# Local Anesthetic Systemic Toxicity in Veterinary Patients: Recognition and Treatment ## Key Takeaways - Local Anesthetic Systemic Toxicity (LAST) is an iatrogenic complication arising from systemic absorption of local anesthetics, leading to central nervous system (CNS) and cardiovascular depression or excitation. The most common cause in veterinary practice is inadvertent intravascular injection during regional anesthesia, rapid absorption from highly vascular sites, or cumulative dosing exceeding metabolic capacity. - Highest-risk drugs include long-acting amides like bupivacaine, with toxicity risk directly correlated to neural blockade potency; no local anesthetic is inherently "safe." Early signs in dogs and cats include perioral paresthesia, agitation, muscle twitching, vocalization, and tachycardia, progressing to seizures and cardiovascular depression. - Immediate management involves stopping injection, securing the airway with 100% oxygen, and initiating intravenous lipid emulsion therapy as a first-line rescue for cardiovascular collapse or refractory CNS signs. Early administration of lipid emulsion is critical for improved outcomes. - Species-specific presentations vary; cats exhibit more pronounced CNS excitation and are more susceptible to bupivacaine cardiotoxicity. Large animals under general anesthesia may present primarily with cardiovascular signs like hypotension and arrhythmias, masking CNS excitation. - Prevention is paramount, utilizing aspiration before injection, incremental dosing, lowest effective concentrations, and ultrasound guidance for high-risk blocks. Sedation or general anesthesia can obscure early CNS warning signs, allowing cardiovascular collapse to be the first recognized manifestation. - Lipid emulsion therapy acts via both pharmacokinetic (drug sink) and pharmacodynamic (cardiotonic) mechanisms. It is indicated for any cardiovascular sign of toxicity or non-resolving seizures, with a bolus followed by a continuous infusion, and repeated boluses if instability persists. --- Local anesthetic systemic toxicity (LAST) is an iatrogenic, potentially fatal complication that follows the absorption of local anesthetic molecules into the systemic circulation in sufficient quantity to produce central nervous system (CNS) and cardiovascular depression or excitation. In veterinary practice, LAST most often arises from inadvertent intravascular injection during regional anesthesia techniques, from rapid absorption at highly vascular injection sites, or from cumulative dosing that exceeds the patient's metabolic and distributive capacity. This article provides the practicing veterinarian with a structured approach to recognizing the early clinical signs of LAST across common companion animal species and to initiating immediate, life-saving treatment, with particular emphasis on intravenous lipid emulsion therapy. The content assumes familiarity with anesthetic drugs, monitoring equipment, and basic cardiopulmonary resuscitation, and it deliberately excludes detailed pharmacokinetic modeling in favor of actionable diagnostic and therapeutic reasoning. The clinical question this article answers is direct: when a patient under or recovering from local or regional anesthesia deteriorates, how does the clinician distinguish LAST from other perioperative emergencies, and what sequence of interventions offers the best chance of survival? The answer requires fluency in the dose-dependent progression of CNS and cardiovascular signs, an understanding of which local anesthetics carry the highest risk, and a working knowledge of lipid emulsion as a rescue therapy. The evidence base for LAST derives largely from human anesthesia literature, experimental animal models, and consensus guidelines, and this article translates those sources into veterinary context while flagging where species differences matter. ## At a Glance | Parameter | Clinical Decision Point | |---|---| | Highest-risk drugs | Bupivacaine and other long-acting amides, risk is potency-related, not agent-specific | | Most common cause | Inadvertent intravascular injection during block placement | | Earliest signs | Perioral paresthesia, agitation, muscle twitching, vocalization, tachycardia | | Cardiovascular collapse | May occur simultaneously with CNS signs or as the first sign under general anesthesia | | Immediate actions | Stop injection, call for help, secure airway, begin lipid emulsion if signs progress | | Lipid emulsion role | First-line rescue for cardiovascular collapse, supportive for CNS toxicity | | Prognostic factor | Time from onset to lipid emulsion administration | | Species variation | Cats show more pronounced CNS excitation, large