Anxiety influences brain wave activity. E-Entropy module-derived spectral entropy is an electroencephalographic derivative used to monitor the depth of sedation. This study assessed the effect of preoperative anxiety on the spectral entropy parameters of response entrophy (RE) and state entrophy (SE).

Trait anxiety was measured in 92 American Society of Anesthesiologists physical status I-II patients with the Spielberger State-Trait Anxiety Inventory (STAI) form X2 and state anxiety with STAI-X1 just before anesthesia. RE, SE, blood pressure and heart rate were measured before induction. Propofol was infused via a target controlled infusion pump. At loss of consciousness (LOC), the effect-site concentration (Ce), RE, SE and total amount of propofol were recorded. Patients were stratified into three groups based on their state and trait anxiety scores to evaluate the effect of anxiety level on entropy values.

STAI-X1 was significantly correlated with RE and SE for LOC (ρ = 0.230, P = 0.028 and ρ = 0.308, P = 0.003, respectively) and also with STAI-X2 (ρ = 0.411, P = 0.001, respectively). SE was higher in the high state anxiety group than in the low state anxiety group (P = 0.017). The other measured variables were not correlated with any anxiety scales.

The state of anxiety increases RE and SE values at LOC induced with propofol. High state anxiety is associated with higher SE than apparent at low state anxiety. When determining the propofol-induced LOC by spectral entropy, anxiety levels should be considered.