Articles: anesthetics.
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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.
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New drugs like alfentanil and midazolam have the primary advantage of metabolizing faster than existing compounds in their class. Because of shorter plasma half-lives, the drugs are well suited for continuous infusion. ⋯ Although some anesthetic drugs can be given safely and effectively by bolus injection, whenever a titrated continuous infusion is appropriate (and physiologically closed-loop delivery is not possible), use of a CACI-type instrument should be the preferred method of administration. With the availability for continuous infusion of alfentanil and midazolam, with their highly desirable pharmacodynamic properties and relatively effervescent pharmacokinetics, we believe that computerized pharmacokinetic model-driven infusion devices will play a significant role in future anesthetic practice.
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Randomized Controlled Trial Clinical Trial
Effect of diluting propofol on the incidence of pain on injection and venous sequelae.
The effect of diluting propofol in 5% dextrose on the incidence of i.v. injection pain was studied in 100 adult patients. Severe injection pain occurred in 32% (16 patients) who received undiluted propofol, compared with 10% (five patients) who received dilute propofol. We concluded that the dilution of propofol significantly reduced the incidence of severe pain during injection without increasing postoperative venous sequelae.