Binding of long-lasting local anesthetics to lipid emulsions

An in vitro evaluation of intravenous lipid emulsion on three common canine toxicants

Objective

To determine whether intravenous lipid emulsion (ILE) therapy significantly reduces the concentration of baclofen, ibuprofen, and/or bromethalin in canine whole blood over time.

Animals

Seven 500 mL bags of canine DEA 1.1 negative blood were divided into aliquots of 125 mL and randomly assigned to one of three treatment groups (baclofen, ibuprofen, bromethalin) or four control groups (a positive control for each treatment group and a negative control group).

Procedures

Injectable ibuprofen (200 mg/kg), baclofen (8 mg/kg), or bromethalin (3 mg/kg) was apportioned into 125 mL aliquots of canine whole blood and incubated for 30 min at 38.5°C. ILE (12.4 mL, Intralipid® ) was added to each sample and the solution vortexed [215 rpm for 15 min at 37°C (98.6°F)]. Samples were obtained at designated time points (0, 15, 30, 60, 180, 360 min), centrifuged, and separated into serum and RBC fractions. Serum samples were ultracentrifuged (22,000 g for 10 min at 37°C) to separate lipid rich and poor fractions. Samples were stored at -80°C prior to analysis.

Results

A significant decrease in total drug concentration was established for bromethalin and its metabolite desmethylbromethalin compared to positive controls. ILE significantly reduced desmethylbromethalin at the 30-and 360-min time points. The remainder of the desmethylbromethalin time points did not reach significance. Bromethalin concentration was significantly reduced at all time points compared to positive controls. Neither baclofen nor ibuprofen had significant changes in concentration.

Conclusion

ILE therapy was effective at reducing the total drug concentration of bromethalin and its metabolite desmethylbromethalin supporting the lipid sink theory. As a single compartment in vitro study, this study does not evaluate other proposed mechanisms of action of ILE therapy. ILE therapy may have other means of significantly decreasing lipophilic drug concentration in cases of toxicosis.

Clinical effects and adverse effects of intravenous lipid emulsion treatment in dogs and cats with suspected poisoning

This retrospective study aimed to evaluate the effects on the clinical signs of poisoning and adverse effects of intravenous lipid emulsion treatment in 82 animals (dogs and cats) with suspected poisonings over 18 months. Physical examination parameters and state of consciousness were documented every hour after the intravenous administration of a bolus of 2 ml/kg and 0.25 ml/kg/min over 60 minutes of a 20% intravenous lipid emulsion. The modified Glasgow coma scale and laboratory findings (blood gas analysis, triglyceride, lactate) were evaluated initially and three hours after discontinuing intravenous lipid emulsion administration. A statistical evaluation of the occurrence of adverse effects and the development of laboratory values was performed. A decrease in respiratory rate in the second control (8-12 hours) after ILE was observed. Three hours after completing of the intravenous lipid emulsion, triglyceride concentration increased about 10 times (p <0.001). Venous carbon dioxide partial pressure, bicarbonate, base excess, as well as the electrolytes sodium, potassium and ionized calcium decreased significantly (p <0.001). Patients who experienced a worsening of the modified Glasgow coma scale had a higher increase in triglyceride concentrations (p = 0.041) and plasma lactate (p = 0.034) and a larger decrease in bicarbonate concentrations (p = 0.053) compared to others. About 54% (n = 44) of the patients showed adverse effects which could be attributed to the administration of intravenous lipid emulsion and may be associated with a higher triglyceride increase. All of them were completely reversible within 33 hours. Adverse effects associated with intravenous lipid emulsion therapy were observed in half of the patients and were associated with a higher increase in triglycerides.

Lipid emulsion treatment for local anesthetic systemic toxicity in pediatric patients: A systematic review

BACKGROUND

Local anesthetic systemic toxicity (LAST) is rare, but fatal; the current widely used treatment is lipid emulsion (LE). The goal of this study was to analyze and review case reports on LE treatment for LAST in pediatric patients.

METHODS

We performed a systematic review using case reports on LE treatment for LAST in pediatric patients, searching PubMed and Scopus databases to March 2023 using the following keywords: ("local anesthetic toxicity" OR "local anesthetic systemic toxicity" OR LAST") AND ("newborn" OR "infant" OR "child" OR "children" OR "adolescent" OR "pediatric") AND ("lipid emulsion" OR "Intralipid").

RESULTS

Our search yielded 21 cases, revealing that nearly 43% patients with LAST were less than 1 year old, and most cases were caused by bupivacaine (approximately 67% cases). "Inadvertent intravascular injection" by anesthesiologists and "overdose of local anesthetics" mainly by surgeons were responsible for 52% and 24% cases of LAST, respectively. LAST occurred in the awake state (52%) and under general anesthesia (48%), mainly causing seizures and arrhythmia, respectively. Approximately 55% of patients received LE treatment in <10 minutes after LAST, mainly improving cardiovascular symptoms. A 20% LE (1.5 mL/kg) dose followed by 0.25 mL/kg/minutes dose was frequently used. LE and anticonvulsants were mainly used in the awake state, whereas LE with or without vasopressors was mainly used under general anesthesia. LE treatment led to full recovery from LAST in 20 cases; however, 1 patient died due to underlying disease.

CONCLUSION

Consequently, our findings reveal that LE is effective in treating pediatric LAST.

Lipid emulsion for xenobiotic overdose: PRO

Infusion of lipid emulsion for drug overdose arose as a treatment for local anaesthetic systemic toxicity (LAST) initially based on laboratory results in animal models with the subsequent support of favourable case reports. Following successful translation to the clinic, practitioners also incorporated lipid emulsion as a treatment for non-local anaesthetic toxicities but without formal clinical trials. Recent clinical trials demonstrate a benefit of lipid emulsion in antipsychotic, pesticide, metoprolol and tramadol overdoses. Formal trials of lipid emulsion in LAST may never occur, but alternative analytic tools indicate strong support for its efficacy in this indication; for example, lipid emulsion has obviated the need for cardiopulmonary bypass in most cases of LAST. Herein, we describe the pre-clinical support for lipid emulsion, evaluate the most recent clinical studies of lipid emulsion for toxicity, identify a possible dose-based requirement for efficacy and discuss the limitations to uncontrolled studies in the field.

Lipid Emulsion to Treat Acute Poisonings: Mechanisms of Action, Indications, and Controversies

Biodetoxification using intravenous lipid emulsion (ILE) in acute poisoning is of growing interest. As well as for local anesthetics, ILE is currently used to reverse toxicity caused by a broad-spectrum of lipophilic drugs. Both pharmacokinetic and pharmacodynamic mechanisms have been postulated to explain its possible benefits, mainly combining a scavenging effect called "lipid sink" and cardiotonic activity. Additional mechanisms based on ILE-attributed vasoactive and cytoprotective properties are still under investigation. Here, we present a narrative review on lipid resuscitation, focusing on the recent literature with advances in understanding ILE-attributed mechanisms of action and evaluating the evidence supporting ILE administration that enabled the international recommendations. Many practical aspects are still controversial, including the optimal dose, the optimal administration timing, and the optimal duration of infusion for clinical efficacy, as well as the threshold dose for adverse effects. Present evidence supports the use of ILE as first-line therapy to reverse local anesthetic-related systemic toxicity and as adjunct therapy in lipophilic non-local anesthetic drug overdoses refractory to well-established antidotes and supportive care. However, the level of evidence is low to very low, as for most other commonly used antidotes. Our review presents the internationally accepted recommendations according to the clinical poisoning scenario and provides the precautions of use to optimize the expected efficacy of ILE and limit the inconveniences of its futile administration. Based on their absorptive properties, the next generation of scavenging agents is additionally presented. Although emerging research shows great potential, several challenges need to be overcome before parenteral detoxifying agents could be considered as an established treatment for severe poisonings.

Sodium bicarbonate reverts electrophysiologic cardiotoxicity of ropivacaine faster than lipid emulsions in a porcine model

Ropivacaine has been described as a safer local anaesthetic (LA); however, serious cardiotoxic accidents have been reported. Intravenous-lipid-emulsion (ILE) therapy during LA intoxication seems to act as an antidote. Sodium bicarbonate is the standard treatment for sodium channel blocker drug toxicity. We compared both antidotes on the reversion of electrophysiologic toxicity induced by ropivacaine. Ropivacaine 5 mg kg^-1 was administered in 24 pigs, and 3 min later, the animals received ILE: 1.5 ml kg^-1  + 0.25 ml kg^-1  min^-1 (ILE group); sodium bicarbonate: 2 mEq kg^-1  + 1 mEq kg^-1  h^-1 (NaHCO₃ group); saline solution (CTL group). Electrophysiological parameters were evaluated for 30 min. The area under the curve (AUC) for the first 5 or 30 min was compared between groups. Ropivacaine induced a lengthening of the PR interval by 17% (P = 0.0001), His-ventricle-interval by 58% (P = 0.001), sinus QRS complex by 56% (P = 0.0001), paced QRS at 150 bpm by 257% (P = 0.0001), and at 120 bpm by 143% (P = 0.0001) in all groups. At 5 min after treatment, sinus QRS in the NaHCO₃ group was shorter than that in the CTL group (AUC_QRS5 , P = 0.003) or ILE group (AUC_QRS5 , P = 0.045). During the first minute, seven of the animals in the NaHCO₃ group vs. two in the ILE or 0 in the CTL group recovered more than 30% of the sinus QRS previously lengthened by ropivacaine (P = 0.003). Sodium bicarbonate reversed the electrophysiological toxicity of ropivacaine faster than ILE and control groups.

