Nitrous Oxide Use Precipitates Pulmonary Embolism: A Case Report

Nitrous oxide (N2O) has a lengthy history of use as an anesthetic and has recently found popularity as a recreational euphoric hallucinogen. The odorless, colorless, non-flammable gas interferes with Vitamin B12 resulting in a cascade of effects, including hyperhomocysteinemia. It has long been proposed that hyperhomocysteinemia adversely affects the cardiovascular system, producing atherogenic and prothrombotic diseases. In this case vignette, we describe a case in which a healthy patient presented with venous thromboembolism (VTE) that we suspect could have been precipitated by daily and significant recreational use of N2O. Anticoagulation therapy was given, and there was a significant improvement in the pulmonary emboli. As recreational use of N2O increases, it is essential to recognize that hyperhomocysteinemia may also produce a thrombotic state.

Nitrous oxide abuse in a 21-year-old female: a case report and review of literature

The abuse of nitrous oxide (N2O) poses a substantial public health challenge. In many countries, including China, regulations governing the utilization and accessibility to N2O remain ambiguous, particularly within the food industry. Here, we report a case of a 21-year-old female who presented with symptoms of subacute combined degeneration (SCD) of the spinal cord due to N2O abuse. The patient exhibited bilateral lower limb numbness and weakness, low serum vitamin B12 levels with elevated homocysteine levels, and lumbar spine magnetic resonance imaging (MRI) revealed abnormal signals of the spinal cord. Following cessation of N2O and comprehensive therapy including methylcobalamin and nerve growth factor, the symptoms significantly improved. A follow-up examination 3 months later showed good progress in gait stability. At a 5-year follow-up, the patient's previous clinical symptoms had completely disappeared, and her quality of life had returned to normal. This case underscores the urgency of raising awareness and prevention of N2O abuse, emphasizing the importance of timely diagnosis and comprehensive treatment for patient recovery. Clear formulation and enforcement of relevant regulatory measures are equally crucial in reducing instances of abuse.

Increased thyroid stimulating hormone (TSH) as a possible risk factor for atherosclerosis in subclinical hypothyroidism

Primary hypothyroidism (PHT) is associated with an increased risk for the development of atherosclerosis (AS) and other cardiovascular disorders. PHT induces atherosclerosis (AS) through the induction of endothelial dysfunction, and insulin resistance (IR). PHT promotes vasoconstriction and the development of hypertension. However, patients with subclinical PHT with normal thyroid hormones (THs) are also at risk for cardiovascular complications. In subclinical PHT, increasing thyroid stimulating hormone (TSH) levels could be one of the causative factors intricate in the progression of cardiovascular complications including AS. Nevertheless, the mechanistic role of PHT in AS has not been fully clarified in relation to increased TSH. Therefore, in this review, we discuss the association between increased TSH and AS, and how increased TSH may be involved in the pathogenesis of AS. In addition, we also discuss how L-thyroxine treatment affects the development of AS.

The safety of nitrous oxide: glass half-full or half-empty?

A systematic review of clinical trials confirms that including nitrous oxide in the gas mixture for general anaesthesia has minor short-term benefits and does not impact most patient safety outcomes. However, no risk-benefit analysis of nitrous oxide should ignore its known environmental effects. If continued nitrous oxide use is supported, strategies to minimise and monitor the contribution of medical nitrous oxide to global warming are vital.

Parkinson's Disease Risk and Hyperhomocysteinemia: The Possible Link

Parkinson's disease (PD) is one of the most common degenerative brain disorders caused by the loss of dopaminergic neurons in the substantia nigra (SN). Lewy bodies and -synuclein accumulation in the SN are hallmarks of the neuropathology of PD. Due to lifestyle changes and prolonged L-dopa administration, patients with PD frequently have vitamin deficiencies, especially folate, vitamin B6, and vitamin B12. These disorders augment circulating levels of Homocysteine with the development of hyperhomocysteinemia, which may contribute to the pathogenesis of PD. Therefore, this review aimed to ascertain if hyperhomocysteinemia may play a part in oxidative and inflammatory signaling pathways that contribute to PD development. Hyperhomocysteinemia is implicated in the pathogenesis of neurodegenerative disorders, including PD. Hyperhomocysteinemia triggers the development and progression of PD by different mechanisms, including oxidative stress, mitochondrial dysfunction, apoptosis, and endothelial dysfunction. Particularly, the progression of PD is linked with high inflammatory changes and systemic inflammatory disorders. Hyperhomocysteinemia induces immune activation and oxidative stress. In turn, activated immune response promotes the development and progression of hyperhomocysteinemia. Therefore, hyperhomocysteinemia-induced immunoinflammatory disorders and abnormal immune response may aggravate abnormal immunoinflammatory in PD, leading to more progression of PD severity. Also, inflammatory signaling pathways like nuclear factor kappa B (NF-κB) and nod-like receptor pyrin 3 (NLRP3) inflammasome and other signaling pathways are intricate in the pathogenesis of PD. In conclusion, hyperhomocysteinemia is involved in the development and progression of PD neuropathology either directly via induction degeneration of dopaminergic neurons or indirectly via activation of inflammatory signaling pathways.

Nitrous oxide abuse leading to extreme homocysteine levels and thrombosis in young adults: a case series

BACKGROUND

Neurologic complications from recreational use of nitrous oxide (N₂O), which are attributed to vitamin B12 deficiency, have been well documented. With increasing dosages and frequency of N₂O use, an additional association with thromboembolisms is becoming apparent.

OBJECTIVES

To assess thrombotic complications of recreational N₂O use.

METHODS

All medical charts at the largest hospital in Amsterdam were searched for N₂O use and subsequent neurologic and/or thrombotic events. For patients with thrombotic events, we extracted data on the risk factors for arterial and venous thrombosis as well as serum vitamin B12 and homocysteine concentrations.

RESULTS

Between January 2015 and May 2021, 326 patients who reported recreational use of N₂O were identified; of these, 17 (5%) patients presented with severe thrombotic events associated with N₂O (71% men; median age, 26 years [range, 18-53 years]), 5 patients presented with arterial thrombosis (3 with acute coronary syndrome, 1 with femoral artery thrombosis, and 1 with middle cerebral artery thrombus), and 12 patients presented with venous thromboembolisms (10 with pulmonary embolisms, 1 with portal vein thrombosis and 1 with cerebral vein thrombosis). Additionally, homocysteine were concentrations severely increased (median, 125 μmol/L [range, 22-253 μmol/L]; reference, <15 μmol/L). Patients reported use of 400 to 6000 g (ie, 50-750 balloons) of N₂O in 1 day. Fifty percent of these patients had experienced neurologic symptoms before the thrombotic event.

CONCLUSION

We describe an alarming incidence of serious thrombotic events among young adults after excessive recreational use of N₂O, accompanied by extremely high homocysteine concentrations. The upward trend in the recreational use of N₂O warrants more awareness of its dangers among both users and medical professionals. Furthermore, these findings could reopen the discussion on possible associations between hyperhomocysteinemia and thrombosis mediated through N₂O.

