Recent advances in understanding the actions and toxicity of nitrous oxide

Neurological Manifestations Induced by Nitrous Oxide Abuse: A Case Series and Review of Literature

INTRODUCTION

Nitrous oxide (NO) abuse is increasing among young people. This can result in severe neurological disorders such as myelopathy and/or peripheral neuropathy. We report the clinical presentations, biological, radiologic and electrophysiological findings of 5 patients hospitalized with neurological symptoms consecutive to NO abuse. In addition, a literature review was conducted to describe the neurological characteristics and to identify factors associated with a poor recovery.

CASE REPORT

Among the 5 patients included, 2 had a myeloneuropathy, 2 had a sensorimotor neuropathy, and 1 had a normal spinal cord magnetic resonance imaging and electromyography despite neurological manifestations consistent with myeloneuropathy. After vitamin B 12 supplementation, recovery was reported in 4 patients, and 1 was lost to follow-up.From the literature review, 154 patients were included [94 males; median age 22 (19 to 26) y; NO exposure 9 (3 to 18) mo]. A myelopathy was identified in 116 patients (75%) and a peripheral neuropathy was documented in 89 patients (58%). Compared with patients who recovered, those with sequelae were more likely to have a motor deficit at presentation ( P <0.001), to use NO regularly ( P <0.001), to have a lower vitamin B 12 level ( P =0.04), and a higher concentration of homocysteine ( P =0.04). A less extensive myelopathy was more frequently found in the group with favorable outcomes ( P =0.002).

CONCLUSION

Neurological disorders caused by NO may be challenging with severe clinical patterns. We identified several factors associated with a poor recovery, to make clinicians aware of NO-induced neurotoxicity.

The efficacy and tolerability of inhaled nitrous oxide in major depressive disorder: a systematic review and meta-analysis

BACKGROUND

Nitrous oxide (N2O) has been initially confirmed by clinical trials to benefit to patients with major depressive disorder (MDD). However, there needs to be a meta-analysis to compare the efficacy and tolerability of N2O in MDD.

METHODS

PubMed, EMBASE, and Cochrane Library were searched for relevant studies up to Jan 1st, 2023. The meta-analysis mainly compared the outcome of the change in depression severity scores, response, remission, and adverse events in patients with MDD receiving 50% N2O and placebo.

RESULTS

Four studies with 133 patients were eventually identified. We found that the N2O group and control group showed an overall significant difference in the change in depression severity score for patients at 2 h, 24 h, and 2 weeks or more (2 h, SMD =  - 0.64, 95% CI - 0.01 to - 0.28, p < 0.0001) (24 h, SMD =  - 0.65, 95% CI - 1.01 to - 0.29, p < 0.0001) (2 weeks, SMD =  - 0.76, 95% CI - 1.16 to - 0.36, p < 0.0001). For the response and remission rate, the long-term effect of N2O was also statistically significant (for the response, RR = 2.33, 95% CI 1.23 to 4.44, p = 0.01) (for the remission, RR = 4.68, 95% CI 1.49 to 14.68, p = 0.008). For safety outcomes, patients treated with N2O had higher odds of nausea or vomiting (RR = 10.15, 95% CI 1.96 to 52.59, p = 0.009).

CONCLUSION

Our study suggested that N2O has a rapid and long-lasting antidepressant effect in patients with MDD. However, the efficacy of lower or titrated concentration of N2O should be further investigated.

Nitrous Oxide-Induced Subacute Combined Degeneration in a 38-Year-Old Pregnant Female After Recreational Use

Nitrous oxide (N2O) misuse creates a diagnostic dilemma due to its clinical presentation, difficulty in identification, and toxicity related to its chronic abuse, with resultant morbidity and mortality. Chronic abuse can lead to myeloneuropathy and subacute combined degeneration in otherwise healthy individuals. Health professionals should be aware of the commercial availability and abuse of N2O by the public, and N2O toxicity should be included in the differential diagnosis in patients presenting with myelopathy of unknown etiology. A case report was conducted on a 38-year-old female at approximately 30 weeks of gestation who presented to the emergency department with worsening bilateral lower extremity numbness, tingling, and weakness. The patient admitted to nitrous oxide inhalation during the two months prior to admission. She reported using four cans of whippets per week (approximately 8 g of N2O per whippet) up to 50 cans per day (400 g N2O) prior to the onset of symptoms. An MRI of the cervical spine was performed, showing T2 hyperintensity from C2 to C6 involving dorsal columns indicative of subacute combined degeneration. The patient was treated with intravenous vitamin B12 due to the clinical and radiographic evidence of nitrous oxide-induced myelopathy. The pathophysiology of N2O toxicity involves the oxidation of the cobalt atom of cobalamin (vitamin B12) from its reduced active 1+ valent state to its oxidized inactive 3+ valent state. This oxidation inactivates the enzyme methionine synthetase. B12 is an essential cofactor for downstream DNA synthesis. Consequently, excess N2O creates functional B12 deficiency leading to irreversible nerve damage if left undiagnosed and untreated.

Objectivation of the Equimolar Mixture of Oxygen and Nitrous Oxide Anxiolytic Effect in Pediatric Dentistry: A Pilot Study

Aim

EMONO is an equimolar mixture of oxygen and nitrous oxide. Studies investigating its anxiolytic effect mostly used behavioral scales for assessing anxiolysis in children during dental care. Observing this effect objectively in a pediatric population could be very interesting.

Materials and methods

We conducted a prospective uncontrolled monocentric pilot study to assess the equimolar mixture of oxygen and nitrous oxide (EMONO) anxiolytic effect in children during dental care by monitoring heart rate (HR) variation.

Results

A statistically significant difference could be highlighted between the HR before the dental care and after 5 minutes of EMONO inhalation, illustrating the anxiolytic effect of EMONO in an objective way. HR variation also suggests that the effect of EMONO seems to prevent a return to the initial level of stress, even during anesthesia.

Conclusion

All of the data in the literature confirm the essential role of nitrous oxide in pediatric dental care. Demonstrating the effectiveness of EMONO by objective criteria is necessary.

Trial registration

Clinical Trials Unique Protocol ID: RC17_0275.

How to cite this article

Clouet R, Dajean-Trutaud S, Grall-Bronnec M, et al. Objectivation of the Equimolar Mixture of Oxygen and Nitrous Oxide Anxiolytic Effect in Pediatric Dentistry: A Pilot Study. Int J Clin Pediatr Dent 2023;16(2):270-275.

Pharmacological Interventions in Labor and Delivery

While there is not a wide range of pregnancy-specific drugs, there are some very specific high-risk areas of obstetric care for which unique pharmacological approaches have been established. In preterm birth, labor induction and augmentation, and the management of postpartum hemorrhage, these pharmacological approaches have become the bedrock in managing some of the most common and problematic areas of antenatal and intrapartum care. In this review, we summarize the existing established and emerging evidence that supports and broadens these pharmacological approaches to obstetric management and its impact on clinical practice. It is clear that existing therapeutics are limited. They have largely been developed from our knowledge of the physiology of the myometrium and act on hormonal receptors and their signaling pathways or on ion channels influencing excitability. Newer drugs in development are mostly refinements of these two approaches, but novel agents from plants and improved formulations are also discussed.

Electrophysiologic Characteristics of Nitrous-Oxide-Associated Peripheral Neuropathy: A Retrospective Study of 76 Patients

BACKGROUND AND PURPOSE

The electrophysiologic characteristics of peripheral neuropathy secondary to nitrous oxide (N₂O) abuse remain unclear. The paper therefore aimed to summarize the electrophysiologic characteristics of N₂O-associated peripheral neuropathy and identify the risk factors of severe nerve injury.

