Wednesday, March 20, 2013

Assessment of Collateral Circulation of the Hand via Pulse Oximetry

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. 

The technique with the pulse oximeter with plethysmography is the same used in Pillow’s article (Pillow and Herrick, 1991).
1. The patients hand is placed in a neutral position with the palm up.
 2. The pulse oximeter probe is placed on the thumb when assessing the ulnar artery and placed on the fifth finger when assessing the radial artery.
3. The monitor is then viewed for a plethysmographic waveform.
4. The radial and ulnar arteries are then occluded until the waveform becomes flat or decreases by greater than 50 percent.
5. After that, the artery being assessed is released.
6. The plethysmographic waveform reappearing within fifteen seconds or less indicates a positive test.