It is possible to perform a double-blind hyperbaric session: a double-blinded randomized trial performed on healthy volunteers.

In hyperbaric medicine, blinded trials are remarkably few, making results susceptible to criticism. The scopes of the present study are to present a method for a double-blinded randomized clinical study and evaluate the validity of the method in a hyperbaric setting. Twenty-two healthy volunteers with no diving experience were included. The volunteers were randomized either to a "therapeutic pressure" group (15 msw, 253 kPa) or to a "placebo" group (2 msw, 120 kPa). The two profiles were made equal regarding noise, temperature and ventilation. The volunteers were asked whether they had been exposed to placebo or therapeutic pressure. They were asked to present their certainness of the answer on a visual analogue scale (VAS). Fisher's exact test calculates a probability of P = 0,328, which indicates that the volunteers have no valid opinion as to whether they were exposed to 15 msw or to 2 msw. It is found that it is possible to perform a blinded treatment on healthy volunteers with no prior diving experience.

Postoperative volume balance: does stroke volume increase in Trendelenburg's position?

In healthy humans, stroke volume (SV) and cardiac output (CO) do not increase with expansion of the central blood volume by head-down tilt or administration of fluid. Here, we exposed 85 patients to Trendelenburg's position about one hour after surgery while cardiovascular variables were determined non-invasively by Modelflow. In Trendelenburg's position, SV (83 ± 19 versus 89 ± 20 ml) and CO (6·2 ± 1·8 versus 6·8 ± 1·8 l/min; both P<0·05) increased, while heart rate (75 ± 15 versus 76 ± 14 b min-1 ) and mean arterial pressure were unaffected (84 ± 15 versus 84 ± 16 mmHg). For the 33 patients (39%) with a > 10% increase in SV (from 78 ± 16 to 90 ± 17 ml) corresponding to an increase in CO from 5·9 ± 1·5 to 6·9 ± 1·6 l min-1 (P<0·05) when tilted head-down, administration of 250 ml Ringer's lactate solution increased SV (to 88 ± 18 ml) and CO (to 6·8 ± 1·7 l min-1 ). In conclusion, determination of SV and/or CO in Trendelenburg's position can be used to evaluate whether a patient is in need of IV fluid as here exemplified after surgery.

Monitoring of neuromuscular transmission.

Considerable advances have been achieved in developing new techniques and equipment for the assessment of neuromuscular transmission during anaesthesia. This paper is a review of the methods currently used in research as well as in daily clinical practice. The principles of nerve stimulation and the evoked muscular response, the function of the nerve stimulator, features of the stimulation electrodes, possible stimulation sites, and the various stimulation patterns with their responses are described. The methods for measurement of neuromuscular function with mechanomyography, electromyography and acceleromyography are reviewed, and commercially available equipment for each purpose is described. The clinical evaluation of the responses to nerve stimulation, and which stimulation patterns to prefer during onset, maintenance and recovery of neuromuscular block are dealt with, as well as possible errors to be encountered. Arguments are given for routine use of neuromuscular monitoring in the clinical setting, and situations where monitoring of neuromuscular function are of particular importance are noted.

[The laryngeal mask: a new alternative to the facial mask and the endotracheal tube]. / Larynxmasken: Et nyt alternativ til ansigtsmasken og endotrakealtuben.

The laryngeal mask is a new airway system for use under anaesthesia which assumes a position between the face mask and the endotracheal tube. Employment of this system achieves several of the advantages of intubation while the disadvantages are avoided. The possibilities which this system offers in cases of difficult intubation are particularly interesting, especially in unexpected.

Pollution with nitrous oxide using laryngeal mask or face mask.

