Free Anesthesiology Assistant Sample Questions
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First Free Anesthesiology Assistant Question
When performing an infraclavicular block, which two muscles will the needle travel through prior to reaching the desired location for blockade?
A) Pectoralis major and pectoralis minor
B) Pectoralis major and serratus anterior
C) Platysma and pectoralis minor
D) Serratus anterior and external intercostal
Answer and Explanations
An infraclavicular nerve block targets the brachial plexus at the level of the cords, which is visualized on ultrasound surrounding the axillary artery. The needle travels through the pectoralis major and pectoralis minor muscles prior to reaching this target.
The infraclavicular block can be used for arm and hand surgery. It takes place at the level of the cords and provides blockade to the arm below the level of the shoulder. An advantage of the infraclavicular block over the axillary nerve block is that if performed medial enough, the infraclavicular block will include the musculocutaneous and axillary nerves. A disadvantage when comparing the infraclavicular block to the axillary block is the risk of pneumothorax if the needle travels too medially with infraclavicular blocks. The intercostobrachial nerve, which originates from T2 and covers the medial upper arm commonly affected by tourniquet pain, is not covered by an infraclavicular block and will require supplementation with a subcutaneous injection of local anesthetic just distal to the axilla. The infraclavicular block can be placed under ultrasound guidance or with nerve stimulation. The lateral, medial, and posterior cords are arranged around the axillary artery. The goal is to deposit local anesthetic circumferentially around the axillary artery. Infraclavicular catheters can also be placed for continuous infusion of local anesthetic. The security of catheters is aided by stabilization from being positioned beneath the pectoralis muscles.
Performing an infraclavicular block consists of positioning a patient supine with the arm abducted ninety degrees at the shoulder. If using ultrasound guidance, the probe is initially placed medial to the coracoid process and inferior to the clavicle as a starting point. Scanning with the probe should allow for the identification of the axillary vasculature, brachial plexus, chest wall musculature, ribs, and pleura. The needle will pass through the skin, pectoralis major, and pectoralis minor with a goal of placing the needle tip below the fascia of the pectoralis minor. The serratus anterior is located deep to the axillary artery and brachial plexus and the needle should not pass through this structure as it is located on top of the pleura. With the needle tip just deep to the axillary artery in the proximity of the posterior cord, local anesthetic can be deposited in a U-shaped pattern around the axillary artery following negative aspiration. While local anesthetic can achieve this spread with a single injection, needle repositioning and multiple depositions of local anesthetic may be necessary to achieve circumferential spread.
In addition to the risk of pneumothorax, other potential complications include intravascular injection due to proximity to the axillary artery and nerve injury.
Did you get it right? The correct answer is: A
Answers B & C & D: The serratus anterior muscle is located deep to the brachial plexus in the typical location of an infraclavicular nerve block. Deep to the serratus anterior is the pleura, so providers should avoid traveling through the serratus anterior due to the risk of causing a pneumothorax. The platysma is located cephalad to the clavicle and is not encountered with infraclavicular blocks. The external intercostal muscles are located between ribs and are uncommonly visualized during infraclavicular blocks with ultrasound. Traveling through this muscle also puts the needle in close proximity to pleura and should be avoided.
Bottom Line: The infraclavicular nerve block is an upper extremity block that targets the brachial plexus at the level of the cords. The lateral, medial, and posterior cords are typically located circumferentially around the axillary artery. The needle passes through the pectoralis major and minor muscles with the goal of depositing local anesthetic around the axillary artery.
TrueLearn Insight: The ultrasound view for this nerve block is the same view used to place an axillary central line.
For more information, see:
ABA Anesthesiology Content Outline, 2014. “Extremity Blocks: Infraclavicular”
Hadzic. Textbook of Regional Anesthesia and Acute Pain Management, 2nd edition. Chapter 32D.
Miller. Anesthesia, 8th edition. Page 1728.
Lamberg JJ. Axillary Central Venous Cannulation for Cardiac Surgery. JLGH, Summer 2017 – Vol. 12, No. 2. Available at http://www.jlgh.org/Past-Issues/Volume-12-Issue-2/Axillary-CVC.aspx
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