Successful Treatment of Amoxapine-Induced Intractable Seizures With Intravenous Lipid Emulsion

BACKGROUND

Amoxapine is a second-generation tricyclic antidepressant with a greater seizure risk than other antidepressants. If administered in large amounts, amoxapine can cause severe toxicity and death. Therefore, it is necessary to terminate seizures immediately if amoxapine toxicity occurs. However, intractable seizures often occur in these patients. We describe a case of intractable seizures caused by amoxapine poisoning, in which intravenous lipid emulsion (ILE) was used successfully.

CASE REPORT

A 44-year-old woman with a history of depression ingested 3.0 g of amoxapine during a suicide attempt. Although she was initially treated with intravenous diazepam, her seizures persisted. Levetiracetam and phenobarbital were then administered, but seizures persisted. Hence, ILE was injected for over 1 min. At 2 min after ILE administration, the patient's status seizures ceased. Recurrence of seizures was observed 30 min after ILE, and the seizures disappeared after re-administration of ILE. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: ILE may be effective in amoxapine intoxication. Emergency physicians may consider ILE as an adjunctive therapy for amoxapine poisoning with a high mortality rate. ILE should be implemented carefully with monitoring of total dosage and adverse events.

Local Anesthesia in Interventional Radiology

Interventional radiology is an evolving field that treats a variety of diseases. Local anesthetics is an important component of pain management during interventional radiologic procedures. It is highly effective and generally safe for routine procedures. However, local anesthetics can be associated with painful initial injection, allergic reactions, and rare but potentially devastating systemic toxicities. Recent evidence has shown that buffered solution and warm local anesthetics may reduce injection discomfort and improve clinical efficacy. Sensible safety practices and prompt recognition/treatment of the systemic toxicity are of paramount importance to provide safe local anesthesia. Interventional radiologists should be familiar with the basic pharmacology, common local anesthetics, optimizing strategies, complications, and management to provide safe and effective local anesthesia for patients.

Effects of intravenous lipid emulsions on the reversal of pacing-induced ventricular arrhythmias and electrophysiological alterations in an animal model of ropivacaine toxicity

INTRODUCTION

Ropivacaine is considered to have a wider margin of cardiovascular safety. However, several reports of ventricular arrhythmias (VA) due to ropivacaine toxicity have been documented. Intravenous lipid emulsions (ILEs) have recently been used successfully in the treatment of local anesthetic intoxication. The main objective of the present study was to evaluate the efficacy of the ILEs in the prevention of pacing-induced-VA and electrophysiological alterations in an animal model of ropivacaine toxicity.

METHODS

Nineteen pigs were anesthetized and instrumentalized. A baseline programmed electrical ventricular stimulation protocol (PEVSP) to induce VA was performed. Ropivacaine (5 mg·kg^-1 + 100 μg·kg^-1·min^-1) followed by normal saline infusion (control group n = 8) or intralipid 20% (1.5 mL·kg^-1 + 0.25 mL·kg^-1·min^-1) for the ILE group (n = 8), were administered three minutes after the ropivacaine bolus. PEVSP was repeated 25 min after the onset of ropivacaine infusion. Pacing-induced VA and electrophysiological abnormalities were assessed in both groups. A sham-control group (n = 3) without ropivacaine infusion was included.

RESULTS

Most of the electrophysiological parameters evaluated were affected by ropivacaine: PR interval by 28% (p = 0.001), AV interval by 40% (p = 0.001), sinus QRS by 101% (p = 0.001), paced QRS at a rate of 150 bpm by 258% (p = 0.001), and at 120 bpm by 241% (p = 0.001). Seven animals (87.5%) in the control group and eight animals (100%) in the ILE group developed sustained-VA (p = 0.30). Successful resuscitation occurred in 100% of animals in the ILE group vs. 57% of animals in the control group, p = 0.038. Pacing-induced-VA terminated at the first defibrillation attempt in 75% of the animals in the ILE group vs. 0% in the control group, p = 0.01.

CONCLUSION

Ropivacaine strongly altered the parameters of ventricular conduction, thus facilitating the induction of VA. ILEs did not prevent pacing-induced VA. However, facilitated resuscitation and termination of VA were delivered at the first defibrillation attempt compared to the control group.

Prediction of drug capturing by lipid emulsions in vivo for the treatment of a drug overdose

Despite the successful treatment of drug intoxications, little information is available to quantitively predict the effect of lipid emulsions on pharmacokinetic features of overdosed drug molecules. We defined two new parameters, drug accommodation capacity and drug capture kinetics, to characterize the drug capture capability of lipid emulsions. By precisely characterizing their drug capture capability, the effect of lipid emulsions on pharmacokinetic features of overdosed drug molecules was quantitively described. This quantitative description enabled an accurate prediction of the reducing extent on the half-life and area under drug concentration-time curve, which was verified by the successful treatment of overdosed propafenone. Moreover, the capture effect prediction using drug capture capability was more accurate than that of directly using logP. Overall, the developed capture capability accurately described the effect of lipid emulsions on drug pharmacokinetic features, which can guide the clinical application of lipid emulsions for the treatment of drug overdose.

Lipid emulsions attenuate the inhibition of carnitine acylcarnitine translocase induced by toxic doses of local anesthetics in rat cardiomyoblasts

The aim of this study was to examine the effects of lipid emulsions on carnitine palmitoyltransferase I (CPT-I), carnitine acylcarnitine translocase (CACT), carnitine palmitoyltransferase II (CPT-II), and the mitochondrial dysfunctions induced by toxic doses of local anesthetics in H9c2 rat cardiomyoblasts. The effects of local anesthetics and lipid emulsions on the activities of CPT-I, CACT, and CPT-II, and concentrations of local anesthetics were examined. The effects of lipid emulsions, N-acetyl-L-cysteine (NAC), and mitotempo on the bupivacaine-induced changes in cell viability, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP), and intracellular calcium levels were examined. CACT, without significantly altering CPT-I and CPT-II, was inhibited by toxic concentration of local anesthetics. The levobupivacaine- and bupivacaine-induced inhibition of CACT was attenuated by all concentrations of lipid emulsion, whereas the ropivacaine-induced inhibition of CACT was attenuated by medium and high concentrations of lipid emulsion. The concentration of levobupivacaine was slightly attenuated by lipid emulsion. The bupivacaine-induced increase of ROS and calcium and the bupivacaine-induced decrease of MMP were attenuated by ROS scavengers NAC and mitotempo, and the lipid emulsion. Collectively, these results suggested that the lipid emulsion attenuated the levobupivacaine-induced inhibition of CACT, probably through the lipid emulsion-mediated sequestration of levobupivacaine.

Predicting Inter-individual Variability During Lipid Resuscitation of Bupivacaine Cardiotoxicity in Rats: A Virtual Population Modeling Study

Introduction

Intravenous lipid emulsions (ILE) have been credited for successful resuscitation in drug intoxication cases where other cardiac life-support methods have failed. However, inter-individual variability can function as a confounder that challenges our ability to define the scope of efficacy for lipid interventions, particularly as relevant data are scarce. To address this challenge, we developed a quantitative systems pharmacology model to predict outcome variability and shed light on causal mechanisms in a virtual population of rats subjected to bupivacaine toxicity and ILE intervention.

Materials and Methods

We combined a physiologically based pharmacokinetic–pharmacodynamic model with data from a small study in Sprague-Dawley rats to characterize individual-specific cardiac responses to lipid infusion. We used the resulting individual parameter estimates to posit a population distribution of responses to lipid infusion. On that basis, we constructed a large virtual population of rats (N = 10,000) undergoing lipid therapy following bupivacaine cardiotoxicity.

Results

Using unsupervised clustering to assign resuscitation endpoints, our simulations predicted that treatment with a 30% lipid emulsion increases bupivacaine median lethal dose (LD₅₀) by 46% when compared with a simulated control fluid. Prior experimental findings indicated an LD₅₀ increase of 48%. Causal analysis of the population data suggested that muscle accumulation rather than liver accumulation of bupivacaine drives survival outcomes.

