For beginners in anaesthesia, self-training with an audiovisual checklist improves safety during anaesthesia induction: A randomised, controlled two-centre study.

BACKGROUND: Beginners in residency programmes in anaesthesia are challenged because working environment is complex, and they cannot rely on experience to meet challenges. During this early stage, residents need rules and structures to guide their actions and ensure patient safety. OBJECTIVE: We investigated whether self-training with an electronic audiovisual checklist app on a mobile phone would produce a long-term improvement in the safety-relevant actions during induction of general anaesthesia. DESIGN, SETTING AND PARTICIPANTS: During the first month of their anaesthesia residency, we randomised 26 residents to the intervention and control groups. The study was performed between August 2013 and December 2014 in two university hospitals in Germany. INTERVENTION: In addition to normal training, the residents of the intervention group trained themselves on well tolerated induction using the electronic checklist for at least 60 consecutive general anaesthesia inductions. MAIN OUTCOME MEASURES: After an initial learning phase, all residents were observed during one induction of general anaesthesia. The primary outcome was the number of safety items completed during this anaesthesia induction. Secondary outcomes were similar observations 4 and 8 weeks later. RESULTS: Immediately, and 4 weeks after the first learning phase, residents in the intervention group completed a significantly greater number of safety checks than residents in the control group 2.8 [95% confidence interval (CI) 0.4 to 5.1, P = 0.021, Cohen's d = 0.47] and 3.7 (95% CI 1.3 to 6.1, P = 0.003, Cohen's d = 0.61), respectively. The difference between the groups had disappeared by 8 weeks: mean difference in the number of safety checks at 8 weeks was 0.4, 95% CI -2.0 to 2.8, P = 0.736, Cohen's d = 0.07). CONCLUSION: The use of an audiovisual self-training checklists improves safety-relevant behaviour in the early stages of a residency training programme in anaesthesia.

Inhaled carbon monoxide protects time-dependently from loss of hypoxic pulmonary vasoconstriction in endotoxemic mice.

BACKGROUND: Inhaled carbon monoxide (CO) appears to have beneficial effects on endotoxemia-induced impairment of hypoxic pulmonary vasoconstriction (HPV). This study aims to specify correct timing of CO application, it's biochemical mechanisms and effects on inflammatory reactions. METHODS: Mice (C57BL/6; n = 86) received lipopolysaccharide (LPS, 30 mg/kg) intraperitoneally and subsequently breathed 50 ppm CO continuously during defined intervals of 3, 6, 12 or 18 h. Two control groups received saline intraperitoneally and additionally either air or CO, and one control group received LPS but breathed air only. In an isolated lung perfusion model vasoconstrictor response to hypoxia (FiO2 = 0.01) was quantified by measurements of pulmonary artery pressure. Pulmonary capillary pressure was estimated by double occlusion technique. Further, inflammatory plasma cytokines and lung tissue mRNA of nitric-oxide-synthase-2 (NOS-2) and heme oxygenase-1 (HO-1) were measured. RESULTS: HPV was impaired after LPS-challenge (p < 0.01). CO exposure restored HPV-responsiveness if administered continuously for full 18 h, for the first 6 h and if given in the interval between the 3(rd) and 6(th) hour after LPS-challenge (p < 0.05). Preserved HPV was attributable to recovered arterial resistance and associated with significant reduction in NOS-2 mRNA when compared to controls (p < 0.05). We found no effects on inflammatory plasma cytokines. CONCLUSION: Low-dose CO prevented LPS-induced impairment of HPV in a time-dependent manner, associated with a decreased NOS-2 expression.

Quality indicators in intensive care medicine for Germany - fourth edition 2022.

The measurement of quality indicators supports quality improvement initiatives. The German Interdisciplinary Society of Intensive Care Medicine (DIVI) has published quality indicators for intensive care medicine for the fourth time now. After a scheduled evaluation after three years, changes in several indicators were made. Other indicators were not changed or only minimally. The focus remained strongly on relevant treatment processes like management of analgesia and sedation, mechanical ventilation and weaning, and infections in the ICU. Another focus was communication inside the ICU. The number of 10 indicators remained the same. The development method was more structured and transparency was increased by adding new features like evidence levels or author contribution and potential conflicts of interest. These quality indicators should be used in the peer review in intensive care, a method endorsed by the DIVI. Other forms of measurement and evaluation are also reasonable, for example in quality management. This fourth edition of the quality indicators will be updated in the future to reflect the recently published recommendations on the structure of intensive care units by the DIVI.

