GUJHS. 2004 April; Vol. 1, No. 3
K. Scott Richey BS, RRT, EMT-P
1The results of this investigation were originally presented at the University of Kansas Medical Center during May 200.
Assessment of collateral circulation of the hand is performed frequently by health care professionals for different purposes. The modified Allen’s test has been the standard assessment tool for the evaluation of collateral circulation of the hand. Researchers and clinicians have found this test easy to apply but suggest that it can be unreliable due to lack of patient cooperation, poor lighting conditions, or differences in skin pigmentation. To help prevent discrepancies of subjectivity researchers have looked into other ways to more objectively assess collateral circulation. One of these techniques is pulse oximetry with plethysmography. The display of the plethysmographic waveform is easier to see than the palmar blush of the modified Allen’s test, making it seem more objective. In order to consistently use pulse oximetry with plethysmography for evaluation of collateral circulation inter-user reliability is necessary. A total of 160 samples were collected, half from each technique, and all were supervised by the author. Out of these samples the modified Allen’s test was normal in all cases. Conversely, the pulse oximetry with plethysmography had two negative results. The modified Allen’s test provided a greater inter-user reliability, which increased with frequency of use.
The assessment of collateral circulation of the hand is performed often by surgeons, anesthesiologists, and Respiratory Care Practitioners (Cook, L, 2001; Galvin and Jones, 1989; Gerhring et al, 2002; Raju, 1986; Van de Louw et al, 2001) and Wisely and Cook, 2001). Surgeons may use this evaluation before performing a radial artery harvest for coronary artery bypass surgery, Anesthesiologists assess collateral circulation of the hand before arterial cannulation and Respiratory Care Practitioners check the collateral circulation before performing radial artery sticks for blood gas analysis. Each health care professional assesses collateral circulation of the hand for a different reason; however, they all primarily use the same evaluation technique.
The Modified Allen’s Test has been the standard assessment tool for the evaluation of collateral circulation of the hand. For Respiratory Care Practitioners this test is the only one specified for radial artery assessment by the American Association for Respiratory Care (AARC) as stated in their Clinical Practice Guidelines (AARC). The Modified Allen’s Test is a simple test, which can be quickly performed to evaluate collateral circulation. However, this needs a cooperative patient who can obey commands. The test requires the examiner to occlude the patient’s ulnar and radial arteries while the patient opens and closes the hand, causing it to blanch. Once the hand is blanched the examiner releases the ulnar artery while continuing to maintain pressure on the radial artery. The return of normal color to the hand is an indication of normal anastomotic flow across the palmer arch. Researchers have found this test to be often unreliable and difficult to apply due to lack of cooperation, poor lighting conditions or differences in skin pigmentation (Cheng et al., 1989). Also, professionals suggest the test is very subjective since each person views palmar blushing differently (Duncan, 1986). To help prevent discrepancies of subjectivity many researchers have looked into other means to more objectively evaluate collateral circulation of the hand.
One of the tools in use in anesthesia departments and during research is the pulse oximeter with plethysmography (Nowak at al., 1986). Pulse oximetry with plethysmography uses photoplethysmography or optical plethysmography. This estimates the percentage of oxyhemoglobin present and pulse rate by changes in light transmission through the sampling site with blood volume changes (Shelly et al., 1993). As blood volume increases, light absorbency increases and transmitted light decreases, and conversely, as the blood volume decreases, absorbency decreases and transmitted light increases. The device mathematically uses these light ratios to determine oxygen saturation and pulse rate (Fuhrman et al., 1992b).
In 1983 and 1985 it was reported that the changes in the amplitude of the plethysmographic waveform were relative to volume change, this providing a visual signal that can be recorded (Fuhrman et al., 1992a). The display of the plethysmograph is easier to see than the palmar blush of the Modified Allen’s test, suggesting that it is more consistent and objective. In order to consistently use the technique of pulse oximetry with plethysmography in the evaluation of collateral circulation of the hand Inter-user reliability is necessary. Since the plethysmograph is easier to see than palmer blushing the pulse oximeter with plethysmography should have a greater inter-user reliability over the Modified Allen’s test.
The Hewlett Packard monitor model 68 (m1176A) with SPO2/Pleth (m1020A) was the pulse oximeter with plethysmography that was used during this investigtaiuon. This monitor is very popular, simple to use and is available in various hospitals in the Kansas City metropolitan area. The monitor used for the study was in the University of Kansas Medical Center, School of Nursing clinical lab. This lab provided sufficient lighting for the evaluation of the modified Allen’s test. A standard wristwatch with a second hand was used to evaluate time for palmar blushing and return of plethysmographic waveform. A Texas Instrument TI 83 calculator was used for statistical analysis.
