Mixture Of Nitrous Oxide Research Articles

Nitrous Oxide for Colonoscopy

Colonoscopy is the gold standard investigation for large bowel disease. With the increase in demand, pressure is on clinics to shorten lengths of time per procedure in addition to maintaining high levels of patient safety. Analgesia has always been the mainstay of adequate pain relief, but it leads to prolonged recovery and lengths of hospital stay, in addition to increased risk of cardio-respiratory side effects. N2O/O2 mixtures have been used for its effective analgesic effect and short half life and provides an alternative method of sedation for colonoscopy procedures. The primary objective was to compare the overall effectiveness of nitrous oxide mixtures to other types of pain relief used during colonoscopy procedures to provide adequate pain/discomfort relief.The secondary objective was to compare between nitrous oxide and other types of pain relief with respect to hospitalisation/recovery time, side effects, patients and endoscopists satisfaction, and colonoscopy completion rates. The following electronic databases were searched: Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library, MEDLINE (1966- present), EMBASE (1980 - present), and the Internet (Google Scholar). Randomised controlled trials which compared nitrous oxide to placebo or active comparators for patients undergoing elective colonoscopic procedures. Patients with known underlying causes of pain/discomfort were excluded. Seven randomised trials were included. Each trial compared a nitrous oxide/oxygen mixture to a placebo or sedation +- other analgesic drugs on patients undergoing elective colonoscopic procedures. The results of these studies were analysed and discussed. There were a total of 547 patients included.There were 257 patients randomised to receive the N2O/O2 mixture (7 studies), while 225 patients received some form of sedation with or without other analgesia (6 studies), and 65 patients received a placebo (3 studies).Four studies showed that N2O/O2 is as good in controlling pain/discomfort as conventional methods, while one showed sedation was better and another study showed N2O/O2 was better.Six of the studies showed that N2O/O2 groups had quicker recovery times and shorter lengths of hospital stays while one study showed that there was no difference between the two groups.Two studies showed that N2O/O2 was safer while one reported that sedation was safer. Nitrous oxide is as efficient and safer than various pain relief methods used during colonoscopy procedures, but further trials are necessary.

Feasibility of a single port Hybrid Propulsion system for a Mars Ascent Vehicle

Developments in hybrid propellants over the last decade make the hybrid motor a viable candidate and possibly an enabling technology for a Mars Ascent Vehicle (MAV) as part of a Mars Sample Return (MSR) campaign. Fast regression rate fuels such as paraffin allow for single port hybrid designs that overcome the disadvantages associated with classical hybrid fuels. Additionally, paraffin has a both a weak and low glass transition temperature, making it an ideal candidate for a Mars application. Nytrox, a high performance oxidizer made of a mixture of nitrous oxide and oxygen, can be chosen to match the temperatures on Mars. The hybrid MAV can survive the harsh Martian environment with minimal or no thermal conditioning and it can meet the design challenges posed by coordinating with the other aspects of MSR.

Accuracy of ten isoflurane vaporisers in current clinical use

There is a lack of independent data regarding the accuracy of isoflurane vaporisers in current clinical use. We studied the accuracy of 10 isoflurane vaporisers (six Penlon Sigma Delta, four Datex-Ohmeda Isotec 5) taken from our operating theatres and anaesthetic rooms. Isoflurane output was measured at a range of fresh gas flow rates using both 100% oxygen and a 1:2 oxygen:nitrous oxide mixture as carrier gas. Within a clinical range of fresh gas flow rates (1-6 l.min(-1)) the worst relative output deviation of each vaporiser was at least ±20%, with under-delivery of isoflurane being commoner than over-delivery. Relative output deviation ranged from -62% to +21%, which could lead to a risk of awareness or overdose. Despite the existence of an in-house calibration schedule, the vaporisers we found in current clinical use under- or occasionally over-delivered isoflurane to a dangerous and unpredictable extent.

