Anesthesiology
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Although plasma concentrations of propofol during anesthesia are well known, the free concentration remains unknown because of uncertainties regarding plasma protein binding, interaction with other protein-bound substances, the level of binding to its lipid carrier, and the use of adjuvants. At elevated surrounding pressure, all general anesthetics require higher concentrations to reach adequate levels of anesthesia. To determine the anesthetic potency of propofol at equilibrium conditions and to study the effects of pressure on propofol-induced anesthesia, Rana pipiens tadpoles were exposed to different concentrations of pure, not emulsified, propofol in aqueous solution. ⋯ For pressure greater than 121 atm abs, an increased excitability of the tadpoles made it difficult to distinguish the righting reflex from involuntary movements. The saturated solubility of propofol in aqueous solution was found to be 1.0 +/- 0.02 mM (mean +/- SD), and the octanol/water partition coefficient was 4,300 +/- 280. Propofol adhered to the correlation between anesthetic potency and octanol/water partition coefficient exhibited by other general anesthetics.(ABSTRACT TRUNCATED AT 250 WORDS)
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Patients with diabetes may have peripheral neuropathy, which may have clinical implications for the use of regional nerve block. The effects of local anesthetics on nerve conduction and nerve fiber injury were tested in control rats and at 4 weeks after the onset of diabetes in rats injected with streptozotocin (50 mg/kg intraperitoneally). Nerve conduction was assessed by recording evoked electrical activity in hindpaw muscles following ipsilateral electrical stimulation of the sciatic nerve near the hip. ⋯ Using a light microscope with a superimposed grid, nerve edema was quantified as the proportion of intersection points falling on extracellular space. Lidocaine induced edema in both control and diabetic nerves, but 4% lidocaine induced significantly more edema in diabetic nerves than in controls. Nerve fiber injury, based on light microscopic scoring of axonal degeneration and demyelination, was not observed in saline-treated nerves.(ABSTRACT TRUNCATED AT 250 WORDS)
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Randomized Controlled Trial Comparative Study Clinical Trial
A randomized, double-blind comparison of lumbar epidural and intravenous fentanyl infusions for postthoracotomy pain relief. Analgesic, pharmacokinetic, and respiratory effects.
Although epidural opioids frequently are used to provide postoperative analgesia, several articles have suggested that the analgesia after epidural fentanyl is similar to that after an equal dose of fentanyl given intravenously. To address this issue further, 29 postthoracotomy patients were studied in a randomized, double-blinded trial comparing a lumbar epidural fentanyl infusion with an intravenous fentanyl infusion for analgesia, plasma fentanyl pharmacokinetics, and respiratory effects for 20 h postoperatively. In all patients in both groups, good analgesia was achieved (pain score less than 3, maximum 10) over a similar time course, although the patients receiving epidural infusion required a significantly larger fentanyl infusion dose than did the patients receiving intravenous infusion (group receiving epidural fentanyl infusion: 1.95 +/- 0.45 micrograms.kg-1.h-1; group receiving intravenous fentanyl infusion: 1.56 +/- 0.36 micrograms.kg-1.h-1; P = 0.0002). ⋯ Similarly, calculated clearance values for the two groups were not significantly different (group receiving epidural fentanyl infusion: 0.95 +/- 0.26 l.kg-1.h-1; group receiving intravenous fentanyl infusion: 0.87 +/- 0.25 l.kg-1.h-1; P = 0.3). Both groups demonstrated a similar degree of mild to moderate respiratory depression postoperatively, which was assessed with continuous respiratory inductance plethysmography and sequential arterial blood gas analysis. Side effects (nausea, vomiting, pruritus) were mild and did not differ between groups.(ABSTRACT TRUNCATED AT 250 WORDS)