Nitrous oxide intoxication: systematic literature review and proposal of new diagnostic possibilities

Background

Nitrous oxide (N2O), also called “laughing gas,” is the most commonly used inhalation anesthetic in dentistry. The N2O is no longer used, because of the long-term neurologic and cardiovascular sequelae. Due to its sedative and euphoric properties, N2O is often used for recreational use or in some erotic activities. Accidental deaths are mainly associated with the uses of N2O: death can occur from sudden cardiac arrhythmia or, most commonly, acute asphyxiation due to hypoxia. This paper aims to study the literature concerning deaths due to N2O intoxication and highlight pathological findings useful for diagnosis when the crime scene investigation does not reveal any evidence.

Materials and methods

The authors conducted the literature search by PubMed and Scopus databases, searching for articles from 1 January 1970 to 1 March 2020 using the key terms: “Nitrous oxide,” “Laughing gas,” “Hypoxic damage,” “Nitrous oxide anesthesia,” and “Nitrous oxide death.”

Results and discussion

A total of 244 articles were collected. Only 26 articles were included in the systematic review. Most of the deaths from intoxication are due to asphyxiation; the diagnosis is often difficult and immunohistochemistry could be helpful. Nitrous oxide increases the intracellular adhesion molecule expression, E- and P-Selectin (markers of the early inflammatory response), and HIF-1 α (indicative of oxidative stress during ischemia-reperfusion).

Conclusion

The macroscopic and microscopic signs of N2O intoxication are non-specific, but N2O has been proven to cause hypoxic damage to the brain. The suspicion of the presence of the gas in the environment should guide the pathologist. Tissue analyzes provide important information; immunohistochemical stains can confirm hypoxic damage through the use of markers such as HIF-1 α, E-Selectin, and P-Selectin.

The effects of cardiovascular and orthopaedic surgery on vitamin concentrations: a narrative review of the literature and mechanisms of action

Given the rise in worldwide chronic diseases, supplemented by an aging population, the volume of global major surgeries, encompassing cardiac and orthopedic procedures is anticipated to surge significantly. Surgical trauma can be accompanied by numerous postoperative complications and metabolic changes. The present review summarized the results from studies assessing the effects of orthopedic and cardiovascular surgery on vitamin concentrations, in addition to exploring the possible mechanisms associated with changes in concentrations. Studies have revealed a potentially severe depletion in plasma/serum concentrations of numerous vitamins following these surgeries acutely. Vitamins C, D and B1 appear particularly vulnerable to significant depletions, with vitamin C and D depletions consistently transpiring into inadequate and deficient concentrations, respectively. The possible multifactorial mechanisms impacting postoperative vitamin concentrations include changes in hemodilution and vitamin utilization, redistribution, circulatory transport and absorption. For a majority of vitamins, there has been a lack of investigation into the effects of both, cardiac and orthopedic surgery. Additionally, studies were predominantly restricted to short-term postoperative investigations, primarily performed within the first postoperative week of surgery. Overall, results indicated that further examination is necessary to determine the severity and clinical significance of the possible depletions in vitamin concentrations that ensue cardiovascular and orthopedic surgery.

A 19-Year-Old Man with a History of Recreational Inhalation of Nitrous Oxide with Severe Peripheral Neuropathy and Central Pulmonary Embolism

Patient: Male, 19-year-old

Final Diagnosis: Peripheral neuropathy • pulmonary embolism • vitamin B₁₂ deficiency

Symptoms: Balance problems • muscle weakness • sensorial deficit • thoracic pain

Medication:—

Clinical Procedure: —

Specialty: Cardiology • Laboratory Diagnostics • Neurology

Perioperative Care of Patients at High Risk for Stroke During or After Non-cardiac, Non-neurological Surgery: 2020 Guidelines From the Society for Neuroscience in Anesthesiology and Critical Care

Perioperative stroke is associated with considerable morbidity and mortality. Stroke recognition and diagnosis are challenging perioperatively, and surgical patients receive therapeutic interventions less frequently compared with stroke patients in the outpatient setting. These updated guidelines from the Society for Neuroscience in Anesthesiology and Critical Care provide evidence-based recommendations regarding perioperative care of patients at high risk for stroke. Recommended areas for future investigation are also proposed.

Vitamin B12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls

Vitamin B₁₂ (cobalamin) is an essential cofactor for two metabolic pathways. It is obtained principally from food of animal origin. Cobalamin becomes bioavailable through a series of steps pertaining to its release from dietary protein, intrinsic factor-mediated absorption, haptocorrin or transcobalamin-mediated transport, cellular uptake, and two enzymatic conversions (via methionine synthase and methylmalonyl-CoA-mutase) into cofactor forms: methylcobalamin and adenosylcobalamin. Vitamin B₁₂ deficiency can masquerade as a multitude of illnesses, presenting different perspectives from the point of view of the hematologist, neurologist, gastroenterologist, general physician, or dietician. Increased physician vigilance and heightened patient awareness often account for its early presentation, and testing sometimes occurs during a phase of vitamin B₁₂ insufficiency before the main onset of the disease. The chosen test often depends on its availability rather than on the diagnostic performance and sensitivity to irrelevant factors interfering with vitamin B₁₂ markers. Although serum B₁₂ is still the most commonly used and widely available test, diagnostics by holotranscobalamin, serum methylmalonic acid, and plasma homocysteine measurements have grown in the last several years in routine practice. The lack of a robust absorption test, coupled with compromised sensitivity and specificity of other tests (intrinsic factor and gastric parietal cell antibodies), hinders determination of the cause for depleted B₁₂ status. This can lead to incorrect supplementation regimes and uncertainty regarding later treatment. This review discusses currently available knowledge on vitamin B₁₂, informs the reader about the pitfalls of tests for assessing its deficiency, reviews B₁₂ status in various populations at different disease stages, and provides recommendations for interpretation, treatment, and associated risks. Future directions for diagnostics of B₁₂ status and health interventions are also discussed.

Recreational Nitrous Oxide Abuse: Prevalence, Neurotoxicity, and Treatment

Nitrous oxide (N₂O), also known as "laughing gas," is a colorless, nonirritating gas. Clinically, it is widely used as an inhaled anesthetic, analgesic, and anxiolytic. In recent years, recreational abuse of N₂O has become increasingly common, especially among young adults and adolescents, but many of them lack awareness of the possible side effects associated with this drug. N₂O abuse can damage multiple systems, especially the nervous system, but the exact mechanism of N₂O toxicity remains controversial. At present, an increasing number of cases of nervous system damage caused by N₂O abuse have been reported both at home and abroad. Discontinuation of N₂O use and timely supplementation with vitamin B12 are essential for a good prognosis. Long-term abuse without timely treatment will eventually lead to irreversible neurological damage. In this article, we discuss the epidemiology of N₂O abuse, neurotoxicity mechanisms, clinical manifestations, relevant auxiliary examinations, treatments, and prognosis to improve social awareness of N₂O exposure risk, especially among users and clinicians.

