed after intestinal IRI. In contrast to I.P. + 100% O₂, isoflurane anesthesia reduced intestinal IRI by preventing ongoing low-flow reperfusion hypotension, limiting intestinal epithelial damage and permeability, and by having anti-inflammatory effects. When translating the aforementioned results of this study to clinical situations, such as intestinal ischemia or transplantation, the potential protective effects of hyperoxygenation and volatile anesthetics require further research.

Two Cases of Fatal Inhalation of Easily Available "Recreational" Substances

ABSTRACT

We present 2 cases of fatal inhalation of easily available highly volatile substances that occurred in a recreational context. Case 1 concerns an 18-year-old man who was found dead with a 25-L plastic bag pulled over his head and a whipped cream steel siphon connected to the bag. The deceased was known to previously have inhaled nitrous oxide. Autopsy results were unremarkable, toxicological analysis using static headspace gas chromatography coupled to mass spectrometry analysis proved the presence of nitrous oxide in lung tissue and blood. Asphyxiation was ascertained as the cause of death. Case 2 describes the death of a 54-year-old man found dead on his bed wearing a rubber gas mask. A bottle with ethyl chloride-containing cold spray was found beside him. Autopsy did not reveal relevant pathological findings; a subsequent toxicological analysis proved the presence of ethyl chloride. Respiratory arrest because of ethyl chloride inhalation was established as the cause of death. The 2 cases presented here demonstrate the danger of easily available, volatile substances with a high potential for abuse. A careful investigation of the death scene, proper specimen collection during the autopsy, and extensive toxicological tests, including headspace gas chromatography coupled to mass spectrometry analysis, are necessary to prove inhalation of these substances.

Comparison of Intracuff Pressure and Postoperative Sore Throat Following Use of Laryngeal Mask Airway Protector With or Without Nitrous Oxide Anesthesia

PURPOSE

In general anesthesia, the laryngeal mask airway (LMA) is a frequently used effective option. The effect of nitrous oxide on intracuff pressure of the LMA and postoperative sore throat is well known; however, there are no studies related to the second-generation LMA Protector. The purpose of this study was to determine the differences in intracuff pressure and postoperative sore throat, depending on the use of nitrous oxide during general anesthesia using the LMA Protector.

DESIGN

This randomized double-blind prospective study was conducted among 88 patients aged 20 to 70 years.

METHODS

The cuff pressure started with a baseline of 40 cm H₂O and was measured using a digital cuff pressure manometer for 30 minutes. Postoperative sore throat, dysphonia, dysphagia, and numeric rating scale scores were also recorded.

FINDINGS

Over time, the intracuff pressure of the nitrous oxide group increased significantly compared with that of the air group. Furthermore, postoperative sore throat and pharyngolaryngeal complications were not significantly different between the two groups.

CONCLUSIONS

Intracuff pressure of the LMA Protector increased during anesthesia using nitrous oxide. When the anesthesia time was less than 2 hours, however, there was no difference in postoperative sore throat.

The relationship between early administration of morphine or nitrous oxide gas and PTSD symptom development

BACKGROUND

Posttraumatic Stress Disorder (PTSD) is a debilitating mental health disorder. Certain drugs, such as morphine and nitrous oxide gas (N₂O), are administered to individuals who just experienced a traumatic event (e.g., soldiers, injured civilians). It is therefore crucial to understand if they incidentally affect PTSD symptom development. Furthermore, such observations could pave the way for the development of pharmacological prevention strategies of PTSD.

METHODS

In this prospective population-based cohort study (n = 2,070), we examined the relationship between morphine or N₂O administration during childbirth, and subsequent childbirth-related PTSD symptoms at eight weeks postpartum. Pain during labour, prior PTSD symptoms, and birth medical severity were included as covariates in the analyses.

RESULTS

In women who developed PTSD symptoms, N₂O administration during childbirth predicted reduced PTSD symptom severity (p < .001, small to medium effect size). A similar tendency was observed for morphine, but was not significant (p < .065, null to small effect size). Both drugs predicted increased PTSD symptoms when combined with severe pain during labour.

LIMITATIONS

This study was observational, thus drug administration was not randomised. Additionally, PTSD symptoms were self-reported.

CONCLUSIONS

Peritraumatic N₂O administration may reduce subsequent PTSD symptom severity and thus be a potential avenue for PTSD secondary prevention. This might also be the case for morphine. However, the role of severe peritraumatic pain in context of drug administration deserves further investigation.

COVID in obstetrics: labor analgesia and cesarean section

PURPOSE OF REVIEW

This review is based on the latest evidence to provide a good standard of care for COVID-19 parturients and protection to healthcare givers.

RECENT FINDINGS

COVID-19 by itself is not an indication for cesarean section. Different publications demonstrated the efficacy of neuraxial analgesia/anesthesia for delivery. Although SARS-CoV-2 was associated with a certain neurotropism, neuraxial block was not associated with neurological damage in COVID-19 parturients, and seems as safe and effective as in normal situations. It permits to avoid a general anesthesia in case of intrapartum cesarean section. Epidural failure is a concern: it may lead to a general anesthesia in case of emergency cesarean section. Local protocols and well-trained anesthesiologists will be helpful. COVID-19 patients require special circuits and every step (transfer to and from theatre, recovery, analgesia, and so on) should be planned in advance. For cesarean section under general anesthesia, personal protection equipment must be enhanced. Postoperative analgesia with neuraxial opioids, NSAIDs, or regional blocks are recommended. COVID-19 and pregnancy increase the risk of thrombosis, so thromboprophylaxis has to be considered and protocolized.

