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

Exploring the Micropore Functional Mechanism of N2O Adsorption by the Eucalyptus Bark-based Porous Carbon

Nitrous oxide (N2O), recognized as a significant greenhouse gas, has received insufficient research attention in the past. In view of their low energy consumption and cost-effectiveness, the application of porous materials in adsorption is increasingly regarded as a potent strategy to reduce N2O pollution. In this study, a series of microporous porous carbons with a preeminent specific surface area (244.54-2018.08 m2 g-1), which are derived from the fast-growing eucalyptus bark, were synthesized by KOH activation at high temperatures. The obtained materials demonstrated a relatively fine N2O capture capability (0.19-0.68 mmol g-1) at normal temperature and pressure. More importantly, the optimal pore size affecting N2O adsorption (0.8 and 1.0 nm) has been detected, which is a meaningful view that has never been put forward in previous studies. The rationality of the N2O adsorption mechanism was also validated by combining the experimental analysis and Grand Canonical Monte Carlo (GCMC) simulation. The calculated results showed that 0.8 and 1.0 nm of the porous carbon were the preferred pore sizes for N2O adsorption, and the interaction force between N2O and the pore wall decreased with the increase of distance. This study provides a significant theoretical basis for the preparation of biomass porous carbon with excellent N2O adsorption performance and practical adsorption application.

Should pipeline nitrous oxide be discontinued in secondary care: A cost-benefit analysis

Background

Nitrous oxide (N2O) has seen a marked decline in its usage in recent years due to its adverse clinical effects. We audited the practice in our department to evaluate the N2O consumption and cost-effectiveness of its supply.

Methodology

Electronic anesthesia records of all patients anesthetized in our main operating rooms in a typical month were reviewed retrospectively, and utilization of N2O was noted in addition to the patient demographics, surgical procedure, and specialty.

Results

A total of 950 patients were anesthetized, and 3.1% received N2O. The annual usage was estimated to be 72,871 liters, with a leakage of 3,883,105 liters to the environment, posing a safety hazard and wasting 149,612.50 SAR.

Conclusion

Notable costs and environmental benefits may be achieved by substituting a piped supply of N2O with portable E-cylinders on demand in operating rooms for rational use.

Influence of nitrous oxide added to general anaesthesia on postoperative mortality and morbidity: a systematic review and meta-analysis

BACKGROUND

Nitrous oxide (N2O) is a common adjuvant to general anaesthesia. It is also a potent greenhouse gas and causes ozone depletion. We sought to quantify the influence of N2O as an adjuvant to general anaesthesia on postoperative patient outcomes.

METHODS

We searched Medline, EMBASE, and Cochrane Central for works published from inception to July 6, 2023. RCTs comparing general anaesthesia with or without N2O were included. Risk ratios (RRs) and standardised mean differences (SMDs) were calculated, along with 95% confidence intervals (CIs), using a random-effects model. Outcomes were derived from the Standardised Endpoints for Perioperative Medicine (StEP) outcome set. Primary outcomes were mortality and organ-related morbidity, and secondary outcomes were anaesthetic and surgical morbidity.

RESULTS

Of 3305 records, 179 full-text articles were assessed, and 71 RCTs, totalling 22 147 patients, were included in the meta-analysis. Addition of N2O to general anaesthesia did not influence postoperative mortality or most morbidity outcomes. N2O increased the incidence of atelectasis (RR 1.62, 95% CI 1.24 to 2.12) and postoperative nausea and vomiting (RR 1.27, 95% CI 1.15 to 1.40), and decreased intraoperative opioid consumption (SMD -0.19, 95% CI -0.35 to -0.04) and time to extubation (MD -2.17 min, 95% CI -3.32 to -1.03 min).

CONCLUSIONS

N2O did not influence postoperative mortality or most morbidity outcomes. Considering the environmental effects of N2O, these findings confirm that current policy recommendations to limit its use do not affect patient safety.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42023443287.

Persistent use of nitrous oxide for anaesthesia in European hospitals despite its harmfulness to the climate - how emission taxation can achieve the coupling of cost-effectiveness and climate protection: observational study

BACKGROUND

Health care has the intrinsic obligation to preserve health. This concept is also applicable to planetary health. Nitrous oxide (N2O) lacks clinical indications in modern anaesthesia, while it is a high-potential greenhouse gas. Its seemingly low cost contrasts with the consequential externalised socio-economic costs due to its contribution to the climate crisis, which is approximately €698 per emitted ton of CO2 equivalent. This difference can be internalised through emission taxation. In this study, we aim to evaluate how much N2O - total amount and converted to CO2 equivalent - is used at a German university hospital and compare this amount to that used at European hospitals. Furthermore, how the cost of N2O usage changes under different emission taxation scenarios is calculated.

METHODS

This trial was a retrospective observational study at a German university hospital with approximately 1,250 beds between 2016 and 2020. Additionally, five European hospitals from the Health Care Without Harm Network were used for comparison from a European perspective. The main outcome parameters were the amount of N2O used, in total and converted to CO2 equivalent, and the total cost at emission taxation of €0, €25, €55 and €698 per ton CO2 equivalent.

