Radial catheterization allen's test

# Overview
The hand is normally supplied by blood from the ulnar and radial arteries. The arteries undergo anastomosis in the hand. Thus, if the blood supply from one of the arteries is cut off, the other artery can supply adequate blood to the hand.  A minority of people lack this dual blood supply.  Allen's test or oximetry/plethysmography should be performed before the procedure to confirm that there is sufficient blood flow in the ulnar artery should there be loss of patency in the radial artery due to either thrombosis or spasm which can result in gangrenous finger or had loss.

# Pre-procedure Assessment

### Patient Evaluation
This is the first step towards a successful transradial PCI.  Effort should be made to assess the following:
- Age - Patients with ages <70 years are better suitable for r-PCI
- Patients' hemodynamic status
- History of previous ipsilateral brachial or transradial procedure
- Strong radial arterial pulse and presence of a normal Allens test

### Radial vs. Ulnar Approach
Although the ulnar artery is rarely used nowadays, it has been successfully attempted in the past with a high success rate comparable to the transradial approach.  Compared with the radial artery, the ulnar artery have been shown to be larger and more prone to access site failures due to its higher rate of spasms and anatomical variations.  Therefore, the transulnar approach is generally reserved as an alternative option in selected cases, and especially when the radial artery is being preserved in anticipation of its usage as a coronary bypass conduit.

### Left vs. Right Radial Artery
Radial artery in right upper extremity is usually used in 90% of cases for catheterization due to both operator and patient convenience with typical catheterization.  Other factors to consider in making a choice between left and right radial artery include the presence of a left internal mammary artery (IMA) graft and the possible future need for a bypass graft conduit from the non-dominant hand.
The following factors favor the use of left radial artery for PCI:
- Short statured patients
- Patients with abdominal obesity who tend to have compressed abdominal aortas
- Evaluation and treatment of infradiaphragmatic pathology
- Left subclavian and left vertebral interventions
- Reduced fluoroscopy time and radiation dose

# The Clinical Implication of Allen's Test
This test is named after Edgar Van Nuys Allen..  The utility of the Allen's test has been questioned, and no direct association with ischemic complications of radial artery cannulation has ever been demonstrated.  In 1983, Slogoff and colleagues reviewed 1,782 radial artery cannulations and found that 25% of them resulted in complete radial artery occlusion, without apparent adverse effects.  A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test.  In addition, the results of Allen's tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections or photo plethysmography.
Modifications to the test have been proposed to improve reliability.
Despite this lack of association with outcomes, the Allen's Test is often performed in clinical practice.

## Performing the Allen's Test
This is used to test the patency of the palmer arch.
- The hand is elevated and the patient/person is asked to make a fist for about 30 secs.
- Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.
- Still elevated, the hand is then opened. It should appear blanched (pallor can be observed at the finger nails).
- Ulnar pressure is released and the color should return in 7 secs.
Inference: Ulnar artery supply to the hand is sufficient and it is safe to cannulate the radial artery
If color does not return or returns after 7 seconds, then the ulnar artery supply to the hand is not sufficient and the radial artery therefore cannot be safely cannulated.
Below is a video demonstrating Allen's test
Reverse Allen's test may be performed in patients who require a second procedure through the same radial site.  In reverse Allen's test, the physician releases pressure over the radial artery rather than the ulnar.  This may detect proximal radial artery disease/occlusion that may be asymptomatic.  Patients with an abnormal Reverse Allen's Test should not undergo a repeat transradial procedure from same radial site.