Oxide Anesthesia Research Articles

How do dental practices respond to changes in scope of practice regulations?

Regulations that restrict the tasks that credentialed workers are allowed to perform may affect a firm's input choices, output, and which part of the market the firm serves. Using dental practice survey data from 1989 to 2014 and a stacked difference-in-differences design, this paper examines the effects of state-level scope of practice regulations on the behavior of dental practices. Results suggest that scope of practice deregulation in regards to dental hygienists' ability to administer nitrous oxide or local anesthesia is associated with fewer dentist visits per week in the short-term, lower patient wait times, and an increased likelihood of treating lower revenue generating publicly insured patients. There is weak evidence that scope of practice deregulation alters a practice's labor inputs.

Inhalation anesthesia in the cat: Development of cuff pressure when using nitrous oxide

During inhalation anesthesia with nitrous oxide in oxygen the pressure in the cuff of the endotracheal tube may increase due to diffusion of nitrous oxide into the cuff. The aim of the study was to investigate the development of cuff pressure during nitrous oxide anesthesia under clinical conditions in feline patients and to identify possible influencing factors such as tube size and gas flow rate. The prospective study included cats scheduled for inhalation anesthesia with nitrous oxide for a minimum duration of 60 minutes at the Department for Small Animals of the University of Leipzig. Cuff pressure was adjusted with a cuff manometer and its development was recorded. In total, the cuff pressure values of 24 cats were recorded. Animals were allocated into groups by tube size (ID 4.0 mm and ID 4.5 mm) and by fresh gas flow rate: low flow rate (0.6 l/min) and high flow rate (3 l/min). During anesthesia, cuff pressure increased over time, with statistical significance occurring from 45 minutes onwards in comparison to the initial cuff pressure (p=0.005). After 60 minutes, there was a mean cuff pressure increase of 3 cmH2O. Despite this moderate mean increase, highly variable pressure values up to 48 cmH2O in individual animals were recorded. No cat reached the termination criterion of 60 cmH2O cuff pressure. Effects of tube size (p=0.63) and flow rate (p=0.334) on the cuff pressure were not evident. After a period of 45 minutes of nitrous oxide administration, a significant increase in cuff pressure occurs in the cat. However, tube size and total gas flow rate do not seem to influence the cuff pressure development. When using nitrous oxide during inhalation anesthesia, regular cuff pressure evaluation and correction are necessary and hence recommended in feline patients. As individual pressure changes may be highly variable, no fixed recommendations for optimal management are possible.

Support-vector classification of low-dose nitrous oxide administration with multi-channel EEG power spectra

Support-vector machines (SVMs) can potentially improve patient monitoring during nitrous oxide anaesthesia. By elucidating the effects of low-dose nitrous oxide on the power spectra of multi-channel EEG recordings, we quantified the degree to which these effects generalise across participants. In this single-blind, cross-over study, 32-channel EEG was recorded from 12 healthy participants exposed to 0, 20, 30 and 40% end-tidal nitrous oxide. Features of the delta-, theta-, alpha- and beta-band power were used within a 12-fold, participant-wise cross-validation framework to train and test two SVMs: (1) binary SVM classifying EEG during 0 or 40% exposure (chance = 50%); (2) multi-class SVM classifying EEG during 0, 20, 30 or 40% exposure (chance = 25%). Both the binary (accuracy 92%) and the multi-class (accuracy 52%) SVMs classified EEG recordings at rates significantly better than chance (p < 0.001 and p = 0.01, respectively). To determine the relative importance of frequency band features for classification accuracy, we systematically removed features before re-training and re-testing the SVMs. This showed the relative importance of decreased delta power and the frontal region. SVM classification identified that the most important effects of nitrous oxide were found in the delta band in the frontal electrodes that was consistent between participants. Furthermore, support-vector classification of nitrous oxide dosage is a promising method that might be used to improve patient monitoring during nitrous oxide anaesthesia.

