Anesthesiology
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Computer-controlled infusion of intravenous dexmedetomidine hydrochloride in adult human volunteers.
This investigation extended the pharmacokinetic analysis of our previous study, of intravenous dexmedetomidine in 10 healthy male volunteers, and prospectively tested the resulting compartmental pharmacokinetics in an additional six subjects using a computer-controlled infusion pump (CCIP) to target four different plasma concentrations of dexmedetomidine for 30 min at each concentration. ⋯ Pharmacokinetics of dexmedetomidine are best described by a three-compartment model. Addition of age, weight, lean body mass, and body surface area do not improve the predictive value of the model. Additional improvement in CCIP accuracy for dexmedetomidine infusions would require magnification modification of the model based on the targeted concentration.
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The tendency of intravenous fluid exiting the heat exchanger of a fluid warmer to cool to room temperature increases as the rate of infusion slows and the length of tubing between the heat exchanger and the patient increases. Thus, slow to moderate flow rates result in the delivery of fluid near room temperature despite the use of a fluid warmer. The volumes infused even at low flow rates may be large relative to the size of infants and children and may result in a significant decrease in patient temperature. ⋯ The Hotline is more effective than conventional warmers at slow flow rates, and may be useful for preventing hypothermia when large volumes of fluid relative to patient size are infused at slow rates.
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The Cp50 (minimal steady state plasma concentration of an intravenous analgesic/anesthetic required to prevent a somatic response in 50% of patients following skin incision) and the Cp50-BAR (minimal plasma concentration of an analgesic/anesthetic required to prevent either a somatic, hemodynamic, or autonomic response in 50% of patients following skin incision) have been recently proposed as a measure, like minimum alveolar concentration (MAC; and MAC-BAR), to establish the relative potency of intravenous analgesics. This study was conducted to establish the Cp50 for fentanyl. ⋯ Comparing these results with the previously published Cp50 of alfentanil, the potency of fentanyl relative to alfentanil is 1:58. Establishing the Cp50, once effect site equilibration has occurred, will allow pharmacodynamic comparisons between the opioids at equipotent concentrations.
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Neuromuscular blockade (NMB) is a frequent component of anesthetic techniques used during surgery in which monitoring of the nervous system is desirable. Because NMB should affect the evoked muscle response to transcranial magnetic stimulation (tcMMEP), their relationship in a primate model was characterized. ⋯ This study indicates that tcMMEP onset latency is not significantly affected by NMB if the degree of blockade in the muscles used for tcMMEP monitoring is not extreme (greater than 0.2 of baseline by m-response amplitude or a TOF ratio of 0.1 or greater). If monitoring of tcMMEP amplitude is desired, partial neuromuscular blockade may be acceptable. However, amplitude reduction may occur during partial NMB. Maintenance of a constant degree of NMB is suggested to minimize amplitude fluctuations.
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Comparative Study
Effects of general anesthetics on intercellular communications mediated by gap junctions between astrocytes in primary culture.
Astrocytes represent a major nonneuronal cell population in the central nervous system (CNS) and are actively involved in several brain functions. These cells are coupled by gap junctions (GJ) into a syncytial-like network resulting in cellular communication through ionic and metabolic exchange between adjacent astrocytes. Whether anesthetics affect astrocyte function is not known. In the present study, the effects of general anesthetics on GJ permeability were investigated in primary cultures of mouse striatal astrocytes. ⋯ These results indicate that general anesthetics differentially affect GJ permeability in cultured astrocytes. This uncoupling effect (closure of gap junctions) may contribute to the mechanisms of action of some anesthetic agents (primarily volatile anesthetics) at the level of the CNS by altering astrocyte communication.