RESULTS

At the peak, 2,104 tCO2 equivalent in N2O was emitted in 2019. The actual cost was €14,040 in this year, while the corresponding socio-economic damage due to the climate crisis was almost €1.5 million. Other European hospitals showed comparable amounts of emissions.

CONCLUSIONS

The annual peak amount of emitted N2O corresponded to the total annual greenhouse gas emission of 188 people in Germany. To achieve a drastic reduction in use, the abandonment of recommendations by anaesthesiologic societies appears necessary, in addition to an internalisation of future costs via emission taxation, which will cause inadequate cost for a medication without relevant benefit or indication. To that end, the inclusion of health sector emissions within national or international greenhouse gas taxation, for example, the European Union Emissions Trading System, appears necessary and expedient in view of the urgent need to address the ecological transformation.

TRIAL REGISTRATION

The trial was registered with the German Clinical Trials Register, identifier DRKS00024973 on 12/04/2021.

Health system decarbonization on obstetric and newborn units

The healthcare industry makes up 4.6 % of greenhouse gas (GHS) emissions worldwide. Although it is not known what proportion of GHGs come from obstetric and newborn units, newborns and pregnant individuals are likely to face some of the largest consequences from climate change. We review the literature in the areas of decarbonization on labor and delivery (L&D) and neonatal units and describe innovations from the fields of surgery and anesthesia. Best practices for L&D include refining disposable equipment packs, decreasing the use of single-use medical devices, adequately triaging waste, and decreasing the use of potent anesthetic gases such as nitrous oxide and desflurane. In neonatal settings, similarly triaging waste and decreasing the use of plastics containing endocrine disrupting chemicals can lower the carbon and environmental footprint and improve neonatal health. Additionally, avoiding unnecessary cesarean deliveries and increasing breastfeeding practices are also likely to improve the carbon footprint of L&D and neonatal units.

A survey of Australian midwives: Experts in nitrous oxide administration within the peripartum setting

PROBLEM

There is little documented evidence of midwives' perspectives regarding the use of nitrous oxide in the peripartum period.

BACKGROUND

Nitrous oxide is an inhaled gas used widely in the peripartum period; usually offered and managed by midwives.

AIM

Explore midwives' knowledge, perceptions, and practices of facilitating women's use of nitrous oxide in the peripartum period.

METHODS

An exploratory cross-sectional survey design was used. Quantitative data were analysed using descriptive and inferential statistics; open-ended responses underwent template analysis.

FINDINGS

Midwives (n = 121) working in three Australian settings reported regularly recommending the use of nitrous oxide and high levels of knowledge and confidence supporting its use. There was a significant association between midwifery experience, and perspectives on women's capacity to use nitrous effectively (p = 0.004); and desire for refresher education (p < 0.001). Midwives working in continuity models were more likely to support women using nitrous oxide in any situation (p = 0.039).

DISCUSSION

Midwives demonstrated expertise in facilitating nitrous oxide use, citing utility to relieve anxiety and distract women from pain or discomfort. Nitrous oxide was identified as an important adjunct to the provision of supportive care requiring midwifery therapeutic presence.

CONCLUSION

This study provides novel insight into midwives' support of nitrous oxide use in the peripartum setting revealing high levels of knowledge and confidence. Recognition of this unique expertise held by midwives is important to ensure transfer and development of professional knowledge and skills and emphasises the need for midwifery leadership in clinical service provision, planning and policy.

Nitrous Oxide Use in Australian Health Care: Strategies to Reduce the Climate Impact

Nitrous oxide is a useful inhaled analgesic. Due to its high global warming potential and ozone-depleting properties, the nitrous oxide emissions related to health care are being increasingly scrutinized. In this narrative review, we will discuss the clinical uses of nitrous oxide relevant to anesthetists, in addition to its contribution as a greenhouse gas. Using available data from Australia, we will explore potential strategies for reducing the impact of those emissions, which are likely to be applicable in other countries. These include destruction of captured nitrous oxide, minimizing nitrous oxide waste and reducing clinical use. Anesthesia clinicians are well placed to raise awareness with colleagues and consumers regarding the environmental impact of nitrous oxide and to promote cleaner alternatives. Reducing use is likely to be the most promising reduction strategy without large-scale changes to infrastructure and subsequent delay in action.

Guidelines for reducing the environmental impact of general anaesthesia

OBJECTIVE

To provide guidelines for reducing the environmental impact of general anaesthesia.

DESIGN

A committee of ten experts from SFAR and SF2H and SFPC learned societies was set up. A policy of declaration of competing interests was applied and observed throughout the guideline-writing process. Likewise, it did not benefit from any funding from a company marketing a health product (drug or medical device). The committee followed the GRADE® method (Grading of Recommendations Assessment, Development and Evaluation) to assess the quality of the evidence on which the recommendations were based.

METHODS

We aimed to formulate recommendations according to the GRADE® methodology for three different fields: anaesthesia vapours and gases; intravenous drugs; medical devices and the working environment. Each question was formulated according to the PICO format (Population, Intervention, Comparator, Outcome). The literature review and recommendations were formulated according to the GRADE® methodology.