Systematic review of the effectiveness of remifentanil in term breech pregnancies undergoing external cephalic version

BackgroundExternal cephalic version (ECV) is a moderately painful procedure used to turn a fetus from a non-vertex to cephalic position. This systematic review and meta-analysis compared intravenous remifentanil with other analgesia or no analgesia or placebo on the success rate and associated pain of ECV. MethodsSystematic searches for randomised controlled trials using remifentanil during ECV for non-cephalic term singleton pregnancies were conducted in EMBASE, MEDLINE and the Cochrane Library to October 2021. The primary outcomes were successful ECV and maternal pain; secondary outcomes included mode of delivery and adverse effects. The Cochrane Risk of Bias tool was used and meta-analysis undertaken if there were ≥2 comparable studies. ResultsFour trials were identified, three placebo-controlled and one vs no analgesia, totalling 482 participants. Comparisons against nitrous oxide or neuraxial anaesthesia were not analysed. Two studies had a low overall risk of bias, and two had some concern for bias. Remifentanil compared with placebo increased the success of ECV by 43% (risk ratio [RR] 1.43; 95% confidence interval [CI] 1.14 to 1.78). Pain scores (0–10) were lower (mean difference −1.97; 95% CI −2.49 to −1.46) whilst there was no impact on caesarean delivery rate (RR 0.97; 95% CI 0.81 to 1.17). Adverse events were rare, with fetal bradycardia observed less often with remifentanil than placebo. ConclusionsRemifentanil increases the procedural success of ECV and reduces pain compared with placebo. Trials were at low risk of bias and contained a sufficient number of participants to have reasonable confidence in this finding.

Postoperative Pulmonary Complications in the ENIGMA II Trial: A Post Hoc Analysis.

Nitrous oxide promotes absorption atelectasis in poorly ventilated lung segments at high inspired concentrations. The Evaluation of Nitrous oxide In the Gas Mixture for Anesthesia (ENIGMA) trial found a higher incidence of postoperative pulmonary complications and wound sepsis with nitrous oxide anesthesia in major surgery compared to a fraction of inspired oxygen of 0.8 without nitrous oxide. The larger ENIGMA II trial randomized patients to nitrous oxide or air at a fraction of inspired oxygen of 0.3 but found no effect on wound infection or sepsis. However, postoperative pulmonary complications were not measured. In the current study, post hoc data were collected to determine whether atelectasis and pneumonia incidences were higher with nitrous oxide in patients who were recruited to the Australian cohort of ENIGMA II. Digital health records of patients who participated in the trial at 10 Australian hospitals were examined blinded to trial treatment allocation. The primary endpoint was the incidence of atelectasis, defined as lung atelectasis or collapse reported on chest radiology. Pneumonia, as a secondary endpoint, required a diagnostic chest radiology report with fever, leukocytosis, or positive sputum culture. Comparison of the nitrous oxide and nitrous oxide-free groups was done according to intention to treat using chi-square tests. Data from 2,328 randomized patients were included in the final data set. The two treatment groups were similar in surgical type and duration, risk factors, and perioperative management recorded for ENIGMA II. There was a 19.3% lower incidence of atelectasis with nitrous oxide (171 of 1,169 [14.6%] vs. 210 of 1,159 [18.1%]; odds ratio, 0.77; 95% CI, 0.62 to 0.97; P = 0.023). There was no difference in pneumonia incidence (60 of 1,169 [5.1%] vs. 52 of 1159 [4.5%]; odds ratio, 1.15; 95% CI, 0.77 to 1.72; P = 0.467) or combined pulmonary complications (odds ratio, 0.84; 95% CI, 0.69 to 1.03; P = 0.093). In contrast to the earlier ENIGMA trial, nitrous oxide anesthesia in the ENIGMA II trial was associated with a lower incidence of lung atelectasis, but not pneumonia, after major surgery.

Factors to Weigh in While Administering Nitrous Oxide Anesthesia [Letter

Factors to Weigh in While Administering Nitrous Oxide Anesthesia [Letter

Factors to Weigh in While Administering Nitrous Oxide Anesthesia [Response to Letter

Factors to Weigh in While Administering Nitrous Oxide Anesthesia [Response to Letter

Effects of Low-Concentration Nitrous Oxide Anesthesia on Patient Anxiety During Cataract Surgery: A Retrospective Cohort Study.

