Neal, Joseph M. MD*; Bernards, Christopher M. MD*; Butterworth, John F. IV MD†; Di Gregorio, Guido MD‡; Drasner, Kenneth MD§; Hejtmanek, Michael R. MD*; Mulroy, Michael F. MD*; Rosenquist, Richard W. MD∥; Weinberg, Guy L. MD‡
Local anesthetics are widely and commonly used throughout medical and dental practice. Although it is rare for patients to manifest serious adverse effects or experience complications secondary to local anesthetic administration, adverse events do occur. These range from the mild symptoms that may follow systemic absorption of local anesthetic from a correctly sited and appropriately dosed regional anesthetic procedure to major central nervous system (CNS) and/or cardiac toxicity (most often from unintentional intravascular injection) that can result in disability or death. A variety of factors influence the likelihood and severity of local anesthetic systemic toxicity (LAST), including individual patient risk factors, concurrent medications, location and technique of block, specific local anesthetic compound, total local anesthetic dose (the product of concentration × volume), timeliness of detection, and adequacy of treatment.
Interest in local anesthetic toxicity has had several peaks, including one that coincided with the initial awareness of local anesthetic toxicities after the introduction of cocaine in 1884, another that followed the linking of fatalities to the use of bupivacaine and etidocaine in the 1970s, and another after the introduction of ropivacaine and levobupivacaine in the late 1980s that continues through the present.1,2 There is suspicion (but scant evidence) that patients undergoing regional anesthesia are now less likely to have LAST than in earlier decades. On the other hand, improved understanding of LAST pathophysiology and new treatment modalities have emerged in the 2000s. Consequently, the American Society of Regional Anesthesia and Pain Medicine (ASRA) commissioned a panel of experts to update recommendations that came from the 2001 ASRA Conference on Local Anesthetic Toxicity. The current Practice Advisory focuses on LAST, which includes cardiac and CNS toxicity consequent to unintended intravascular injection or delayed tissue uptake. The advisory does not address tissue-related local anesthetic neurotoxicity, allergy, or the production of methemoglobinemia by local anesthetics.
A 2006 survey of US academic anesthesiology departments found no uniform, well-designed, rational approach for management of local anesthetic toxicity.3 The ASRA Practice Advisory Panel was also formed to correct this deficiency by identifying key practice modifications targeted specifically at improving prevention, diagnosis, and treatment of LAST. Our recommendations reflect our view of the primacy of prevention of LAST as the most effective intervention for enhancing patient safety.
This practice advisory is derived from human and animal experimental studies related to the prevention, diagnosis, and treatment of LAST in adults and children. All available English-, German-, and French-language reports of human and animal scientific inquiry were considered, including randomized controlled trials (RCTs), observational studies, case series, and case reports. Key word literature searches were undertaken using major literature search engines such as the National Library of Medicine's PubMed, Ovid, and Google Search. Article bibliographies were cross-checked for references not identified by search engines.
The ASRA Board of Directors appointed the Panel at their fall 2007 meeting. The Panel consists of recognized experts on local anesthetic toxicity and/or guideline development and includes all authors of this article. This group was responsible for the initial literature search, assimilation of materials, expert opinion, development of recommendations, and writing the accompanying supporting articles. Individuals neither received direct financial support for their participation nor did any participants other than Drs. Weinberg and Butterworth declare a potential conflict of interest (see appended declaration). The ASRA received no direct financial support from industry or other grants to underwrite expenses (travel support for the panel) related to this initiative.
As suggested by recognized instruments for guideline development such as the Appraisal of Guidelines for Research & Evaluation,4 every effort was made to ensure the integrity and validity of the process leading to the recommendations made herein. External input, appraisal, and validity were sought using the following mechanisms. The Panel's recommendations were circulated to a separate group of experts selected on the basis of their demonstrated interest and/or expertise in local anesthetic toxicity (Appendix 1). General input was also sought by contacting the Editors-in-Chief of major journals for medical and dental specialties that commonly use local anesthetics (Appendix 2). Comments from these 2 groups were considered and incorporated when appropriate, and particularly as they related to content, interpretation, and clarity of the recommendations. One week before presentation in open forum at the May 3, 2008, ASRA meeting in Cancun, Mexico, meeting registrants were e-mailed a copy of the recommendations. Open comment was solicited primarily with regard to clarity and soundness of the recommendations. After finalizing recommendations, the Practice Advisory summary document and accompanying review articles were submitted to Regional Anesthesia and Pain Medicine for publication, where they were subjected to the journal's standard peer-review process. Readers are encouraged to read the accompanying reviews, which provide the details that led to recommendations contained within this summary article.
