Electromyographic assessment of blink reflexes correlates with a clinical scale of depth of sedation/anaesthesia and BIS during propofol administration.

Abstract

General anaesthesia is characterized by loss of consciousness, amnesia and obtundation of reflex responses to noxious stimuli. Quantifying the blink reflex may reflect the depression of reflex arches induced by anaesthetics and thus being informative on the anaesthetic state. The relation between the electrically evoked blink reflexes and the depth of sedation and anaesthesia induced with intravenous propofol was investigated. Twenty patients received propofol by target-controlled infusion to create a stepwise deepening of sedation and anaesthesia. Depth of anaesthesia was assessed using the observer's assessment of anaesthesia and sedation (OAAS) scale, and by bispectral EEG analysis (BIS). Probit analysis was used to estimate the predicted propofol effect site concentrations producing unconsciousness, no response to noxious stimulation, and loss of blink reflex components. Latency of the first (R1) and second (R2) blink component increased, whereas duration and area decreased with increasing depth of sedation and anaesthesia. A reasonably strong correlation between OAAS and the areas of R1 and R2 components was found (Spearman's rho = 0.92 and 0.89). The areas of R1 and R2 and the OAAS also correlated with BIS (Spearman's rho = 0.91, 0.88 and 0.90). EC(50) and EC(95) for loss of R1 were 2.8 (95% CI: 2.5-3.2) micro g/ml and 4.6 (95% CI: 4.1-5.5) micro g/ml, respectively. Our results suggest that the differential sensitivity of the components of the blink reflex could be useful in monitoring depth of sedation and light levels of anaesthesia during the administration of propofol. Both OAAS and BIS correlate similarly with the blink reflex components.