Asian Cardiovasc Thorac Ann 2006;14:105-108
© 2006 Asia Publishing EXchange Ltd
Correlation of Modified Allen Test with Doppler Ultrasonography
Kerim Cagli, MD,
Alper Uzun, MD,
Mustafa Emir, MD,
Vedat Bakuy, MD,
Mahmut Ulas, MD,
Erol Sener, MD
Cardiovascular Surgery Clinic, Turkiye Yuksek Ihtisas Hospital, Ankara, Turkey
For reprint information contact: Vedat Bakuy, MD Tel: 90 532 626 5104 Fax: 90 312 291 2525 Email: vedatbakuy{at}yahoo.com, Abay Kunanbay Cad. No: 36 D: 2, Kavaklidere, Ankara 06700, Turkey.
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ABSTRACT
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The feasibility of using modified Allen tests to evaluate arterial circulation in the forearm for possible radial artery grafting, and the correlation of these tests with Doppler ultrasonography, were examined. The hand circulation of 50 patients scheduled for coronary artery bypass grafting was assessed by plethysmography, pulse oximetry, and pencil Doppler, as well as Doppler ultrasonography. Flow, velocity, and diameter of the radial, ulnar, and snuffbox arteries were recorded, and radiological screening indices were evaluated to establish a standard set of criteria. The results of modified Allen tests by plethysmography and pulse oximetry demonstrated the dominance of the ulnar artery. The indices of flow x diameter and velocity x diameter, obtained from Doppler ultrasound measurements, confirmed the dominance of the ulnar artery. When compression was applied to the arteries sequentially, significant alterations were found. The arterial circulation in the forearm can be safely evaluated by the modified Allen tests with plethysmography, pulse oximetry, and pencil Doppler, as these results correlated with Doppler ultrasound.
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INTRODUCTION
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The radial artery (RA) has gained widespread acceptance as a conduit for coronary artery bypass grafting (CABG) in the last 3 decades.1 Advantages include excellent early and midterm patency rates, greater freedom from late conduit atherosclerosis, ease of handling, and minimal donor-site discomfort.2 The Allen test and Doppler ultrasonography (USG) have been increasingly used in screening for hand collateral circulation.3 The Allen test is a simple and cost-effective method, but there is still some debate about whether it is a valid screening test. Doppler USG has a number of benefits.3 However, one of its drawbacks is that there are no established criteria for differentiating between normal and abnormal Doppler USG results. Several studies have attempted to establish a set of criteria.4 All reports have agreed on the need for a dynamic component comparing Doppler USG signals with and without compression of the RA. Moreover, the criteria for an abnormal result vary from study to study, depending on which vessels are scanned. The specific aims of this study were to evaluate Doppler USG in assessing hand circulation, to establish the criteria for defining an abnormal Doppler USG dynamic test result, and to validate the modified Allen tests.
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PATIENTS AND METHODS
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Fifty patients who were eligible for CABG surgery were entered into this study. Ulnar and radial arteries of 50 nondominant hands were examined. Patients with a history of trauma to the upper extremity, recent cannulation, or other vascular pathology were excluded from the study. A modified Allen test was performed by 3 different methods (pencil Doppler, plethysmography, and pulse oximetry) in all 50 patients (33 men, 17 women; mean age, 56.3 ± 9.8 years). Measurements of flow, velocity, and diameter of the radial, ulnar, and snuffbox arteries were obtained by color duplex Doppler USG. Indices of flow x diameter, velocity x diameter, flow/velocity, ulnar flow/total flow, radial flow/total flow, ulnar velocity/total velocity, and radial velocity/total velocity were also analyzed and the calculated values were used to establish standard criteria for differentiating between normal and abnormal Doppler USG results.
Doppler USG examinations were performed the day before the operation by the same radiologist, using color duplex Doppler USG with a 7.5 MHz linear transducer (GE LOGIQ 700; GE Medical Systems, Milwaukee, WI, USA). Ultrasonography was used to identify the RA, ulnar artery (UA), and snuffbox arteries in the forearm while patients were sitting comfortably in a chair with their forearms and hands positioned at the level of the heart. After measuring the diameters of all examined arteries, peak systolic speed (cm·sec–1) and flow volume (mL·sec–1) were recorded. By moving the probe from side to side across the vessel, the center of the artery could be located readily by a characteristic noise produced at the frequency of the pulse rate. When a steady state was achieved, the RA and UA were firmly compressed one by one and measurements of the radial, ulnar, and snuffbox arteries were recorded. For indices used in the dynamic evaluation of fluids, velocity and flow were multiplied by diameter for each artery. Velocity and flow of the UA and RA were added and the total values were used to calculate the UA and RA velocity and flow ratios.
With the forearm slightly extended, the Doppler pencil probe was placed at an angle of 30° over the expected anatomic position of the artery. When the characteristic blood flow pattern was obtained, both arteries were compressed by an accompanying physician until there was no flow recorded, and held for 30 sec. The time to regain the usual flow pattern from the distal part of the UA was recorded after the RA was decompressed. The procedure was repeated when the UA was decompressed.
A plethysmography sensor was applied to the index finger in the neutral position of the forearm, and existing blood flow amplitude was recorded. After taking adequate recordings, the RA and UA were steadily compressed until the systolic blood flow trace disappeared. Once radial compression was removed, the time to regain flow was recorded, and the procedure was repeated with the UA. The technique was also performed with a pulse oximeter placed on the second digit. Thus, modified Allen tests were performed by 3 different methods in each patient.
