๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
ANESTHESIA OF THE NAIL UNIT
The choice of anesthetic will depend on the pain expected postoperatively. Plain 1% or 2% lidocaine and ropivacaine (2โmg/ml) have a more rapid onset while 0.5% bupivacaine provides adequate anesthesia after 15โminutes; there is a longer duration of anesthesia with the latter two local anesthetics (see Ch. 143). Multiple studies involving thousands of patients support the premise that lidocaine with epinephrine (adrenaline) can be safely injected into digits, as long as patients have no history of peripheral vascular compromise and the recommended volume is injected (see below). However, as nail surgery is usually performed with a tourniquet, there is little need for the vasoconstrictive effect of epinephrine.
Pain during anesthesia comes from several factors: the needle prick, rapid injection, and acidity of the anesthetic. In order to reduce these side effects, the surgeon should use thin needles (30-gauge), inject very slowly, and buffer the lidocaine (see Ch. 143).
Anesthesia can be administered as a nerve block (distal digital block) or as infiltrative anesthesia (wing procedure). In the distal digital block, the needle is inserted vertically, 1โcm lateral and proximal to the junction of the proximal and lateral folds; here 0.5โml of the anesthetic is injected in order to anesthetize the dorsal nerve branch (Fig. 149.3A). The needle is then advanced vertically towards the palmar surface, where an additional 0.5โml is injected around the palmar nerve branch. The procedure is then repeated on the opposite side to obtain full anesthesia of the nail unit. This nerve block has several advantages over the proximal digital (ring) block: (1) the onset of action is quicker; (2) less volume of anesthetic is required; (3) less risk of injuring the neurovascular bundles at the base of the finger; and (4) the injection is more comfortable.
In the wing procedure, anesthetic is injected to produce a dermal wheal at the most proximal portion of the lateral nail fold. The anesthetic progressively diffuses distally within the lateral nail fold, thus resembling a wing. Moving distally around the nail, anesthetic is repeatedly injected into the distal edge of the previously anesthetized skin until the surgical field is adequately numbed (Fig. 149.3B). The associated tissue edema provides a certain degree of hemostasis. Injecting a longer-acting anesthetic (e.g. bupivacaine) postoperatively provides prolonged anesthesia and reduces bleeding after removal of the tourniquet due to the extra liquid-based pressure on the lateral digital arteries.