No evidence of memory processing during propofol-remifentanil target-controlled infusion anesthesia with bispectral index monitoring in cardiac surgery

Abstract

Objective: Auditory information presented during anesthesia can activate memory. Surgical stimulation may enhance memory formation. The authors' hypothesis is that implicit memory processing is not preserved during unconsciousness, even in the presence of a surgical stimulus.

Design: A double-blind randomized controlled trial.

Setting: A single-institution, university hospital.

Participants: Thirty-eight adults undergoing cardiac surgery.

Interventions: Patients were randomized to continuously hear either disc A or B during surgery. On each disc, 20 different words were recorded.

Measurements and main results: Implicit and explicit memory were tested. The study design was that each group served as a control for the other. The responses from both groups on both lists allowed the authors to compare the likeliness of correctly identifying the words from a list whether it was heard while under anesthesia or not. During the interview, no patient had explicit recall as investigated by the free recall test, and no one reported dreaming. As for implicit memory processing, the difference between the mean rate of correct answers on the word-stem completion test for the disc the patients heard (3.42% for disc A and 13.15% for disc B) or did not hear (3.15% for disc A and 14.73% for disc B) was not statistically significant (p = 0.95 for A and p = 0.42 for B).

Conclusions: Explicit and implicit memory were not detectable in patients anesthetized with an effect-site target-controlled infusion of propofol and remifentanil with bispectral index monitoring. These results suggest that there is no memory processing under anesthesia in the surgical setting.