BACKGROUND: As environmental pollution by nitrous oxide may influence the health of the personnel working in operating theatres, the incidence and magnitude of nitrous oxide (N2O) leakage, when using a face mask or a laryngeal mask airway (LMA) for controlled ventilation, were studied in 34 patients scheduled for elective cystoscopy. METHODS: A semi-closed gas delivery ventilation system with active scavenging was used. The N2O concentrations were measured every 8 s at a position 30 cm above the patient's mouth with a N2O gas monitor (GD 200, Simrad Optronics). RESULTS: When using a face mask, the leakage of N2O resulted in a N2O concentration of 157 (85-332) p.p.m. (parts per million) (median concentration and 25% and 75% percentiles). With the LMA, a lower median concentration of N2O of 60 (28-126) p.p.m. was found (P=0.04). With the face mask, a concentration above 100 p.p.m. was found during 51% of the exposure time compared to 24% of the time in the LMA group. CONCLUSION: Environmental pollution was less with the LMA than the face mask, but under the conditions of the study both modes of airway management were associated with levels of N2O peak concentrations in the breathing zone of anaesthetists that are deemed to be excessively high by the Danish National Institute for Occupational Safety.

Isobutyl-nitrite-induced methemoglobinemia; treatment with an exchange blood transfusion during hyperbaric oxygenation.

A young man was accidentally intoxicated with isobutyl nitrite by a threefold lethal dose. Due to nitrites' ability to change hemoglobine into methemoglobine the patient showed signs of severe hypoxia, which could not be treated by conventional means. Therefore the patient was rapidly transferred to a hyperbaric chamber. The patient was treated with pure oxygen at 283 kPa under which a blood exchange transfusion was performed. The patient fully recovered.

Perioperative monitoring of neuromuscular transmission using acceleromyography prevents residual neuromuscular block following pancuronium.

The frequency of postoperative residual neuromuscular block following the use of the long-acting non-depolarizing muscle relaxants is high, and manual evaluation of the response to nerve stimulation does not eliminate the problem. In this prospective and randomized study we evaluated the hypothesis that perioperative use of acceleromyography would allow for a more rational and precise administration of the long-acting muscle relaxant pancuronium resulting in a decrease in 1) the incidence and severity of postoperative residual neuromuscular block, 2) the amount of pancuronium used, and 3) the time from end of surgery to tracheal extubation. Forty adult patients were randomized into two groups, one managed without the use of a nerve stimulator, the other monitored using train-of-four (TOF) nerve stimulation and acceleromyography. All patients were anaesthetized with diazepam, fentanyl, thiopentone, nitrous oxide, and in some patients halothane, and they all received pancuronium 0.08-0.1 mg kg-1 for tracheal intubation, and 1-2 mg for maintenance of neuromuscular block. Neostigmine 2.5 mg preceded by atropine 1 mg was administered for reversal. In the patients managed without a nerve stimulator, the trachea was extubated when the anaesthetist judged the neuromuscular function to have recovered adequately for upper airway protection and spontaneous ventilation. In patients monitored with acceleromyography, the trachea was extubated when the TOF ratio was above 0.70. In all 40 patients, TOF ratio was measured using mechanomyography immediately after tracheal extubation and the patients were evaluated for clinical signs of residual neuromuscular block.(ABSTRACT TRUNCATED AT 250 WORDS)

Residual neuromuscular block is a risk factor for postoperative pulmonary complications. A prospective, randomised, and blinded study of postoperative pulmonary complications after atracurium, vecuronium and pancuronium.

BACKGROUND: After anaesthesia involving pancuronium a high incidence of both residual neuromuscular block and postoperative pulmonary complications (POPC) has been reported. The aim of this study was to compare the incidence of POPC following the use of pancuronium, atracurium, and vecuronium, and to examine the effect of residual neuromuscular block on the incidence of POPC. METHODS: A total of 691 adult patients undergoing abdominal, gynaecological, or orthopaedic surgery under general anaesthesia were randomised to receive either pancuronium, atracurium, or vecuronium. Perioperatively, the response to train-of-four (TOF) nerve stimulation was evaluated manually. Postoperatively, the TOF ratios were measured mechanomyographically, and through a 6-day follow-up the patients were examined for pulmonary complications. RESULTS: The incidence of residual block, defined as a TOF ratio < 0.7, was significantly higher in the pancuronium group (59/226: 26%) than in the atracurium/vecuronium groups (24/450: 5.3%). In the pancuronium group, significantly more patients with residual block developed POPC (10/59: 16.9%) as compared to patients without residual block (8/167: 4.8%). In the atracurium/vecuronium groups, the incidence of POPC was not significantly different in patients with (1/24: 4.2%) or without (23/426: 5.4%) residual block. Multiple regression analysis indicated that abdominal surgery, age, long-lasting surgery, and a TOF ratio < 0.7 following the use of pancuronium were potential risk factors for the development of POPC. CONCLUSION: Postoperative residual block caused by pancuronium is a significant risk factor for development of POPC.