Grading the Strength of Recommendations
There are no RCTs evaluating serious human LAST; future RCTs are unlikely because of the rarity of these complications and the associated difficulty of obtaining informed consent for medical interventions in critical illness. Common strength-of-evidence schemas that are based on RCT-level evidence are therefore inappropriate for the topic of human LAST but are appropriate for animal studies. Hence, the Practice Advisory's recommendations are based on a modification of a Classification of Recommendations and Levels of Evidence schema that was developed by the American Heart Association (Table 1).5 The panel wishes to emphasize that assigning a Level of Evidence B or C should not be construed as implying that the associated recommendation is supported by conflicting data or is limited by conflicting interpretations of the available data. Rather, such recommendations reflect our recognition of the importance of the particular question as it relates to LAST, and to the reality that the specific question is either yet to be addressed by a RCT or does not lend itself to experimental inquiry in humans.
As with previous ASRA-sponsored practice advisories, our recommendations should be viewed as guidelines that are based on existing literature and expert opinion. The scientific literature that provided the basis for these guidelines and recommendations is imperfect and always evolving. Animal studies should be interpreted with knowledge of species differences, variations in laboratory systems, and differing experimental models. The hypothesis being tested may limit the conclusions one can make, along with extrapolations to the clinical setting. Literature comprising case reports may be biased toward positive outcomes because clinicians are reluctant to present their cases that have poor outcome, and case reports without a "teaching point" will almost never be accepted for publication.6 Therefore, some local anesthetics, for example, ropivacaine or levobupivacaine, might seem safer than is the case, and specific treatments, for example, lipid emulsion, might fail more often than the literature indicates. Some of our recommendations are based on expert opinion alone. The nature of practice advisories is that they address issues of controversy and uncertainty. We strive to acknowledge these controversies, but then to offer our best advice within the setting of uncertainty. Particularly when addressing more controversial issues, our recommendations tend to err toward conservative management.
Our recommendations are intended to promote quality patient care; nevertheless, rigid observance of our recommendations may not guarantee a specific patient outcome. Our recommendations are not meant to be interpreted as standard of care and they should never supersede sound medical judgment. Those who apply these recommendations will determine their value. As with all practice advisories, these recommendations will be subject to timely revision as warranted by the evolution of technology, scientific evidence, and clinical experience.7
Local anesthetic systemic toxicity has been recognized and reported since shortly after the introduction of cocaine into clinical practice in the 1880s. From the outset, systemic toxicity was associated with seizures and respiratory failure.8 It is unclear when direct cardiac toxicity was recognized as a major component of systemic toxicity, rather than an associated adverse effect. The systemic toxic effects of cocaine and cocaine's propensity to cause local tissue toxicity in part led to Einhorn's development of procaine in 1904. Unfortunately, LAST continued to be a major patient safety concern, so much so that the American Medical Association (AMA) established the Committee for the Study of Toxic Effects of Local Anesthetics in the early 1920s.9 It became clear that local anesthetics were not only capable of causing death but that cardiac arrest could precede seizures or even occur in the absence of seizures. The AMA Committee stopped short of suggesting a ban on cocaine, but emphasized the primacy of a clear airway to optimize oxygenation and ventilation, a theme that Daniel Moore and Donald Bridenbaugh10 would continue to stress throughout the mid and late 20th century. The potent lipid-soluble local anesthetics bupivacaine and etidocaine were introduced into clinical practice in the 1960s and 1970s, respectively. By 1969, bupivacaine had been linked to fetal death in 1:900 women who received a paracervical block, admittedly without a clear understanding as to whether bupivacaine itself, the paracervical block technique, or some combination thereof was the responsible etiologic factor. Not until the late 1970s was bupivacaine linked to fatal cardiac arrest in otherwise healthy adult patients. The report of Prentice11 and Albright's oft-cited editorial1 set in motion the events that would lead the US Food and Drug