PurposeWe investigated the effects of 30% low-concentration nitrous oxide (N2O) anesthesia on anxiety, pain, and vital signs and the patient population that would benefit from low-concentration N2O anesthesia during cataract surgery.Patients and MethodsSixty-three patients who underwent cataract surgery due to visual impairment from cataracts were included in this single-center retrospective cohort study conducted at the Ophthalmology Department of Shinseikai Toyama Hospital, Japan. Fifty eyes of 39 patients received a combination of local and N2O anesthesia (N2O group), and 30 eyes of 24 patients received local anesthesia without N2O anesthesia (Air group). The primary outcome measures were visual analogue scale (VAS) scores for patient anxiety, pain, and vital signs. The secondary outcome measures were the patient population.ResultsThe change in the VAS scores for anxiety and pain decreased significantly (p = 0.002 and p = 0.014, respectively) in the N2O group (−15.6 ± 22.9 and 12.4 ± 14.9, respectively) compared with that in the Air group (1.2 ± 20.6 and 24.2 ± 22.4, respectively). The systolic and diastolic blood pressure changes did not significantly differ between both groups (p = 0.093 and p = 0.23, respectively). The change in heart rate decreased significantly (p = 0.001) in the N2O group (−4.8 ± 4.8 bpm) compared with that in the Air group (−0.6 ± 5.8 bpm). Multivariate analyses demonstrated that the change in anxiety level in the N2O group correlated significantly with patient age (p = 0.045) and preoperative VAS score for anxiety (p = 0.0001), whereas the change in anxiety level in the Air group did not correlate with any factor.ConclusionLow-concentration N2O anesthesia showed beneficial effects on intraoperative anxiety and pain during cataract surgery; this may aid the stabilization of intraoperative vital signs. Moreover, low-concentration N2O anesthesia during cataract surgery could benefit young patients and patients with high levels of preoperative anxiety.

Comparison of recovery times by using bispectral index monitoring versus end-tidal agent concentration monitoring in patients undergoing inhalational general anaesthesia.

Background and Aims:End-tidal anaesthetic gas concentration (ETAG) and bispectral index (BIS) are both used to monitor depth of anaesthesia. Maintaining an accurate depth of anaesthesia helps in early post-operative recovery. This study compared the recovery times from sevoflurane–nitrous oxide anaesthesia using ETAG monitoring with BIS monitoring.Methods:Four hundred and two patients undergoing elective surgeries under sevoflurane- nitrous oxide anaesthesia were enroled in this double blinded parallel group prospective randomised trial and allocated into two groups. The depth of anaesthesia was monitored using BIS in BIS group (n = 202) and end-tidal sevoflurane concentration (EtSevo) in ETAG group (n = 200). The time to extubation and recovery were compared between the groups. Parametric, non-parametric and categorical variables were compared using Student’s ‘t’ test, Wilcoxon’s rank sum test and Chi-square test, respectively.Results:Time to extubation (min) [BIS group – 10, 5; ETAG group – 10, 5 (median, inter-quartile range, IQR), P = 0.32] and time to recovery (min) [BIS group – 14, 6; ETAG group – 13.5, 7 (median, IQR), P = 0.34] did not differ significantly between the two groups. The EtSevo concentration (vol%) was significantly higher in the BIS group at 5 min [BIS group – 1.2, 0.4; ETAG group – 1.0, 0.4 (median, IQR), P < 0.001], 30 min [BIS group – 1.1, 0.4; ETAG group – 1.0, 0.3 (median, IQR), P = 0.002] and 120 min [BIS group – 1.11 ± 0.28; ETAG group – 0.96 ± 0.27 (mean ± standard deviation), P = 0.014] after induction of anaesthesia.Conclusions:BIS and ETAG monitoring are associated with comparable recovery profiles. ETAG monitoring is associated with significantly less sevoflurane consumption.