RESULTS

The experts' work on the synthesis and application of the GRADE® method led to the formulation of 17 recommendations. Since the GRADE® method could not be entirely applied to all of the questions, some of the recommendations were formulated as expert opinions.

CONCLUSION

Based on strong agreement between experts, we produced 17 recommendations designed to guide reducing the environmental impact of general anaesthesia.

Changes in cerebral connectivity and brain tissue pulsations with the antidepressant response to an equimolar mixture of oxygen and nitrous oxide: an MRI and ultrasound study

Nitrous oxide (N2O) has recently emerged as a potential fast-acting antidepressant but the cerebral mechanisms involved in this effect remain speculative. We hypothesized that the antidepressant response to an Equimolar Mixture of Oxygen and Nitrous Oxide (EMONO) would be associated with changes in cerebral connectivity and brain tissue pulsations (BTP). Thirty participants (20 with a major depressive episode resistant to at least one antidepressant and 10 healthy controls-HC, aged 25-50, only females) were exposed to a 1-h single session of EMONO and followed for 1 week. We defined response as a reduction of at least 50% in the MADRS score 1 week after exposure. Cerebral connectivity of the Anterior Cingulate Cortex (ACC), using ROI-based resting state fMRI, and BTP, using ultrasound Tissue Pulsatility Imaging, were compared before and rapidly after exposure (as well as during exposure for BTP) among HC, non-responders and responders. We conducted analyses to compare group × time, group, and time effects. Nine (45%) depressed participants were considered responders and eleven (55%) non-responders. In responders, we observed a significant reduction in the connectivity of the subgenual ACC with the precuneus. Connectivity of the supracallosal ACC with the mid-cingulate also significantly decreased after exposure in HC and in non-responders. BTP significantly increased in the three groups between baseline and gas exposure, but the increase in BTP within the first 10 min was only significant in responders. We found that a single session of EMONO can rapidly modify the functional connectivity in the subgenual ACC-precuneus, nodes within the default mode network, in depressed participants responders to EMONO. In addition, larger increases in BTP, associated with a significant rise in cerebral blood flow, appear to promote the antidepressant response, possibly by facilitating optimal drug delivery to the brain. Our study identified potential cerebral mechanisms related to the antidepressant response of N2O, as well as potential markers for treatment response with this fast-acting antidepressant.

Day-surgery adult patients with obesity and obstructive sleep apnea: Current controversies and concerns

Obesity and obstructive sleep apnea are considered independent risk factors that can adversely affect perioperative outcomes. A combination of these two conditions in the ambulatory surgery patient can pose significant challenges for the anesthesiologist. Nevertheless, these patients should not routinely be denied access to ambulatory surgery. Instead, patients should be appropriately optimized. Anesthesiologists and surgeons must work together to implement fast-track anesthetic and surgical techniques that will ensure successful ambulatory outcomes.

Inhaled nitrous oxide for painful procedures in children and youth: a systematic review and meta-analysis

OBJECTIVES

The objective of this study was to synthesize indication-based evidence for N₂O for distress and pain in children.

STUDY DESIGN

We included trials of N₂O in participants 0-21 years, reporting distress or pain for emergency department procedures. The primary outcome was procedural distress. Where meta-analysis was not possible, we used Tricco et al.'s classification of "neutral" (p ≥ 0.05), "favorable," or "unfavorable" (p < 0.05, supporting N₂O or comparator, respectively). We used the Cochrane Collaboration's Risk of Bias tool and the Grading of Recommendations Assessment, Development, and Evaluation system to evaluate risk of bias and quality of evidence, respectively.

RESULTS

We included 30 trials. For pain using the Visual Analog Scale (0-100 mm) during IV insertion, 70% N₂O (delta:-16.5; 95%CI:-28.6 to -4.4; p = 0.008; three trials; I² = 0%) and 50% N₂O plus eutectic mixture of local anesthetics (EMLA) (delta:-1.2; 95%CI:-2.1 to -0.3; p = 0.007; two trials; I² = 43%) were superior to EMLA. 50% N₂O was not superior to EMLA (delta:-0.4; 95%CI:-1.2 to 0.3; p = 0.26; two trials; I² = 15%). For distress and pain during laceration repair, N₂O was "favorable" versus each of SC lidocaine, oxygen, and oral midazolam but "neutral" versus IV ketamine (five trials). For distress and pain during fracture reduction (three trials), N₂O was "neutral" versus each of IM meperidine plus promethazine, regional anesthesia, and IV ketamine plus midazolam. For distress and pain during lumbar puncture (one trial), N₂O was "favorable" versus oxygen. For distress and pain during urethral catheterization (one trial), N₂O was "neutral" versus oral midazolam. For pain during intramuscular injection (one trial), N₂O plus EMLA was "favorable" versus N₂O and EMLA alone. Common adverse effects of N₂O included nausea (4.4%), agitation (3.7%), and vomiting (3.6%) AEs were less frequent with N₂O alone (278/1147 (24.2%)) versus N₂O plus midazolam (48/52 (92.3%)) and N₂O plus fentanyl (123/201 (61.2%)).

