Nitrous Oxide and Long-Term Morbidity and Mortality in the ENIGMA Trial

Lethal nitrous oxide (N2O) intoxication during surgery: the contribution of immunohistochemistry in identifying the cause of death: a case report

BACKGROUND

Nitrous oxide (N2O) is a gas used in medicine for its analgesic, anxiolytic and amnesic properties. It is a drug considered safe if adequately administered. In the literature, accidental N2O-related deaths are rare. They are mostly related to inhalation of this substance for recreational and autoerotic purposes; rarely are reported deaths due to incorrect administration of medical gas in anesthesia. The diagnosis of death from acute N2O intoxication is complex and is generally an exclusion diagnosis: the macroscopic and microscopic post-mortem signs are entirely nonspecific. Furthermore, the circumstantial data are not always supportive and can even be confusing, mainly if the death occurred inside a hospital.

CASE PRESENTATION

We describe a particular case of death from acute nitrous oxide poisoning in a hospital environment, of a Caucasian male of 72-years-old. The intoxication occurred during a minimally invasive vascular surgery due to an incorrect assembly of the supply lines of medical gases (O2 and N2O). The identification of the cause of death resulted from the analysis of circumstantial data, macroscopic and microscopic autoptic findings, and immunohistochemical investigations based on the search for antibodies anti E-selectin, P-selectin, and HIF 1-α.

CONCLUSION

Although not pathognomonic of asphyxiation by N2O, the latter molecules are a valid and early marker of hypoxic insult. Therefore, in concert with all other findings, it may constitute valid support for the forensic pathologist to ascertain the cause of death in case of suspected intoxication by N2O.

Impact of pharmacological interventions on intrapulmonary shunt during one-lung ventilation in adult thoracic surgery: a systematic review and component network meta-analysis

BACKGROUND

Intrapulmonary shunt is a major determinant of oxygenation in thoracic surgery under one-lung ventilation. We reviewed the effects of available treatments on shunt, Pao₂/FiO₂ and haemodynamics through systematic review and network meta-analysis.

METHODS

Online databases were searched for RCTs comparing pharmacological interventions and intrapulmonary shunt in thoracic surgery under one-lung ventilation up to March 30, 2022. Random-effects (component) network meta-analysis compared 24 treatments and 19 treatment components. The Confidence in Network Meta-Analysis (CINeMA) framework assessed evidence certainty. The primary outcome was intrapulmonary shunt fraction during one-lung ventilation.

RESULTS

A total of 55 RCTs were eligible for systematic review (2788 participants). The addition of N₂O (mean difference [MD]=-15%; 95% confidence interval [CI], -25 to -5; P=0.003) or almitrine (MD=-13%; 95% CI, -20 to -6; P<0.001) to propofol anaesthesia were efficient at decreasing shunt. Combined epidural anaesthesia (MD=3%; 95% CI, 1-5; P=0.005), sevoflurane (MD=5%; 95% CI, 2-8; P<0.001), isoflurane (MD=6%; 95% CI, 4-9; P<0.001), and desflurane (MD=9%; 95% CI, 4-14; P=0.001) increased shunt vs propofol. Almitrine (MD=147 mm Hg; 95% CI, 58-236; P=0.001), dopexamine (MD=88 mm Hg; 95% CI, 4-171; P=0.039), and iloprost (MD=81 mm Hg; 95% CI, 4-158; P=0.038) improved Pao₂/FiO₂. Certainty of evidence ranged from very low to moderate.

CONCLUSIONS

Adding N₂O or almitrine to propofol anaesthesia reduced intrapulmonary shunt during one-lung ventilation. Halogenated anaesthetics increased shunt in comparison with propofol. The effects of N₂O, iloprost, and dexmedetomidine should be investigated in future research. N₂O results constitute a research hypothesis currently not backed by any direct evidence. The clinical availability of almitrine is limited.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42022310313.

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.

Thromboembolic complications of recreational nitrous oxide (ab)use: a systematic review

The recreatinal use of nitrous oxide has become more common in recent years, especially in adolescents and young adults. It has been mainly associated with medical conditions like megaloblastic anemia and (myelo)neuropathy. We report on the thromboembolic complications, a less known side effect, associated with recreational inhalation of nitrous oxide. An extensive literature search was performed for publications reporting on the thromboembolic complications associated with recreational nitrous oxide abuse. Data about sex, age, location of thrombosis, laboratory findings, therapy and outcome were collected. A total of 13 case reports or case series were identified comprising a total of 14 patients. The reported thromboembolic side effects included deep venous thrombosis, pulmonary embolism, mesenterial-, portal and splenic vein thrombosis, cerebral sinus thrombosis, cortical vein thrombosis, stroke, acute myocardial infarction and peripheral artery thromboembolism. These side effects are possibly mediated by the interaction of nitrous oxide with vitamin B12, a cofactor of the methionine synthase complex, which eventually results in elevation of plasma levels of homocysteine. Despite being a known risk factor for cardiovascular disease, the exact pathophysiological mechanism remains unclear. Cessation of nitrous oxide inhalation is necessary to prevent recurrent thrombosis. Nitrous oxide abuse may thus result in a wide spectrum of thromboembolic complications. One should be aware of this etiology, especially in a young person with no obvious risk factors for cardiovascular disease. Spreading awareness is important to inform people about the potentially serious side effects associated with nitrous oxide inhalation.