Flame burning speeds and combustion characteristics of undiluted and nitrogen-diluted hydrogen–nitrous oxide mixtures

In the present study, some explosive properties of undiluted and nitrogen-diluted H 2–N 2O mixtures were characterized. Laminar burning speeds and the explosion-induced pressure rises were determined experimentally for a range of mixture equivalence ratios ( ϕ = 0.15 − 1.0 ) , dilutions ( 0 − 55 % N 2 ) , and initial pressures ( 20 − 80 kPa ) . The measured burning speeds were used to validate laminar burning speed computations using a detailed chemical kinetic mechanism. The computations were then used to estimate burning speeds at high initial pressure and low dilution conditions that could not be measured experimentally. The results demonstrate that hydrogen–nitrous oxide mixtures exhibit laminar burning speeds as large as 350 cm/s and pressure rise coefficients ( K g ) as large as 35 MPa m/s. Also, flames in lean mixtures are shown to be highly unstable which can lead to flame acceleration and possible deflagration-to-detonation transition.

Evaluation of Analgesic Effect of Equimolar Mixture of Oxygen and Nitrous Oxide Inhalation During Percutaneous Biopsy of Focal Liver Lesions:: A Double-blind Randomized Study

Percutaneous liver biopsy for tumors performed under local anesthesia is still a painful procedure. The aim of this study was to evaluate the patient's reaction and the analgesic efficacy and safety of an equimolar mixture of oxygen and nitrous oxide (EMONO) inhalation. A monocenter, prospective, randomized and double-blind controlled study was performed including 99 adult patients undergoing ultrasound controlled liver biopsy for tumors. 50 patients received an EMONO and 49 patients received a placebo. Pain was evaluated by patients before and after the procedure using a Visual Analog Scale. Analgesic control, defined by the difference between the final and initial VAS scores (Δ), was significantly better in the EMONO group than in the placebo group (Δ = 17.8 ± 25.5 mm vs 30.1 ± 32.6 mm; P = .045. The number of patients who would agree to undergo another liver biopsy under the same conditions was significantly higher in the EMONO group than the placebo group (92.0% vs 75.5%, P = .026). There were no side-effects from the administration of an EMONO. This study shows that patients receiving an EMONO had a higher analgesic control after percutaneous biopsy of focal liver lesions than patients in the placebo group. Moreover, acceptance of additional biopsies was higher in the EMONO group.

Accidental Intrathecal Injection of Aminophylline in Spinal Anesthesia

Accidental Intrathecal Injection of Aminophylline in Spinal Anesthesia

Critical energy for direct initiation of spherical detonations in H 2/N 2O/Ar mixtures

Although the detonation phenomenon in hydrogen–nitrous oxide mixtures is a significant issue for nuclear waste storage facilities and development of propulsion materials, very limited amount of critical energy data for direct initiation – which provides a direct measure of detonability or sensitivity of an explosive mixture − is available in literature. In this study, the critical energies for direct blast initiation of spherical detonations in hydrogen–nitrous oxide–Ar mixtures obtained from laboratory experiments and theoretical predictions at different initial conditions (i.e., different initial pressure, equivalence ratio and amount of argon dilution) are reported. In the experiments, direct initiation is achieved via a spark discharge from a high voltage and low inductance capacitor and the initiation energy is estimated accordingly from the current output. Characteristic detonation cell sizes of hydrogen–nitrous oxide–Ar mixtures are estimated from chemical kinetics using a recently updated reaction mechanism. A correlation expression is developed as a function of initial pressure, argon dilution and equivalence ratio, which is fitted to provide good estimation of the experimental measured data. The direct link between cell size and critical energy for direct blast initiation is then analyzed. Good agreement is found between experimental results and theoretical predictions, which make use of the cell size estimation correlation and the semi-empirical surface energy model. The effects of the initial pressure, equivalence ratio and the amount of Ar dilution on the critical initiation energy H 2–N 2O–Ar mixtures are investigated. By comparing the critical energies with those of H 2–O 2–Ar mixtures, it is shown that H 2–N 2O mixtures are more detonation sensitive with smaller initiation energies than H 2–O 2 mixtures at the same initial pressure, equivalence ratio and amount of argon dilution, except for higher diluted condition with amount of argon in the mixture above 20%. Attempt is made to explain the critical energy variation and comparison between the two H 2–N 2O–Ar and H 2–O 2–Ar mixtures from the induction length analysis and detonation instability consideration.