Should nitrous oxide ever be used in oncology patients receiving methotrexate therapy?

Nitrous oxide (N₂ O) is frequently used for short anesthesia/analgesia in children undergoing painful or repetitive procedures. Children with acute lymphoblastic leukemia (ALL) require repeated lumbar punctures with direct instillation of intrathecal chemotherapy, usually the anti-folate agent methotrexate, during their treatment. These procedures are frequently performed under anesthesia. Concerns have been intermittently raised about a drug interaction between methotrexate and N₂ O that may potentiate the undesirable side effects of methotrexate, including neurotoxicity. However, the clinical evidence consists mainly of isolated case reports leading to a lack of consensus among pediatric anesthetists about the relative risk benefits of using N₂ O in children with ALL. In this article, we review the biochemical basis and scientific observations that suggest a significant interaction between N₂ O and methotrexate due to their dual inhibition of the key enzyme methionine synthase. The possible role of this interaction in potentiating neurotoxicity in children with cancer is discussed, and arguments and counterarguments about the clinical significance of this largely theoretical relationship are explored. Following comprehensive review of all the available data, we make the case for the circumstantial evidence being sufficiently compelling to prompt a review of practice by pediatric anesthetists and call for a precautionary approach by avoiding the use of N₂ O in children receiving concurrent methotrexate.

Disrupted folate metabolism with anesthesia leads to myelination deficits mediated by epigenetic regulation of ERMN

Background

Exposure to anesthetics during early life may impair cognitive functions. However, the underlying mechanisms remain largely unknown. We set out to determine effects of sevoflurane anesthesia on folate metabolism and myelination in young non-human primates, mice and children.

Methods

Young rhesus macaque and mice received 2.5 to 3% sevoflurane daily for three days. DNA and RNA sequencing and immunohistochemistry among others were used in the studies. We performed unbiased transcriptome profiling in prefrontal cortex of rhesus macaques and mice after the sevoflurane anesthesia. We constructed a brain blood barrier-crossing AAV-PHP.EB vector to harbor ERMN expression in rescue studies. We measured blood folate levels in children after anesthesia and surgery.

Findings

We found that thymidylate synthase (TYMS) gene was downregulated after the sevoflurane anesthesia in both rhesus macaque and mice. There was a reduction in blood folate levels in children after the anesthesia and surgery. Combined with transcriptome and genome-wide DNA methylation analysis, we identified that ERMN was the primary target of the disrupted folate metabolism. Myelination was compromised by the anesthesia in the young mice, which was rescued by systematic administration of folic acid or expression of ERMN in the brain through brain-specific delivery of the adeno-associated virus. Moreover, folic acid and expression of ERMN alleviated the cognitive impairment caused by the sevoflurane anesthesia in the mice.

Interpretation

General anesthesia leads to disrupted folate metabolism and subsequently defects in myelination in the developmental brain, and ERMN is the important target affected by the anesthesia via epigenetic mechanisms.

Global Burden Related to Nitrous Oxide Exposure in Medical and Recreational Settings: A Systematic Review and Individual Patient Data Meta-Analysis

The risk of adverse effects of nitrous oxide (N₂O) exposure is insufficiently recognized despite its widespread use. These effects are mainly reported through case reports. We conducted an individual patient data meta-analysis to assess the prevalence of clinical, laboratory, and magnetic resonance findings in association with N₂O exposure in medical and recreational settings. We calculated the pooled estimates for the studied outcomes and assessed the potential bias related to population stratification using principal component analysis. Eighty-five publications met the inclusion criteria and reported on 100 patients with a median age of 27 years and 57% of recreational users. The most frequent outcomes were subacute combined degeneration (28%), myelopathy (26%), and generalized demyelinating polyneuropathy (23%). A T2 signal hyperintensity in the spinal cord was reported in 68% (57.2–78.8%) of patients. The most frequent clinical manifestations included paresthesia (80%; 72.0–88.0%), unsteady gait (58%; 48.2–67.8%), and weakness (43%; 33.1–52.9%). At least one hematological abnormality was retrieved in 71.7% (59.9–83.4%) of patients. Most patients had vitamin B12 deficiency: vitamin B12 <150 pmol/L (70.7%; 60.7–80.8%), homocysteine >15 µmol/L (90.3%; 79.3–100%), and methylmalonic acid >0.4 µmol/L (93.8%; 80.4–100%). Consistently, 85% of patients exhibited a possibly or probably deficient vitamin B12 status according to the cB12 scoring system. N₂O can produce severe outcomes, with neurological or hematological disorders in almost all published cases. More than half of them are reported in the setting of recreational use. The N₂O-related burden is dominated by vitamin B12 deficiency. This highlights the need to evaluate whether correcting B12 deficiency would prevent N₂O-related toxicity, particularly in countries with a high prevalence of B12 deficiency.

European Society of Anaesthesiology Task Force on Nitrous Oxide: a narrative review of its role in clinical practice

Nitrous oxide (N₂O) is one of the oldest drugs still in use in medicine. Despite its superior pharmacokinetic properties, controversy remains over its continued use in clinical practice, reflecting in part significant improvements in the pharmacology of other anaesthetic agents and developing awareness of its shortcomings. This narrative review describes current knowledge regarding the clinical use of N₂O based on a systematic and critical analysis of the available scientific literature. The pharmacological properties of N₂O are reviewed in detail along with current evidence for the indications and contraindications of this drug in specific settings, both in perioperative care and in procedural sedation. Novel potential applications for N₂O for the prevention or treatment of chronic pain and depression are also discussed. In view of the available evidence, we recommend that the supply of N₂O in hospitals be maintained while encouraging its economic delivery using modern low flow delivery systems. Future research into its potential novel applications in prevention or treatment of chronic conditions should be pursued to better identify its role place in the developing era of precision medicine.

Hyperhomocysteinemia Causes Chorioretinal Angiogenesis with Placental Growth Factor Upregulation

Hyperhomocysteinemia is a risk factor for atherosclerosis, which may also be associated with retinal vascular disease, diabetic retinopathy, retinal vein occlusion, and glaucoma. For this study, we established a hyperhomocysteinemia animal model to explore homocysteine (hcy)-related choroidal angiogenesis and possible related factors. We injected Sprague Dawley (SD) rats with different concentrations of hcy and performed color fundus imaging, fluorescein angiography, image-guided optical coherence tomography, and retinal histology to observe the retinal and choroidal changes. Subsequently, we observed prominent choroidal vasculature with congested and tortuous retinal and choroidal vessels in fundus angiographies of the hyperhomocysteinemia animal model. In the histological study, the choroidal capillaries proliferated in the hcy-treated eyes, mimicking choroidal neovascularization. Disrupted retinal pigment epithelium (RPE), abnormal branching vascular network (BVN), and polyp-like structures were also observed in the hcy-treated eyes. Furthermore, we found that placental growth factor (PlGF), but not vascular epithelial growth factor (VEGF), was the key mediating factor of this phenomenon. Our findings suggest that hyperhomocysteinemia might cause choroidal angiogenesis.

