Anesthesiology
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The actions of two new steroidal nondepolarizing neuromuscular blocking agents, structurally related to vecuronium, have been compared with those of succinylcholine in anesthetized cats and pigs. Both new compounds (Org 7617 and Org 9616) exhibited properties typical of nondepolarizing relaxants in each species. Org 9616 was one-fifth (ED50 cat tibialis 154 micrograms.kg-1) and Org 7617 was one-tenth (ED50 cat tibialis 287 micrograms.kg-1) as potent as vecuronium as a neuromuscular blocking drug. ⋯ Both compounds produced a decrease in arterial blood pressure. This was more pronounced with Org 7617. In addition, Org 9616 produced a slight increase in heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Absence of agonistic or antagonistic effect of flumazenil (Ro 15-1788) in dogs anesthetized with enflurane, isoflurane, or fentanyl-enflurane.
This study determined the effects of flumazenil on the anesthetic requirements (MAC) of the dog for isoflurane (group 1; n = 6), enflurane (group 2; n = 7), and a combination of fentanyl-enflurane (group 3; n = 6). Control MAC in each group was determined by the tail-clamp method. Each animal in groups 1 and 2 received four iv incremental doses of flumazenil: 0.5, 1.0, 1.5, and 4.5 mg/kg, and isoflurane MAC or enflurane MAC was determined after each dose. ⋯ In group 3, plasma fentanyl concentrations remained stable at 12.5 +/- 3.0 ng/ml (mean +/- SD) throughout the experiment and reduced enflurane MAC by 60 +/- 8%. The addition of flumazenil changed neither the fentanyl concentration in plasma (12.2 +/- 3.8 ng/ml) nor its reduction of enflurane MAC (61 +/- 7%). In conclusion, the absence of effect of flumazenil on the MAC of enflurane, isoflurane, or a fentanyl-enflurane combination suggests that they do not interact with the benzodiazepine receptor.
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The incidence of failed local anesthetic axillary blockade varies but can be as high as 20-30%. The authors propose to evaluate the safety of supplementing an axillary block with mepivacaine 30 min after the initial injection. An axillary blockade was performed on 10 healthy patients scheduled for forearm or hand surgery using a new catheter technique. ⋯ Plasma levels of mepivacaine were estimated at frequent intervals for 5 h after the initial injection. There were no symptoms or signs of local anesthetic toxicity, and plasma levels of mepivacaine remained below those that usually caused symptoms. In conclusion, the authors conclude that mepivacaine 1% with epinephrine (10.5 mg/kg) can be safely administered in divided doses into the axillary sheath within a 31-min period.
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Comparative Study
Depressant effects of volatile anesthetics upon rat and amphibian ventricular myocardium: insights into anesthetic mechanisms of action.
To clarify the mechanisms by which volatile anesthetics may depress myocardial contractility, the depressant effects of equivalent concentrations of isoflurane, enflurane and halothane were compared in rat and frog ventricular myocardium, preparations which differ markedly in excitation-contraction coupling. In Tyrode solution, right ventricular papillary muscles from rat exhibited very large, rapidly developing contractions after rest, with a subsequent negative force-frequency relation as the stimulation rate was increased to 0.1, 0.25, 0.5, 1, 2, and 3 Hz. The large contractions after rest and at 0.1 Hz were depressed by 0.75% halothane and 1.7% enflurane to about 60% of control, but less so by 1.3% isoflurane (approximately 0.8 MAC). ⋯ These results suggest that halothane is more potent than isoflurane in reducing the amount of Ca2+ rapidly released from the sarcoplasmic reticulum (as observed in rat), as well as in depressing entry of extracellular Ca2+ to activate myofibrils (as in frog). Enflurane appears to have intermediate potency with actions distinct from halothane and isoflurane. The greater potency of halothane may also be due in part to greater direct depression of actin-myosin ATPase.