CONCLUSIONS

There is sufficient evidence to recommend N₂O plus topical anesthetic for IV insertion and laceration repair. Adverse effects are greater when combined with other sedating agents.

Occupational Exposure to Inhalational Anesthetics and Teratogenic Effects: A Systematic Review

(1) Background: In the current healthcare environment, there is a large proportion of female staff of childbearing age, so, according to existing conflicting studies, the teratogenic effects that inhalational anesthetics may have on exposed pregnant workers should be assessed. This investigation aims to analyze the teratogenic effects of inhalational anesthetics in conditions of actual use, determining any association with spontaneous abortion or congenital malformations. (2) Methods: A systematic review was carried out according to the PRISMA statement based on PICO (problem of interest–intervention to be considered–intervention compared–outcome) (Do inhalational anesthetics have teratogenic effects in current clinical practice?). The level of evidence of the selected articles was evaluated using the SIGN scale. The databases used were PubMed, Embase, Scopus, Web of Science, Google academic and Opengrey. Primary studies conducted in professionals exposed to inhalational anesthetics that evaluate spontaneous abortions or congenital malformations, conducted in any country and language and published within the last ten years were selected. (3) Results: Of the 541 studies identified, 6 met all inclusion criteria in answering the research question. Since many methodological differences were found in estimating exposure to inhalational anesthetics, a qualitative systematic review was performed. The selected studies have a retrospective cohort design and mostly present a low level of evidence and a low grade of recommendation. Studies with the highest level of evidence do not find an association between the use of inhalational anesthetics and the occurrence of miscarriage or congenital malformations. (4) Conclusions: The administration of inhalational anesthetics, especially with gas extraction systems (scavenging systems) and the adequate ventilation of operating rooms, is not associated with the occurrence of spontaneous abortions or congenital malformations.

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

RATIONALE

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

PATIENT CONCERNS

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

DIAGNOSIS

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

INTERVENTION AND OUTCOMES

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

LESSONS

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

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.

Guidelines for Perioperative Care in Elective Abdominal and Pelvic Surgery at Primary and Secondary Hospitals in Low-Middle-Income Countries (LMIC's): Enhanced Recovery After Surgery (ERAS) Society Recommendation

Background

This is the first Enhanced Recovery After Surgery (ERAS®) Society guideline for primary and secondary hospitals in low–middle-income countries (LMIC’s) for elective abdominal and gynecologic care.

Methods

The ERAS LMIC Guidelines group was established by the ERAS® Society in collaboration with different representatives of perioperative care from LMIC’s. The group consisted of seven members from the ERAS® Society and eight members from LMIC’s. An updated systematic literature search and evaluation of evidence from previous ERAS® guidelines was performed by the leading authors of the Colorectal (2018) and Gynecologic (2019) surgery guidelines (Gustafsson et al in World J Surg 43:6592–695, Nelson et al in Int J Gynecol Cancer 29(4):651–668). Meta-analyses randomized controlled trials (RCTs), prospective and retrospective cohort studies from both HIC’s and LMIC’s were considered for each perioperative item. The members in the LMIC group then applied the current evidence and adapted the recommendations for each intervention as well as identifying possible new items relevant to LMIC’s. The Grading of Recommendations, Assessment, Development and Evaluation system (GRADE) methodology was used to determine the quality of the published evidence. The strength of the recommendations was based on importance of the problem, quality of evidence, balance between desirable and undesirable effects, acceptability to key stakeholders, cost of implementation and specifically the feasibility of implementing in LMIC’s and determined through discussions and consensus.

Results

In addition to previously described ERAS® Society interventions, the following items were included, revised or discussed: the Surgical Safety Checklist (SSC), preoperative routine human immunodeficiency virus (HIV) testing in countries with a high prevalence of HIV/AIDS (CD4 and viral load for those patients that are HIV positive), delirium screening and prevention, COVID 19 screening, VTE prophylaxis, immuno-nutrition, prehabilitation, minimally invasive surgery (MIS) and a standardized postoperative monitoring guideline.

Conclusions

These guidelines are seen as a starting point to address the urgent need to improve perioperative care and to effect data-driven, evidence-based care in LMIC’s.

Beyond the epidural: Alternatives to neuraxial labor analgesia

Labor creates an intense pain experienced by women across the world. Although neuraxial analgesia is the most effective treatment of labor pain, in many cases, it may not be undesired, not available, or have contraindications. In addition, satisfaction with labor analgesia is not only determined by the efficacy of analgesia but a woman's sense of agency and involvement in the childbirth experience are also key contributors. Providing safe choices for labor analgesia and support is central to creating a tailored, safe, and effective analgesic treatment plan with high maternal satisfaction. Healthcare provider knowledge of various nonneuraxial analgesic options, including efficacy, contraindications, safe clinical implementation, and side effects of various techniques is needed for optimal patient care and satisfaction. Future rigorous scientific studies addressing all of these labor analgesia options are needed to improve our understanding. This review summarizes the current published literature for commonly available non-neuraxial labor analgesic options.

