British journal of anaesthesia
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Randomized Controlled Trial Comparative Study Clinical Trial
Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position.
We have compared ease of insertion, oropharyngeal leak pressure, directly measured pharyngeal mucosal pressure and anatomical position (assessed fibreoptically) for the size 4 and size 5 laryngeal mask airway (LMA) in 20 male and 20 female patients. Microchip pressure sensors were attached to the LMA at locations corresponding to the piriform fossa, hypopharynx, base of the tongue, lateral and posterior pharynx, and the oropharynx. Oropharyngeal leak pressure, mucosal pressure and fibreoptic position were recorded during inflation of the cuff from 0 to 30 ml in 10-ml increments. ⋯ For both males and females, fibreoptic position was similar. We conclude that the size 5 LMA is optimal in males, but either size is suitable for females. The shape of the pharynx may be different between males and females.
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Comparative Study Clinical Trial Controlled Clinical Trial
Comparison of bispectral index, 95% spectral edge frequency and approximate entropy of the EEG, with changes in heart rate variability during induction of general anaesthesia.
We have compared bispectral index (BIS), 95% spectral edge frequency (SEF) and approximate entropy (ApEn) in 37 patients during induction and recovery from a short general anaesthetic. Heart rate variability (HRV) was also compared during induction only. These indices were noted at the start of induction, when a syringe held between the thumb and fingertips was dropped, at insertion of a laryngeal mask or tracheal tube (tube insertion), at incision, at the end of surgery, on return of the gag reflex and when the patient could follow a verbal command. ⋯ Using logistic regression, the indices were compared both individually and in combination as to the power of distinguishing awake (at pre-induction) from asleep (at tube insertion) states. BIS had the best predictive power, with a sensitivity of 97.3%, specificity 94.4%, positive predictive value 94.7% and negative predictive value 97.1%. A combination of the indices conferred no additional predictive advantage.
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Gastric pressure and volume were measured in 20 pregnant women during emergency Caesarean section under general anaesthesia with neuromuscular block. Mean gastric pressure was 11 (range 4-19) mm Hg and we can predict that 99% of women undergoing emergency Caesarean section with neuromuscular block are likely to have gastric pressures of less than 25 mm Hg (mean + 3 SD). ⋯ Gastric pressure decreased significantly after delivery (P < 0.001) to 8 mm Hg. Although we measured large gastric volumes (mean 112 (range 20-350) ml), there was no correlation between gastric volume and gastric pressure.
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Case Reports
Failure to prevent an anaphylactic reaction to a second neuromuscular blocking drug during anaesthesia.
Skin testing is used widely to determine the drug responsible for an anaphylactic reaction during anaesthesia. When a neuromuscular blocking drug in incriminated as the cause of a reaction, it is usual for neuromuscular blocking drugs which do not produce positive skin tests to be considered safe for subsequent use during anaesthesia. We describe three patients in whom false negative skin tests led to a second severe anaphylactic reaction to another neuromuscular blocking drug.
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Genotoxicity related to waste anaesthetic gas exposure is controversial. We have investigated the frequency of sister chromatid exchanges in peripheral lymphocytes of operating room personnel exposed to trace concentrations of isoflurane and nitrous oxide. Occupational exposure was recorded using a direct reading instrument. ⋯ Personnel were exposed to an 8-h time-weighted average of nitrous oxide 11.8 ppm and isoflurane 0.5 ppm. After exposure, sister chromatid exchange frequency was increased significantly (mean 9.0 (SD 1.3) vs 8.0 (1.4) in exposed and control personnel, respectively) (P < 0.05). We conclude that exposure to even trace concentrations of waste anaesthetic gases may cause genetic damage comparable with smoking 11-20 cigarettes per day.