The subjects selected for this study were selected primarily for convenience from the University of Kansas Medical Center Respiratory Care Education, 2002 junior class. The class consisted of five females and four males, ranging in age between 20 and 31 years of age. Each student was familiar with performing the modified Allen’s test and using pulse oximetry with plethysmography. However, the students had never used plethysmography as a tool to assess collateral circulation of the hand. The subjects tested denied wrist or hand injuries, circulation deficits or vision problems. Permission for the study was granted by the University of Kansas School of Respiratory Care Education. The subjects were informed of the purpose of the study and each participant signed an informed consent form.
The modified Allen’s test and the pulse oximetry with plethysmography assessment techniques were described and demonstrated to the test subjects. The modified Allen’s test was performed by holding the test subjects hand in a neutral position with the palm up, occluding the radial and ulnar arteries. The test subjects opened and closed their hands (without hyper-extending the fingers) until it blanched, then the artery being assessed was released (either the radial or ulnar). A positive test required blushing of the palm in fifteen seconds or less.
The technique with the pulse oximeter with plethysmography was the same used in Pillow’s article (Pillow and Herrick, 1991).The subject was instructed to hold the hand in a neutral position with the palm up. The pulse oximeter probe was placed on the thumb when assessing the ulnar artery and placed on the fifth finger when assessing the radial artery. The monitor was then viewed for a plethysmographic waveform. The radial and ulnar arteries were then occluded until the waveform became flat or decreased by greater than 50 percent. After that, the artery being assessed was released. The plethysmographic waveform reappearing within fifteen seconds or less indicated a positive test.
The test subjects were randomly assigned a number one through nine for assessment and sampling order. The subjects each assessed five people, assessing both radial and ulnar arteries on both hands, with the assigned technique. (See Figure 1)
|Test 1||Test 2||Test 3||Test 4||Test 5|
|1||2||3||4||5||Subject Being Tested|
|3||4||5||6||7||Modified Allens Test|
|5||6||7||8||9||Modified Allens Test|
|7||8||9||1||2||Modified Allens Test|
|9||1||2||3||4||Modified Allen’s Test|
Figure 1: Experimental design of patient participation
Data was collected on five subjects; each subject was tested eight times on both hands. The radial and ulnar arteries were equally assessed. A total of 160 samples were collected, 80 from the modified Allen’s test and 80 from the pulse oximeter with plethysmography. Out of these samples the modified Allen’s test was normal in all cases with the palmar blush being noted within a mean of 3.6 seconds after releasing either artery. Conversely, the pulse oximeter with plethysmography had two negative results, each in the left ulnar artery sampled from two different subjects. Alternatively, all of the other 78 samples performed with the pulse oximeter with plethysmography were positive. The mean was 4.86 seconds for the return of the plethysmographic waveform. The modified Allen’s test seemed to provide a greater inter-user reliability compared to the pulse oximeter with plethysmography due to a smaller range, 10 compared to 18 and a smaller standard deviation 1.85 compared to 3.56.
This study results show that pulse oximeter with plethysmography doesn’t provide a greater inter-user reliability over the modified Allen’s test in cooperative, healthy, hemodynamically stable subjects. The modified Allen’s test is a simple test with inter-user reliability seemed to increasing with frequency of use (see figures 2 & 3 where MAT is the modified Allen’s test and POX is pulse oximetry with plethysmography).
Figure 2 Figure 3
Considering the two negative results with the pulse oximeter, these results were most likely due to motion, one of the pulse oximeters limitations (see table 1). This is projected, since the other samples were positive with significant lower times (see figures 4 & 5).
|Limitations of Pulse Oximetry|
|2. Abnormal Hemoglobin’s|
|3. Sensor exposure to ambient light|
|4. Skin pigmentation|
|5. Nail polish|
|6. Intravascular dyes|
Figure 4 Figure 5
The sample times for the pulse oximeter with plethysmography may be more consistent if the research protocol is stricter. For example, a specific number of plethysmographic waveforms reappearing should have been set to determine adequate reperfusion. In the absence of this, no number was recorded and each subject’s assessment of reperfusion occurred at a different number of plethysmographic waveforms (see figure 6). Even though the results conflicted with the proposed hypothesis, they were comparable to prior research stating that the modified Allen’s test and pulse oximeter showed strong correlation in the measurement of collateral circulation of the hand (Cheng et al., 1989; Fuhrman et al., 1992a and b; Pillow and Herrick, 1991). For these techniques to be properly compared they should be researched on a wider variety of subjects in various hospital environments.
The author gratefully acknowledges the assistance of Dr. M. Worth, and Dr. P.J. Mathews.