Association between preoperative serum homocysteine and delayed neurocognitive recovery after non-cardiac surgery in elderly patients: a prospective observational study

BACKGROUND

Homocysteine, folate, and vitamin B₁₂ involved in 1-carbon metabolism are associated with cognitive disorders. We sought to investigate the relationships between these factors and delayed neurocognitive recovery (dNCR) after non-cardiac surgery.

METHODS

This was a prospective observational study of patients (n = 175) who were ≥ 60 years of age undergoing non-cardiac surgery. Patients were evaluated preoperatively and for 1 week postoperatively by using neuropsychological tests and were divided into dNCR or non-dNCR groups according to a Z-score ≤ - 1.96 on at least two of the tests. The relationship between the occurrence of dNCR and preoperative levels of homocysteine, folate, and vitamin B₁₂ was analyzed. Univariate and multivariable logistic regression analyses were conducted to identify factors associated with dNCR.

RESULTS

Delayed neurocognitive recovery was observed in 36 of 175 patients (20.6%; 95% confidence interval [CI], 14.5-26.6%) 1 week postoperatively. Patients who developed dNCR had significantly higher median [interquartile range (IQR)] homocysteine concentrations (12.8 [10.9,14.4] μmol/L vs 10.6 [8.6,14.7] μmol/L; P = 0.02) and lower folate concentrations (5.3 [4.2,7.3] ng/mL vs 6.9 [5.3,9.5] ng/mL; P = 0.01) than those without dNCR. Compared to the lowest tertile, the highest homocysteine tertile predicted dNCR onset (odds ratio [OR], 3.9; 95% CI, 1. 3 to 11.6; P = 0.02), even after adjusting for age, sex, education, and baseline Mini Mental State Examination.

CONCLUSIONS

Elderly patients with high homocysteine levels who underwent general anesthesia for non-cardiac surgery have an increased risk of dNCR. This knowledge could potentially assist in the development of preventative and/or therapeutic measures.

TRIAL REGISTRATION

NCT03084393 ( https://www.clinicaltrials.gov ).

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.

Plaque erosion causing ST-elevation myocardial infarction after consumption of cannabis and N2O in a 27-year old man: a case report

Background

The recreational drugs cannabis and nitrous oxide (N₂O) are known for pro-atherogenic effects and are associated with an elevated risk of myocardial infarction. These cardiovascular effects might be underestimated by the public. Culprit-lesion composition of myocardial infarctions associated with cannabis and N₂O has been unknown so far. This case report aims to raise the awareness of the adverse cardiovascular effects of cannabis and N₂O and reports, for the first time, optical coherence tomography (OCT) findings of the culprit lesion.

Case presentation

This is a case report of a 27-year old man with anterior ST-segment-elevation myocardial infarction (STEMI) after intoxication with cannabis and N₂O. Coronary angiography and OCT revealed plaque erosion with subsequent subtotal thrombotic occlusion of the left anterior descending artery that was successfully treated with 1 drug-eluting stent. The patient was symptom free at 6 months follow-up and had been able to abstain from drug consumption.

Conclusions

This is the first case to demonstrate the association between cannabis and N₂O abuse and plaque erosion on OCT in a young man with STEMI. In contrast to smoking, whose adverse effects are well-known, the cardiovascular effects of cannabis and N₂O might be underestimated. These adverse effects should gain more awareness in the public to prevent early vascular events in young adults.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-021-01953-3.

Inhaled Anesthetics: Environmental Role, Occupational Risk, and Clinical Use

Inhaled anesthetics have been in clinical use for over 150 years and are still commonly used in daily practice. The initial view of inhaled anesthetics as indispensable for general anesthesia has evolved during the years and, currently, its general use has even been questioned. Beyond the traditional risks inherent to any drug in use, inhaled anesthetics are exceptionally strong greenhouse gases (GHG) and may pose considerable occupational risks. This emphasizes the importance of evaluating and considering its use in clinical practices. Despite the overwhelming scientific evidence of worsening climate changes, control measures are very slowly implemented. Therefore, it is the responsibility of all society sectors, including the health sector to maximally decrease GHG emissions where possible. Within the field of anesthesia, the potential to reduce GHG emissions can be briefly summarized as follows: Stop or avoid the use of nitrous oxide (N2O) and desflurane, consider the use of total intravenous or local-regional anesthesia, invest in the development of new technologies to minimize volatile anesthetics consumption, scavenging systems, and destruction of waste gas. The improved and sustained awareness of the medical community regarding the climate impact of inhaled anesthetics is mandatory to bring change in the current practice.

