The effect of bupivacaine on myocardial tissue hypoxia and acidosis during ventricular fibrillation

Systematic review of the effect of intravenous lipid emulsion therapy for local anesthetic toxicity

BACKGROUND

Following national and regional recommendations, intravenous lipid emulsion (ILE) has become established in clinical practice as a treatment for acute local anesthetic (LA) toxicity, although evidence of efficacy is limited to animal studies and human case reports. A collaborative lipid emulsion workgroup was therefore established by the American Academy of Clinical Toxicology to review the evidence on the effect of ILE for LA toxicity.

METHODS

We performed a systematic review of the literature published through 15 December 2014. Relevant articles were determined based on pre-defined inclusion and exclusion criteria. Pre-treatment experiments, pharmacokinetic studies not involving toxicity and studies that did not address antidotal use of ILE were excluded.

RESULTS

We included 113 studies and reports. Of these, 76 were human and 38 animal studies. One publication included both a human case report and an animal study. Human studies included one randomized controlled crossover trial involving 16 healthy volunteers. The subclinical LA toxicity design did not show a difference in the effects of ILE versus saline. There was one case series and 73 case reports of ILE use in the context of toxicity (83 patients) including CNS depression or agitation (n = 45, 54%), seizures (n = 49, 59%), hypotension, hypertension, EKG changes, arrhythmias (n = 39, 47%), cardiac arrest (n = 18, 22%), cardiopulmonary resuscitation, and/or requirement for endotracheal intubation and/or mechanical ventilation (n = 35, 42%). There were 81 (98%) survivors including 63 (76%) with no reported sequelae from the LA poisoning or ILE, although the presence or absence of sequelae was not reported in 15 (18%) cases. Animal studies included 29 randomized controlled studies, three observational studies, five case series, and one case report; bupivacaine was used in 29 of these reports (76%). Of 14 controlled experiments in animals, eight showed improved survival or time to return of spontaneous circulation and five no benefit of ILE versus saline or non-ILE treatments. Combining ILE with epinephrine improved survival in five of the six controlled animal experiments that studied this intervention. The studies were heterogeneous in the formulations and doses of ILE used as well as the doses of LA. The body of the literature identified by this systematic review yielded only a very low quality of evidence.

CONCLUSION

ILE appears to be effective for reversal of cardiovascular or neurological features in some cases of LA toxicity, but there is currently no convincing evidence showing that ILE is more effective than vasopressors or to indicate which treatment should be instituted as first line therapy in severe LA toxicity.

Safety Evaluation of EXPAREL (DepoFoam Bupivacaine) Administered by Repeated Subcutaneous Injection in Rabbits and Dogs: Species Comparison

EXPAREL (bupivacaine extended-release liposome injection), DepoFoam bupivacaine, is in development for prolonged postsurgical analgesia. Repeat-dose toxicity studies were conducted in rabbits and dogs to compare the potential local and systemic toxicities of EXPAREL and bupivacaine HCl (Bsol), and the reversibility of any effects. Dogs tolerated much larger doses than rabbits. EXPAREL-related minimal-to-moderate granulomatous inflammation was noted at the injection sites. In recovery animals, the granulomatous inflammation was observed less frequently and was characterized by an increased number of multinucleated giant cells. These effects were considered a normal response to liposomes and nonadverse. Rabbits are more sensitive than dogs. In rabbits, convulsions were noted with EXPAREL and more frequently with Bsol; a NOAEL was not identified. In dogs, EXPAREL was well tolerated (NOAEL > 30 mg/kg/dose). The cumulative exposure of EXPAREL in these studies is well in excess of the proposed maximum single-dose exposure that is intended in humans.

Effect of bupivacaine on sevoflurane-induced preconditioning in isolated rat hearts

Volatile anesthetics protect the heart against ischemia-reperfusion injury. As an adjunct to general anesthesia, local and regional application of bupivacaine is often used. However, systemic plasma levels of bupivacaine might be cardiodepressant and interfere with sevoflurane-induced cardioprotection. Effects of bupivacaine on sevoflurane-induced cardioprotection were assessed in isolated Langendorff-perfused rat hearts subjected to 35 min of global ischemia followed by 60 min reperfusion. Hearts (n=40) were randomized to different groups: 1. CONTROL; 2. Bupivacaine: addition of 0.125 or 1.0 μg/ml bupivacaine to the perfusate for 40 min prior to ischemia-reperfusion; 3. Sevoflurane: preconditioning induced by three times 5-min episodes of sevoflurane (2.5 vol.%) prior to ischemia-reperfusion; 4. Bupivacaine-sevoflurane: combined application of bupivacaine and sevoflurane. After ischemia-reperfusion, cardioprotection was assessed from infarct size and recovery of ventricular function, and phosphorylation levels of glycogen synthase kinase 3β (GSK3β) and 5'AMP activated protein kinase (AMPK) were determined. Infarct size was reduced in the sevoflurane and bupivacaine-sevoflurane groups (Sevo: 23±7% and Bupi-Sevo: 23±5% vs.

CONTROL

59±6%, P<0.05). In the bupivacaine group infarct size was reduced as well (34±3%). In the sevoflurane and bupivacaine-sevoflurane groups the recovery of left ventricular function (+dP/dt) was improved (Sevo: 59±2% and Bupi-Sevo: 59±2% vs.

CONTROL

47±3%, P<0.05), but not in the bupivacaine group (48±3%). AMPK and GSK3β phosphorylation were increased by sevoflurane but not by bupivacaine. Sevoflurane-induced cardioprotection was not affected by bupivacaine in the non-cardiotoxic range. Bupivacaine alone also reduced infarct size. Both anesthetics activated different signaling kinases, indicating the existence of different cardioprotective intracellular signaling cascades.

New model of ventricular fibrillation

The purpose of this study was to develop a more efficient and stable model of ventricular fibrillation (VF) in the isolated rabbit heart, because there is not a satisfactory model with this animal. We also observed the effects of increasing extracellular calcium in the stability and reversibility of the arrhythmia. After suspending the hearts in a classical Langendorff preparation, VF was induced by burst stimulation (current = 2.0 mA, pulse duration = 3 milliseconds, frequency = 50 Hz, voltage = 10 V, duration of stimulation = 5 minutes). The hearts were then divided into 2 groups, A and B. The hearts in group B were perfused with a modified Krebs-Henseleit solution, which contained twice as much calcium as the solution used in the other group. The rate of success with this model was 100% for both groups. The hearts fibrillated up to 30 minutes in group A and more than 40 minutes in group B, longer then all studies ever published in rabbit hearts. Ventricular fibrillation reverted to sinus rhythm in 100% of the hearts of group A when treated with an antifibrillatory drug, whereas no reversion at all was observed in the hearts of group B. We conclude that high extracellular calcium makes the reversion to sinus rhythm more difficult in this model. Our high rate of success and the exceptionally stable and long-lasting VF turn our model very effective for the study of antiarrhythmic interventions in the isolated rabbit heart.