METHODS

The electrophysiologic results and clinical data of patients with peripheral neuropathy secondary to N₂O abuse at our hospital between 2018 and 2020 were analyzed retrospectively, and their electrophysiologic changes were summarized.

RESULTS

Most patients exhibited decreased sensory and motor nerve conduction velocities (75% and 76%), decreased sensory nerve and compound motor action potentials (57% and 59%), and prolonged distal motor latency (59%), while a response was absent in 36%. These findings indicate that N₂O abuse can result in generalized injury to sensory and motor nerves. Electrophysiologic results indicated axonal neuropathy in 37 cases (49%), demyelinating peripheral neuropathy in 4 (5%), and mixed neuropathy in 12 (16%). Peripheral nerve injury was more common in the lower limbs (72%) than in the upper limbs (42%, p<0.0001). The upper and lower limbs were primarily affected by sensory nerve demyelination (35%) and motor axonal injury (67%), respectively. Subgroup analysis indicated that longer N₂O exposure and longer disease course were associated with more-severe motor axonal injury in the lower limbs.

CONCLUSIONS

N₂O-associated peripheral neuropathy can lead to sensory and motor nerve injury, with axonal injury being the most common. Injuries were more severe in the lower limbs. Prolonged N₂O exposure and disease course increased the severity of motor axonal injury in the lower limbs.

Nitrous oxide: a unique official French addictovigilance national survey

Introduction

Nitrous oxide has become over the last few years a public health problem in many countries. France has a dedicated health monitoring system dedicated to the surveillance of the abuse, dependence and consequences associated with the use of psychoactive substances coordinated by the French National Agency for the Safety of Medicines and Health Products.We present the French national survey of nitrous oxide.

Materials and methods

We analyzed all the cases with nitrous oxide from 2012 to 2021: number of notifications, characteristics of the subjects and consumption, consequences reported and their evolutions over time. In addition, we have made a special focus on the four main complications reported.

Results

A total of 525 cases were received with an exponential increase since 2019. We observed changes in the characteristics of the notifications with an increase in the proportion of women [42.7% in 2021 vs. 30.8% in 2020 (p = 0.02)]; an increase in the quantities consumed (use of cylinders); a negative evolution of the contexts of use with a search for self-therapeutic effects and use in violent contexts; an increasing trend of the severity of cases [78.1% in 2021 vs. 70.0% in 2020 (p = 0.07)].The main effects were substance use disorders and/or associated criteria (82.5%), neurological disorders (75.4%), psychiatric symptoms (15.4%) and cardiovascular events (8.6%). In terms of evolution, we observed a significant increase in cases with a use disorder and an increase in neurological complications. Moreover, new serious effects, notably cardiovascular events were reported.

Discussion

The combination of high availability, varied effects from euphoria to relief of discomfort in a stressful global pandemic context and the development of dependence could explain the rapid growth of consumption and the seriousness of the cases.It must now be taken into account that (i) Substance use disorders are associated with nitrous oxide consumption; (ii) clinicians must consider "nitrous oxide" in young subjects presenting different types of manifestations; and (iii) stopping consumption is imperative and is the first treatment. In this context, an addictological assessment must also be carried out.

Mechanisms Involved in the Neurotoxicity and Abuse Liability of Nitrous Oxide: A Narrative Review

The recreational use of nitrous oxide (N₂O) has increased over the years. At the same time, more N₂O intoxications are presented to hospitals. The incidental use of N₂O is relatively harmless, but heavy, frequent and chronic use comes with considerable health risks. Most importantly, N₂O can inactivate the co-factor cobalamin, which, in turn, leads to paresthesia's, partial paralysis and generalized demyelinating polyneuropathy. In some patients, these disorders are irreversible. Several metabolic cascades have been identified by which N₂O can cause harmful effects. Because these effects mostly occur after prolonged use, it raises the question of whether N₂O has addictive properties, explaining its prolonged and frequent use at high dose. Several lines of evidence for N₂O's dependence liability can be found in the literature, but the underlying mechanism of action remains controversial. N₂O interacts with the opioid system, but N₂O also acts as an N-methyl-D-aspartate (NMDA) receptor antagonist, by which it can cause dopamine disinhibition. In this narrative review, we provide a detailed description of animal and human evidence for N₂O-induced abuse/dependence and for N₂O-induced neurotoxicity.

Clinical feature and sural biopsy study in nitrous oxide-induced peripheral neuropathy

Objective

The objective was to analyze the clinical characteristics and pathological characteristics of sural biopsy in nitrous oxide (N₂O) -induced peripheral neuropathy.

Methods

We recruited 18 patients with N₂O abuse-induced neurological disorders and reported their demographic data, clinical manifestations, laboratory examinations, and nerve conduction studies. Seven patients underwent sural nerve biopsy pathologic examination.

Results

All 18 patients had polyneuropathy, the nerve conduction results showed significant reductions in motor and sensory amplitudes, slowing of conduction velocities, and prolongation of latencies in most tested nerves compared to the controls. Toluidine blue staining of semi-thin sections of sural nerve biopsy showed decreased myelinated nerve fiber density, increased thin myelinated nerve fiber density, and axonal regeneration. Electron microscopy showed axonal degeneration and nerve regeneration.

Conclusion

The main manifestations of peripheral nerve damage caused by the abuse of N₂O are lower limb weakness and distal sensory disorder. The nerve conduction study results demonstrated that mixed axonal and demyelinating neuropathy was the most common type of neuropathy. Sural biopsy showed the main pathological change was chronic axonal degeneration.

Peripheral polyneuropathy and acute psychosis from chronic nitrous oxide poisoning: A case report with literature review

RATIONALE

Nitrous oxide (NO) is a commonly used drug in medical practice, restoration, and the automobile industry. Recreational abuse is an emerging public health problem owing to its accessibility and drug properties.

PATIENT CONCERNS

A 25-year-old male was hospitalized with acute psychosis and lower-extremity sensorimotor proprioceptive ataxia due to nitrous oxide abuse.

DIAGNOSIS

Laboratory studies confirmed a vitamin B12 deficiency. Magnetic resonance imaging of the spinal cord showed normal findings. Electrophysiological testing confirmed length-dependent sensorimotor polyneuropathy, with a predominant motor component and axonal degeneration.

INTERVENTION AND OUTCOMES

Abstinence from toxic substances was suggested, and vitamin B12 substitution was introduced. The patient was lost to follow up.

LESSONS

Nitrous oxide toxicity is multisystemic and is thought to result from vitamin B12 inactivation. Recent case reports postulated direct paranodal lesions resulting from nitrous oxide consumption. Neurological, neuropsychiatric, and hematological toxicities are among those explored in this case report. Correction of the functional vitamin B12 status and nitrous oxide abstinence are essential in the treatment process.

Analysis of clinical characteristics and prognostic factors in 110 patients with nitrous oxide abuse

PURPOSE

To review the clinical symptoms, auxiliary examination findings, and outcomes of patients with nitrous oxide (N₂ O) abuse, and analyze the factors that affect outcomes.

METHODS

Patients with N₂ O abuse treated in the Department of Neurology between January 2018 and December 2020 were included. The clinical data of these patients were collected, and follow-up was conducted to determine the outcomes.