Conclusion

Our results represent a successful prediction of complex, dynamic physiological outcomes over a virtual population. Despite being informed by very limited data, our mechanistic model predicted a plausible range of treatment outcomes that accurately predicts changes in LD₅₀ when extrapolated to putatively toxic doses of bupivacaine. Furthermore, causal analysis of the predicted survival outcomes indicated a critical synergy between scavenging and direct cardiotonic mechanisms of ILE action.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40268-021-00353-4.

Lipid Emulsion Restoration of Myocardial Contractions After Bupivacaine-Induced Asystole In Vitro: A Benefit of Long- and Medium-Chain Triglyceride Over Long-Chain Triglyceride

BACKGROUND

The relative efficacies of a long- and medium-chain triglyceride (LCT/MCT) emulsion and an LCT emulsion for treatment of bupivacaine (BPV)-induced cardiac toxicity are poorly defined.

METHODS

After inducing asystole by BPV, varied concentrations (1%-12%) of either LCT/MCT (Lipofundin; B. Braun, Melsungen, Germany) or LCT emulsion (Intralipid; Fresenius Kabi, Upsala, Sweden) were applied to observe the recovery of stimulated contractile responses and contractile forces in either a recirculating or washout condition for 60 minutes, using guinea pig papillary muscles. The recirculation condition was used to demonstrate BPV binding by lipid emulsion. The washout condition was used to determine whether the time-dependent recovery of contraction is due to their metabolic enhancement. Oxfenicine, an inhibitor of carnitine palmitoyltransferase I in heart mitochondria, was used to evaluate the effect of each lipid emulsion on mitochondrial metabolic inhibition by BPV. To examine the effect of the lipid emulsion alone on contractility, either lipid emulsion was examined. BPV concentrations in solution and myocardial tissues were measured.

RESULTS

In the recirculating condition, LCT/MCT emulsions (2%-12%) restored regular stimulated contractile responses in all muscles. Eight percent and 12% LCT/MCT emulsions led to complete recovery of contractile forces after 30 minutes. Meanwhile, LCT emulsions (4%-12%) did not restore regular stimulated contractile responses in some muscles (6, 3, and 2 in 9 muscles each in 4%, 8%, and 12% emulsions, respectively). Partial recovery, approximately 60%, of contractile forces was observed with 8% and 12% LCT emulsions. In the washout experiments, after asystole, LCT/MCT emulsions (1%-12%) restored contractility to baseline levels earlier and greater than LCT emulsion. Partial recovery, approximately 60%, was observed with a high concentration of LCT emulsion (12%). In the oxfenicine-pretreated group, the contractile recovery was enhanced with LCT/MCT emulsion but showed no change with LCT emulsion. Contractile depression by 40% was observed with high concentrations of LCT emulsion alone (8% and 12%), whereas no depression or enhanced contraction was observed with LCT/MCT emulsion (1%-12%) alone. Both types of lipid emulsions (2%-12%) caused concentration-related reductions of tissue BPV levels; LCT/MCT emulsions reduced tissue BPV levels slightly greater than LCT emulsion in a recirculating condition.

CONCLUSIONS

An LCT/MCT emulsion was more beneficial than an LCT emulsion in terms of local anesthetic-binding and metabolic enhancement for treating acute BPV toxicity. The metabolic benefit of MCT, combined with the local anesthetic-binding effect of LCT, in an LCT/MCT emulsion may improve contractile function better than an LCT emulsion in an isolated in vitro animal myocardium model.

Detoxification effects of long-chain versus a mixture of medium- and long-chain triglyceride-based fat emulsion on propafenone poisoning

In the present study, we aimed to compare the detoxifying effects of two fat emulsions containing either long-chain triglyceride or a mixture of medium-chain and long-chain triglycerides in the propafenone-poisoned rat model. Rats were randomly divided into 3 groups according to the fat emulsions used: long-chain triglyceride-based fat emulsion (LL) group; medium-chain and long-chain triglyceride-based fat emulsion (ML) group; normal saline (NS) group. Propafenone was continuously pumped (velocity=70 mg/kg per h) until the mean blood pressure dropped to 50% of basal level. Then, LL/ML fat emulsions or NS was intravenously infused instantly with a loading-dose (1.5 mL/kg) and a maintenance dose (0.25 mL/kg per min) for 1 h. Subsequently, the propafenone was added to plasma (3.5 μg/mL) in vitro, mixed with three doses of LL or ML (1, 2, or 4%). Finally, after centrifugation, the concentration of propafenone was measured. Rats treated with LL exhibited accelerated recovery, characterized by higher blood pressure and heart rate. Rats in both the LL and ML groups demonstrated decreased propafenone in plasma (time-points: 15, 25, and 60 min). However, rats that received LL showed lower propafenone in myocardial tissue at the end of detoxification treatment. Rats in the ML group had the lowest value of pH, the minimum content of HCO₃^-, and the highest production of lactic acid at the end. In the in vitro experiments, propafenone decreased more dramatically in the LL group compared to the ML group. Long-chain triglyceride fat emulsion had a better effect on treating propafenone poisoning in rats.

Effective management of acute postoperative pain using intravenous emulsions of novel ketorolac prodrugs: in vitro and in vivo evaluations

The aim was to prepare intravenous fat emulsions (IFEs) of ketorolac (KTL) ester prodrugs and to investigate the pharmacokinetics and pharmacodynamics of these formulations. Three prodrugs of KTL (KTL-IS, KTL-AX and KTL-BT) were synthesized as a means to increase the lipid solubility of KTL. All KTL prodrugs with higher Log P values presented increased tendency to partition into a blank IFE using extemporaneous addition method - the encapsulation efficiency of KTL-IS IFE and KTL-BT IFE was more than 97%. The particle sizes and zeta potentials of these two formulations were comparable to that of the blank IFE. PK studies in rabbits showed significant larger AUC0-8h (646.969 ± 154.326 mg/L•h-1 for KTL-IS IFE and 559.426 ± 103.057 mg/L•h-1 for KTL-BT IFE) than that of ketorolac tromethamine (KTL-T) injectable (286.968 ± 63.045 mg/L•h-1) and approximately 2-fold increases in the elimination t1/2 over KTL-T. In a rat postoperative pain model, the paw withdrawal thresholds and the paw withdrawal latency after I.V. KTL prodrug IFEs were significantly higher than that after I.V. KTL-T at 3~4 h. Effective controlling of acute postoperative pain in a longer duration can be achieved by using non-addictive ketorolac derivatives intraveneous emulsions.

Superior Efficacy of Lipid Emulsion Infusion Over Serum Alkalinization in Reversing Amitriptyline-Induced Cardiotoxicity in Guinea Pig

BACKGROUND

Tricyclic antidepressants (TCAs) are a major cause of fatal drug poisoning due to their cardiotoxicity. Alkalinization by sodium bicarbonate (NaHCO3) administration, the first-line therapy for TCA-induced cardiotoxicity, can occasionally yield insufficient efficacy in severe cases. Because most TCAs are highly lipophilic, lipid emulsion may be more effective than alkalinization. However, it remains to be determined whether lipid emulsion is more beneficial than alkalinization in reversing amitriptyline-induced cardiotoxicity.

METHODS

Hemodynamic variables were recorded from in vivo guinea pig models and Langendorff-perfused hearts. Whole-cell patch-clamp experiments were conducted on enzymatically isolated ventricular cardiomyocytes to record fast sodium currents (INa). Lipid solutions were prepared using 20% Intralipid. The pH of the alkaline solution was set at 7.55. We assessed the effect of lipid emulsion on reversing amitriptyline-induced cardiotoxicity, in vivo and in vitro, compared to alkalinization. The data were evaluated by Student t test, 1-way repeated-measures analysis of variance, or analysis of covariance (covariate = amitriptyline concentration); we considered data statistically significant when P < .05.

RESULTS

In the in vivo model, intervention with lipids significantly reversed the amitriptyline-induced depression of mean arterial pressure and prolongation of QRS duration on electrocardiogram more than alkalinization (mean arterial pressure, mean difference [95% confidence interval]: 19.0 mm Hg [8.5-29.4]; QRS duration, mean difference [95% confidence interval] -12.0 milliseconds [-16.1 to -7.8]). In the Langendorff experiments, perfusion with 1% and 2% lipid solutions demonstrated significant recovery in left ventricular developed pressure (LVdevP), maximum change rate of increase of LVdevP (dP/dtmax) and rate-pressure product compared with alkaline solution (LVdevP [mm Hg], alkaline 57 ± 35, 1% lipid 94 ± 12, 2% lipid 110 ± 14; dP/dtmax [mm Hg/s], alkaline 748 ± 441, 1% lipid 1502 ± 334, 2% lipid 1753 ± 389; rate-pressure product [mm Hg·beats·minute], alkaline 11,214 ± 8272, 1% lipid 19,025 ± 8427, 2% lipid 25,261 ± 4803 with analysis of covariance). Furthermore, lipid solutions (0.5%-4%) resulted in greater recovery of hemodynamic parameters at 3 μM amitriptyline. Amitriptyline inhibited INa in a dose-dependent manner: the half-maximal inhibitory concentration (IC50) was 0.39 μM. The IC50 increased to 0.75 μM in the alkaline solution, 3.2 μM in 1% lipid solution, and 6.1 μM in 2% lipid solution. Furthermore, the lipid solution attenuated the use-dependent block of sodium channels by amitriptyline more than alkaline solution. On 30 consecutive pulses at 1 Hz, the current decreased to 50.1 ± 2.1, 60.3 ± 1.9, and 90.4% ± 1.8% in standard, alkaline, and 1% lipid solution, respectively. Even 0.5% lipid solution showed greater effects than the alkaline solution in all experiments.

