Multicenter randomized comparison of the efficacy and safety of xenon and isoflurane in patients undergoing elective surgery

BACKGROUND

All general anesthetics used are known to have a negative inotropic side effect. Since xenon does not have a negative inotropic effect, it could be an interesting future general anesthetic. The aim of this clinical multicenter trial was to test the hypothesis of whether recovery after xenon anesthesia is faster compared with an accepted, standardized anesthetic regimen and that it is as effective and safe.

METHOD

A total of 224 patients in six centers were included in the protocol. They were randomly assigned to receive either xenon (60 +/- 5%) in oxygen or isoflurane (end-tidal concentration, 0.5%) combined with nitrous oxide (60 +/- 5%). Sufentanil (10 mcirog) was intravenously injected if indicated by defined criteria. Hemodynamic, respiratory, and recovery parameters, the amount of sufentanil, and side effects were assessed.

RESULTS

The recovery parameters demonstrated a statistically significant faster recovery from xenon anesthesia when compared with isoflurane-nitrous oxide. The additional amount of sufentanil did not differ between both anesthesia regimens. Hemodynamics and respiratory parameters remained stable throughout administration of both anesthesia regimens, with advantages for the xenon group. Side effects occurred to the same extent with xenon in oxygen and isoflurane-nitrous oxide.

CONCLUSION

This first randomized controlled multicenter trial on the use of xenon as an inhalational anesthetic confirms, in a large group of patients, that xenon in oxygen provides effective and safe anesthesia, with the advantage of a more rapid recovery when compared with anesthesia using isoflurane-nitrous oxide.

Prolonged isoflurane sedation of intensive care unit patients with the Anesthetic Conserving Device

OBJECTIVE

To test the efficacy and patient safety of a new method for administering isoflurane for prolonged sedation in the intensive care unit.

DESIGN

Randomized controlled trial.

SETTING

Multidisciplinary university intensive care unit, January 2002 to July 2003.

PATIENTS

Forty ventilator-dependent intensive care unit patients 18-80 yrs old, expected to need >12 hrs sedation.

INTERVENTIONS

Patients were randomized to sedation with inhaled isoflurane via the Anesthetic Conserving Device or intravenous midazolam infusion. Study duration was 96 hrs or until extubation.

MEASUREMENTS AND MAIN RESULTS

Primary end points were wake-up times from termination of sedative administration and proportion of time within a predefined desired interval on a sedation scale (Bloomsbury Sedation Score). Practical and patient-related complications with the Anesthetic Conserving Device were noted. Hemodynamic, hepatic, and renal side effects were monitored. Wake-up times were significantly shorter in the isoflurane group than in the control group (time to extubation [mean +/- sd] 10 +/- 5 vs. 252 +/- 271 mins, time to follow verbal command 10 +/- 8 vs. 110 +/- 132 mins). Proportion of time within the desired sedation interval was comparable between groups (isoflurane 54%, midazolam 59% of sedation time). Few minor practical problems with this new method for isoflurane administration were noted. No serious complications related to either sedative drug occurred. We found no hemodynamic, hepatic, or renal adverse effects related to either sedative protocol.

CONCLUSIONS

Isoflurane via the Anesthetic Conserving Device is a safe and efficacious method for sedation in the intensive care unit, with short wake-up times after termination of administration. The Anesthetic Conserving Device allows easily titratable administration of isoflurane without costly equipment and can be safely managed by nursing staff.

Gum Elastic Bougie-guided Insertion of the ProSeal™ Laryngeal Mask Airway Is Superior to the Digital and Introducer Tool Techniques

Background

The authors compare three techniques for insertion of the ProSeal laryngeal mask airway.

Methods

Two hundred forty healthy patients aged 18-80 yr were randomly allocated for ProSeal laryngeal mask airway insertion using the digital, introducer tool (IT), or gum elastic bougie (GEB)-guided techniques. The digital and IT techniques were performed according to the manufacturer's instructions. The GEB-guided technique involved priming the drain tube with the GEB, placing the GEB in the esophagus under direct vision, and inserting the ProSeal laryngeal mask airway using the digital technique with the GEB as a guide. Failed insertion was defined by any of the following criteria: (1) failed pharyngeal placement; (2) malposition (air leaks, negative tap test results, or failed gastric tube insertion if pharyngeal placement was successful); and (3) ineffective ventilation (maximum expired tidal volume < 8 ml/kg or end-tidal carbon dioxide > 45 mmHg if correctly positioned). Any visible or occult blood was noted. Sore throat, dysphonia, and dysphagia were assessed 18-24 h postoperatively.