Choroidal infarction following ophthalmic artery chemotherapy

Background

Methylenetetrahydrofolate reductase (MTHFR) genetic mutations and intra-procedural inhaled nitrous oxide (N₂O) independently increase blood levels of homocysteine, a compound associated with thrombosis. Patients with MTHFR mutations who also receive N₂O during ophthalmic artery chemotherapy (OAC) for retinoblastoma may have a heightened thrombotic risk.

Case presentations

Single-center retrospective review of pediatric patients with advanced retinoblastoma who received OAC and developed choroidal infarcts. Four retinoblastoma patients with advanced intraocular disease (2 males, 2 females: 13-58 months) experienced choroidal infarcts within the one-month period after OAC, in which procedural N₂O induction was used (duration between 21 and 58 min). All 4 patients had MTHFR (chromosome 1p, position 36.22) genetic abnormalities: one was homozygous for the C677T mutation, one was C677T heterozygous, one was A1298C heterozygous, and one was heterozygous for both C677T and A1298C. In all 4 patients, indirect ophthalmoscopy and fundus photography showed marked disturbance of the retinal pigment epithelium and optical coherence tomography (OCT) confirmed thinning of the choroid. Follow-up time ranged from 15 to 46 months (median 21 months).

Conclusions

Choroidal infarction in eyes treated with OAC developed in children who were both deficient in at least one working allele of the MTHFR gene (heterozygous or homozygous) and received N₂O induction during OAC.

Past, present, and future of nitrous oxide

INTRODUCTION

For a drug that has been omnipresent for nearly 200 years, nitrous oxide's (N2O) future seems less certain than its illustrious past. Environmental concerns are coming to the fore and may yet outweigh important clinical benefits.

SOURCES OF DATA

After determining the scope of the review, the authors used PubMed with select phrases encompassing the words in the scope. Both preclinical and clinical reports were considered.

AREAS OF AGREEMENT

The analgesic and anaesthetic advantages of N2O remain despite a plethora of newer agents.

AREAS OF CONTROVERSY

N2O greenhouse gas effect and its inhibition of key enzymes involved in protein and DNA synthesis have provided further fuel for those intent on eliminating its further clinical use.

GROWING POINTS

The use of N2O for treatment-resistant depression has gained traction.

AREAS TIMELY FOR DEVELOPING RESEARCH

Comparative studies for N2O role in combatting the prescription opioid analgesic epidemic may well provide further clinical impetus.

Nitrous oxide-based versus nitrous oxide-free general anaesthesia and accidental awareness during general anaesthesia in surgical patients

BACKGROUND

Accidental awareness during general anaesthesia (AAGA) is when a patient unintentionally becomes conscious during a procedure performed with general anaesthesia and subsequently has explicit recall of this event. Incidence estimates for AAGA vary, with the most common estimate being one to two cases per 1000 general anaesthetics. Evidence linking nitrous oxide use and an increased risk of AAGA has come from observational studies data but the literature is contradictory, with some studies finding a protective effect of nitrous oxide.

OBJECTIVES

To assess the effect of general anaesthesia including nitrous oxide on the risk of AAGA in patients aged five years and over.

SEARCH METHODS

We searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and trial registers ((www.clinicaltrials.gov), the WHO International Clinical Trials Registry Platform (www.who.int/ictrp/network/en/) and Current Controlled Trials (www.isrctn.com/)) for eligible studies on December 9 2015. In addition, we conducted forward and backward citation searching using key identified papers.

SELECTION CRITERIA

We considered all randomized controlled trials (RCTs), including quasi-randomized studies and cluster-randomized studies, of participants aged five years or older receiving general anaesthesia for any type of surgery.We included trials in which participants receiving general anaesthesia that included nitrous oxide for maintenance at a concentration of at least 30% were compared with participants receiving no nitrous oxide during general anaesthesia. The intervention group must have received nitrous oxide in conjunction with an additional anaesthetic. We excluded studies where the depth of anaesthesia differed between the study arms. For inclusion in the review, studies needed to state in their methods that they planned to assess AAGA. We defined this as when a patient becomes conscious during a procedure performed with general anaesthesia and subsequently has explicit recall of this event.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane to identify studies. We extracted data and conducted 'Risk of bias' assessment using the Covidence database.

MAIN RESULTS

We included 15 studies. The total number of participants included in the analyses was 3520. Most studies were small with fewer than 120 participants, although two larger studies with 2012 and 671 participants were included. There was considerable variation in many of the study characteristics, including the anaesthetics used. The concentrations of nitrous oxide varied between 50% and 70%, and half of the studies used clinical signs and haemodynamic changes to monitor depth of anaesthesia.As it was not possible to blind the anaesthetist to the anaesthetic used, we rated all studies at high risk of performance bias and we therefore downgraded the quality of evidence by one level for risk of bias using the GRADE approach. Other types of bias were generally low, or were rated unclear due to missing information.No studies were designed to measure AAGA as the primary outcome, and were therefore statistically underpowered to answer this review question. Despite the inclusion of 3520 participants, only three awareness events were reported by two studies. In one study the event was due to technical failure. Due to the rarity of the events, we did not consider it appropriate to pool the data, and we therefore downgraded the quality of evidence by a further level for imprecision using GRADE.

AUTHORS' CONCLUSIONS

It is not possible to draw any conclusions from this review. The included studies were mainly small (fewer than 120 participants) and there were limited estimates of effect, with only two studies reporting any events. We cannot therefore determine whether the use of nitrous oxide in general anaesthesia increases, decreases or has no effect on the risk of accidental awareness.

Neurologic, psychiatric, and other medical manifestations of nitrous oxide abuse: A systematic review of the case literature

BACKGROUND/OBJECTIVES

Nitrous oxide (N2 O) is known to have abuse potential, although debate regarding the toxic effects of such abuse continues. Our objective was to review the case literature and present the neurologic, psychiatric and medical consequences of N2 O abuse.

METHODS

A systematic literature review was completed for case reports using keywords "nitrous oxide" with "abuse/abusing" or "misuse/misusing" or "overuse/overusing" or "addiction." Non-English-language cases and cases not involving direct toxic effects of N2 O were excluded as were commentaries or personal essays. Clinical presentation, frequency of N2 O abuse, laboratory studies, imaging, ancillary tests, treatments and outcomes were collected from case reports.

RESULTS

Our review returned 335 Pubmed, 204 Web of Science, 73 PsycINFO, 6 CINAHL, 55 EMBASE and 0 Grey Literature results, and after exclusion and removal of duplicates, 91 individual cases across 77 publications were included. There were also 11 publications reporting 29 cases of death related to N2 O abuse. The majority of cases (N = 72) reported neurologic sequelae including myeloneuropathy and subacute combined degeneration, commonly (N = 39) with neuroimaging changes. Psychiatric (N = 11) effects included psychosis while other medical effects (N = 8) included pneumomediastinum and frostbite. Across all cases N2 O abuse was correlated with low or low-normal Vitamin B12 (cyanocobalamin) levels (N = 52) and occasionally elevated homocysteine and methylmalonic acid.