Double-blind comparison of the variability in spontaneous recovery of cisatracurium- and vecuronium-induced neuromuscular block in adult and elderly patients.

BACKGROUND: This study was designed to compare variability in the offset of two neuromuscular blocking agents with different elimination pathways. METHODS: The spontaneous recovery profiles of cisatracurium and vecuronium were compared in adult (18-64 years) and elderly (> or =65 years) patients receiving N2O/O2/fentanyl/propofol anaesthesia. Patients were randomised to receive an initial bolus dose and maintenance doses of 3xED95, respectively, 0.6xED95 for cisatracurium (0.15 and 0.03 mg.kg-1) or 2xED95, respectively, and 0.4xED95 for vecuronium (0.1 and 0.02 mg.kg(-1)), as recommended in their prescribing information. Administration of the study drugs was double-blinded, and neuromuscular transmission was monitored using mechanomyography of the evoked response of the adductor pollicis, following ulnar nerve stimulation. RESULTS: The clinically effective duration (minutes) of the initial bolus dose, defined as the mean time to 25% T1 recovery (+/-SD), for the adult and elderly patients was 53.5+/-9.8 and 57.3+/-11.5 for cisatracurium, respectively, and 34.1+/-9.0 and 47.5+/-14.4 for vecuronium, respectively. The duration of spontaneous sufficient recovery (SSR), defined as the mean (+/-SD) time interval in minutes from 25% T1 recovery to a T4:T1 ratio > or =0.8 after the last bolus dose, for the adult, respectively, elderly patients was 28.3+/-8.0 and 31.7+/-10.0 for cisatracurium and 38.5+/-13.2 and 60.3+/-26.1 for vecuronium. CONCLUSION: Whereas both the clinically effective duration and the duration of SSR are comparable between the adult and the elderly patients receiving cisatracurium, they differ substantially between these two age groups for vecuronium. Furthermore, the variability in offset is significantly lower in patients receiving cisatracurium, especially in the elderly, which may be of particular clinical interest.

Remifentanil vs. alfentanil infusion in non-paralysed patients: a randomized, double-blind study.

BACKGROUND AND OBJECTIVE: Remifentanil has a short duration of action and constant elimination, which allow administration of high doses, without prolonging recovery. Remifentanil has been compared to alfentanil, as part of a total intravenous anaesthetic technique, where remifentanil provided better anaesthetic conditions than alfentanil, without adverse effect on recovery. However, these results were obtained during anaesthesia involving neuromuscular blockade, which may mask both signs of insufficient anaesthesia and side-effects such as muscle rigidity. The aim of this study was to compare remifentanil with alfentanil for anaesthesia without neuromuscular blockade. METHODS: We performed a prospective, randomized, double-blind, four-centre study to compare remifentanil infusion 15 microg kg(-1) h(-1) and alfentanil infusion 60 microg kg(-1) h(-1), using a total intravenous technique for non-paralysed patients, and the laryngeal mask airway for airway management. We enrolled 192 patients, 18-65 yr of age with ASA I-II, undergoing minor surgery. The primary endpoint was the number of patients having pre-defined responses to surgical stimulation. A number of secondary criteria was evaluated to assess undesirable properties of the procedures. RESULTS: In the alfentanil group, 85% of patients responded to surgical stimulation, vs. 35% in the remifentanil group (P < 0.0001). No difference was found in recovery data, or in any other parameter than those related to insufficient anaesthesia. CONCLUSIONS: The remifentanil-based technique provided significantly better anaesthetic conditions than the alfentanil-based technique in the setting of this study, without causing any significant adverse effects.