Subanesthetic Concentrations of Desflurane and Propofol Suppress Recall of Emotionally Charged Information

Abstract

Whether anesthetized patients register emotionally charged information remains controversial. We tested this possibility using subanesthetic concentrations of propofol or desflurane. Twenty-two volunteers (selected for hypnosis susceptibility) received propofol and desflurane (on separate occasions, and in a random order) at a concentration 1.5-2 times each individual's minimum alveolar anesthetic concentration (MAC)-awake (or equivalent for propofol). We gave vecuronium, intubated the trachea of each volunteer, controlled ventilation, and then presented a neutral (control) drama or a "crisis" drama stating that the oxygen delivery system had failed, assigning crisis and control dramas in a blinded, randomized, and balanced manner. One day later, interviewers blinded to the assigned drama conducted a 2-h structured interview (including hypnosis) to determine whether the contents of the interviews after crisis and control dramas differed. In addition, messages permitting subsequent assessment of learning of matter-of-fact information (Trivial Pursuit-type question task and a behavior task) were presented at the anesthetic concentration just sufficient to prevent response to command in each volunteer. No analyses of the tasks involving matter-of-fact information revealed learning except one which correlated hypnosis susceptibility with behavior task performance. Both propofol and desflurane suppressed memory of the crisis. Consistent with previous findings for isoflurane and nitrous oxide, propofol and desflurane suppressed learning of matter-of-fact information at concentrations just above MAC-awake, except that volunteers' susceptibility to hypnosis correlated with performance of a behavior suggested during anesthesia. Propofol and desflurane suppressed learning of emotionally charged information at anesthetic concentrations 1.5-2 times MAC-awake (less than MAC), a different result from that previously reported for ether.

Investigations of Hypesthesia: Using Anesthetics to Explore Relationships between Consciousness, Learning, and Memory

“…None of these tests showed memory for the stimuli presented during hypesthesia. Chortkoff et al (1995) also failed to demonstrate learning during hypesthesia. They presented the message and the facts to subjects receiving just enough anesthetic to stop them from responding to commands to squeeze the experimenter's hand.…”

“…The studies discussed so far tell us that light hypesthesia disrupts explicit but not implicit memory and that deeper hypesthesia abolishes all memory, even for salient stimuli such as surgery or Chortkoff et al's (1995) ''crisis.'' However, they tell us little about the pattern of change in memory formation with loss of consciousness; thus the extent to which implicit memory resists loss of consciousness remains unclear.…”

Inhibition of learning and memory by general anesthetics

“…56 Memory for emotional encounters was blocked by sub-anesthetic concentrations of sevoflurane (0.25%), desflurane (1.5-2 times MAC-awake), and propofol (1.5-2 times MAC-awake). 57,58 At MAC-equivalent concentrations, some anesthetics are more effective than others at preventing memory. For example, both isoflurane and nitrous oxide suppressed memory in a dose-dependent manner, although isoflurane was more effective than MAC-equivalent concentrations of nitrous oxide.…”

Patients' memories of events during general anaesthesia

“…This study raised the possibility that patients may still retain the ability to process auditory information, whilst being sufficiently anaesthetised to remain unresponsive to surgical stimulation and lacking any explicit recall of events [17]. Thirty years later, Levinson repeated this study, but failed to replicate his original findings [18].…”

“…They actually range from 30 to 100 Hz and may overlap with the beta band (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). It is believed that an important function of the '40-Hz' rhythm is to bind together the many discontinuous cortical networks needed in the conscious process.…”