Local Anesthesia Tintinalli Chap. 37

1. Local AnesthesiaTintinalli Chap. 37 Prepared by Darren Shiley, D.O.

2. Local Anesthesia • Cocaine • First isolated in Europe between 1859-1860 • Toxic and addictive effects were rapidly noticed resulting in patient deaths and addicted medical staff • Ester Local Anesthetics • Tropocaine • Eucaine • Benzocaine • Procaine • Tetracaine • Amide Local Anesthetics • Lidocaine • Mepivacaine • Prilocaine • Bupivacaine

3. Local Anesthetic Agents • Synthetic drugs derived from cocaine • Weak bases supplied in an acidic solution • Anesthetic action produced by drug molecules interrupting and temporarily stopping conduction

4. Epinephrine • Acts through vasoconstriction • Avoided in end-arterial field • Advantages • Provides longer duration of anesthesia • Promotes wound hemostasis • Slows systemic absorption • Decreases potential for toxicity • Allows greater volume to be used for extensive laceration repair

5. Toxicity of Local Anesthetics • Related to potency and duration of action • Serious adverse reactions more common in amides than the esters • Enhanced by hypercarbia, hypoxemia, and acidosis • Usually due to inadvertent IV injection or excessive dose

6. CNS Toxicity • Due to conduction block • Directly related to lipid solubility • Symptoms range from perioral tingling and numbness to confusion, seizure and coma • Seizure activity is a warning for impending ventricular arrhythmias and cardiovascular collapse

7. Cardiovascular Toxicity • Dose-dependent • Mediate through sodium channel blockade within the heart • Worsened by pregnancy • Effects include myocardial depression and ventricular dysrhythmias • Bupivacaine has highest incidence and is contraindicated for use in regional anesthesia

8. Methemoglobinemia • Prilocaine and benzocaine cause oxidation of ferric form of hemoglobin to ferrous form • Visible cyanosis results when concentration exceeds 1.5 g/dL • Usually benign

9. Amide Local Anesthetics • Lidocaine • Most commonly used anesthetic in the ED • Excellent efficacy and low toxicity profile • Rapid onset and intermediate duration of action • Prilocaine • Low CV toxicity profile • May cause methemoglobinemia after large IV bolus • Used with lidocaine in EMLA cream • Bupivacaine • Slow onset and long duration of action • High CV toxicity potential • Use in prolonged procedures or when longer postprocedural anesthesia is required • Mepivacaine • Rapid onset and intermediate duration of action • Intermediate toxicity

10. Ester Local Anesthetics • Procaine • Slow onset • Short acting • Very short half-life • Tetracaine • Slow onset • Long duration of action • Injectable for spinal anesthesia • Topical for use on eye, mucous membranes, and skin

11. Alternative Agents • Diphenhydramine • Effective local anesthetic • Injection more painful than lidocaine • Can cause tissue irritation and skin necrosis • Benzyl Alcohol • As effective as lidocaine • Short duration usually requiring additional injections during procedure

12. Local Anesthetic Infiltration • Most common use of local anesthetics in ED • Rapid onset • Low risk of systemic toxicity • Used for wound repair and invasive procedures • Lidocaine for short procedures and bupivacaine for longer procedures

13. Minimizing Pain of Infiltration • 27- or 30-gauge needle • Deep, slow infiltration • Buffered lidocaine • Sodium bicarbonate reduces pain • Warm lidocaine • 37-42 degrees C • Injection through wound margins • Distraction techniques

14. Topical Anesthetics • Used to reduce discomfort of local procedures • Work better on head and neck than extremities • Advantages • Painless • Do not distort wound edges • May provide good hemostasis if formulation includes a vasoconstrictive agent

15. Topical Anesthetics • TAC • 0.5% Tetracaine, 0.05% Adrenaline, 11.8% Cocaine • Other mixtures are cheaper, have less toxicity, and do not contain a controlled substance • LET • 4% Lidocaine, 0.1% Epinephrine, 0.5% Tetracaine • Prepared in single-use 5-ml vials • Applied directly to wound for 20-30 minutes • Avoid contact with mucous membranes, fingers/toes, ear pinna, penis, and tip of nose

16. Topical Anesthetics • EMLA • Eutectic Mixture of Local Anesthetics (2.5% Lidocaine and 2.5% Prilocaine) • Available preparation is nonsterile and should only be applied to intact skin • Applied directly to skin and covered with occlusive dressing • Analgesia at 1 hour, peak at 2 hours • Lidocaine • Available in solution, ointment, cream and jelly preparations • Commonly used to facilitate placement of urinary catheters, nasogastric tubes, and fiberoptic scopes

17. Other Topical Anesthetic Agents • Benzocaine • Used for mucosal anesthesia to relieve pain from oral ulcers, wounds, inflammation and to facilitate passage of nasogastric tubes or endoscopy • Iontophoresis • Delivery of topical anesthetic with mild electrical current • Ethyl Chloride • Skin refrigerant or vapocoolant delivered by a spray • Causes anesthesia for 30-60 seconds • Not for use on mucosal surfaces

18. Regional Anesthetic Procedures • Can minimize opiate use • Decreases need for procedural sedation • Should be administered in lowest dosage that results in an effective block • Epinephrine can be added to enhance duration, efficacy, reliability, and safety

19. Peripheral Nerve Blocks • Advantageous for procedures on the digits, hand, and foot • Require less total anesthetic • Often less painful than local infiltration • Onset of anesthesia may be up to 15 minutes • Document neurovascular status prior to block • Complications include nerve injury and systemic toxicity

20. Wrist Blocks • Used for lacerations of the hand • Median Nerve • Ulnar Nerve • Radial Nerve

21. Digital Nerve Block • More rapid onset than metacarpal block • Used for laceration repair, I&D of paronychia, or finger/toenail removal • Large volumes of anesthetic can result in compartment syndrome

22. Foot Blocks • Anesthesia for surgical procedures of the foot • Sensation to foot supplied by 5 different nerves • Posterior Tibial Nerve • Sural Nerve • Saphenous Nerve • Superficial Peroneal Nerve • Deep Peroneal Nerve • Most blocks involve at least 2 nerves • Contraindications include peripheral vascular disease and traumatic circulatory compromise

23. Facial and Oral Blocks • Anesthesia to commonly injured areas • Forehead, chin, lips, nose, tongue, ear • Often require blockade of more than one nerve • Topical EMLA cream or refrigerant sprays should be applied prior to injection • 2% lidocaine can be applied to oral mucosa • Avoid direct infiltration of pinna d/t risk of tissue necrosis

24. Femoral Nerve Block • Effective for relieving pain of femoral neck fracture • Useful in multiple trauma patient

25. Intercostal Block • Management of pain following chest trauma or from a chest tube • Contraindications include local soft tissue disease and contralateral pneumothorax • High systemic absorption and toxicity

26. Hematoma Blocks • Simple, quick, and effective for closed fracture reduction • Not as efficacious as IV Regional (Bier’s) Block

27. Intravenous Regional Block (Bier’s) • IV infusion of local anesthetic distal to an inflated pneumatic tourniquet • Used for fracture reductions, large laceration repair, and foreign body removal • Most commonly used for upper extremity procedures • Duration is 30-60 minutes • Requires continuous monitoring and patient NPO for 4 hours • Contraindications include peripheral vascular disease, raynaud syndrome, sickle cell disease, cardiac conduction abnormalities, hypertension, cellulitis, and children under 5