Acute Pain & Procedural Sedation — Part 2: Opioid Analgesics & Regional Anesthesia in the ED
Opioid dosing tables, equianalgesic conversions, intranasal fentanyl, opioid stewardship, risk assessment tools, ultrasound-guided nerve blocks, local anesthetic agents, and LAST protocol.
3. Opioid Analgesics
Opioids remain an important component of the ED analgesic armamentarium for moderate-to-severe pain that is refractory to non-opioid therapies. However, the contemporary approach positions opioids as second- or third-line agents in most clinical scenarios, used at the lowest effective dose for the shortest duration necessary. The emergency department has been identified as a significant contributor to new persistent opioid use — studies show that 6–8% of opioid-naive patients who receive an ED opioid prescription continue using opioids at 1 year. This underscores the importance of evidence-based opioid prescribing practices.1 2 3
3.1 Opioid Dosing Tables
3.1.1 Adult Opioid Dosing
| Drug | Route | Dose | Onset | Peak | Duration | Key Notes |
|---|---|---|---|---|---|---|
| Morphine | IV | 0.05–0.1 mg/kg (typical: 2–4 mg) | 3–5 min | 10–20 min | 2–4 hours | Titrate in 2 mg increments q5–10 min; histamine release may cause hypotension, pruritus |
| Morphine | IM | 0.1–0.15 mg/kg (typical: 5–10 mg) | 10–30 min | 30–60 min | 3–5 hours | Avoid IM route when IV available; erratic absorption |
| Morphine | PO (IR) | 15–30 mg | 30–60 min | 60–120 min | 3–5 hours | Use immediate-release formulations only in the ED |
| Hydromorphone | IV | 0.005–0.015 mg/kg (typical: 0.5–1 mg) | 3–5 min | 10–20 min | 2–4 hours | 5–7× more potent than morphine; titrate in 0.25–0.5 mg increments; less histamine release than morphine |
| Hydromorphone | PO | 2–4 mg | 30–60 min | 60–120 min | 3–5 hours | Reserve for moderate-to-severe pain refractory to non-opioids |
| Fentanyl | IV | 0.5–1.5 mcg/kg (typical: 25–100 mcg) | 1–2 min | 3–5 min | 30–60 min | Short acting; ideal for procedures; minimal histamine release; minimal hemodynamic effects |
| Fentanyl | IN | 1.5–2 mcg/kg (max 100 mcg per nostril) | 5–10 min | 15–20 min | 30–60 min | Via MAD (mucosal atomization device); max volume 1 mL per nostril; use 50 mcg/mL concentration; divide dose between nares if >100 mcg |
| Fentanyl | Nebulized | 2–4 mcg/kg in 3 mL NS | 5–10 min | 15–20 min | 30–60 min | Emerging route; needle-free; evidence supports efficacy for acute pain |
| Oxycodone | PO (IR) | 5–10 mg | 15–30 min | 30–60 min | 3–6 hours | Common discharge analgesic; start at 5 mg for opioid-naive patients |
| Oxycodone/Acetaminophen | PO | 5/325 mg (1–2 tablets) | 15–30 min | 30–60 min | 3–6 hours | Do not exceed acetaminophen 3000 mg/day from all sources |
| Hydrocodone/Acetaminophen | PO | 5/325 mg (1–2 tablets) | 15–30 min | 30–60 min | 4–6 hours | Schedule II opioid; same acetaminophen precautions |
| Tramadol | PO | 50–100 mg | 30–60 min | 60–120 min | 4–6 hours | Max 400 mg/day; weak opioid + SNRI; seizure risk (especially with SSRIs/SNRIs); serotonin syndrome risk |
