Purpose
Lipid emulsion is the only specific antidote for local anesthetic systemic toxicity, but no dose-finding study has been conducted. We compared 3 published regimens and alternative schedules that deliver the same dose in different ways using a human model of intravenous bupivacaine overdose.
Methods
A 14-compartment human bupivacaine model was independently reimplemented without fitted parameters, replacing first-order lipid elimination with a saturable term. Toxicity was modeled as 112.5 mg administered intravenously over 3 minutes. Benefit was defined as the predicted maximum decrease in myocardial bupivacaine within 30 minutes, and harm as the predicted relative lipid load, indexed by peak plasma triglyceride concentration. Neither measure is a validated surrogate.
Results
The 3 guidelines specify the same doses but different bolus durations: 1 minute versus 2–3 minutes. At a matched dose of 12 mL/kg, myocardial bupivacaine decreased by 30.5% with the 1-minute bolus and 24.9% with the 2.5-minute bolus, with the same lipid load. The completed American Society of Regional Anesthesia and Pain Medicine regimen (7.64 mL/kg) achieved a 24.6% decrease versus 24.9% with 12 mL/kg; thus, complete regimens differ in schedule as well as dose. Repeating the 1-minute bolus twice, for a total of 4.5 mL/kg, achieved a 31.9% decrease with 62% less emulsion. Start time had the greatest effect: the best regimen achieved a 41.8% decrease when started at the end of the injection, but only 9.6% when started at 10 minutes.
Conclusion
In this bupivacaine model, bolus duration distinguished the regimens more than dose did, and delay had a greater effect than either, eliminating most of the benefit without changing the lipid load. Treatment should begin at the first signs of toxicity, and 20% lipid emulsion should be immediately available wherever local anesthetics are used.

Objectives

There are controversies about the analgesic effects of intraaarticular morphine and local anethetics bupivacaine. This study sought to compare the effects of saline with mor-phine, bupivacaine with or without epinephrine, administrated intraarticularly upon pos-toperative pan following arthroscopic knee surgery under general anesthesia.

Methods

In a double-blined, randommized manner, 40 patients received one of saline(20ml, n=10), morphine(1mg in 20ml NaCl, n=10), bupivacaine(0.25%, 20ml, n=10), bu-pivacaine with epinephrine(0.25%, 20ml, 200ug of epinephrine, n=10) intaarticularly at the completion of surgery. The pain scores by VAS were determined after 1,2,3,4 and 24 hours after intraarticular administration.

Results

There were no significant statistical differences between four groups in the pain score. The maximal pain scores were 37.5 in control group, 48.0 in morphine group, 33.6 in bupivacaine group postoperative 1 hour and 32.9 in bupivacaine with epinephrine group pos-toperative 2 hours. The pain scores were decreased as the time went by and were minimin as 21.4 in control group, 17.6 in morphine group, 11.2 in bupivacaine group and 12.3 in bu-pivacaine with epinephrine group 24 hour postoperatively.

Conclusion

Though there were no significant statistical significances with those doses, there were tendencies that the bupivacaine group with or without epinephrine had the postoperative analgesic effect rather than control group, and morphine group had a slow onset of analgesic ef-fect. So, we should study to decide the dose or volume of the drugs and appropriate time to evaluate for the anagesic effects after knee arthroscopy further.