Final report on international comparison CCQM-K68: Nitrous oxide in synthetic air

Nitrous oxide (N2O) is one of six greenhouse gases that are regulated by the Kyoto Protocol and has a Global Warming Potential (GWP) that is 296 times that of carbon dioxide. Global levels of nitrous oxide have increased at a rate of 0.25%/yr (0.8 ppb/yr) during the last ten years. In order to monitor levels of nitrous oxide in the atmosphere, it is necessary to use measurement standards with demonstrated equivalence at the highest level of accuracy.This report describes the results of a key comparison of standard gas mixtures of nitrous oxide in synthetic air at an amount fraction of 320 nmol/mol. This key comparison is part of the programme of the Gas Analysis Working Group (GAWG) of the CCQM to demonstrate the equivalence of the standards and measurement capabilities of the NMIs for greenhouse gases. It will support the development of measurement capability at the NMIs for nitrous oxide with uncertainties within the target set by the Global Atmospheric Watch (GAW) programme of the WMO for its global monitoring networks.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The effects of temperature on nitrous oxide and oxygen mixture homogeneity and stability.

BackgroundFor many long standing practices, the rationale for them is often lost as time passes. This is the situation with respect to the storage and handling of equimolar 50% nitrous oxide and 50% oxygen volume/volume (v/v) mixtures.MethodsA review was undertaken of existing literature to examine the developmental history of nitrous oxide and oxygen mixtures for anesthesia and analgesia and to ascertain if sufficient bibliographic data was available to support the position that the contents of a cylinder of a 50%/50% volume/volume (v/v) mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage and if justification could be found for the standard instructions given for handling before use.ResultsAfter ranking and removing duplicates, a total of fifteen articles were identified by the various search strategies and formed the basis of this literature review. Several studies were identified that confirmed that 50%/50% v/v mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage. The effect of temperature on the change of phase of the nitrous oxide in this mixture was further examined by several authors. These studies demonstrated that although it is possible to cause condensation and phase separation by cooling the cylinder, by allowing the cylinder to rewarm to room temperature for at least 48 hours, preferably in a horizontal orientation, and inverting it three times before use, the cylinder consistently delivered the proper proportions of the component gases as a homogenous mixture.ConclusionsThe contents of a cylinder of a 50%/50% volume/volume (v/v) mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage. The standard instructions given for handling before are justified based on previously conducted studies.

Oxygen atom kinetics in silane–hydrogen–nitrous oxide mixtures behind reflected shock waves

Resonance Absorption Spectroscopy has been used to study the O-atom dynamics behind reflected shock waves in highly argon diluted silane–hydrogen–nitrous oxide mixtures in the temperature range 1606–2528 K and at total pressures from 234 to 584 kPa. The absorptions at 130.5 nm of N 2O, SiH 4 and Si have been taken into account to compare simulated and experimental absorption profiles. A detailed kinetic model has been also used to interpret the results and reaction pathway and sensitivity analyses have been performed to underline important elementary reactions. A comparison with the O-atom kinetic in silane–nitrous oxide and hydrogen–nitrous oxide mixtures is also proposed.