3.1.2 Pediatric Opioid Dosing (Weight-Based)
| Drug | Route | Dose | Frequency | Max Single Dose | Key Notes |
|---|---|---|---|---|---|
| Morphine | IV | 0.05–0.1 mg/kg | Every 2–4 hours | 4 mg initial (titrate) | Start at low end of range; titrate to effect |
| Morphine | PO | 0.2–0.5 mg/kg | Every 4–6 hours | 15 mg | Use liquid formulation for accurate dosing |
| Fentanyl | IV | 0.5–1 mcg/kg | Every 1–2 hours | 50 mcg initial | Short-acting; ideal for brief procedures |
| Fentanyl | IN | 1.5–2 mcg/kg | May repeat once after 10 min | 100 mcg per nostril | Via MAD device; preferred needle-free route for children; well tolerated |
| Hydromorphone | IV | 0.01–0.015 mg/kg | Every 2–4 hours | 1 mg initial | Reserve for severe pain; more potent than morphine |
| Oxycodone | PO | 0.05–0.15 mg/kg | Every 4–6 hours | 10 mg | Liquid formulation available (5 mg/5 mL) |
3.1.3 Intranasal Fentanyl: Detailed Protocol
Intranasal fentanyl via the mucosal atomization device (MAD) has become a standard of care for rapid, needle-free analgesia in the ED, particularly for pediatric patients and patients without IV access:4 5
| Parameter | Detail |
|---|---|
| Concentration | Use 50 mcg/mL preparation (most common); 100 mcg/mL available but requires smaller volumes |
| Adult dose | 1.5–2 mcg/kg; typical dose 100–200 mcg total |
| Pediatric dose | 1.5–2 mcg/kg |
| Maximum per nostril | 100 mcg (or 1 mL volume per nostril to avoid runoff and maintain mucosal contact) |
| Administration | Attach MAD device to syringe; insert into nostril at 45-degree angle; deliver half the dose into each nostril as a fine mist |
| Volume limitation | If total volume exceeds 1 mL per nostril, divide the dose across both nares and wait 5 minutes for absorption before delivering any additional volume |
| Repeat dosing | May repeat 50% of initial dose once at 10–15 minutes if needed |
| Onset | 5–10 minutes |
| Bioavailability | ~70–90% (superior to oral; approaches IV) |
| Advantages | No IV required; painless; rapid; well-accepted by children; no first-pass metabolism |
3.2 Equianalgesic Opioid Conversion Table
The following table provides approximate equianalgesic doses for commonly used ED opioids. These ratios are approximate and should be used as starting points for dose calculations, with individual titration based on clinical response. Incomplete cross-tolerance (typically 25–50% dose reduction when switching opioids) should be applied when rotating between agents.6
| Opioid | IV/IM Dose | PO Dose | PO:IV Ratio | Duration |
|---|---|---|---|---|
| Morphine | 10 mg | 30 mg | 3:1 | 3–4 hours |
| Hydromorphone | 1.5 mg | 7.5 mg | 5:1 | 3–4 hours |
| Fentanyl | 100 mcg (0.1 mg) | N/A (transmucosal ~200 mcg) | N/A | 0.5–1 hour |
| Oxycodone | N/A (no IV form) | 20 mg | N/A | 3–6 hours |
| Hydrocodone | N/A (no IV form) | 30 mg | N/A | 4–6 hours |
| Tramadol | N/A (no IV in US) | 120–150 mg | N/A | 4–6 hours |
Conversion example: Morphine 4 mg IV is approximately equianalgesic to hydromorphone 0.6 mg IV, fentanyl 40 mcg IV, or oxycodone 8 mg PO.
