Allen’s Test
Content of this page :
- Introduction
- Anatomy and Physiology
- Procedure
- Purpose
Introduction
Anatomy and Physiology
Radial Artery:
- Originates from the brachial artery at the level of the elbow.
- Runs along the lateral aspect of the forearm.
- Supplies blood to the lateral part of the hand and thumb.
Ulnar Artery:
- Also originates from the brachial artery at the level of the elbow.
- Runs along the medial aspect of the forearm.
- Supplies blood to the medial part of the hand and fingers.
- Contributes significantly to the superficial and deep palmar arches.
Superficial Palmar Arch:
- Formed predominantly by the ulnar artery, with a contribution from the radial artery.
- Provides blood to the fingers and palm.
Deep Palmar Arch:
- Formed predominantly by the radial artery, with a contribution from the ulnar artery.
- Supplies the deep structures of the hand.
Procedure
The Allen test is a straightforward procedure that can be performed at the bedside with minimal equipment. Here are the steps involved:
Patient Preparation: The patient is asked to sit comfortably with their hands relaxed on their lap or a table.
Occlusion of Arteries: The examiner compresses both the radial and ulnar arteries at the wrist, effectively stopping blood flow to the hand.
Hand Clenching: The patient is instructed to make a fist several times until the palm appears blanched, indicating that the blood has been drained from the hand.
Release of Ulnar Artery: The examiner then releases pressure on the ulnar artery while maintaining compression on the radial artery.
Observation: The examiner observes the hand for color changes, specifically looking for the return of normal color to the palm within 5 to 15 seconds.
Purpose
The primary purpose of the Allen test is to evaluate the patency of the arteries supplying blood to the hand. This assessment is particularly important before procedures such as arterial blood gas sampling or the insertion of a radial artery catheter. Ensuring that the ulnar artery can provide sufficient blood flow if the radial artery is compromised is crucial to prevent ischemia and potential complications.