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PubMed1997

Interaction of nitric oxide with non-haem iron sites of Escherichia coli bacterioferritin: reduction of nitric oxide to nitrous oxide and oxidation of iron(II) to iron(III).

The bacterioferritin (BFR) of Escherichia coli consists of 24 identical subunits, each containing a dinuclear metal-binding site consisting of two histidines and four carboxylic acid residues. Earlier studies showed that the characterization of iron binding to BFR could be aided by EPR analysis of iron-nitrosyl species resulting from the addition of NO to the protein [Le Brun, Cheesman, Andrews, Harrison, Guest, Moore and Thomson (1993) FEBS Lett. 323, 261-266]. We now report data from gas chromatographic head space analysis combined with EPR spectroscopy to show that NO is not an inert probe: iron(II)-BFR catalyses the reduction of NO to N2O, resulting in oxidation of iron(II) at the dinuclear centre and the subsequent detection of mononuclear iron(III). In the presence of excess reductant (sodium ascorbate), iron(II)-BFR also catalyses the reduction of NO to N2O, giving rise to three mononuclear iron-nitrosyl species which are detectable by EPR. One of these, a dinitrosyl-iron complex of S = 1/2, present at a maximum of one per subunit, is shown by EPR studies of site-directed variants of BFR not to be located at the dinuclear centre. This is consistent with a proposal that the diferric form of the centre is unstable and breaks down to form mononuclear iron species.

Bacterial Proteins↗
PubMed1997

Dose-response and concentration-response relation of rocuronium infusion during propofol-nitrous oxide and isoflurane-nitrous oxide anaesthesia.

The dose-response and concentration-response relation of rocuronium infusion was studied in 20 adult surgical patients during propofol-nitrous oxide and isoflurane (1 MAC)-nitrous oxide anaesthesia. Neuromuscular block was kept constant, initially at 90% and then at 50% with a closed-loop feedback controller. At 90% block the steady-state infusion of rocuronium was 0.55 +/- 0.16 mg kg-1 h-1 and the corresponding concentration 1714 +/- 281 ng mL-1 in patients receiving propofol. At 50% block the corresponding infusion rate was 0.27 +/- 0.11 mg kg-1 h-1 and the concentration 1077 +/- 244 ng mL-1, respectively. At 50% block isoflurane reduced the rate of infusion by 52% (P < 0.005) and the concentration by 59% (P < 0.001); at 90% block both the mean infusion rate and the concentration of rocuronium were reduced by 35% (P < 0.005). The mean rocuronium clearance at 50% block was unaffected by the type of anaesthesia; it was 4.1 +/- 1.6 and 4.9 +/- 2.7 mL kg-1 min-1 in the groups receiving propofol and isoflurane anaesthesia, respectively. We conclude that isoflurane reduces the infusion requirements of rocuronium by changing the pharmacodynamic behaviour.

Adolescent↗
PubMed1988

Inspired oxygen and nitrous oxide concentrations in volunteers during nitrous oxide sedation with a Hudson mask.

Ten volunteers were given varying ratios of oxygen and nitrous oxide at 4, 6 and 8 litres per minute using a Hudson mask delivery system. Maximum and minimum inspired oxygen concentrations, maximum inspired nitrous oxide concentrations and end tidal carbon dioxide concentrations were measured using the Datex Cardiocap CCI-104 monitor. Although pharyngeal oxygen fraction varies with the Hudson mask because the inspiratory flow exceeds the entrainment of the mask by a variable amount during much of the cycle, at 8 litres/minute flow with a ratio of 3 to 5, oxygen to nitrous oxide, safe levels of oxygen were delivered (range of means 26-31%) with basal nitrous oxide levels (mean maximum inspired N2O, 34%). When nitrous oxide sedation is used clinically, nitrous oxide must be used with consideration of safe oxygen levels. This study did not detect unsafe pharyngeal oxygen levels in the ratios investigated, where the maximum delivered nitrous oxide concentration was 75%.

Humans↗
PubMed1984

Nitrous oxide sedation in dentistry. A comparison between Rotameter settings, pharyngeal concentrations and blood levels of nitrous oxide.

Nitrous oxide concentrations (V/V) at the delivery Rotameters block, nasal mask, pharynx and venous blood, were compared. There was a dilution of approximately 50% of the delivered nitrous oxide at the nasal mask which was further reduced in the pharynx. Venous blood concentrations 10 minutes after inhalation of nitrous oxide were low but as would be calculated from pharyngeal concentrations. After 5 minutes of oxygenation venous blood nitrous oxide concentrations were still relatively high. A total of 92% of subjects experienced a satisfactory effect with 30% nitrous oxide or less in the pharynx.

Adult↗
PubMed1991

Recovery profile after desflurane-nitrous oxide versus isoflurane-nitrous oxide in outpatients.