Results

Insertion was more frequently successful with the GEB-guided technique at the first attempt (GEB, 100%; digital, 88%; IT, 84%; both P < 0.001), but success after three attempts was similar (GEB, 100%; digital, 99%; IT, 98%). The time taken to successful placement was similar among groups at the first attempt but was shorter for the GEB-technique after three attempts (GEB, 25 +/- 14 s; digital, 33 +/- 19 s; IT, 37 +/- 25 s; both: P < 0.003). There were no differences in the frequency of visible blood, but occult blood occurred less frequently with the GEB-guided technique (GEB, 12%; digital, 29%; IT, 31%; both: P < 0.02) but was similar among techniques if insertion was successful at the first attempt. There were no differences in postoperative airway morbidity. CONCLUSION The GEB-guided insertion technique is more frequently successful than the digital or IT techniques. The authors suggest that the GEB-guided technique may be a useful backup technique for when the digital and IT techniques fail.

Rapid sequence induction: a national survey of practice

We performed a national postal survey exploring anaesthetists' practice in rapid sequence induction. All respondents used pre-oxygenation, although the technique employed, and its reliability, varied. Thiopental and succinylcholine, given after waiting for signs of loss of consciousness, were the most widely used drugs for rapid sequence induction. Propofol and rocuronium were used by more than a third of respondents, and most respondents (75%) also routinely administered an opioid. Cricoid pressure was used universally but the practice of its application varied widely. The commonest aids used if intubation was difficult were the gum elastic bougie, the long laryngoscope blade and the laryngeal mask. After failed intubation, approximately half of respondents would maintain the supine position. Failure to intubate at rapid sequence intubation had been seen by 45% of respondents but harm was uncommon. In contrast, 28% had seen regurgitation, which frequently led to considerable harm and to three deaths. In spite of this, practice of a failed intubation drill was uncommon (15%) and anaesthetic assistants were rarely known to practice application of cricoid pressure. Consultants were less likely than trainees to use rocuronium as a muscle relaxant, and more likely to choose morphine if administering an opioid. They were less likely to practice a failed intubation drill. Other aspects of practice varied little between grades. This survey suggests that many anaesthetists do not follow best practice when performing a rapid sequence induction.

Airway protection by the laryngeal mask. A barrier to dye placed in the pharynx

Methylene blue was placed in the pharynx of 64 patients undergoing anaesthesia with the laryngeal mask. No leak of dye into the larynx was detected on fibreoptic inspection of the inside of the mask in any subject. The use of the laryngeal mask as a means of protecting the airway during procedures such as minor nasal operations is therefore supported.

Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway

PURPOSE

To compare two airway management techniques, face mask (FM) with oropharyngeal airway and laryngeal mask airway (LMA), with respect to the effectiveness of positive pressure ventilation and airway maintenance.

METHODS

After induction of anaesthesia, two airway management techniques (FM or LMA) and three peak pressures (20, 25 and 30 cm H2O) were randomly applied during controlled ventilation in 60 patients. Data collected included inspiratory and expiratory volumes and presence of gastro-oesophageal insufflation. Leak was calculated by subtracting the expiratory from the inspiratory volume, expressed as a fraction of the inspiratory volume.

RESULTS

Expiratory volumes (mean +/- SD) at 20, 25 and 30 cm H2O for LMA ventilation were 893 +/- 260, 986 +/- 276 and 1006 +/- 262 respectively, and for FM ventilation 964 +/- 264, 1100 +/- 268 and 1116 +/- 261. Leak fractions at 20, 25 and 30 cm H2O for LMA ventilation were 0.21 +/- 0.15, 0.24 +/- 0.18 and 0.26 +/- 0.18 respectively, and for FM ventilation 0.14 +/- 0.09, 0.14 +/- 0.09 and 0.12 +/- 0.08. The frequency of gastro-oesophageal insufflation was 1.6%, 5% and 5% for the LMA and 5%, 15% and 26.6% for the FM for ventilation pressures of 20, 25 and 30 cm H2O respectively which was greater with LMA use.

