Use of a modified oxygen microelectrode and laser-doppler flowmetry to monitor changes in oxygen tension and microcirculation in a flap

Flap failure is a clinical problem in free tissue transfer, and there is no reliable device for monitoring the tissue. Differentiating between an arterial occlusion and venous congestion is also a problem. A study was undertaken to monitor viability in a pedicled groin flap and to compare two different monitoring methods. The oxygen tension in the flap, measured with a modified Clark-type microelectrode (tip diameter = 3 to 8 mu m; 90 percent response within 2.6 +/- 0.5 seconds), was compared with changes in blood no fl in the nap, measured with a laser-Doppler probe. Ln 11 Sprague-Dawley rats, the changes in oxygen tension and blood new in the pedicled groin flap were studied after cramping and subsequent reperfusion of the artery or vein. After occlusion of the artery to the Bap, oxygen tension decreased to a stable value (i.e., the recording level remained unchanged for 30 seconds), from 19.5 +/- 1.8 to 0.3 +/- 0.1 mmHg,after 193 +/- 25 seconds; blood flow decreased to a stable value, from 117 +/- 21 to 54 +/- 18 perfusion units, after 26 +/- 6 seconds. Clamping of the vein resulted in a decrease in oxygen tension, fi-om 17.1 +/- 1.8 to 1.4 +/- 0.7 mmHg, after 416 +/- 67 seconds, and blood flow decreased to a stable value, from 90 +/- Ti to 35 +/- 6 perfusion units, after 107 +/- 27 seconds. The results of this study show that there is a difference in oxygen tension and blood flow responses between arterial and venous occlusion and that it may be possible with both methods to distinguish arterial from venous occlusion. However, although oxygen tension measurements are slightly slower in response than laser-Doppler measurements, the values are more reliable as a diagnostic tool for interpretation of a vessel occlusion.