Administration and the 3 manufacturers of bupivacaine issuing a "Dear Doctor" letter withdrawing obstetric analgesia as an indication for 0.75% bupivacaine and warning against its further use in paracervical block and intravenous regional anesthesia. Despite the clinical release of the apparently less cardiotoxic single enantiomers ropivacaine and levobupivacaine in the late 1980s, serious morbidity and mortality from cardiac toxicity continued.2 In the 1990s, animal research gave hope that lipid emulsions might prove to be an antidote for LAST.12 The first case reports of successful rescue of humans experiencing refractory cardiac toxicity came in the mid 2000s.13 Today, research is ongoing to refine issues related to lipid emulsion therapy for severe LAST and its prodromes.14
FREQUENCY, MODELS, AND MECHANISMS
What is known regarding LAST is derived primarily from 3 sources-epidemiologic studies that attempt to define incidence in specific patient populations, case series and case reports that describe clinical manifestations of toxicity and/or treatment,2 and animal studies that aim to establish relative toxicity, elucidate mechanisms, and identify cofactors that promote or attenuate their occurrence. Epidemiologic studies report statistics that vary widely depending on how toxicity is defined, the clinical scenario in which it occurs, and how the data were collected. For example, death from the application of cocaine or tetracaine to mucous membranes to facilitate otolaryngological procedures was reported in 1951 to occur in 7 of 39,278 patients (1.8:10,000).15 Seizures associated with brachial plexus blockade, particularly the interscalene and supraclavicular approaches (where local anesthetics may be unintentionally injected into an artery feeding the brain), have been reported in up to 79 in 10,000 patients from a single institutional database.16 Yet a large surveillance study of French anesthesiologists determined the overall frequency of seizures to be 0 to 25 in 10,000, depending on the type of block performed. Interestingly, there were no cardiac arrests secondary to LAST reported in this series.17 Information from case reports and series offers insights into clinical scenarios of LAST2 but is unable to define mechanisms. Human RCTs of local anesthetic toxicity will likely never be performed because of ethical and logistical concerns. Thus, most of what is understood regarding the mechanisms of LAST and its treatment comes from animal studies, yet there is limited consensus among investigations as to which animal model best reflects human toxicity. Even basic mechanistic information is controversial with regard to which anesthetic binding site, ion channel, signaling pathway, or enzyme is most important in CNS or cardiac toxicity or their treatment.
When one interprets animal studies of LAST, it is important to consider the model chosen by the investigators to study their hypothesis and what specific clinical circumstance the model is intended to mimic.18 Variables include in vivo whole animal models versus in vitro isolated heart versus tissue culture; whole cell, ion channel, or subcellular organelle models; large animal versus small animal; awake versus anesthetized; and bolus dosing versus infusion models. Other important features will influence the interpretation of the findings, including the chosen metrics and parameters of interest, the timing of such measures, or the presence of confounders such as hypoxia. Although each of these approaches provides specific advantage, there is no consensus that any model truly mimics clinical toxicity. For instance, many cases of toxicity occur in patients with underlying ischemic or other cardiac disease, which is not readily modeled in standard experimental animals or preparations. Given that summarizing the mechanisms of LAST assuredly represents an oversimplification, in general, it seems that cardiac toxicity results predominantly from the binding and inhibition of Na channels by local anesthetics. Notably, inhibition of cardiac conduction follows a rank order similar to local anesthetic potency for generating neural blockade.19 When compared with lidocaine, cardiac conduction channels are bound more rapidly and for longer duration by the more potent local anesthetics bupivacaine, etidocaine, and ropivacaine,20 albeit less avidly by their S(−) isomers.21 Such evidence notwithstanding, a vast array of other inotropic and metabotropic cell signaling systems are affected by local anesthetics and have been implicated in mediating symptoms and signs of LAST. Furthermore, virtually every component of oxidative phosphorylation is inhibited by potent local anesthetics; this observation provides support for mitochondrial metabolism as an important, potential target of local anesthetics and could help explain why symptoms of LAST include predominantly the organs least tolerant of anaerobic metabolism (heart and brain).
