Monitoring of flaps by measurement of intracapillary haemoglobin oxygenation with EMPHO II: experimental and clinical study.

OBJECTIVE To find out whether measurements of intracapillary haemoglobin oxygenation made with the non-invasive Erlangen microlightguide spectrophotometer (EMPHO II) provided accurate data about the oxygen supply as well as the blood flow to free flaps in rats and humans. DESIGN Experimental, and prospective open clinical study. SETTING University hospital, Germany. ANIMALS and SUBJECTS Thirty male Wistar rats and 20 patients who underwent microsurgical transplant of free flaps (radial forearm, n = 8; osteocutaneous fibula, n = 7; and myocutaneous from the lateral thigh, n = 5). INTERVENTIONS Measurement of the haemoglobin oxygenation of the skin before, during, and after transfer of the flap. MAIN OUTCOME MEASURES Reproducibility and mean curves for haemoglobin oxygenation and haemoglobin concentration. RESULTS All values were reproducible, and there were only slight fluctuations. Uninjured skin in rats (baseline value) oxygenation of the total haemoglobin concentration ranged from 15% to 45% (mean 23%). After the flaps were raised there was a slight increase (to a mean of 37%), probably as a result of reactive hyperaemia. There was a rapid decrease within a few minutes of arterial occlusion, and residual oxygenation of up to 20% after perfusion stopped. The flap was totally deoxygenated after 1 h. Venous occlusion caused a similar pattern and all flaps were deoxygenated by 30 min. In the clinical study ligation of the vascular pedicle caused a massive reduction in values but after anastomosis there was significantly higher haemoglobin oxygenation (P = 0.05) and this continued to increase postoperatively. There were no complications and oxygenation gradually and continuously decreased from the base of the flap to the periphery. CONCLUSION The non-invasive EMPHO II provides reliable and easily assessable data about the circulation and supply of oxygen to a transplanted free flap.