CONCLUSIONS

Lipid emulsion significantly suppressed amitriptyline-induced INa, inhibition, which was likely related to the marked improvement in hemodynamic status observed in vivo and in isolated perfused hearts. These results suggest the superiority of lipid emulsion as the first-line therapy for TCA-induced cardiotoxicity compared to alkalinization therapy.

The Effects of Lipid Emulsion, Magnesium Sulphate and Metoprolol in Amitriptyline-Induced Cardiovascular Toxicity in Rats

The aim of this study was to evaluate the effects of metoprolol, lipid emulsion and MgSO₄ which can be recommended for prevention of long QT that is one of the lethal consequences of amitriptyline intoxication. Thirty Sprague-Dawley male rats were included. Five groups respectively received the following: saline intraperitoneally (i.p.); amitriptyline (AMT) 100 mg/kg per os (p.o.) and saline i.p.; AMT 100 mg/kg p.o. and 5 mg/kg metoprolol i.p.; AMT 100 mg/kg p.o. and 20 ml/kg lipid emulsion i.p.; AMT 100 mg/kg p.o. and 75 mg/kg MgSO₄ i.p. After 1 h, all groups were analysed by ECG recordings in DII lead; their blood was taken for biochemical examination and euthanasia was performed. For histological examination, cardiac tissues were removed and sections were prepared. QTc was significantly reduced in treatment groups compared to the AMT+saline group. When compared with the AMT+saline, lipid emulsion did not affect pro-BNP and troponin levels in biochemical analysis, but it significantly reduced Caspase 3 expression in histological examination. In the group treated with AMT and metoprolol, there was no significant effect on Caspase 3 expression. In MgSO₄-treated group, there was a significant decrease in troponin, pro-BNP and urea levels biochemically and significant decrease in Caspase 3 expression histologically when compared with the control group. With further studies including clinical studies, MgSO₄, lipid emulsion or metoprolol may be used to improve AMT-induced cardiotoxicity. They can possibly become alternative approaches in the future for suicidal or accidental intoxication of tricyclic antidepressant in emergency departments.

The Mechanisms Underlying Lipid Resuscitation Therapy

The experimental use of lipid emulsion for local anesthetic toxicity was originally identified in 1998. It was then translated to clinical practice in 2006 and expanded to drugs other than local anesthetics in 2008. Our understanding of lipid resuscitation therapy has progressed considerably since the previous update from the American Society of Regional Anesthesia and Pain Medicine, and the scientific evidence has coalesced around specific discrete mechanisms. Intravenous lipid emulsion therapy provides a multimodal resuscitation benefit that includes both scavenging (eg, the lipid shuttle) and nonscavenging components. The intravascular lipid compartment scavenges drug from organs susceptible to toxicity and accelerates redistribution to organs where drug (eg, bupivacaine) is stored, detoxified, and later excreted. In addition, lipid exerts nonscavenging effects that include postconditioning (via activation of prosurvival kinases) along with cardiotonic and vasoconstrictive benefits. These effects protect tissue from ischemic damage and increase tissue perfusion during recovery from toxicity. Other mechanisms have diminished in favor based on lack of evidence; these include direct effects on channel currents (eg, calcium) and mass-effect overpowering a block in mitochondrial metabolism. In this narrative review, we discuss these proposed mechanisms and address questions left to answer in the field. Further work is needed, but the field has made considerable strides towards understanding the mechanisms.

Low dose Intralipid resuscitation improves survival compared to ClinOleic in propranolol overdose in rats

Background

Medication overdose is a prevalent issue and despite mixed reports of efficacy, the use of intravenous lipid emulsions, notably Intralipid^®, for the management of toxicity from lipid-soluble drugs is becoming increasingly prevalent. Whether alternative lipid emulsion formulations have similar efficacy for resuscitation compared to Intralipid is not known. Here, we compared the efficacy of Intralipid and ClinOleic^® for resuscitation following overdose with the lipid-soluble beta-adrenergic antagonist propranolol.

Methods

Male Sprague-Dawley rats (age 3–4 months) were anesthetized with isoflurane and instrumented for direct hemodynamic assessments. In Study One, rats (n = 22) were pre-treated with Intralipid 20% (n = 12) or ClinOleic 20% (n = 10) to determine whether the hemodynamic effects of propranolol could be prevented. In Study Two, rats were randomly assigned to Intralipid 20% (1, 2, or 3 mL/kg IV, n = 21) or ClinOleic 20% (1, 2, or 3 mL/kg IV, n = 20) resuscitation groups following propranolol overdose (15 mg/kg IV). In Study Three the effect of Intralipid 20% (1 mL/kg IV, n = 3) and ClinOleic 20% (1 mL/kg IV, n = 3) in the absence of propranolol was investigated. The primary endpoint in all studies was survival time (up to a maximum of 120 minutes), and secondary endpoints were time to achieve 50%, 75%, and 90% of baseline hemodynamic parameters.

Results

In Study One, pre-treatment with Intralipid prior to propranolol administration resulted in prolonged survival compared to pre-treatment with ClinOleic at low doses (1 mL/kg; P = 0.002), but provided no benefit at higher doses (3 mL/kg; P = 0.95). In Study Two, Intralipid conferred a survival advantage over ClinOleic, with 18/21 rats surviving 120 minutes in the Intralipid group and only 4/20 survivors in the ClinOleic group (P<0.0001). Median survival times (with interquartile ranges) for rats treated with Intralipid, and ClinOleic, and saline were 120 (80.5–120) min, 21.5 (3.25–74.5) min, and 1 (0.25–2.5) min respectively (P<0.001). Only 3/21 rats in the Intralipid group survived less than 30 minutes, whereas 12/20 ClinOleic treated rats had survival times of less than 30 minutes. The number of rats achieving 75%, and 90% of baseline mean arterial pressure was also greater in the Intralipid group (P<0.05 for both values). Treatment in Study Three did not alter survival times.

Conclusions

Low-dose Intralipid (1, 2, or 3 mL/kg IV) confers a survival advantage up to 120 minutes post-propranolol overdose (the end-point of the experiment) and better hemodynamic recovery compared to ClinOleic (1, 2, or 3 mL/kg IV) in rats with propranolol overdose. As health care centres choose alternate intravenous lipid emulsions, limited availability of Intralipid could impact efficacy and success of overdose treatment for lipid-soluble drugs.

Linoleic Acid Attenuates the Toxic Dose of Bupivacaine-Mediated Reduction of Vasodilation Evoked by the Activation of Adenosine Triphosphate-Sensitive Potassium Channels

The goal of this study was to investigate the effect of lipid emulsion on a toxic dose of local anesthetic-mediated reduction of vasodilation evoked by the ATP-sensitive potassium (K_ATP) channel agonist levcromakalim. The effect of lipid emulsion (LE) and linoleic acid on the local anesthetic-mediated reduction of vasodilation and membrane hyperpolarization evoked by levcromakalim was assessed in isolated endothelium-denuded vessels (rat aorta and mesenteric artery) and aortic vascular smooth muscle cells. The effect of LE and linoleic acid on K_ATP channel activity in transfected HEK-293 cells was investigated, as was the effect of LE on bupivacaine concentration. The efficacy of LE in attenuating the local anesthetic-mediated reduction of vasodilation evoked by levcromakalim was correlated with the lipid solubility of the local anesthetic. Linoleic acid attenuated the bupivacaine-mediated reduction of vasodilation evoked by levcromakalim. LE decreased the bupivacaine-mediated reduction of membrane hyperpolarization evoked by levcromakalim but did not significantly alter the mepivacaine-mediated reduction. LE and linoleic acid both reversed the bupivacaine-mediated decrease of K_ATP activity and enhanced K_ATP activity. LE decreased the bupivacaine concentration. Linoleic acid may be the major contributor to LE-induced attenuation of bupivacaine-mediated reduction of vasodilation evoked by levcromakalim via the direct activation of K_ATP channels and indirect effects.

