Anesthesia and analgesia
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Perioperative hypothermia usually results largely from pharmacologic inhibition of normal thermoregulatory control. Midazolam is a commonly used sedative and anesthetic adjuvant whose thermoregulatory effects are unknown. We therefore tested the hypothesis that midazolam administration impairs thermoregulatory control. ⋯ Similarly, midazolam decreased the shivering threshold: 35.9 +/- 0.3 degrees C vs 35.3 +/- 0.6 degrees C (P = 0.03). The sweating-to-vasoconstriction (interthreshold) range, therefore, increased from 0.2 +/- 0.1 degrees C to 0.7 +/- 0.3 degrees C (P = 0.002). Although statistically significant, this relatively small increase contrasts markedly with the 3-5 degrees C interthreshold ranges produced by clinical doses of volatile anesthetics, propofol, and opioids.(ABSTRACT TRUNCATED AT 250 WORDS)
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Anesthesia and analgesia · Aug 1995
Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: a prospective blind study.
We conducted a prospective, blind study to determine whether a difficult endotracheal intubation could be predicted preoperatively by evaluation of one or more anatomic features of the head. In 471 adults presenting for elective surgery, the size of the tongue relative to the oral cavity was assessed according to the Mallampati classification (oropharyngeal class), and the distance between the chin and thyroid cartilage (thyromental distance) and the angle at full extension of the head (head extension) were measured. ⋯ Assignment to oropharyngeal Class 3, a thyromental distance < or = 7 cm, and a head extension < or = 80 degrees, considered either alone or in various combinations, had low sensitivity and positive predictive values in identifying patients with airways that were difficult to intubate, but high specificity and negative predictive values. We conclude that these three tests are of little value in predicting difficult intubation in adults, although the likelihood of an easy endotracheal intubation is high when they yield negative results.
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Anesthesia and analgesia · Aug 1995
Electroencephalographic characteristics of emergence from propofol/sufentanil total intravenous anesthesia.
We recorded the electroencephalogram (EEG) in 16 patients during propofol/sufentanil total intravenous anesthesia to determine whether EEG changes might predict imminent awakening during emergence. Changes in absolute and relative power in four frequency bands, median frequency (MF), 95th percentile frequency (F95), and two frequency band power ratios (beta/alpha and (alpha+beta)/delta) were quantified. ⋯ Of the individual spectral variables, only a 50% decrease in absolute alpha power was more than 90% sensitive and specific in predicting eye opening. We conclude that, although pronounced EEG changes occur during emergence from propofol/sufentanil anesthesia, the EEG does not reliably predict eye opening.
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Anesthesia and analgesia · Aug 1995
Exhaled flow monitoring can detect bronchial flap-valve obstruction in a mechanical lung model.
Flap-valve obstruction to expiratory flow (V) in a major bronchus can result from inspissated secretions, blood, or foreign body. During inhalation, increasing airway caliber preserves inspired V past the obstruction; during exhalation, decreasing airway diameter causes airflow obstruction and even frank gas trapping. We reasoned that the resultant sequential, biphasic exhalation of the lungs would be best detected by measuring exhaled V versus time. ⋯ Airway P could not differentiate between bronchial and tracheal flap-valve obstruction because P decreased abruptly in both conditions. The flow-volume loop displayed less distinctive changes than the flow-time plot, in part because the flow-volume loop was data (flow) plotted against its time integral (volume), with loss of temporal data. In this mechanical lung model, we conclude that bronchial flap-valve obstruction was best detected by the flow-time plot, which could measure the sequential emptying of the lungs.
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Anesthesia and analgesia · Aug 1995
Comparative StudyLocal anesthetic neurotoxicity does not result from blockade of voltage-gated sodium channels.
To investigate whether local anesthetic neurotoxicity results from sodium channel blockade, we compared the effects of intrathecally administered lidocaine, bupivacaine, and tetrodotoxin (TTX), the latter a highly selective sodium channel blocker, on sensory function and spinal cord morphology in a rat model. First, to determine relative anesthetic potency, 25 rats implanted with intrathecal catheters were subjected to infusions of lidocaine (n = 8), bupivacaine (n = 8), or TTX (n = 9). The three drugs produced parallel dose-effect curves that differed significantly from one another: the EC50 values for lidocaine, bupivacaine, and TTX were 28.2 mM (0.66%), 6.6 mM (0.19%), and 462 nM, respectively. ⋯ Significant sensory impairment again occurred after infusion of bupivacaine, but not after infusion of TTX or saline. Neuropathologic evaluation revealed moderate to severe nerve root injury in bupivacaine-treated animals; histologic changes in TTX- and saline-treated animals were minimal, similar, and restricted to the area adjacent to the catheter. These results indicate that local anesthetic neurotoxicity does not result from blockade of the sodium channel, and suggest that development of a safer anesthetic is a realistic goal.