Anesthesiology
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The ability of opioids to produce complete general anesthesia is controversial. Nitrous oxide (N2O) is often added to fentanyl-based anesthetics to produce unconsciousness and amnesia. The addition of N2O may adversely affects fentanyl's hemodynamic stability and safety. The purpose of this study was to determine the physiologic consequences of combining N2O with fentanyl in newborn animals. ⋯ Fentanyl (3,000 micrograms/kg) when combined with 50% N2O in O2 produced a plane of general anesthesia in newborn lambs in which the behavioral responses to painful stimuli were abolished. The response to sound was never eliminated, nor was cerebral oxygen consumption decreased. The combination of 50% N2O in O2, 3,000 micrograms/kg fentanyl, tracheal intubation, and mechanical ventilation did not depress heart rate, blood pressure, or blood flow to any of the major organs, except the kidneys.
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Recent experimental data indicate that anesthesia is often associated with significant changes in brain concentrations of dopamine (DA), an inhibitory neurotransmitter located in restricted, but functionally important, areas such as the striatum. Whether the presynaptic DA nerve endings represent potential targets for anesthetics remains unknown. Therefore, the current study was designed to investigate the effects of volatile anesthetics, thiopental, and ketamine on both spontaneous and depolarization-evoked DA release from striatal synaptosomes in the rat. ⋯ The authors conclude that: (1) volatile anesthetics, thiopental, and ketamine exert significant changes in both spontaneous and depolarization-evoked 3H-DA release in the rat striatum; (2) enflurane uniquely enhances NMDA-receptor mediated dopamine release; and (3) the results obtained from these receptor-mediated effects (AMPA and NMDA) may apply to postsynaptic, as well as presynaptic, glutamate receptors.
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Mivacurium's rapid onset and short duration of action in children suggests that intramuscular administration might treat laryngospasm and facilitate tracheal intubation without producing prolonged paralysis. Accordingly, the authors measured the neuromuscular effects of intramuscular mivacurium in anesthetized infants and children. ⋯ Although ventilatory depression preceded twitch depression, both occurred later with intramuscular mivacurium than would be expected after intravenous mivacurium or intramuscular succinylcholine. The authors speculate that the onset of intramuscular mivacurium is too slow to treat laryngospasm or to facilitate routine tracheal intubation in infants or children, despite administration of large doses.