Use of lipid emulsion therapy in local anesthetic overdose

The use of intravenous lipid emulsion (ILE) therapy as antidote in systemic toxicity of certain agents has gained widespread support. There are increasing data suggesting use of ILE in reversing from local anesthetic-induced systemic toxicity severe, life-threatening cardiotoxicity, although findings are contradictory. Efficiency of ILE was demonstrated in animal studies in the treatment of severe impairment of cardiac functions, via a mechanism for trapping lipophilic drugs in an expanded plasma lipid compartment (“lipid sink”). In patients with hemodynamic compromise and/or cardiovascular collapse due to lipid-soluble agents, ILE may be considered for resuscitation in the acute setting by emergency physicians. The most common adverse effects from standard ILE include hypertriglyceridemia, fat embolism, infection, vein irritation, pancreatitis, electrolyte disturbances and allergic reactions. The advantages of ILE include an apparent wide margin of safety, relatively low cost, long shelf-life, and ease of administration.

Lipid emulsion in local anesthetic toxicity

PURPOSE OF REVIEW

Enthusiasm for regional anesthesia has been driven by multimodal benefits to patient outcomes. Despite widespread awareness and improved techniques (including the increasing use of ultrasound guidance for block placement), intravascular sequestration and the attendant risk of local anesthetic systemic toxicity (LAST) remains. Intravenous lipid emulsion (ILE) for the treatment of LAST has been endorsed by anesthetic regulatory societies on the basis of animal study and human case report data. The accumulated mass of reporting now permits objective interrogation of published literature.

RECENT FINDINGS

Although incompletely elucidated the mechanism of action for ILE in LAST seemingly involves beneficial effects on initial drug distribution (i.e., pharmacokinetic effects) and positive cardiotonic and vasoactive effects (i.e., pharmacokinetic effects) acting in concert. Recent systematic review by collaborating international toxicologic societies have provided reserved endorsement for ILE in bupivacaine-induced toxicity, weak support for ILE use in toxicity from other local anesthetics, and largely neutral recommendation for all other drug poisonings. Work since publication of these recommendations has concluded that there is a positive effect on survival for ILE when animal models of LAST are meta-analyzed and evidence of a positive pharmacokinetic effect for lipid in human models of LAST.

SUMMARY

Lipid emulsion remains first-line therapy (in conjunction with standard resuscitative measures) in LAST. Increasing conjecture as to the clinical efficacy of ILE in LAST, however, calls for high-quality human data to refine clinical recommendations.

Lipid Emulsion for Treating Local Anesthetic Systemic Toxicity

Lipid emulsion has been shown to be an effective treatment for systemic toxicity induced by local anesthetics, which is reflected in case reports. A systemic review and meta-analysis confirm the efficacy of this treatment. Investigators have suggested mechanisms associated with the lipid emulsion-mediated recovery of cardiovascular collapse caused by local anesthetic systemic toxicity; these mechanisms include lipid sink, a widely accepted theory in which highly soluble local anesthetics (particularly bupivacaine) are absorbed into the lipid phase of plasma from tissues (e.g., the heart) affected by local-anesthetic-induced toxicity; enhanced redistribution (lipid shuttle); fatty acid supply; reversal of mitochondrial dysfunction; inotropic effects; glycogen synthase kinase-3β phosphorylation associated with inhibition of the mitochondrial permeability transition pore opening; inhibition of nitric oxide release; and reversal of cardiac sodium channel blockade. The current review includes the following: 1) an introduction, 2) a list of the proposed mechanisms, 3) a discussion of the best lipid emulsion treatment for reversal of local anesthetic toxicity, 4) a description of the effect of epinephrine on lipid emulsion-mediated resuscitation, 5) a description of the recommended lipid emulsion treatment, and 6) a conclusion.

Liposome supported peritoneal dialysis in rat amitriptyline exposure with and without intravenous lipid emulsion

Liposome supported peritoneal dialysis is a recently described technique which may eventually be applicable in the clinical scenario of the intoxicated patient. We evaluated the hypothesis that intravenous injection of lipid emulsion (ILE) would augment acidic pH gradient liposome supported peritoneal dialysis (LSPD). Orogastrically amitriptyline dosed rats were treated with either Sodium bicarbonate (NaHCO3) intravenously and standard intraperitoneal dialysate (Group A); NaHCO3 intravenously and LSPD (Group B); or ILE and LSPD (Group C). The primary endpoint was dialysate amitriptyline concentration after a 60 min dwell. Secondary analysis included an estimate of extraction ratio for peritoneal blood flow (ERs). There were significantly higher intraperitoneal concentrations of amitriptyline and ERs in the two groups treated with LSPD (Group B, p = 0.02, Group C, p < 0.01 vs. Group A). There was no observed effect for ILE on intraperitoneal amitriptyline concentration or ERs (p > 0.20). LSPD increased the amitriptyline concentration in peritoneal dialysate. No further increase was demonstrated with ILE. This may be either because such an effect is absent, or type II error. Exploratory analysis suggests LSPD may be driven by total rather than free drug concentrations.

Recovery From Ropivacaine-Induced or Levobupivacaine-Induced Cardiac Arrest in Rats: Comparison of Lipid Emulsion Effects

BACKGROUND

Lipid emulsion treatment appears to have application in the treatment of local anesthetic-induced cardiac arrest. To examine whether the efficacy of lipid resuscitation in the treatment of local anesthetic-induced cardiac arrest is affected by lipophilicity, the effects of lipid infusions were compared between levobupivacaine-induced (high lipophilicity) and ropivacaine-induced (lower lipophilicity) rat cardiac arrest model.

METHODS

A total of 28 female Sprague-Dawley rats were anesthetized using sevoflurane, which subsequently underwent tracheostomy, followed by femoral artery and vein cannulation. Two hours after the discontinuation of sevoflurane, either levobupivacaine 0.2% (n = 14) or ropivacaine 0.2% (n = 14) was administered at a rate of 2 mg/kg/min to the awake rats. When the pulse pressure decreased to 0, the infusion of local anesthetic was discontinued, and treatment with chest compressions and ventilation with 100% oxygen were immediately initiated. The total doses of local anesthetics needed to trigger the first seizure and pulse pressure of 0 mm Hg were calculated. The 2 groups were each subdivided into a lipid emulsion group (n = 7) and a control group (n = 7). In the lipid emulsion group, 20% lipid emulsion was administered intravenously (5 mL/kg bolus plus continuous infusion of 0.5 mL/kg/min), while in the control group, the same volume of normal saline was administered. Chest compressions were discontinued when the rate-pressure product had increased by more than 20% of baseline.

RESULTS

The cumulative doses of levobupivacaine and ropivacaine that produced seizures and 0 pulse pressure showed no significant difference. Mean arterial blood pressure (MAP) values were higher in the levobupivacaine group than in the ropivacaine group after resuscitation was initiated (P < .05). In levobupivacaine-induced cardiac arrest, heart rate and MAP values were higher in the lipid group than in the control group after starting resuscitation (P < .05); all rats in the lipid group achieved spontaneous circulation (rate-pressure product >20% baseline), while only 2 of 7 rats in the control group achieved spontaneous circulation at 10 minutes. In ropivacaine-induced cardiac arrest, there were no significant differences in heart rate and MAP between the lipid and control groups from the start of resuscitation to 10 minutes; spontaneous circulation returned in 6 of 7 lipid group rats, but in only 2 of 7 control group rats at 10 minutes.

CONCLUSIONS

Lipid emulsion treatment was more effective for levobupivacaine-induced cardiac arrest than for ropivacaine-induced cardiac arrest. Although lipid therapy is also effective for ropivacaine-induced cardiac arrest, it takes more time than in levobupivacaine-induced cardiac arrest. This suggests that the lipophilicity of local anesthetics influences the efficacy of lipid infusion when treating cardiac arrest caused by these drugs.

Intralipid Restoration of Myocardial Contractions Following Bupivacaine-Induced Asystole: Concentration- and Time-Dependence In Vitro

BACKGROUND

The concentration- and time-response relationships of lipid emulsion (LE; Intralipid) on the recovery of myocardial contractility following bupivacaine (BPV)-induced asystole are poorly defined.

METHODS

After achieving asystole by 500-μM BPV, varied concentrations of LE were applied to determine the recovery of stimulated contractile responses and contractions in the cardiac tissues of guinea pigs at a 1.2-Hz stimulation rate. These experiments were performed with LE in either a recirculating (2%-16%) or washout (nonrecirculating) condition (0.05%-12%) for 60 minutes. The effect of LE itself (0.05%-12%) was examined. Oxfenicine was used to evaluate the metabolic action of LE to reverse asystole. BPV concentrations in solution and myocardial tissues were measured.