Local anesthetics also differ with regard to their CNS toxicity. The cardiovascular (CV)/CNS ratio describes the dose required to produce CV arrhythmias versus that required to produce seizures. This ratio tends to be lower with bupivacaine compared with lidocaine, which implies a reduced safety margin for the potent compounds when detecting impending cardiac toxicity based on premonitory CNS signs. These more potent local anesthetics indeed generate arrhythmias at lower concentrations compared with lidocaine and mepivacaine. At comparable doses in dogs, bupivacaine and etidocaine caused severe arrhythmias without decreased contractility, while lidocaine caused the opposite, that is, depressed myocardial contractility without arrhythmia.22-24 However, once plasma concentrations reach higher levels, local anesthetics of all potencies are capable of producing severe myocardial depression.25
This Practice Advisory emphasizes the primacy of prevention in reducing the frequency and severity of LAST, yet no single intervention has been identified that can reliably eliminate risk. Central to prevention is limiting the opportunity for intravascular injection or tissue uptake of local anesthetic, which is best accomplished by early detection of intravascular needle or catheter placement. If an intravascular injection does occur, it should ideally contain the lowest possible dose of local anesthetic. To these ends, various intravascular identification methods have been proposed since the description of the epinephrine test dose by Moore and Batra in 1981.26 Literature review suggests that the frequency of LAST associated with epidural anesthesia may have decreased subsequently by 10- to 100-fold.27 Conversely, actual published reports of LAST have increased recently, most likely because of renewed interest and new information related to the introduction of the less cardiotoxic stereoisomers ropivacaine and levobupivacaine and to clinical experience with successful lipid emulsion rescue.2
Local anesthetic dose can be limited by several methods. Total dose (the product of volume × concentration) should be tailored to the minimum mass of local anesthetic molecules necessary to achieve the desired clinical effect. Evidence suggests that most peripheral nerve blocks are performed with significantly larger doses than are necessary to achieve desired clinical end points28; these data are further supported by ultrasound-guided regional anesthesia (UGRA)29 and continuous perineural catheter30 studies that document adequate blockade using exceedingly small doses of properly placed local anesthetic.31 Dose reduction may be particularly important for those patients thought to be at greater risk of LAST, for example, those patients at extremes of age (<4 months or >70 years) or those with cardiac conduction defect or a history of ischemic heart disease. Neither body weight nor body mass index correlates with local anesthetic plasma levels after a specific dose in adults; the correlation is more accurate in children. Block site, intrinsic vasoactivity of the local anesthetic, use of epinephrine, and patient-related factors such as cardiac, renal, or hepatic dysfunction are more important predictors of local anesthetic plasma levels than either body weight or body mass index.
When the above noted factors that may predispose to LAST are present, reduction of local anesthetic dose is intuitively logical, yet there are no established parameters to guide actual dose reduction.32 Incremental injection of 3 to 5 mL of local anesthetic with a concomitant pause for at least one circulation time before further injection is a time-honored recommendation with intuitive appeal, but with no objective efficacy data. Practical considerations suggest that the potential benefit from this approach could be outweighed by prolonging overall injection time with an attendant risk of needle movement. Of note, circulation times are increased with lower extremity injection compared with upper extremity injection. Aspiration of needles and catheters, although recommended, may fail to identify intravascular placement in at least 2% of patients.33 Substituting the less potent levoenantiomers ropivacaine or levobupivacaine might reduce the potential for systemic toxicity Nonetheless, these drugs are potentially toxic and the theoretical benefit of chirality becomes less important with increasing doses, particularly among patients at greater than normal risk for local anesthetic toxicity. It is possible that risk inherent to comorbidities such as ischemic heart disease, conduction defects or low output states far outweighs the potential risk reduction of using levoenantiomers.
