British journal of anaesthesia
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Randomized Controlled Trial Clinical Trial
Effect of nitrous oxide on myogenic motor potentials evoked by a six pulse train of transcranial electrical stimuli: a possible monitor for aortic surgery.
Intraoperative recording of myogenic motor potentials evoked by transcranial electrical stimulation (tcMEP) is a method of monitoring the integrity of the vulnerable motor pathways during thoracoabdominal aortic aneurysm (TAAA) surgery. Deflation of the left lung during TAAA surgery may result in impairment of arterial oxygenation. Ventilation with nitrous oxide may cause further desaturation. ⋯ There was no significant difference in the coefficients of variation for tcMEP between the three nitrous oxide anaesthetic regimens. Our results suggest that increasing doses of nitrous oxide reduce the MEP waveform to six pulse transcranial electrical stimulation, but even with 60% nitrous oxide in oxygen, the tcMEP were recordable and as reproducible as with 20% and 40% nitrous oxide regimens. The method is sufficiently robust for use in aortic surgery.
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Clinical Trial
Patient-maintained propofol sedation as premedication in day-case surgery: assessment of a target-controlled system.
We have assessed the efficacy and safety of a system which allowed 20 patients undergoing day-case anaesthesia to operate a target-controlled infusion of propofol to provide anxiolytic premedication. A target-controlled infusion of propofol was started with a target blood concentration of 1 microgram ml-1, and the patient was allowed to increase the target by 0.2 microgram ml-1 by operating a control button. There was a lockout time of 2 min and a maximum target concentration of 3 micrograms ml-1. ⋯ No patient became oversedated and all remained cardiovascularly stable. Two individuals required low-dose supplementary oxygen for mild arterial oxygen desaturation but there were no instances of airway obstruction. Patient satisfaction with the system was high.
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Propofol may cause profound bradycardia and asystole, which are mediated indirectly via cardiac innervation but could involve direct effects on the sino-atrial (SA) node and the conducting system of the heart. To test the hypothesis that propofol may also activate Bezold-Jarisch reflexes to cause bradycardia, 5-hydroxytryptamine (5-HT), veratridine and propofol were injected into the left ventricle of the heart in both intact and vagotomized rabbits. 5-HT and veratridine produced an acute, rapid, dose-dependent decrease in mean heart rate (delta HR) and a decrease in mean arterial pressure (delta MAP) together with transient but severe depression and abolition of renal sympathetic nerve activity (RSNA). ⋯ Propofol depressed but did not abolish RSNA, and bilateral vagotomy had no effect on any of these responses. These results indicate that the cause of acute bradycardia after administration of propofol does not involve the Bezold-Jarisch reflex.
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Randomized Controlled Trial Comparative Study Clinical Trial
Neuropeptide Y response to tracheal intubation in anaesthetized children: effects of clonidine vs midazolam as premedication.
We have determined if tracheal intubation causes an increase in neuropeptide Y (NPY), a marker of major adrenergic activation, and investigated if rectal premedication with clonidine 2.5 micrograms kg-1 might be capable of attenuating the stress response to tracheal intubation compared with midazolam 300 micrograms kg-1, in 20 paediatric patients (1-9 yr). Prospective randomization was performed in a double-blind manner. ⋯ There was no significant difference between the two groups. We conclude that the adrenergic stress reaction in response to tracheal intubation in children was short-lived and of limited magnitude, as indicated by the lack of NPY release.