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Local Anesthetic Systemic Toxicity (LAST)
Local anesthetics are among the most widely used drugs in medicine. They are given for nerve blocks, epidurals, and spinals, and they are also injected by surgeons, dentists, dermatologists, and other clinicians who infiltrate tissue directly. When enough local anesthetic reaches the bloodstream, it can affect the brain and the heart. This is called local anesthetic systemic toxicity, or LAST. It may begin with agitation, a metallic taste, or ringing in the ears, and it can progress to seizures, dangerous heart rhythms, or cardiac arrest.
LAST is uncommon, but it is time-critical. When it leads to a bad outcome, three questions matter. Was the dose and technique reasonable? Was the patient monitored closely enough that toxicity would be noticed early? And once it was noticed, did the team respond the way published guidance describes? This article explains how a physician expert approaches each question.
How often does LAST occur?
The published figures are low, but they are not zero.
- A prospective registry of 12,668 ultrasound-guided peripheral nerve blocks by Sites and colleagues (Regional Anesthesia and Pain Medicine, 2012) recorded seizures at 0.08 per 1,000 blocks and no cardiac arrests. The authors concluded that LAST is extremely uncommon in that setting.
- A review of recent case reports and registries by Gitman and Barrington (Regional Anesthesia and Pain Medicine, 2018) found 47 published cases from March 2014 to November 2016. Penile blocks accounted for 23% and local infiltration for 17%, with the rest from extremity, torso, and neuraxial blocks. Seizure was the most common presenting feature. Registry data put the incidence at about 0.27 per 1,000 peripheral nerve blocks.
Two points follow. First, LAST is not limited to anesthesiologists or to the operating room. Second, a low rate does not answer whether a particular event was preventable or was managed well.
The guidance that frames the standard-of-care discussion
The American Society of Regional Anesthesia and Pain Medicine (ASRA) has published practice advisories on LAST. The third advisory (Neal and colleagues, Regional Anesthesia and Pain Medicine, 2018) updates recommendations on prevention, recognition, and treatment. It describes a trend toward delayed presentation, which the authors link to ultrasound guidance, local infiltration techniques, and continuous infusions. It identifies small patient size and sarcopenia as added risk factors. It also notes that a growing number of events occur outside the traditional hospital setting and involve clinicians other than anesthesiologists.
ASRA also publishes a one-page checklist for managing LAST. The 2020 version (Neal, Neal, and Weinberg, 2021) was updated in response to user feedback, simulation studies, and advances in medical knowledge. In general terms, the checklist covers calling for help, airway management, seizure control, early use of lipid emulsion therapy, and changes to standard cardiac life support. An expert should identify which version was current on the date of care, and should describe these documents as practice advisories and cognitive aids rather than rigid rules.
Prevention: what the records should show
A careful review of prevention usually asks:
- Drug and dose. Which local anesthetic was used, at what concentration and total volume? Was the total dose reasonable for the patient's size, age, and medical condition? Were doses from different clinicians, such as a block followed by surgical infiltration, added together?
- Adjuvants. Were additives used to extend the block? Adjuvants may allow a smaller total local anesthetic dose, a point discussed in the regional anesthesia literature.
- Technique. Was injection incremental, with pauses to watch for warning signs? Was aspiration or a test dose used where appropriate? Was ultrasound used, and is the needle and spread documented?
- Monitoring. Was the patient on standard monitors during and after the injection? Was someone watching who could recognize early symptoms?
- Delayed risk. For continuous catheters or large infiltrations, did monitoring continue long enough to catch a delayed reaction?
Recognition and rescue
Because symptoms can be subtle at first, record review often focuses on the timeline. When did the first unusual symptom appear? Was it charted? How long was it until a seizure, arrhythmia, or collapse, and what happened in between?
Typical rescue questions include:
- Was lipid emulsion available in the area where the block or injection took place?
- Was it given, and when, relative to the first signs of toxicity?
- Were seizures treated and the airway supported promptly?
- If cardiac arrest occurred, was resuscitation adjusted for local anesthetic toxicity, as the ASRA checklist describes?
- Was the patient observed for an appropriate period afterward, given that cardiovascular instability can recur?
The code sheet, anesthesia record, nursing notes, and pharmacy records often have different timestamps. Reconciling them is usually the core of the analysis.
Causation questions
Not every seizure or arrhythmia near the time of a block is LAST. An expert considers other causes, such as a pre-existing seizure disorder, cardiac disease, low blood sugar, other medications given at the same time, or a vasovagal event. The timing of symptoms relative to the injection, the total dose, and any measured drug levels can help separate these possibilities. Where LAST is confirmed, the separate question is whether earlier recognition or faster treatment would likely have changed the outcome.
Records that usually matter
- The anesthesia record and block procedure note, including drug, concentration, volume, and timing
- The operative note and any surgical infiltration doses
- Medication administration records and pharmacy dispensing records
- Monitoring data and vital-sign trends, including any downloaded monitor data
- Code or rapid-response records, with timestamps
- The facility's LAST protocol and the location of lipid emulsion on the date of care
The published background behind this review
Dr. Urits was first author of A Comprehensive Review and Update of the Use of Dexmedetomidine for Regional Blocks (Psychopharmacology Bulletin, 2020). It reviews dexmedetomidine as an adjuvant in regional blocks and notes that adjuvants that prolong sensory and motor block can reduce the total amount of local anesthetic needed. He also co-authored Buprenorphine as an adjuvant to local anesthetics in peripheral nerve blocks (Korean Journal of Pain, 2019). His opinions rest on the complete record, the peer-reviewed literature, and generally accepted methodology.
Key takeaways
- LAST is uncommon, but it occurs across many specialties and settings, not only in anesthesia.
- Prevention questions center on total dose, incremental injection, and monitoring.
- Rescue questions center on recognition, the availability and timing of lipid emulsion, and resuscitation measured against the ASRA guidance in effect at the time.
- A clear, time-stamped timeline is usually the key to understanding what happened.
References
- Sites BD, Taenzer AH, Herrick MD, et al. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks: an analysis from a prospective clinical registry. Reg Anesth Pain Med. 2012;37(5):478-482. Abstract: https://pubmed.ncbi.nlm.nih.gov/22705953/
- Gitman M, Barrington MJ. Local Anesthetic Systemic Toxicity: A Review of Recent Case Reports and Registries. Reg Anesth Pain Med. 2018;43(2):124-130. Abstract: https://pubmed.ncbi.nlm.nih.gov/29303925/
- 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(2):113-123. Abstract: https://pubmed.ncbi.nlm.nih.gov/29356773/
- Neal JM, Neal EJ, Weinberg GL. American Society of Regional Anesthesia and Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version. Reg Anesth Pain Med. 2021;46(1):81-82. Abstract: https://pubmed.ncbi.nlm.nih.gov/33148630/
- Urits I, Virgen CG, Alattar H, et al. A Comprehensive Review and Update of the Use of Dexmedetomidine for Regional Blocks. Psychopharmacol Bull. 2020;50(4 Suppl 1):121-141. Abstract: https://pubmed.ncbi.nlm.nih.gov/33633422/
- Viswanath O, Urits I. Buprenorphine as an adjuvant to local anesthetics in peripheral nerve blocks. Korean J Pain. 2019;32(3):231-232. Abstract: https://pubmed.ncbi.nlm.nih.gov/31257833/
Related: Anesthesia Medication and Medication Error Cases
Educational information only. Not legal or medical advice.
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