Impact of COVID-19 on Continuing Medical Education-Results of an Online Survey Among Users of a Non-profit Multi-Specialty Live Online Education Platform.

Background: The Coronavirus Disease-2019 (COVID-19) pandemic accelerated digitalization in medical education. Continuing medical education (CME) as a substantial component of this system was relevantly affected. Here, we present the results of an online survey highlighting the impact on and the role of online CME. Methods: An online survey of 44 questions was completed by users of a German online CME platform receiving an invitation via newsletter. CME habits, requirements, personal perception, and impact of the pandemic were inquired. Standard statistical methods were applied. Results: A total of 2,961 responders took the survey with 2,949 completed surveys included in the final analysis. Most contributions originated from Germany, Austria, and Switzerland. Physicians accounted for 78.3% (57.5% hospital doctors) of responses followed by midwives (7.3%) and paramedics (5.7%). Participating physicians were mainly board-certified specialists (69%; 55.75% hospital specialists, 13.25% specialists in private practice). Frequent online lectures at regular intervals (77.8%) and combined face-to-face and online CME (55.9%) were favored. A duration of 1-2 h was found ideal (57.5%). Technical issues were less a major concern since the pandemic. Conclusion: A shift from face-to-face toward online CME events was expectedly detected since the outbreak. Online CME was accelerated and promoted by the pandemic. According to the perception of users, the CME system appears to have reacted adequately to meet their demand but does not replace human interaction.

Effects of ketamine on hypoxic pulmonary vasoconstriction in the isolated perfused lungs of endotoxaemic mice.

BACKGROUND AND OBJECTIVE: During sepsis and endotoxaemia, hypoxic pulmonary vasoconstriction (HPV) is impaired. Sedation of septic patients in ICUs is performed with various anaesthetics, most of which have pulmonary dilatory properties. Ketamine is a sympathetic nervous system-activating anaesthetic that preserves cardiovascular stability. The effects of ketamine on the pulmonary vasculature and HPV during sepsis have not been characterized yet. METHODS: Therefore, isolated lungs of mice were perfused with ketamine (0, 0.1, 1.0, and 10 mg kg(-1) body weight min) 18 h following intraperitoneal injection of lipopolysaccharide (LPS); untreated mouse groups served as controls (n = 7 per group, respectively). Pulmonary artery pressure (PAP) and pressure-flow curves during normoxic (FiO(2) = 0.21) and hypoxic (FiO(2) = 0.01) ventilation were obtained. RESULTS: HPV was reduced in endotoxaemic animals when compared with controls (means +/- SD; DeltaPAP control 103 +/- 28% vs. LPS 23 +/- 25%, P < 0.05). Ketamine caused a dose-dependent reduction of HPV in the lungs of control (DeltaPAP 0 mg kg(-1) min(-1) ketamine 103 +/- 28% vs. 10 mg kg(-1) min(-1) ketamine 28 +/- 21%, P < 0.05) and septic animals (DeltaPAP 0 mg kg(-1) min(-1) ketamine 23 +/- 25% vs. 10 mg kg(-1) min(-1) ketamine 0 +/- 4%, P < 0.05). Analysis of pressure-flow curves revealed that ketamine partly reversed the endotoxin-induced changes in basal pulmonary vascular wall properties rather than interfering with the HPV response itself. CONCLUSION: Ketamine modified baseline pulmonary vascular properties, resulting in a reduced HPV responsiveness in untreated mice. Further, ketamine counteracted the LPS-induced changes in pulmonary vascular pressure-flow relationships, but did not affect impaired HPV in this murine endotoxaemia model.

Biologic effects of nitrous oxide: a mechanistic and toxicologic review.

Nitrous oxide is the longest serving member of the anesthesiologist's pharmacologic armamentarium but remains a source of controversy because of fears over its adverse effects. Recently, the Evaluation of Nitrous oxide In a Gas Mixture for Anaesthesia (ENIGMA) trial reported that nitrous oxide use increases postoperative complications; further preclinical reports have suggested that nitrous oxide may contribute to neurocognitive dysfunction in the young and elderly. Therefore, nitrous oxide's longevity in anesthetic practice is under threat. In this article, the authors discuss the evidence for the putative toxicity of nitrous oxide, from either patient or occupational exposure, within the context of the mechanism of nitrous oxide's action. Although it would seem prudent to avoid nitrous oxide in certain vulnerable populations, current evidence in support of a more widespread prescription from clinical practice is unconvincing.