Impact of Opioid Analgesia and Inhalation Sedation Kalinox on Pain and Radial Artery Spasm during Transradial Coronary Angiography

With respect to the transfemoral approach, transradial procedures enable a drastic reduction of bleeding events and are associated with a reduction of mortality. Radial artery spasm (RAS) is one of the most common complications and may lead to patient discomfort and procedural failure. Currently, there is no consensus on the optimal sedation protocol to avoid RAS. The aim of this study was to investigate the respective impact of opioids analgesia and inhalation sedation with a 50% nitrous oxide/oxygen premix (Kalinox) on pain and occurrence of RAS during transradial coronary procedures. Consecutive patients undergoing transradial coronary angiography were prospectively enrolled in one, single center observational study (Nouvel Hôpital Civil, Strasbourg, France). Patients received opioids analgesia or inhalation sedation with Kalinox. The primary endpoints of the study were the incidence of a pain scale ≥5/10 and the occurrence of RAS. The secondary endpoints were the incidence of side effects. A total of 325 patients were enrolled (185 in the opioids analgesia group, 140 in the Kalinox group). RAS and pain scale ≥5 rates were not significantly different in the opioids analgesia and Kalinox groups (respectively 13.5% vs. 10.0% and 16.2% vs. 11.4%). Headache was more frequently observed in the Kalinox group (6.4% vs. 0.0%; p = 0.002). By multivariate analysis, female gender, BMI <25 kg/m², puncture difficulty, the use of plastic needle and 6F sheath were identified as independent predictors of RAS. Procedural inhalation sedation by Kalinox is as safe as opioids analgesia during transradial coronary angiography.

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.

The sharp rise of neurological disorders associated with recreational nitrous oxide use in China: a single-center experience and a brief review of Chinese literature

INTRODUCTION

In recent years, there has been a sharp increase in the number of patients with neurological disorders associated with recreational use of nitrous oxide (N₂O) in China. Here, we summarize the clinical characteristics of patients with neurological disorders associated with N₂O abuse diagnosed in our Hospital. Further, we conducted a literature search on recent cases reported in mainland China to improve the awareness of the outbreak of neurological disorders associated with N₂O abuse.

METHODS

We retrospectively collected data of patients diagnosed with neurological disorders associated with recreational use of N₂O in Shengjing Hospital of China Medical University from January 2018 to June 2019, and performed a literature search using the "nitrous oxide" and "neurological disorder" as keywords in the Chinese literature databases of WANFANG and CNKI and the English literature databases of Pubmed and Web of Science RESULTS: We enrolled 43 patients (average age: 21.9 ± 3.3 years). The main clinical manifestations were weakness and paresthesia in the four extremities and unsteady gait. Further, most patients showed significantly lower levels of serum vitamin B12 (169.4 ± 79.1 pg/mL) and increased homocysteine levels (78.1 ± 32.2 μmol/L). MRI of the spinal cord showed longitudinal high T2 signal lesions in the dorsal spinal cord in some patients. Moreover, electromyography showed sensory and motor nerve axonal damage combined with demyelination, which was relatively more severe in the lower limbs. There was rapid improvement of the symptoms after treatment with intramuscular injections of vitamin B12 and the overall prognosis was good. The literature search indicated that the number of published papers and related patients showed a rapid annual increase since the first Chinese case reported in 2016 CONCLUSION: Recreational use of N₂O is an emerging public health problem in China that needs prompt action from the society and government. Early diagnosis and treatment allow a good overall prognosis.

A model of lipid dysregulation and altered nutrient status in Alzheimer's disease

INTRODUCTION

Dysregulated lipid metabolism and nutrient status are thought to play a role in the pathophysiology of Alzheimer's disease (AD). However, the precise involvement is not well understood, and it remains unclear exactly how such dysregulated lipid metabolism and altered nutrient status, especially changes in phosphatidylcholine, B12, and folate, are connected to the hallmark pathology in AD (i.e., amyloidogenesis).

METHODS

We have postulated that genetic susceptibility (i.e., APOE ε4/ε4) to environmental exposure to emissions of nitrous oxide (N2O) could underlie the onset of AD and its early neuropsychiatric correlates.