All data are expressed as mean ± standard deviation and analyzed by the unpaired Student t test for comparison of mean values of continuous variables, and by the chi-squared test for categorical variables. A p-value 
0.05 was considered to be significant. The Tukey multiple comparisons procedure was used for post hoc tests. Correlation was sought between the modified Allen tests and Doppler ultrasonography.
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RESULTS
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Modified Allen tests performed by plethysmography and pulse oximetry using probes placed on the distal part of the second digit showed that the ulnar pulse was less than the radial pulse. Although measurements by plethysmography demonstrated the dominance of the UA, there was no significant difference; however, when pulse oximetry was applied, the UA was significantly more dominant (Table 1
). Oxygen saturation recorded by pulse oximetry was 94.5% ± 1.52% for the RA and 94.84% ± 1.53% for the UA ( p = 0.871). The results of the modified Allen test using pencil Doppler confirmed the dominance of the UA, but it was not significant. Doppler USG revealed no significant variation between flow, diameter, and velocity of both arteries (Table 2), but there was a statistically meaningful divergence between the indices of flow x diameter and velocity x diameter. Although the flow and velocity ratios of both arteries indicated UA dominance, they were not significantly different. On compression of either artery separately, the flow, diameter, and velocity of the other artery was evaluated (Table 3). The results supported UA dominance, and only the difference in velocity was significant. However, the increase in flow in the snuffbox artery was significant when the arteries were occluded individually (Table 4).
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DISCUSSION
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Radial artery grafts were introduced as CABG conduits in 1973 by Carpentier and colleagues.5 Unfortunately, high occlusion rates of up to 30% were reported within a few years, and utilization of the RA was completely abandoned.6,7 Acar and colleagues8 decided to reinvestigate use of the RA for CABG in 1992 after angiograms showed completely patent RA grafts after 10 years. The Allen test has become useful for assessing the RA as an alternative arterial graft, and it has been modified many times by cardiovascular surgeons to study the arterial circulation and vascular anatomy of the hand. It does not need any device or expertise, and it can easily demonstrate the adequacy of collateral circulation.3 The original test was limited by false positive and false negative results and by its subjectivity. Modified Allen tests were developed to make the evaluations more objective. In the first modified Allen test, pulse oximetry was used.3 The pulse oximeter probe is placed on the thumb, the RA and UA are palpated and occluded by compression until the pulse waves disappear. The UA is decompressed and the time to regain the waveform of saturation is measured. If the period is < 12 sec, the UA is accepted as adequate for the circulation of the hand. Dietl and Benoit9 demonstrated that the Allen test can be used for evaluation of collateral circulation but it must be confirmed by Doppler ultrasound when the time is > 6 sec. When the perfusion time to the fingers is < 5 sec it is strongly positive, between 5–9 sec is mildly positive, but > 10 sec is accepted as negative.10
The adequacy of collateral circulation should be demonstrated before RA utilization, and different techniques are used in various clinics. Angiography is the gold standard for demonstration of arterial sufficiency.11 However, it is indicated only in special conditions because of its invasive nature, high cost, and risk of anaphylaxis. Starnes and colleagues12 measured blood pressure from the first and second digits to minimize false results, and they accepted blood pressure dropping > 40 mm Hg with RA compression as positive. The snuffbox artery, a side branch of the RA, lies from the dorsal face to the palmar face of the arm between the first metacarpal and second carpal ossis. Measurement of flow and velocity of the snuffbox artery with compression of the RA can give valuable information about the collateral circulation of the hand, because this part is accepted as the endpoint of the UA. In this evaluation, the normal finding is flow reversal, if there is no flow, the hand is at risk of ischemia after harvesting the RA.13 Despite collateral circulation being found to be adequate in preoperative and intraoperative evaluations, some cases of ischemic hand were reported; they were bypassed with reversed cephalic vein.14 An accessory RA may also be found and the RA may have some anatomic variations (9.6%), such as tortuosity (5.2%).15,16
In this study, evaluation of ulnar and radial arteries by pulse oximetry, plethysmography, pencil Doppler (pulsed wave), and Doppler USG (continuous wave) indicated dominance of the UA, but few parameters were statistically significant because of the small patient population. Despite this, the indices of flow x diameter and velocity x diameter were significant. Our results of radial and ulnar artery measurements with Doppler USG agree with previous reports. An increase in flow and velocity on compression was sought with UA dominance. Examination of the snuffbox artery revealed that velocity and flow were affected by radial manipulations because of the anatomic connection to the RA. When there is insufficient collateral circulation, this arterial territory is perfused from the dominant UA. As a result of velocity and flow assessment of the snuffbox artery with compression of the RA, we obtained higher values than those derived from compression of the UA.
Three different modified Allen tests demonstrated UA dominance in the forearm and hand circulation. Pencil Doppler and plethysmography results were almost the same, but re-flow time was shorter in pulse oximetry measurements. As sound concentration in Doppler ultrasound and the electrical amplitude concentration in plethysmography are the mainstays of these techniques, erythrocyte concentration must be over a particular value, and a certain time must pass before recording. However, it is possible to detect the amount of oxygen by pulse oximetry even with a very low concentration of erythrocytes in the capillaries.
As a result of unreliability due to subjectivity, modified Allen tests should be supported by Doppler USG with detailed examinations. It is possible to apply pulse oximetry, plethysmography, and pencil Doppler simply and safely as modified Allen tests to evaluate the anatomic variations of forearm and hand arterial circulation, which makes the Allen test more objective. New indices obtained from Doppler ultrasound measurements may be used safely to confirm the results of these tests when there is doubt.
Presented at the 12th Annual Meeting of the Asian Society for Cardiovascular Surgery, Istanbul, Turkey, April 18–22, 2004.
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REFERENCES
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ABSTRACT
INTRODUCTION
