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Monitoring: Equipment and Computers

Validity of the modified observer's assessment of alertness/sedation scale (MOAA/S) during low dose propofol sedation

3AP6-3

Kowalski, R.; Mahon, P.; Boylan, G.; McNamara, B.; Shorten, G.

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European Journal of Anaesthesiology (EJA): June 2007 - Volume 24 - Issue - p 26-27
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Background and Goal: The MOAA/S scale a measure of alertness/sedation is used widely in clinical research. It is derived from the original Observer's Assessment of Alertness/Sedation scale. This scale was originally validated for use with midazolam. The observer rates patient responsiveness, speech and facial expression/eye movements. The modified form uses only the responsiveness component of the original scale [Awake (5) - Unresponsive (1)]. We set out to determine the sensitivity and specificity of the MOAA/S scale to detect characteristic EEG changes that occur during conscious propofol sedation. These changes are: decreased alpha amplitude and drop out, enhanced beta activity and/or the presence of theta waves.

Materials and Methods: 12 unpremedicated ASA I patients were recruited. Propofol was administered using a target effect site controlled infusion. The starting concentration was 0.5 μg/ml, this increased in 0.5 μg/ml increments at four minute intervals. The study duration was 16 minutes. Multi-channel (19) EEG was recorded continuously. MOAA/S score was recorded at one minute intervals. The EEG was later graded by a blinded clinical neurophysiologist. A grade representing evidence of sedation was assigned to each four minute period corresponding to a fixed propofol concentration.

Results and Discussions: There were 48 study periods each of four minutes duration. Characteristic EEG changes associated with sedation were present in 29 (Table 1).

Table 1
Table 1

MOAA/S score was 100% specific and 59% sensitive in identifying patients with EEG evidence of sedation. MOAA/S failed to identify sedation in 41 % of patients (negative prediction value 61%).

Conclusion: MOAA/S failed to identify sedation (as defined by EEG) in 41% of ASA I patients receiving low dose propofol sedation.

Reference:

J Clin Psychopharmacol 1990; 10: 244-51.
    © 2007 European Society of Anaesthesiology