Anaesthesia
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The aim of this study was to determine whether measurement of pre-operative brain natriuretic peptide can significantly improve risk stratification of vascular surgical patients. The study endpoint was postoperative raised troponins. Net reclassification improvement was determined for risk categories based on the Revised Cardiac Risk Index. ⋯ Reclassification based on the optimal discriminatory point significantly improved risk stratification (net reclassification improvement 38.3% (95% CI 9.3-67.3%), p = 0.01 for the entire cohort and 70.3% (95% CI 27.1-113.6%), p = 0.002 for intermediate risk patients). The brain natriuretic peptide tertiles only improved stratification of intermediate risk patients (net reclassification improvement 50.0% (95% CI 16.7-83.3%), p = 0.01). We have shown that measurement of pre-operative brain natriuretic peptide is relevant in the context of risk assessment in this cohort of patients.
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Clinical Trial
Remifentanil as single agent to facilitate awake fibreoptic intubation in the absence of premedication.
Remifentanil is increasingly being used as the primary agent to provide sedation during awake fibreoptic nasal intubation. In this observational study, we aimed to determine the optimal effect site concentration of remifentanil, using a target controlled infusion based on the Minto pharmacological model, to provide optimal safe intubation conditions without the use of other sedatives/premedication and/or spray-as-you-go local anaesthesia. ⋯ No serious adverse event occurred during any of these procedures. These preliminary findings suggest that this is a feasible and safe technique for awake fibreoptic nasal intubation.
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The effect of lipid emulsion on depth of anaesthesia following thiopental administration to rabbits.
Intravenous lipid emulsion has proven benefit in lipophilic drug-induced cardiotoxicity. Its effect in reversal of central nervous system depression secondary to overdose with lipophilic psychotropic agents remains uncertain. Twenty adult New Zealand White rabbits were anaesthetised with 20 mg.kg(-1) thiopental and randomised to receive either 4 ml.kg(-1) saline 0.9% or 4 ml.kg(-1) lipid emulsion 20% immediately afterwards. ⋯ The greatest BIS differential was observed immediately following treatment (mean (SD) BIS 75.0 (9.5) for saline vs 58.6 (10.4) for lipid, 95% CI 5.75-27.1; p < 0.001). No difference was observed in duration of anaesthesia (mean (SD) 15.5 (0.8) min for saline vs 15.6 (0.7) min for lipid, p = 0.86). Lipid emulsion administration may serve to increase central nervous system depression in the early phase of lipophilic toxin distribution.
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Gap junction blockade is a possible mechanism by which general anaesthetic drugs cause unconsciousness. We measured the sensitivity of connexin36 knockout mice to the hypnotic effects of isoflurane and propofol. The experimental endpoint was recovery of the righting reflex of the anaesthetised animals during 0.2% step-reductions in isoflurane concentration, or following intraperitoneal injection of propofol (100 mg.kg(-1) ). ⋯ The half maximal effective concentration (EC50) for recovery of righting reflex was 0.37% for connexin36 knockout vs 0.49% for wild-type animals (p < 0.001). For propofol, connnexin36 knockout animals showed more rapid loss of righting reflex than wild-type animals (mean (SD) 2.8 (0.13) vs 3.8 (0.27) min); and young (< 60 days) connexin36 knockout animals remained anaesthetised for longer than young wild-type mice (47.2 (2.9) vs 30.5 (1.7) min; p < 0.00001). These findings suggest that the hypnotic effects of anaesthetic drugs may be moderately enhanced by gap junction blockade.