WBR0348

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::An anesthesiology resident is prepping a patient for open reduction and internal fixation of a radial fracture. He is attempting his first axillary brachial plexus block. He begins by carefully palpating the axillary artery, trying to keep 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 pooring 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 sometimes cause hypothermia due to their inhibition of tonic thermoregulatory vasoconstriction.
Answer B	AnswerB::Hyperthermia
Answer B Explanation	AnswerBExp::Hyperthemia, specifically malignant hyperthermia can be seen with 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 causes 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 is a local anaesthetic used in nerve blocks, epidurals, and intrathecal anesthesia. It acts by binding to neuronal sodium channels and blocking sodium influx. This leads to a block of depolarization. Although with proper handling bupivacaine is relatively safe, when injected accidentally into the bloodstream, it is associated with significant cardiotoxicity. By the same mechanism, it blocks sodium channels in the cardiac muscle fiber often leading to bradicardia, hypotension and eventual cardiac arrest. Several reports have shown serious cardiotoxicity with difficult resuscitation especially in pregnant women. Several meausres have been introduced to decrease toxicity from anesthetic drugs including better 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. Reference: Mulroy MF. Systemic toxicity and cardiotoxicity from local anesthetics: incidence and preventive measures. Reg Anesth Pain Med. 2002;27(6):556-61. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Bupivacaine, WBRKeyword::cardiotoxicity, WBRKeyword::local anesthetics
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::