RESULTS AND DISCUSSION

The current theoretical editorial describes, using clinical, preclinical, and in vitro evidences, how this model contributes not only to amyloidogenesis but also other nonopioid effects, specifically altered lipid metabolism, depletion of vitamin B12, and disruption of the folate-mediated one carbon metabolic pathway.

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.

Exposure to 60% oxygen promotes migration and upregulates angiogenesis factor secretion in breast cancer cells

Peri-operative factors, including anaesthetic drugs and techniques, may affect cancer cell biology and clinical recurrence. In breast cancer cells, we demonstrated that sevoflurane promotes migration and angiogenesis in high fractional oxygen but not in air. Follow-up analysis of the peri-operative oxygen fraction trial found an association between high inspired oxygen during cancer surgery and reduced tumor-free survival. Here we evaluated effects of acute, high oxygen exposure on breast cancer cell viability, migration and secretion of angiogenesis factors in vitro. MDA-MB-231 and MCF-7 breast cancer cells were exposed to 21%, 30%, 60%, or 80% v/v O₂ for 3 hours. Cell viability at 24 hours was determined by MTT and migration at 24 hours with the Oris™ Cell Migration Assay. Secretion of angiogenesis factors at 24 hours was measured via membrane-based immunoarray. Exposure to 30%, 60% or 80% oxygen did not affect cell viability. Migration of MDA-MB-231 and MCF-7 cells was increased by 60% oxygen (P = 0.012 and P = 0.007, respectively) while 30% oxygen increased migration in MCF-7 cells (P = 0.011). These effects were reversed by dimethyloxaloylglycine. In MDA-MB-231 cells high fractional oxygen increased secretion of angiogenesis factors monocyte chemotactic protein 1, regulated on activation normal T-cell expressed and vascular endothelial growth factor. In MCF-7 cells, interleukin-8, angiogenin and vascular endothelial growth factor secretion was significantly increased by high fractional oxygen. High oxygen exposure stimulates migration and secretion of angiogenesis factors in breast cancer cells in vitro.

The effect of a perioperative ketamine infusion on the incidence of chronic postsurgical pain-a pilot study

Chronic postsurgical pain (CPSP) is a common and debilitating complication of major surgery. We undertook a pilot study at three hospitals to assess the feasibility of a proposed large multicentre placebo-controlled randomised trial of intravenous perioperative ketamine to reduce the incidence of CPSP. Ketamine, 0.5 mg/kg pre-incision, 0.25 mg/kg/hour intraoperatively and 0.1 mg/kg/hour for 24 hours, or placebo, was administered to 80 patients, recruited over a 15-month period, undergoing abdominal or thoracic surgery under general anaesthesia. The primary endpoint was CPSP in the area of the surgery reported at six-month telephone follow-up using a structured questionnaire. Fourteen patients (17.5%) reported CPSP (relative risk [95% confidence interval] if received ketamine 1.18 [0.70 to 1.98], P=0.56). Four patients in the treatment group and three in the control group reported ongoing analgesic use to treat CPSP and two patients in each group reported their worst pain in the previous 24 hours at ≥3/10 at six months. There were no significant differences in adverse event rates, quality of recovery scores, or cumulative morphine equivalents consumption in the first 72 hours. Numeric Rating Scale pain scores (median [interquartile range, IQR]) for average pain in the previous 24 hours among those patients reporting CPSP were 17.5 [0 to 40] /100 with no difference between treatment groups. A large (n=4,000 to 5,000) adequately powered multicentre trial is feasible using this population and methodology.

Acute ST-Elevation Myocardial Infarction, a Unique Complication of Recreational Nitrous Oxide Use

A 28-year-old male was admitted to hospital with an acute ST-elevation myocardial infarction. This was in the context of recreational abuse of nitrous oxide. The prevalence of nitrous oxide use in Australia has not been formally quantified, however it is the second most commonly used recreational drug in the United Kingdom. Nitrous oxide has previously been shown to increase serum homocysteine levels. This patient was discovered to have an elevated homocysteine level at baseline, which was further increased after nitrous oxide consumption. Homocysteine has been linked to endothelial dysfunction and coronary atherosclerosis and this case report highlights one of the dangers of recreational abuse of nitrous oxide.

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.

Peri-operative cardiac protection for non-cardiac surgery

Cardiovascular complications are an important cause of morbidity and mortality after non-cardiac surgery. Pre-operative identification of high-risk individuals and appropriate peri-operative management can reduce cardiovascular risk. It is important to continue chronic beta-blocker and statin therapy. Statins are relatively safe and peri-operative initiation may be beneficial in high-risk patients and those scheduled for vascular surgery. The pre-operative introduction of beta-blockers reduces myocardial injury but increases rates of stroke and mortality, possibly due to hypotension. They should only be considered in high-risk patients and the dose should be titrated to heart rate. Alpha-2 agonists may also contribute to hypotension. Aspirin continuation can increase the risk of major bleeding and offset the benefit of reduced myocardial risk. Contrary to the initial ENIGMA study, nitrous oxide does not seem to increase the risk of myocardial injury. Volatile anaesthetic agents and opioids have been shown to be cardioprotective in animal laboratory studies but these effects have, so far, not been conclusively reproduced clinically.