animals may present with recumbency and arrhythmia | ## Mechanisms of Toxicity Local anesthetics exert their therapeutic effect by blocking voltage-gated sodium channels in nerve membranes, preventing depolarization and impulse propagation. At toxic concentrations, the same channel blockade becomes systemic. Sodium channel blockade in the myocardium slows conduction velocity, prolongs the QRS complex, and predisposes to reentrant arrhythmias. In the CNS, local anesthetics first inhibit inhibitory pathways, producing a paradoxical excitatory state, then depress all neuronal activity as concentrations rise further. The longer-acting amide agents, particularly bupivacaine, bind cardiac sodium channels with high affinity and slow dissociation kinetics, which explains their disproportionate cardiotoxicity relative to equipotent doses of shorter-acting agents. Experimental models comparing the single enantiomer drugs ropivacaine and levobupivacaine to racemic bupivacaine consistently show that the former produce less severe cardiovascular depression and are more readily resuscitated, as summarized in [in vivo comparisons of long-acting amide toxicity in animal models](https://pubmed.ncbi.nlm.nih.gov/12567336/). The relationship between neural blockade potency and systemic toxicity is tightly linked across virtually all available local anesthetics. Agents that are more potent for nerve block are correspondingly more potent for systemic toxicity, with some stereochemistry-related exceptions. This means no local anesthetic is inherently "safe" from a toxicity standpoint, the margin between effective dose and toxic dose narrows as potency increases. [A review of the acute toxicity of local anesthetics](https://pubmed.ncbi.nlm.nih.gov/20738226/) emphasizes that all agents in the class can produce direct cardiovascular depression and CNS excitotoxicity, and that the pattern of cardiac failure differs by agent. The shorter-acting drugs such as lidocaine and procaine tend to cause myocardial contractile failure, whereas the longer-acting agents more often produce malignant ventricular arrhythmias and cardiac arrest. ## Risk Factors and Clinical Scenarios Patient factors modify the threshold for LAST. Geriatric patients carry increased risk because age-related reductions in muscle mass and cardiac output alter drug distribution, and concurrent comorbidities reduce physiologic reserve. [A review of local anesthetic toxicity in the geriatric population](https://pubmed.ncbi.nlm.nih.gov/31598909/) notes that inadvertent overdosing accounts for a substantial proportion of toxicity cases in older human patients, a finding that translates directly to veterinary patients with reduced hepatic metabolism or renal clearance. Neonates and pediatric patients have lower concentrations of alpha-1 acid glycoprotein, leaving more drug unbound and pharmacologically active. Cats are particularly sensitive to CNS excitation from local anesthetics, and their limited hepatic glucuronidation capacity slows amide metabolism. The most dangerous clinical scenario is the intended epidural, nerve block, or local infiltration that deposits drug directly into a vessel. Aspiration before injection reduces but does not eliminate this risk, because a needle can move between aspiration and injection. Other scenarios include repeated boluses that accumulate beyond the dosing interval, infiltration into inflamed or highly vascular tissue where absorption is rapid, and accidental intravenous administration of a drug drawn into the wrong syringe. The use of ultrasound guidance for block placement has reduced the frequency of intravascular injection in human practice, but [reviews of local anesthetic systemic toxicity](https://pubmed.ncbi.nlm.nih.gov/31598909/) confirm that LAST continues to occur even with ultrasound, because the needle tip can lie within a vessel that is not visualized or the drug can be injected during needle movement. ## Species-Specific Presentation The clinical expression of LAST varies by species, and the veterinarian must adjust expectations accordingly. In dogs, the earliest signs are typically CNS excitation: restlessness, panting, muscle fasciculations, and vocalization, followed by generalized seizures. Tachycardia and hypertension accompany the excitatory phase. As toxicity deepens, CNS depression replaces excitation, bradycardia develops, and hypotension progresses to cardiovascular collapse. In cats, the excitatory phase is more pronounced and may include aggressive behavior, hypersalivation, and pronounced mydriasis before seizures supervene. Cats also appear more susceptible to the cardiotoxic effects of bupivacaine at lower plasma concentrations than dogs. In horses and ruminants, the presentation is often dominated by cardiovascular signs because these patients are usually under general anesthesia when blocks are performed, masking CNS signs. Sudden hypotension, bradyarrhythmia, or ventricular arrhythmia in a horse receiving a regional block should raise immediate suspicion of LAST. Recumbency in a standing patient that has just received a local anesthetic infusion for a standing procedure is another sentinel event. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific dosing and monitoring guidance that should be reviewed before performing regional techniques in less common species. ## Prevention as the First Line of Defense Prevention is the most effective treatment for LAST. Every local anesthetic injection should be preceded by aspiration, incremental dosing, and observation between aliquots. The total dose should be calculated for the individual patient, not assumed from a standard protocol, and the lowest effective concentration and volume should be used. For high-risk blocks such as intercostal, brachial plexus, or epidural, ultrasound guidance should be used whenever available. Sedation or general anesthesia does not protect the patient from LAST, it only obscures the early CNS warning signs, allowing the first recognized manifestation to be cardiovascular collapse. Continuous infusions require the same vigilance as bolus dosing, with periodic reassessment of cumulative dose against body weight and duration of infusion. ## Recognition: Clinical Signs and Diagnostic Reasoning The clinical expression of LAST follows a predictable neuroexcitatory then cardiovascular sequence, although the rate of progression varies with the specific agent, the route of administration, and the patient's physiologic reserve. [Mather's review of acute local anesthetic toxicity](https://pubmed.ncbi.nlm.nih.gov/20738226/) emphasizes that all local anesthetics can produce both central nervous system excitotoxicity and direct cardiovascular depression, and the balance between these effects differs by drug. Longer-acting agents such as bupivacaine are more likely to cause malignant arrhythmias and sudden cardiac collapse, whereas shorter-acting agents such as lidocaine and mepivacaine more often produce myocardial contractile failure. This distinction matters clinically because the presenting arrhythmia pattern, also the drug name, should guide the resuscitation strategy. ### Early Neurologic Signs In dogs, the earliest detectable signs are typically perioral twitching, facial muscle fasciculations, and agitation. As plasma concentration rises, generalized tremors, ataxia, and vocalization appear. Cats show a similar sequence but often progress faster, and their subtle early signs can be mistaken for emergence delirium or pain-related restlessness. Seizures may be focal or generalized and are frequently the event that prompts the clinician to suspect LAST instead of a primary neurologic problem. The critical diagnostic point is temporal association. Signs that begin within seconds to a few minutes after injection, particularly after a regional block or epidural, should be assumed to represent intravascular injection or rapid systemic absorption until proven otherwise. Delayed onset, up to 30 to 60 minutes after administration, can occur with large-volume infiltration or with use of long-acting agents in highly vascular tissues. ### Cardiovascular Signs Cardiovascular manifestations follow a biphasic pattern. Early tachycardia and hypertension reflect sympathetic activation and CNS excitation. This phase is brief and easily missed, particularly in an anesthetized patient under inhalant anesthesia where heart rate and blood pressure are already being manipulated. The subsequent phase of myocardial depression produces bradycardia, hypotension, widening of the QRS complex, and progressive conduction block. Ventricular arrhythmias, including torsades de pointes and ventricular fibrillation, are more characteriztic of bupivacaine and ropivacaine toxicity. [Groban's review of long-acting amide toxicity in intact animal models](https://pubmed.ncbi.nlm.nih.gov/12567336/) notes that the single-enantiomer agents ropivacaine and levobupivacaine are consistently less cardiotoxic than racemic bupivacaine at equi-anesthetic doses, but they are not devoid of risk. ### The Recognition Table The table below organizes the clinical findings by phase and provides the diagnostic weight of each finding. Use it at the bedside when LAST is suspected. | Phase | Clinical Finding | Diagnostic Weight | Typical Timing After Injection | |---|---|---|---| | Prodromal | Perioral paresthesia, metallic