CONCLUSIONS/SCIENTIFIC SIGNIFICANCE

N2 O abuse represents a significant problem because of the difficulty involved with identification and the toxicity related to chronic abuse including possible death. Health professionals should be aware of the toxic effects of N2 O and be able to identify potential N2 O abuse. (Am J Addict 2016;25:358-369).

Nitrous oxide-based techniques versus nitrous oxide-free techniques for general anaesthesia

BACKGROUND

Nitrous oxide has been used for over 160 years for the induction and maintenance of general anaesthesia. It has been used as a sole agent but is most often employed as part of a technique using other anaesthetic gases, intravenous agents, or both. Its low tissue solubility (and therefore rapid kinetics), low cost, and low rate of cardiorespiratory complications have made nitrous oxide by far the most commonly used general anaesthetic. The accumulating evidence regarding adverse effects of nitrous oxide administration has led many anaesthetists to question its continued routine use in a variety of operating room settings. Adverse events may result from both the biological actions of nitrous oxide and the fact that to deliver an effective dose, nitrous oxide, which is a relatively weak anaesthetic agent, needs to be given in high concentrations that restrict oxygen delivery (for example, a common mixture is 30% oxygen with 70% nitrous oxide). As well as the risk of low blood oxygen levels, concerns have also been raised regarding the risk of compromising the immune system, impaired cognition, postoperative cardiovascular complications, bowel obstruction from distention, and possible respiratory compromise.

OBJECTIVES

To determine if nitrous oxide-based anaesthesia results in similar outcomes to nitrous oxide-free anaesthesia in adults undergoing surgery.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014 Issue 10); MEDLINE (1966 to 17 October 2014); EMBASE (1974 to 17 October 2014); and ISI Web of Science (1974 to 17 October 2014). We also searched the reference lists of relevant articles, conference proceedings, and ongoing trials up to 17 October 2014 on specific websites (http://clinicaltrials.gov/, http://controlled-trials.com/, and http://www.centerwatch.com).

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing general anaesthesia where nitrous oxide was part of the anaesthetic technique used for the induction or maintenance of general anaesthesia (or both) with any general anaesthesia using a volatile anaesthetic or propofol-based maintenance of anaesthesia but no nitrous oxide for adults undergoing surgery. Our primary outcome was inhospital case fatality rate. Secondary outcomes were complications and length of stay.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted the outcome data. We used meta-analysis for data synthesis. Heterogeneity was examined with the Chi² test and by calculating the I² statistic. We used a fixed-effect model if the measure of inconsistency was low for all comparisons (I² statistic < 50%); otherwise we used a random-effects model for measures with high inconsistency. We undertook subgroup analyses to explore inconsistency and sensitivity analyses to evaluate whether the results were robust. We assessed the quality of evidence of the main outcomes using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system.

MAIN RESULTS

We included 35 trials (13,872 adult participants). Seven included studies were at low risk of bias. We identified eight studies as awaiting classification since we could not obtain the full texts, and had insufficient information to include or exclude them. We included data from 24 trials for quantitative synthesis. The results of meta-analyses showed that nitrous oxide-based techniques increased the incidence of pulmonary atelectasis (odds ratio (OR) 1.57, 95% confidence interval (CI) 1.18 to 2.10, P = 0.002), but had no effects on the inhospital case fatality rate, the incidence of pneumonia, myocardial infarction, stroke, severe nausea and vomiting, venous thromboembolism, wound infection, or the length of hospital stay. The sensitivity analyses suggested that the results of the meta-analyses were all robust except for the outcomes of pneumonia, and severe nausea and vomiting. Two trials reported length of intensive care unit (ICU) stay but the data were skewed so were not pooled. Both trials reported that nitrous oxide-based techniques had no effects on the length of ICU stay. We rated the quality of evidence for two outcomes (pulmonary atelectasis, myocardial infarction) as high, four outcomes (inhospital case fatality rate, stroke, venous thromboembolism, length of hospital stay) as moderate, and three (pneumonia, severe nausea and vomiting, wound infection rate) as low.

AUTHORS' CONCLUSIONS

Given the evidence from this Cochrane review, the avoidance of nitrous oxide may be reasonable in participants with pre-existing poor pulmonary function or at high risk of postoperative nausea and vomiting. Since there are eight studies awaiting classification, selection bias may exist in our systematic review.

Perioperative stroke

PURPOSE

Perioperative stroke is associated with significant morbidity and mortality, with an incidence that may be underappreciated. In this review, we examine the significance, pathophysiology, risk factors, and evidence-based recommendations for the prevention and management of perioperative stroke.

SOURCE

This is a narrative review based on literature from the PubMed database regarding perioperative stroke across a broad surgical population. The Society for Neuroscience in Anesthesiology and Critical Care recently published evidence-based recommendations for perioperative management of patients at high risk for stroke; these recommendations were analyzed and incorporated into this review.

PRINCIPAL FINDINGS

The incidence of overt perioperative stroke is highest in patients presenting for cardiac and major vascular surgery, although preliminary data suggest that the incidence of covert stroke may be as high as 10% in non-cardiac surgery patients. The pathophysiology of perioperative stroke involves different pathways. Thrombotic stroke can result from increased inflammation and hypercoagulability; cardioembolic stroke can result from disease states such as atrial fibrillation, and tissue hypoxia from anemia can result from the combination of anemia and beta-blockade. Across large-scale database studies, common risk factors for perioperative stroke include advanced age, history of cerebrovascular disease, ischemic heart disease, congestive heart failure, atrial fibrillation, and renal disease. Recommendations for prevention and management of perioperative stroke are evolving, though further work is needed to clarify the role of proposed modifiable risk factors such as perioperative anticoagulation, antiplatelet therapy, appropriate transfusion thresholds, and perioperative beta-blockade.

CONCLUSIONS

Perioperative stroke carries a significant clinical burden. The incidence of perioperative stroke may be higher than previously recognized, and there are diverse pathophysiologic mechanisms. There are many opportunities for further investigation of the pathophysiology, prevention, and management of perioperative stroke.

Homocysteine levels after nitrous oxide anesthesia for living-related donor renal transplantation: a randomized, controlled, double-blind study

BACKGROUND

Nitrous oxide anesthesia increases postoperative homocysteine concentrations. Renal transplantation candidates present with higher homocysteine levels than patients with no renal disease. We designed this study to investigate if homocysteine levels are higher in subjects receiving nitrous oxide for renal transplantation compared with subjects undergoing nitrous oxide free anesthesia.