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 and Serious Long-term Morbidity and Mortality in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II Trial

Background

The Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II trial randomly assigned 7,112 noncardiac surgery patients at risk of perioperative cardiovascular events to 70% N2O or 70% N2 groups. The aim of this follow-up study was to determine the effect of nitrous oxide on a composite primary outcome of death and major cardiovascular events at 1 yr after surgery.

Methods

One-year follow-up was conducted via a medical record review and telephone interview. Disability was defined as a Katz index of independence in activities of daily living score less than 8. Adjusted odds ratios and hazard ratios were calculated as appropriate for primary and secondary outcomes.

Results

Among 5,844 patients evaluated at 1 yr, 435 (7.4%) had died, 206 (3.5%) had disability, 514 (8.8%) had a fatal or nonfatal myocardial infarction, and 111 (1.9%) had a fatal or nonfatal stroke during the 1-yr follow-up period. Exposure to nitrous oxide did not increase the risk of the primary outcome (odds ratio, 1.08; 95% CI, 0.94 to 1.25; P = 0.27), disability or death (odds ratio, 1.07; 95% CI, 0.90 to 1.27; P = 0.44), death (hazard ratio, 1.17; 95% CI, 0.97 to 1.43; P = 0.10), myocardial infarction (odds ratio, 0.97; 95% CI, 0.81 to 1.17; P = 0.78), or stroke (odds ratio, 1.08; 95% CI, 0.74 to 1.58; P = 0.70).

Conclusion

These results support the long-term safety of nitrous oxide administration in noncardiac surgical patients with known or suspected cardiovascular disease.

Postanesthesia Care for the Elderly Patient

PURPOSE

As the general population lives longer, the perioperative physician is more likely to encounter disease states that increase in incidence in an aging population. This review focuses on anesthetic considerations for rational drug choices during the perioperative care of elderly patients. The primary aim of the review was to identify intraoperative and postanesthetic considerations for diseases associated with advancing age; it includes highlights of the commonly impaired major organs (eg, cardiovascular, pulmonary, neurologic, renal, hepatic systems). We also outline an approach to frequent issues that arise in the immediate postsurgical period while caring for these patients.

METHODS

A systematic review was performed on aspects of the perioperative and postoperative periods that relate to the elderly. A list of pertinent key words was derived from the authors, and a PubMed database search was performed.

FINDINGS

The anesthesiologist must account for changes in various organ systems that affect perioperative care, including the cardiovascular, pulmonary, renal, hepatic, and central nervous systems. The pharmacokinetic principles frequently differ and are often unpredictable because of anatomic changes and decreased renal and hepatic function. The most important pharmacodynamic consideration is that elderly patients tend to exhibit an exaggerated hypoactivity after anesthesia.

IMPLICATIONS

Before surgery, it is essential to identify those patients at risk for delirium and other commonly encountered postanesthesia scenarios. Failure to manage these conditions appropriately can lead to an escalation of care and prolonged hospitalization.

Nitrous oxide persistently alleviates pain hypersensitivity in neuropathic rats: A dose-dependent effect

BACKGROUND

Despite numerous pharmacological approaches, there are no common analgesic drugs that produce meaningful relief for the majority of patients with neuropathic pain. Although nitrous oxide (N2O) is a weak analgesic that acts via opioid-dependent mechanisms, it is also an antagonist of the N-methyl-D-aspartate receptor (NMDAR). The NMDAR plays a critical role in the development of pain sensitization induced by nerve injury.

OBJECTIVE

Using the chronic constriction injury of the sciatic nerve in male rats as a preclinical model of neuropathic pain, the first aim of the present study was to evaluate the lowest N2O concentration and the shortest time of N2O postinjury exposure that would produce persistent relief of neuropathic pain. The second aim was to compare the effects of N2O with gabapentin, a reference drug used in human neuropathic pain relief.

METHODS

Changes in the nociceptive threshold were evaluated using the paw pressure vocalization test in rats.

RESULTS

Among the various N2O concentrations tested, which ranged from 25% to 50%, only 50% N2O single exposure for 1 h 15 min induced a persistent (minimum of three weeks) and significant (60%) reduction in pain hypersensitivity. A single gabapentin dose (75 mg⁄kg to 300 mg⁄kg, intraperitoneally) induced an acute (1 h to 1 h 30 min) dose-dependent effect, but not a persistent effect such as that observed with N2O.