RESULTS

In the recirculation condition, partial recovery of contractile forces was observed for 60 minutes at 4%, 8%, and 12% LE. A contracture followed after exposure to 16% LE in some asystolic muscles. In the washout experiments, following asystole, LE (0.05%-12%) had no effect on the recovery time of the first and regular contractile responses. LE (0.1%-8%) restored contractility to baseline levels after 45 minutes; partial recovery was shown with lower (0.05%) and higher (12%) concentrations. Oxfenicine did not alter the recovery of contractile forces. Contractile depression was observed with 12% LE alone. Concentration-related reduction of tissue BPV concentration by LE was observed in both circulating conditions.

CONCLUSIONS

LE induced time- and concentration-dependent recovery of stimulated myocardial contractions from BPV-induced asystole. The lipid uptake effect, along with other undefined mechanisms of LE, seems to contribute to the recovery of contractile function; however, the LE effect on myocardial metabolism is less likely involved at this concentration (500 μM) of BPV.

Amitriptyline-induced ventricular tachycardia: a case report

Background

In Bangladesh, each emergency physician faces amitriptyline overdose nearly a day. An acute cardiovascular complication, one of the worst complications is mainly responsible for the mortality in tricyclic overdose. Recently, we managed ventricular tachycardia in a young female presented with an impaired consciousness 10 h after intentionally ingesting 2500 mg amitriptyline. Here, we report it, discuss how the electrocardiography is vital to acknowledge and predict it and its’ complications and also the recent update of the management of it.

Case presentation

A young married Bangladeshi-Bengali girl, 25-year-old, having a history of disharmony with her husband, came with an impaired consciousness after intentionally ingesting 2500 mg amitriptyline about 10 h before arrival. There was blood pressure 140/80 mmHg, heart rate 140 beats-per-min, temperature 103 °F, Glasgow coma scale 10/15, wide complex tachycardia with QRS duration of 178 ms in electrocardiography, blood pH 7.36. Initially, treated with 100 ml 8.4% sodium bicarbonate. After that, QRS duration came to 100 ms in electrocardiography within 10 min of infusion. To maintain the pH 7.50–7.55 over the next 24 h, the infusion of 8.4% sodium bicarbonate consisting of 125 ml dissolved in 375 ml normal saline was started and titrated according to the arterial blood gas analysis. Hence, a total dose of 600 mmol sodium bicarbonate was given over next 24 h. In addition to this, gave a 500 ml intravenous lipid emulsion over 2 h after 24 h of admission as she did not regain her consciousness completely. Afterward, she became conscious, though, in electrocardiography, ST/T wave abnormality persisted. So that, we tapered sodium bicarbonate infusion slowly and stopped it later. At the time of discharge, she was by heart rate 124/min, QRS duration 90 ms in electrocardiogram along with other normal vital signs.

Conclusion

Diagnosis of amitriptyline-induced ventricular tachycardia is difficult when there is no history of an overdose obtained. Nevertheless, it should be performed in the clinical background and classic electrocardiographic changes and wise utilization of sodium bicarbonate, intravenous lipid emulsion, and anti-arrhythmic drugs may save a life.

The Effect of Lipid Emulsion on Pharmacokinetics of Bupivacaine in Rats: Long-Chain Triglyceride Versus Long- and Medium-Chain Triglyceride

BACKGROUND

Lipid infusions have been proposed to treat local anesthetic-induced cardiac toxicity. This study compared the effects of long-chain triglyceride (LCT) emulsions with those of long- and medium-chain triglyceride (LCT/MCT) emulsions on the pharmacokinetics of bupivacaine in a rat model.

METHODS

After administration of intravenous infusion of bupivacaine at 2 mg·kg·min for 5 minutes in Sprague-Dawley (SD) rats, either Intralipid 20%, an LCT emulsion (LCT group, n = 6), or Lipovenoes 20%, an LCT/MCT emulsion (LCT/MCT group, n = 6), was infused at 2mg·kg·min for 5 minutes. The concentrations of total plasma bupivacaine and bupivacaine that were not bound by lipid (lipid unbound) were measured by a liquid chromatography-tandem mass spectrometric method. A 2-compartmental analysis was performed to calculate the lipid-bound percentage of bupivacaine and its pharmacokinetics.

RESULTS

In the LCT group, the clearance (15 ± 2 vs 10 ± 1 mL·min·kg, P = .003) was higher; the volume of distribution (0.57 ± 0.10 vs 0.36 ± 0.11 L·kg, P = .007) and K21 (0.0100 ± 0.0018 vs 0.0070 ± 0.0020 min, P = .021, P' = .032) were larger; and the area under the blood concentration-time curve 0 - t; (605 ± 82 vs 867 ± 110 mgL·min, P =.001) and the area under the blood concentration-time curve (0 - ∞) (697 ± 111 vs 991 ± 121 mgL·min, P =.001) were less, when compared with the LCT/MCT group.

CONCLUSIONS

LCT emulsions are more effective than LCT/MCT emulsions in the metabolism of bupivacaine through demonstration of a superior pharmacokinetic profile.

Successful use of lipid emulsion to resuscitate a foal after intravenous lidocaine induced cardiovascular collapse

BACKGROUND

Lipid emulsion has been reported to be effective for the treatment of local anaesthetic overdoses in rats, dogs and man.

OBJECTIVES

To describe the successful treatment of cardiovascular lidocaine toxicity in a foal with intravenous lipid administration.

STUDY DESIGN

Observational study: case report.

METHODS

An 8-month-old Arabian cross foal was anaesthetised for removal of the right alar fold and nasal plate. Anaesthesia was maintained with isoflurane in oxygen and lidocaine administered with a loading dose followed by a continuous rate infusion (CRI). The anaesthetic period was uneventful and 30 min before expected termination of the procedure lidocaine infusion was stopped. A sudden drop in mean arterial blood pressure was then observed. The ECG signal was lost, the end tidal CO₂ tension dropped from 40 to 10 mmHg, corneal reflex was absent and asystole diagnosed. Cardiopulmonary resuscitation manoeuvres were immediately initiated, but epinephrine and atropine were unsuccessfully administered. Lipid emulsion was administered and the heart rate and arterial blood pressure gradually returned to normal.

RESULTS

The foal recovered consciousness 3 h later, regained its sternal position, was responsive and 20 h later was able to stand up alone.

MAIN LIMITATIONS

It will be necessary to evaluate a greater number of cases to determine the effectiveness of lipids in foals intoxicated with lidocaine.

CONCLUSION

Intravenous lipid emulsion may be helpful in the treatment of potentially lethal cardiotoxicity attributable to lidocaine overdose in the foal.

Giving Priority to Lipid Administration Can Reduce Lung Injury Caused by Epinephrine in Bupivacaine-Induced Cardiac Depression

BACKGROUND AND OBJECTIVES

Epinephrine is usually administered in concert with a lipid emulsion during local anesthetic toxicity. However, the timing and role of epinephrine administration in combination with a lipid emulsion remain unclear. Specifically, the temporal association of epinephrine and lipid emulsion administration with related changes in pulmonary vascular pressures that may lead to pulmonary edema and hemorrhage needs to be determined.

METHODS

This study consisted of 2 parts, experiments A and B. In experiment A, 24 adult male Sprague-Dawley rats were randomly divided into 3 groups (n = 8) to receive 1 of 3 treatments. All rats were anesthetized with an intraperitoneal injection of chloral hydrate, and anesthesia was maintained by sevoflurane. Each treatment group was initially given an infusion of bupivacaine (15 mg/kg) in order to produce cardiac depression. Group 1 (A-LEN) received a 30% lipid infusion (3 mL/kg) followed by a rapid epinephrine bolus (10 μg/kg), which was then followed by a normal saline infusion (3 mL/kg). Group 2 (A-NEL) first received a normal saline infusion (3 mL/kg) followed by a rapid epinephrine bolus, which was then followed by a 30% lipid emulsion. Group 3 (A-NEN, considered a control group) first received a normal saline infusion (3 mL/kg) followed by a rapid epinephrine bolus (10 μg/kg), which was then followed by another normal saline infusion (3 mL/kg). Lipid and normal saline infusions were administered over 1 minute, whereas epinephrine was injected rapidly. The continuous monitoring of blood pressure, heart rate, pulmonary arterial pressure, and pulmonary venous pressure occurred for 30 minutes. After the 30-minute monitoring period, lung tissue was sampled, and bronchoalveolar lavage fluid was collected. In experiment B, the experimental model and resuscitation protocol were similar to experiment A (B-LEN and B-NEL groups). In this arm of the experiment, bupivacaine concentrations of cardiac tissue were determined after the second minute of normal saline infusion.