3.3 Opioid Prescribing Best Practices
Evidence-based opioid prescribing recommendations for ED discharge:1 2 3 7
| Principle | Implementation |
|---|---|
| Lowest effective dose | Prescribe the lowest dose that provides adequate pain relief; start with 5 mg oxycodone or equivalent |
| Shortest duration | Limit to 3 days (preferred) or 7 days maximum for most acute conditions; provide only enough for the anticipated duration of severe pain |
| PDMP check | Query the state Prescription Drug Monitoring Program before prescribing opioids to any patient; many states mandate this by law |
| Naloxone co-prescribing | Co-prescribe intranasal naloxone (4 mg Narcan nasal spray) for patients receiving >50 MME/day, those with history of overdose, concurrent benzodiazepine use, or other high-risk features |
| Avoid long-acting formulations | Never initiate extended-release or long-acting opioids from the ED |
| No benzodiazepine co-prescription | Avoid prescribing opioids and benzodiazepines simultaneously (FDA black box warning) |
| Patient education | Provide written and verbal instructions on safe use, storage, disposal, and signs of overdose |
| Follow-up | Ensure patients receiving opioid prescriptions have follow-up within 3–7 days with a primary care provider or specialist |
| Alternatives first | Document that non-opioid alternatives have been considered or tried before prescribing opioids |
| Functional goals | Frame the analgesic goal as functional improvement (ability to sleep, move, perform ADLs) rather than complete pain elimination |
3.4 Opioid Risk Assessment Tools
3.4.1 Opioid Risk Tool (ORT)
The ORT is a brief, validated screening tool to estimate risk of opioid misuse before prescribing:8
| Risk Factor | Female Score | Male Score |
|---|---|---|
| Family history of substance abuse: | ||
| — Alcohol | 1 | 3 |
| — Illegal drugs | 2 | 3 |
| — Prescription drugs | 4 | 4 |
| Personal history of substance abuse: | ||
| — Alcohol | 3 | 3 |
| — Illegal drugs | 4 | 4 |
| — Prescription drugs | 5 | 5 |
| Age 16–45 years | 1 | 1 |
| History of preadolescent sexual abuse | 3 | 0 |
| Psychological disease: | ||
| — ADD/ADHD, OCD, bipolar, schizophrenia | 2 | 2 |
| — Depression | 1 | 1 |
Score interpretation:
| Score | Risk Category | Action |
|---|---|---|
| 0–3 | Low risk | Standard precautions; consider opioid if clinically indicated |
| 4–7 | Moderate risk | Enhanced precautions; shorter supply; close follow-up; PDMP check mandatory |
| ≥8 | High risk | Avoid opioid prescribing if possible; if opioids necessary, very short course with close monitoring; consider addiction medicine referral |
3.4.2 STOP (Screening Tool for Opioid Prescribing) Criteria
The STOP criteria identify patients in whom ED opioid prescribing should be avoided or minimized:2
| Criterion | Detail |
|---|---|
| S — Substance use disorder history | Active or past opioid use disorder, other substance use disorders |
| T — Tolerance/physical dependence | Patients already on chronic opioid therapy (refer to their prescriber) |
| O — Other high-risk features | History of overdose, concurrent benzodiazepine use, psychiatric comorbidity, PDMP showing multiple prescribers |
| P — Pain type not responsive to opioids | Chronic non-cancer pain, fibromyalgia, chronic headache (opioids may worsen these conditions) |
4. Regional Anesthesia in the Emergency Department
Ultrasound-guided regional anesthesia has transformed ED pain management over the past decade. Emergency physician-performed nerve blocks provide superior analgesia compared with systemic opioids for many conditions, reduce opioid requirements, have fewer systemic side effects, and allow for earlier mobilization and discharge. Regional anesthesia is now recognized as a core emergency medicine competency.9 10 11
4.1 Ultrasound-Guided Nerve Blocks
4.1.1 Femoral Nerve Block
Indication: Hip fracture, femoral shaft fracture, anterior thigh pain9 10
| Parameter | Detail |
|---|---|
| Position | Supine with leg in neutral position |
| Ultrasound | High-frequency linear probe; inguinal crease; identify femoral artery, femoral vein (medial), and femoral nerve (lateral to artery, deep to fascia iliaca) |
| Landmark | Femoral nerve lies lateral to the femoral artery, deep to the fascia lata and fascia iliaca, at the level of the inguinal crease |
| Needle | 22-gauge, 50–100 mm echogenic block needle |
| Approach | In-plane from lateral to medial |
| Target | Deposit local anesthetic immediately surrounding the femoral nerve beneath the fascia iliaca |
| Volume | 15–20 mL in adults; 0.3–0.5 mL/kg in children (max 20 mL) |
| Agent | Bupivacaine 0.25–0.5% or ropivacaine 0.2–0.5% (for prolonged analgesia); lidocaine 1–2% (for shorter duration) |
| Onset | 10–20 minutes |
| Duration | 4–8 hours (bupivacaine/ropivacaine); 1–3 hours (lidocaine) |
| Motor block | Quadriceps weakness expected; counsel fall risk; do not allow weight-bearing |
| Complications | Vascular puncture (identify femoral artery); nerve injury (rare); local anesthetic systemic toxicity (LAST) |
4.1.2 Fascia Iliaca Compartment Block (FICB)
Indication: Hip fracture (neck, intertrochanteric, subtrochanteric), femoral shaft fracture, anterior thigh surgery9 10 12
The FICB has become the preferred regional block for hip fractures in the ED because it is technically simpler than the femoral nerve block, has a wider zone of analgesia (covers the femoral, lateral femoral cutaneous, and obturator nerves), and can be performed with either ultrasound or landmark technique.