RESULTS

The average age of the 110 patients with N₂ O abuse was 21.4 ± 4.2 years (range: 14-33 years). Clinical presentation primarily included neurological symptoms, such as limb numbness and/or weakness (97%), psychiatric symptoms, changes in appetite, and skin hyperpigmentation. Laboratory test results were characterized by vitamin B₁₂ deficiency (60%, 34 out of 57 cases) and high homocysteine level (69%, 31 out of 45 cases). Electromyography indicated mixed axonal and demyelination injury (92%, 80 out of 87 cases). Motor and sensory nerves were simultaneously involved, and injury primarily involved the lower limbs. One hundred and seven (97%) patients were clinically diagnosed with peripheral neuropathy, of whom 26 (24%) exhibited spinal abnormalities on magnetic resonance imaging, supporting a diagnosis of subacute combined degeneration. Treatment included N₂ O withdrawal and vitamin B₁₂ supplementation. Reexamination of six patients indicated that treatment was effective. Follow-up was completed for 51 patients. Thirty-four patients (67%) recovered completely, 17 patients (33%) had residual limb numbness, and only one patient experienced relapse. Sex was an independent prognostic factor; the outcomes of female patients were better than that of male patients.

CONCLUSION

The recreational use of N₂ O has largely expanded among youth in recent decades, which has become a growing public health concern in China. It highlights the importance of the recognition of various clinical symptoms, particularly limb numbness and/or weakness related to the cases of N₂ O abuse. The therapeutic administration of vitamin B₁₂ supplementation and N₂ O withdrawal can make the overall prognosis good, especially for female patients.

[Acute and chronic toxicities associated with the use and misuse of nitrous oxide: An update]

Nitrous oxide (N₂O) is used since the eighteenth century as an anesthetic and analgesic but also for recreational use. If the labelled uses of N₂O and their modalities are nowadays perfectly framed, the misuse of N₂O takes very alarming proportions among teenagers and young adults. This misuse is the cause of acute (hypoxia, barotrauma, burns, neuropsychiatric disorders) and chronic complications if repeated (myeloneuropathy, anemia, thrombosis, inhalant use disorder). The main mechanism of the latter is mainly related to a functional deficit in vitamin B12 induced by N₂O. The management of acute complications is symptomatic. The management of chronic complications is based on vitamin B12 supplementation. The best biomarker of chronic N₂O exposure is the elevation of the plasmatic level of methylmalonic acid. In all cases of recreational misuses, addiction treatment is necessary to prevent complications or their worsening by providing information in order to stop consumption.

Assessing the antinociceptive effect of nitrous oxide to tetanic stimulation in anaesthetised patients with new intra-operative nociception monitors: An observational study

BACKGROUND

Nitrous oxide (N2O) has been used since the 19th century for its analgesic, antinociceptive and anxiolytic effects during surgical procedures in awake and anaesthetised patients. However, quantification of noxious stimuli that occur under general anaesthesia is a constant challenge for anaesthesiologists, and recently two new indices have been developed to assess intra-operative nociception.

OBJECTIVE

The aim of this study was to quantify with new indices as well as with more classical clinical parameters the antinociceptive effect of N2O during general anaesthesia.

DESIGN

Prospective, open label, patient-blinded, observational and descriptive trial.

SETTING

Single-centre academic hospital.

PARTICIPANTS

Forty American Society of Anesthesiologists' physical status 1 to 3 patients undergoing general anaesthesia for elective abdominal surgery via laparotomy were recruited.

MAIN OUTCOMES MEASURES

Intra-operative pain was assessed using a standardised electrical stimulation of the forearm (tetanic stimulation at 70 mA, 100 Hz for 30 s), at 0, 25 and 50% inhaled N2O/O2. Heart rate (HR), mean arterial blood pressure, bispectral index, the analgesia nociception index and the nociception level (NOL) index were used to evaluate intra-operative nociception before and after each standardised tetanic stimulation.

RESULTS

There was a 16% reduction of the analgesia nociception index reaction, a 31% reduction of the NOL reaction and a 51% reduction of the HR reaction to a standardised electrical tetanic nociceptive stimulation during administration of 50% N2O. Administration of 50 or 25% inhaled N2O produced the same quality of antinociception based on HR and NOL index analyses. HR and the NOL index were the best parameters to identify the antinociceptive effect of intra-operatively administered N2O.

CONCLUSION

In anaesthetised patients, our study demonstrated clinically significant antinociceptive properties of N2O. Our results showed that low concentrations of N2O (25%) are as effective as higher concentrations (50%) to achieve a significant antinociceptive effect. These findings may help decrease negative effects of using higher concentrations of N2O, including its side effects and its environmental pollution.

TRIAL REGISTRATION

ClinicalTrials.gov registration identifier: NCT02701478.

Prognostic indicators of subacute combined degeneration from B12 deficiency: A systematic review

OBJECTIVE

A systematic review was conducted on published data of subacute combined degeneration (SCD) from B12 deficiency to investigate potential prognostic indicators of final ambulatory function in affected patients. TYPE: Systematic review.

LITERATURE SURVEY

Records published from 1999 through 2018 were searched on the electronic databases MEDLINE, PUBMED, and SCOPUS. The publication language was restricted to English and French.

METHODOLOGY

Records that described cases of SCD from B12 deficiency in patients ≥16 years of age at onset were included. From a final total of 66 cases of SCD identified, ambulation scores were assigned based on the clinical descriptions reported. Patient characteristics, clinical manifestations, and ambulatory function were reported descriptively. Subanalyses on potential prognostic indicators were performed.

SYNTHESIS

Greater ambulatory function at diagnosis was associated with recovery of normal ambulatory function at follow-up (P < .001). Nearly 90% of patients walking unsupported at diagnosis made a complete recovery regardless of etiology. For patients initially walking with support, 22% of cases from impaired B12 digestion/absorption made a complete recovery compared with ≥50% of cases from other etiologies. For patients initially requiring a wheelchair, 33% of cases from impaired digestion/absorption were able to walk with support compared with ≥50% of cases from other etiologies. The total B12 administered over the course of treatment was correlated with improved ambulation (P = .024) for all patients, with a higher B12 replacement regimen associated with better outcomes in patients who were unable to walk unsupported at diagnosis (number needed to treat = 4).

CONCLUSIONS

Initial ambulatory function may be a useful clinical marker of the severity of spinal cord dysfunction and final functional outcome. Etiological risk factors influenced both clinical manifestations and final walking ability in SCD, suggesting a distinct pathophysiological mechanism among the causes. In addition, a more intensive B12 replacement regimen may improve ultimate ambulatory function in advanced cases of SCD.

Nitrous Oxide for Labor Analgesia: What We Know to Date

Background: Although nitrous oxide (N₂O) has been used since the 1880s for labor analgesia, its popularity has only recently increased in the United States. In 2011, only 3 centers in the country offered N₂O, but as of 2020, several hundred labor units have adopted its use.

Methods: We reviewed the literature and summarize the mechanism of action, clinical uses, and efficacy of N₂O for labor analgesia, as well as patient satisfaction related to its use.

Results: N₂O has several proposed mechanisms of action that make it a viable option for all 3 stages of labor and postpartum procedures. N₂O has been shown to be a safe option for both mom and baby during labor and delivery. Studies support N₂O as an analgesic for laboring. Even though 40% to 60% of women who use N₂O convert to a labor epidural analgesia, satisfaction surveys indicate that analgesia is not the only factor contributing to the use of N₂O during labor.

Conclusion: The use of N₂O has increased in labor and delivery units across the United States since 2011. Despite inferior analgesic properties compared to epidural analgesia, N₂O offers a safe alternative for many parturients who want a greater sense of control and mobility.