METHODS

Data from 59 patients scheduled for living-related donor renal transplantation surgery were analyzed in this randomized, controlled, blinded, parallel-group, longitudinal trial. Patients were assigned to receive general anesthesia with (flowmeter was set at 2 L/min nitrous oxide and 1 L/min oxygen) or without nitrous oxide (2 L/min air and 1 L/min oxygen). We evaluated levels of total homocysteine and known determinants, including creatinine, folate, vitamin B12, albumin, and lipids. We evaluated factor V and von Willebrand factor (vWF) to determine endothelial dysfunction and creatinine kinase myocardial band (CKMB)-mass, troponin T to show myocardial ischemia preoperatively in the holding area (T1), after discontinuation of anesthetic gases (T2), and 24 hours after induction (T3).

RESULTS

Compared with baseline, homocysteine concentrations significantly decreased both in the nitrous oxide (22.3 ± 16.3 vs 11.8 ± 9.9; P < .00001) and nitrous oxide-free groups (21.5 ± 15.3 vs 8.0 ± 5.7; P < .0001) at postoperative hour 24. The nitrous oxide group had significantly higher mean plasma homocysteine concentrations than the nitrous oxide-free group (P = .021). The actual homocysteine difference between groups was 3.8 μmol/L.

CONCLUSION

This study shows that homocysteine levels markedly decrease within 24 hours after living-related donor kidney transplantation. Patients receiving nitrous oxide have a lesser reduction, but this finding is unlikely to have a clinical relevance.

Anaesthetic concerns during adrenalectomy for Cushing′s syndrome with known hyperhomocysteinemia

Maintenance of homeostasis during anaesthesia in the patient with two major metabolic disorders whose systemic effects either compliment or contradict each other is a challenge to the anaesthesiologist. A 25-year-old male patient with Cushing's syndrome and known hyperhomocysteinemia was scheduled for open adrenalectomy. Both these disorders compound the hypercoagulable state and differ in glucose metabolism. In addition, obesity, difficult airway, electrolyte and metabolic derangements that accompany Cushing's syndrome warrant special attention. He was on anticoagulant therapy and inferior vena cava filter following an episode of pulmonary thromboembolism with deep vein thrombosis. Perioperative hydrocortisone was administered. Thoracic epidural catheter was placed at T10–T11 interspace, standard general anaesthesia was administered without nitrous oxide. Patient was extubated following an uneventful procedure and discharged home on 10^th post-operative day. Understanding the anaesthetic implications and the pathophysiological interactions of multiple metabolic disorders with a potential for multisystem involvement is key to the successful management of these patients.

The Effect of Vitamin B12 Infusion on Prevention of Nitrous Oxide-induced Homocysteine Increase: A Double-blind Randomized Controlled Trial

OBJECTIVE

Nitrous oxide is a common inhalation anesthetic agent in general anesthesia. While it is widely accepted as a safe anesthetic agent, evidence suggests exposure to this gas, leads to hyperhomocysteinemia. The present study aimed to evaluate the effects of single-dose intravenous infusions of vitamin B12, before and after the induction of nitrous oxide anesthesia on homocysteine levels after the surgery.

METHODS

This double-blind randomized controlled trial was conducted on 60 patients who were scheduled for elective surgery under general anesthesia, presumably lasting for more than two hours. The subjects were randomly allocated to three groups of 20. For the first group, vitamin B12 solution (1 mg/100 ml normal saline) and 100 ml of normal saline (placebo), were infused before and after the induction of anesthesia, respectively. The second group received placebo and vitamin B12 infusion before and after the induction of anesthesia, respectively. The third group received placebo infusions at both times. Homocysteine levels were measured before and 24 hours after the surgery.

RESULTS

The mean homocysteine and vitamin B12 levels were significantly different within the three groups (p<0.001). In patients who had been infused with vitamin B12 before the surgery, homocysteine levels were significantly lower than the other two groups. In the placebo group, homocysteine levels significantly increased after the surgery.

CONCLUSION

Nitrous oxide causes hyperhomocysteinemia after general anesthesia. Since vitamin B12 infusion is a safe and inexpensive method to decrease homocysteine levels in these patients, it may be recommended for patients undergoing nitrous oxide anesthesia to be used before induction of anesthesia.

Nitrous oxide-related postoperative nausea and vomiting depends on duration of exposure

BACKGROUND

Inclusion of nitrous oxide in the gas mixture has been implicated in postoperative nausea and vomiting (PONV) in numerous studies. However, these studies have not examined whether duration of exposure was a significant covariate. This distinction might affect the future place of nitrous oxide in clinical practice.

METHODS

PubMed listed journals reporting trials in which patients randomized to a nitrous oxide or nitrous oxide-free anesthetic for surgery were included, where the incidence of PONV within the first 24 postoperative hours and mean duration of anesthesia was reported. Meta-regression of the log risk ratio for PONV with nitrous oxide (lnRR PONVN2O) versus duration was performed.

RESULTS

Twenty-nine studies in 27 articles met the inclusion criteria, randomizing 10,317 patients. There was a significant relationship between lnRR PONVN2O and duration (r = 0.51, P = 0.002). Risk ratio PONV increased 20% per hour of nitrous oxide after 45 min. The number needed to treat to prevent PONV by avoiding nitrous oxide was 128, 23, and 9 where duration was less than 1, 1 to 2, and over 2 h, respectively. The risk ratio for the overall effect of nitrous oxide on PONV was 1.21 (CIs, 1.04-1.40); P = 0.014.

CONCLUSIONS

This duration-related effect may be via disturbance of methionine and folate metabolism. No clinically significant effect of nitrous oxide on the risk of PONV exists under an hour of exposure. Nitrous oxide-related PONV should not be seen as an impediment to its use in minor or ambulatory surgery.

Does anaesthesia with nitrous oxide affect mortality or cardiovascular morbidity? A systematic review with meta-analysis and trial sequential analysis

BACKGROUND

The role of nitrous oxide in modern anaesthetic practice is contentious. One concern is that exposure to nitrous oxide may increase the risk of cardiovascular complications. ENIGMA II is a large randomized clinical trial currently underway which is investigating nitrous oxide and cardiovascular complications. Before the completion of this trial, we performed a systematic review and meta-analysis, using Cochrane methodology, on the outcomes that make up the composite primary outcome.

METHODS

We used conventional meta-analysis and trial sequential analysis (TSA). We reviewed 8282 abstracts and selected 138 that fulfilled our criteria for study type, population, and intervention. We attempted to contact the authors of all the selected publications to check for unpublished outcome data.

RESULTS

Thirteen trials had outcome data eligible for our outcomes. We assessed three of these trials as having a low risk of bias. Using conventional meta-analysis, the relative risk of short-term mortality in the nitrous oxide group was 1.38 [95% confidence interval (CI) 0.22-8.71] and the relative risk of long-term mortality in the nitrous oxide group was 0.94 (95% CI 0.80-1.10). In both cases, TSA demonstrated that the data were far too sparse to make any conclusions. There were insufficient data to perform meta-analysis for stroke, myocardial infarct, pulmonary embolus, or cardiac arrest.

CONCLUSION

This systematic review demonstrated that we currently do not have robust evidence for how nitrous oxide used as part of general anaesthesia affects mortality and cardiovascular complications.