How can a clinician reduce the risk of LAST? Although imperfect, intravascular test dosing remains the most reliable marker of intravascular injection. Of the various options described, only fentanyl and epinephrine meet suggested standards for reliability and applicability.34 Intravenous fentanyl 100 μg has been shown to reliably produce drowsiness or sedation in laboring patients.27 With regard to epinephrine, 10 to 15 μg/mL epinephrine has a positive predictive value and 80% sensitivity in detecting intravascular injection in adults if heart rate increases by 10 beats per minute or higher or systolic blood pressure increases by 15 mm Hg or higher. For children, intravascular epinephrine 0.5 μg/kg is associated with a 15-mm Hg increase or higher in systolic blood pressure. Nevertheless, epinephrine test doses are unreliable in the elderly, or in patients who are sedated, taking β-blockers, or anesthetized with general or neuraxial anesthesia. Epinephrine is also controversial with regard to its role in nerve injury. Although epinephrine has been shown in animal models to worsen local anesthetic-induced neurotoxicity, it is unclear if the additive injury in humans is clinically relevant over and above that caused primarily by the local anesthetic itself.35 The frequency of seizures during performance of peripheral nerve block was similar to the frequency of permanent nerve injury in one major study (1.2 versus 2.4 in 10,000, respectively).36 Notably, severe LAST, but not nerve injury, has the potential to cause death.
Ultrasound guidance may reduce the frequency of vascular puncture, but there are no RCTs that confirm or refute an actual reduction of LAST.37 Two large case series present conflicting results-one found a statistically significant (P = 0.001) reduction in the number of vascular punctures occurring under UGRA versus peripheral nerve stimulation, but no difference in LAST.38 The other series reported a significant (P = 0.044) reduction in seizures with ultrasound-assisted nerve localization versus peripheral nerve stimulation.39 Although intravascular injection can be observed during UGRA,40 case reports describe symptomatic intravascular injection despite its use.41 Whether generation of a hypoechoic region consequent to injected local anesthetic is a sufficient monitor of intravascular injection to warrant omission of epinephrine is the subject of considerable debate, particularly when one considers the frequent needle movements inherent to UGRA techniques versus the generally fixed needle techniques associated with nonultrasound blocks. Thus, prevention of intravascular injection is perhaps best accomplished with a combination of UGRA and epinephrine test dosing. Because the literature offers no firm guidance and no method of detection is perfect, meticulous attention to detail remains the most important asset for prevention. Recommendations for preventing LAST are given in Table 2.
CLINICAL DIAGNOSIS OF SYSTEMIC TOXICITY
The classic description of LAST includes subjective symptoms of CNS excitement such as auditory changes, circumoral numbness, metallic taste, and agitation that then progress to seizures and/or CNS depression (coma, respiratory arrest). In classic descriptions of LAST, cardiac toxicity does not occur without preceding CNS toxicity. When LAST occurs secondary to direct intravascular injection (particularly with injection into the carotid or vertebral arteries), premonitory symptoms can be bypassed and the patient can rapidly develop seizure activity that may progress to cardiac excitation (hypertension, tachycardia, ventricular arrhythmias). With greatly increased blood concentrations, cardiac excitation may be followed by cardiac depression (bradycardia, asystole, decreased contractility, and hypotension). Particularly with the most potent local anesthetics, cardiac toxicity may occur simultaneously with seizure activity or even precede it.
Despite this classic description, case reports of LAST emphasize the extreme variability of its presentation, including timing of onset, initial manifestations, and duration. We found an atypical presentation was reported in approximately 40% of published cases of LAST. In these instances, symptoms were delayed by 5 mins or more or occurred with only CV signs of toxicity. The practitioner's vigilance is of critical importance in recognizing these early signs of LAST, appreciating their variable presentation, and having a low threshold for considering LAST in patients that have received potentially toxic doses of local anesthetics and manifest atypical or unexpected signs and symptoms.
Local anesthetic systemic toxicity continues to be a major source of morbidity and mortality in regional anesthesia practice. Recent American Society of Anesthesiologists Closed Claims data note that LAST accounted for one-third of claims for death or brain damage associated with regional anesthesia.42 Conversely, physicians tend to report and publish their successes rather than their failures-in our review of 93 separate LAST events contained within 74 reports, there was only 1 death. Our review spanned 30 years, yet 65% of the reports were published in the last 10 years. From this review, several patterns emerge. First, two-thirds of patients were female and nearly half the cases were in patients at the extremes of age-16% were younger than 16 years and 30% were older than 60 years. More than 90% of cases involved the most potent local anesthetics, that is, bupivacaine, ropivacaine, and levobupivacaine. Less than 1 in 5 cases involved continuous infusion techniques and half of these were in children. Although analysis of case reports only establishes association rather than cause-and-effect, it is interesting to note that more than one-third of reports of cardiac and CNS toxicity involved patients with underlying cardiac, neurologic, or metabolic disease, for example, diabetes, renal failure, isovaleric academia.