A new mechanistic approach for the treatment of chronic neuropathic pain with nitrous oxide integrated from a systems biology narrative review

The limitations of the currently available treatments for chronic neuropathic pain highlight the need for safer and more effective alternatives. The authors carried out a focused review using a systems biology approach to integrate the complex mechanisms of nociception and neuropathic pain, and to decipher the effects of nitrous oxide (N2O) on those pathways, beyond the known effect of N2O on N-methyl-D-aspartate receptors. This review identified a number of potential mechanisms by which N2O could impact the processes involved in peripheral and central sensitization. In the ascending pathway, the effects of N2O include activating TWIK-related K+ channel 1 potassium channels on first-order neurons, blocking voltage-dependent calcium channels to attenuate neuronal excitability, attenuating postsynaptic glutamatergic receptor activation, and possibly blocking voltage-dependent sodium channels. In the descending pathway, N2O induces the release of endogenous opioid ligands and stimulates norepinephrine release. In addition, N2O may mediate epigenetic changes by inhibiting methionine synthase, a key enzyme involved in DNA and RNA methylation. This could explain why this short-acting analgesic has shown long-lasting anti-pain sensitization effects in animal models of chronic pain. These new hypotheses support the rationale for investigating N2O, either alone or in combination with other analgesics, for the management of chronic neuropathic pain.

Case Study: Naltrexone for the Treatment of Nitrous Oxide Use

BACKGROUND

Using a clinical case example, we describe and discuss the use of oral naltrexone as a novel treatment strategy for nitrous oxide use. Nitrous oxide is an inhalant drug that is readily available and legally obtained. Though frequency of reported cases of substance use disorder for nitrous oxide is low, previous case reports have described severe neurological and psychiatric harms associated with chronic use. Despite this, evidence for pharmacotherapy is currently lacking. Clinical studies have shown variable efficacy for naltrexone across a number of substances including alcohol, nicotine, and stimulants.

CASE

We present here a case of a 41-year-old man with a substance use disorder for nitrous oxide who was reportedly using of up to four hundred 8 g canisters of nitrous oxide per day. Oral naltrexone was initiated at 50 mg daily in an attempt to decrease cravings. The dose was subsequently titrated to 100 mg daily, resulting in a decrease in nitrous oxide use to less than sixty 8 g canisters per week over a 1-month timeframe.

DISCUSSION

Previous literature surrounding naltrexone provides both a plausible mechanism of action for craving reduction as well as a precedent for its use across a number of substances. To our knowledge, use of naltrexone for nitrous oxide use has not been previously described. While clinical studies are currently lacking, this case highlights naltrexone as a possible treatment strategy for nitrous oxide use, with potential to reduce significant harms associated with chronic use.

Reversible Neuropsychiatric Disturbances Caused by Nitrous Oxide Toxicity: Clinical, Imaging and Electrophysiological Profiles of 21 Patients with 6-12 Months Follow-up

PURPOSE

Nitrous oxide (N₂O) abuse has become an increasingly severe problem in China. The aim of the study was to summarize the features of N₂O-induced neurology and enhance the awareness of this disease among physicians.

PATIENTS AND METHODS

We retrospectively reviewed the clinical, imaging, electrophysiological characteristics and the prognosis of patients with N₂O neurotoxicity in our hospital from January 2016 to August 2019.

RESULTS

Twenty-one patients (average age: 22.6±4.6 years) were collected. Eighty-six percent (18/21) patients presented with acute or subacute neurological disorders as their initial symptoms. The remaining fourteen percent (3/21) had psychiatric symptoms as the earliest symptoms. With progression, movement dysfunction appeared in ninety percent (19/21) of the patients with fifty-three percent (10/19) presented with weakness limited to both lower extremities. Sixty-two percent (13/21) of the patients presented with subjective sensory deficit. Seventy-one percent (15/21) had vibration sense impairment and positive Romberg's sign. Sixty-seven percent of the patients had hyporeflexia or areflexia. Fourteen percent (3/21) showed positive Babinski's sign. Seventy-eight percent (14/18) showed significantly increased homocysteine (HCY) level and only seventeen percent (3/18) showed decreased serum vitamin B₁₂ level. T₂ hyperintensity involving the posterior columns and lateral columns with inverted V sign in cervical spinal MRI had been observed in forty-seven percent (8/17) of the patients. Axonal peripheral neuropathy occurred in eighty-five percent (17/20) of the patients. The level of serum vitamin B₁₂ and HCY, as well as imaging findings, were rapidly recovered after supplementation of Vitamin B₁₂.

CONCLUSION

The N₂O-induced neuropsychiatric disturbances mainly occurred in the young groups and should be recognized by clinicians. The prognosis of N₂O intoxication is relatively good.

Nitrous Oxide Reduces Pain Associated With Local Anesthetic Injections

BACKGROUND

Local anesthetic injections can be painful and distressing.

OBJECTIVE

The aim of this study was to determine whether nitrous oxide, ice, vibration, or topical anesthetic improves analgesia for local anesthetic injections.

METHOD

A cohort study of 400 patients undergoing Mohs micrographic surgery with local anesthetic was conducted. Patients received no intervention (n = 200), ice (n = 50), topical anesthetic cream (n = 50), vibration device (n = 50), or nitrous oxide (n = 50). Pain was rated using the Visual Analogue Scale (VAS) and Wong-Baker FACES Pain Rating Scale.

RESULTS

Without intervention, mean VAS was 4.2 and FACES was 4.6. Nitrous oxide was the most successful in reducing pain (mean VAS 1.6 vs. 4.2, P < .01, FACES 1.2 vs. 4.6, P < .01). Topical ice reduced pain (mean VAS 3.0 vs. 4.2, P < .01, FACES 3.0 vs. 4.6, P < .01). Vibration reduced pain (mean VAS 3.5 vs. 4.2, P < .01, FACES 3.6 vs. 4.6, P < .01). Higher pain scores were associated with age <50 (P = .02), male sex (P = .05), and surgery on the nose, lip, ear, or eyelid (P = .02).

CONCLUSION

Nitrous oxide, ice, and vibration reduce injection pain. These interventions are especially useful for younger males undergoing surgery on the nose, lip, ear, or eyelid.

Elucidating Unique Axonal Dysfunction Between Nitrous Oxide Abuse and Vitamin B12 Deficiency

Introduction: Abuse of nitrous oxide (N₂O) has an unusually high lifetime prevalence in developed countries and represents a serious concern worldwide. Myeloneuropathy following the inhalant abuse is commonly attributed to the disturbance of vitamin B12 metabolism, with severe motor deficits are often noted. The present study aims to elucidate its underlying pathophysiology.

Methods: Eighteen patients with N₂O abuse or vitamin B12 deficiency were recruited. Comprehensive central and peripheral neuro-diagnostic tests were performed, including whole spine MRI, and thermal quantitative sensory testing (QST). Specifically, paired motor and sensory nerve excitability tests were performed in order to obtain a complete picture of the sensorimotor axonal damage.

Results: The mean duration of N₂O exposure for the N₂O abuse patients was 17.13 ± 7.23 months. MRI revealed T2 hyperintensity in 87.5% of the N₂O abuse patients and 50% of the vitamin B12 deficiency patients. In N₂O abuse patients, the motor nerve excitability test showed decreased in peak response (7.08 ± 0.87 mV, P = 0.05), increased latency (7.09 ± 0.28 ms, P < 0.01), increased superexcitability (−32.95 ± 1.74%, P < 0.05), and decreased accommodation to depolarizing current [TEd (40–60 ms) 56.53 ± 0.70%, P < 0.05]; the sensory test showed only decreased peak response (30.54 ± 5.98 μV, P < 0.05). Meanwhile, motor test in vitamin B12 deficiency patients showed only decreased accommodation to depolarizing current [TEd (40–60 ms) 55.72 ± 1.60%, P < 0.01]; the sensory test showed decreased peak response (25.86 ± 3.44 μV, P < 0.05) increased superexcitability (−28.58 ± 3.71%, P < 0.001), increased subexcitability (8.31 ± 1.64%, P < 0.05), and decreased accommodation to depolarizing current [TEd (peak) 67.31 ± 3.35%, P < 0.001].

