Local Anesthetic Infiltration Techniques: Wound Margin Injection

Peripheral nerve block techniques include digital nerve blocks targeting finger/toe nerves for digit procedures; plexus blocks injecting near nerve networks (brachial, lumbar, sacral, celiac, stellate ganglion) for larger limb or regional anesthesia; field blocks infiltrating around surgical sites (inguinal hernia example); and infiltration blocks directly injecting into subcutaneous tissue to block cutaneous nerves supplying skin sensation. These techniques provide targeted anesthesia by blocking pain signal transmission at peripheral nerve sites.

This extensive section covers advanced regional anesthesia techniques. Neuraxial anesthesia includes spinal anesthesia (injecting 1.5-3ml directly into CSF at L3-L4/L4-L5 interspace using 25-27 gauge spinal needles for C-sections and lower body surgeries, with post-procedure flat positioning to prevent CSF leakage) and epidural anesthesia (injecting into epidural space using 18-gauge Tuohy needles at T7-L4 levels with loss of resistance technique). Specialized regional anesthesia covers dental blocks (inferior alveolar, mental, infraorbital nerves for tooth procedures) and facial blocks (infraorbital, mental, supraorbital, auriculotemporal nerves for cosmetic procedures). All techniques require sterile technique, aspiration before injection, and monitoring for complications.

Subtenons block technique: topical anesthesia, eyelid speculum, inferior nasal quadrant entry 3-4mm from limbus. Create buttonhole in conjunctiva/Tenon's layer with closed scissors to form thin channel through equator. Insert 19G 25mm blunt cannula along scleral curvature and inject 3-4ml local anesthetic. Advantages: less pain, semi-blind procedure, lesser volume (3-5ml), no IOP rise, achievable eyelid akinesia. Disadvantages: unsuitable for repeat surgeries due to scarring, variable akinesia, requires surgical skill. Four facial nerve block techniques: O'Brien's (anterior to tragus above mandibular condyle), modified O'Brien (inferior to earlobe), Atkinson (along inferior edge of zygomatic bone, needle passed upward toward ear), and infiltration (above eyebrow/below inferior margin).

This video teaches essential regional nerve blocks that emergency physicians can perform without ultrasound, including the three-in-one femoral nerve block (for hip fractures), lateral femoral cutaneous nerve block (for meralgia paresthetica and road rash), ulnar nerve block (for hand lacerations and foreign bodies), infraorbital and superior orbital blocks (for facial repairs), scissor blocks (for ear and penile procedures), and ankle blocks (typically requiring ultrasound guidance). The key advantages of nerve blocks over local anesthesia include reduced lidocaine usage (avoiding toxicity at 4.5 mg/kg without epinephrine or 7 mg/kg with epinephrine), better pain control for extended procedures, and decreased administrative burden compared to procedural sedation. These blocks are particularly valuable for facial repairs (cosmesis priority), hand procedures, and orthopedic trauma management.

This comprehensive section covers multiple nerve block techniques essential for regional anesthesia. Facial blocks include supraorbital nerve (2.5 cm lateral from midline at eyebrow level), infraorbital nerve (45-degree injection below foramen until bone contact), and mental nerve (lateral approach at 45 degrees). Ear blocks target three nerves: greater auricular (1 cm below earlobe), lesser occipital (1 cm posterior to ear), and auriculotemporal (1 cm anterior to tragus). Wrist blocks include median nerve (between flexor carpi radialis and palmaris longus tendons) and radial nerve (subcutaneous infiltration to distal wrist dorsum). Digital blocks require 4 ml total (1 ml per side), injected from dorsum toward palmar aspect, with critical safety consideration of lidocaine dosing (3 mg/g without adrenaline) to prevent ischemia.

Local Anesthetic Systemic Toxicity (LAST) is a life-threatening emergency caused by excessive plasma concentrations of local anesthetic, leading to neurologic and cardiovascular collapse; early recognition of subtle neurologic symptoms (tinnitus, circumoral numbness, metallic taste, muscle twitching) is critical before cardiac involvement, followed by immediate cessation of injection, airway management with 100% oxygen (avoiding hyperventilation), and rapid initiation of Lipid Emulsion Therapy (20% solution) with specific dosing protocols: 100 mL bolus over 2-3 minutes for patients >70 kg or 1.5 mL/kg bolus for patients <70 kg, followed by 0.25 mL/kg/min infusion, with repeat boluses and rate doubling allowed if unstable, while avoiding vasopressin, beta-blockers, calcium channel blockers, lidocaine, and large-dose propofol; continuous monitoring is essential post-rescue due to potential redistribution and recurrence.

Local Anaesthetic Systemic Toxicity (LAST) is a rare but life-threatening emergency occurring when local anesthetic enters the bloodstream in toxic amounts, causing central nervous system and cardiovascular collapse; immediate management requires stopping the injection, calling for help, managing ABCs, and administering intravenous lipid emulsion (1.5 ml/kg bolus followed by 15 ml/kg/hour infusion), with prevention through careful patient assessment, ultrasound-guided injection, and aspiration to avoid intravascular placement.

