The answer is maybe and sometimes. Most investigators have agreed that giving a benzodiazepine has little effect on memory of events that have occurred before the drug was given (retrograde amnesia). In contrast most investigators believe that midazolam has a variable antegrade effect on explicit memory; that is the patient has no recall of events occurring after the drug is given. The amnesic dose of midazolam is not well defined. In part this is due to variable definitions of the term amnesia; in part due to a large number of poorly designed under powered studies that fail in some degree to address the specific question, and, finally, the amnesia after a specific dose of midazolam is some poorly defined function of the intensity of the stimulation; that is stronger stimuli may produce recall. As a general rule, doses of midazolam titrated to levels of sedation at which the patient no longer responds to name appear to have a very high probability of producing amnesia (these doses are on the order of 0.1 mg/kg i.v.). Miller et al (1) examined amnesia after three different dose levels of midazolam (0.07, 0.10 and 0.13 mg/kg) along with fentanyl 0.1 mg for dental extraction with local anesthesia. Fifteen percent of patients with the lowest dose of midazolam remembered some part of the tooth extraction and 10% of patients in the two higher dose groups had recollection. Ghoneim et al (2) determined the amnesic effects of midazolam (0.03 or 0.06 mg/kg i.v.) in volunteers receiving a subanesthetic dose of isoflurane (0.2% end tidal). Both doses of midazolam abolished recall of word lists. In contrast Miller et al (3) found a high level of intraoperative awareness with recall in a group of patients infused with 100 mcg/kg/min propofol and alfentanil (0.5 mcg/kg/min) and given various doses of midazolam for arthroscopic surgery. Six of 90 patients had awareness with recall. Of these, four of 21 patients did not receive midazolam, one of 24 received 0.015 mg/kg and one of 22 received 0.045 mg/kg midazolam i.v. Bulach et al (4) examined the effects of 2, 5, or 10 mg midazolam on retrograde and antegrade memory for events when it was given just prior to general anesthesia. There was no retrograde amnesia. The degree of antegrade amnesia was a function of dose with 5 or 10 mg doses producing better amnesia than the 2 mg dose. My conclusions are as follows: 1) amnesia after midazolam is variable, 2) amnesia is considerably more likely when the drug is titrated to a level of sedation at which the patient is not longer responding to their name, 3) a fixed dose of 2 mg will produce amnesia in some patients, 4) a dose based on body weight will probably be more effective particularly when doses are in the range of 0.05 – 0.1 mg/kg.
1. Miller RI: Duration of amnesia associated with midazolam/fentanyl intravenous sedation. Oral Maxillofac Surg 1989;47:155-158
2. Ghoneim MM et al: Interaction of subanaesthetic concentration of isoflurane with midazolam: effects on responsiveness, learning and memory. BJA 1998;80:581-587
3. Miller DR: Midazolam and awareness with recall during total intravenous anaesthesia. Can J Anaesth 1996;43:946-53
4. Bulach R: Double-blind randomized controlled trial to determine extent of amnesia with midazolam given immediately before general anaesthesia. BJA 2005;94:300-5
David S. Smith, M.D, Ph.D.