Local Anesthesia - How to ?
Local Anesthetics for Percutaneous Musculoskeletal Procedures—a cornerstone resource for healthcare professionals seeking in-depth knowledge on advanced pain relief methods. Delve into the intricacies of ester and amide anesthetics, their precise mechanisms of action on sodium channels, and the strategic blockade of nerve impulses to mitigate discomfort during interventional procedures.
Uncover the nuances of maximum dosage and effective delivery methods tailored to diverse patient needs. Grasp the significance of pH levels in the efficacy of anesthesia in inflamed tissues and learn about the differential sensitivity among nerve fibers that underscores the order of sensation loss.
| Category | Details | Notes | |
|---|---|---|---|
| Anesthetic Types | Ester: procaine, chloroprocaine, cocaine, tetracaine; Amide: lidocaine, bupivacaine, mepivacaine, etidocaine | Ester hydrolyzed by pseudocholinesterase; Amides metabolized by liver | |
| Mechanism of Action | Parameter | Details | Clinical Significance |
| Primary Site of Action | Cell membrane; specific sites within Na+ channels | Key interaction point for anesthetic effect | |
| Mechanism of Action | Blocks Na+ transient increase on depolarization; affects voltage-gated Na+ channels | Decreases excitability, slows impulse conduction, can abolish action potential | |
| Action on Other Channels | Can block K+ channels at higher concentrations | Conduction blockade without significant change in resting membrane potential | |
| Sensitivity by Fiber Type | Autonomic, small unmyelinated C fibers (mediating pain sensation), and Aδ fibers (mediating pain and temperature sensations) are more sensitive than Aγ, Aβ, and Aα fibers (posture, touch, pressure and motor information) | Explains the order of sensation loss post-administration: pain, cold, warmth, touch, deep pressure, motor function | |
| Differential Blockade | Small fibers blocked preferentially due to shorter passive propagation distance | Sensory fibers, particularly pain fibers, are affected first and more markedly | |
| State-Dependent Blockade | More marked at higher frequencies and longer depolarization durations | Sensory fibers, which have higher firing rates, are preferentially blocked over motor fibers | |
| pH Dependence | Effectiveness decreases with lower extracellular pH | Inflamed tissues with lower pH may require higher doses for efficacy | |
| Potency & Duration | Etidocaine > Lidocaine > Mepivacaine; | ||
| Allergies | Rare, often to ester-type; Cross-reactivity uncommon | Symptoms can include wheezing, arrest, shock. | |
| Lidocaine Dosage | Max subcutaneous dose: 7 mg/kg or <500 mg; 2% (20 mg/mL) preferred, except for infections (1%) | For 70 kg adult: 25 mL of 2%, or 50 mL of 1% lidocaine | |
| Efficacy Factors | Not well-suited for intramedullary processes | Increased intramedullary pressure (needle displacing local tissue) causes pain; Periosteum and IV analgesia can help | |
| Administration Tips | Skin wheal creation is painful therefore apply deeper injection before skin wheal | ||
| Infection Considerations | Consider bacteriostatic/bactericidal effects; Minimize local anesthesia if infection is suspected | Maximize IV sedation; 1% lidocaine preferred for suspected infections | |
| Epinephrine Use | Causes vasoconstriction; limits local anesthetic uptake | Avoid in unstable angina, arrhythmia, or peripheral procedures on extremities | |
| Adverse Reactions | Rare hypersensitivity, potential neurotoxicity at high concentrations, CNS and cardiovascular effects with intravascular injection | Allergic reactions, CNS stimulation or depression, respiratory failure, myocardial effects |