What are Palmar Arch Test and AV Fistula?
The Palmar Arch Test (PAT), also known as Allen’s Test, is a specialty test performed to evaluate the patency of the arteries in the hand prior to radial or ulnar artery harvesting in artery bypass procedures or before the surgical creation of an upper extremity hemodialysis fistula or graft.
How to Perform PAT (Allen's Test)
The PAT procedure provides a clinical assessment of the collateral circulation to the hand to determine if arterial harvesting is possible. The test is quite simple and involves sequential compression of the radial and ulnar arteries, and determining the physiological effect on the blood flow circulation in the hand. The blood flow assessment can be performed by different means, with the most popular method being with PPG sensors (Photo-plethysmography).
Additional diagnosis options include digit blood pressure measurements, PVR measurements (Pulse Volume Recording), and Doppler blood flow measurements. When using PPG sensors, it is preferred to use at least 2 PPG sensors, which are placed on the two extreme digits (digit 1 and digit 5). The Palmar Arch Test protocol begins by measuring the resting PPG waveforms, then measuring the waveforms after selected compressions (compression of the radial artery, ulnar artery, or both), and finally measuring the waveforms after the release of the selected compression. A similar protocol is applied when using digit pressure, Doppler, or PVR assessment.
Compression is typically performed by manually compressing the selected artery or arteries. This procedure allows the examiner to evaluate whether the result of the compression is impeded or loss of blood flow to parts of the hand. Thus, significant reduction or loss of blood flow to areas of the hand suggests that removing that particular artery may jeopardize hand performance if the artery is removed.
Using the Falcon for PAT Measurements
The Falcon has a dedicated Palmar Arch Test (PAT) protocol, which is designed to complete the assessment in guided procedures per the accepted guidelines. While the standard clinical assessment is with PPG sensors on the 2 extreme digits, the Falcon has the ability to place a PPG sensor on each of the 5 digits and perform the test simultaneously for all digits for optimal clinical assessment.
The Falcon also supports digit blood pressure measurements pre- during and post-arterial compression.
In addition, digit Doppler and/or PVR measurements can be performed with the Falcon.
The PAT protocol includes schematic pictures, which help visualize to the examiner the required compression stage. The measured waveforms are clearly marked with automatic cursors to indicate when artery compression begins and when the compression is released. Thus, a quick visual assessment of the effect of compression on blood flow to the different parts of the hand is possible.
All sensors are color-coded, simplifying the interaction with the software. Zoom in and out of the waveforms allows to quickly qualitatively determine whether a specific arterial compression has a patent collateral circulation or that harvesting the vessel will jeopardize the hand.
Expected Results of Palmar Arch Test
A decrease in the ipsilateral signal when compressing an artery, whether PPG waveform, blood pressure, PVR waveform, or Doppler spectrum, is indicative of impaired collateral circulation in the hand, and is generally considered as a contraindication to arterial harvesting.
For blood pressure assessment, a Finger Brachial Index (FBI) greater than 0.9 is considered normal.
FBI is defined as the digit pressure divided by the ipsilateral brachial pressure. The determination of what is considered a significant drop in digit pressure varies in the literature but is in the range of a drop of 40 mmHg after radial/ulnar artery compression.
Example of a Palmar Arch Test specialty test performed
on a patient using Viasonix Falcon/PRO. First, the Radial artery was compressed on two extreme digits, and then the Ulnar artery was compressed on the same digits.
Selected Literature on Palmar Arch Test
Preoperative Assessment of Hand Circulation by Means of Doppler Ultrasonigraphy and the Modified Allen Test, Permyos Ruengsakulrach et al., J Thorac Cardiovasc Surg 2001;121:526-31
Assessment of collateral circulation to the hand prior to radial artery harvest, Joseph Habib, Laureen Baetz and Bhagwan Satiani, Vascular Medicine 17(5) 352– 361
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