The perioperative use of nitrous oxide: renaissance of an old gas or funeral of an ancient relict?

PURPOSE OF REVIEW

Conflicting reports about adverse events following nitrous oxide (N(2)O) application have spurred a discussion whether N(2)O should be abandoned from clinical practice. Concurrently, N(2)O is increasingly used as a single anesthetic agent in medical procedures. This article reviews and discusses reports about the present use of N(2)O.

RECENT FINDINGS

Multiple publications demonstrate an increasing use of N(2)O as a procedural analgesic and sedative. Results from the Evaluation of Nitrous Oxide in the Gas Mixture for Anesthesia trial have been contrasted by recent studies reporting no increased risk for perioperative complications, particularly related to the cardiovascular and cerebrovascular system. Recent studies show that electroencephalogram-based anesthesia depth monitoring is not compatible with the use of N(2)O because of its distinct influence on electroencephalogram wave patterns. The clinical relevance of the proposed neurotoxicity, immunosuppression and influence on methionine metabolism remains unclear. Recently, its acute and long-term analgesic potency has been proven. Occupational exposure might pose a relevant health hazard.

SUMMARY

Based on the present literature, abolishment of N(2)O is controversial. When avoided in patients at risk for adverse events, N(2)O is still a valuable supplement to general anesthesia and a potent procedural analgesic drug. In the latter, its use by nonanesthesiologists should be discouraged.

[Impact of the decrease of nitrous oxide use on the consumption of halogenated agents]

OBJECTIVE

Nitrous oxide (N2O) toxicity and its impact on pollution lead to restrict its use. A decrease of N2O consumption should increase the hypnotic inhaled consumption. This monocentric study estimated consumptions and costs of halogenated agents (HA) and N2O over 5 years when the N2O consumption was reduced.

STUDY DESIGN

Retrospective from a computerized database.

PATIENTS

Between 2006 and 2010, 34,097 procedures were studied after two meetings exposing the risks of the N2O.

METHODS

At the end of anesthesia, consumptions of hypnotic agents (millilitres transmitted by the injectors and the blender) were archived in the database. The annual consumption of agents was obtained by adding the individual consumptions, then divided by the annual number of cases. The costs were given by the hospital pharmacy from invoices.

RESULTS

N2O consumption per anesthesia constantly decreased during the study, from 75.1L by act to 22.7L. The sum of the annual consumptions of N2O and air did not change suggesting that total fresh gas flow remained stable. Between 2006 and 2010, the sevoflurane consumption by act increased by 25%, from 16.5 to 20.6mL, and desflurane consumption by 37%, from 46.1 to 63.1mL by patient. The costs of the administration of hypnotic agents remained stable.

CONCLUSION

N2O consumption decrease had an impact on the consumption of HA. The cost reduction of the N2O was counterbalanced by the increase of halogenated vapor cost. The profit of the ecological impact of the reduction in N2O use could be quantified.

Nitrous oxide and perioperative outcomes

There is emerging evidence related to the effects of nitrous oxide on important perioperative patient outcomes. Proposed mechanisms include metabolic effects linked to elevated homocysteine levels and endothelial dysfunction, inhibition of deoxyribonucleic acid and protein formation, and depression of chemotactic migration by monocytes. Newer large studies point to possible risks associated with the use of nitrous oxide, although data are often equivocal and inconclusive. Cardiovascular outcomes such as stroke or myocardial infarction were shown to be unchanged in previous studies, but the more recent Evaluation of Nitrous Oxide in the Gas Mixture for Anesthesia I trial shows possible associations between nitrous oxide and increased cardiovascular and pulmonary complications. There are also possible effects on postoperative wound infections and neuropsychological function, although the multifactorial nature of these complications should be considered. Teratogenicity linked to nitrous oxide use has not been firmly established. The use of nitrous oxide for routine anesthetic care may be associated with significant costs if complications such as nausea, vomiting, and wound infections are taken into consideration. Overall, definitive data regarding the effect of nitrous oxide on major perioperative outcomes are lacking. There are ongoing prospective studies that may further elucidate its role. The use of nitrous oxide in daily practice should be individualized to each patient's medical conditions and risk factors.

Nitrous oxide: are we still in equipoise? A qualitative review of current controversies

This review considers the current position of nitrous oxide in anaesthetic practice and balances potential beneficial and disadvantageous effects. The classic adverse characteristics of nitrous oxide, such as diffusion hypoxia, expansion of gas-filled spaces, and postoperative nausea and vomiting, are often cited as reasons to avoid this old drug. Recent concerns regarding neurotoxicity, adverse cardiovascular outcomes, and wound complications have further hardened many practitioners against nitrous oxide. New evidence and underpinning mechanistic data, however, suggest potential beneficial effects on the central nervous system, cardiovascular system, and acute and chronic pain. While we await the outcome of large studies including ENIGMA-II, many clinicians have already decided against this agent. The authors argue that this abandonment may be premature. Clinical Trial Registration None required.

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.

[Do anesthetic techniques influence postoperative outcomes? Part I]

The influence of anesthetic technique on postoperative outcomes has opened a wide field of research in recent years. High-risk patients undergoing non-cardiac surgery are those who have higher incidence of postoperative complications and mortality. A proper definition of this group of patients should focus maximal efforts and resources to improve the results. In view of the significant reduction in postoperative mortality and morbidity in last 20 years, perioperative research should take into account new indicators to investigate the role of anesthetic techniques on postoperative outcomes. Studies focused on the evaluation of intermediate outcomes would probably discriminate better effectiveness differences between anesthetic techniques. We review some of the major controversies arising in the literature about the impact of anesthetic techniques on postoperative outcomes. We have grouped the impact of these techniques into 9 major investigation areas: mortality, cardiovascular complications, respiratory complications, postoperative cognitive dysfunction, chronic postoperative pain, cancer recurrence, postoperative nausea/vomiting, surgical outcomes and resources utilization. In this first part of the review, we discuss the basis on postoperative outcomes research, mortality, cardiovascular and respiratory complications.

The association between nitrous oxide and postoperative mortality and morbidity after noncardiac surgery

BACKGROUND

Nitrous oxide (N2O) has been widely used in clinical anesthesia for >150 years. However, use of N2O has decreased in recent years because of concern about the drug's metabolic side effects. But evidence that routine use of N2O causes clinically important toxicity remains elusive. We therefore evaluated the relationship between intraoperative N2O administration and 30-day mortality as well as a set of major inpatient postoperative complications (including mortality) in adults who had general anesthesia for noncardiac surgery.

METHODS

We evaluated 49,016 patients who had noncardiac surgery at the Cleveland Clinic between 2005 and 2009. Among 37,609 qualifying patients, 16,961 were given N2O ("nitrous," 45%) and 20,648 were not ("nonnitrous," 55%). Ten thousand seven hundred fifty-five nitrous patients (63% of the total) were propensity score-matched with 10,755 nonnitrous patients. Matched nitrous and nonnitrous patients were compared on 30-day mortality and a set of 8 in-hospital morbidity/mortality outcomes.