Thirty-eight healthy outpatients undergoing elective surgical procedures lasting 1-3 h were randomly assigned to receive either desflurane 3% (approximately 0.5 MAC) or isoflurane 0.6% (approximately 0.5 MAC) for maintenance of general anesthesia with nitrous oxide 60% in oxygen after a standardized induction sequence consisting of fentanyl 3 micrograms.kg-1, thiopental 4 mg.kg-1, and succinylcholine 1-1.5 mg.kg-1, intravenously. Although anesthetic conditions were similar during operations in the two treatment groups, significant differences were noted in the recovery profiles as measured by elimination kinetics, psychometric testing, and visual analog scales (to assess subjective feelings). The time required for the end-tidal concentration to decrease by 50% was 2.5 +/- 0.8 min for desflurane vs. 9.5 +/- 3.4 min for isoflurane (mean +/- standard deviation [SD]). Times to awakening and ability to follow simple commands were significantly shorter after desflurane than after isoflurane (5.1 +/- 2.4 vs. 10.2 +/- 7.7 min 6.5 +/- 2.3 min vs. 11.1 +/- 7.9 min, respectively). Postoperatively, patients who received desflurane exhibited less impairment of cognitive function (as measured using the Digit-Symbol Substitution Test) than did those who received isoflurane. Furthermore, visual analog scores indicated that patients receiving desflurane experienced significantly less discomfort (pain), drowsiness, fatigue, clumsiness, and confusion in the early postoperative period. We conclude that desflurane may offer clinical advantages over isoflurane when used for maintenance of anesthesia during outpatient surgical procedures.

Adult↗
PubMed1996

Sevoflurane-nitrous oxide or halothane-nitrous oxide for paediatric bronchoscopy and gastroscopy.

We have studied 120 infants and children, in three age groups (3-11 months, 1-5 yr and 6-15 yr), to compare anaesthesia with sevoflurane or halothane for bronchoscopy or gastroscopy, or both. Premedication or i.v. anaesthetic agents were not used. Patients were allocated randomly to receive either 7% sevoflurane or 3% halothane in 66% nitrous oxide in oxygen for induction of anaesthesia. The same inspired mixture was continued during bronchoscopy while the concentration of the inhalation agent was reduced by 50% during gastroscopy. Induction times were shorter for infants than for children and shorter for sevoflurane than for halothane. Cardiac arrhythmias were significantly more frequent during halothane than during sevoflurane anaesthesia. Physiological and psychomotor recovery were more rapid after sevoflurane than after halothane. At 24-h follow-up, children who received sevoflurane had significantly less nausea and vomiting. We conclude that sevoflurane was superior to halothane for paediatric bronchoscopy and gastroscopy.

Adolescent↗
PubMed1991

Comparison of sufentanil-nitrous oxide anaesthesia with fentanyl-nitrous oxide anaesthesia in geriatric patients undergoing major abdominal surgery.

We have measured haemodynamic changes and plasma concentrations of catecholamines during sufentanil-nitrous oxide and fentanyl-nitrous oxide anaesthesia in a controlled, randomized, double-blind study of 20 geriatric patients (age 65-86 yr) undergoing major abdominal surgery. Fentanyl 7 micrograms kg-1 followed by infusion of 3 micrograms kg-1 h-1 was compared with sufentanil 1 micrograms kg-1 followed by 0.4 micrograms kg-1 h-1. The opioid was supplemented with 60-67% nitrous oxide in oxygen. Haemodynamic changes, plasma concentrations of catecholamines (by high pressure liquid chromatography) and opioids (by radioimmunoassay), and myocardial lactate extraction were measured in the awake state, and at defined times during anaesthesia and surgery. Haemodynamic state was stable during induction and tracheal intubation in both groups, while during stressful operative periods there were increases in mean arterial pressure (17% in the fentanyl group; 11% in the sufentanil group), heart rate (fentanyl 20%, sufentanil 14%) and plasma concentrations of catecholamines (adrenaline: fentanyl 316%, sufentanil 86%; noradrenaline: fentanyl 78%, sufentanil 186%) in both groups. Sufentanil was similar to fentanyl in attenuating the haemodynamic and hormonal responses to surgical stimulation. In two patients in the fentanyl group and three in the sufentanil group, myocardial lactate production was observed temporarily, indicating myocardial ischaemia caused by surgical stress.

Abdomen↗
PubMed1989

Randomized comparison of outcome after propofol-nitrous oxide or enflurane-nitrous oxide anaesthesia in operations of long duration.

