About This Topic

This information provides clinical context for the IV Lipid Emulsion Dosing Calculator. Local Anesthetic Systemic Toxicity (LAST) is a rare but life-threatening adverse event following the administration of local anesthetics. Intravenous (IV) 20% lipid emulsion therapy is a primary treatment, acting as a “lipid sink” to sequester the lipophilic anesthetic molecules from target tissues in the heart and brain.

Calculator Outputs Explained

The tool calculates a complete dosing regimen based on patient parameters and the latest ASRA guidelines. The key outputs are:

• Initial Bolus (mL): The rapid, initial dose to quickly establish therapeutic lipid levels. For adults >70 kg, this is a fixed 100 mL. For others, it is weight-based (1.5 mL/kg).
• Infusion Rate (mL/min and mL/hr): The continuous infusion started immediately after the bolus to maintain lipid levels and prevent recurrence of toxicity.
• Repeat Bolus Doses (mL): Additional boluses that can be administered if the patient remains hemodynamically unstable.
• Maximum Total Dose (mL): A critical safety ceiling (approximately 12 mL/kg) for the first 30 minutes of treatment to mitigate the risk of adverse effects from lipid overload.

How to Use the Calculator

Accurate inputs are essential for correct dose calculation in this emergency setting. Follow these steps:

1. Enter Patient Weight: Input the patient’s actual weight. The calculator will convert lbs to kg if needed.
2. Enter Patient Height and Gender: These values are used to calculate the Ideal Body Weight (IBW). For patients whose actual weight is more than 120% of their IBW, dosing is based on IBW to prevent lipid overload.
3. Select Patient Type:
   • >70 kg (Adult): Select this for the simplified protocol recommended for most adults, which uses a fixed 100 mL initial bolus.
   • <70 kg / Pediatric: Select this for a strictly weight-based calculation (1.5 mL/kg), which is crucial for smaller adults, children, and underweight patients.

Dosing Overview

The administration protocol for 20% lipid emulsion in LAST is a multi-step process designed for rapid intervention and sustained support.

Initial Treatment

Upon recognition of LAST, immediately administer the initial bolus over approximately one minute. Simultaneously, start the maintenance infusion. This two-part approach quickly achieves and then maintains the necessary plasma lipid concentration.

Managing Persistent Instability

If hemodynamic instability continues after the initial bolus and infusion start, the bolus can be repeated up to two more times. After the second bolus, consider doubling the infusion rate. Constant patient monitoring is critical to guide these decisions.

Switching Therapies

This section addresses changes in treatment during a LAST event. The established rescue protocol is based on 20% lipid emulsion. Switching to other concentrations (e.g., 10% or 30%) is not recommended as safety and efficacy data are lacking. If the patient does not respond to the full lipid emulsion protocol, management must escalate to other advanced life support measures, including notifying the nearest facility with cardiopulmonary bypass (CPB) capability.

Missed Dose

This concept does not apply. IV lipid emulsion for LAST is an emergency, one-time rescue therapy, not a scheduled medication with a dosing interval. It is administered only during an active toxicity event.

Safety Alerts

• Maximum Dose: Strictly adhere to the maximum recommended dose of 12 mL/kg to avoid complications like hyperlipidemia, pancreatitis, and fat overload syndrome.
• Monitoring: Continuous hemodynamic monitoring (ECG, blood pressure) is essential. Laboratory monitoring for triglycerides, lipase, and amylase may be warranted after the event.
• Allergies: Use with caution in patients with known allergies to eggs or soy products, as these are components of the emulsion.
• Propofol: Do not use propofol as a substitute for 20% lipid emulsion. While lipid-based, its concentration is too low, and its sedative and cardiodepressant effects can worsen the clinical picture.

Frequently Asked Questions (FAQ)

Why is Ideal Body Weight (IBW) used for some patients?

For obese patients (actual weight >120% of IBW), dosing based on actual weight could lead to excessive lipid administration. Basing the dose on IBW provides a safer, effective dose while minimizing the risk of fat overload.

What concentration of lipid emulsion should be used?

Only 20% intravenous lipid emulsion (e.g., Intralipid® 20%) is recommended. Protocols and dosing calculations are based on this specific concentration.

What are the signs and symptoms of LAST?

Symptoms can range from mild (tinnitus, metallic taste, agitation) to severe (seizures, cardiac arrhythmias, cardiovascular collapse). Any CNS or cardiac symptom after a local anesthetic injection should raise suspicion for LAST.

Can I use Propofol to treat LAST?

No. While propofol is a lipid-based medication, its lipid content is insufficient for treating LAST, and its potent cardiorespiratory depressant effects can worsen the patient’s condition.

What should I do if the patient doesn’t respond to lipid therapy?

Continue ACLS with LAST-specific modifications. The primary focus shifts to supportive care and preparing for advanced interventions like cardiopulmonary bypass (CPB).

How long should the infusion continue?

The infusion should continue for at least 15 minutes after hemodynamic stability is achieved. Tapering the infusion rather than stopping it abruptly is recommended.

Is this protocol different for children?

The principles are the same, but dosing is strictly based on weight (IBW if obese). The calculator’s “<70 kg / Pediatric” setting applies this principle.

Can lipid emulsion be used for other drug toxicities?

Yes, it is considered a potential antidote for other lipophilic drug overdoses (e.g., tricyclic antidepressants, calcium channel blockers). However, its use in these situations is off-label, and consultation with a poison control center or medical toxicologist is strongly advised.

References

1. Neal, J. M., et al. (2018). The American Society of Regional Anesthesia and Pain Medicine Checklist for Managing Local Anesthetic Systemic Toxicity: 2017 Version. Regional Anesthesia and Pain Medicine, 43(2), 150-153. View on PubMed
2. American Society of Regional Anesthesia and Pain Medicine (ASRA). (2021). ASRA Local Anesthetic Systemic Toxicity Checklist. View Guideline
3. Gitman, M., & Fettiplace, M. R. (2019). Local Anesthetic Systemic Toxicity. In StatPearls. StatPearls Publishing. View on NCBI
4. FDA Drugs@FDA Database. Example Prescribing Information for Intralipid 20%. Search on FDA.gov