RESULTS

Inhalation of N2O intraoperatively was associated with decreased odds of 30-day mortality (odds ratio [OR]: 97.5% confidence interval, 0.67, 0.46-0.97; P = 0.02). Furthermore, nitrous patients had an estimated 17% (OR: 0.83, 0.74-0.92) decreased odds of experiencing major in-hospital morbidity/mortality than nonnitrous (P < 0.001). Among the individual morbidities, intraoperative N2O use was only associated with significantly lower odds of having pulmonary/respiratory morbidities (OR, 95% Bonferroni-adjusted CI: 0.59, 0.44-0.78).

CONCLUSIONS

Intraoperative N2O administration was associated with decreased odds of 30-day mortality and decreased odds of in-hospital mortality/morbidity. Aside from its specific and well-known contraindications, the results of this study do not support eliminating N2O from anesthetic practice.

Interrelationships of undernutrition and neurotoxicity: food for thought and research attention

The neurotoxic actions of chemical agents on humans and animals are usually studied with little consideration of the subject's nutritional status. States of protein-calorie, vitamin and/or mineral undernutrition are associated with a range of neurodevelopmental, neurological and psychiatric disorders, commonly with involvement of both the central and the peripheral nervous system. Undernutrition can modify risk for certain chemical-induced neurologic diseases, and in some cases undernutrition may be a prerequisite for neurotoxicity to surface. In addition, neurologic disease associated with undernutrition or neurotoxicity may show similarities in clinical and neuropathological expression, especially in the peripheral nervous system. The combined effects of undernutrition and chemical neurotoxicity are most relevant to people with low incomes who experience chronic hunger, parasitism and infectious disease, monotonous diets of plants with neurotoxic potential (notably cassava), environmental pollution from rapid industrial development, chronic alcohol abuse, or prolonged treatment with certain therapeutic drugs. Undernutrition alone or in combination with chemical exposure is also important in high-income societies in the setting of drug and alcohol abuse, old age, food faddism, post-bariatric surgery, and drug treatment for certain medical conditions, including cancer and tuberculosis. The nutritional demands of pregnancy and lactation increase the risk of fetal and infant undernutrition and chemical interactions therewith.

Cognitive impairment and vitamin B12: a review

BACKGROUND

This review examines the associations between low vitamin B12 levels, neurodegenerative disease, and cognitive impairment. The potential impact of comorbidities and medications associated with vitamin B12 derangements were also investigated. In addition, we reviewed the evidence as to whether vitamin B12 therapy is efficacious for cognitive impairment and dementia.

METHODS

A systematic literature search identified 43 studies investigating the association of vitamin B12 and cognitive impairment or dementia. Seventeen studies reported on the efficacy of vitamin B12 therapy for these conditions.

RESULTS

Vitamin B12 levels in the subclinical low-normal range (<250 ρmol/L) are associated with Alzheimer's disease, vascular dementia, and Parkinson's disease. Vegetarianism and metformin use contribute to depressed vitamin B12 levels and may independently increase the risk for cognitive impairment. Vitamin B12 deficiency (<150 ρmol/L) is associated with cognitive impairment. Vitamin B12 supplements administered orally or parenterally at high dose (1 mg daily) were effective in correcting biochemical deficiency, but improved cognition only in patients with pre-existing vitamin B12 deficiency (serum vitamin B12 levels <150 ρmol/L or serum homocysteine levels >19.9 μmol/L).

CONCLUSION

Low serum vitamin B12 levels are associated with neurodegenerative disease and cognitive impairment. There is a small subset of dementias that are reversible with vitamin B12 therapy and this treatment is inexpensive and safe. Vitamin B12 therapy does not improve cognition in patients without pre-existing deficiency. There is a need for large, well-resourced clinical trials to close the gaps in our current understanding of the nature of the associations of vitamin B12 insufficiency and neurodegenerative disease.

Retrospective approach to methylenetetrahydrofolate reductase mutations in children

Methylenetetrahydrofolate reductase reduces methyltetrahydrofolate, a cosubstrate in the remethylation of homocysteine, from methylenetetrahydrofolate. Congenital defects, hematologic tumors, and intrauterine growth retardation can occur during childhood. This study evaluated clinical and laboratory treatment approaches in children diagnosed with methylenetetrahydrofolate reductase mutations. Our group included 23 boys and 14 girls, aged 103.4 ± 70.8 months S.D. Clinical findings of patients and homocysteine, vitamin B12, folate, hemogram, electroencephalography, cranial magnetic resonance imaging, and echocardiography data were evaluated in terms of treatment approach. Our patients' findings included vitamin B12 at 400.4 ± 224.6 pg/mL S.D. (normal range, 300-700 pg/mL), folate at 10.1 ± 4.5 ng/mL S.D. (normal range, 1.8-9 ng/mL), and homocysteine at 8.4 ± 4.7 μmol/L S.D. (normal range, 5.5-17 μmol/L). Eighty-eight percent of patients demonstrated clinical findings. In comparisons involving categorical variables between groups, χ(2) tests were used. No relationship was evident between mutation type, laboratory data, and clinical severity. All mothers who had MTHFR mutations and had babies with sacral dimples had taken folate supplements during pregnancy. To avoid the risk of neural tube defects, pregnant women with a MTHFR mutation may require higher than normally recommended doses of folic acid supplementation for optimum health.

Nitrous oxide anesthesia and plasma homocysteine in adolescents

BACKGROUND

Nitrous oxide inactivates vitamin B(12), inhibits methionine synthase, and consequently increases plasma total homocysteine (tHcy). Prolonged exposure to nitrous oxide can lead to neuropathy, spinal cord degeneration, and even death in children. We tested the hypothesis that nitrous oxide anesthesia causes a significant increase in plasma tHcy in children.

METHODS

Twenty-seven children (aged 10-18 years) undergoing elective major spine surgery were enrolled, and serial plasma samples from 0 to 96 hours after induction were obtained. The anesthetic regimen, including the use of nitrous oxide, was at the discretion of the anesthesiologist. Plasma tHcy was measured using standard enzymatic assays.

RESULTS

The median baseline plasma tHcy concentration was 5.1 μmol/L (3.9-8.0 μmol/L, interquartile range) and increased in all patients exposed to nitrous oxide (n = 26) by an average of +9.4 μmol/L (geometric mean; 95% confidence interval, 7.1-12.5 μmol/L) or +228% (mean; 95% confidence interval, 178%-279%). Plasma tHcy peaked between 6 and 8 hours after induction of anesthesia. One patient who did not receive nitrous oxide had no increase in plasma tHcy. Several patients experienced a severalfold increase in plasma tHcy (maximum +567%). The increase in plasma tHcy was strongly correlated with the duration and average concentration of nitrous oxide anesthesia (r = 0.80; P < 0.001).

CONCLUSIONS

Pediatric patients undergoing nitrous oxide anesthesia develop significantly increased plasma tHcy concentrations. The magnitude of this effect seems to be greater compared with adults; however, the clinical relevance is unknown.