CONCLUSION

Ventilation was adequate in all patients using both techniques. Leak was pressure dependent and greater with LMA use. Most of the leak was vented to the atmosphere via the pharynx. Gastro-oesophageal insufflation was more frequent with ventilation using the face mask. LMA use with positive pressure ventilation would appear to be a better airway management method than the face mask.

A survey of anaesthetic misadventures

Reports of anaesthetic misadventures were regularly collected in the Anaesthetic Department of a district general hospital, to identify recurring problems. Eighty-one misadventures, none of which had serious outcome, were reported during a 6-month period, in which 8312 anaesthetics were administered. Human error was more frequently responsible than equipment failure, and failure to perform a normal check was the factor most frequently associated. Local hazard warnings were circulated when necessary to members of the Department, and the reports formed the basis of departmental discussion and teaching.

A prospective evaluation of clinical tests for placement of laryngeal mask airways

BACKGROUND

Reliable tests of correct anatomic placement of the laryngeal mask airway (LMA) may enhance safety during use and minimize the need for fiberoptic instrumentation during airway manipulation through the device. This study assessed the correlation between the outcomes of nine clinical tests to place the LMA and the anatomic position of the device as graded on a standard fiberoptic scale.

METHODS

During 150 anesthetics, the outcome of nine clinical tests of correct placement was individually scored as satisfactory (positive) or unsatisfactory (negative) for clinical use of the LMA. Anatomic placement was assessed (by fiberoptic evaluation) by an anesthesiologist, who was blinded to the placement of the device, as grade 1, vocal cords not seen; grade 2, cords plus the anterior epiglottis seen; grade 3, cords plus the posterior epiglottis seen; and grade 4, only vocal cords seen. The outcomes of clinical tests were correlated with fiberoptic grade.

RESULTS

Tests that correlated with the fiberoptic grade were the ability to generate an airway pressure of 20 cm water, the ability to ventilate manually, a black line on the LMA in midline, anterior movement of the larynx, outward movement of the LMA on inflation of the cuff, and movements of the reservoir bag with spontaneous breathing. Two tests, ability to generate airway pressure of 20 cm water and ability to ventilate manually, correlated with fiberoptic grades 4 and 3 combined (i.e., the epiglottis was supported by the LMA) and grade 2 (the epiglottis was not supported by the LMA). Tests with poor correlation with fiberoptic grade were the presence of resistance at the end of insertion, inability to advance LMA after inflation of the cuff, and presence of a capnographic trace.

CONCLUSIONS

The outcome of clinical tests correlates with the anatomic placement of LMAs, as judged by fiberoptic examination. Two tests that best correlated with the fiberoptic grade were the ability to generate airway pressure of 20 cm water and the ability to ventilate manually.

The Triservice anaesthetic apparatus

The Triservice anaesthetic apparatus is a draw-over using ambient air as the primary carrier gas. Its modules are a self-inflating bag, a vaporiser, a supplementary oxygen regulator and a ventilator; each is described. The outputs of halothane and trichloroethylene were measured with changes of temperature, continuous and intermittent gas flows and with alteration in barometric pressure. The output of oxygen from the Houtonox regulator was measured and the effect of the oxygen supplementation on the inspired oxygen concentration determined. The resistance to airflow of the apparatus was also measured and the effect of extreme cold observed. The merits, limitations and the way in which the equipment may be used are discussed. A carrying case with equipment for 10 anaesthetics is illustrated.

Inhalation anesthesia in experimental radiotherapy: a reliable and time-saving system for multifractionation studies in a clinical department

An inhalation anesthesia system has been employed to overcome several of the limitations associated with the use of sodium pentobarbital and other i.p. administered anesthetics in experimental radiotherapy. The described method is reliable and time-saving. The depth and duration of anesthesia are easily controllable. Only 4 deaths have occurred with more than 6000 animal exposures. The use of polystyrene jigs is shown to provide adequate thermal isolation. Oxygen as a carrier of the anesthetic agent is expected to prevent a reduced tissue oxygenation and its radiobiological consequences. The whole system is constructed as a mobile unit in which up to 16 mice or rats can be anesthetized simultaneously and irradiated in a single field with clinical treatment equipment during short time intervals between patient irradiations. The described advantages of this method make it specially suited for experiments with protracted fractionation schedules.