Maternal-Newborn Health System Changes and Outcomes in Ontario, Canada, During Wave 1 of the COVID-19 Pandemic—A Retrospective Study

ObjectiveTo determine the population-level impact of COVID-19 pandemic–related obstetric practice changes on maternal and newborn outcomes. MethodsSegmented regression analysis examined changes that occurred 240 weeks pre-pandemic through the first 32 weeks of the pandemic using data from Ontario’s Better Outcomes Registry & Network. Outcomes included birth location, length of stay, labour analgesia, mode of delivery, preterm birth, and stillbirth. Immediate and gradual effects were modelled with terms representing changes in intercepts and slopes, corresponding to the start of the pandemic. ResultsThere were 799 893 eligible pregnant individuals included in the analysis; 705 767 delivered in the pre-pandemic period and 94 126 during the pandemic wave 1 period. Significant immediate decreases were observed for hospital births (relative risk [RR] 0.99; 95% CI 0.98–0.99), length of stay (median change –3.29 h; 95% CI –3.81 to –2.77), use of nitrous oxide (RR 0.11; 95% CI 0.09–0.13) and general anesthesia (RR 0.69; 95% CI 0.58– 0.81), and trial of labour after cesarean (RR 0.89; 95% CI 0.83–0.96). Conversely, there were significant immediate increases in home births (RR 1.35; 95% CI 1.21–1.51), and use of epidural (RR 1.02; 95% CI 1.01–1.04) and regional anesthesia (RR 1.01; 95% CI 1.01–1.02). There were no significant immediate changes for any other outcomes, including preterm birth (RR 0.99; 95% CI 0.93–1.05) and stillbirth (RR 1.11; 95% CI 0.87–1.42). ConclusionProvincial health system changes implemented at the start of the pandemic resulted in immediate clinical practice changes but not insignificant increases in adverse outcomes.

Развитие анестезиологии в Украине: путь от искусства к науке

Историю хирургии можно разделить на два основных этапа: до 1846 года и после него. В этой работе авторы представили в хронологическом порядке основные этапы развития анестезиологии в Украине, сосредоточив внимание на врачах, которые впервые проводили хирургические вмешательства под общим и местным обезболиванием. В 1846 году по инициативе В.А. Караваева и А.П. Вальтера, учеников Н.И. Пирогова, при Киевском университете была организована комиссия по изучению влияния эфира на организм. Исследовав в эксперименте влияние эфира на животный организм, В.А. Караваев 18 февраля 1847 года сделал первую в Киеве операцию под эфирным наркозом. Вторую в Украине операцию под эфирным наркозом выполнил Т.Л. Ванцетти в Харькове 28 февраля 1847 года. А уже к концу 1847 года хлороформный наркоз в Киеве применил В.А. Караваев. В 1871 году в Харькове В.Ф. Грубе выполнил первую операцию под наркозом закисью азота. В 80–90-е годы XIX века в хирургическую практику широко внедряются методы местной и проводниковой анестезии кокаином. Украинские хирурги были пионерами местной анестезии. В 1886 году киевский хирург А.И. Лукашевич провел на себе и на других здоровых людях опыты по применению проводниковой анестезии. Выпускник медицинского факультета Киевского университета Св. Владимира В.Ф. Войно-Ясенецкий в Санкт-Петербурге в 1915 году издает монографию «Регионарная анестезия», иллюстрированную автором. В послереволюционный период обезболиванию уделяют все больше внимания, количество хирургов, проводящих операции с обезболиванием, растет в геометрической прогрессии. Возникает потребность в постоянном надзоре за состоянием пациента и в медперсонале, который будет его проводить. Это и было началом формирования анестезиологии как науки и отдельной специальности.

