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[Cognitive functions and cerebral oxygenation of older patients after general and regional anaesthesia].

OBJECTIVE
The aim of the present study was to show the influence of cerebral oxygenation (regional cerebral oxygen saturation rSO(2) by near infrared spectroscopy) and of the nocturnal arterial oxygen saturation (SatO(2) by pulse oximetry) on the restitution of cognitive functions in patients aged between 40 and 85 years scheduled for elective hip arthroplasty.


METHODS
A total of 40 patients (ASA II) were randomized to be operated either in general anaesthesia or regional anaesthesia. The patients were additionally classified by age (40-64 years and 65-85 years). Cognitive functions were tested 14-16 h pre-operatively (t0), 1.5 h post-operatively (t1) and at the first and third postoperative days (t2 and t3). During testing, as well as during surgery and postoperatively until t1, rSO(2) was continuously measured. SatO(2) was measured in the night before surgery (N0) and for 3 nights after surgery (N1, N2, N3) between 22.00 p.m. and 5.00 a.m. These measurements were divided into interval groups (80-83%, 84-87%, 88-91%, 92-95%, 96-100%).


RESULTS
Almost all cognitive functions were significantly reduced at t1 in all groups compared to t0, but recovered up to the third postoperative day (t3). RSO(2) in contrast was significantly reduced in all groups compared to t0 at the third postoperative day (t3). The relative proportion of the intervals compared to the total measurement time for SatO(2) shifted in both anaesthesia procedures: before surgery (N0) the most frequented interval was 96-100%, after surgery (N1, N2) it was 88-91%. There was no correlation between rSO(2), the restitution of the tested cognitive functions and SatO(2).


CONCLUSIONS
Cognitive functions recovered completely during the first 3 postoperative days in patients scheduled for elective hip surgery under general or regional anaesthesia regardless of age and type of anaesthesia. This restitution of cognition occurred despite a significant decrease of cerebral oxygenation (rSO(2)) and despite an increase of nocturnal hypoxaemic intervals. Changes of the rsO(2) up to 3% below the baseline values (measured by NIRS) do not predict cognitive restitution. A minimal limiting value of the rSO(2) could not be defined.