CONCLUSIONS

These preclinical results suggest that N2O is advantageous for long-lasting neuropathic pain relief after sciatic nerve injury compared with other drugs used in humans such as gabapentinoids or NMDAR antagonists. The present preclinical study provides a rationale for developing comparative clinical studies.

Recreational nitrous oxide use: Prevalence and risks

Nitrous oxide (N2O; laughing gas) is clinically used as a safe anesthetic (dentistry, ambulance, childbirth) and appreciated for its anti-anxiety effect. Since five years, recreational use of N2O is rapidly increasing especially in the dance and festival scene. In the UK, N2O is the second most popular recreational drug after cannabis. In most countries, nitrous oxide is a legal drug that is widely available and cheap. Last month prevalence of use among clubbers and ravers ranges between 40 and almost 80 percent. Following one inhalation, mostly from a balloon, a euphoric, pleasant, joyful, empathogenic and sometimes hallucinogenic effect is rapidly induced (within 10 s) and disappears within some minutes. Recreational N2O use is generally moderate with most users taking less than 10 balloons of N2O per episode and about 80% of the users having less than 10 episodes per year. Side effects of N2O include transient dizziness, dissociation, disorientation, loss of balance, impaired memory and cognition, and weakness in the legs. When intoxicated accidents like tripping and falling may occur. Some fatal accidents have been reported due to due to asphyxia (hypoxia). Heavy or sustained use of N2O inactivates vitamin B12, resulting in a functional vitamin B12 deficiency and initially causing numbness in fingers, which may further progress to peripheral neuropathy and megaloblastic anemia. N2O use does not seem to result in dependence. Considering the generally modest use of N2O and its relative safety, it is not necessary to take legal measures. However, (potential) users should be informed about the risk of vitamin B12-deficiency related neurological and hematological effects associated with heavy use.

Effects of Anesthetic Management on Early Postoperative Recovery, Hemodynamics and Pain After Supratentorial Craniotomy

Various clinical trials have assessed how intraoperative anesthetics can affect early recovery, hemodynamics and nociception after supratentorial craniotomy. Whether or not the difference in recovery pattern differs in a meaningful way with anesthetic choice is controversial. This review examines and compares different anesthetics with respect to wake-up time, hemodynamics, respiration, cognitive recovery, pain, nausea and vomiting, and shivering. When comparing inhalational anesthetics to intravenous anesthetics, either regimen produces similar recovery results. Newer shorter acting agents accelerate the process of emergence and extubation. A balanced inhalational/intravenous anesthetic could be desirable for patients with normal intracranial pressure, while total intravenous anesthesia could be beneficial for patients with elevated intracranial pressure. Comparison of inhalational anesthetics shows all appropriate for rapid emergence, decreasing time to extubation, and cognitive recovery. Comparison of opioids demonstrates similar awakening and extubation time if the infusion of longer acting opioids was ended at the appropriate time. Administration of local anesthetics into the skin, and addition of corticosteroids, NSAIDs, COX-2 inhibitors, and PCA therapy postoperatively provided superior analgesia. It is also important to emphasize the possibility of long-term effects of anesthetics on cognitive function. More research is warranted to develop best practices strategies for the future that are evidence-based.

The effects of high perioperative inspiratory oxygen fraction for adult surgical patients

BACKGROUND

Available evidence on the effects of a high fraction of inspired oxygen (FIO2) of 60% to 90% compared with a routine fraction of inspired oxygen of 30% to 40%, during anaesthesia and surgery, on mortality and surgical site infection has been inconclusive. Previous trials and meta-analyses have led to different conclusions on whether a high fraction of supplemental inspired oxygen during anaesthesia may decrease or increase mortality and surgical site infections in surgical patients.

OBJECTIVES

To assess the benefits and harms of an FIO2 equal to or greater than 60% compared with a control FIO2 at or below 40% in the perioperative setting in terms of mortality, surgical site infection, respiratory insufficiency, serious adverse events and length of stay during the index admission for adult surgical patients.We looked at various outcomes, conducted subgroup and sensitivity analyses, examined the role of bias and applied trial sequential analysis (TSA) to examine the level of evidence supporting or refuting a high FIO2 during surgery, anaesthesia and recovery.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, BIOSIS, International Web of Science, the Latin American and Caribbean Health Science Information Database (LILACS), advanced Google and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) up to February 2014. We checked the references of included trials and reviews for unidentified relevant trials and reran the searches in March 2015. We will consider two studies of interest when we update the review.