Laryngeal mask anaesthesia for repair of cleft palate

A method of anaesthesia for repair of cleft palate is described. The baby had Pierre Robin syndrome and tracheal intubation had proved to be impossible.

Pre-oxygenation--how long?

Pre-oxygenation was studied in 12 fit volunteers and 20 patients using an oxygen flow of 8 litres/minute delivered from a standard anaesthetic machine via a Magill or Bain breathing attachment. End-tidal nitrogen concentrations of 4% or less were achieved within 3 minutes; the fastest times were achieved using the Magill breathing system when the reservoir bag was filled with oxygen prior to application to the face. Gas-tight fits of face masks on patients were found to be essential.

A Randomized Controlled Trial Comparing the ProSeal™ Laryngeal Mask Airway with the Laryngeal Tube Suction in Mechanically Ventilated Patients

Background

The ProSeal Laryngeal Mask Airway (PLMA) (Laryngeal Mask Company, Henley-on-Thames, United Kingdom) is a new laryngeal mask with a modified cuff designed to improve its seal and a drain tube for gastric tube placement. Similarly, the Laryngeal Tube Suction (LTS) (VBM Medizintechnik Gmbh, Sulz a.N, Germany) is a new laryngeal tube that also has an additional channel for gastric tube placement. This study compared the placement and functions of these two devices.

Methods

One hundred fifty patients undergoing general anesthesia for elective surgery were randomly allocated to the PLMA (n = 75) or LTS (n = 75). Oxygenation and ventilation, ease of insertion, fiberoptic view, oropharyngeal leak pressure, ventilatory data, ease of gastric tube insertion, and postoperative airway morbidity were determined.

Results

After successful insertion of the devices in 96% of patients with the PLMA and in 94.4% with the LTS it was possible to maintain oxygenation, ventilation, and respiratory mechanics during the entire duration of surgery. Successful first and second attempt insertion rates were 57 patients (76%) and 15 patients (20%), respectively, for the PLMA and 60 patients (80%) and 11 patients (14.6%), respectively, for the LTS. Airway placement was unsuccessful with the PLMA in three patients and with the LTS in four patients. Time to achieve an effective airway was 36 +/- 24 s with the PLMA versus 34 +/- 25 s with the LTS. Gastric tube insertion was possible in 97.3% of patients with the PLMA and in 96% with the LTS.

Conclusions

With respect to both physiologic and clinical function, the PLMA and LTS are similar and either device can be used to establish a safe and effective airway in mechanically ventilated anesthetized adult patients.

The Bain anaesthetic system. An assessment during controlled ventilation

The Bain anaesthetic breathing system-a modified Mapleson 'D' circuit10-had been evaluated during anaesthesia using controlled ventilation. Results obtained from over 140 patients show that a highly predictable PaCO2 may be obtained by adjusting the fresh gas inflow according to body weight in patients weighing over 40 kg (mean PaCO2 at a fresh gas inflow of 70 ml/kg/minute=40.8 mmHg; mean PaCO2 at a fresh gas inflow of 100 ml/kg/minute=34.3 mmHg). The circuit is long enough to provide flexibility but may even be doubled in length without affecting performance. Simple lung ventilators delivering air or oxygen may be used satisfactorily as anaesthetic ventilators for patients of all ages. In addition, the circuit is lightweight, disposable but re-usable, facilitates pollution control and is easily used as an independent resuscitator. It is suggested that it may qualify as a universal breathing system.