In our reviewed single injection cases, the median time from injection to first symptom was 52.5 seconds (interquartile range, 30-180 seconds), which suggests direct injection into an artery supplying the brain or a large intravascular bolus containing sufficient local anesthetic dose to cause CNS symptoms even after first pass clearance through the lungs. For this same group of cases, the mean time to first symptom was 89 seconds (95% confidence interval, 67-120 seconds). Most other reports noted first symptoms between 1 and 5 mins of injection, suggesting partial intravascular injection, lower extremity injection, and/or tissue uptake. Importantly, approximately 25% of cases described symptoms first appearing more than 5 mins after injection (one report described a 60-min delay), which emphasizes the importance of prolonged observation of patients receiving potentially toxic doses of local anesthetic. Local anesthetic systemic toxicity may occur as frequently as 1:1000 peripheral nerve blocks,43 but it is likely that most of these cases involve minor subjective symptoms that do not progress to frank CNS or cardiac toxicity. Of those cases serious enough to report and publish, 45% involved only CNS signs and symptoms, whereas 44% involved both CNS and cardiac manifestations. Reported cases rarely presented with only cardiac signs and symptoms.2
Our overall analysis of case reports suggests that although LAST tends to follow classic presentations, variations are common. Although seizure was the most common presenting symptom, less than 20% of cases involved any of the classic prodromal symptoms such as auditory changes, metallic taste, or disinhibition. Thus, practitioners are advised to be ever-vigilant of potential LAST, particularly in patients at the extremes of age who may have underlying cardiac, pulmonary, renal, hepatic, metabolic, or neurologic disease. Importantly, LAST does not always manifest itself as obvious seizure or cardiac arrhythmias in close temporal relationship to local anesthetic injection. Practitioners should consider the diagnosis of impending LAST in patients that develop unexplained agitation or CNS depression, or unexplained signs of CV compromise, for example, progressive hypotension, bradycardia, or ventricular arrhythmia, even if more than 15 mins after local anesthetic injection.2 Recommendations for diagnosing LAST are contained in Table 3.
Treatment priorities for LAST include airway management, circulatory support, and promoting the diminution of the systemic effects of local anesthetics. Unlike the case for treatment of "conventional" cardiac arrest, the key to successful care of LAST patients is recognizing the primacy of airway management. As reported by Moore and colleagues a half century ago,10,44 prevention of hypoxia and acidosis by immediate restoration of oxygenation and ventilation can either halt progression to CV collapse and seizure or facilitate resuscitation. Subsequent laboratory investigations confirm this concept.45 If seizures occur, they should be rapidly controlled to prevent injury to the patient and acidosis. The Panel recommends that benzodiazepines are the ideal drugs to treat seizures because they have limited potential for cardiac depression. In the absence of readily available benzodiazepine, propofol or thiopental are acceptable alternatives; however, their potential for worsening existing hypotension or cardiac depression requires using the lowest effective dose. The Panel recognizes that further experience with lipid infusion could lead to its use in preference to benzodiazepines. If tonic-clonic movements persist despite these measures, small doses of succinylcholine may be considered to rapidly stop muscular activity (continued seizure activity exacerbates hypoxia and systemic acidosis), being mindful that seizure activity and acidosis will continue unless interrupted with a sedative hypnotic agent.46
Local anesthetic-induced cardiac arrest requires rapid restoration of coronary perfusion pressure to improve myocardial contractility and theoretically to washout local anesthetics from cardiac tissues through improved tissue perfusion. Maintenance of cardiac output and oxygen delivery to tissues is critical for prevention and treatment of acidosis. It is important to recognize that cardiac arrest or arrhythmia associated with LAST represents a substantially different medical problem from the more typical out-of-hospital scenarios addressed by Advanced Cardiac Life Support Guidelines. Although standard dose (1 mg) epinephrine may restore circulation and initially improve blood pressure, it is also highly arrhythmogenic. Furthermore, in animal studies of local anesthetic-induced cardiac arrest, epinephrine resulted in poorer outcomes from bupivacaine-induced asystole than did lipid emulsion,47 whereas vasopressin also showed very poor outcomes and was associated with pulmonary hemorrhage.48 Therefore, the Panel advises that if used in treating LAST, lower than "standard" initial doses of epinephrine are suggested (<1 μg/kg). On the basis of animal studies, consideration should be given to avoiding vasopressin. In recalcitrant cases of LAST in which there is inadequate response to epinephrine and other standard therapies, cardiopulmonary bypass should be considered as a bridging therapy until tissue levels of local anesthetic have cleared.
