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

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.

Updated meta-analysis on intraoperative inspired fraction of oxygen and the risk of surgical site infection in adults undergoing general and regional anesthesia

This updated meta-analysis aims at exploring whether the use of systematic high vs low intraoperative oxygen fraction (FiO2) may decrease the incidence of postoperative surgical site infection during general (GA) or regional anesthesia (RA). PubMed, Cochrane CENTRAL, ClinicalTrials.gov databases were searched from January 1st, 1999 and July, 1st 2022, for randomized and quasi-randomized controlled trials that included patients in a high and low FiO2 groups and reported the incidence of SSI. The meta-analysis was conducted with a DerSimonian and Laird random-effects model. Thirty studies (24 for GA and 6 for RA) totaling 18,055 patients (15,871 for GA and 2184 for RA) were included. We have low-to-moderate-quality evidence that high FiO2 (mainly 80%) was not associated with a reduction of SSI incidence compared to low FiO2 (mainly 30%) in all patients (RR 0.90, 95%CI 0.79-1.03). Moderate inconsistency existed between studies (I2 = 38%). Subgroup analyses showed a moderate protective effect in patients undergoing GA (RR 0.86, 95%CI 0.75-0.99) (low level of evidence), while high FiO2 was not associated with a reduction of SSI in patients undergoing RA (RR 1.17, 95%CI 0.90-1.52) (moderate level of evidence). Sensitivity analyses restricted to patients ventilated without nitrous oxide (n = 20 studies), to patients operated from abdominal surgeries (n = 21 studies), and to patients suffering from deep SSI (n = 13 studies), all showed the absence of any significant effect of high FiO2. As a conclusion there is no compelling evidence that high FiO2 can improve postoperative patient's outcome on its own when good SSI prevention practices are properly applied. Recent well-designed and adequately powered randomized controlled trials add further weight to these results.

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.

Effects of high versus low inspiratory oxygen fraction on postoperative clinical outcomes in patients undergoing surgery under general anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To determine whether high perioperative inspired oxygen fraction (FiO₂) compared with low FiO₂ has more deleterious postoperative clinical outcomes in patients undergoing non-thoracic surgery under general anesthesia.

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

High perioperative FiO₂ (≥0.8) vs. low FiO₂ (≤0.5).

MEASUREMENTS

The primary outcome was mortality within 30 days. Secondary outcomes were pulmonary outcomes (atelectasis, pneumonia, respiratory failure, postoperative pulmonary complications [PPCs], and postoperative oxygen parameters), intensive care unit (ICU) admissions, and length of hospital stay. A subgroup analysis was performed to explore the treatment effect by body mass index (BMI).

MAIN RESULTS

Twenty-six trials with a total 4991 patients were studied. The mortality in the high FiO₂ group did not differ from that in the low FiO₂ group (risk ratio [RR] 0.91, 95% confidence interval [CI] 0.42-1.97, P = 0.810). Nor were there any significant differences between the groups in such outcomes as pneumonia (RR 1.19, 95% CI 0.74-1.92, P = 0.470), respiratory failure (RR 1.29, 95% CI 0.82-2.04, P = 0.270), PPCs (RR 1.05, 95% CI 0.69-1.59, P = 0.830), ICU admission (RR 0.94, 95% CI 0.55-1.60, P = 0.810), and length of hospital stay (mean difference [MD] 0.27 d, 95% CI -0.28-0.81, P = 0.340). The high FiO₂ was associated with postoperative atelectasis more often (risk ratio 1.27, 95% CI 1.00-1.62, P = 0.050), and lower postoperative arterial partial oxygen pressure (MD -5.03 mmHg, 95% CI -7.90- -2.16, P < 0.001)_. In subgroup analysis of BMI >30 kg/m², these parameters were similarly affected between the groups.

CONCLUSIONS

The use of high FiO₂ compared to low FiO₂ did not affect the short-term mortality, although it may increase the incidence of atelectasis in adult, non-thoracic patients undergoing surgical procedures. Nor were there any significant differences in other secondary outcomes.

Effect of dexmedetomidine on delirium during sedation in adult patients in intensive care units: A systematic review and meta-analysis

STUDY OBJECTIVE

To compare the effect of sedation protocols with and without dexmedetomidine on delirium risk and duration in adult patients in intensive care units (ICUs).