[Epidemiology and Pathophysiology of the acute respiratory distress syndrome (ARDS)]. / Epidemiologie und Pathophysiologie des akuten Lungenversagens (ARDS).

Despite the implementation of a multimodal concept of treatment, the acute respiratory distress syndrome (ARDS) is still afflicted with high mortality rates. A reasonable application and combination of possible treatment strategies, such as prone position, positive end-expiratory pressure (PEEP), restrictive volume therapy or nitric oxide (NO), requires pathophysiological and epidemiological knowledge. In the following article we describe basic pathophysiological parameters in development, progression and therapy of ARDS. Furthermore, we try to elucidate possible reasons for considerable limitations of multicentric studies in this field.

Medical students teaching basic life support to school children as a required element of medical education: a randomised controlled study comparing three different approaches to fifth year medical training in emergency medicine.

OBJECTIVES: Basic life support (BLS) by doctors has been shown to be of poor quality. To improve medical education training should be simplified, and simultaneously the learner should be involved more actively. To combine both ideas we trained medical students to give BLS courses and sent them to teach school children. This was a requirement for their emergency medicine course. Our model was compared to conventional teaching. DESIGN: Medical students were assigned at random to one of three groups. Group 1 ("university") attended a conventional university BLS/ALS course. Group 2 ("EMS") accompanied a BLS vehicle of the emergency medical service (EMS) after suitable preparation. Group 3 ("school") was instructed to teach BLS and then sent to teach at schools. MAIN OUTCOME MEASURES: Clinically significant BLS skills, and overall BLS skills, each assessed by structured clinical examination (SCE). Theoretical knowledge assessed by written (open question) test. RESULTS: Clinically relevant mistakes were seen in 37.5% in group 1 ("university"), compared to 28.8% in group 2 ("EMS"), and 11.3% in group 3 ("school"). Highly significant differences were shown between "school" and "EMS" (p=0.011), and between "school" and "university" (p<0.001). In practical testing for overall performance the "university" group reached a median of 78.8% (25th-75th percentile 69.2-84.6%), group "EMS" reached 76.9% (69.2-88.5%), and group "school" 84.6% (76.9-90.0). Group "school" showed significant advantages over "university" (p=0.015) and "EMS" (p=0.010). Written test results did not differ statistically. CONCLUSION: Medical students teaching BLS to school children as a compulsory element of their own medical training showed superior practical skills as compared to conventional teaching. Theoretical knowledge was equivalent to the control groups, although their course contained less theoretical information.

Quality indicators in intensive care medicine for Germany - third edition 2017.

Quality improvement in medicine is depending on measurement of relevant quality indicators. The quality indicators for intensive care medicine of the German Interdisciplinary Society of Intensive Care Medicine (DIVI) from the year 2013 underwent a scheduled evaluation after three years. There were major changes in several indicators but also some indicators were changed only minimally. The focus on treatment processes like ward rounds, management of analgesia and sedation, mechanical ventilation and weaning, as well as the number of 10 indicators were not changed. Most topics remained except for early mobilization which was introduced instead of hypothermia following resuscitation. Infection prevention was added as an outcome indicator. These quality indicators are used in the peer review in intensive care, a method endorsed by the DIVI. A validity period of three years is planned for the quality indicators.

Nitric oxide-dependent inhibition of alveolar fluid clearance in hydrostatic lung edema.

Formation of cardiogenic pulmonary edema in acute left heart failure is traditionally attributed to increased fluid filtration from pulmonary capillaries and subsequent alveolar flooding. Here, we demonstrate that hydrostatic edema formation at moderately elevated vascular pressures is predominantly caused by an inhibition of alveolar fluid reabsorption, which is mediated by endothelial-derived nitric oxide (NO). In isolated rat lungs, we quantified fluid fluxes into and out of the alveolar space and endothelial NO production by a two-compartmental double-indicator dilution technique and in situ fluorescence imaging, respectively. Elevation of hydrostatic pressure induced Ca(2+)-dependent endothelial NO production and caused a net fluid shift into the alveolar space, which was predominantly attributable to impaired fluid reabsorption. Inhibition of NO production or soluble guanylate cyclase reconstituted alveolar fluid reabsorption, whereas fluid clearance was blocked by exogenous NO donors or cGMP analogs. In isolated mouse lungs, hydrostatic edema formation was attenuated by NO synthase inhibition. Similarly, edema formation was decreased in isolated mouse lungs of endothelial NO synthase-deficient mice. Chronic heart failure results in endothelial dysfunction and preservation of alveolar fluid reabsorption. These findings identify impaired alveolar fluid clearance as an important mechanism in the pathogenesis of hydrostatic lung edema. This effect is mediated by endothelial-derived NO acting as an intercompartmental signaling molecule at the alveolo-capillary barrier.