Ultrasound-Guided Technique:
| Parameter | Detail |
|---|---|
| Position | Supine |
| Ultrasound | High-frequency linear probe placed at the inguinal crease; identify the fascia lata (superficial), fascia iliaca (deep), and iliacus muscle |
| Needle | 22-gauge, 80–100 mm echogenic needle |
| Approach | In-plane from lateral to medial |
| Target | Deposit local anesthetic in the plane between the fascia iliaca and the iliacus muscle; aim for circumferential spread beneath the fascia iliaca |
| Volume | 30–40 mL in adults (larger volume needed for fascial plane spread); 0.5–1 mL/kg in children (max 40 mL) |
| Agent | Bupivacaine 0.25% or ropivacaine 0.2–0.375% (dilute concentration with larger volume) |
Landmark Technique (Dalens method):
- Draw a line from the anterior superior iliac spine (ASIS) to the pubic tubercle
- Divide this line into thirds; mark the junction of the lateral third and middle third
- Insert a blunt-tip needle perpendicular to skin at this point
- Advance until two distinct “pops” (fascial clicks) are felt — first through fascia lata, second through fascia iliaca
- Aspirate to confirm non-vascular placement; inject 30–40 mL of local anesthetic
4.1.3 Interscalene Brachial Plexus Block
Indication: Shoulder dislocation, proximal humerus fracture, shoulder surgery, acute shoulder pain9 11
| Parameter | Detail |
|---|---|
| Position | Supine or semi-recumbent with head turned slightly to contralateral side |
| Ultrasound | High-frequency linear probe placed in the transverse plane at the level of the cricoid cartilage over the lateral neck; identify the brachial plexus nerve roots (C5, C6, C7) between the anterior and middle scalene muscles (“traffic light” or “stoplight” sign) |
| Needle | 22-gauge, 50 mm echogenic needle |
| Approach | In-plane from lateral to medial (preferred) or medial to lateral |
| Target | Deposit local anesthetic between the C5 and C6 nerve roots within the interscalene groove |
| Volume | 10–15 mL in adults; 0.2–0.3 mL/kg in children |
| Agent | Bupivacaine 0.25–0.5% or ropivacaine 0.2–0.5% |
| Onset | 10–20 minutes |
| Duration | 6–12 hours (bupivacaine/ropivacaine) |
| Complications | Phrenic nerve palsy (ipsilateral diaphragm paralysis — occurs in up to 100% of interscalene blocks; avoid in patients with contralateral phrenic nerve dysfunction, severe COPD, or respiratory compromise); Horner syndrome; recurrent laryngeal nerve block (hoarseness); vertebral artery injection; pneumothorax (rare with US guidance); epidural/intrathecal injection (very rare) |
4.1.4 Serratus Anterior Plane Block (SAPB)
Indication: Rib fractures (especially lateral ribs 2–9), chest wall pain, chest tube insertion10 11 13
| Parameter | Detail |
|---|---|
| Position | Supine with ipsilateral arm abducted, or lateral decubitus |
| Ultrasound | High-frequency linear probe placed in the sagittal plane at the mid-axillary line over ribs 4–5; identify the latissimus dorsi (superficial), serratus anterior (deep to latissimus), and the rib/intercostal muscles |
| Needle | 22-gauge, 80–100 mm echogenic needle |
| Approach | In-plane, cranial to caudal or caudal to cranial |
| Target | Superficial SAPB: deposit local anesthetic between the latissimus dorsi and the serratus anterior muscles. Deep SAPB: deposit between the serratus anterior and the external intercostal muscle/rib (deep approach may provide better coverage of the lateral cutaneous branches of the intercostal nerves) |
| Volume | 20–30 mL in adults; 0.5 mL/kg in children (max 30 mL) |
| Agent | Bupivacaine 0.25% or ropivacaine 0.2–0.375% |
| Onset | 15–30 minutes |
| Duration | 6–12 hours |
| Coverage | Lateral chest wall (T2–T9); provides analgesia for lateral rib fractures but may not cover posterior or anterior fractures completely |
| Advantages | Low risk of pneumothorax (needle stays superficial to ribs); no risk of epidural/intrathecal injection; technically straightforward |
4.1.5 Erector Spinae Plane Block (ESPB)
Indication: Rib fractures (especially posterior), thoracic back pain, thoracic surgical analgesia11 13
| Parameter | Detail |
|---|---|
| Position | Seated or lateral decubitus |
| Ultrasound | High-frequency linear probe placed in the parasagittal plane, 2–3 cm lateral to the spinous process; identify the erector spinae muscle group overlying the transverse process |
