Allen's test performed by pulse oximeter

[Ultrasound guided radial artery cannulation: procedure description and literature review]

Arterial catheterization is the second most common invasive procedure performed in critical care units. These devices are essential in certain types of patients (the hemodinamically unstable or those who require regular evaluation of the gasometric values). Complications related to arterial cannulation are relatively scarce. However, there are no reliable indicators to predict the occurrence of radial artery occlusions or ischemic lesions in the hand after a radial cannulation procedure has been performed. Ultrasound-guided catheter insertion has been used for years to guide central venous cannulation in critical care, but its use has been more limited for arterial catheterization. This paper aims to describe the technique of ultrasound-guided radial artery catheterization and reviews the most important research papers that have evaluated the safety and efficacy of this procedure in the adult population.

Radial artery cannulation: a comprehensive review of recent anatomic and physiologic investigations

Consistent anatomic accessibility, ease of cannulation, and a low rate of complications have made the radial artery the preferred site for arterial cannulation. Radial artery catheterization is a relatively safe procedure with an incidence of permanent ischemic complications of 0.09%. Although its anatomy in the forearm and the hand is variable, adequate collateral flow in the event of radial artery thrombosis is present in most patients. Harvesting of the radial artery as a conduit for coronary artery bypass grafting, advances in plastic and reconstructive surgery of the hand, and its use as an entry site for cardiac catheterization has provided new insight into the collateral blood flow to the hand and the impact of radial arterial instrumentation. The Modified Allen's Test has been the most frequently used method to clinically assess adequacy of ulnar artery collateral flow despite the lack of evidence that it can predict ischemic complications in the setting of radial artery occlusion. Doppler ultrasound can be used to evaluate collateral hand perfusion in an effort to stratify risk of potential ischemic injury from cannulation. Limited research has demonstrated a beneficial effect of heparinized flush solutions on arterial catheter patency but only in patients with prolonged monitoring (>24 h). Conservative management may be equally as effective as surgical intervention in treating ischemic complications resulting from radial artery cannulation. Limited clinical experience with the ultrasound-guided arterial cannulation method suggests that this technique is associated with increased success of cannulation with fewer attempts. Whether use of the latter technique is associated with a decrease in complications has not yet been verified in prospective studies. Research is needed to assess the safety of using the ulnar artery as an alternative to radial artery cannulation because the proximity and attachments of the ulnar artery to the ulnar nerve may potentially expose it to a higher risk of injury.

Evaluation of the ulnopalmar arterial arches with pulse oximetry and plethysmography: comparison with the Allen's test in 1010 patients

BACKGROUND

To avoid ischemic hand complications, the percutaneous transradial approach is only performed in patients with patent hand collateral arteries, which is usually evaluated with the modified Allen's test (MAT). This qualitative test measures the time needed for maximal palmar blush after release of the ulnar artery compression with occlusive pressure of the radial artery. The objectives were to evaluate the patency of the hand collateral arteries and to compare MAT with combined plethysmography (PL) and pulse oximetry (OX) tests before the percutaneous transradial approach.

METHODS

Patients referred to the catheterization laboratory were prospectively examined with MAT, PL, and OX tests. PL readings during radial artery compression were divided into 4 types: A, no damping; B, slight damping of pulse tracing; C, loss followed by recovery; or D, no recovery of pulse tracing within 2 minutes. OX results were either positive or negative. Results of both tests were compared in 1010 consecutive patients.

RESULTS

MAT results < or =9 seconds on either hand were seen in 93.7% of patients. PL and OX types A, B, or C on either hand were seen in 98.5% of patients. On the basis of the MAT < or =9 seconds criteria, 6.3% of patients were excluded from the transradial approach, whereas with PL and OX types A, B, and C, only 1.5% of patients were excluded. There was more exclusion in men and with increasing age by using both methods.

CONCLUSIONS

In the evaluation of hand collaterals, PL and OX were found to be more sensitive than MAT. When applied to transradial approach screening, only 1.5% of patients were not suitable candidates for the transradial approach.

Preoperative evaluation of the radial forearm free flap patient with the objective Allen's test

OBJECTIVE

The conventional subjective Allen's test (SAT) can be problematic because of its subjective nature. The objective Allen's test (OAT) was used before surgery to reliably and objectively assess forearm vascular flow in anticipation of harvesting a radial forearm free flap (RFFF) for use in head and neck reconstruction.