Conclusion: Compared to vitamin B12 deficiency, N₂O abuse patients showed prominent motor superexcitability changes and less prominent sensory superexcitability changes, hinting a unique pathological process different from that of vitamin B12 deficiency. N₂O abuse might cause axonal dysfunction not only by blocking methionine metabolism but also by toxicity affecting the paranodal region.

Nitrous oxide/oxygen mixture for analgesia in adult cancer patients with breakthrough pain: A randomized, double-blind controlled trial

BACKGROUND

The aim of this study was to assess the efficacy of a fixed nitrous oxide/oxygen mixture for the management of breakthrough cancer pain.

METHODS/DESIGN

A double-blind, placebo-controlled, randomized clinical trial was undertaken in the Medical ward of Tumor Hospital of General Hospital of Ningxia Medical University. 240 cancer patients with breakthrough pain were recruited and randomly received a standard pain treatment (morphine sulphate immediate release) plus a pre-prepared nitrous oxide/oxygen mixture, or the standard pain treatment plus oxygen. The primary endpoint measure was the numerical rating scale (NRS) score measured at baseline, 5 and 15 min after the beginning of treatment, and at 5 min post treatment.

RESULT

In all, analysis of pain score (NRS) at 5 min after the beginning of treatment shown a significant decrease in nitrous oxide/oxygen mixture treated patients with 2.8 ± 1.3 versus 5.5 ± 1.2 in controls (p < 0.01). At 15 min during the intervention, the mean pain score for nitrous oxide/oxygen was 2.0 ± 1.1 compared with 5.6 ± 1.3 for oxygen (p < 0.01).

CONCLUSION

This study shows that self-administered nitrous oxide/oxygen mixture was effective in reducing moderate to severe breakthrough pain among patients with cancer.

SIGNIFICANCE

The management of breakthrough cancer pain is always a challenge due to its temporal characteristics of rapid onset, moderate to severe in intensity, short duration (median 30-60 min). Our study find that self-administered nitrous oxide/oxygen mixture was effective in reducing moderate to severe breakthrough cancer pain.

Evidence for the involvement of opioid system in the antidepressant-like effect of ascorbic acid

Considering the involvement of the opioid system in major depressive disorder (MDD), mainly concerning refractory MDD, and the evidence that ascorbic acid may exert a beneficial effect for the treatment of this disorder, this study investigated the involvement of the opioid system in the antidepressant-like effect of ascorbic acid in the tail suspension test (TST). Treatment of Swiss mice with the non-selective opioid receptor antagonist naloxone (1 mg/kg, i.p.) prevented the reduced immobility time caused by ascorbic acid (1 mg/kg, p.o.) in the TST. Additionally, administration of the selective μ1-opioid receptor antagonist, naloxonazine (10 mg/kg, i.p.), also abolished the antidepressant-like action of the same dose of ascorbic acid in the TST. We also investigated the possible relationship between the opioid system and NMDA receptors in the mechanism of action of ascorbic acid or ketamine (0.1 mg/kg, i.p.) in the TST. Treatment of mice with naloxone (1 mg/kg, i.p.) blocked the synergistic antidepressant-like effect of ascorbic acid (0.1 mg/kg. p.o.) and MK-801 (0.001 mg/kg, p.o., a non-competitive NMDA receptor antagonist) in the TST. Combined administration of ketamine and MK-801 induced a synergistic antidepressant-like action, and naloxone partially abolished this effect. Our results indicate that the antidepressant-like effect of ascorbic acid in the TST appears to be dependent on the activation of the opioid system, especially μ1-opioid receptors, which might be an indirect consequence of NMDA receptor inhibition elicited by ascorbic acid administration.

The IMPROVE Guidelines (Ischaemia Models: Procedural Refinements Of in Vivo Experiments)

Most in vivo models of ischaemic stroke target the middle cerebral artery and a spectrum of stroke severities, from mild to substantial, can be achieved. This review describes opportunities to improve the in vivo modelling of ischaemic stroke and animal welfare. It provides a number of recommendations to minimise the level of severity in the most common rodent models of middle cerebral artery occlusion, while sustaining or improving the scientific outcomes. The recommendations cover basic requirements pre-surgery, selecting the most appropriate anaesthetic and analgesic regimen, as well as intraoperative and post-operative care. The aim is to provide support for researchers and animal care staff to refine their procedures and practices, and implement small incremental changes to improve the welfare of the animals used and to answer the scientific question under investigation. All recommendations are recapitulated in a summary poster (see supplementary information).

Should Nitrous Oxide Be Used for Laboring Patients?

Nitrous oxide, long used during labor in Europe, is gaining popularity in the United States. It offers many beneficial attributes, with few drawbacks. Cost, safety, and side effect profiles are favorable. Analgesic effectiveness is highly variable, yet maternal satisfaction is often high among the women who choose to use it. Despite being less effective in treating labor pain than neuraxial analgesic modalities, nitrous oxide serves the needs and preferences of a subset of laboring parturients. Nitrous oxide should, therefore, be considered for inclusion in the repertoire of modalities used to alleviate pain and facilitate effective coping during labor.

Molecular and Integrative Physiological Effects of Isoflurane Anesthesia: The Paradigm of Cardiovascular Studies in Rodents using Magnetic Resonance Imaging

To-this-date, the exact molecular, cellular, and integrative physiological mechanisms of anesthesia remain largely unknown. Published evidence indicates that anesthetic effects are multifocal and occur in a time-dependent and coordinated manner, mediated via central, local, and peripheral pathways. Their effects can be modulated by a range of variables, and their elicited end-effect on the integrative physiological response is highly variable. This review summarizes the major cellular and molecular sites of anesthetic action with a focus on the paradigm of isoflurane (ISO) - the most commonly used anesthetic nowadays - and its use in prolonged in vivo rodent studies using imaging modalities, such as magnetic resonance imaging (MRI). It also presents established evidence for normal ranges of global and regional physiological cardiac function under ISO, proposes optimal, practical methodologies relevant to the use of anesthetic protocols for MRI and outlines the beneficial effects of nitrous oxide supplementation.

Up: The rise of nitrous oxide abuse. An international survey of contemporary nitrous oxide use

In recent years the recreational use of inhaled nitrous oxide gas (N2O) is becoming increasingly popular, yet little is known about the characteristics of its users or the effects they experience. This paper presents original research from the 2014 Global Drug Survey (GDS) (n=74,864). GDS runs the largest survey of recreational drug use in the world. The findings confirm N2O as a very common drug of use, in particular in the UK and US (38.6% and 29.4% lifetime prevalence). In the UK N2O was reported to be the eighth most commonly used substance. N2O was generally consumed via gas-filled balloons, at festivals and clubs where use of other substances was common. The vast majority of users use infrequently, and their use is not associated with significant harm. However, there appears to be a subpopulation of heavy users who may be using in a dependent pattern. Analysis of last year N2O users (n=4883), confirms that N2O is associated with hallucinations and confusion (which may be the desired effects) and persistent numbness and accidental injury (27.8%, 23.9%, 4.3% and 1.2% of last year users, respectively). Accidental injury is associated with the highest number of 'hits' per session, suggesting a dose-response relationship. The presence of significant harm is discussed in the light of public education on the risks of N2O use and harm-reduction strategies appropriate to N2O use. Further work needs to be completed to confirm the presence of persistent neurological symptoms in recreational users.

