Articles: anesthetics.
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J. Pharmacol. Exp. Ther. · May 1977
Conduction-blocking concentrations of anesthetics increase with nerve axon diameter: studies with alcohol, lidocaine and tetrodotoxin on single myelinated fibers.
The equilibrium blocking concentrations of benzyl alcohol, lidocaine and tetrodotoxin just sufficient to block nerve impulse conduction were determined on myelinated single fibers of the bullfrog. For all three anesthetics it was found that the fastest conducting fibers (45 m/sec; about 18 micron diameter) required about 4 times higher blocking concentrations than the slowest fibers (8 m/sec; about 3 micron diameter). ⋯ J. Physiol. 10: 267-274, 1960), it is concluded that smaller myelinated fibers are more sensitive to anesthetic blockade.
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The cardiocirculatory responses to equianaesthetic concentrations (MAC 0.5 and MAC 1.0 plus 67% N2O) of halothane, methoxyflurane, enflurane and isoflurane were studied in a total of 35 closed-chest dogs during ventilation controlled to produce normocapnia. Each anaesthetic produced a dose-related decrease in mean arterial pressure and in values reflecting cardiac function. These included cardiac output, stroke volume, left ventricular max dp/dt and ejection fraction. ⋯ Parallel with the depression in cardiac performance and blood pressure as two of the main predictors of energy demand, myocardial oxygen consumption was found to be significantly reduced by each of the anaesthetics. The ratio of the external work of the left ventricle to its oxygen consumption indicated that myocardial efficiency deterioated. The clinical implications are discussed.
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The clinical effectiveness and safety of compounded mixtures of lidocaine + bupivacaine and chloroprocaine + bupivacaine for either epidural or brachial-plexus block was studied in 48 adult patients. Of the several alternatives, chloroprocaine + bupivacaine with epinephrine was found the best choice for patients with typical plasma cholinesterase.
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Acta Anaesthesiol Scand · Jan 1977
Comparative StudyHypoxia-induced vasoconstriction in isolated perfused lungs exposed to injectable or inhalation anesthetics.
Investigations during the last two decades have revealed a tendency to inpaired pulmonary gas exchange in patients during general anesthesia. In the awake state, arterial hypoxemia is counteracted by a mechanism which tends to normalize the ventilation/perfusion ratio of the lungs by way of a hypoxia-induced vasoconstriction in poorly ventilated areas. This results in a redistribution of perfusion to more adequately ventilated lung regions. ⋯ The experiments showed that the response was unaffected by N2O and injectable anesthetics, while a reversible, dose-dependent damping effect was demonstrated for the volatile inhalation anesthetics, ether, halothane and methoxyflurance. The effect could be demonstrated at blood concentrations comparable to those used in clinical anesthesia, and it was not due to a general paralysis of the vascular smooth muscle. The findings might, at least in part, explain the occurrence of arterial hypoxemia during general inhalation anesthesia.