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LETTER TO THE EDITOR

Minimum Effective Dose of Bupivacaine Required for Transurethral Procedures Remains Uncertain

Department of Anaesthesiology, Pain and Perioperative Medicine (Dutta) Critical Care Medicine; Sir Ganga Ram Hospital; New Delhi, India; duttaamitabh{at}yahoo.co.in (Taneja)

To the Editor:

The recent paper by Zohar et al. (1) establishing the minimum effective dose of bupivacaine required for brief transurethral procedures in elderly patients raises an important concern in that the four groups in the investigation were not matched. In other words, the final drug solution was prepared by adding a variable amount of 10% dextrose to the opioid—0.5% bupivacaine solution in each group (Table 1). Recently, Mcleod (2) demonstrated that density of spinal anesthetic solution increases linearly and significantly with addition of increasing concentrations (1%–8%) of dextrose to 0.5% bupivacaine. Given that a change in the density of spinal anesthetic solution as little as 0.0006 mg/mL may influence drug spread (3) and solutions with density greater than 1.0018 are expected to behave hyperbarically (4), the final clinical effect may be different for different level of hyperbaricity. This statement is endorsed by Kampe et al.’s (5) failure to achieve adequate block height with hyperbaric bupivacaine-opioid solution.

REFERENCES

1. Zohar E, Noga Y, Rislick U, Leibovitch I, Fredman B. Intrathecal anesthesia for elderly patients undergoing short transurethral procedures: a dose-finding study. Anesth Analg 2007;104:552–4[Abstract/Free Full Text]
2. Mcleod GA. Density of spinal anesthestic solutions of bupivacaine, laevobupivacaine, and ropivacaine with and without dextrose. Br J Anaesth 2004;92:547–51[Abstract/Free Full Text]
3. Stienstra R, Gielen M, Kroon JW, Van Poorten F. The influence of temperature and speed of injection on the distribution of a solution containing bupivacaine and methylene blue in a spinal canal model. Reg Anesth 1990;15:6–11[Medline]
4. Barash PG, Cullen BF, Stoelting RK. Epidural and spinal anesthesia. In: Clinical Anesthesia. 3rd ed. Philadelphia: Lippincott-Raven, 1997:654
5. Kampe S, Pietruck C, Diefenbach C. Density determination of bupivacaine and bupivacaine-opioid mixtures for spinal anesthesia. Anesth Analg 2003;96:1234[Free Full Text]

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