Current status of nitrous oxide use in pediatric patients

Nitrous oxide is one of the most commonly used inhalational anesthetic agents used in practice. It is a cost-effective, pleasant, safe, and versatile anesthetic agent with many desirable properties like good quality analgesia, decreased awareness, accelerated induction and recovery from anesthesia, and reduced utilization of other expensive inhalational agents with potential cost savings. The use of nitrous oxide has been questioned by a lot of studies and case reports perceiving its adverse systemic, hematological, immune, and neurologic adverse effects. However, the literature in the recent past has tried to resolve the controversies related to its use. The concerns over an increase in cardiovascular complications and mortality following nitrous oxide use have been negated by recent data. However, its use in certain vulnerable populations like children with cobalamin and folate deficiency or defects in their metabolic pathways remains a cause of concern for its toxic effects. In this narrative review, we aim to discuss the pharmacological properties of nitrous oxide, the potential advantages and drawbacks of the use of nitrous oxide in children, address the neurodevelopmental and other systemic effects, and throw light on the evidence regarding the safety of nitrous oxide use and its current role in pediatric procedural sedation and anesthesia practice. The literature related to its use in the pediatric population for painful procedures and surgeries has been summarized.

Nitrous Oxide Sedation Asynchronous Curriculum for Pediatric Emergency Medicine Providers

This technical report describes a nitrous oxide sedation training curriculum for pediatric emergency medicine providers. This curriculum was used during the novel coronavirus disease 2019 (COVID-19) pandemic where in-person classroom training was significantly limited. We demonstrate a model for concept and equipment learning with video-guided self-practice in place of in-person training with a facilitator. A similar model can be utilized for other equipment or concept training.

Management of postoperative nausea and vomiting in adults: current controversies

PURPOSE OF REVIEW

Postoperative nausea and vomiting (PONV) continue to plague the surgical patient population with an adverse impact on postoperative outcomes. The aim of this review is to critically assess current evidence for PONV management, including studies evaluating baseline risk reduction and antiemetic prophylaxis, to provide a pragmatic approach to prevention and treatment of PONV in routine clinical practice.

RECENT FINDINGS

Multiple recent reviews and guidelines have been published on this topic with some limitations. In the current ERAS era, all patients irrespective of their PONV risk should receive two to three antiemetics for prophylaxis. Patients at a high risk of PONV [i.e. prior history of PONV, history of motion sickness, high opioid requirements after surgery (e.g. inability to use nonopioid analgesic techniques)] should receive three to four antiemetics for prophylaxis.

SUMMARY

This review provides a practical approach to PONV prevention based on recent literature.

General anesthetic techniques for enhanced recovery after surgery: Current controversies

General anesthesia technique can influence not only immediate postoperative outcomes, but also long-term outcomes beyond hospital stay (e.g., readmission after discharge from hospital). There is lack of evidence regarding superiority of total intravenous anesthesia over inhalation anesthesia with regards to postoperative outcomes even in high-risk population including cancer patients. Optimal balanced general anesthetic technique for enhance recovery after elective surgery in adults includes avoidance of routine use preoperative midazolam, avoidance of deep anesthesia, use of opioid-sparing approach, and minimization of neuromuscular blocking agents and appropriate reversal of residual paralysis. Given that the residual effects of drugs used during anesthesia can increase postoperative morbidity and delay recovery, it is prudent to use a minimal number of drug combinations, and the drugs used are shorter-acting and administered at the lowest possible dose. It is imperative that the discerning anesthesiologist consider whether each drug used is really necessary for accomplishing perioperative goals.

Quantitative Assessment of Nitrous Oxide Levels in Room Air of Operation Theaters and Recovery Area: An Observational Study

Background:

Nitrous oxide has been used during surgical anesthesia for many years. However, information about occupational exposure and related risks due to N₂O exposure to the health care personnel in India are still poorly understood. Here, we measured the residual N₂O levels during the working time of operation theatre room air in our tertiary care hospital.

Material and Methods:

The air samples were collected from different anesthesia exposure zones on different days for quantitative analysis of available N₂O in the room air in respective areas. Nitrous oxide concentrations in the ambient air were also measured to compare outdoor and indoor levels.

Observations and Results:

Nitrous oxide mixing ratios were found to be 65.61 ± 0.05 ppm, 281.63 ± 0.43 ppm, and 165.42 ± 0.42 ppm in elective surgical theatres of the hospital on three different days whereas in emergency operation theatres of the same hospital levels of N₂O were 166.75 ± 0.07 ppm, 510.19 ± 0.30 ppm and 2443.92 ± 0.64 ppm during same period. In elective pediatric surgical theatres levels of N₂O were found to be 1132.55 ± 0.70 ppm and 362.21 ± 0.13 ppm on two days of reading respectively. Outdoor levels of N₂O in contrast found 0.32 ± 0.01 ppm and was lower by a factor of 1000.

Conclusion:

We observed the very high ambient concentration of N₂O in the surgical theatre's environment (up to 2443 ppm) and recovery areas (up to 50 ppm). It was 5 to 50 times higher ambient concentration of N₂O than REL in OT area and 200-7000 times higher ambient concentration of N₂O than outdoor ambient air in all surgical theaters other than CTVS OTs.