A chemical kinetic study of the oxidation of silane by nitrous oxide, nitric oxide and oxygen

Silane–nitrous oxide mixtures are widely used in the semi-conductor manufacturing industry. Although these mixtures are potentially hazardous, their explosive properties are not very well characterised. In the present study, the high temperature kinetics of highly argon diluted silane–nitrous oxide mixtures has been examined. The dynamics of oxygen atoms behind reflected shock waves has been studied by Atomic Resonance Absorption Spectroscopy at temperatures between 1725 and 2584K and pressures from 231 to 601kPa. In order to take into account the effect of silane molecule and silicon atom absorption at 130.5nm, absorption cross section determinations have been performed. In our experimental conditions (compositions and observation times), steady state oxygen atom concentrations have been observed at low temperatures, after few hundreds of microseconds. At high temperatures, the initial fast increase of oxygen atom concentration was followed by a period of consumption. A kinetic model that reproduces very well the experimental absorption profiles has been developed. Important reactions have been underlined through sensitivity and reaction pathway analyses. Previous experimental results from the literature for the oxidation of silane by nitrous oxide, nitric oxide and oxygen behind reflected shock waves have also been compared to the results coming from the kinetic model.

Effect of nitrous oxide on cisatracurium infusion demands: a randomized controlled trial

BackgroundRecent studies have questioned our previous understanding on the effect of nitrous oxide on muscle relaxants, since nitrous oxide has been shown to potentiate the action of bolus doses of mivacurium, rocuronium and vecuronium. This study was aimed to investigate the possible effect of nitrous oxide on the infusion requirements of cisatracurium.Methods70 ASA physical status I-III patients aged 18-75 years were enrolled in this randomized trial. The patients were undergoing elective surgery requiring general anesthesia with a duration of at least 90 minutes. Patients were randomized to receive propofol and remifentanil by target controlled infusion in combination with either a mixture of oxygen and nitrous oxide (Nitrous oxide/TIVA group) or oxygen in air (Air/TIVA group). A 0.1 mg/kg initial bolus of cisatracurium was administered before tracheal intubation, followed by a closed-loop computer controlled infusion of cisatracurium to produce and maintain a 90% neuromuscular block. Cumulative dose requirements of cisatracurium during the 90-min study period after bolus administration were measured and the asymptotic steady state rate of infusion to produce a constant 90% block was determined by applying nonlinear curve fitting to the data on the cumulative dose requirement during the study period.ResultsController performance, i.e. the ability of the controller to maintain neuromuscular block constant at the setpoint and patient characteristics were similar in both groups. The administration of nitrous oxide did not affect cisatracurium infusion requirements. The mean steady-state rates of infusion were 0.072 +/- 0.018 and 0.066 +/- 0.017 mg * kg-1 * h-1 in Air/TIVA and Nitrous oxide/TIVA groups, respectively.ConclusionsNitrous oxide does not affect the infusion requirements of cisatracurium.Trial registrationClinicalTrials.gov NCT01152905; European Clinical Trials Database at http://eudract.emea.eu.int/2006-006037-41.

Sevoflurane-emergence agitation: effect of supplementary low-dose oral ketamine premedication in preschool children undergoing dental surgery

The use of sevoflurane in paediatric anaesthesia which could enable rapid recovery is complicated by the frequent occurrence of emergence agitation. The aim of this study was to test the efficacy of supplementing midazolam-based oral premedication with low-dose oral ketamine in reducing sevoflurane-related emergence agitation. Ninety-two healthy preschool children who have been scheduled for elective dental procedures under general anaesthesia were allocated into two groups (46 patients for each): group M received oral midazolam 0.5 mg kg(-1), whereas group KM received similar premedication in addition to ketamine 2 mg kg(-1). Acceptance of drug mixture and onset of action were monitored over the next 30 min. Induction of anaesthesia was carried out using sevoflurane 8 vol% in 100% oxygen via face mask. Anaesthesia was maintained with sevoflurane 1.5-2 vol% in oxygen-nitrous oxide mixture. Following extubation, standard scoring scale was used for assessing quality of emergence. Agitation parameters were measured using a five-point scale. Agitated children were managed by giving intravenous increments of fentanyl 1 microg kg(-1). The time of hospital discharge allowance was recorded. Vast majority of children accepted the premedication. There were no significant differences between both groups regarding recovery from sevoflurane and allowance of hospital discharge. Onset of action of premedication was shorter in group KM. Similarly, postoperative agitation score and rescue fentanyl consumption were markedly lower in group KM upon admission to the postanaesthesia care unit (P<0.01). Adding a low dose of oral ketamine to midazolam-based oral premedication in preschool children undergoing dental surgery reduced emergence agitation without delaying hospital discharge.

