MODIFIED ALLEN TEST AND RADIL ART CANNULATION

[jafo1964]

At the beginning let me confess that although recommended we seldom seem to follow the MODIFIED ALLEN'S TEST before we start A-lines on radial arteries of patient

Now the case scenario

A 32 year old lady was taken over by us in the surgical ICU after a major laprotomy for catecholamine secreting tumour. Her pre-operative co-morbities included hypertension, LVH and severe anaemia. All of them were corrected to optimal levels
Anaesthesia consisted of GA/ CV supplemented by a thoracic epidural. Intra-operatively she had her IJV cannulated but was maintained on ANIBP for lack of transducing facilities.
Intra-op problems included need for vasodilators initially and later vasopressors/ inotropes including Noradrenaline and Dopamine. She also received massive blood transfusion to replace her loss
Post-operatively she was put on elective ventilation.
Day 2 when we took her over, she had signs of septicaemia, myocardial dysfunction and a host of multisystem problems and was still on the ventilator.

All standard treatment protocols were inititated and to permit repeated ABG analysis and also to monitor CO and other variables including Systolic Pressure Variation, it was decided to put the patient on VIGLEO the PICCO monitor of Edward Lifesciences.
As per requirement, her left Radial artery was cannulated using a 18G cannula using the regular tranfixation technique. ALLENS TEST NOT DONE. Procedure was uneventful and tracings on the A-line were good.

24 hours later patient's left hand distal to the A-line became discoloured, cold and clammy. A diagnosis of vascular insufficiency was made. Causes seem to be multiple, but definitely also included suspected insufficiency of the palmar arch, which was not tested..
A-line was removed. Vascular opinion confirmed vascular insufficiency and patient was put on Heparin

We eventually lost the patient to MOFS,  but the blood flow to the affected limb did not improve.

NOW THE DILEMMA
A large number of papers are available that question the specificity and sensitivity of MODIFIED ALLEN"S TEST. All our Cardiothoracic surgery patients also do not have this test prior to their arterial cannulation
So do we need to perform it mandatorily

Although I did search I never found this out
What is the difference between ALLEN'S TEST and MODIFIED ALLEN'S TEST

Should this test be done only for arterial cannulation or also before we prick the artery for taking an ABG sample
Would leaving out this test and ending up with a very rare complication like this amount to negligence

Keenly looking forward to your inputs and experiences

regs

[shivdatta]

The Allen Test was first described by Edgar Van Nuys Allen in Mayo's Clinics. It is performed with the patient sitting, with his/her hands supinated on the knees. Standing at the patient's side with your fingers around his/her wrist, compress the tissue over the radial artery. Check for the return of color with flush in the thumb nail.

This test was modified by Ryan, the procedure of which is as follows:
•   Instruct the patient to clench his/her fist, or if the patient is unable, you may close the hand tightly.
•   Using your fingers, apply occlusive pressure to both the ulnar and radial arteries. This maneuver obstructs blood flow to the hand. Allow a few minutes for the blood to drain from the hand while the patient opens and closes his/her hands several times.
•   While applying occlusive pressure to both the arteries, have the patient relax his/her hand. Blanching of the palm and fingers should occur. If it does not, you have not completely occluded the arteries with your fingers.
•   Release the pressure on the ulnar artery while keeping the radial artery occluded. Normal skin color should return to the ulnar side of the palm in 1-2 seconds, followed by quick restoration of normal color to the entire palm. The usual values are:
o   < 7 sec is normal
o   8-14 sec is borderline
o   >15 sec in the hand and >10 sec in the foot is taken as abnormal and radial artery puncture is contraindicated.
•   This normal flushing of the hand is considered to be a positive modified Allen's test  which denotes that the ulnar artery is patent and has good blood flow. A negative modified Allen's test is one in which the hand does not flush within the specified time period.

[LOSKOTA]

HERE'S A TRICK TO DOCUMENT THE PALMAR CIRCULATION:

PUT A PULSE OXIMETER ON THE INDEX FINGER OCCLUDE BOTH THE RADIAL AND ULNAR BLOOD FLOW
WATCH THE PULSE OX TRACING/WAVE FORM DROP TO ZERO
RELEASE THE ULNAR OCCLUSION (HOLD DOWN THE RADIAL OCCLUSION) AND DOCUMENT THE RETURN OF BLOOD FLOW AND PULSE OX WAVE FORM ON THE INDEX FINGER.
No need to go through all the elevation and subjective evaluations of color changes etc.

[Dr. Mian]

A few comments:

1.  I don't routinely (or ever) do the clinical (modified) Allen's test before arterial cannulation because I've been told it is not a reliable test of collateral circulation to the hand.

2.  A CT surgeon once told me that Allen's test using doppler is a very good test of collateral circulation and in fact is necessary before taking a radial artery graft.

3.  I am used to using 20 g angiocaths for arterial cannulation; so I wonder if an 18g would be more prone to vascular occlusion.

4.  I read once that the ulnar a. is usually larger in diameter than the radial artery, and have found it to be a suitable site for ABP even after I had attempted to cannulate the ipsilateral radial a.

5.  I would imagine that this pt's underlying medical condition played a large part in her vascular insufficiency given the possibility of need for strong pressors (clamping down on the peripheral vessels) and possible hypercoagulability.