Lipid emulsion therapy can be instrumental in facilitating resuscitation, most probably by acting as a "lipid sink" that draws down the content of lipid-soluble local anesthetics from within cardiac tissue, thereby improving cardiac conduction, contractility, and coronary perfusion.49 We recommend an initial bolus of 1.5 mL/kg (lean body mass) 20% lipid emulsion, followed by an infusion of 0.25 mL/kg per minute continued for 10 mins after hemodynamic stability is attained. Failure to achieve stability should prompt an additional bolus and increase of infusion rate to 0.5 mL/kg per minute. Approximately 10 mL/kg lipid emulsion for 30 mins is recommended as an upper limit for initial administration.46
There are several as yet unanswered questions regarding lipid emulsion therapy. Initial recommendations conservatively suggested that it be used only after standard resuscitative attempts had failed, but recent case reports6,50-52 support the early use of lipid emulsion at the first sign of arrhythmia from suspected LAST, prolonged seizure activity, or rapid progression of the toxic event. Because tissue depots of local anesthetic can redistribute to the circulation over time and delayed recurrence of severe toxicity has been reported, we recommend that any patient with significant LAST be observed for at least 12 hrs. There is no evidence that one formulation of lipid emulsion is superior to another for the treatment of LAST. However, it is important to note that propofol is not a substitute for lipid emulsion therapy because of its low lipid content (10%), the large volumes required for the benefit of lipid in resuscitation (hundreds of milliliters) and the direct cardiac depressant effects of propofol. Our recommendations for the treatment of LAST are presented in Table 4. Those recommendations are summarized in Appendix 3, which is available online in two sizes and can be printed and laminated for display in areas where potentially toxic doses of local anesthetics are used. (See Supplemental Digital Content 1, http://links.lww.com/AAP/A17, for a condensed version of Appendix 3, and Supplemental Digital Content 2, http://links.lww.com/AAP/A18, for a full-size version).
It is apparent that continued investigation is needed to guide future methods for preventing and treating LAST. Improved, less toxic, longer-acting local anesthetics are desired. Novel delivery methods may reduce the dose required to achieve clinical anesthesia and analgesia. Examples include both current technology (UGRA) and delivery methods in development, such as capsaicin coinjection53 and sustained release microspheres or liposomes.54 We hope that continued laboratory investigation will lead to improved resuscitation methods. Alternative formulations of lipid emulsion or new agents designed to increase partitioning, binding, capture, or otherwise neutralizing local anesthetic molecules hold the promise of a rapid, effective antidote to LAST. Further refinement is needed with regard to the ideal timing of lipid emulsion therapy, along with identification of potential toxicities or adverse effects.
Our understanding of the mechanisms of LAST, although incomplete, has increased significantly since local anesthesia was introduced more than a century ago. Stepwise improvements in our knowledge regarding prevention, diagnosis, and treatment have likely led to a reduction in fatalities associated with LAST; it is less certain whether the frequency of nonfatal seizures and cardiac events has also declined, particularly those events associated with peripheral nerve block (as opposed to epidural techniques). Although probably linked to the recent development of UGRA and lipid emulsion therapy, the resurgence of published reports of LAST, (particularly involving successful resuscitation) suggests that LAST remains a significant clinical problem. Considering (1) the extensive use of local anesthetics, (2) the frequent use of doses sufficient to cause significant morbidity or mortality, and (3) the imperfect nature of our ability to prevent, detect, and treat these complications, it remains the responsibility of all clinicians using local anesthetics to understand their potential for severe systemic toxicity and to be prepared to respond immediately to these events when they occur.
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