DESIGN

A meta-analysis of randomized controlled trials.

REVIEW METHODS

We searched the Cochrane Central Register of Controlled Trials, PubMed, EMBASE, and ISI Web of Science from inception to September 3, 2020. We included studies comparing the effect of dexmedetomidine-based sedation on delirium risk with non-dexmedetomidine-based sedation in adult patients in ICUs. We pooled the data using a random-effects model using Review Manager 5.2, and assessed publication bias using Stata 11.0. The quality of evidence was rated using the Grading of Recommendations, Assessment, Development and Evaluation system.

MAIN RESULTS

We included 36 studies involving 9623 participants. The use of dexmedetomidine was associated with reduced risk of delirium (risk ratio [RR], 0.63; 95% confidence interval [CI], 0.54-0.75; very low-quality evidence), but higher incidences of hypotension and bradycardia during hospital stay. Dexmedetomidine was also associated with shorter durations of ICU stay, hospital stay and mechanical ventilation. Dexmedetomidine did not affect ICU mortality (RR, 1.01; 95% CI, 0.89-1.14; low-quality evidence), hospital mortality (RR, 1.01; 95% CI, 0.91-1.12; very low-quality evidence), or 30-day mortality (RR, 0.77; 95% CI, 0.58-1.01; moderate-quality evidence), or duration of delirium (mean difference, -0.74 days; 95% CI, -1.83 to 0.36 days; very low-quality evidence). We identified publication bias for risk and duration of delirium, length of ICU stay, and hospital stay.

CONCLUSIONS

Low- or very low-quality evidence suggests that dexmedetomidine was associated with a clinically-small reduction of delirium risk, ICU/hospital stay and mechanical ventilation duration, but were not associated with improved mortality or shorter delirium duration in ICU patients. These findings were inconclusive because of publication bias, heterogeneity, and limited sample size. Significant adverse effects of dexmedetomidine include hypotension and bradycardia. PROSPERO registration number: CRD42018095358.

Effects of dexmedetomidine on delirium and mortality during sedation in ICU patients: a systematic review and meta-analysis protocol

INTRODUCTION

Delirium is very common in patients admitted to intensive care unit (ICU), and may worsen survival in these patients. Several meta-analyses have evaluated the antidelirium effects of dexmedetomidine in ICU patients, but their findings were inconsistent. Recently, several large multicentre randomised clinical trials (RCTs) were published, but they have not yet to be included in any meta-analysis. We will conduct a meta-analysis adding these data to evaluate the effects of dexmedetomidine on delirium and mortality in ICU patients, aiming to terminate controversy and provide robust evidence for guiding clinical practice.

METHODS AND ANALYSIS

The Cochrane Central Register of Controlled Trials, PubMed, Embase, ISI Web of Science will be searched from inception to 31 December 2018 for relevant RCTs. Two reviewers will independently screen the identified citations. After quality appraisal and data extraction of included studies, we will conduct meta-analyses for outcomes of interest, including delirium, mortality, length of ICU/hospital stay, time to extubation, ICU costs and adverse effects. The statistical heterogeneity among studies will be assessed by the χ² test and quantified by the I² statistics. We will undertake subgroup analyses to explore heterogeneity and sensitivity analyses to evaluate whether the results are robust. Potential publication bias will be assessed by funnel plot and Egger's test. At last, the quality of evidence of the main outcomes will be rated using the Grading of Recommendations Assessment, Development and Evaluation system.

ETHICS AND DISSEMINATION

The present study is a meta-analysis based on published studies, thus ethical approval is not needed. Our review will elucidate whether dexmedetomidine could decrease the incidence of delirium and improve survival in ICU patients. Our findings may help clinicians to choose optimal sedative agents for ICU patients. The results of this meta-analysis will be submitted to a peer reviewed journal for publication.

PROSPERO REGISTRATION NUMBER

CRD42018095358.