Serotonin transporter protein in pulmonary hypertensive rats treated with atorvastatin.

HMG-CoA-reductase inhibitors (statins) influence lipid metabolism and have pleiotropic effects. Several statins reduce various forms of pulmonary hypertension (PH) in animal models. The relationship between atorvastatin and expression of serotonin transporter protein (5-HTT) remains unknown. This study focused on the effects of atorvastatin on the course of monocrotaline (MCT)-induced PH and its relation to 5-HTT expression. Male Sprague-Dawley rats were challenged with MCT with or without subsequent daily oral treatment with 0.1, 1, and 10 mg/kg of atorvastatin for 28 days. Over the 4-wk course, the progression of PH was followed by transthoracic echocardiography [pulmonary artery pressure was assessed by pulmonary artery flow acceleration time (PAAT), an estimate reciprocal to pulmonary artery pressure], and, at the end of the 4-wk course, invasive right ventricular pressure, right ventricular weight, quantitative morphology, and 5-HTT expression were measured. MCT caused significant PH as early as 7 days after injection. Atorvastatin treatment increased PAAT and reduced right ventricular pressure, right ventricular hypertrophy, and vascular remodeling over the 4-wk course. MCT challenge was associated with increased pulmonary vascular 5-HTT expression, and atorvastatin treatment reduced the 5-HTT expression. MCT-induced PH over the course of 4 wk can be easily followed by transthoracic echocardiography, and atorvastatin is effective in reducing the PH. Atorvastatin's effects are associated with a decrease of 5-HTT expression.

Inhalation of the phosphodiesterase-3 inhibitor milrinone attenuates pulmonary hypertension in a rat model of congestive heart failure.

BACKGROUND: Most patients with congestive heart failure (CHF) develop pulmonary venous hypertension, but right ventricular afterload is frequently further elevated by increased pulmonary vascular resistance. To investigate whether inhalation of a vasodilatory phosphodiesterase-3 inhibitor may reverse this potentially detrimental process, the authors studied the effects of inhaled or intravenous milrinone on pulmonary and systemic hemodynamics in a rat model of CHF. METHODS: In male Sprague-Dawley rats, CHF was induced by supracoronary aortic banding, whereas sham-operated rats served as controls. Milrinone was administered as an intravenous infusion (0.2-1 microg.kg body weight.min) or by inhalation (0.2-5 mg/ml), and effects on pulmonary and systemic hemodynamics and lung water content were measured. RESULTS: In CHF rats, intravenous infusion of milrinone reduced both pulmonary and systemic arterial blood pressure. In contrast, inhalation of milrinone predominantly dilated pulmonary blood vessels, resulting in a reduced pulmonary-to-systemic vascular resistance ratio. Repeated milrinone inhalations in 20-min intervals caused a stable reduction of pulmonary artery pressure. No hemodynamic effects were detected when 0.9% NaCl was administered instead of milrinone or when milrinone was inhaled in sham-operated rats. No indications of potentially adverse effects of milrinone inhalation in CHF, such as left ventricular volume overload, were detected. Moreover, lung edema was significantly reduced by repeated milrinone inhalation. CONCLUSION: If these results can be confirmed in humans, inhalation of nebulized milrinone may present a novel, effective, safe, and pulmonary selective strategy for the treatment of pulmonary venous hypertension in CHF.

4-Aminopyridine restores impaired hypoxic pulmonary vasoconstriction in endotoxemic mice.

