Electromyographic assessment of blink and corneal reflexes during midazolam administration: useful methods for assessing depth of anesthesia?
BACKGROUND
There are at least three components of the anesthetic state: loss of consciousness, amnesia and obtundation of reflex responses to noxious stimuli. To investigate the third component, we used a standard electrical stimulus to evoke a blink reflex, which was electromyographically recorded. These data may give information on the anesthetic state.


METHODS
The relation between the electrically evoked blink and corneal reflexes and the depth of sedation and anesthesia induced with intravenous midazolam was investigated. Ten patients received i.v. increments of midazolam (1 mg, 2 mg, 3 mg, 3 mg, 3 mg, etc., until a 21-mg total dose) to create a step-wise deepening of sedation and anesthesia. Depth of anesthesia was assessed by the Observer's Assessment of Alertness/Sedation (OAAS) scale, ranging from 5 ( = awake and alert) to 0 ( = no motor response to tetanic stimulation).


RESULTS
Latency of the first (R1) and second (R2) blink components and the corneal (C) reflex component increased, whereas duration and area decreased with increasing depth of sedation and anesthesia. R1 was last seen at an OAAS score [mean (SD)] of 1.8 (0.8), R2 at a score of 3.1 (1.1), C at a score of 3.8 (0.8), and R3 at 4.8 (0.5). These end-points were all statistically different from each other, except R2 vs. C.


CONCLUSIONS
Our results suggest that the differential sensitivity of the components of the blink reflex could be useful to monitor depth of sedation and light levels of anesthesia during the administration of midazolam.
Mourisse
J
J
Department of Anesthesiology, University Medical Center Nijmegen, HB, Nijmegen, The Netherlands. j.mourisse@anes.umcn.nl
Gerrits
W
W
Lerou
J
J
van Egmond
J
J
Zwarts
M J
MJ
Booij
L
L
D000328:Adult; D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous; D001767:Blinking / Q000502:physiology*; D003315:Cornea / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography / Q000187:drug effects*; D005260:Female; D006185:Habituation, Psychophysiologic / Q000187:drug effects; D006801:Humans; D008297:Male; D008874:Midazolam; D011237:Predictive Value of Tests; D012018:Reflex / Q000187:drug effects*; D015203:Reproducibility of Results
D018686:Anesthetics, Intravenous; D008874:Midazolam