A health-based recommended occupational exposure limit for nitrous oxide using experimental animal data based on a systematic review and dose-response analysis

BACKGROUND

Nitrous oxide (N₂O) is a common inhalation anaesthetic used in medical, paramedical, and veterinary practice. Since the mid 1950's, concerns have been raised regarding occupational exposure to N₂O, leading to many epidemiological and experimental animal studies. Previous evaluations resulted in the classification of N₂O as a possible risk factor for adverse reproductive health outcomes based on animal data. Human data were deemed inadequate primarily because of simultaneous co-exposures to other risk factors for adverse reproductive and developmental outcomes, including other anaesthetic gases. Since previous evaluations, controversies regarding N₂O use remained and new approaches for dose response modelling have been adopted, calling for an update and re-evaluation of the body of evidence. This review aims to assess available animal evidence on N₂O reproductive and developmental outcomes to inform a health-based recommended occupational exposure limit (OEL) for N₂O with a benchmark dose-response modelling (BMD) approach.

METHODS

Comprehensive searches in PubMed, EMBASE, and Web of Science were performed to retrieve all relevant studies addressing reproductive and developmental outcomes related to inhalation of N₂O in animals. The articles retrieved were screened based on title-abstract and full text by two independent reviewers. After data extraction, an overview of all studies was created for the different endpoints, namely foetal outcomes (e.g., resorption), female outcomes (e.g. implantations), and male outcomes (e.g. sperm count). A subset of studies reporting on exposure relevant to workplace settings and with a sufficient number of tested doses were included in dose-response modelling using the BMD approach.

RESULTS

In total, 15.816 articles were retrieved, of which 47 articles were finally included while 4 of those were used for the quantitative data synthesis. The overall risk of bias was judged to be probably high (using OHAT risk of bias tool) and unclear (using SYRCLE's risk of bias tool). From eligible rat studies, three studies provided an acceptable result by fitting a Hill model to the dose-response data. The resulting benchmark dose lower bounds (BMDLs) from three studies converged to an average (±sd) exposure level of 925 ± 2 mg/m³ at an additional risk of one standard deviation of implantation losses above those observed in the control group (i.e. reduced number of live foetuses/mother). For extrapolation from rats to humans, an uncertainty factor of 10 was used and an additional factor of 5 was applied to account for interindividual variability within the population of workers.

CONCLUSION

With this systematic review, all available evidence for reproductive toxicity and adverse developmental outcomes in animals resulting from inhalation exposure to N₂O was used to derive a health-based OEL recommendation of 20 mg/m³ as 8-h time-weighted average.

Towards Quantum-Chemical Modeling of the Activity of Anesthetic Compounds

The modeling of the activity of anesthetics is a real challenge because of their unique electronic and structural characteristics. Microscopic approaches relevant to the typical features of these systems have been developed based on the advancements in the theory of intermolecular interactions. By stressing the quantum chemical point of view, here, we review the advances in the field highlighting differences and similarities among the chemicals within this group. The binding of the anesthetics to their partners has been analyzed by Symmetry-Adapted Perturbation Theory to provide insight into the nature of the interaction and the modeling of the adducts/complexes allows us to rationalize their anesthetic properties. A new approach in the frame of microtubule concept and the importance of lipid rafts and channels in membranes is also discussed.

The association of nitrous oxide on length of stay in the postanesthesia care unit: a retrospective observational study

PURPOSE

To assess whether intraoperative use of nitrous oxide (N₂O) as an adjunct to general anesthesia is associated with a shorter length of stay in the postanesthesia care unit (PACU).

METHODS

We analyzed data from adult patients who underwent non-cardiothoracic surgery under general anesthesia between May 2008 and December 2018. We assessed the association between intraoperative low- and high-dose N₂O and PACU length of stay.

RESULTS

A total of 148,284 patients were included in the primary analysis. After adjusting for a priori defined confounders, a high dose of N₂O significantly decreased PACU length of stay, with a calculated difference of -9.1 min (95% confidence interval [CI], -10.5 to -7.7; P < 0.001). Patients who received high-dose N₂O had a lower incidence of both short- and prolonged-duration of intraoperative hypotension (adjusted odds ratio [aOR], 0.85; 95% CI, 0.83 to 0.88; P < 0.001 and aOR, 0.76; 95% CI, 0.73 to 0.80; P < 0.001, respectively) and received a lower total intraoperative vasopressor dose (-0.04 mg of norepinephrine equivalents; 95% CI, -0.06 to -0.01; P = 0.01). The effect of high-dose N₂O on PACU length of stay was modified by surgical complexity (adjusted absolute difference: -26.1 min; 95% CI, -29.2 to -23.1; P < 0.001; P for interaction < 0.001), and most pronounced in patients who underwent complex surgery and received intraoperative antiemetic therapy (adjusted absolute difference: -38.9 min; 95% CI, -43.1 to -34.6; P < 0.001; P for interaction < 0.001).

CONCLUSIONS

Nitrous oxide was dose-dependently associated with a decreased PACU length of stay. The effect was clinically relevant (> 30 min difference) in patients who underwent complex surgical procedures and received intraoperative antiemetic therapy.