A randomized, prospective, comparative study was performed to evaluate induction characteristics, haemodynamic changes and recovery in 60 ASA I-II patients undergoing mainly gynaecological laparotomies with either propofol or thiopentone-enflurane anaesthesia. The propofol group (n = 30) received 2 mg.kg-1 propofol for induction of anaesthesia followed by propofol infusion. The thiopentone-enflurane group (n = 30) received thiopentone 4 mg.kg-1 for induction followed by enflurane (0.5-2 per cent). All patients received nitrous oxide (66 per cent] in oxygen begun one minute after tracheal intubation, and fentanyl (1.5 micrograms.kg-1) four minutes prior to induction. Other drugs administered during or after anaesthesia were similar among the groups. Haemodynamic measurements were similar between propofol and enflurane groups except after tracheal intubation when the mean arterial pressure was lower in the propofol group (P less than 0.05). The propofol group had significantly less (P less than 0.01) emesis in the recovery room than the enflurane group. The propofol group experienced significantly less (P less than 0.05) dizziness, depression/sadness and hunger than the enflurane group in the postoperative period as assessed with a visual analogue questionnaire. We conclude that propofol provided better outcome than enflurane in terms of these nonvital but annoying outcome measures after relatively long intra-abdominal operations.

Adult↗
PubMed1988

Propofol-nitrous oxide versus thiopental-isoflurane-nitrous oxide for general anesthesia.

One hundred and twenty patients undergoing elective operations were randomly assigned to receive anesthesia with either thiopental, 4 mg/kg-isoflurane, 0.2-3%-nitrous oxide, 60-70% (control) or propofol, 2 mg/kg-propofol infusion, 1-20 mg/min-nitrous oxide, 60-70% (propofol). Although anesthetic conditions were similar during the operation, differences were noted in the recovery characteristics. For non-major (superficial) surgical procedures, the times to awakening, responsiveness, orientation, and ambulation were significantly shorter in the propofol group (4 +/- 3, 5 +/- 4, 6 +/- 4, and 104 +/- 36 min) than in the control group (8 +/- 7, 9 +/- 7, 11 +/- 9, and 142 +/- 61 min, respectively). In addition, less nausea and vomiting (20 vs. 45%) and significantly less psychomotor impairment was noted in the non-major propofol (vs. control) group. Following major abdominal operations, recovery characteristics did not differ between propofol and control groups. Delayed emergence (greater than 20 min), significant psychometric impairment, and a high overall incidence of postoperative side effects (55-60%) were noted in both drug treatment groups. The authors conclude that propofol-nitrous oxide compares favorably to thiopental-isoflurane-nitrous oxide for maintenance of anesthesia during short outpatient procedures. However, for major abdominal operations, propofol anesthesia does not appear to offer any clinically significant advantages over a standard inhalational anesthetic technique.

Adult↗
PubMed1999

Comparison of sevoflurane-nitrous oxide and propofol-alfentanil-nitrous oxide anaesthesia for minor gynaecological surgery.

We studied 44 patients undergoing minor gynaecological surgery, anaesthetized in random order with sevoflurane-nitrous oxide or propofol-alfentanil-nitrous oxide. Operating conditions, recovery and postoperative nausea and vomiting (PONV) were assessed. For postoperative analgesia, all patients were given ketoprofen 100 mg rectally at the end of anaesthesia. Patients and gynaecologists were equally satisfied with both anaesthetic techniques. Patients given propofol woke up (3.5 vs 6.5 min), became orientated (5.0 vs 7.5 min) and were able to walk (57 vs 69 min) significantly (P < 0.05) earlier than those given sevoflurane, but there were no differences in times to achieve home readiness (166 vs 149 min) or in psychomotor recovery between the two groups. Intrauterine bleeding and PONV were more common with sevoflurane (incidence of PONV 64%) than with propofol anaesthesia (incidence of PONV 5%). We conclude that propofol-alfentanil is preferable to sevoflurane in ultra-short anaesthesia for minor gynaecological surgery.

Adult↗
PubMed1999

Propofol-nitrous oxide versus sevoflurane-nitrous oxide for strabismus surgery in children.

Vomiting is a common problem following strabismus surgery. We compared the effects of propofol-N2O and sevoflurane-N2O on the incidence of oculocardiac reflex and postoperative nausea and vomiting. Forty unpremedicated children, aged 3-15 years were randomly assigned to two groups of 20 patients. In group 1, anaesthesia was induced and maintained with propofol infusion (173 +/- 41 micrograms.kg-1.min-1). In group 2, anaesthesia was induced with N2O (66%) in O2 and incremental sevoflurane via face mask and maintained with sevoflurane. Both groups received 66% N2O in O2 throughout surgery. The overall incidence of vomiting and antiemetic requirement in the first 24 h was significantly higher in sevoflurane-N2O group than propofol-N2O group (P < 0.05). The propofol-N2O group had significantly more episodes of oculocardiac reflex than sevoflurane-N2O group (P < 0.05). Propofol-N2O anaesthesia results in a significantly lower incidence of postoperative vomiting, yet a significantly higher incidence of oculocardiac reflex.

Adolescent↗