RESULTS

The A-LEN group produced the best rate pressure product when compared with the A-NEL or A-NEN group (P = 0.045, P = 0.011, respectively). In regard to pulmonary venous pressure, the A-LEN group was lower than the A-NEL or A-NEN group (P = 0.031, P = 0.006, respectively). Animals in the A-NEL and A-NEN groups rapidly developed pulmonary edema after infusion of epinephrine. The wet-to-dry ratio of the lungs in the A-LEN group was lower than that of the lungs in the A-NEL group (P = 0.024).The lung permeability index of the A-LEN group was lower than that of the A-NEL group (P = 0.011). In experiment B, concentrations of bupivacaine in cardiac tissue and plasma of the B-LEN group were lower than those of the B-NEL group (P = 0.001, P = 0.03, respectively).

CONCLUSIONS

Giving priority to the administration of a lipid emulsion before the administration of epinephrine can reduce lung injury in bupivacaine-induced cardiac depression in rats.

Local anesthetic toxicity: acute and chronic management

Local anesthetics are commonly used medicines in clinical settings. They are used for pain management during minor interventional treatments, and for postoperative care after major surgeries. Cocaine is the well‐known origin of local anesthetics, and the drug and related derivatives have long history of clinical usage for more than several centuries. Although illegal use of cocaine and its abuse are social problem in some countries, other local anesthetics are safely and effectively used in clinics and hospitals all over the world. However, still this drug category has several side‐effects and possibilities of rare but serious complications. Acute neurotoxicity and cardiac toxicity are derived from unexpected high serum concentration. Allergic reactions are observed in some cases, especially following the use of ester structure drugs. Chronic toxicity is provoked when nerve fibers are exposed to local anesthetics at a high concentration for a long duration. Adequate treatments for acute toxic reactions can secure complete recovery of patients, and careful use of drugs prevents long‐lasting neurological complications. In addition to respiratory and circulatory management, effectiveness of lipid rescue in the acute toxicity treatment has been certified in many clinical guidelines. Prevention of the use of high concentration of local anesthetics is also validated to be effective to decrease the possibility of nerve fiber damage.

Lipid Therapy for Intoxications

This review discusses the use of intravenous lipid emulsion (ILE) in the treatment of intoxications with lipophilic agents in veterinary medicine. Despite growing scientific evidence that ILE has merit in the treatment of certain poisonings, there is still uncertainty on the optimal composition of the lipid emulsion, the dosing, the mechanism of action, and the efficacy. Therefore, a critical view of the clinician on the applicability of this modality in intoxications is still warranted. The use of ILE therapy is advocated as an antidote in cases of intoxications with some lipophilic substances.

Local infiltration analgesia in knee and hip arthroplasty efficacy and safety

Background

This is a secondary publication of a PhD thesis. Local infiltration analgesia (LIA) is a new multimodal wound infiltration method for treating postoperative pain after knee and hip arthroplasty. This method is based on systematic infiltration of a mixture of ropivacaine, a long acting local anaesthetic, ketorolac, a cyclooxygenase inhibitor (NSAID), and adrenalin around all structures subject to surgical trauma in knee and hip arthroplasty.

Aims

Paper I: to assess whether pain relief after LIA in total knee arthroplasty (TKA) is as effective as femoral block. Paper II: to assess whether the plasma concentration of ropivacaine and ketorolac after LIA in TKA reaches levels linked to toxicity. Paper III: to assess whether the plasma concentration of unbound ropivacaine after LIA in THA reaches levels linked to toxicity and if it is higher in THA as compared to TKA. Paper IV: to assess whether the plasma concentration of ketorolac after LIA in THA reaches levels linked to toxicity, and whether administration of ketorolac in LIA is safer as compared to the intramuscular route.

Methods

Two patient cohorts of 40 patients scheduled for elective total knee arthroplasty (TKA) and 15 patients scheduled for total hip arthroplasty (THA) contributed to this work. In a randomized trial the efficacy of LIA in TKA with regard to pain at rest and upon movement was compared to femoral block.

Results

Both methods result in a high quality pain relief and similar morphine consumption during the 24 h monitoring period. In the same patient cohort the maximal total plasma concentration of ropivacaine was below the established toxic threshold for most patients. All patients in the THA cohort were subjected to the routine LIA protocol. In these patients both the total and unbound plasma concentration of ropivacaine was determined. The concentration was below the established toxic threshold. As ropivacaine binds to α–1 acid glycoprotein (AAG) we assessed the possibility that increased AAG may decrease the unbound concentration of ropivacaine. A 40% increase in AAG was detected during the first 24 h after surgery, however the fraction of unbound ropivacaine remained the same. There was a trend towards increased C max of ropivacaine with increasing age and decreasing creatinine clearance but the statistical power was too low to draw any conclusion. Administration of 30 mg ketorolac according to the LIA protocol both in TKA and THA resulted in a similar C max as previously reported after 10 mg intramuscular ketorolac. Neither age, nor body weight or BMI, nor creatinine clearance, correlates to maximal ketorolac plasma concentration or total exposure to ketorolac (AUC).

Conclusion

LIA provides good postoperative analgesia which is similar to femoral block after total knee arthroplasty. The plasma concentration of ropivacaine seems to be below toxic levels in most TKA patients. The unbound plasma concentration of ropivacaine in THA seems to be below the toxic level.

Implication

The use of ketorolac in LIA may not be safer than other routes of administration, and similar restrictions should be applied in patients at risk of developing side effects.

Effect of Intralipid® on the Dose of Ropivacaine or Levobupivacaine Tolerated by Volunteers

Background

Rapid intravenous administration of lipid emulsion has become the standard treatment of severe local anesthetic systemic toxicity. This experiment in volunteers aimed at determining the effect of Intralipid® administration on the time to neurologic symptoms.

Methods

Ropivacaine or levobupivacaine was infused intravenously in 16 volunteers (8 mg/min up to 120 mg) with 120 ml Intralipid® 20% (Fresenius, Paris France) or placebo infused at T + 2 min). Each subject received all four treatments in a crossover manner. The infusion was stopped after the intended dose had been administered or on occurrence of incipient neurologic signs of toxicity. The primary outcome was time-to-event. In addition, blood ropivacaine and levobupivacaine concentrations were measured.

Results

The dose infused was not different whether volunteers received placebo (81.7 ± 22.3 vs. 80.8 ± 31.7 mg, ropivacaine vs. levobupivacaine) or Intralipid® (75.7 ± 29.1 vs. 69.4 ± 26.2 mg, ropivacaine vs. levobupivacaine), P = 0.755, Intralipid® versus placebo groups. Plasma concentrations were best modeled with an additional volume of distribution associated with Intralipid®. Simulations suggested that decreased peak concentrations would be seen if Intralipid® was given during a period of increasing concentrations after extravascular administration.

Conclusions

At modestly toxic doses of ropivacaine or levobupivacaine, we were unable to find any effect of the infusion of Intralipid® on the time to early signs of neurologic toxicity in volunteers. Peak concentration was decreased by 26 to 30% in the subjects receiving Intralipid®. Simulations showed that Intralipid® might prevent the rapid increase of local anesthetic concentration after extravascular administration.

Amniotic fluid embolism: diagnosis and management

OBJECTIVE

We sought to provide evidence-based guidelines regarding the diagnosis and management of amniotic fluid embolism.

STUDY DESIGN

A systematic literature review was performed using MEDLINE, PubMed, EMBASE, and the Cochrane Library. The search was restricted to English-language articles published from 1966 through March 2015. Priority was given to articles reporting original research, in particular randomized controlled trials, although review articles and commentaries were consulted. Abstracts of research presented at symposia and scientific conferences were not considered adequate for inclusion. Evidence reports and published guidelines were also reviewed, and additional studies were located by reviewing bibliographies of identified articles. Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology was used for defining the strength of recommendations and rating quality of the evidence. Consistent with US Preventive Task Force guidelines, references were evaluated for quality based on the highest level of evidence.

RESULTS AND RECOMMENDATIONS

We recommend the following: (1) we recommend consideration of amniotic fluid embolism in the differential diagnosis of sudden cardiorespiratory collapse in the laboring or recently delivered woman (GRADE 1C); (2) we do not recommend the use of any specific diagnostic laboratory test to either confirm or refute the diagnosis of amniotic fluid embolism; at the present time, amniotic fluid embolism remains a clinical diagnosis (GRADE 1C); (3) we recommend the provision of immediate high-quality cardiopulmonary resuscitation with standard basic cardiac life support and advanced cardiac life support protocols in patients who develop cardiac arrest associated with amniotic fluid embolism (GRADE 1C); (4) we recommend that a multidisciplinary team including anesthesia, respiratory therapy, critical care, and maternal-fetal medicine should be involved in the ongoing care of women with AFE (Best Practice); (5) following cardiac arrest with amniotic fluid embolism, we recommend immediate delivery in the presence of a fetus ≥23 weeks of gestation (GRADE 2C); (6) we recommend the provision of adequate oxygenation and ventilation and, when indicated by hemodynamic status, the use of vasopressors and inotropic agents in the initial management of amniotic fluid embolism. Excessive fluid administration should be avoided (GRADE 1C); and (7) because coagulopathy may follow cardiovascular collapse with amniotic fluid embolism, we recommend the early assessment of clotting status and early aggressive management of clinical bleeding with standard massive transfusion protocols (GRADE 1C).