taste, agitation | Moderate, often missed | Seconds to 2 minutes | | CNS excitation | Tremors, fasciculations, ataxia, vocalization | High | 1 to 5 minutes | | CNS depression | Seizures, obtundation, coma | High | 2 to 10 minutes | | Cardiovascular excitation | Tachycardia, hypertension | Low, transient | 1 to 3 minutes | | Cardiovascular depression | Bradycardia, hypotension, QRS widening | High | 3 to 15 minutes | | Cardiovascular collapse | Ventricular arrhythmias, asystole, pulseless electrical activity | Definitive | Variable, may be first sign with bupivacaine | A patient who presents with seizures and then develops bradycardia and QRS widening after a regional block has LAST until proven otherwise. Do not delay treatment to pursue alternative diagnoses. The differential for perianesthetic seizures includes hypoxia, intracranial disease, and other drug toxicities, but the procedural context and the cardiovascular progression are what distinguish LAST. ## Immediate Treatment: The First Ten Minutes Treatment priority follows the ABC sequence with two modifications specific to LAST: aggressive airway management to prevent hypoxia and acidosis, and early administration of intravenous lipid emulsion. [The AAHA anesthesia and monitoring guidelines for dogs and cats](https://www.aaha.org/resources/2020-aaha-anesthesia-and-monitoring-guidelines-for-dogs-and-cats/) emphasize continuous monitoring of ventilation and perfusion in all anesthetized patients, and this becomes urgent when toxicity is suspected. ### Airway and Breathing Secure the airway immediately. Hypoxia and hypercapnia potentiate local anesthetic toxicity by shifting the balance toward more severe CNS and cardiac depression. Intubate if not already intubated, ventilate with 100% oxygen, and confirm capnographic evidence of ventilation. Treat seizures with a benzodiazepine as first-line therapy. Propofol can be used if a benzodiazepine is ineffective, but be aware that propofol itself causes myocardial depression and may worsen hypotension in a patient already compromised by local anesthetic effects. ### Circulation Establish intravenous access if not already present. If the suspected injection was into a specific regional site, consider whether the local anesthetic can be aspirated or the block site flushed, but do not delay systemic treatment for this maneuver. Begin fluid resuscitation with a balanced crystalloid solution. If the patient is hypotensive or has arrhythmias, proceed directly to lipid emulsion therapy instead of waiting for crystalloid resuscitation to show effect. ## Lipid Emulsion Therapy: Indications and Administration Intravenous lipid emulsion is the specific antidote for LAST. [Harvey and Cave's review of lipid emulsion in local anesthetic toxicity](https://pubmed.ncbi.nlm.nih.gov/28692439/) summarizes the evidence base as providing reserved endorsement for bupivacaine-induced toxicity, weak support for other local anesthetics, and a positive effect on survival when animal models are meta-analyzed. The mechanism appears to involve both a pharmacokinetic effect, where the lipid phase acts as a sink that draws local anesthetic away from target tissues, and a pharmacodynamic effect with direct cardiotonic and vasoactive actions. ### When to Start Start lipid emulsion when there is any cardiovascular sign of toxicity, including hypotension, bradycardia, or arrhythmia, or when seizures do not terminate promptly with benzodiazepines. Do not wait for cardiac arrest. Earlier administration is associated with better outcomes, and the risk of adverse effects from the lipid emulsion itself is low when standard dosing is used. ### Dosing Structure Current recommendations follow a bolus followed by a continuous infusion. The specific milligram per kilogram doses and infusion rates vary between published protocols and between veterinary and human references, and the evidence base in veterinary patients is extrapolated largely from human case reports and animal experiments. Consult a current veterinary formulary or the most recent published consensus guidelines before administering lipid emulsion, and have the dosing chart posted in the treatment area so it is available during an emergency. The bolus is given over one to two minutes, and the infusion is typically continued for 30 to 60 minutes. If cardiovascular instability persists after the initial bolus, the bolus can be repeated, and the infusion rate can be increased. ### Monitoring During Lipid Emulsion Therapy Monitor the electrocardiogram continuously, blood pressure every one to two minutes during the acute phase, and capnography if the patient is intubated. Pulse oximetry is useful but can be misleading