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Dependence of explicit and implicit memory on hypnotic state in trauma patients
G H Lubke1, C Kerssens, H Phaf
1Vrije Universiteit Amsterdam, The Netherlands. gh.lubke@psy.vu.nl
Anesthesiology
|March 17, 1999
Summary
Intraoperative awareness is linked to hypnosis depth. Memory, particularly implicit memory, declined as the bispectral index (a measure of anesthetic effect) decreased during surgery.
Area of Science:
- Anesthesiology
- Neuroscience
- Cognitive Psychology
Background:
- The relationship between intraoperative awareness and anesthesia depth remains unclear.
- This study investigates if memory probability decreases with increasing hypnotic state depth.
Purpose of the Study:
- To determine the relationship between hypnotic state depth and memory of intraoperative events.
- To differentiate between explicit and implicit memory formation during anesthesia.
Main Methods:
- Patients undergoing surgery were exposed to auditory stimuli (words).
- Anesthetic depth was monitored using the bispectral index (BIS) and other indicators.
- Postoperative memory was assessed using a word stem completion test, analyzed with the process dissociation procedure.
Main Results:
- General memory performance decreased as BIS values declined.
- Implicit memory was significant at BIS levels of 40-60, while explicit memory was not reliably detected.
- An individual differences model, where memory depends on hypnotic depth, fit the data better than a model assuming equal memory performance.
Conclusions:
- Memory formation during surgery is dependent on the depth of hypnosis.
- Observed memory performance is primarily implicit, indicating auditory processing even at lower BIS levels.
- Anesthesia depth, specifically measured by BIS, is a critical factor in preventing intraoperative memory.