A 42-year-old previously healthy man comes to the office due to an enlarging mole. The patient has had a mole on his forearm for the past several years, and it has rapidly increased in size over the past 4 months. Physical examination shows an 8-mm raised lesion with variegated pigmentation and ill-defined borders on the right forearm. Excisional biopsy of the lesion is planned. Local anesthesia is administered via an infiltrating injection of lidocaine mixed with epinephrine. Which of the following is the most likely impact of mixing the latter medication with the anesthetic agent?

Question

A 42-year-old previously healthy man comes to the office due to an enlarging mole.  The patient has had a mole on his forearm for the past several years, and it has rapidly increased in size over the past 4 months.  Physical examination shows an 8-mm raised lesion with variegated pigmentation and ill-defined borders on the right forearm.  Excisional biopsy of the lesion is planned.  Local anesthesia is administered via an infiltrating injection of lidocaine mixed with epinephrine.  Which of the following is the most likely impact of mixing the latter medication with the anesthetic agent?

Quizplus · Accepted Answer

11ec160b_3c08_2246_9249_63d7ad0a80e4_MD0001_00 Lidocaine is a local anesthetic that blocks transmission from free nerve endings. It is often mixed with epinephrine, which causes profound vasoconstriction when injected subcutaneously. This results in the following: (Choice A) Although epinephrine acts as a catecholamine neurotransmitter in the CNS, it mediates autonomic functions in the peripheral nervous system. Glutamate and substance P are the main neurotransmitters of pain sensation in the peripheral nervous system. (Choices B and D) Local anesthetics are weak bases that exist in charged and uncharged forms; the uncharged form must diffuse through the cell membrane and bind the inside portion of sodium channels in order to prevent depolarization. Increased acidity in the surrounding tissue results in more anesthetic molecules remaining in the charged form, preventing them from penetrating the cell membrane to exert an effect. Therefore, sodium bicarbonate is often added to lidocaine with epinephrine to increase the pH, which improves potency. This increase in pH also decreases pain at the injection site. (Choice C) Medications interact synergistically when they produce the same result by different mechanisms (eg, opioids + acetaminophen). Epinephrine does not produce anesthesia, so although it prolongs the duration of anesthesia, it does not act synergistically to increase the anesthetic effect. Educational objective: Epinephrine is often added to lidocaine to produce vasoconstriction, which prolongs lidocaine's duration of action, decreases bleeding during the procedure, and reduces systemic lidocaine absorption.

A 42-Year-Old Previously Healthy Man Comes to the Office Due