STUDY DESIGN AND SETTING

Retrospective analysis of 65 patients undergoing both preoperative SAT and OAT was completed at the University of Kansas Medical Center between December 1994 and March 1998.

RESULTS

The sensitivity and specificity of the SAT compared with the sensitivity and specificity of the OAT were only 65% and 76%, respectively. In 40 patients with at least 1 forearm with a positive SAT, only 1 (2.5%) patient was found by OAT to have vasculature that would not have allowed safe RFFF harvest in either forearm. In contrast, of the 25 patients with equivocal or negative SAT results in both arms, 18 (72%) were found by OAT to be safe candidates for RFFF harvests.

CONCLUSIONS

The OAT is an objective measure of forearm vascular flow and is superior to conventional SAT in RFFF donor-site selection.

Comparison of digital blood pressure, plethysmography, and the modified Allen's test as means of evaluating the collateral circulation to the hand

The collateral circulation to the hand was evaluated on 70 hands of healthy volunteers. Comparisons were made between the results of the modified Allen's test alone and the Allen's test combined with either plethysmography or digital blood pressure. The modified Allen's test requires patient cooperation and the results can be subjective. Plethysmography does not require patient cooperation and produces a signal that varies directly with flow; however, this is not a quantifiable signal. Digital blood pressure (measured by the 2300 Finapres noninvasive blood pressure monitor, Ohmeda, Englewood, CO, USA) also requires no patient cooperation. The values produced are of clinical value and reproducible. Both the plethysmograph and digital blood pressure monitors were able to demonstrate the dominant arterial vessel of the hand. The digital blood pressure monitor produces an objective recordable numerical value, an accepted clinical parameter, and it does not require patient cooperation. The use of a digital blood pressure monitor may prove to be an acceptable alternative to the traditional Allen's test.

Evaluation of collateral circulation of the hand

In 1929, Edgar V. Allen described a noninvasive evaluation of the patency of the arterial supply to the hand of patients with thromboangitis obliterans (Am J Med Sci 1929; 178:237). In the early 1950s, Allen's test was modified (Wright I. Vascular diseases in clinical practice. Chicago: Year Book Medical Publishers, 1952) for use as a test of collateral circulation prior to arterial cannulation. This test involves the examiner occluding the patient's ulnar and radial arteries while the patient makes a fist, causing the hand to blanch. The patient is then asked to extend the fingers. After the hand is open, the examiner releases the ulnar artery while continuing to maintain pressure on the radial artery. Adequate collateral circulation is felt to be indicated by return of normal color to the hand. The patient is instructed not to hyperextend the fingers when opening the hand. Hyperextension may cause a decrease in perfusion to the arch, possibly resulting in a false interpretation of the Allen test (Anesthesiology 1972;37:356). The modified Allen's test can be performed quickly and easily, but it is susceptible to error. (With Allen's original test, both hands were tested simultaneously. The patient clenched both fists tightly for 1 minute while the examiner compressed one artery of each hand. This method helps diagnose complete occlusion, just as Allen intended. The test was later modified, however, to evaluate the adequacy of collateral circulation. To perform the modified Allen's test, the examiner compresses both arteries while the patient's fist are clenched.(ABSTRACT TRUNCATED AT 250 WORDS)

The Allen's test: analysis of four methods

Forty nonrandomly selected hands were studied with use of four types of Allen's test: (1) the digital systolic blood pressure method, (2) the subjective method, (3) the pulse oximeter method, and (4) the laser Doppler flowmetry method. The digital systolic blood pressure method, regarded as the standard, indicated abnormal pressure in three hands. Laser Doppler flowmetry gave the same results as those obtained by the digital systolic pressure method and, in addition, was easier to perform. Pulse oximetry falsely indicated adequacy of the collateral circulation in two of the three hands with abnormal digital systolic pressure. Eleven hands, including the three with abnormal digital systolic pressure, were abnormal according to the subjective method. The results of the present study indicate the following: (1) the laser Doppler Allen's test is accurate, quick, and easy to perform; (2) the pulse oximeter Allen's test should not be used because of potentially dangerous consequences to the patient in the event of a falsely normal result; and (3) the subjective Allen's test can be used as a quick screening test.