Unilateral bronchospasm during microcatheter manipulation in an interventional neuroradiology suite

To the Editor: Bronchospasm during general anesthesia has many etiologies, including the patient’s intrinsic disease and mechanical, chemical or neurogenic causes [1, 2]. Reactions to drugs used for embolization and contrast drugs are important causes of bronchospasm in patients undergoing interventional radiological procedures [3, 4]. Unilateral bronchospasm per se is a known but rare entity. We report a case where manipulations of intercostal artery by a microcatheter led to acute unilateral bronchospasm. A 2-year-old girl weighing 12 kg and 65 cm in height was electively scheduled for glue embolization of dorsal (D2) spinal arteriovenous malformation under general anesthesia. Her preoperative respiratory and cardiovascular examinations were normal. The child was premedicated with oral atropine 0.3 mg an hour before the procedure. General anesthesia was induced with propofol 2 mg kg and fentanyl 2 lg kg. A 4-mm ID uncuffed endotracheal tube was placed after complete muscle relaxation, which was achieved with the administration of rocuronium 1 mg kg. The tube was fixed at the 12 cm mark at the angle of the mouth. Anesthesia was maintained with isoflurane in a mixture of nitrous oxide and oxygen (2:1) and intermittent boluses of fentanyl 1 mcg kg and rocuronium 0.1 mg kg. The procedure was performed in the supine position. Forty-five minutes later, the patient had a sudden increase in airway pressure (from 10 to 22 cm H2O) followed by an increase in expired carbon dioxide partial pressure (from 34 to 48 mmHg) and a decrease in peripheral oxygen saturation. On auscultation of the chest, air entry was found to be diminished on the left side along with wheezing and ronchi all over the left lung field. Possible causes of intraoperative bronchospasm such as endobronchial displacement of the tracheal tube, oropharyngeal secretions and inadequate depth of anesthesia and analgesia were ruled out, and after proper oral and tracheal tube suctioning, a combination of theophylline and etophylline was administered along with hydrocortisone. By this time the radiologist had stopped the procedure, as the patient was being managed for bronchospasm. The radiographic image of the chest did not reveal any obvious abnormality and the lung fields appeared normal. On discussing with the radiologist, it was found that he was manipulating the microcatheter through intercostal artery on the side concerned when the problem was noted. Nearly 30–40 min later, following conservative management, the bronchospasm was relieved and the procedure was allowed to continue. The unilateral nature of bronchospasm rules out the possibility of contrast media as the etiology of intraoperative bronchospasm in our patient. The onset and presence of spasm exclusively on the side of catheter manipulation in the intercostal artery is highly suggestive of the possible etiology. It is likely that stimulation of the bronchial artery at its origin from the intercostal artery might have produced vessel spasm and triggered a series of events resulting in bronchospasm. Though it is difficult to speculate about the exact mechanism of bronchospasm, the possibility of some neural or chemical mediators can always be anticipated, as bronchial musculature is always under the influence of parasympathetic tone. Subsequent negotiation of the catheter through the vessel at a later stage did not produce K. Reddy H. Prabhakar (&) N. Yadav G. P. Singh Department of Neuroanaesthesiology, Neurosciences Center, 7th floor, All India Institute of Medical Sciences, New Delhi 110029, India e-mail: prabhakarhemanshu@rediffmail.com

Nitrous oxide and isoflurane are synergistic with respect to amplitude and latency effects on sensory evoked potentials