A retrospective cohort study on red blood cell morphology changes in pre-school age children under nitrous oxide anesthesia

BackgroundMegaloblastic anemia or bone marrow changes could occur after prolonged nitrous oxide inhalation via vitamin B12 inactivation related DNA synthesis impairment. Previous researches have studied hematological changes with nitrous oxide exposure, but only in adults or adolescents. Pre-school age children with active hematopoietic red bone marrow are more vulnerable to potential side effects of nitrous oxide and might experience growth impairment. The purpose of our study was to analyze red blood cell morphology changes under nitrous oxide anesthesia in pre-school age children.MethodsOne hundred thirty-six children under 5 years old scheduled for hemivertebra resection were analyzed. According to fresh gas type in anesthesia records, 71 children who received nitrous oxide in oxygen during anesthesia maintenance were categorized into the nitrous oxide group and the other 65 who received air in oxygen were the air group. Complete blood counts in perioperative period were assessed for anemia, macrocytosis, microcytosis, anisocytosis, hyperchromatosis and hypochromatosis. The peak value and change percentage were calculated for mean corpuscular volume and red cell distribution width.ResultsForty-two children in the air group (64.6%) and 30 in the nitrous oxide group (42.3%) developed anemia (P = 0.009). None developed macrocytosis in both groups. Postoperative mean corpuscular volume peaked (mean [95% confidence interval]) at 83.7(82.9–84.4) fL, and 83.2(82.4–83.9) fL and postoperative red cell distribution width at 13.8% (13.4–14.2%), and 13.9% (13.6–14.2%) for the air group and the nitrous oxide group. Both the relative change of mean corpuscular volume (P = 0.810) and red cell distribution width (P = 0.456) were similar between the two groups.ConclusionsNo megaloblastic red blood cell changes were observed with nitrous oxide exposure for 4 h in pre-school age children undergoing hemivertebra resection.

Safety of Nitrous Oxide Anesthesia in a Selected Group of Patients Undergoing Neurosurgery: An Exploratory Subgroup Analysis of the ENIGMA Trials.

The Evaluation of Nitrous Oxide in the Gas Mixture for Anesthesia (ENIGMA)-I and ENIGMA-II were randomized clinical trials that assessed the safety of nitrous oxide anesthesia in patients undergoing noncardiac surgery. In this study, we performed an exploratory pooled analysis of both ENIGMA trials to assess the safety of nitrous oxide in a selected group of patients undergoing neurosurgery. Data from each ENIGMA trial were collated into a single database. Information regarding patient demographics, comorbidities, medication use, anesthesia, surgical procedure, and postoperative complications was extracted. Multivariate logistic regression was conducted for postoperative complications to assess the risk associated with nitrous oxide. A total of 830 patients were included in our analysis: 417 received nitrous oxide anesthesia, and 413 received nitrous oxide-free anesthesia. Baseline patient and perioperative characteristics were comparable. Procedural data were available for 535 patients (64%); of these, 507 (95%) underwent spinal neurosurgery and 28 (5%) underwent cranial neurosurgery. Patients in the nitrous oxide group had lower inspired oxygen concentration (30% vs. 38%; P<0.001) and end-tidal volatile agent concentration (0.56 vs. 0.89 minimal alveolar concentration equivalents; P<0.001) compared with the nitrous oxide-free group. Use of nitrous oxide was not associated with increased risk of postoperative complications (myocardial infarction, cardiac arrest, stroke, infection, severe vomiting, fever, pneumonia, pneumothorax, blood transfusion, venous thromboembolism, or death) (odds ratio: 1.22; 95% confidence interval: 0.89-1.65; P=0.22) or prolonged length of hospital stay (median 5.0 vs. 4.2 d for nitrous oxide and nitrous oxide-free groups; P=0.28). Nitrous oxide did not increase the risk of postoperative complications or prolonged length of hospital stay in the neurosurgical cohort enrolled in the ENIGMA-I and ENIGMA-II trials.

