Simultaneous determination of unbound ropivacaine in rat blood and brain using microdialysis.

To investigate the pharmacokinetics of ropivacaine in rat blood and brain, a sensitive HPLC method and microdialysis were developed for the simultaneous determination of unbound ropivacaine in rat blood and brain. Adult, male Sprague-Dawley rats (290-350 g) were anesthetized with sodium pentobarbital (50 mg/kg, i.p.). Two microdialysis probes were inserted, one into the jugular vein toward right atrium, and one into the brain striatum of rats. Ropivacaine (5 mg/kg, i.v.) was then administered via the femoral vein. Blood and brain dialysates were collected and eluted with a mobile phase containing methanol-acetonitrite-20 mM monosodium phosphoric acid (pH 5.5) (10:40:50, v/v/v) in a liquid chromatographic system. Separation of ropivacaine was achieved by a CN column (Phenomenex Luna, 250x4.6 mm, particle size 5 microm; Torrance, CA, USA) within 10 min. The UV detector wavelength was set at 205 nm and the detection limit of ropivacaine was 20 ng/ml. The intra- and inter-day accuracy and precision of the analyses were less than 10% in the ranges of 0.02-5 microg/ml. The pharmacokinetic data were calculated from the individual animal measurements of dialysate concentration versus time. This method exhibits no endogenous interference and its sensitivity is sufficient for the determination of biological samples. The present results confirm that microdialysis sampling followed by LC separation with UV detection represents a viable approach for the measurement of free ropivacaine in rat brain and plasma.

Propofol-sodium thiopental admixture reduces pain on injection.

BACKGROUND: Propofol injection associated with a high incidence of pain is well known. Propofol and sodium thiopental mixture has recently been reported to be used for cost saving and able to reduce pain on injection. METHODS: This prospective, randomized, double blind trial was designed to compare the efficacy of different percentages of propofol and sodium thiopental mixture in minimizing propofol injection pain. 146 ASA class 1 patients were assigned to seven groups (pure propofol, pure sodium thiopental, and propofol premixed with 10%, 20%, 30%, 40%, and 50% of sodium thiopental). The intensity of pain was graded and recorded as severe, moderate, mild and no pain according to the response of the patients to the injection. RESULTS: The intensity of injection pain was significantly greater for pure propofol than the others while it was not significantly different among the other groups in comparison. CONCLUSIONS: Sodium thiopental, when added to propofol, can significantly reduce propofol injection pain. This attenuation effect was noted even with as low as 10 volume % of sodium thiopental.

Fatal hyperkalemia during rapid and massive blood transfusion in a child undergoing hip surgery--a case report.

We report a girl who developed severe and fatal hyperkalemia following rapid and massive blood transfusion during surgery. She was 7-year-old, 20-kg in weight, and received wide resection of the femoral bone with custom prosthesis implant because of malignant femoral osteosarcoma. During the procedure, bleeding was active and profuse and amounted to about 3,000 mL in 4 h, eventuating in shock. Despite rapid transfusion with 15 units of packed red blood cells (RBC) still she remained hypotensive and hypovolemic. When we switched to give her whole blood, actually 100 mL having been given, widening of QRS complex followed immediately by cardiac arrest developed. Cardiopulmonary resuscitation although started at once was unsuccessful. At this juncture, arterial blood gas analysis showed acidosis and severe hyperkalemia (10.3 mmol/L), possibly resulting from transfusion of blood of older storage. The case reminded us once again the importance and necessity of the use of potassium-low blood component (fresh, saline-washed RBCs) in case of massive and rapid blood transfusion especially in pediatric patients with hypovolemia and low cardiac output.