BACKGROUND: Hypoxic pulmonary vasoconstriction (HPV) is impaired during inflammatory lung processes such as pneumonia or the acute respiratory distress syndrome. Voltage-gated potassium channels play a central role in mediating HPV. The aim of this study was to determine whether 4-aminopyridine (4-AP), a known voltage-gated potassium channel inhibitor, may restore HPV in sepsis. METHODS: The effects of 0.01, 0.1, and 1.0 mm 4-AP on HPV responsiveness were assessed in isolated lungs of untreated mice and of mice 18 h after lipopolysaccharide injection (20 mg/kg intraperitoneal Escherichia coli 0111:B4 lipopolysaccharide). HPV was quantified as the increase in perfusion pressure in response to hypoxic ventilation in percent of baseline perfusion pressure. Intrinsic pulmonary vascular resistance (R0) and pulmonary vascular distensibility (alpha) were determined by nonlinear regression analysis of pulmonary vascular pressure-flow curves generated during normoxic and hypoxic ventilation, respectively. RESULTS: HPV was impaired in lungs isolated from lipopolysaccharide-challenged mice. Addition of 4-AP to the perfusate did not alter HPV responsiveness in untreated mice but dose dependently restored HPV in endotoxemic mice. Analysis of pulmonary vascular pressure-flow curves revealed that 4-AP (1) counteracted the observed lipopolysaccharide-induced changes in alpha and R0 under normoxic conditions and (2) augmented the hypoxia-induced increase in R0 in lungs of endotoxemic mice. CONCLUSIONS: This study demonstrates that lipopolysaccharide-induced pulmonary vascular hyporesponsiveness to hypoxia can be restored by 4-AP in murine endotoxemia and, thus, may be a new therapeutic approach to treat patients with hypoxemia due to impaired HPV.

Inducible nitric oxide synthase and heme oxygenase-1 in the lung during lipopolysaccharide tolerance and cross tolerance.

OBJECTIVE: Pretreatment with low-dose lipopolysaccharide protects cells/organs against a subsequent lethal Gram-negative (lipopolysaccharide tolerance) or Gram-positive (cross tolerance) stimulus. We determined whether this occurs in the rat lung. The involvement of inducible nitric oxide synthase and heme oxygenase-1 was evaluated. DESIGN: Laboratory study. SETTING: University hospital laboratory. SUBJECTS: Anesthetized male Wistar rats. INTERVENTIONS: To test the hypothesis, rats received saline or lipopolysaccharide (1 mg/kg). At 2, 4, 8, 16, or 24 hrs later, blood samples and lung tissue were taken to determine messenger RNA, protein concentration, and activity of inducible nitric oxide synthase and heme oxygenase-1. In additional experiments, rats were challenged with lipopolysaccharide (1 mg/kg) and subjected to Gram-negative (lipopolysaccharide) or Gram-positive (lipoteichoic acid and peptidoglycan) shock 24 hrs later. These studies were carried out in the presence and absence of inducible nitric oxide synthase or heme oxygenase-1 inhibitors (1400W or tin protoporphyrin IX). Following 6 hrs of shock, lung tissue was taken to determine lung damage and heme oxygenase-1 concentration and activity. MEASUREMENTS AND MAIN RESULTS: In the rat lung, lipopolysaccharide (1 mg/kg) induced a significant increase in inducible nitric oxide synthase protein at 8 hrs with a corresponding increase in plasma nitrate/nitrite at 8-16 hrs. Simultaneously, heme oxygenase-1 messenger RNA transcripts were observed at 8-16 hrs, and maximal expression of the protein followed (24 hrs). Pretreatment with low-dose lipopolysaccharide reduced myeloperoxidase activity (neutrophil infiltration) and wet-dry ratio (pulmonary edema) in the lungs of animals subjected to Gram-negative or Gram-positive shock, demonstrating tolerance. Pretreatment with low-dose lipopolysaccharide and the selective inducible nitric oxide synthase inhibitor 1400W reduced heme oxygenase-1 protein expression, and lung protection was abolished. Tin protoporphyrin IX did not affect heme oxygenase-1 expression, but heme oxygenase activity and lung protection were significantly reduced. CONCLUSIONS: We propose that nitric oxide (most likely inducible nitric oxide synthase derived) regulates the induction of heme oxygenase-1 in the lung, which in turn plays an important part in pulmonary protection during lipopolysaccharide tolerance and cross tolerance.

Role of endogenous nitric oxide in endotoxin-induced alteration of hypoxic pulmonary vasoconstriction in mice.

