Background and objective: Many anaesthesiologists still interpret haemodynamic responses as signs of insufficient cortical suppression. The aim was to illustrate how haemodynamics may only poorly reflect the level of cortical suppression and that electroencephalographic monitoring could indicate different relationships between cortical effects and haemodynamics.
Methods: Anaesthesia was induced with thiopental (7 mg kg−1), and fentanyl (2 μg kg−1) with succinylcholine (1.5 mg kg−1) for neuromuscular blockade in the 11 patients of Group 1. In Group 2 (n = 15), thiopental (7 mg kg−1) and succinylcholine (1.5 mg kg−1) were given. In Group 3, the patients (n = 13) received thiopental (7 mg kg−1), fentanyl (2 μg kg−1) and cisatracurium (0.1 mg kg−1), and they were intubated 3 min later than the patients in Groups 1 and 2. We determined conventional electroencephalographic (EEG) variables and classified 14 EEG stages in real-time ranging from A (=1), indicating full wakefulness, to F1 (=14), at profound cortical suppression.
Results: All groups had profound cortical suppression 45 s after thiopental administration, which rapidly decreased (EEG stage, 11 (6–13) versus 7 (2–13) at 4 min, P < 0.0001). Decreasing EEG stages were associated with increasing SEF 95, relative α and β power and decreasing relative δ power. During tracheal intubation, profound cortical suppression remained unchanged in Groups 1 and 2. In Group 3, cortical suppression had decreased before laryngoscopy (P < 0.005). In Group 2, 11 patients had heart rate responses to tracheal intubation, whereas only two responded in Group 1 (P = 0.015) and three in Group 3 (P = 0.02). Thirteen patients in Group 2 had arterial pressure responses, and five in Group 1 (P = 0.038). Circulatory responses did not differ between Groups 1 and 3.
Conclusions: Electroencephalographic monitoring was suitable to indicate in real-time that haemodynamics only poorly reflect rapidly changing levels of cortical suppression, and how haemodynamics and cortical activity depend on the applied combination of hypnotic and analgesic drugs during anaesthesia induction with thiopental.