Shows where each agent's strength in the syringe (C₂) sits against product-label ranges, with selected trial evidence. It does not predict whether a block will work: that depends on block site, volume, objective (surgical anaesthesia or postoperative analgesia) and technique.

Mixtures. Mixing dilutes every agent, e.g. 1:1 bupivacaine 0.5% + lidocaine 2% gives 0.25% + 1%. A 2026 RAPM meta-analysis (10 RCTs, ultrasound-guided blocks) found no significant difference in sensory or motor onset versus the long-acting agent alone, and a shorter sensory block (about 2 h), all at very low certainty. Individual trials vary. US lidocaine and bupivacaine labels state that mixing local anaesthetics is not recommended because of insufficient data.

Lidocaine HCl injection (plain), DailyMed ↗Marcaine / Marcaine with Epinephrine (bupivacaine), DailyMed ↗Naropin (ropivacaine), DailyMed ↗Lidocaine 1% vs 1.5% vs 2% infraclavicular RCT, PubMed ↗Ropivacaine 0.5% vs 0.75% meta-analysis ↗Mixtures meta-analysis, RAPM 2026 ↗

• For adult single-shot infiltration and peripheral / fascial-plane blocks only. Not for neuraxial, IV regional, tumescent, paracervical, intra-articular, continuous infusion or pediatric dosing.
• Ultrasound and incremental dosing do not eliminate LAST.
• Every dose given earlier in the same episode stays counted. No automatic time-based reset. Pregnancy, frailty, comorbidity or obesity need an individualized decision.
• Adding fractions across agents in a mixture is a conservative screening heuristic, not a clinically validated toxicity score.
• Dosing weight follows AAGBI/SOBA 2015 (lean body weight when BMI ≥ 30). The formulas are not validated in pregnancy, amputation or severe fluid overload; use clinical judgement.
• The dose check assumes the whole syringe is injected.
• Epinephrine credit is applied only to a single, undiluted lidocaine or bupivacaine preparation verified as 1:200,000. Any mixture or added saline uses plain ceilings.
• Concentration warnings flag likely unit errors against usual injectable strengths. They are not dose rules.

Ceiling policy 1.0.0 (unchanged). v1.4.0 added the dosing-weight rule and v1.9.1 the epinephrine-credit rule below • Reviewed 7 November 2026. The app applies the lower of a mg/kg screening value and an absolute cap.

Dosing weight (v1.4.0). Without sex and height the dose check is marked unverified, never reassuring. BMI ≥ 30: lean body weight (Janmahasatian), following AAGBI/SOBA 2015, which states it is safer to calculate local anaesthetic dose on lean body weight. BMI < 30: actual weight. Ideal body weight (Devine) is offered as a conservative alternative, as used by the BNF and the Association of Anaesthetists' nomogram. No weight above actual weight is ever used. ASRA 2017 identifies small patient size and sarcopenia as LAST risk factors.

IBW (Devine): men 50 + 0.9 × (height cm − 152); women 45.5 + 0.9 × (height cm − 152)
LBW (Janmahasatian): men 9270 × TBW ÷ (6680 + 216 × BMI); women 9270 × TBW ÷ (8780 + 244 × BMI)

What each number is.

• Product-label maxima: lidocaine 4.5 mg/kg up to 300 mg plain and 7 mg/kg up to 500 mg with epinephrine; bupivacaine 175 mg plain and 225 mg with epinephrine.
• App screening policy (not label): bupivacaine 2 mg/kg plain and 2.5 mg/kg with epinephrine; ropivacaine 2 mg/kg up to 200 mg; adding fractions across agents; no time-based reset; the dosing-weight rule; the epinephrine-credit rule; the LAST weight convention.
• Efficacy evidence: the strength guide only. It never changes a ceiling.

Epinephrine credit (app policy). The higher ceiling is applied only for lidocaine or bupivacaine with epinephrine verified as 1:200,000, given as a single undiluted preparation. Mixed or diluted syringes, unknown concentrations and ropivacaine use the plain ceiling. If the same drug was given both plain and with epinephrine, the plain ceiling applies to every dose of it.

* Ropivacaine 2 mg/kg is an app-specific precautionary screening rule, not a single universal labeled maximum. Adult field-block labeling includes doses up to 200 mg; major nerve block ranges differ. Epinephrine credit is never given for ropivacaine.

If the same drug is given both with and without epinephrine, the plain ceiling applies to every dose of that drug. Verified epinephrine affects only its own agent.

Lidocaine HCl injection (plain) label ↗Lidocaine HCl and epinephrine label ↗Marcaine / Marcaine with Epinephrine (bupivacaine) label ↗Naropin (ropivacaine) label ↗ASRA LAST checklist ↗AAGBI/SOBA: Peri-operative management of the obese surgical patient 2015 ↗ASRA Third Practice Advisory on LAST, 2017 ↗

Web links may not open offline. Keep the locally approved prescribing references and a physical LAST rescue protocol at the bedside.