The New Perilaryngeal Airway (CobraPLA™) Is as Efficient as the Laryngeal Mask Airway (LMA™) but Provides Better Airway Sealing Pressures

The Laryngeal Mask Airway (LMA) is a frequently used efficient airway device, yet it sometimes seals poorly, thus reducing the efficacy of positive-pressure ventilation. The Perilaryngeal Airway (CobraPLA) is a novel airway device with a larger pharyngeal cuff (when inflated). We tested the hypothesis that the CobraPLA was superior to the LMA with regard to insertion time and airway sealing pressure and comparable to the LMA in airway adequacy and recovery characteristics. After midazolam and fentanyl administration, 81 ASA physical status I-II outpatients having elective surgery were randomized to receive an LMA or CobraPLA. Anesthesia was induced with propofol (2.5 mg/kg IV), and the airway was inserted. We measured 1) insertion time; 2) adequacy of the airway (no leak at 15-cm-H2O peak pressure or tidal volume of 5 mL/kg); 3) airway sealing pressure; 4) number of repositioning attempts; and 5) sealing quality (no leak at tidal volume of 8 mL/kg). At the end of surgery, gastric insufflation, postoperative sore throat, dysphonia, and dysphagia were evaluated. Data were compared with unpaired Student's t-tests, chi2 tests, or Fisher's exact tests; P < 0.05 was significant. Patient characteristics, insertion times, airway adequacy, number of repositioning attempts, and recovery were similar in each group. Airway sealing pressure was significantly greater with CobraPLA (23 +/- 6 cm H2O) than LMA (18 +/- 5 cm H2O, P < 0.001). The CobraPLA has insertion characteristics similar to the LMA but better airway sealing capabilities.

Ambient isoflurane pollution and isoflurane consumption during intensive care unit sedation with the Anesthetic Conserving Device*

OBJECTIVE

To examine ambient isoflurane pollution, scavenging efficacy, and isoflurane consumption using the Anesthetic Conserving Device (ACD) for prolonged isoflurane sedation in the intensive care unit.

DESIGN

Prospective observational study.

SETTING

Multidisciplinary university intensive care unit.

PATIENTS

Fifteen adult ventilator-dependent intensive care unit patients sedated with isoflurane for 12-96 hrs.

INTERVENTIONS

Isoflurane was infused to the ACD for sedation of study subjects. Changing of the ACD, isoflurane syringe, and opening of the respiratory circuit were performed in a standardized fashion according to investigator instructions. Active scavenging of waste gas from the ventilator was performed in ten patients; in five patients no active scavenging was performed.

MEASUREMENTS AND MAIN RESULTS

Continuous spectrophotometric measurement of ambient isoflurane pollution in parts per million (ppm) at 0.5 m from the patient's head and passive lapel dosimeter sampling for ten staff nurses over 8-hr shifts. Isoflurane requirement and agent consumption were registered in all patients. Spectrophotometric readings (0.1 +/- 0.2 ppm) were well below internationally recommended long-term exposure limits in all cases. Isoflurane peaks during nursing procedures were brief, infrequent, and of low amplitude. There was no observed difference between isoflurane trace levels with or without an active scavenging system in use. Passive dosimeter values were also low, ranging from undetectable to 0.16 ppm. Mean isoflurane consumption was 2.1 +/- 1.0 mL/hr. This is approximately one fourth of predicted and previously reported consumption of isoflurane with vaporizer-administered sedation in the intensive care unit setting.

CONCLUSIONS

In the present setting, isoflurane via the ACD is an environmentally safe method of sedation provided users follow instructions for standardizing procedures with potential spillage of isoflurane. This method of sedation requires considerably less isoflurane than with traditional vaporizer technique.

Flammability of endotracheal tubes in oxygen and nitrous oxide enriched atmosphere

Endotracheal tube (ETT) fire has been reported secondary to laser and electrocautery ignition. The flammability of polyvinylchloride (PVC), silicone (Si), and red rubber (RR) ETTs in oxygen (O2) and/or nitrous oxide (N2O) in nitrogen was determined and compared by means of the O2 and N2O indices of flammability. The O2 index of flammability is the minimum O2 fraction in nitrogen that will support candle-like flame using a standard ignition source. The O2 index of flammability for PVC ETTs is 0.263, for Si 0.189, and for RR 0.176. The N2O index of flammability is the minimum N2O fraction in N2 that will support candle-like flame using a standard ignition source. The N2O index of flammability for PVC ETTs is 0.456, for Si ETTs 0.414, and for RR ETTs 0.374. The indices are additive. Flammability is a valid method of comparing safety of various endotracheal tube materials. There is a need for new endotracheal tube material with a higher index of flammability. The significance of these findings and the clinical applications are discussed.