during low cardiac output states. Serial blood gas analysis will detect the metabolic acidosis that accompanies severe toxicity and will guide bicarbonate therapy if pH falls below 7.1. Serum triglyceride levels can be checked if the infusion is prolonged, but routine measurement is not required for short-duration therapy. ## Refractory Toxicity and Advanced Resuscitation Patients who do not respond to lipid emulsion and standard resuscitation within five to ten minutes require escalation. This is the point where species and patient status change the approach. In dogs, defibrillation should be used for ventricular fibrillation or pulseless ventricular tachycardia. In cats, the smaller thoracic volume and higher defibrillation threshold relative to body size make successful defibrillation less likely, and the priority shifts to pharmacologic management and open-chest resuscitation if the chest is already open for another procedure. Vasopressors are indicated for persistent hypotension. Epinephrine is the first-line agent, but use reduced doses compared with standard cardiac arrest protocols, because high-dose epinephrine can worsen local anesthetic toxicity by increasing myocardial oxygen demand and promoting arrhythmias. Amiodarone is preferred over lidocaine for ventricular arrhythmias in this setting, because additional lidocaine will compound the toxicity. Avoid calcium channel blockers and beta blockers, as they potentiate the myocardial depression caused by local anesthetics. ### When to Stop Resuscitation should continue for at least 30 to 60 minutes in cases of bupivacaine toxicity, because successful outcomes after prolonged resuscitation have been reported. [The systematic review by Cave and Harvey on lipid emulsion as an antidote](https://pubmed.ncbi.nlm.nih.gov/19845549/) documents cases of successful resuscitation from cardiac arrest caused by lipophilic drug toxicity, and the authors note that the evidence, while limited, supports persistence in resuscitation efforts. The decision to stop is based on the same criteria used for any cardiac arrest: refractory asystole or pulseless electrical activity without any return of spontaneous circulation despite maximal therapy, and the absence of a reversible cause that has not been addressed. ## Documentation and Case Review Document the timeline of events precisely, including the time of local anesthetic administration, the dose and volume given, the route, the first sign of toxicity, and the sequence of interventions. Record the lipid emulsion bolus time and dose, the infusion rate, and the patient's response at each monitoring point. This documentation serves three purposes: it supports the medical record, it provides data for practice-level quality improvement, and it contributes to the published evidence base, which remains limited in veterinary medicine. [The WSAVA Global Pain Council guidelines](https://wsava.org/global-guidelines/global-pain-council-guidelines/) encourage practices to audit their analgesic and anesthetic protocols, and a structured review of any LAST event should examine whether the block technique, dose calculation, or monitoring protocol could be modified to prevent recurrence. ## Recognized Complications and Failure Modes Local anesthetic systemic toxicity can evolve through several distinct failure patterns, each with characteriztic detection points. The first is delayed-onset toxicity from slow absorption. This occurs most often after large-volume infiltration, interpleural administration, or block placement in highly vascular regions without epinephrine co-administration. Detection depends on extended post-procedural monitoring, since signs may appear 30 to 60 minutes after injection instead of during the procedure itself. The second pattern is biphasic toxicity, where initial neurologic signs resolve spontaneously but cardiovascular depression follows minutes later. This sequence reflects differential tissue partitioning and can mislead the clinician into believing the episode has passed. The third pattern is refractory cardiovascular collapse, which may present as the first recognizable sign in heavily sedated or anesthetized patients where neurologic signs are masked. In this setting, progressive bradycardia, widening QRS complexes, and hypotension may be the only clues before arrest. A fourth failure mode involves liposomal bupivacaine formulations. These preparations can produce toxicity with a substantially delayed onset, sometimes hours after administration, because drug release from the liposomal matrix continues over time. The geriatric population appears to be at disproportionately increased risk for toxicity owing to relevant