[Does intraoperative hyperventilation improve neurological functions of older patients after general anaesthesia?]

Abstract

The purpose of the study was to investigate the effect of intraoperative hyperventilation on postoperative cognitive functions.

Methods: A total of 120 patients (60 older and 60 younger than 65 years old) were allocated randomly to group I "hyperventilation" (p(et)CO(2)=30 mmHg) or group II "normoventilation" (p(et)CO(2)=45 mmHg). Before the operation and on days 1, 3 and 6 after the operation, a battery of neuropsychological tests was performed (concentration endurance test d2, number connection test, digit symbol test). A decline of 20% in at least one test was regarded as postoperative cognitive deficit (POCD). Anaesthesia was maintained with isoflurane in nitrous oxide/oxygen supplemented with fentanyl.

Results: In all patients pooled, POCD was present in 26 patients (22%). In patients older than 65 years, POCD was present in 3 cases after hyperventilation and 13 cases after normoventilation ( p<0.01). In younger subjects, 5 cases of POCD were diagnosed in each ventilation group. Furthermore, POCD was more severely pronounced in older patients after normoventilation.

Conclusion: In older patients, POCD occurred more frequently after intraoperative normoventilation. We assume that a reduced amount of noxious substances reach the brain after hyperventilation, because hyperventilation reduces the cerebral blood flow.