Anesthesiology
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Randomized Controlled Trial Comparative Study Clinical Trial
The thermoregulatory threshold in humans during nitrous oxide-fentanyl anesthesia.
Narcotics and nitrous oxide (N2O) inhibit thermoregulatory responses in animals. The extent to which N2O/fentanyl anesthesia lowers the thermoregulatory threshold in humans was tested by measuring peripheral cutaneous vasoconstriction using skin-surface temperature gradients (forearm temperature-fingertip temperature) and the laser Doppler perfusion index. Fifteen unpremedicated patients were anesthetized with N2O (70%) and fentanyl (10 micrograms/kg iv bolus followed by 4 micrograms.kg-1.h-1 infusion) during elective, donor nephrectomy. ⋯ Four hypothermic patients developed a passive thermal steady state without becoming sufficiently cold to trigger vasoconstriction. Thus, active thermoregulation occurs during N2O/fentanyl anesthesia but does not occur until core temperatures are approximately 2.5 degrees C lower than normal. The thermoregulatory threshold during N2O/fentanyl anesthesia is similar to that previously determined during halothane (34.4 +/- 0.2 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Fentanyl suppression of nociceptive neurons in the superficial dorsal horn of the cat.
This study was designed to examine the influence of spinally administered fentanyl on the spontaneous and noxiously evoked activity of high threshold (HT) and wide dynamic range (WDR) neurons in the superficial layers (lamina I and II) of the dorsal horn of cats made decerebrate and in which the spinal cord had been transected. Single unit activity was recorded using extracellular microelectrode recording techniques. Neuronal activity was evoked by the presentation of noxious radiant heat (51 degrees C) to the cells' receptive fields on the hind paws. ⋯ Within 30 minutes 10 and 25 micrograms of fentanyl reduced the mean evoked activity of WDR neurons to 61% and 19% of control values, respectively, and 25 and 50 micrograms of fentanyl reduced the mean evoked activity of HT neurons to 70% and 47% of control values, respectively. Naloxone reversed the suppression seen in all cells studied. The results of the present study demonstrate that HT neurons are significantly less suppressed by the spinal administration of fentanyl than WDR neurons located in the same superficial layers of the dorsal horn.(ABSTRACT TRUNCATED AT 250 WORDS)
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Randomized Controlled Trial Comparative Study Clinical Trial
Intrathecal morphine reduces the minimum alveolar concentration of halothane in humans.
The authors hypothesized that the analgesia provided by intraspinal opiates would decrease anesthetic requirement. To test this hypothesis, 20 women undergoing major gynecologic surgery were divided randomly into two groups. ⋯ MAC for halothane was 0.81% in the control group and 0.46% in the intrathecal morphine group (P = 0.024). The reduction in anesthetic requirement due to intrathecal morphine is greater than that produced by low to moderate doses of systemically administered opiates.
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Comparative Study
I653 and isoflurane produce similar dose-related changes in the electroencephalogram of pigs.
I653 is a new volatile anesthetic structurally similar to enflurane and isoflurane. Since enflurane can induce convulsions, whereas isoflurane progressively depresses cortical electrical activity, the authors believed it important to assess the effect of I653 on the EEG (in both the "time" and "frequency" domain). The EEG was assessed visually and quantitatively, and a new EEG parameter was introduced. ⋯ At equipotent concentrations, I653 and isoflurane had the same effect on EEG parameters. Increasing doses of either I653 or isoflurane caused decreasing amplitude and frequency and increasing suppression. Hypocapnea during either agent slightly increased high-frequency activity, and slightly decreased burst suppression.
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Comparative Study
Preparation of anesthesia machines for patients susceptible to malignant hyperthermia.
Malignant hyperthermia is a potentially lethal syndrome that can be triggered by inhaled anesthetics. Thus, it may be appropriate to utilize equipment that minimizes exposure of susceptible patients to inhaled anesthetics. The rate of release of anesthetic stored in anesthesia delivery systems is unknown. ⋯ Isoflurane washed out 3-4 times faster than halothane. Residual halothane concentration was approximately equal to tenfold greater when the fresh gas flow was 1 l/min rather than 10 l/min: 194 versus 19 ppm after 1 h of washout. Using a 10-l/min fresh gas flow, halothane concentrations in samples obtained from the Y-piece were similar with original or fresh soda lime but were more than tenfold lower after the fresh gas outlet hose and circle system were replaced (approximately equal to 50 ppm vs. approximately equal to 5 ppm after 5 min of washout).(ABSTRACT TRUNCATED AT 250 WORDS)