SELECTION CRITERIA

We included randomized clinical trials that compared a high fraction of inspired oxygen with a routine fraction of inspired oxygen during anaesthesia, surgery and recovery in individuals 18 years of age or older.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data independently. We conducted random-effects and fixed-effect meta-analyses, and for dichotomous outcomes, we calculated risk ratios (RRs). We used published data and data obtained by contacting trial authors.To minimize the risk of systematic error, we assessed the risk of bias of the included trials. To reduce the risk of random errors caused by sparse data and repetitive updating of cumulative meta-analyses, we applied trial sequential analyses. We used Grades of Recommendation, Assessment, Development and Evaluation (GRADE) to assess the quality of the evidence.

MAIN RESULTS

We included 28 randomized clinical trials (9330 participants); in the 21 trials reporting relevant outcomes for this review, 7597 participants were randomly assigned to a high fraction of inspired oxygen versus a routine fraction of inspired oxygen.In trials with an overall low risk of bias, a high fraction of inspired oxygen compared with a routine fraction of inspired oxygen was not associated with all-cause mortality (random-effects model: RR 1.12, 95% confidence interval (CI) 0.93 to 1.36; GRADE: low quality) within the longest follow-up and within 30 days of follow-up (Peto odds ratio (OR) 0.99, 95% CI 0.61 to 1.60; GRADE: low quality). In a trial sequential analysis, the required information size was not reached and the analysis could not refute a 20% increase in mortality. Similarly, when all trials were included, a high fraction of inspired oxygen was not associated with all-cause mortality to the longest follow-up (RR 1.07, 95% CI 0.87 to 1.33) or within 30 days of follow-up (Peto OR 0.83, 95% CI 0.54 to 1.29), both of very low quality according to GRADE. Neither was a high fraction of inspired oxygen associated with the risk of surgical site infection in trials with low risk of bias (RR 0.86, 95% CI 0.63 to 1.17; GRADE: low quality) or in all trials (RR 0.87, 95% CI 0.71 to 1.07; GRADE: low quality). A high fraction of inspired oxygen was not associated with respiratory insufficiency (RR 1.25, 95% CI 0.79 to 1.99), serious adverse events (RR 0.96, 95% CI 0.65 to 1.43) or length of stay (mean difference -0.06 days, 95% CI -0.44 to 0.32 days).In subgroup analyses of nine trials using preoperative antibiotics, a high fraction of inspired oxygen was associated with a decrease in surgical site infections (RR 0.76, 95% CI 0.60 to 0.97; GRADE: very low quality); a similar effect was noted in the five trials adequately blinded for the outcome assessment (RR 0.79, 95% CI 0.66 to 0.96; GRADE: very low quality). We did not observe an effect of a high fraction of inspired oxygen on surgical site infections in any other subgroup analyses.

AUTHORS' CONCLUSIONS

As the risk of adverse events, including mortality, may be increased by a fraction of inspired oxygen of 60% or higher, and as robust evidence is lacking for a beneficial effect of a fraction of inspired oxygen of 60% or higher on surgical site infection, our overall results suggest that evidence is insufficient to support the routine use of a high fraction of inspired oxygen during anaesthesia and surgery. Given the risk of attrition and outcome reporting bias, as well as other weaknesses in the available evidence, further randomized clinical trials with low risk of bias in all bias domains, including a large sample size and long-term follow-up, are warranted.

1-1-12 one-step wash-in scheme for desflurane low flow anesthesia: performance without nitrous oxide

Background

We reported a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N₂O) low flow anesthesia that is simple, rapid, and predictable. There remain some situations where N₂O should be avoided, which limits the generalizability of this wash-in scheme. The objective of our study was to determine the performance of this scheme in contexts where N₂O is not used.

Methods

We recruited 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow of air:O₂ 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain P_ACO₂ at 30–35 mmHg.

Results

The alveolar concentration of desflurane (F_AD) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N₂O was used. An F_AD of 7% was achieved in 6 minutes. An F_AD of 1% to 7% occurred at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes. The rise in heart rate during wash-in was statistically significant, although not clinically so. There was a slight but statistically significant decrease in blood pressure, but this had no clinical significance.

Conclusion

Performance of the 1-1-12 wash-in scheme is independent of the use of N₂O. Respective F_ADs of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes.

The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II): a randomised, single-blind trial

BACKGROUND

Nitrous oxide is commonly used in general anaesthesia but concerns exist that it might increase perioperative cardiovascular risk. We aimed to gather evidence to establish whether nitrous oxide affects perioperative cardiovascular risk.

METHODS

We did an international, randomised, assessor-blinded trial in patients aged at least 45 years with known or suspected coronary artery disease having major non-cardiac surgery. Patients were randomly assigned via automated telephone service, stratified by site, to receive a general anaesthetic with or without nitrous oxide. Attending anaesthetists were aware of patients' group assignments, but patients and assessors were not. The primary outcome measure was a composite of death and cardiovascular complications (non-fatal myocardial infarction, stroke, pulmonary embolism, or cardiac arrest) within 30 days of surgery. Our modified intention-to-treat population included all patients randomly assigned to groups and undergoing induction of general anaesthesia for surgery. This trial is registered at ClinicalTrials.gov, number NCT00430989.