Local anesthetic toxicity presents with circumaural numbness, tinnitus, twitching, seizures, coma, respiratory arrest, and cardiac toxicity. Treatment follows a systematic approach: establish airway and hyperventilate with 100% oxygen, suppress seizures with benzodiazepines (avoid propofol in hypotensive patients), and address hypoxia/acidosis/hypercarbia. Lipid emulsion therapy (20%, 1.5 mL/kg bolus then continuous infusion) is the definitive treatment. Avoid vasopressin, calcium channel blockers, beta blockers, and additional local anesthetics. For VFib, avoid lidocaine and consider amiodarone. Prolonged resuscitation and cardiopulmonary bypass may be required.

Local Anesthetic Systemic Toxicity (LAST) is a rare but potentially fatal complication of regional anesthesia caused by excessive local anesthetic entering systemic circulation, characterized by initial central nervous system symptoms (perioral numbness, metallic taste, tinnitus, dizziness, seizures) followed by cardiovascular collapse (hypotension, dysrhythmias, cardiac arrest), with bupivacaine being particularly dangerous due to its high lipid solubility and strong cardiac binding; effective management requires immediate cessation of the anesthetic, supportive care, and administration of Intravenous Lipid Emulsion (ILE) according to ASRA guidelines (100 mL 20% ILE bolus over 2-3 min plus 200-250 mL infusion over 15-20 min for patients >70 kg, or 1.5 mL/kg bolus plus 0.25 mL/kg/min infusion for those <70 kg), which acts as a 'lipid sink' to sequester the anesthetic and provide fatty acids for myocardial function.

Local anesthetic systemic toxicity (LAST) presents with CNS or cardiovascular symptoms, or both. CNS signs include perioral paresthesia, metallic taste, seizures, and respiratory arrest; cardiovascular signs include conduction disturbances, hypotension, and cardiac arrest. Risk factors include high lipid solubility, patient factors (extremes of age, pregnancy, organ disease), and technique factors (paravertebral, fascial plane, continuous catheters). Treatment requires immediate cessation, airway management, oxygen, and early lipid emulsion therapy (100 mg bolus then 250 mg/15 min infusion). Benzodiazepines control seizures; small epinephrine doses (<1 mcg/kg) manage cardiovascular issues; avoid vasopressin.

Absolute contraindications for vasoconstrictor use include uncontrolled cardiac insufficiency, uncontrolled hypertension, acute myocardial infarction within 6 months, recent coronary artery bypass surgery, unstable angina pectoris, certain arrhythmias (Wolff-Parkinson-White syndrome), untreated congestive heart failure, and uncontrolled hyperthyroidism. Relative contraindications include systolic BP above 160 mmHg, diastolic above 100 mmHg, history of myocardial infarction more than 6 months ago, controlled arrhythmias with pacemaker, controlled diabetes, controlled hypertension, and controlled cardiac insufficiency.

Vasoconstrictors reduce systemic absorption of local anesthetics, decreasing toxicity and prolonging anesthesia duration. Epinephrine (adrenaline) is the most potent and commonly used vasoconstrictor, acting through alpha-1 adrenergic receptors with a half-life of 1-3 minutes. Noradrenaline has slightly less potency and may cause more significant cardiovascular effects. Phenylephrine is 20 times less potent than epinephrine and is a pure alpha-agonist, useful in cardiovascular disease patients. Phentolamine is 6 times less potent than epinephrine and is associated with prilocaine. Vasoconstrictors are contraindicated in uncontrolled hypertension, heart failure, recent MI/stroke, uncontrolled diabetes, hyperthyroidism, pheochromocytoma, and sulfito sensitivity.

Vasoconstrictors have absolute contraindications where they should never be used: Uncontrolled hypertension (blood pressure not managed medically), Uncontrolled hyperthyroidism (thyroid hormone levels not stabilized), and Uncontrolled diabetes mellitus (blood glucose not regulated). In these cases, vasoconstrictors can worsen underlying pathology. Patients must be stabilized medically before elective dental procedures involving vasoconstrictor-containing anesthetics.

Vasoconstrictors are pharmacological agents that delay local anesthetic absorption, increasing duration and creating bloodless surgical fields. They have pH 3.3-4 (vs 5.5-6 without vasoconstrictor). Types include catecholamines (adrenaline/epinephrine) and synthetics (phenylephrine). Contraindications include hyperthyroidism, uncontrolled diabetes, uncontrolled hypertension, recent childbirth, glaucoma, coronary insufficiency, pheochromocytoma, and poorly vascularized areas (ears, nose, genitals) due to necrosis risk.

Epinephrine is the most effective and safest vasoconstrictor for dentistry, but its use requires understanding contraindications. Absolute contraindications include hypertension (>160/100 mmHg), recent MI (<6 months), recent stroke (<6 months), CABG/stent placement, unstable angina, certain arrhythmias, uncontrolled CHF, uncontrolled hyperthyroidism, sulfa allergy, and illicit drug use. Alternative vasoconstrictors include felypressin (prilocaine 3% with 0.03 UI) or no vasoconstrictor. The principle that 'the difference between medicine and poison is dosage' applies universally.