The aim of this study was to investigate the effects of a positional change of regional cerebral oxygen saturation values (rSO2) because of the sitting position, before and after the administration of general anaesthesia. Twenty five consecutive patients of ASA class I or II undergoing shoulder surgery under general anaesthesia were chosen to participate in this study. Recordings of rSO2 values were performed in each patient of the study in two periods. In the first period rSO2 values were measured before anaesthesia induction in supine position and at 5 min after placing the patient in the sitting position. In the second period rSO2 values were measured in supine position 5 min after anaesthesia induction and at 5, 10, 15, 20, 25, 30 min after placing the patient in the sitting position. At all time intervals haemodynamic parameters, hemoglobin and SpO2 were recorded. Additionally, during the second time interval end-tidal CO2 (ETCO2) and temperature were also recorded.
Prior to anaesthesia induction no significant difference of rSO2 values were noted between supine and sitting position. During the second phase of the study a significant (p<0.01) reduction of the rSO2 values was measured after placing the patient in the sitting position, at all recording time intervals. At 5 and 10 min after placing the patient in the sitting position a significant (p<0.05) reduction of ΕΤCO2 was also noted. The other parameters did not show significant changes.
The present study shows that placing the patients in the sitting position after anaesthesia induction causes significant decrease in regional cerebral oxygen saturation.