| Needle | 22-gauge, 80–100 mm echogenic needle |
| Approach | In-plane, cranial to caudal |
| Target | Deep to the erector spinae muscle, superficial to the transverse process; deposit local anesthetic in this fascial plane |
| Volume | 20–30 mL in adults; 0.5 mL/kg in children (max 30 mL) |
| Agent | Bupivacaine 0.25% or ropivacaine 0.2–0.375% |
| Onset | 15–30 minutes |
| Duration | 6–12 hours |
| Coverage | Posterior and lateral chest wall; mechanism involves spread of local anesthetic through the costotransverse foramen to the paravertebral and intercostal spaces |
| Advantages | Very safe: needle target is a bony backstop (transverse process); minimal risk of pneumothorax; simple technique |
4.1.6 Forearm Nerve Blocks (Radial, Ulnar, Median)
Indication: Hand and wrist lacerations, fractures, dislocations, foreign body removal, abscess drainage9 11
Radial Nerve Block at the Wrist:
| Parameter | Detail |
|---|---|
| Position | Forearm pronated, wrist in neutral |
| Landmark | Anatomical snuffbox at the level of the radial styloid; radial artery is the key landmark |
| Technique | Inject 3–5 mL of local anesthetic subcutaneously across the dorsal-radial aspect of the wrist, from the radial artery laterally around the radial styloid to the mid-dorsal wrist (field block) |
| Coverage | Dorsal hand, dorsal thumb, dorsal index and middle fingers (proximal phalanges) |
Ulnar Nerve Block at the Wrist:
| Parameter | Detail |
|---|---|
| Position | Forearm supinated, wrist in neutral |
| Landmark | Ulnar nerve lies between the flexor carpi ulnaris tendon and the ulnar artery at the level of the ulnar styloid |
| Technique (US-guided) | Identify the ulnar nerve adjacent to the ulnar artery on the volar-ulnar wrist; deposit 3–5 mL of local anesthetic around the nerve |
| Technique (landmark) | Insert needle between the flexor carpi ulnaris tendon and the ulnar artery at the proximal wrist crease; advance 5–10 mm; aspirate; inject 3–5 mL |
| Coverage | Ulnar 1.5 digits (small finger and ulnar half of ring finger, both palmar and dorsal); hypothenar eminence |
Median Nerve Block at the Wrist:
| Parameter | Detail |
|---|---|
| Position | Forearm supinated, wrist in slight extension |
| Landmark | Median nerve lies between the palmaris longus and flexor carpi radialis tendons at the proximal wrist crease (deep to the flexor retinaculum) |
| Technique (US-guided) | Identify the median nerve (honeycomb appearance) between the tendons; deposit 3–5 mL around the nerve |
| Technique (landmark) | Insert needle between palmaris longus and flexor carpi radialis at the proximal wrist crease; advance until a fascial “pop” is felt (through flexor retinaculum); aspirate; inject 3–5 mL |
| Coverage | Palmar surface of thumb, index, middle, and radial half of ring finger; dorsal fingertips of the same digits |
4.1.7 Ankle Block (Five-Nerve Block)
Indication: Forefoot and midfoot procedures, fractures, lacerations, abscess drainage, foreign body removal9 11
The ankle block involves blocking all five nerves that provide sensation to the foot:
| Nerve | Location | Technique | Coverage |
|---|---|---|---|
| Posterior tibial nerve | Posterior to medial malleolus, behind the posterior tibial artery | Identify the artery by palpation or US; inject 3–5 mL immediately posterior to the artery | Sole of foot, plantar toes |
| Sural nerve | Between the lateral malleolus and the Achilles tendon | Inject 3–5 mL subcutaneously between the lateral malleolus and Achilles tendon | Lateral foot, lateral heel, small toe |
| Deep peroneal nerve | Between the extensor hallucis longus and extensor digitorum longus tendons, lateral to the dorsalis pedis artery | Inject 3–5 mL deep to the extensor retinaculum, lateral to the artery | Web space between first and second toes |
| Superficial peroneal nerve | Subcutaneous at the anterior ankle | Inject 5–10 mL subcutaneously across the anterior ankle (field block from lateral malleolus to medial) | Dorsum of foot and toes (except first web space) |
| Saphenous nerve | Anterior to medial malleolus, adjacent to the great saphenous vein | Inject 3–5 mL subcutaneously anterior to the medial malleolus | Medial foot, medial ankle |
Total local anesthetic volume: 20–30 mL; use dilute concentrations (bupivacaine 0.25% or lidocaine 1%) to stay within maximum dose limits.
