Pain Control and Anxiety Management
Pain control and anxiety management: calculate, then inject carefully
Local anesthesia depends on anatomy, drug chemistry, and patient factors. The pain pathway involves transduction, transmission, modulation, and perception. Local anesthetics are weak bases; in inflamed acidic tissue, more drug is ionized and less crosses the nerve membrane, which is why injection into an abscess may fail. Epinephrine prolongs anesthesia, reduces bleeding, and limits systemic absorption, but it must be used cautiously in patients with significant cardiovascular disease.
Know maximum doses. For 2% lidocaine with 1:100,000 epinephrine, the commonly taught limit is 7 mg/kg with epinephrine, not to exceed 500 mg. One 1.8-mL cartridge contains 36 mg of lidocaine, so a 70-kg patient’s calculated limit is about 490 mg-roughly 13 cartridges-but the absolute cap and epinephrine dose may govern first. Aspirate before injecting, use the smallest effective volume, and monitor for syncope, tachycardia, and methemoglobinemia (benzocaine).
Nitrous oxide and sedation questions test levels of sedation, monitoring, and contraindications. Nitrous oxide is anxiolytic, not general anesthesia; avoid in patients who cannot cooperate or have certain respiratory conditions. Traps: assuming more anesthetic fixes inflammation; ignoring epinephrine limits; and recapping needles.
Rule of thumb: calculate the milligram limit before drawing up, not after. Example: a 50-kg patient has a lidocaine limit of about 350 mg with epinephrine, or about 9.7 cartridges of 2% lidocaine-still check the epinephrine ceiling and the clinical need.