Local Anesthetic Systemic Toxicity (LAST)

Overview: 

Local Anesthetic Systemic Toxicity (LAST) refers to the effects, signs, and symptoms that systemic absorption of local anesthetic (LA) has on the body. Every time LA is administered, independent of the route, a variable part of this drugs gets absorbed systemically and can cause specific signs and symptoms, depending on the concentration of the LA in the blood. 

Clinical Use: 

Symptoms of LAST

The signs and symptoms of last correlate with the serum concentration of local anesthetic. This has been well documented for lidocaine, as shown in the following graph:

Figure 1: Relationship of signs and symptoms of lidocaine toxicity to serum concentration

 

Time from LA injection to Onset of Symptoms

It is important to notice, that these symptoms don’t necessarily progress in the described order and that, if a higher amount of LA gets absorbed at once (e.g., accidental intravascular injection), the presenting symptom can be seizure or even cardiac arrest.

In terms of timeline, there seems to be a shift from intravascular injection to slower systemic absorption, which is reflected by the onset time of LAST after the injection of LA. According to the latest findings, in 22% of cases the first signs and symptoms occurred later than 30 minutes after injection:

Figure 2: Percentage of cases in relation to time of onset of symptoms

Treatment of LAST

If LAST is suspected, the following steps should be undertaken:

  1. Stop injection, when any signs of intravascular injection occur!
  2. Call for help! (get qualified assistance, get LAST kit, get checklist)
  3. Arrange for CPB (alert nearest facility, may be necessary if ACLS and IV lipid emulsion fail)
  4. Manage the airway (give 100% O2, if necessary, control ventilation with facemask, supraglottic device or ETT, prevent hypoxia and acidosis, as both potentiate LAST)
  5. Suppress seizure (reduce oxygen consumption, prevent hypoxia and hypercarbia, prevent patient injury. Benzos preferred, could use propofol or thiopental, but with caution, succinylcholine will terminate tonic-clonic muscle activity, but not CNS electrical activity)
  6. Manage arrhythmias and provide cardiovascular support
    1. May have to perform CPR for a prolonged time
    2. Administer amiodarone as first line antiarrhythmic (usual doses per ACLS), avoid lidocaine and other sodium channel blockers
    3. Reduce bolus dose of epinephrine to ≤ 1 mcg/kg to avoid arrhythmogenic effects (this is based on animal studies and the optimal dose of epi is unknown).
    4. Avoid vasopressin (in an animal model, vasopressin was associated with poor hemodynamic and metabolic outcomes).
    5. Avoid calcium channel as well as beta blockers (potential for exacerbating hypotension).
  7. Administer lipid rescue
    1. Precise volumes and rates of lipid emulsion are not crucial. Administer 20% lipid emulsionalong with ACLS or when neurotoxicity occurs
    2. Bolus (100ml over 2 -3 minutes for >70 kg), followed by infusion (see checklist below)
    3. Repeat bolus once or twice and double infusion rate for persistent cardiovascular instability (see ASRA Fig 3)
    4. Continue infusion for at least 10 minutes after hemodynamic stability is achieved
    5. Maximum dose ~ 12 ml/kg
    6. Propofol is not a substitute for 20 % lipid emulsion
  8. Transfer patient to monitored setting

 

ASRA Local Anesthesia Society Checklist

The American Society of Regional Anesthesia (ASRA) has created a checklist for the management of LAST which summarizes the above-mentioned information and will conclude this module:

Figure 3: ASRA checklist for the management of LAST, updated 12/1/2020

References: 

Neal JM, Barrington MJ, Fettiplace MR, et al. The third American Society of Regional Anesthesia and Pain Medicine practice advisory on local anesthetic systemic toxicity: executive summary 2017. Reg Anesth Pain Med. 2018;43:113–123

El-Boghdadly K, Pawa A, Chin KJ. Local anesthetic systemic toxicity: current perspectives. Local Reg Anesth. 2018;11:35-44

Neal JM, Neal EJ, Weinberg GL. American Society of Regional Anesthesia and Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version. Regional Anesthesia & Pain Medicine Published Online First: 04 November 2020, updated 01 December 2020

UpToDate: Local Anesthetic Systemic Toxicity by Warren L, Pak A. Accessed online on 12/2/2020

Author: 
Matthias R. Braehler