Leukocyte DNA Damage and Wound Infection after Nitrous Oxide Administration

Background:

Nitrous oxide inactivates methionine synthase and may lead to DNA damage and wound infection. By using single-cell gel electrophoresis (comet assay), the authors determined the effect of nitrous oxide on DNA damage in circulating leukocytes.

Methods:

In this double-blind, randomized controlled trial, 91 patients undergoing major colorectal surgery were randomized to receive 70% nitrous oxide (n = 31) or nitrous oxide-free anesthesia using 30 (n = 30) or 80% (n = 30) oxygen. Venous blood was collected before and 24 h after surgery. The primary outcome was extent of DNA damage, quantified as the percentage of DNA staining intensity in the comet tail using digital fluorescence microscopy. Incidence of postoperative wound infection was also recorded.

Results:

Nitrous oxide exposure was associated with a two-fold increase in the percentage of DNA intensity in tail (P = 0.0003), but not in the 30 (P = 0.181) or 80% oxygen groups (P = 0.419). There was a positive correlation between the duration of nitrous oxide exposure and extent of DNA damage, r = 0.33, P = 0.029. However, no correlation was observed in nitrous oxide-free patients. The proportions of postoperative wound infection, using the Centers for Disease Control and Prevention criteria, were 19.4% (6 of 31) in the 70% nitrous oxide group and 6.7% (2 of 30) in both the 30 and 80% oxygen groups, P = 0.21. An increase in DNA damage was associated with a higher risk of wound infection, adjusted odds ratio (95% CIs): 1.19 (1.07–1.34), P = 0.003.

Conclusions:

Nitrous oxide increased DNA damage compared with nitrous oxide-free anesthesia and was associated with postoperative wound infection.

Inhaled analgesia for pain management in labour

BACKGROUND

Many women would like to have a choice in pain relief during labour and also would like to avoid invasive methods of pain management in labour. Inhaled analgesia during labour involves the self-administered inhalation of sub-anaesthetic concentrations of agents while the mother remains awake and her protective laryngeal reflexes remain intact. Most of the agents are easy to administer, can be started in less than a minute and become effective within a minute.

OBJECTIVES

To examine the effects of all modalities of inhaled analgesia on the mother and the newborn for mothers who planned to have a vaginal delivery.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2012), ClinicalTrials.gov, and Current Controlled Trials (2 June 2012), handsearched conference proceedings from the American Society of Clinical Anesthesia (from 1990 to 2011), contacted content experts and trialists and searched reference lists of retrieved studies.

SELECTION CRITERIA

Randomised controlled trials comparing inhaled analgesia with other inhaled analgesia or placebo or no treatment or other methods of non-pharmacological pain management in labour.

DATA COLLECTION AND ANALYSIS

Review authors independently assessed trials for eligibility, methodological quality and extracted all data. Data were double checked for accuracy.

MAIN RESULTS

Twenty-six studies, randomising 2959 women, were included in this review.Inhaled analgesia versus a different type of inhaled analgesia Pain relief was measured using a Visual Analogue Scale (VAS) from 0 to 100 mm where 100 corresponds to the most relief. Pain intensity was measured using a VAS from 0 to 100 mm, where 0 corresponds to no pain at all and 100 corresponds to the worst pain. The highest score for pain relief is the most positive in contrast to 'pain intensity' in which the higher score is more negative. Flurane derivatives were found to offer better pain relief than nitrous oxide in first stage of labour as measured by a lower pain intensity score (average mean difference (MD) 14.39, 95% confidence interval (CI) 4.41 to 24.37, three studies, 70 women), also a higher pain relief score for flurane derivatives compared with nitrous oxide (average MD -16.32, 95% CI -26.85 to -5.79, two studies, 70 women). Substantial heterogeneity was found in the analyses of pain intensity (P = 0.003) and in the analysis of pain relief (P = 0.002).These findings should be considered with caution because of the questionable design of the included cross-over trials. More nausea was found in the nitrous oxide group compared with the flurane derivatives group (risk ratio (RR) 6.60 95% CI 1.85 to 23.52, two studies, 98 women).Inhaled analgesia versus placebo or no treatment Placebo or no treatment was found to offer less pain relief compared to nitrous oxide (average RR 0.06, 95% CI 0.01 to 0.34, two studies, 310 women; MD -3.50, 95% CI -3.75 to -3.25, one study, 509 women). However, nitrous oxide resulted in more side effects for women such as nausea (RR 43.10, 95% CI 2.63 to 706.74, one study, 509 women), vomiting (RR 9.05, 95% CI 1.18 to 69.32, two studies, 619 women), dizziness (RR 113.98, 95% CI 7.09 to 1833.69, one study, 509 women) and drowsiness (RR 77.59, 95% CI 4.80 to 1254.96, one study, 509 women) when compared with placebo or no treatment.There were no significant differences found for any of the outcomes in the studies comparing one strength versus a different strength of inhaled analgesia, in studies comparing different delivery systems or in the study comparing inhaled analgesia with TENS.Due to lack of data, the following outcomes were not analysed within the review: sense of control; satisfaction with childbirth experience; effect on mother/baby interaction; breastfeeding; admission to special care baby unit; poor infant outcomes at long-term follow-up; or costs.

AUTHORS' CONCLUSIONS

Inhaled analgesia appears to be effective in reducing pain intensity and in giving pain relief in labour. However, substantial heterogeneity was detected for pain intensity. Furthermore, nitrous oxide appears to result in more side effects compared with flurane derivatives. Flurane derivatives result in more drowsiness when compared with nitrous oxide. When inhaled analgesia is compared with no treatment or placebo, nitrous oxide appears to result in even more side effects such as nausea, vomiting, dizziness and drowsiness. There is no evidence for differences for any of the outcomes comparing one strength verus a different strength of inhaled analgesia, comparing different delivery systems or comparing inhaled analgesia with TENS.

Single sevoflurane exposure decreases neuronal nitric oxide synthase levels in the hippocampus of developing rats

BACKGROUND

The use of general anaesthetics in young children and infants has raised concerns regarding the adverse effects of these drugs on brain development. Sevoflurane might have harmful effects on the developing brain; however, these effects have not been well investigated.

METHODS

Postnatal day 7 (P7) Sprague-Dawley rats were continuously exposed to 2.3% sevoflurane for 6 h. We used the Fox battery test and Morris water maze (MWM) to examine subsequent neurobehavioural performance. Cleaved caspase-3 and neuronal nitric oxide synthase (nNOS) were quantified by immunoblotting, and the Nissl staining was used to observe the histopathological changes in the hippocampus.

RESULTS

A single 6 h sevoflurane exposure at P7 rats resulted in increased cleaved caspase-3 expression and decreased nNOS levels in the hippocampus, and induced the loss of pyramidal neurones in the CA1 and CA3 subfields of the hippocampus at P7-8. These changes were accompanied by temporal retardation of sensorimotor reflexes. However, neither the Fox battery test at P1-21 nor the MWM test at P28-32 showed differences between the air- and sevoflurane-treated groups.

CONCLUSIONS

Although early exposure to sevoflurane increases activated caspase-3 expression and neuronal loss and decreases nNOS in the neonatal hippocampus, it does not affect subsequent neurobehavioural performances in juvenile rats.