Plasma corticosterone, epinephrine, and norepinephrine levels increase during administration of nitrous oxide in rats

Nitrous oxide (N2O) is a gaseous drug with abuse potential. Despite its common clinical use, little is known about whether N2O administration activates the HPA axis and/or the sympathetic adrenomedullary system. The goal of this study was to determine whether 60% N2O alters plasma concentrations of corticosterone (CORT), epinephrine (EPI), and norepinephrine (NE) in male Long-Evans rats. A gas-tight swivel assembly in the lid of a gas administration chamber allowed the remote collection of blood samples from an indwelling jugular vein catheter at four time-points: baseline and at 30, 60, and 120 min during a two-hour administration of 60% N2O. Relative to baseline, plasma CORT (n = 9) was significantly elevated at all three time-points during N2O inhalation (mixed model analysis, p = .001) and plasma EPI and NE levels were each significantly elevated (n = 8, p ≤ .001) at the 30 min assessment. EPI then declined and did not differ from baseline at the 60 and 120 min assessments (p > .05) whereas NE remained elevated (120 min, p = .001). Administration of 60% N2O increases circulating CORT, EPI, and NE, supporting N2O as a physiological stressor. An N2O-induced increase in CORT is consistent with the observation that addictive drugs typically activate the HPA axis causing increased plasma levels of glucocorticoids. Allostatic models of drug addiction typically involve stress systems and the possible role of stress hormones in N2O-induced allostatic dysregulation is discussed.

The role of nitrous oxide in stroke

Stroke that is caused by poor blood flow into the brain results in cell death, including ischemia stroke due to lack of blood into brain tissue, and hemorrhage due to bleeding. Both of them will give rise to the dysfunction of brain. In general, the signs and symptoms of stroke are the inability of feeling or moving on one side of body, sometimes loss of vision to one side. Above symptoms will appear soon after the stroke has happened. If the symptoms and signs happen in 1 or 2 hours, we often call them as transient ischemic attack. Moreover, hemorrhagic stroke often leads to severe headache. It is known that neuronal death can happen after stroke, and it depends upon the activation of N-methyl-D-aspartate (NMDA) excitatory glutamate receptor which is the goal for a lot of neuroprotective agents. Nitrous oxide was discovered by Joseph Priestley in 1772, and then he and his friends, including the poet Coleridge and Robert Sauce, experimented with the gas. They found this gas could make patients loss the sense of pain and still maintain consciousness after inhalation. Shortly the gas was used as an anesthetic, especially in the field of dentists. Now, accroding to theme of Helene N. David and other scientists, both of nitrous oxide at 75 vol% and xenon at 50 vol% could reduce ischemic neuronal death in the cortex by 70% and decrease NMDA-induced Ca²⁺ influx by 30%. Therefore, more clinical and experimental studies are important to illuminate the mechanisms of how nitrous oxide protects brain tissue and to explore the best protocol of this gas in stroke treatment.

Effects of remifentanil versus nitrous oxide on postoperative nausea, vomiting, and pain in patients receiving thyroidectomy: Propensity score matching analysis

Remifentanil and nitrous oxide (N2O) are 2 commonly used anesthetic agents. Both these agents are known risk factors for postoperative nausea and vomiting (PONV). However, remifentanil and N2O have not been directly compared in a published study. Remifentanil can induce acute tolerance or hyperalgesia, thus affecting postoperative pain. The objective of this retrospective study is to compare the effects of remifentanil and N2O on PONV and pain in patients receiving intravenous patient-controlled analgesia (IV-PCA) after thyroidectomy.We analyzed the electronic medical records of 992 patients receiving fentanyl-based IV-PCA after thyroidectomy at Chung-Ang University Hospital from January 1, 2010 to April 30, 2016. We categorized the patients according to anesthetic agents used: group N2O (n = 745) and group remifentanil (n = 247). The propensity score matching method was used to match patients in the 2 groups based on their covariates. Finally, 128 matched subjects were selected from each group.There were no differences between groups for all covariates after propensity score matching. The numeric rating scale for nausea (0.55 ± 0.88 vs 0.27 ± 0.76, P = 0.01) was higher and complete response (88 [68.8%] vs 106 [82.8%], P = 0.001) was lower in group N2O compared with group remifentanil on postoperative day 0. However, the visual analog scale score for pain (3.47 ± 2.02 vs 3.97 ± 1.48, P = 0.025) was higher in group remifentanil than group N2O on postoperative day 0.In patients receiving IV-PCA after thyroidectomy, postoperative nausea was lower but postoperative pain was higher in group remifentanil.

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.