FINDINGS

Of 10,102 eligible patients, we enrolled 7112 patients between May 30, 2008, and Sept 28, 2013. 3543 were assigned to receive nitrous oxide and 3569 were assigned not to receive nitrous oxide. 3483 patients receiving nitrous oxide and 3509 not receiving nitrous oxide were assessed for the primary outcome. The primary outcome occurred in 283 (8%) patients receiving nitrous oxide and in 296 (8%) patients not receiving nitrous oxide (relative risk 0·96, 95% CI 0·83–1·12; p=0·64). Surgical site infection occurred in 321 (9%) patients assigned to nitrous oxide, and in 311 (9%) patients in the no-nitrous oxide group (p=0·61), and severe nausea and vomiting occurred in 506 patients (15%) assigned to nitrous oxide and 378 patients (11%) not assigned to nitrous oxide (p<0·0001).

INTERPRETATION

Our findings support the safety profile of nitrous oxide use in major non-cardiac surgery. Nitrous oxide did not increase the risk of death and cardiovascular complications or surgical-site infection, the emetogenic effect of nitrous oxide can be controlled with antiemetic prophylaxis, and a desired effect of reduced volatile agent use was shown.

FUNDING

Australian National Health and Medical Research Council; Australian and New Zealand College of Anaesthetists; Heart and Stroke Foundation of Quebec, Heart and Stroke Foundation of Ontario, Canada; General Research Fund of the Research Grant Council, Hong Kong Special Administrative Region, China.

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 myelopathy in a pediatric patient

OBJECTIVE

Nitrous oxide myelopathy is rare in children. We report a 16-year-old girl who presented at the pediatric emergency department with progressive ascending numbness in 4 limbs for 1 week and sensory ataxia for 4 days. The patient had frequently inhaled nitrous oxide for recreation over the preceding 3 months. Her serum vitamin B12, homocysteine, and folate levels were within normal ranges. Magnetic resonance imaging of the spinal cord T2-weighted images series showed hyperintensities in the central and dorsal cervical spinal cord section over C1 to C6 and suspicious of hyperintensities in the thoracic spinal section over T7 and T8.

CONCLUSIONS

Myelopathy due to nitrous oxide should be considered in a differential diagnosis when adolescents develop neurologic symptoms after nitrous oxide inhalation abuse.

The neurotoxicity of nitrous oxide: the facts and "putative" mechanisms

Nitrous oxide is a widely used analgesic agent, used also in combination with anaesthetics during surgery. Recent research has raised concerns about possible neurotoxicity of nitrous oxide, particularly in the developing brain. Nitrous oxide is an N-methyl-d-aspartate (NMDA)-antagonist drug, similar in nature to ketamine, another anaesthetic agent. It has been linked to post-operative cardiovascular problems in clinical studies. It is also widely known that exposure to nitrous oxide during surgery results in elevated homocysteine levels in many patients, but very little work has investigated the long term effect of these increased homocysteine levels. Now research in rodent models has found that homocysteine can be linked to neuronal death and possibly even cognitive deficits. This review aims to examine the current knowledge of mechanisms of action of nitrous oxide, and to describe some pathways by which it may have neurotoxic effects.

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.

Post-surgical pain syndromes: a review for the non-pain specialist

PURPOSE

This is a selective narrative review of the latest information about the epidemiology, impact, and prevention of chronic post-surgical pain (CPSP), intended primarily for those without a special interest in pain medicine.

PRINCIPAL FINDINGS

Chronic post-surgical pain is an important problem in terms of personal impact. It has staggering economic implications, exerts powerful negative effects on the quality of life of many of those it afflicts, and places a significant burden on chronic pain treatment services in general. It is well known that surgery at certain body sites is apt to cause CPSP, but emerging evidence shows a strong correlation between CPSP and demographic (young age, obesity, and female sex) and psychological characteristics (anxiety, depression, stress, and catastrophizing). Severe acute pain is a strong risk factor for CPSP, and this adds yet more weight to the argument that acute pain should be controlled effectively. In specific circumstances, CPSP can be reduced by regional anesthetic techniques, infiltration of local anesthetic, or preoperative use of gabapentin. The ability of other known interrupters of afferent nociceptive transmission-commonly used to reduce CPSP when administered at the time of surgery-is currently unproven, as is the hypothesis that the use of remifentanil during surgery worsens CPSP.

CONCLUSIONS

Reduction of CPSP is a worthy long-term outcome for anesthesia providers to consider as they plan the perioperative care of their patients. More evidence is needed about the effect of currently used analgesics and other perioperative techniques on CPSP.