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Vecuronium dissolved in normal saline exaggerates pain on intravenous injection.

BACKGROUND
On some anesthetic occasions, many patients complained of pain at the site of injection when vecuronium, dissolved in normal saline, was administered intravenously. The aims of this study was to compare the incidence of pain on i.v. injection of vecuronium either dissolved in normal saline or in a solvent provided by the pharmaceutical manufacturer.


METHODS
We studied eighty patients of ASA physical status class I-II undergoing elective surgery under general anesthesia. Patients were arranged randomly to receive intravenous 0.1 mg/kg vecuronium dissolved either in solvent (n = 40) or in normal saline (n = 40) through the catheter indwelling in a vein on the dorsum of hand over 5 seconds. Immediately after injection, a nurse was appointed to score the degree of pain. Induction of anesthesia was accomplished with thiopental and fentanyl 30 seconds after vecuronium administration.


RESULTS
Vecuronium dissolved in normal saline induced severe pain more frequently during injection than that dissolved in solvent (27.5% versus 10%). There was no significant difference in pH between these two solutions (3.87 versus 4.08). However, vecuronium dissolved in normal saline showed higher osmolality than that dissolved in solvent (425 +/- 7 mOsm/kg versus 149 +/- 3 mOsm/kg).


CONCLUSIONS
Pain resulting from intravenous injection of vecuronium can be aggravated if normal saline was used as the solvent. Increased osmolality may also be responsible for this phenomenon.