Combinations of anesthetic agents are frequently employed to produce the desired clinical effect. No systematic study has been conducted on the effect of the combination of nitrous oxide with a potent inhalational agent such as isoflurane on sensory evoked responses. Median nerve somatosensory evoked responses from the cervical and cortical regions (SSEP), auditory brainstem responses (ABR) and flash visual evoked responses (VEP) were tested in baboons. The latency and amplitude of the major response peaks were recorded at five proportionate mixtures of isoflurane (I) and nitrous oxide (N(2)O) (0.8% I only, 0.6% I/20% N(2)O, 0.4% I/40% N(2)O, 0.2% I/60% N(2)O, and 79% N(2)O only). A similar set of experiments were also conducted with 0.8% isoflurane and 0.6% halothane. All data were normalized to 0.8% isoflurane only and Dunnett's method of analysis used to determine which mixtures deviated from the reference values with 0.8% isoflurane. Several combinations of isoflurane with nitrous oxide produced increases in latency (ABR: wave V, VEP, SSEP cervical and cortical) and decreases in amplitude (ABR: amplitude ratio V/I, VEP, cortical SSEP) from that expected if the effects were additive. No deviations were observed with combinations of isoflurane and halothane. These studies are consistent with drug synergy when isoflurane is mixed with nitrous oxide. This suggests that if these agents are considered for anesthesia when sensory evoked responses are to be monitored that the combination of these agents may produce more amplitude and latency changes than expected from a proportionate mixture of the individual agents.

Hyperoxia in Pediatric Anesthesia: Time for Reconsideration?

Hyperoxia in Pediatric Anesthesia: Time for Reconsideration?

Physico-chemical, structural and physical properties of hydrogenated silicon oxinitride films elaborated by pulsed radiofrequency discharge

Films prepared by radiofrequency pulsed plasma enhanced chemical vapor deposition from a mixture of silane (SiH 4) and nitrous oxide (N 2O) were studied. Variation of operating conditions (flow rate, deposition temperature ...) resulted in films with chemical compositions changing from hydrogenated silicon oxynitride (SiO x N y :H) to silicon oxide (SiO x :H). Infrared and Rutherford backscattering spectroscopy studies of the as-deposited films revealed different SiO x arrangements disturbed by Si–N bonds and H–Si ≡ Si (3 − x) O x clusters depending on the substrate temperature and the N 2O/SiH 4 ratio. For films obtained using low N 2O/SiH 4 rations and annealed at temperature higher than 1273 K, Raman spectroscopy and microscopy analyses revealed the presence of silicon nanocrystals embedded in a matrix containing Si, O, and N. Spectroscopic ellipsometry revealed the presence of silicon nanocrystals along with two other amorphous phases (SiO x N y and SiO 2) in annealed samples. The electrical characteristics of annealed films obtained from capacitance–voltage measurements indicated a stable charge trapping in ultra-thin SiO x N y layers. These preliminary results suggest that Si -nc containing silicon oxynitride layers can be potential candidates to be used in the floating gate fabrication of memory devices.

Surgery in sitting position in patient with ventriculoperitoneal shunt in situ may be hazardous!

