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Neal D. Futran, MD, DMD; Brendan C. Stack, Jr, MD; Christopher Hollenbeak, MA; John E. Scharf, MD

Arch Otolaryngol Head Neck Surg. 2000;126:659-662.

Background  Monitoring strategies have been developed to address the issue of detecting postoperative free flap ischemia in an effort to permit intervention and flap salvage. No one existing noninvasive method has been widely accepted in a clinical setting. Green light photoplethysmography (GLP) uses a diode to transmit green light into a tissue. Reflected light from hemoglobin in dermal capillary red blood cells is analyzed as light intensity along a frequency spectrum. A pure peak signal (1-2 Hz) is identified and provides a way to distinguish between perfused and nonperfused tissue.

Design  Prospective, blinded comparison.

Subjects  Sixty of 72 consecutive patients considered for free flap reconstruction were enrolled in a protocol to evaluate the efficacy of GLP.

Intervention  After free flap elevation, but before pedicle ligation, 120-second baseline measurements were obtained; 120-second measurements then occurred 5 minutes after the onset or release of individual venous or arterial occlusion. Signals were processed by fast Fourier transfer; a mean alternating current–direct current (AC/DC) ratio was cultivated for each signal. All data were analyzed in a blinded fashion.

Results  The AC/DC ratio of GLP was statistically significant across all flap perfusion states (P<.001). Each condition resulted in a unique GLP signal within 5 minutes of manipulation of each vessel.

Conclusions  Green light photoplethysmography with AC/DC ratio analysis provides a rapid, precise method with which to determine flap ischemia and can differentiate venous compromised and arterial compromised flaps almost immediately after the onset of an ischemic insult. It may provide a clinically useful tool for postoperative free flap monitoring.

From the Departments of Otolaryngology–Head and Neck Surgery, University of Washington School of Medicine, Seattle (Dr Futran), and St Louis University School of Medicine, St Louis, Mo (Dr Stack); the Graduate Health Administration Program, Washington University School of Medicine, St Louis (Mr Hollenbeak); and the Department of Anesthesiology, University of South Florida School of Medicine, Tampa (Dr Scharf).

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