The purpose of this study was to determine whether brain oxyhaemoglobin–deoxyhaemoglobin coupling was altered by anaesthesia or intubation-induced stress.

This was a prospective observational study in the operating room. Thirteen patients (ASA I and II) undergoing spinal or peripheral nerve procedures were recruited. They were stabilized before surgery with mask ventilation of 100% oxygen. Anaesthesia was induced with 2 μg kg−1 fentanyl and 3 mg kg−1 thiopental. Laryngoscopy and intubation were performed 4 min later. After intubation, desflurane anaesthesia (FiO2=1.0) was adjusted to maintain response entropy of the electroencephalogram at 40–45 for 20 min. Prefrontal cortex oxyhaemoglobin and deoxyhaemoglobin were determined every 2 s using frequency domain near-infrared spectroscopy. Blood pressure, heart rate and response entropy were collected every 10 s.

Awake oxyhaemoglobin and deoxyhaemoglobin were 18.9 ± 2.3 μmol (mean ± SD) and 12.7 ± 0.8 μmol, respectively, and neither changed significantly during induction. Intubation increased oxyhaemoglobin by 37% (P < 0.05) and decreased deoxyhaemoglobin by 16% (P < 0.05), and both measures returned to baseline within 20 min of desflurane anaesthesia. Blood pressure, heart rate and electroencephalogram response entropy increased during intubation, and the increase in heart rate correlated with the increase in brain oxygen saturation (r = 0.48, P < 0.05).

Intubation-related stress increased oxyhaemoglobin related to electroencephalogram and autonomic activation. Stress-induced brain stimulation may be monitored during anaesthesia using frequency domain near-infrared spectroscopy.