comorbidities and decreased muscle mass, and this consideration applies to veterinary patients with similar frailty profiles [Local Anesthetic Toxicity in the Geriatric Population](https://pubmed.ncbi.nlm.nih.gov/31598909/). Detection requires vigilance beyond the immediate periprocedural period, particularly in patients with cardiac or hepatic disease. ## Common Errors and Corrective Actions Less experienced clinicians frequently misinterpret early neurologic signs as emergence from sedation or as a reaction to the procedure itself. Muscle fasciculations, vocalization, or agitation in a lightly sedated patient may be dismissed as pain or dysphoria. The corrective action is to maintain a low threshold for considering LAST whenever local anesthetic has been administered in the preceding hour, and to apply the recognition framework described earlier in this article instead of attributing signs to alternative causes. A second error is delaying lipid emulsion therapy while pursuing repeated boluses of vasopressors or antiarrhythmics. The evidence base for lipid emulsion in bupivacaine-induced toxicity is stronger than for other local anesthetics, and current recommendations support early administration once toxicity is recognized [Lipid emulsion in local anesthetic toxicity](https://pubmed.ncbi.nlm.nih.gov/28692439/). The corrective action is to treat lipid emulsion as a first-line resuscitative agent in confirmed or strongly suspected LAST, not as a last resort. A third error involves dosing errors from concentration confusion. Bupivacaine 0.5% and 0.75% solutions, and lidocaine 1% and 2% solutions, are easily confused when syringes are not labeled at the time of drawing. The corrective action is to have a second person verify drug, concentration, and volume before administration, and to use prefilled syringes or color-coded labels where available. ## Limitations of the Evidence The evidence base for LAST treatment in veterinary patients is extrapolated largely from human case reports, animal laboratory studies, and consensus guidelines. Direct comparative data in dogs and cats are limited. The mechanism of lipid emulsion therapy appears to involve both pharmacokinetic effects on drug distribution and pharmacodynamic cardiotonic effects acting in concert, but the relative contribution of each remains incompletely defined [Lipid emulsion in local anesthetic toxicity](https://pubmed.ncbi.nlm.nih.gov/28692439/). Expert opinion differs on the role of lipid emulsion for toxicity from agents other than bupivacaine, with systematic reviews providing only weak support for other local anesthetics [Systematic review of the effect of intravenous lipid emulsion therapy for non-local anesthetics toxicity](https://pubmed.ncbi.nlm.nih.gov/26852931/). Species differences in susceptibility are recognized but not fully characterized. Longer-acting local anesthetics are more likely to cause cardiac death by malignant arrhythmias, while shorter-acting agents more often produce cardiac contraction failure [The acute toxicity of local anesthetics](https://pubmed.ncbi.nlm.nih.gov/20738226/). Whether this distinction translates to clinically meaningful differences in resuscitation approach across species is uncertain. ## Troubleshooting Table | Observation | Likely Cause | Discriminating Check | |---|---|---| | Fasciculations or agitation 20 to 40 minutes after block | Delayed systemic absorption | Recheck heart rate and ECG, measure blood pressure, consider lipid emulsion if signs progress | | Sudden bradycardia with wide QRS in anesthetized patient | Cardiovascular phase of LAST, possibly masked neurologic phase | Compare current ECG to baseline, check end-tidal CO2, assess pulse quality | | Hypotension unresponsive to vasopressors | Refractory LAST or alternative cause such as hemorrhage | Review total local anesthetic dose, check for surgical bleeding, escalate to lipid emulsion if LAST suspected | | Recurrent arrhythmias after initial resuscitation | Ongoing drug redistribution or inadequate lipid dosing | Reassess lipid infusion rate, check perfusion parameters, consider prolonged monitoring | ## Referral and Reporting Referral to a specialty or emergency facility is warranted when a patient requires mechanical ventilation, develops recurrent arrhythmias, or fails to stabilize within 30 minutes of appropriate treatment. Consultation with a veterinary toxicologist or a human poison center with veterinary experience is appropriate for refractory cases or when lipid emulsion dosing is uncertain. Laboratory involvement may include serial blood gas analysis, electrolyte measurement, and cardiac troponin assessment in patients with suspected myocardial