A phase 2 trial of inhaled nitrous oxide for treatment-resistant major depression

Nitrous oxide at 50% inhaled concentration has been shown to improve depressive symptoms in patients with treatment-resistant major depression (TRMD). Whether a lower concentration of 25% nitrous oxide provides similar efficacy and persistence of antidepressant effects while reducing the risk of adverse side effects is unknown. In this phase 2 clinical trial (NCT03283670), 24 patients with severe TRMD were randomly assigned in a crossover fashion to three treatments consisting of a single 1-hour inhalation with (i) 50% nitrous oxide, (ii) 25% nitrous oxide, or (iii) placebo (air/oxygen). The primary outcome was the change on the Hamilton Depression Rating Scale (HDRS-21). Whereas nitrous oxide significantly improved depressive symptoms versus placebo (P = 0.01), there was no difference between 25 and 50% nitrous oxide (P = 0.58). The estimated differences between 25% and placebo were -0.75 points on the HDRS-21 at 2 hours (P = 0.73), -1.41 points at 24 hours (P = 0.52), -4.35 points at week 1 (P = 0.05), and -5.19 points at week 2 (P = 0.02), and the estimated differences between 50% and placebo were -0.87 points at 2 hours (P = 0.69), -1.93 points at 24 hours (P = 0.37), -2.44 points at week 1 (P = 0.25), and -7.00 points at week 2 (P = 0.001). Adverse events declined substantially with dose (P < 0.001). These results suggest that 25% nitrous oxide has comparable efficacy to 50% nitrous oxide in improving TRMD but with a markedly lower rate of adverse effects.

The use of esketamine sedation in the emergency department for manipulation of paediatric forearm fractures: A 5 year study

The purpose of this study is to assess the use of esketamine as procedural sedation for the reduction of paediatric forearm fractures in the emergency department (ED). A retrospective analysis was undertaken of forearm fractures between 1^st January 2012 to 31^st December 2016 which were treated with manipulation in ED using esketamine sedation. Patient demographics and fracture configuration were collected. Patient radiographs were evaluated and cast index calculated. 151 patients (103 male, 48 female) were included (average age of 8.5 [1 to 15]). Four (2.6%) patients were lost to final follow up. 11 (7%) fractures were not accepted after initial manipulation and required formal surgical management under general anaesthetic. At one week follow up, a further 5 (3%) fractures displaced requiring operative management. 100% of patients who slipped at one week had a cast index greater than 0.8 [average 0.86, 95% CI 0.80-0.92]. At final follow up successful reduction was achieved in 89.1% (131/144) of patients. No adverse events occurred following administration of esketamine. This study provides evidence that manipulation of paediatric forearm fractures using esketamine as procedural sedation in the ED is comparable to other methods in achieving acceptable outcomes. This is in addition to the potential for cost savings. However, future studies formally assessing cost effectiveness and patient outcomes are needed.

Virtual reality vs. Kalinox® for management of pain in intensive care unit after cardiac surgery: a randomized study

Introduction

The management of pain and anxiety remains a challenge in the intensive care unit. By distracting patients, virtual reality (VR) may have a role in painful procedures. We compared VR vs. an inhaled equimolar mixture of N₂O and O₂ (Kalinox®) for pain and anxiety management during the removal of chest drains after cardiac surgery.

Methods

Prospective, non-inferiority, open-label study. Patients were randomized, for Kalinox® or VR session during drain removal. The analgesia/nociception index (ANI) was monitored during the procedure for objective assessment of pain and anxiety. The primary endpoint was the ΔANI (ANI_min − ANI₀) during the procedure, based on ANIm (average on 4 min). We prespecified VR as non-inferior to Kalinox® with a margin of 3 points. Self-reported pain and anxiety were also analysed using numeric rate scale (NRS).

Results

200 patients were included, 99 in the VR group and 101 in the Kalinox® group; 90 patients were analysed in both groups in per-protocol analysis. The median age was 68.0 years [60.0–74.8]. The ΔANI was − 15.1 ± 12.9 in the Kalinox® group and − 15.7 ± 11.6 in the VR group (NS). The mean difference was, therefore, − 0.6 [− 3.6 to 2.4], including the non-inferiority margin of 3. Patients in the VR group had a significantly higher pain NRS scale immediately after the drain removal, 5.0 [3.0–7.0] vs. 3.0 [2.0–6.0], p = 0.009, but no difference 10 min after. NRS of anxiety did not differ between the two groups.

Conclusion

Based on the ANI, the current study showed that VR did not reach the statistical requirements for a proven non-inferiority vs. Kalinox® in managing pain and anxiety during chest drain removal. Moreover, VR was less effective based on NRS. More studies are needed to determine if VR might have a place in the overall approach to pain and anxiety in intensive care units.

