Anesthesia and analgesia
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Anesthesia and analgesia · Aug 1997
The effects of sevoflurane on population spikes in CA1 and dentate gyrus of the rat hippocampus in vitro.
We studied the effects of sevoflurane on population spikes (PSs) in two synaptic pathways in rat hippocampal slices. Stimulating electrodes were placed on Schaffer collateral fibers or perforant path to activate inputs to CA1 pyramidal neurons or dentate gyrus (DG) neurons, respectively. Extracellular glass microelectrodes were used to record PSs. The paired-pulse stimulus was used to induce the paired-pulse facilitation (PPF). Sevoflurane (0.4-5.0 vol%) significantly decreased the amplitudes of PSs of CA1 and DG in a dose-dependent and reversible manner (25% effective dose values were 4.1 and 0.9 vol%, respectively). The stimulus-response relationships for PS amplitudes revealed that sevoflurane increased the threshold for PS generation in CA1 and DG. Sevoflurane (2.0 vol%) significantly enhanced PPF from 127% and 263% to 153% and 494% in CA1 and DG, respectively. The results imply that the effects of sevoflurane on PSs are greater in DG than in CA1 neurons, that sevoflurane enhances the PPF in both CA1 and DG, and that the actions of sevoflurane are not similar to those of other volatile or intravenous anesthetics previously reported in hippocampal preparations. ⋯ The volatile anesthetic sevoflurane alters neural excitability of individual pathways in the hippocampus in a manner different from other general anesthetics. The results are consistent with a site-specific mechanism of action for general anesthesia.
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Anesthesia and analgesia · Aug 1997
The effects of chronic tacrine therapy on d-tubocurarine blockade in the soleus and tibialis muscles of the rat.
Tacrine (THA) is an anticholinesterase drug used to manage Alzheimer's dementia, but it is not clear how its chronic use might affect response to nondepolarizing muscle relaxants. We determined the magnitude and time course of the effects of chronic oral THA and of intravenous (IV) THA on d-tubocurarine (dTC) blockade at the soleus and tibialis muscles. Six groups of adult rats were given 10 mg/kg THA twice daily by gavage for 1, 2, 4, or 8 wk (chronic THA groups), or 1 mL of saline twice daily by gavage for 1-8 wk (control), or IV THA approximately 20 min before (acute), and the cumulative dose-response curves of dTC at the tibialis and soleus muscles were determined during indirect train-of-four stimulation in the anesthetized, mechanically ventilated rat. ⋯ Chronic THA increased both the ED50 and ED95 of dTC 1.5- to 2-fold (P > or = 0.05), and this effect tended to decrease with duration of THA therapy. We conclude that chronic THA therapy in rats causes resistance to dTC, with a tendency for the resistance to decrease with time, probably because of down-regulation of postsynaptic acetylcholine receptors. The same may apply to Alzheimer's patients taking THA chronically.
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Anesthesia and analgesia · Aug 1997
Randomized Controlled Trial Comparative Study Clinical TrialThe effects of epidural fentanyl on hemodynamic responses during emergence from isoflurane anesthesia and tracheal extubation: a comparison with intravenous fentanyl.
To investigate the effects of epidural fentanyl infusion on hemodynamic responses to recovery of consciousness and tracheal extubation, we studied 50 unpremedicated patients scheduled for abdominal hysterectomy. All patients underwent epidural catheterization and blind infusion of placebo and study drug. Patients were assigned randomly to three groups: Group I received epidural and intravenous (i.v.) bolus injections and infusion of saline at the rate of 0.2 mL x kg(-1) x h(-1); Group II received an i.v. injection of fentanyl 2 microg/kg for 30 s followed by 25 ng x kg(-1) x min(-1), and Group III received epidural injection and infusion using the same administration regimen as Group II. ⋯ The incidence of coughing during and after extubation was also lower with Group III. Suppression of respiratory rate prior to tracheal extubation was similar in the two groups receiving fentanyl. These findings suggest that the significant reduction in arterial pressures responses to tracheal extubation due to epidural fentanyl infusion may arise from more suppression of cough reflex than i.v. fentanyl infusion, which could be provided by the spinal action of epidural fentanyl as well as the supraspinal action.
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Anesthesia and analgesia · Aug 1997
Randomized Controlled Trial Comparative Study Clinical TrialEpidural meperidine after cesarean section: the effect of diluent volume.
We investigated the effect of diluent volume on analgesia and systemic absorption from epidural meperidine after cesarean section in a randomized, double-blind study. At the first request for postoperative analgesia, 36 parturients were given epidural meperidine 25 mg diluted with saline to either 2 mL (12.5 mg/mL), 5 mL (5 mg/mL), or 10 mL (2.5 mg/mL). Visual analog pain scores measured in the first 30 min were greater in the 2-mL group compared with both the 5-mL group (P = 0.028) and the 10-mL group (P = 0.031). ⋯ No adverse side effects were recorded. Previous work has suggested that injection of epidural opioids in large volumes increases the potential risk of respiratory depression from cephalad spread of the drug. Therefore, we conclude that analgesia is optimum when epidural meperidine is administered diluted to 5 mL.