A comparison of pulse oximetry and laser Doppler flowmetry in monitoring sequential vascular occlusion in a rabbit ear model.

The ultimate success of any free flap transfer depends not only on the experience of the given surgical team, but also requires constant vigilance in the perioperative period to assure continued anastomotic patency. Clinical acumen remains the 'industry' standard, but adjunctive monitoring devices are important to reinforce these subjective evaluations. We routinely use laser Doppler flowmetry in spite of known drawbacks, including expense. On the other hand, we know that pulse oximetry is a possible and readily available alternative. The efficacy of these two monitoring systems was directly compared in a New Zealand white rabbit central artery and vein ear model. Arterial occlusion was immediately recognized by a precipitous drop in flow and oxygen saturation (SaO2). A rapid drop in flow after venous occlusion with a trend to zero was also noted with laser Doppler flowmetry. The SaO2 had a very slow but steady gradual decline, but values remained in the range of normoxemia for a prolonged time. Because a minimum threshold of SaO2 for predicting venous occlusion was elusive, the usefulness of pulse oximetry for monitoring microsurgical composite tissue transfers is limited.