Dear Editor: Complications in sitting position are encountered more often than other surgical positions [1]. Literature search did not reveal any case demonstrating development of an extradural hematoma as a result of surgery in sitting position. We report a case of a 4-year-old female child, weighing 10 kg, admitted in our neurosurgical ward with complaints of headache, vomiting, and difficulty in walking for the last 6 months. A magnetic resonance image scan revealed a contrast enhanced lesion in the pineal region suggestive of pineal tumor. She had earlier undergone endoscopic biopsy removal and a right ventriculoperitoneal shunt surgery. Her medical history was unremarkable, and all preoperative routine investigations were within normal limits. She was scheduled for an elective midline suboccipital craniectomy in sitting position. Following a standard fasting protocol, the child was premedicated with oral atropine 0.4 mg, an hour before surgery. Inside the operation theater routine monitors were attached. General anesthesia was induced with fentanyl 20 mcg and thiopentone 50 mg. To facilitate tracheal intubation with cuffed tube size 5.0, rocuronium 10 mg was administered. Anesthesia was maintained with isoflurane in oxygen and nitrous oxide mixture and intermittent boli of fentanyl 1 mcg/kg and rocuronium 0.1 mg/kg. A double lumen central venous catheter was placed in the right subclavian vein. An arterial line placed in the right dorsalis pedis artery allowed continuous monitoring of blood pressure. The child was placed in sitting position with head supported in a three-pin head rest. A near total excision of the tumor was performed by supracerebellar infratentorial approach. The surgical and anesthetic course lasting approximately 4 h was uneventful. There was no episode of venous air embolism. It was planned to mechanically ventilate the lungs until spontaneous reversal of neuromuscular blockade. The patient was shifted for routine CT scan postoperatively, which revealed a large pneumocephalus (Fig. 1a) along with a high right parietal hematoma measuring 4.8× 1.3 cm (Fig. 1b). However, there was no midline shift and mass effect visible on the scan. A burr hole evacuation of hematoma was performed, and patient was weaned off mechanical ventilation on the second postoperative day. A repeat CT scan revealed resolving pneumocephalus, and no other abnormality. We believe that the ventriculoperitoneal shunt tube in situ may have resulted in such a complication. Excessive drainage of cerebrospinal fluid via the drain could have resulted in intracranial hypotension causing rupture of bridging veins, leading to hematoma formation. H. Prabhakar :G. P. Singh :A. Bindra Department of Neuroanaesthesiology, All India Institute of Medical Sciences, New Delhi, India 110029

Spherical expanding flames in H 2–N 2O–Ar mixtures: flame speed measurements and kinetic modeling

Although ignition of hydrogen–nitrous oxide mixtures is a serious issue for nuclear waste storage and semi-conductor manufacturing, available flame speed data have not been recently updated and thermodiffusive stability is not known. In order to palliate this, the flame speed of a hydrogen–nitrous oxide mixture diluted in Ar (60% mol) was measured in a spherical bomb as a function of equivalence ratio. The initial pressure and temperature were held constant around ambient conditions. It is shown that the unstretched flame speed of the hydrogen–nitrous oxide mixture is relatively low for a hydrogen-based mixture, with a maximum of 56 cm/s for the stoichiometric condition. Further, hydrogen–nitrous oxide–argon flames appear unstable with respect to thermodiffusive effects at an equivalence ratio of 1. The downward flammability limit of hydrogen–nitrous oxide–argon was observed for hydrogen content of 8 mol%. The modeling of these experimental data has been performed with three recently developed models. All kinetic schemes give satisfactory predictions of the experimentally observed data. Sensitivity and reaction pathway analysis have demonstrated that the dynamic of the system is dominated by the reaction N 2O + H = N 2 + OH which governs the rate of energy release.

Sédation par kétamine en prévention de la douleur liée aux gestes invasifs en oncologie pédiatrique

Procedural sedation and analgesia for children is widely practiced. Since 2005 to 2007, we evaluated the safety and efficacy of ketamine to control pain induced by diagnostic procedures in pediatric oncology patients. Eight hundred fifty procedures were carried out in 125 patients aged 2 to 16 years. We associated EMNO (inhaled equimolar mixture of nitrous oxide and oxygen), atropin (oral or rectal), midazolam (oral or rectal) and ketamin (intravenous). An anesthesiologist injected ketamin. Average dose of ketamine was 0.33 to 2 mg/kg depending on number and invasiveness of procedures. This method requires careful monitoring and proper precautions. With these conditions, no complication was observed. All patients were effectively sedated. These results indicate that ketamine - in association with EMNO, atropine and midazolam - is safe and effective in pain management induced by diagnostic procedures in pediatric oncology patients. The sedative regimen of intravenous ketamine has greatly reduced patient, family and practitioners anxiety for diagnostic and therapeutic procedures.