Functionalized lipids and surfactants for specific applications

Synthetic lipids and surfactants that do not exist in biological systems have been used for the last few decades in both basic and applied science. The most notable applications for synthetic lipids and surfactants are drug delivery, gene transfection, as reporting molecules, and as support for structural lipid biology. In this review, we describe the potential of the synergistic combination of computational and experimental methodologies to study the behavior of synthetic lipids and surfactants embedded in lipid membranes and liposomes. We focused on select cases in which molecular dynamics simulations were used to complement experimental studies aiming to understand the structure and properties of new compounds at the atomistic level. We also describe cases in which molecular dynamics simulations were used to design new synthetic lipids and surfactants, as well as emerging fields for the application of these compounds. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.

The possible role of intravenous lipid emulsion in the treatment of chemical warfare agent poisoning

Organophosphates (OPs) are cholinesterase inhibitors that lead to a characteristic toxidrome of hypersecretion, miosis, dyspnea, respiratory insufficiency, convulsions and, without proper and early antidotal treatment, death. Most of these compounds are highly lipophilic. Sulfur mustard is a toxic lipophilic alkylating agent, exerting its damage through alkylation of cellular macromolecules (e.g., DNA, proteins) and intense activation of pro-inflammatory pathways. Currently approved antidotes against OPs include the peripheral anticholinergic drug atropine and an oxime that reactivates the inhibited cholinesterase. Benzodiazepines are used to stop organophosphate-induced seizures. Despite these approved drugs, efforts have been made to introduce other medical countermeasures in order to attenuate both the short-term and long-term clinical effects following exposure. Currently, there is no antidote against sulfur mustard poisoning. Intravenous lipid emulsions are used as a source of calories in parenteral nutrition. In recent years, efficacy of lipid emulsions has been shown in the treatment of poisoning by fat-soluble compounds in animal models as well as clinically in humans. In this review we discuss the usefulness of intravenous lipid emulsions as an adjunct to the in-hospital treatment of chemical warfare agent poisoning.

Effects of Acidification and Alkalinization on the Lipid Emulsion-Mediated Reversal of Toxic Dose Levobupivacaine-Induced Vasodilation in the Isolated Rat Aorta

The goal of this in vitro study was to examine the effects of pre-acidification and pre-akalinization on the lipid emulsion-mediated reversal of toxic dose levobupivacaine-induced vasodilation in isolated rat aorta. Isolated aortic rings with and without the nitric oxide synthase inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) were exposed to four types of Krebs solution (pH 7.0, 7.2, 7.4, and 7.6), followed by the addition of 60 mM potassium chloride. When the toxic dose of levobupivacaine (3 × 10(-4) M) produced a stable and sustained vasodilation in the isolated aortic rings that were precontracted with 60 mM potassium chloride, increasing lipid emulsion concentrations (SMOFlipid(®): 0.24, 0.48, 0.95 and 1.39%) were added to generate concentration-response curves. The effects of mild pre-acidification alone and mild pre-acidification in combination with a lipid emulsion on endothelial nitric oxide synthase (eNOS) phosphorylation in human umbilical vein endothelial cells were investigated by Western blotting. Mild pre-acidification caused by the pH 7.2 Krebs solution enhanced the lipid emulsion-mediated reversal of levobupivacaine-induced vasodilation in isolated endothelium-intact aortic rings, whereas mild pre-acidification caused by the pH 7.2 Krebs solution did not significantly alter the lipid emulsion-mediated reversal of the levobupivacaine-induced vasodilation in isolated endothelium-denuded aortic rings or endothelium-intact aortic rings with L-NAME. A lipid emulsion attenuated the increased eNOS phosphorylation induced by the pH 7.2 Krebs solution. Taken together, these results suggest that mild pre-acidification enhances the lipid emulsion-mediated reversal of toxic dose levobupivacaine-induced vasodilation in the endothelium-intact aorta via the inhibition of nitric oxide.

Hemodynamic changes with high infusion rates of lipid emulsion. Experimental study in swine

PURPOSE

To evaluate hemodynamic changes caused by sole intravenous infusion of lipid emulsion with doses recommended for treatment of drug-related toxicity.

METHODS

Large White pigs underwent general anesthesia, tracheal intubation was performed, and mechanical ventilation was instituted. Hemodynamic variables were recorded using invasive blood pressure and pulmonary artery catheterization. Baseline hemodynamic measurements were obtained after a 30-minute stabilization period. An intravenous bolus injection of 20% lipid emulsion at 1.5 ml/kg was administered. Additional hemodynamic measurements were made after 1 minute, followed by a continuous intravenous lipid infusion of 0.25 ml/kg/min. Further measurements were carried out at 10, 20 and 30 minutes, when the infusion was doubled to 0.5 ml/kg/min. Assessment of hemodynamic changes were then made at 40, 50 and 60 minutes.

RESULTS

Lipid infusion did not influence cardiac output or heart rate, but caused an increase in arterial blood pressure, mainly pulmonary blood pressure due to increased vascular resistance. Ventricular systolic stroke work consequently increased with greater repercussions on the right ventricle.

CONCLUSION

In doses used for drug-related toxicity, lipid emulsion cause significant hemodynamic changes with hypertension, particularly in the pulmonary circulation and increase in vascular resistance, which is a factor to consider prior to use of these solutions.

Differential effects of short- and long-term bupivacaine treatment on α1-adrenoceptor-mediated contraction of isolated rat aorta rings and the reversal effect of lipid emulsion

AIM

Arterial function is significantly influenced by bupivacaine at both clinically relevant concentrations and toxic concentrations, but the underlying mechanisms are not fully understood. In the present study we investigated the role of α1-adrenoceptors in bupivacaine effects on isolated rat aortas.

METHODS

Isolated aortic rings were prepared from rats and suspended in an organ bath. Phenylephrine (Phe)-induced vasoconstriction and acetylcholine (ACh)-induced vasodilation were recorded through an isometric force transducer connected to a data acquisition system.

RESULTS

Administration of bupivacaine (30-300 μmol/L) produced mild vasoconstriction, and this response declined with repeated administrations. Treatment of the aortic rings with bupivacaine (3-30 μmol/L) for 20 min enhanced Phe-induced vasoconstriction, while treatment for 40 min suppressed Phe-induced vasoconstriction. Both the short- and long-term bupivacaine treatment suppressed ACh-induced vasodilation. Incubation of the aortic rings with 0.2%-0.6% lipid emulsion (LE) for 100 min significantly increased the pD2 and Emax values of Phe-induced vasoconstriction, and incubation with 0.4% LE for 100 min reversed the inhibition of bupivacaine on vasoconstriction induced by Phe (30 μmol/L). In contrast, incubation with LE suppressed ACh-induced vasodilation, even at a lower concentration and with a 5-min incubation.

CONCLUSION

Bupivacaine exerts dual effects on α1-adrenoceptor-mediated vasoconstriction of isolated rat aortic rings: short-term treatment enhances the response, while long-term treatment inhibits it; the inhibition may be reversed via long-term incubation with LE.

Parenteral emulsions and liposomes to treat drug overdose

Drug overdoses from both pharmaceutical and recreational drugs are a major public health concern. Although some overdoses may be treated with specific antidotes, the most common treatment involves providing supportive care to allow the body to metabolize and excrete the toxicant. In many cases, supportive care is limiting, ineffective, and expensive. There is a clear medical need to improve the effectiveness of detoxification, in particular by developing more specific therapies or antidotes for these overdoses. Intravenous lipid emulsions (ILEs) have been investigated as a potential treatment for overdoses of local anesthetics and other hydrophobic drugs. While ILE therapy has been successful in several cases, its use beyond local anesthetic systemic toxicity is controversial and its mechanism of detoxification remains a subject of debate. ILEs were not originally developed to treat overdose, but clarifying the mechanisms of detoxification observed with ILE may allow us to design more effective future treatments. Liposomes are highly biocompatible and versatile formulations, thus it was a natural step to explore their use for drug overdose therapy as well. Several researchers have designed liposomes using a variety of approaches including surface charge, pH gradients, and inclusion of enzymes in the liposome core to optimize the formulations for detoxification of a specific drug or toxicant. The in vitro results for drug sequestration by liposomes are very promising and animal trials have in some cases shown comparable performance to ILE at reduced lipid dosing. This narrative review summarizes the current status and advances in the use of emulsions and liposomes for detoxification and also suggests several areas in which studies are needed for developing future therapies.