This Month ... That Year! Snippets from the History of Anesthesia

Article| April 2021 This Month ... That Year! Snippets from the History of Anesthesia Lalitha Sundararaman, MBBS, MD Lalitha Sundararaman, MBBS, MD Search for other works by this author on: This Site PubMed Google Scholar ASA Monitor April 2021, Vol. 85, e1–e2. https://doi.org/10.1097/01.ASM.0000742752.25272.02 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Search Site Citation Lalitha Sundararaman; This Month ... That Year! Snippets from the History of Anesthesia. ASA Monitor 2021; 85:e1–e2 doi: https://doi.org/10.1097/01.ASM.0000742752.25272.02 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentAll PublicationsASA Monitor Search Advanced Search Topics: cooley's anemia, dentists, ether, ethyl, ethers, homicide, nitrous oxide, oxygen, snow - weather, chloroform, dentistry April saw many seminal events cardinal to the growth of anesthesia. Dentists, epidemiologists, and military physicians all made their mark in history through their contributions to anesthesiology. Through the ages, the month of April saw anesthesiology shaping into a more definite science with momentous papers such as Arthur Guedel's famous classification of the stages of ether anesthesia. But at the other end of the spectrum, April also saw the downright acrimonious arguments against the use of oxygen with nitrous oxide anesthesia in the fear that it would “dilute it.” This seems farcical now but was much believed in the 1890s. April 7, 1847: The first obstetric anesthetic is administered Nathan Cooley Keep: Dentist, anesthesiologist and forensic scientist. This man did it all! Nathan Cooley Keep administered the first obstetric anesthetic in the United States in Cambridge, Massachusetts. Keep was... © 2021 American Society of Anesthesiologists (ASA), All Rights Reserved.2021 You do not currently have access to this content.

Comparison of Intracuff Pressure and Postoperative Sore Throat Following Use of Laryngeal Mask Airway Protector With or Without Nitrous Oxide Anesthesia

PurposeIn general anesthesia, the laryngeal mask airway (LMA) is a frequently used effective option. The effect of nitrous oxide on intracuff pressure of the LMA and postoperative sore throat is well known; however, there are no studies related to the second-generation LMA Protector. The purpose of this study was to determine the differences in intracuff pressure and postoperative sore throat, depending on the use of nitrous oxide during general anesthesia using the LMA Protector. DesignThis randomized double-blind prospective study was conducted among 88 patients aged 20 to 70 years. MethodsThe cuff pressure started with a baseline of 40 cm H2O and was measured using a digital cuff pressure manometer for 30 minutes. Postoperative sore throat, dysphonia, dysphagia, and numeric rating scale scores were also recorded. FindingsOver time, the intracuff pressure of the nitrous oxide group increased significantly compared with that of the air group. Furthermore, postoperative sore throat and pharyngolaryngeal complications were not significantly different between the two groups. ConclusionsIntracuff pressure of the LMA Protector increased during anesthesia using nitrous oxide. When the anesthesia time was less than 2 hours, however, there was no difference in postoperative sore throat.

Utility and safety of low-concentration nitrous oxide anesthesia in ptosis surgery.

To evaluate the utility of low-concentration nitrous oxide (N2O) anesthesia in ptosis surgeryThis study was a retrospective consecutive case series that included 54 successive patients with blepharoptosis who underwent bilateral levator aponeurosis advancement and on whom skin resection performed by the same surgeon between August 2016 and July 2017. Among these patients, 27 were operated with a local anesthesia injection (air group) and 27 with a local anesthesia injection and low-concentration N2O anesthesia (N2O group). All N2O cases used a total of 6 L of gas comprising 70% oxygen and 30% N2O. Preoperative and postoperative blood pressure (BP) and heart rate (HR) and intraoperative pain, anxiety, nausea, and memory were measured immediately after surgery using visual analog scale score (VASS). Additionally, perioperative side effects were examined.There was no significant difference in age, sex, and preoperative and postoperative margin reflex distance (MRD) between the 2 groups (all P > .05). The intraoperative mean peripheral oxygen saturation was significantly higher (97.5% ± 1.6% vs 99.5% ± .6%, P < .001), intraoperative HR was significantly lower (78.2 ± 12.8 vs 70.7 ± 11.6 bpm, P = .02), and operation time was significantly shorter (33.1 ± 8.1 vs 29.4 ± 10.3 minutes, P = .03) in the N2O group than in the air group.Difference between intraoperative and preoperative systolic BP (BPs) (+15.8 ± 18.0 vs + 3.1 ± 21.7 mm Hg, P = .02), diastolic BP (BPd) (+7.0 ± 17.4 vs −2.3 ± 13.6 mm Hg, P = .04), and HR (3.2 ± 8.5 vs −3.9 ± 9.4 bpm, P = .01) was significantly lower in the N2O group than in the air group.VASS of intraoperative pain was significantly lower in the N2O group than in the air group (49.5 ± 24.7 vs 22.6 ± 14.9, P < .001), whereas intraoperative anxiety and memory did not present significant differences between the groups (P = .09 and P = .45, respectively). Intraoperative nausea score was 0 for all cases in both groups. There was no other side effect.Ptosis surgery with anesthesia using 30% N2O may effectively suppress intraoperative BP and HR along with pain and shorten the operation time without side effects such as nausea.

