Board Review: Potpourri

Sat, 07/17/2021 - 10:15pm

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A 37 year old male presents to your Emergency Department in Tucson, Arizona after being bitten by a rattlesnake while hiking in the desert. The envenomation took place approximately two hours ago as the patient was hiking in the desert and had to walk many miles back to his car. On exam, there are two punctate wounds located in the right calf with significant swelling, erythema, and tenderness extending proximally past the knee. The patient is given multiple doses of anti-venom and monitored for 72 hours. Which laboratory abnormality is an indication that the patient is at high risk for post-discharge recurrence of symptoms?

A. CK greater than 10,000 on admission

B. Initial platelets 220K with increase to 250K after anti-venom

C. Fibrinogen of 600 mg/dL

D. INR of .8 on admission with repeat level 1.2

Answer- B. Initial platelets of 220k with increase to 250k after anti-venom

Given the patient’s location, the patient was most likely bitten by a rattlesnake. This patient is demonstrating signs of envenomation (swelling, erythema, tenderness) and requires anti-venom. In these patients, it is important to obtain baseline labs such as CBC, BMP, PT-INR, PTT, D-Dimer, Fibrinogen. Treatment is crotaline Fab antivenom (CroFab), which is given as 4-12 vials (depending on severity) in 250cc normal saline over 1 hour. Labs should be repeated after treatment to assess for change. The patient can be given additional doses until symptoms and labs stabilize. Patients must be stable and not require CroFab for at least 24 hours prior to discharge. Indications for post-discharge recurrence include:

Hypofibrinogenemia
Prolonged PT or PTT
Elevated INR
Thrombocytopenia
Elevated D-Dimer- even in setting of normal fibrinogen level
Improvement of platelets by over 20k with administration of CroFab, which indicates that the venom is persistently impacting the platelets and they will likely continue to drop without anti-venom