Background

Data from various animal studies indicate that lipid infusion increases resistance to local anesthetic toxicity and improves success of resuscitation from local anesthetic overdose. This work was initiated by a chance observation made during a series of experiments testing whether a lipid infusion would increase arrhythmias during bupivacaine toxicity.

The investigators had noted that a patient with carnitine deficiency exhibited extreme sensitivity to bupivacaine induced cardiac arrhythmias. They postulated that bupivacaine might interfere with carnitine metabolism. Carnitine is an essential component of the biochemical pathways that transport fatty acids into mitochondria where, under normal aerobic conditions, they provide the majority of cardiac energy needs. Other investigators had shown that intracellular fatty acid derivatives accumulate during myocardial ischemia and postulated that they contribute to ischemia-induced arrhythmias. The reasoning was that if bupivacaine induced arrhythmias by inhibiting carnitine-mediated mitochondrial fatty-acid uptake, then a pretreating infusion of lipids might aggravate such arrhythmias. The opposite was found. Infusing lipids into rats made them more resistant to bupivacaine-induced asystole.

The next series of experiments confirmed in anesthetized rats that lipid infusion improves the success of resuscitation from bupivacaine toxicity. Subsequent studies in dogs showed that whether given immediately after the bupivacaine, or several minutes later, lipid infusion significantly improved recovery from an otherwise fatal dose of bupivacaine (10mg/kg). In those experiments all six treated animals rapidly recovered normal hemodynamic parameters while none of the controls survived.

The question of using this treatment in patients has sparked some controversy in the anesthesia literature. The hallmark of local anesthetic-induced cardiac arrest is relative resistance to standard resuscitative measures, hence there would seem to be little to lose in trying the method in someone who has failed ACLS and is effectively dead. Some authors have used the discussion to emphasize, rightly, the importance of preventing such occurrences. However, such good intentions don’t obviate the need to contemplate alternative resuscitative measures when an unexpected catastrophe does occur. ….and unfortunately, they do…and will. The main problem is the inability to perform clinical trials of a treatment for patients in extremis from a rare event. The numbers will simply not be sufficient to make meaningful comparisons of treatment options. Hence, the importance of clinical case reports from which we can infer some limited measure of efficacy.