Quantitative Real Time Measurement of Microsurgical Free Tissue Perfusion with Thermodilution Technology

The objectives of this reported study were to introduce a new technology for monitoring free tissue perfusion in reconstructive microsurgery, to present the first clinical experience with this technology with free tissue transplants and replants, and to discuss clinical relevance and utility.

Effective monitoring is essential for the detection of microvascular problems. Identification of initial changes in blood flow allows for early intervention that may allow for salvage. The Bowman Perfusion Monitor uses an implantable 0.9-mm thermodiffusion probe that enables the measurement of tissue perfusion through the calculation of convective heat loss. The device is FDA approved and has proven its clinical utility in solid organ transplantation and neurosurgery. The authors evaluated this system for the monitoring of free tissue transplants and digital replants.

From October, 2003 to April, 2004, 22 patients were monitored with the Bowman perfusion system; these included 16 free tissue transfers (5 fasciocutaneous flaps, 8 muscle flaps, 3 toe flaps) and 6 digital replants. The thermodiffusion probe was inserted into the substance of the free flaps and into digital pulp pads. Levels of perfusion were measured in units of ml/100 g-min and were continuously recorded and displayed throughout the postoperative period. Data were collected simultaneously with the implantable Doppler and with fluorescein washout.

The monitor was simple to use and without complications from the probe. Once placed within the tissue bed, it was able to pick up perfusion readings in the early perioperative period and continue until postoperative day 5 (mean: 4 days). Readings were not obtainable in three patients. Mean perfusion data for free tissue transplants: 30.5 ml/100 g-min (range: 11 to 52) for fasciocutaneous flaps; 35.1 ml/100 g-min (range: 28 to 35) for toe transplants; 15.5 ml/100 g-min (range: 4 to 29) for muscle flaps. Mean perfusion data for digital replants: 35.1 ml/100 g-min (range: 12 to 90). There were no false negatives and two true positives. Cases were reported: one, a venous thrombosis in a second toe transplant; two, an arterial thrombosis in a revascularized digit. Both cases were salvaged with emergent exploration and were illustrated in detail.

The Bowman Perfusion Monitor provides an effective means of monitoring free tissue transplants and replants. Its significant advantages include real time, continuous, quantitative perfusion data in units of perfusion (cc/100 g-min) with simplicity in design and use. Other advantages and disadvantages were discussed. The monitor detected two cases of clinically significant thrombotic events which aided in their salvage. Thermodilution technology through the Bowman monitor holds great promise in postoperative monitoring and characterization of free tissue transplants and replants in microsurgery.