Pulmonary vasoconstriction in response to alveolar hypoxia (HPV) is frequently impaired in patients with sepsis or acute respiratory distress syndrome or in animal models of endotoxemia. Pulmonary vasodilation due to overproduction of nitric oxide (NO) by NO synthase 2 (NOS2) may be responsible for this impaired HPV after administration of endotoxin (LPS). We investigated the effects of acute nonspecific (N(G)-nitro-L-arginine methyl ester, L-NAME) and NOS2-specific [L-N6-(1-iminoethyl)lysine, L-NIL] NOS inhibition and congenital deficiency of NOS2 on impaired HPV during endotoxemia. The pulmonary vasoconstrictor response and pulmonary vascular pressure-flow (P-Q) relationship during normoxia and hypoxia were studied in isolated, perfused, and ventilated lungs from LPS-pretreated and untreated wild-type and NOS2-deficient mice with and without L-NAME or L-NIL added to the perfusate. Compared with lungs from untreated mice, lungs from LPS-challenged wild-type mice constricted less in response to hypoxia (69 +/- 17 vs. 3 +/- 7%, respectively, P < 0.001). Perfusion with L-NAME or L-NIL restored this blunted HPV response only in part. In contrast, LPS administration did not impair the vasoconstrictor response to hypoxia in NOS2-deficient mice. Analysis of the pulmonary vascular P-Q relationship suggested that the HPV response may consist of different components that are specifically NOS isoform modulated in untreated and LPS-treated mice. These results demonstrate in a murine model of endotoxemia that NOS2-derived NO production is critical for LPS-mediated development of impaired HPV. Furthermore, impaired HPV during endotoxemia may be at least in part mediated by mechanisms other than simply pulmonary vasodilation by NOS2-derived NO overproduction.

Gadolinium chloride-induced improvement of postischemic hepatic perfusion after warm ischemia is associated with reduced hepatic endothelin secretion.

Selective Kupffer cell blockade by gadolinium chloride (GdCl(3)) pretreatment of liver donors previously proved to be effective in reducing ischemia/reperfusion injury in rat liver transplants. Physiological mechanisms of this effect have not been specified so far. Vasoactive peptides are involved in liver blood flow regulation. We tested the hypothesis, that hepatic hemodynamic effects of GdCl(3) pretreatment are mediated by intrahepatic endothelin-1 (ET) secretion in a standardized porcine model of warm liver ischemia and reperfusion. Standardized warm hepatic ischemia (45 min) was induced after laparotomy in intubation narcoses (ITN) by Pringle-maneuver in pigs (n = 12). Animals were either pretreated with GdCl(3) (20 mg/kg i.v.) or sodium chloride 0.9% (control group) in a randomized manner 24 h before investigation. Relaparotomy was performed at day 7. Before, during ischemia and until 6 h after liver reperfusion, transhepatic blood flow (portal venous + hepatic artery flow) was defined by ultrasonic flow probes and hepatic parenchymous microcirculation evaluated by implanted thermodiffusion electrodes. ET plasma concentrations were analyzed (commercial RIA) at all time points in the hepatic veins after selective canulation. GdCl(3) pretreatment of animals markedly improved hepatic macro- and microperfusion before and particularly after warm ischemia. Mean ET plasma concentrations in the hepatic vein were significantly lower before, 6 h and 7 days after ischemia, compared with controls. Kupffer cell destruction by GdCl(3) pretreatment improves hepatic micro- and macroperfusion after warm ischemia, thus indicating reduced ischemia/reperfusion injury. Documented reduction of postischemic liver blood flow impairment after GdCl(3) pretreatment could be mediated by a decreased hepatic ET secretion, as hemodynamic effects were associated with significantly reduced ET plasma levels in hepatic veins.

Toxicity of nitrous oxide.

Nitrous oxide interacts with vitamin B12 resulting in selective inhibition of methionine synthase, a key enzyme in methionine and folate metabolism. Thus, nitrous oxide may alter one-carbon and methyl-group transfer most important for DNA, purine and thymidylate synthesis. Long-term exposure to high concentrations of nitrous oxide may cause megaloblastic bone-marrow depression and neurological symptoms. Exposure to higher doses for less than 6 hours, as in clinical anaesthesia, are considered harmless. Recent studies seem to suggest a correlation between nitrous oxide anaesthesia and hyperhomocysteinaemia which is accepted to be an independent risk factor for coronary artery disease. As for today, available data do not support the notion that exposure to trace amounts of nitrous oxide is associated with impaired fertility or an increased risk of developing cancer. Emission of nitrous oxide from medical use is estimated to contribute less than 0.05% to total annual greenhouse gas emission.