There is accumulating evidence that inappropriate depth of anaesthesia is associated with increased risk of postoperative complications including risk of death. The aim of this study was to identify factors determining the effective end-tidal concentration (EEtC) of desflurane, duration of wash in and wash out phase, and to estimate the risk of perioperative awareness in patients undergoing elective neurosurgical procedure.

All patients with American Society of Anesthesiologists (ASA) physical status I-III scheduled for elective neurosurgical procedure under general anaesthesia are studied. In each individual, the manufacturer recommended age-corrected end-tidal concentrations of desflurane is set and achieved initially. Individual effective end-tidal concentration (EEtC) of desflurane is then defined according to entropy parameters and maintained in the targeted range of static and response entropy 40-50. Effective analgesia is maintained according to surgical plethysmographic index (SPI) and dose of muscle relaxants according to neuromuscular transmission monitoring (TOF). Comorbidity, regular intake of alcohol and medication, smoking, sex, weight, height, and age are recorded. Postoperative questionnaire is used to reveal the intraoperative awareness.

Inclusion Criteria:

• ASA I-III
• elective neurosurgical procedure under general anaesthesia
• Age between 18 and 78
• elective procedures with estimated duration 1 - 3 hours

Exclusion Criteria:

• Glasgow coma scale GCS below 14
• other rhythm than sinus
• pacemaker stimulation
• planned postoperative ventilation