Correlation of viability and laser Doppler flowmetry in ischemic flaps.

Microvascular blood flow was measured by a laser Doppler flowmeter in rabbit epigastric island flaps made ischemic at 37 degrees C for either 6.5 hr (Group 1; n = 13) or 17.5 hr (Group 2; n = 4). Contralateral flaps raised without ischemia were used as controls. The survival of ischemic flaps in these groups at 7 days was 69 and 0%, respectively. After 6.5 hr of ischemia, microvascular blood flow in the ischemic flap was approximately 20% below that in the control flap for the first 3-4 days postoperatively, presumably reflecting ischemic damage to parts of the cutaneous microcirculation; thereafter, flow was not significantly different from controls up to 7 days postoperatively. Failed 6.5-hr ischemic flaps had initial sluggish blood flow which slowed to zero usually within 4 days postoperatively. After 17.5 hr ischemia, negligible microvascular flow was detectable postoperatively. Failure in the microcirculation as detected by the flowmeter occurred well in advance of any noticeable physical changes in the flap. It is concluded that the percentage ischemic flap flow of control flap flow for each animal (at any selected time up to 24 hr after revascularization) reliably predicts the viability of the flap after 7 days.