To the Editor:
Kudos to Kudoh et al. (1) on their recent publication on small-dose ketamine. I respectfully submit two concerns. First, they cited Dundee and Wyant (2) to substantiate their statement that “ketamine produces posthypnotic emergence reactions, such as hallucinations or delirium after surgery” but fail to document the presence or absence of either of these phenomenon in their patients in either the Results or the Discussion.
Second, they describe the induction as 1 mg/kg ketamine and 1.5 mg/kg propofol without specifying either the subjective endpoints of hypnosis from the visual analog scale, VAS (3), the observer’s assessment of alertness/sedation, OAA/S (4) or the possibly more objective bispectral index (BIS) monitor (5). Blocking hallucinations from ketamine (6) in my pre-BIS experience involves titrating the propofol to a loss of lid reflex (LLR) and loss of verbal response (LVR) and in the BIS monitored era, titrating to 70–75 before administering the ketamine. My specific concern is if the brain level of propofol is inadequate to shield the brain from Kudoh et al.’s 1 mg/kg dose of ketamine, patients may experience hallucinations or emergence delirium needlessly.
Barry L. Friedberg, MD
1. Kudoh A, Takahira Y, Katagai H, et al. Small-dose ketamine improves the postoperative state of depressed patients. Anesth Analg 2002; 95: 114.
2. Dundee JW, Wyant G. Intravenous anesthesia. 2nd ed. Edinburgh, Scotland: Churchill Livingstone, 1988.
3. Maxwell C. Sensitivity and accuracy of the visual analogue scale: a psychophysical classroom experiment. Br J Clin Pharmacol 1978; 6: 15.
4. Chernik DA, Gillings D, Laine H, et al. Validity and reliability of the observer’s assessment of alertness/sedation scale: study with intravenous midazolam. J Clin Psychopharmacol 1991; 10: 244.
5. Kearse LA, Rosow C, Zaslavsky A, et al. Bispectral analysis of the electroencephalogram predicts conscious processing of information during propofol sedation and hypnosis. Anesthesiology 1998; 88: 25.
6. Friedberg BL. Hypnotic doses of propofol block ketamine induced hallucinations. Plast Reconstr Surg 1993; 91: 196.