Pain management for women in labour: an overview of systematic reviews

BACKGROUND

The pain that women experience during labour is affected by multiple physiological and psychosocial factors and its intensity can vary greatly.  Most women in labour require pain relief. Pain management strategies include non-pharmacological interventions (that aim to help women cope with pain in labour) and pharmacological interventions (that aim to relieve the pain of labour).

OBJECTIVES

To summarise the evidence from Cochrane systematic reviews on the efficacy and safety of non-pharmacological and pharmacological interventions to manage pain in labour. We considered findings from non-Cochrane systematic reviews if there was no relevant Cochrane review.

METHODS

We searched the Cochrane Database of Systematic Reviews (The Cochrane Library 2011, Issue 5), The Cochrane Database of Abstracts of Reviews of Effects (The Cochrane Library 2011, Issue 2 of 4), MEDLINE (1966 to 31 May 2011) and EMBASE (1974 to 31 May 2011) to identify all relevant systematic reviews of randomised controlled trials of pain management in labour. Each of the contributing Cochrane reviews (nine new, six updated) followed a generic protocol with 13 common primary efficacy and safety outcomes. Each Cochrane review included comparisons with placebo, standard care or with a different intervention according to a predefined hierarchy of interventions. Two review authors extracted data and assessed methodological quality, and data were checked by a third author. This overview is a narrative summary of the results obtained from individual reviews.

MAIN RESULTS

We identified 15 Cochrane reviews (255 included trials) and three non-Cochrane reviews (55 included trials) for inclusion within this overview. For all interventions, with available data, results are presented as comparisons of: 1. Intervention versus placebo or standard care; 2. Different forms of the same intervention (e.g. one opioid versus another opioid); 3. One type of intervention versus a different type of intervention (e.g. TENS versus opioid). Not all reviews included results for all comparisons. Most reviews compared the intervention with placebo or standard care, but with the exception of opioids and epidural analgesia, there were few direct comparisons between different forms of the same intervention, and even fewer comparisons between different interventions. Based on these three comparisons, we have categorised interventions into: " What works" ,"What may work", and "Insufficient evidence to make a judgement".WHAT WORKSEvidence suggests that epidural, combined spinal epidural (CSE) and inhaled analgesia effectively manage pain in labour, but may give rise to adverse effects. Epidural, and inhaled analgesia effectively relieve pain when compared with placebo or a different type of intervention (epidural versus opioids). Combined-spinal epidurals relieve pain more quickly than traditional or low dose epidurals. Women receiving inhaled analgesia were more likely to experience vomiting, nausea and dizziness.When compared with placebo or opioids, women receiving epidural analgesia had more instrumental vaginal births and caesarean sections for fetal distress, although there was no difference in the rates of caesarean section overall. Women receiving epidural analgesia were more likely to experience hypotension, motor blockade, fever or urinary retention. Less urinary retention was observed in women receiving CSE than in women receiving traditional epidurals. More women receiving CSE than low-dose epidural experienced pruritus.  WHAT MAY WORKThere is some evidence to suggest that immersion in water, relaxation, acupuncture, massage and local anaesthetic nerve blocks or non-opioid drugs may improve management of labour pain, with few adverse effects.  Evidence was mainly limited to single trials. These interventions relieved pain and improved satisfaction with pain relief (immersion, relaxation, acupuncture, local anaesthetic nerve blocks, non-opioids) and childbirth experience (immersion, relaxation, non-opioids) when compared with placebo or standard care. Relaxation was associated with fewer assisted vaginal births and acupuncture was associated with fewer assisted vaginal births and caesarean sections.INSUFFICIENT EVIDENCEThere is insufficient evidence to make judgements on whether or not hypnosis, biofeedback, sterile water injection, aromatherapy, TENS, or parenteral opioids are more effective than placebo or other interventions for pain management in labour. In comparison with other opioids more women receiving pethidine experienced adverse effects including drowsiness and nausea. 

AUTHORS' CONCLUSIONS

Most methods of non-pharmacological pain management are non-invasive and appear to be safe for mother and baby, however, their efficacy is unclear, due to limited high quality evidence. In many reviews, only one or two trials provided outcome data for analysis and the overall methodological quality of the trials was low. High quality trials are needed.There is more evidence to support the efficacy of pharmacological methods, but these have more adverse effects. Thus, epidural analgesia provides effective pain relief but at the cost of increased instrumental vaginal birth.It remains important to tailor methods used to each woman's wishes, needs and circumstances, such as anticipated duration of labour, the infant's condition, and any augmentation or induction of labour.A major challenge in compiling this overview, and the individual systematic reviews on which it is based, has been the variation in use of different process and outcome measures in different trials, particularly assessment of pain and its relief, and effects on the neonate after birth. This made it difficult to pool results from otherwise similar studies, and to derive conclusions from the totality of evidence. Other important outcomes have simply not been assessed in trials; thus, despite concerns for 30 years or more about the effects of maternal opioid administration during labour on subsequent neonatal behaviour and its influence on breastfeeding, only two out of 57 trials of opioids reported breastfeeding as an outcome. We therefore strongly recommend that the outcome measures, agreed through wide consultation for this project, are used in all future trials of methods of pain management.

Nitrous oxide for labor analgesia: expanding analgesic options for women in the United States

Nitrous oxide (N2O) is a commonly used labor analgesic in many Western countries, but is used infrequently in the United States. The University of California at San Francisco has been offering N2O for labor analgesia for more than 30 years. Vanderbilt University Medical Center recently began offering N2O as an option for pain relief in laboring women. Many women report that N2O provides effective pain relief during labor and argue that it should be made more widely available in the United States. This article discusses the use of N2O for pain management during labor, including its history, properties, clinical indications, and use and environmental safety issues. Practical issues regarding implementation of N2O service in a medical center setting are also discussed.

Nitrous oxide and perioperative cardiac morbidity (ENIGMA-II) Trial: rationale and design

BACKGROUND

Globally there are >200 million major surgical procedures undertaken annually, and about 20% of these involve patients who have coronary artery disease. Many receive nitrous oxide, which impairs methionine synthase, thus inhibiting folate synthesis and increasing postoperative homocysteine levels. Nitrous oxide anesthesia leads to postoperative endothelial dysfunction, and there is some evidence that it increases myocardial ischemia and, possibly, myocardial infarction. We have initiated the Nitrous oxide and perioperative cardiac morbidity (ENIGMA-II) Trial to test the hypothesis that in inpatients undergoing anesthesia for major noncardiac surgery, avoidance of nitrous oxide will reduce the incidence of death and major cardiovascular events.

METHODS

ENIGMA-II is a 7,000-patient, international randomized trial involving patients at risk of coronary artery disease undergoing noncardiac surgery. The patients, health care providers (except for the anesthesiologists), data collectors, and outcome adjudicators are blinded to whether patients receive nitrous oxide-containing or nitrous oxide-free anesthetic. The primary outcome is a composite of death and major nonfatal events (ie, myocardial infarction, cardiac arrest, pulmonary embolism, and stroke) at 30 days after surgery.

RESULTS

At present, ENIGMA-II has randomized >1,000 patients in 22 hospitals in 5 countries. To date, patients' mean age is 70 years, 66% are men, 38% have a history of coronary artery disease, 19% have a history of cerebrovascular disease, and 84% have a history of hypertension. Most patients have undergone intra-abdominal 28%, vascular 32%, and orthopedic 16% surgery.

CONCLUSIONS

The ENIGMA-II Trial will be the largest study yet conducted to ascertain the benefits and risks of removing nitrous oxide from the gas mixture in anesthesia. The results of this large international trial will guide the clinical care of the hundreds of millions of adults undergoing noncardiac surgery annually.