W Harry Archer's collection of Horace Wells letters are still available. A commentary on a new publication

The definitive account of the life and work of Horace Wells, the dentist from Hartford, Connecticut, who experimented with nitrous oxide anesthesia in 1844, is that published by W Harry Archer for the centenary of Wells's work. A major source of original material was a collection of letters, by Wells and others, that Archer found in the house in Hartford, Vermont, in which Wells was born. In later support for Wells being better recognized for his role in the introduction of general anaesthesia, Richard J Wolfe and Leonard F Menczer published a collection of essays in 1994. However, their preparation was hampered by their (mis)understanding that the ‘Archer’ letters (which were lodged in the Pittsburgh University Library) were “missing”, a belief which continued, but has been disproved by a new author. Before his death, John Bunker encouraged his anthropologist daughter, Emily, to continue a project he had been planning on the history of anesthesia, and the result is a new book, “Horace and Elizabeth: Love and Death and Painless Dentistry”. First and foremost Ms Bunker has discovered that the Archer Letters are very much available, and has been greatly helped by the University of Pittsburgh Library in producing her book. She has used reproductions and transcriptions of the letters (some previously unpublished) and other contemporary documents to illustrate Wells's role in the great discovery. Some of the material, especially from before the ‘Colton’ demonstration of 1844 is remarkable; it is almost like hearing the story from Wells himself.

Closed reduction of paediatric forearm fractures: nitrous oxide versus general anaesthetic.

Nitrous oxide with intranasal fentanyl is safe and effective in performing closed reduction of paediatric forearm fractures; however, the difference in outcome when compared to those performed under general anaesthesia (GA) is unclear. We aim to compare the outcomes of closed reduction of paediatric forearm fractures under nitrous oxide versus GA. This retrospective study based on a prospective change in protocol reviewed the medical records and radiographs of patients with forearm fractures who presented to a tertiary paediatric centre, and who subsequently underwent closed reduction under either nitrous or GA. Data on patient demographics, type and site of fracture and the method of casting were collected. The primary outcomes were loss of reduction, the need for repeat intervention and the rate of complications. There were 301 and 362 patients in the nitrous and GA groups respectively. The overall re-intervention rate was 7.6% in the nitrous group versus 5.0% in the GA group (P = 0.155). There was no significant difference in loss of reduction which involved 9.0% in the nitrous group and 11.3% in the GA group (P = 0.320). There was no significance difference in overall complications. Nausea and vomiting comprised the majority of adverse events. Closed reduction of paediatric forearm fractures performed under nitrous oxide with intranasal fentanyl is safe, effective and achieves comparable re-intervention rates and adverse events to those performed under GA in the operating theatre.

Source-level Cortical Power Changes for Xenon and Nitrous Oxide-induced Reductions in Consciousness in Healthy Male Volunteers.