Trial registration NCT, NCT03956264. Registered 20 May 2019, https://clinicaltrials.gov/ct2/show/NCT03956264

Enhanced recovery pathways for ambulatory surgery

PURPOSE OF REVIEW

Implementation of enhanced recovery pathways have allowed migration of complex surgical procedures from inpatient setting to the outpatient setting. These programs improve patient safety and patient-reported outcomes. The present article discusses the principles of enhanced recovery pathways in adults undergoing ambulatory surgery with an aim of improving patient safety and postoperative outcomes.

RECENT FINDINGS

Procedure and patient selection is one of the key elements that influences perioperative outcomes after ambulatory surgery. Other elements include optimization of comorbid conditions, patient and family education, minimal preoperative fasting and adequate hydration during the fasting period, use of fast-track anesthesia technique, lung-protective mechanical ventilation, maintenance of fluid balance, and multimodal pain, nausea, and vomiting prophylaxis.

SUMMARY

Implementation of enhanced recovery pathways requires a multidisciplinary approach in which the anesthesiologist should take a lead in collaborating with surgeons and perioperative nurses. Measuring compliance with enhanced recovery pathways through an audit program is essential to evaluate success and need for protocol modification. The metrics to assess the impact of enhanced recovery pathways include complication rates, patient reported outcomes, duration of postoperative stay in the surgical facility, unplanned hospital admission rate, and 7-day and 30-day readmission rates.

Effects of nitrous oxide on glycinergic transmission in rat spinal neurons

We investigated the effects of nitrous oxide (N₂O) on glycinergic inhibitory whole-cell and synaptic responses using a "synapse bouton preparation," dissociated mechanically from rat spinal sacral dorsal commissural nucleus (SDCN) neurons. This technique can evaluate pure single- or multi-synaptic responses from native functional nerve endings and enable us to accurately quantify how N₂O influences pre- and postsynaptic transmission. We found that 70 % N₂O enhanced exogenous glycine-induced whole-cell currents (I_Gly) at glycine concentrations lower than 3 × 10^-5 M, but did not affect I_Gly at glycine concentrations higher than 10^-4 M. N₂O did not affect the amplitude and 1/e decay-time of both spontaneous and miniature glycinergic inhibitory postsynaptic currents recorded in the absence and presence of tetrodotoxin (sIPSCs and mIPSCs, respectively). The decrease in frequency induced by N₂O was observed in sIPSCs but not in mIPSCs, which was recorded in the presence of both tetrodotoxin and Cd²⁺, which block voltage-gated Na⁺ and Ca²⁺ channels, respectively. N₂O also decreased the amplitude and increased the failure rate and paired-pulse ratio of action potential-evoked glycinergic inhibitory postsynaptic currents. N₂O slightly decreased the Ba²⁺ currents mediated by voltage-gated Ca²⁺ channels in SDCN neurons. We found that N₂O suppresses glycinergic responses at synaptic levels with presynaptic effect having much more predominant role. The difference between glycinergic whole-cell and synaptic responses suggests that extrasynaptic responses seriously modulate whole-cell currents. Our results strongly suggest that these responses may thus in part explain analgesic effects of N₂O via marked glutamatergic inhibition by glycinergic responses in the spinal cord.

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.

Clinical, Electrophysiological and Radiological Features of Nitrous Oxide-Induced Neurological Disorders

PURPOSE

We summarized the clinical manifestations, laboratory and electrodiagnostic characteristics and magnetic resonance imaging (MRI) findings of nitrous oxide (N₂O) abuse-induced neurological disorders.

PATIENTS AND METHODS

We retrospectively reviewed 33 patients with N₂O abuse-induced neurological disorders and reported their demographic data, clinical manifestations, laboratory examinations, nerve conduction studies, together with spinal and brain MRI.

RESULTS

The most frequent clinical manifestations included numbness and weakness in the extremities and unspecified gait disturbance. Low serum vitamin B₁₂ levels were found in 9 patients, and high homocysteine levels were noted in 27 patients. Nerve conduction studies showed a sensory-motor neuropathy. Sixteen patients showed bilateral high-intensity T2 signal within the posterior column on spinal MRI, and four patients showed cerebral white matter lesions on brain MRI.

CONCLUSION

N₂O abuse has become a significant public health problem because of the severe neurological disorders related to chronic abuse. Clinical physicians should be aware of the toxic effects of N₂O.

Pro-Con Debate: Nitrous Oxide for Labor Analgesia

This Pro-Con debate will provide the practitioner with an evidence-based knowledge approach to assist the clinician in determining whether to employ (Pro) or not to employ (Con) this technique in the obstetrical suite for labor analgesia. Nitrous oxide has been used safely in dentistry and medicine for many centuries. However, accumulating preclinical and clinical evidence increasingly suggests previously unrecognized adverse maternal and fetal effects of nitrous oxide, which warrants reconsideration of its use in pregnant women and a more detailed informed consent. Nitrous oxide is associated with metabolic, oxidative, genotoxic, and transgenerational epigenetic effects in animals and humans that may warrant limiting its usefulness in labor. This debate will discuss and review the clinical uses, advantages, and disadvantages of nitrous oxide on occupational effects of nitrous oxide exposure, neuroapoptosis, FDA warning on inhalational anesthetics and the developing brain, research limitations, occupational exposure safety limits, effects on global warming, and potential for diversion.