Evidence for the involvement of the opioid system in the antidepressant-like effect of folic acid in the mouse forced swimming test

The opioid system has been implicated in major depression and in the mechanism of action of antidepressants. This study investigated the involvement of the opioid system in the antidepressant-like effect of the water-soluble B-vitamin folic acid in the forced swimming test (FST). The effect of folic acid (10 nmol/site, i.c.v.) was prevented by the pretreatment of mice with naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist), naltrindole (3 mg/kg, i.p., a selective delta-opioid receptor antagonist), naloxonazine (10 mg/kg, i.p., a selective mu(1)-opioid receptor antagonist, 24 h before), but not with naloxone methiodide (1 mg/kg, s.c., a peripherally acting opioid receptor antagonist). In addition, a sub-effective dose of folic acid (1 nmol/site, i.c.v.) produced a synergistic antidepressant-like effect in the FST with a sub-effective dose of morphine (1 mg/kg, s.c.). A further approach was designed to investigate the possible relationship between the opioid system and NMDA receptors in the mechanism of action of folic acid in the FST. Pretreatment of the animals with naloxone (1 mg/kg, i.p.) prevented the synergistic antidepressant-like effect of folic acid (1 nmol/site, i.c.v.) and MK-801 (0.001 mg/kg, i.p., a non-competitive NMDA receptor antagonist). Together the results firstly indicate that the anti-immobility effect of folic acid in the FST is mediated by an interaction with the opioid system (mu(1) and delta), likely dependent on the inhibition of NMDA receptors elicited by folic acid.

Alpha-chloralose is a suitable anesthetic for chronic focal cerebral ischemia studies in the rat: a comparative study

alpha-Chloralose is widely used as an anesthetic in studies of the cerebrovasculature because it provides robust metabolic and hemodynamic responses to functional stimulation. However, there have been no controlled studies of focal ischemia in the rat under alpha-chloralose anesthesia. Artificially ventilated rats were prepared using 1.2-1.5% isoflurane anesthesia for filament occlusion of the right middle cerebral artery (MCA), and anesthesia was either switched to alpha-chloralose (60 mg/kg bolus, 30 mg/kg/h; n=10) or was maintained on 1% isoflurane (n=10). Following temporary MCA occlusion EEG was monitored from a screw electrode and changes in cerebral blood flow (rCBF) measured with a laser Doppler probe placed over the ischemic cortex. This study shows that alpha-chloralose is a safe anesthetic for ischemia studies and provides excellent survival. Compared with isoflurane, the cortical and total infarct volumes are larger in the alpha-chloralose-anesthetized animals, while the functional outcome at 72 h is similar. The total duration of peri-infarct flow transients (PIFTs) is also significantly longer in alpha-chloralose-anesthetized animals. The average amplitude of the flow transients showed a good correlation with the extent of edema in all animals as did the total duration of non-convulsive seizures (NCS) in the alpha-chloralose-anesthetized animals.

Nitrous oxide inhibits glutamatergic transmission in spinal dorsal horn neurons

The effects of nitrous oxide (N2O) are thought to be mediated by several pharmacological pathways at different levels of the central nervous system. Here, we focus on excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord with respect to its importance for the nociceptive processing. The effects of 50% N2O on electrically evoked and spontaneous excitatory glutamatergic transmission and on the response to exogenous administration of N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptor agonists were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. Peak amplitudes of Adelta- and C-fiber evoked monosynaptic NMDA- and AMPA-receptor-mediated excitatory postsynaptic currents (EPSCs) were decreased in the presence of N2O. N2O reduced the peak amplitude and integrated area of exogenous NMDA- and AMPA-induced currents. Moreover N2O changed the distribution of miniature EPSC amplitude, but not frequency distribution in most neurons. N2O inhibits glutamatergic transmission in the superficial dorsal horn by modulating the NMDA- and AMPA-receptors. Our findings raise the possibility that the antinociceptive effect of N2O may be directly mediated at the level of the spinal cord.

Preoperative folate and homocysteine status in patients undergoing major surgery

BACKGROUND & AIMS

Patients with folate deficiency and elevated homocysteine (Hcy) levels have increased risk of cerebrovascular and cardiovascular disease. They may also be at increased risk of complications after surgery because nitrous oxide interferes with folate metabolism. The aim of this study was to assess the incidence of folate deficiency and hyperhomocysteinemia in patients presenting for major surgery. We also tested the utility of a brief preoperative medical and dietary questionnaire to identify those with low folate or elevated Hcy levels.

METHODS

We enrolled 390 patients and obtained a preoperative fasting blood sample from each of the study participants (folate [n=386], homocysteine [n=387]).

RESULTS

Although only one patient had folate deficiency preoperatively (incidence +/-SD folate and Hcy concentrations were 23.7+/-5.2 nmol/l and 9.4+/-4.2 micromol/l, respectively. There was a negative correlation between folate and Hcy, r=-0.27, P<0.001. Multivariate analyses indicated that vegan status and folate supplementation prevented low folate status (P<0.05), while age of the patient, and history of heart failure and anaemia predicted elevated Hcy concentration.

CONCLUSIONS

Some factors identified by a brief medical and dietary questionnaire are associated with folate and homocysteine status. Hyperhomocysteinaemia occurs in about 7.5% of surgical patients; however, both low folate status and elevated Hcy concentration are less likely in those taking folate or vitamin B supplements. This has implications for patients undergoing nitrous oxide anaesthesia because of its inhibition of folate metabolism, and should prompt clinicians to consider folate and other nutritional supplementation before elective surgery.

Nitrous Oxide Administered by the Plastic Surgeon for Repair of Facial Lacerations in Children in the Emergency Room

BACKGROUND

The purpose of this study was to investigate a means of providing pain relief during repair of facial lacerations in children in the emergency room.

METHODS

This study was conducted in the emergency room of a tertiary care, university-affiliated hospital. Fifty percent nitrous oxide was administered by the surgeon who sutured the laceration. A nurse monitored the child throughout the procedure. At the end of the procedure, pain scores were evaluated by the surgeon and nurse using the FLACC (face, legs, activity, cry, and consolability) scale, a structured observational-behavioral scale for measurement of pain.

RESULTS

Sixty patients between the ages of 1 and 16 years participated in the study. Of these, 15 were sutured using standard care (lidocaine infiltration), and 45 children received nitrous oxide in addition to lidocaine infiltration. Nitrous oxide was administered for an average of 11.9 +/- 5.1 minutes (range, 4 to 30 minutes). Forty-three children recovered to preprocedure activity in less than 1 minute. Two children recovered in less than 3 minutes. Average FLACC scores during infiltration and suturing were significantly lower in the nitrous oxide group compared with controls (infiltration, 1.9 of 10 versus 9.7 of 10; suturing, 2 of 10 versus 8.8 of 10). Forceful restraining was necessary in all the controls, whereas in the nitrous oxide group mild force was required in only 15 percent. Seventy percent of the children receiving nitrous oxide had no side effects. Vomiting and nausea were the most common (17 percent), transient side effects. No respiratory or cardiovascular side effects occurred.

CONCLUSIONS

Nitrous oxide can be safely administered by plastic surgeons while suturing facial lacerations in the emergency room. The fast onset and rapid recovery characteristics of nitrous oxide provide a convenient environment for performing short surgical procedures. This safe method for provision of analgesia and anxiolysis may be appealing to plastic surgeons for ambulatory procedures (e.g., suture removal, expander inflation, Botox injection, injection of various fillers) in pediatric and adult populations.