A Dual Wavelength Spectrophotometer for Use in Plastic Surgery

The use of free flaps is well established in plastic and reconstructive surgery. However, some 10% of free flaps fail in the first 48 postoperative hours. Of these flaps 83% can be saved with immediate surgical intervention (Furnas and Rosen, 1991). A monitor of tissue viability is therefore required which should be continuous, easily interpreted and should reliably indicate changes in flap perfusion, particularly venous ischaemia which has been shown to be the most detrimental to rate of survival and area of survival of both skin and myocutaneous flaps (Thorniley et al., 1998). It should also, ideally, distinguish venous ischaemia from that caused by arterial or total occlusion. Recent studies have shown near infrared spectroscopy to satisfy many of these requirements as a monitor of flap perfusion (Irwin et al., 1995; Thorniley et al., 1998). However this technique, intended as it is for cerebral monitoring, is over-specified and more expensive than is necessary for our needs. The aim of this work is to compare our new device with NIRS using standard occlusion tests to establish whether this device can distinguish venous from total occlusions as effectively as a commercial NIRS device. Dual wavelength near-infrared instruments have been in use for some time in a variety of applications (Mancini et al., 1991; Chance et al, 1992; Chance, 1994). Our device differs in the use of an inexpensive, readily available dual light source from a pulse oximeter probe and signal processing by a “Lab View virtual instrument” residing on a laptop computer. The resulting instrument is small, easily portable and can use a miniature, sterilisable probe suitable for clinical use.