SUMMARY

Anesthetic care for delivery in COVID-19 parturients should include neuraxial blocks. Special attention should be paid on the risk of thrombosis.

Association of Self-Administered Nitrous Oxide for Labor Analgesia With Maternal and Neonatal Process and Outcome Measures

OBJECTIVE

To describe patterns of use of self-administered nitrous oxide (N₂O) during labor and to determine if maternal and neonatal process and outcome measures differ for women who use N₂O compared to women who do not use N₂O.

DESIGN

Retrospective, full-census, observational cohort.

SETTING

An upper midwestern U.S., urban, 75-bed quaternary perinatal center with more than 5,000 annual births.

PARTICIPANTS

The participants included two groups of women: 400 who used N₂O during labor and a comparison group of 6,733 who met N₂O eligibility but did not use N₂O.

METHODS

We used descriptive statistics to examine patterns of use of N₂O during labor between January 2015 and March 2017. We examined associations of N₂O with process (length of first and second stages of labor, time from hospital admission to birth, time from birth to hospital discharge, and total length of stay) and outcome measures (shoulder dystocia, instrumentation, vaginal lacerations, Apgar scores at 5 minutes, nursery disposition) using multivariate linear, logistic, and ordinal regression models.

RESULTS

Three percent (12/400) of women who used N₂O discontinued because of side effects. Among participants with vaginal births who used N₂O, 17.6% (62/352) used N₂O as the only form of pain medication during labor. We found no significant differences in maternal and neonatal outcome measures between the two groups. Among the process measures examined, we found a mean 2-hour-longer time from admission to birth and total length of stay in the N₂O group (p < .05) compared to the non-N₂O group.

CONCLUSION

Most participants who used N₂O (290/352, 82.3%) transitioned to other pain modalities during labor. Maternal and neonatal process and outcome measures were comparable relative to other pain management modalities, with the exception of longer time durations for two measures.

Use of Nitrous Oxide in Office-based Urologic Procedures: A Review

Nitrous oxide (N₂O) is underutilized in ambulatory urology. Here, we review available data regarding application, efficacy, and side effect profile of N₂O in ambulatory urologic procedures. Data were available from 11 studies. N₂O has been described in the setting of transrectal ultrasound-guided prostate biopsies, flexible cystoscopy, ureteral stent placement, and extracorporeal shockwave lithotripsy in adult patients and catheterization in children. Studies showed significant improvements in peri-procedural pain and anxiety relative to alternative (or none) forms of analgesia. Adverse effects were rare and self-limited. More widespread use of N₂O may result in cost savings and better patient tolerance with outpatient procedures.

Pharmacotherapy during Pregnancy: An Endodontic Perspective

Odontogenic pain affects up to 54.9% of pregnant women^1-3. This pain is often associated with pulpal and/or periapical infections that pose risks to women and their fetus. The American Dental Association in collaboration with the American College of Obstetricians and Gynecologists developed a consensus statement to affirm the importance of timely and appropriate oral health care as a critical component of a healthy pregnancy⁴. However, limited knowledge of endodontic procedure safety and related medication use often result in the avoidance of treatment during pregnancy. This article, a collaborative effort by specialists from endodontics, pediatric dentistry, and obstetrics, reviews the current evidence on the safety of medications commonly used in endodontics including local anesthetics, analgesics, anxiolytics, and antibiotics.

A Fixed Nitrous Oxide and Oxygen Mixture for Analgesia in Children With Leukemia With Lumbar Puncture-induced Pain: A Randomized, Double-blind Controlled Trial

CONTEXT

Leukemia is the most common cancer in the childhood population. Lumbar puncture (LP) plays central role in the diagnosis and treatment process, but options for analgesia are limited.

OBJECTIVES

The present study aims to evaluate the efficacy of a fixed N₂O/O₂ mixture to reduce pain in children with leukemia during LP as compared with placebo.

METHODS

A double-blind, placebo-controlled, and randomized clinical trial involving children who needed LP for diagnosis or treatment was conducted in the pediatrics department of the General Hospital of Ningxia Medical University. Eligible patients were randomly assigned to inhale either a fixed N₂O/O₂ mixture or O₂. The primary endpoint was the maximal pain level felt by the patient during the procedure measured using a numerical rating scale (0-10).

RESULTS

One-hundred fourteen consecutive patients were enrolled in this study and randomized. Pain scores during the procedure showed a significant decrease in N₂O/O₂ mixture-treated patients to 1.05 ± 1.40 versus 8.00 ± 2.13 in controls (P < 0.01). No serious adverse effects were attributed to N₂O/O₂ mixture inhalation. Analysis of the satisfaction of patients receiving N₂O/O₂ mixture indicated that medical staff were satisfied with this treatment.

CONCLUSIONS

This study demonstrated that self-administered fixed N₂O/O₂ is efficient to reduce pain related to LP in children with leukemia.