4.1.8 Digital Nerve Block (Traditional and WALANT)
Indication: Finger/toe lacerations, fractures, dislocations, nail procedures, paronychia drainage9 14
Traditional Digital Block (transthecal or web space approach):
| Technique | Method | Volume | Notes |
|---|---|---|---|
| Dorsal approach | Insert 27-gauge needle at the dorsolateral base of the digit; advance toward the palmar surface; aspirate; inject 1–2 mL on each side of the digit (total 2–4 mL) | 2–4 mL per digit | Blocks both digital nerves; ring block technique |
| Transthecal (single injection) | Insert needle into the flexor tendon sheath at the level of the palmar digital crease at the base of the finger; inject 2 mL of local anesthetic into the tendon sheath | 2 mL per digit | Single injection; local anesthetic tracks along the sheath to bathe both digital nerves; less painful than the dorsal approach |
| Web space approach | Insert needle into the web space between adjacent digits; inject 1–2 mL on each side | 2–4 mL per digit | May be less painful than dorsal approach |
WALANT (Wide-Awake Local Anesthesia No Tourniquet):
| Parameter | Detail |
|---|---|
| Concept | Combines local anesthetic with epinephrine in the digit to provide both anesthesia and a bloodless field, eliminating the need for a digital tourniquet |
| Solution | Lidocaine 1% with epinephrine 1:100,000 (or buffered with 1 mL of 8.4% sodium bicarbonate per 10 mL lidocaine-epinephrine) |
| Injection site | Inject subcutaneously at the surgical/procedural site and around the digit as needed |
| Volume | 2–4 mL per digit |
| Safety | The historical prohibition against epinephrine in digits has been definitively overturned by large case series (>3,000 cases) demonstrating no digital ischemia; the WALANT technique is now widely accepted |
| Advantages | No tourniquet pain; longer duration of anesthesia; improved hemostasis; allows assessment of tendon repairs under active motion |
| Caution | Avoid in patients with peripheral vascular disease, Raynaud phenomenon, or digital compromise |
4.2 Local Anesthetic Agents: Comparison Table
| Agent | Class | Onset | Duration (plain) | Duration (with epinephrine) | Max Dose (plain) | Max Dose (with epi) | pKa | Notes |
|---|---|---|---|---|---|---|---|---|
| Lidocaine | Amide | Rapid (2–5 min) | 1–2 hours | 2–4 hours | 4.5 mg/kg | 7 mg/kg | 7.7 | Most widely used; fastest onset; excellent for infiltration, nerve blocks, and topical use |
| Bupivacaine | Amide | Slow (10–20 min) | 4–8 hours | 6–12 hours | 2.5 mg/kg | 3 mg/kg | 8.1 | Long-acting; gold standard for prolonged blocks; higher cardiotoxicity risk than ropivacaine |
| Ropivacaine | Amide | Moderate (10–15 min) | 4–8 hours | 6–10 hours | 3 mg/kg | 3.5 mg/kg | 8.1 | Long-acting; less cardiotoxic than bupivacaine; less motor block (sensory-motor differential); preferred for many blocks |
| Mepivacaine | Amide | Rapid (3–5 min) | 1.5–3 hours | 2–4 hours | 4.5 mg/kg | 7 mg/kg | 7.6 | Intermediate duration; onset similar to lidocaine; good alternative |
| Chloroprocaine | Ester | Very rapid (1–2 min) | 30–60 min | 60–90 min | 11 mg/kg | 14 mg/kg | 9.1 | Ultra-short acting; rapid ester hydrolysis = very low systemic toxicity; useful for short procedures |
| Procaine | Ester | Slow (5–10 min) | 30–60 min | 60–90 min | 7 mg/kg | 9 mg/kg | 8.9 | Rarely used; slow onset; short duration; historical significance |