injury. Regulatory reporting obligations vary by jurisdiction. In the United States, adverse drug events involving local anesthetics may be reported to the FDA through the veterinary adverse event reporting system, and the AVMA provides practice resources that describe current reporting expectations [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). Clinicians should also review institutional protocols after any LAST event to identify preventable causes, particularly dosing errors or inadequate monitoring. ## Frequently Asked Questions ### How do I manage LAST when I do not have lipid emulsion on hand? Begin standard resuscitation immediately. Secure the airway, provide 100% oxygen, and treat arrhythmias and hypotension with agents appropriate for the patient's species and hemodynamic status. If cardiac arrest occurs, perform high-quality CPR and continue it while arrangements are made to obtain lipid emulsion from a nearby emergency or referral hospital. The evidence supporting lipid emulsion is strongest for bupivacaine-induced toxicity, with weaker support for other local anesthetics, so its absence should not delay conventional resuscitative measures. Document the absence of the drug and the steps taken to obtain it. After the event, review your hospital's emergency drug inventory and consider stocking lipid emulsion if local anesthetic procedures are performed regularly. [Intravenous lipid emulsion as antidote beyond local anesthetic toxicity](https://pubmed.ncbi.nlm.nih.gov/19845549/) provides context on the breadth of lipid emulsion utility, while [AAHA anesthesia and monitoring guidelines](https://www.aaha.org/resources/2020-aaha-anesthesia-and-monitoring-guidelines-for-dogs-and-cats/) address emergency preparedness in companion animal practice. ### What should I record in the medical record after a LAST event? Record the local anesthetic used, the calculated dose, the route and site of administration, and the time from injection to first signs. Document every clinical sign in chronological order, including vital parameters, neurologic status, and electrocardiogram findings. Note the timing and dose of every intervention, including oxygen, fluids, atropine, vasopressors, and lipid emulsion. Record the patient's response to each intervention and the time to clinical recovery. Include a narrative of the suspected cause, such as intravascular injection or cumulative overdose, and the steps taken to prevent recurrence. Finally, document client communication and any referral discussions. This record supports case review and may be requested if the case is reported to a pharmacovigilance program. [The acute toxicity of local anesthetics](https://pubmed.ncbi.nlm.nih.gov/20738226/) reviews the mechanisms that should inform your documented assessment. ### How does LAST recognition differ in exotic or production animal species? Neurologic signs are often subtler or faster in prey species. Ruminants may show muscle fasciculations, recumbency, or bloat before cardiovascular collapse, while horses may display agitation, sweating, or ataxia. Birds and small mammals can deteriorate rapidly from relatively small volumes, so weight-based dosing and careful aspiration before injection are critical. Cardiovascular monitoring may be limited by equipment availability, making serial assessment of mucous membrane color, pulse quality, and heart rate more important. In production animals, consider withdrawal intervals for any adjunctive drugs used during resuscitation, and consult [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) for reporting obligations. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific guidance on local anesthetic use and toxicity across domestic species. ### What do I tell a client whose pet experienced a local anesthetic reaction? Explain that the patient received a local anesthetic to control pain and that a rare complication occurred in which the drug entered the bloodstream or was absorbed in excess. Describe the signs you observed and the treatment provided in terms the owner can understand, emphasizing that the team recognized the problem and responded immediately. Be honest about the severity: some patients recover fully with supportive care, while others require prolonged hospitalization. Avoid assigning blame to any individual, but do describe the steps that will be taken to prevent recurrence, such as lower doses, different drug selection, or enhanced monitoring. Provide written discharge instructions and a clear point of contact for concerns. The [AVMA practice resources](https://www.avma.org/resources-tools) include guidance on client communication and professional conduct following