Investigations of the electrophysiology of gaseous anesthetics xenon and nitrous oxide are limited revealing inconsistent frequency-dependent alterations in spectral power and functional connectivity. Here, the authors describe the effects of sedative, equivalent, stepwise levels of xenon and nitrous oxide administration on oscillatory source power using a crossover design to investigate shared and disparate mechanisms of gaseous xenon and nitrous oxide anesthesia. Twenty-one healthy males underwent simultaneous magnetoencephalography and electroencephalography recordings. In separate sessions, sedative, equivalent subanesthetic doses of gaseous anesthetic agents nitrous oxide and xenon (0.25, 0.50, and 0.75 equivalent minimum alveolar concentration-awake [MACawake]) and 1.30 MACawake xenon (for loss of responsiveness) were administered. Source power in various frequency bands were computed and statistically assessed relative to a conscious/pre-gas baseline. Observed changes in spectral-band power (P < 0.005) were found to depend not only on the gas delivered, but also on the recording modality. While xenon was found to increase low-frequency band power only at loss of responsiveness in both source-reconstructed magnetoencephalographic (delta, 208.3%, 95% CI [135.7, 281.0%]; theta, 107.4%, 95% CI [63.5, 151.4%]) and electroencephalographic recordings (delta, 260.3%, 95% CI [225.7, 294.9%]; theta, 116.3%, 95% CI [72.6, 160.0%]), nitrous oxide only produced significant magnetoencephalographic high-frequency band increases (low gamma, 46.3%, 95% CI [34.6, 57.9%]; high gamma, 45.7%, 95% CI [34.5, 56.8%]). Nitrous oxide-not xenon-produced consistent topologic (frontal) magnetoencephalographic reductions in alpha power at 0.75 MACawake doses (44.4%; 95% CI [-50.1, -38.6%]), whereas electroencephalographically nitrous oxide produced maximal reductions in alpha power at submaximal levels (0.50 MACawake, -44.0%; 95% CI [-48.1,-40.0%]). Electromagnetic source-level imaging revealed widespread power changes in xenon and nitrous oxide anesthesia, but failed to reveal clear universal features of action for these two gaseous anesthetics. Magnetoencephalographic and electroencephalographic power changes showed notable differences which will need to be taken into account to ensure the accurate monitoring of brain state during anaesthesia.

Hypoxia-Ischemia and Hypothermia Independently and Interactively Affect Neuronal Pathology in Neonatal Piglets with Short-Term Recovery

Therapeutic hypothermia is the standard of clinical care for moderate neonatal hypoxic-ischemic encephalopathy. We investigated the independent and interactive effects of hypoxia-ischemia (HI) and temperature on neuronal survival and injury in basal ganglia and cerebral cortex in neonatal piglets. Male piglets were randomized to receive HI injury or sham procedure followed by 29 h of normothermia, sustained hypothermia induced at 2 h, or hypothermia with rewarming during fentanyl-nitrous oxide anesthesia. Viable and injured neurons and apoptotic profiles were counted in the anterior putamen, posterior putamen, and motor cortex at 29 h after HI injury or sham procedure. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) identified genomic DNA fragmentation to confirm cell death. Though hypothermia after HI preserved viable neurons in the anterior and posterior putamen, hypothermia prevented neuronal injury in only the anterior putamen. Hypothermia initiated 2 h after injury did not protect against apoptotic cell death in either the putamen or motor cortex, and rewarming from hypothermia was associated with increased apoptosis in the motor cortex. In non-HI shams, sustained hypothermia during anesthesia was associated with neuronal injury and corresponding viable neuron loss in the anterior putamen and motor cortex. TUNEL confirmed increased neurodegeneration in the putamen of hypothermic shams. Anesthetized, normothermic shams did not show abnormal neuronal cytopathology in the putamen or motor cortex, thereby demonstrating minimal contribution of the anesthetic regimen to neuronal injury during normothermia. We conclude that the efficacy of hypothermic protection after HI is region specific and that hypothermia during anesthesia in the absence of HI may be associated with neuronal injury in the developing brain. Studies examining the potential interactions between hypothermia and anesthesia, as well as with longer durations of hypothermia, are needed.