4.3 Local Anesthetic Systemic Toxicity (LAST)
LAST is a life-threatening complication of regional anesthesia that results from inadvertent intravascular injection or systemic absorption of local anesthetic exceeding toxic thresholds. Every clinician performing regional anesthesia must be prepared to recognize and treat LAST. The mortality rate has decreased dramatically since the introduction of lipid emulsion rescue therapy.15 16
4.3.1 Signs and Symptoms of LAST
LAST typically progresses through CNS toxicity before cardiovascular toxicity, but either system may present first, and cardiac arrest can occur without premonitory CNS symptoms (especially with bupivacaine).
| System | Early Signs | Late/Severe Signs |
|---|---|---|
| CNS | Perioral numbness and tingling; metallic taste; tinnitus; lightheadedness; visual disturbances; agitation; confusion; slurred speech | Seizures (generalized tonic-clonic); loss of consciousness; coma; respiratory arrest |
| Cardiovascular | Hypertension; tachycardia (initial sympathetic response) | Hypotension; bradycardia; conduction abnormalities (prolonged PR, QRS widening); ventricular arrhythmias (VT, VF); asystole; cardiovascular collapse |
Risk factors for LAST:
- Extremes of age (neonates, elderly)
- Low muscle mass and body weight
- Hepatic impairment (reduced amide metabolism)
- Cardiac disease (reduced cardiac output slows redistribution)
- Acidosis (increases unbound local anesthetic)
- Pregnancy (reduced protein binding)
- Renal impairment
- Concurrent medications reducing hepatic blood flow (beta-blockers)
4.3.2 LAST Treatment Protocol: Lipid Emulsion Rescue
| Step | Action | Detail |
|---|---|---|
| 1 | Stop the injection | Immediately cease all local anesthetic injection |
| 2 | Call for help | Activate code team; obtain lipid emulsion (Intralipid 20%) |
| 3 | Airway management | Ventilate with 100% oxygen; secure the airway if needed |
| 4 | Seizure treatment | Benzodiazepines (midazolam 2–4 mg IV or diazepam 5–10 mg IV); avoid propofol as primary seizure treatment (may worsen cardiac depression) — small doses acceptable if benzodiazepines unavailable |
| 5 | Lipid emulsion 20% (Intralipid) | Bolus: 1.5 mL/kg IV over 1 minute (approximately 100 mL for a 70-kg patient) |
| 6 | Lipid infusion | Infusion: 0.25 mL/kg/min (approximately 250 mL over 15–20 minutes for a 70-kg patient) |
| 7 | Repeat bolus | If cardiovascular stability is not restored: repeat 1.5 mL/kg bolus (may repeat 1–2 times at 3–5 min intervals) |
| 8 | Increase infusion | If still unstable: double the infusion rate to 0.5 mL/kg/min |
| 9 | Maximum lipid dose | Do not exceed 12 mL/kg total over the first 30 minutes |
| 10 | ACLS with modifications | If cardiac arrest ensues: standard ACLS with modifications — avoid vasopressin, calcium channel blockers, beta-blockers, and lidocaine; reduce epinephrine doses to <1 mcg/kg; continue lipid emulsion; consider cardiopulmonary bypass or ECMO if refractory |
| 11 | Monitoring | Observe for at least 30–60 minutes after resolution (local anesthetic redistribution may cause recurrence); admit for observation |
Key principle: Lipid emulsion acts as a “lipid sink,” binding the highly lipophilic local anesthetic molecules and drawing them away from cardiac sodium channels and brain tissue. It also provides a direct myocardial energy substrate.
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