adverse events. ### Can I use a local anesthetic again in a patient that survived LAST? Yes, but only after careful reconsideration of the risk-benefit balance. Choose a different drug class or a shorter-acting agent with a lower toxicity profile, reduce the total dose, and use the lowest concentration that achieves adequate blockade. Consider alternative analgesic techniques, such as systemic analgesia or a different regional approach. If local anesthesia is essential, ensure intravenous access, incremental injection with frequent aspiration, and continuous monitoring throughout the procedure and recovery period. Document the prior event prominently in the record and discuss the plan with the owner. The geriatric population illustrates how age and comorbidities increase susceptibility, so apply extra caution in older patients with cardiac or hepatic disease. [Local anesthetic toxicity in the geriatric population](https://pubmed.ncbi.nlm.nih.gov/31598909/) reviews these risk factors in detail. ### When should I refer a patient after successful initial resuscitation? Refer when the patient requires intensive care capabilities beyond your hospital, such as continuous electrocardiogram monitoring, mechanical ventilation, or advanced arrhythmia management. Refer if neurologic signs persist beyond a few hours, if arrhythmias recur despite treatment, or if there is evidence of end-organ damage such as elevated cardiac troponin or persistent metabolic acidosis. Transfer the patient once hemodynamically stable enough for transport, and send a complete summary of the event, including drug doses and response times. Call the receiving facility before departure to ensure they are prepared. In some jurisdictions, adverse drug events may also warrant reporting to a national pharmacovigilance scheme, so check local requirements. The [WSAVA Global Pain Council Guidelines](https://wsava.org/global-guidelines/global-pain-council-guidelines/) discuss analgesic safety and the role of referral in complex pain management cases. ## Related Clinical & Scientific Guides * [Anesthetic Machine Leak Testing and Pressure Checks: A Step-by-Step Protocol](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthetic-machine-leak-testing-pressure-checks) * [Anesthetic Depth Assessment: Reflexes, Eye Position, and Ventilation](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthetic-depth-assessment-reflexes-eye-position) * [Anesthesia for Patients with Obesity: Challenges and Solutions](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthesia-patients-obesity-challenges-solutions) ## References and Further Reading - [Local Anesthetic Toxicity in the Geriatric Population.](https://pubmed.ncbi.nlm.nih.gov/31598909/). 2020. - [The acute toxicity of local anesthetics.](https://pubmed.ncbi.nlm.nih.gov/20738226/). 2010. - [Central nervous system and cardiac effects from long-acting amide local anesthetic toxicity in the intact animal model.](https://pubmed.ncbi.nlm.nih.gov/12567336/). 2003. - [Lipid emulsion in local anesthetic toxicity.](https://pubmed.ncbi.nlm.nih.gov/28692439/). 2017. - [Intravenous lipid emulsion as antidote beyond local anesthetic toxicity: a systematic review.](https://pubmed.ncbi.nlm.nih.gov/19845549/). 2009. - [Systematic review of the effect of intravenous lipid emulsion therapy for non-local anesthetics toxicity.](https://pubmed.ncbi.nlm.nih.gov/26852931/). 2016. - [AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats](https://www.aaha.org/resources/2020-aaha-anesthesia-and-monitoring-guidelines-for-dogs-and-cats/). AAHA. - [WSAVA Global Pain Council Guidelines](https://wsava.org/global-guidelines/global-pain-council-guidelines/). WSAVA. - [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual. ## Related Articles - [Anesthetic Complications: Recognition and Initial Management](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthetic-complications-recognition-initial-management) - [Anesthetic Complications in Cats: Recognition and Salvage](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthetic-complications-cats-recognition-and-salvage) - [Electrocardiogram Monitoring in Anesthetized Veterinary Patients: Arrhythmia Recognition](/knowledge/veterinary-medicine/anesthesia-analgesia/ecg-monitoring-anesthetized-veterinary-patients-arrhythmia) - [Anesthesia for Patients with Cancer: Paraneoplastic Syndromes](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthesia-patients-cancer-paraneoplastic-syndromes) - [Anesthesia for Patients with Sepsis: Hemodynamic Support](/knowledge/veterinary-medicine/anesthesia-analgesia/anesthesia-patients-sepsis-hemodynamic-support) > This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.