WBR0348
| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology |
| Sub Category | SubCategory::Neurology |
| Prompt | [[Prompt::An anesthesiology resident, prepping a patient for open reduction and internal fixation of a radial fracture, attempts his first axillary brachial plexus block. He begins by carefully palpating the axillary artery, keeping it fixed between two fingers, and then inserts a needle slightly above the artery. He then advances the needle and injects 250 mg of bupivacaine. While withdrawing the needle, the resident notices significant bright red blood flowing out of the needle tubing and realizes that he might have accidentally injected the anesthetic intravascularly. Which of the following signs should be expected to occur in this patient?]] |
| Answer A | AnswerA::Hypothermia |
| Answer A Explanation | [[AnswerAExp::Volatile anesthetics can cause hypothermia due to their inhibition of tonic thermoregulatory vasoconstriction.]] |
| Answer B | AnswerB::Hyperthermia |
| Answer B Explanation | AnswerBExp::Hyperthemia, specifically malignant hyperthermia, can result from the adminstration of succinycholine, pancuronium, and other muscle relaxants, as well as inhaled anesthetics. Malignant hyperthermia is almost never assoicated with bupivacaine. |
| Answer C | AnswerC::Hypertension and tachycardia |
| Answer C Explanation | [[AnswerCExp::Bupivacaine can cause cardiotoxicity and arrest, with initial signs being hypotension and bradycardia, rather than hypertension and tachycardia.]] |
| Answer D | AnswerD::Hypotension and bradycardia |
| Answer D Explanation | [[AnswerDExp::Hypotension and bradycardia are the earliest signs of bupivacaine cardiotoxicity.]] |
| Answer E | AnswerE::Respiratory arrest |
| Answer E Explanation | AnswerEExp::Respiratory arrest is not a complication of bupivacaine injection. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Bupivacaine, a local anaesthetic used in nerve blocks, epidurals, and intrathecal anesthesia, acts by binding to neuronal sodium channels and blocking sodium influx, leadimg to a block of depolarization. With proper handling bupivacaine is relatively safe, but when accidentally injected into the bloodstream, it is associated with significant cardiotoxicity. By the same mechanism, bupivacaine blocks sodium channels in the cardiac muscle fibers often leading to bradicardia, hypotension, and eventual cardiac arrest. Several reports have demonstrated serious cardiotoxicity with difficult resuscitation, especially in pregnant women. Several meausres have been introduced to decrease toxicity from anesthetic drugs, including improved teaching and monitoring of students, as well as technical steps such as aspiration, incremental injection, dose control, and the use of test doses. Educational Objective: Bupivacaine can cause significant cardiotoxicity by blocking cardiac sodium channels. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Bupivacaine, WBRKeyword::cardiotoxicity, WBRKeyword::local anesthetics, WBRKeyword::cardiovascular, WBRKeyword::cardiology, WBRKeyword::hypotension, WBRKeyword::bradycardia |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |