Noninvasive Monitoring of Microcirculatory Perfusion and Oxygenation in Subcutaneous Microsurgical Flaps

Postoperative monitoring is indispensable for early detection of compromised flap perfusion and thus successful salvage rates of 70% and more.[1] However, clinical evaluation is closely connected to the experience of the examiner and to the visual accessibility of the transferred tissue. Assessment of tissue and skin perfusion by laser Doppler technology has been reported to shorten the time of pedicle division of groin flaps for reconstruction of the traumatized hand by quantitative data.[2] [3]

However, laser Doppler flowmetry only provides information on the capillary blood flow as surrogate for the arterial inflow to the capillary bed. This technology is not able to measure tissue oxygenation or postcapillary venous filling pressures, which indicate venous congestion as one of the foremost reasons of free flap necrosis. Thus, isolated perfusion values provided by laser Doppler flowmetry alone are not sufficient to clearly distinguish between venous and arterial thrombosis. As venous stasis seems to be even more detrimental than arterial occlusion, it is important to distinguish between impaired arterial inflow and compromised venous outflow.[4]

The combination of laser Doppler flowmetry and spectrophotometry (oxygen-to-see system; O2C) not only demonstrates capillary inflow based on capillary perfusion but also provides data on tissue oxygenation and postcapillary venous filling pressures by spectrophotometry using a single noninvasive probe. The clinical efficiency of this new method has recently been reported in 61 patients who underwent tumor reconstruction in the head and neck region using free fasciocutaneous radial forearm flaps.[5] We used this technology[6] in a 24-year-old male patient requiring a complex facial reconstruction after orbital evisceration at the age of 10 years to cure a retinoblastoma. Subsequent radiotherapy had led to a left-sided hemiatrophy of the bony and soft tissue structures of the face. To address the remaining soft tissue depression, the patient was scheduled for autologous tissue augmentation using a microsurgical latissimus dorsi flap. Baseline microcirculation of the affected left orbital region after orbital evisceration and radiotherapy due to retinoblastoma was tremendously reduced compared with the healthy right orbital region. Microsurgical transplantation of a split latissimus dorsi flap led to an increase of periorbital tissue oxygenation and capillary blood flow nearly approaching the level of the healthy orbit. At postoperative day 6, the orbital tissue oxygenation was increased two- to fivefold throughout the reconstructed orbit reaching nearly the level of periorbital tissue oxygenation of the healthy side.

Clinical evaluation by direct vision is limited or impossible when the tissue transplants are completely covered by the local soft tissue envelope to prevent a color mismatch of the skin paddle of the flap and the skin of the recipient site. The combined use of spectrophotometry and laser Doppler flowmetry enables the examiner to get a thorough impression of the flap microcirculation regarding capillary inflow, flap oxygenation, as well as postcapillary venous filling pressures.

REFERENCES

• 1 Brown J S, Devine J C, Magennis P, Sillifant P, Rogers S N, Vaughan E D. Factors that influence the outcome of salvage in free tissue transfer.  Br J Oral Maxillofac Surg. 2003;  41 16-20
• 2 Cheng M H, Chen H C, Wei F C, See L C, Lee H Y, Wang C J. Combined ischemic preconditioning and laser Doppler measurement for early division of pedicled groin flap.  J Trauma. 1999;  47 89-95
• 3 Edwards D P, Chapman P. Pulse oximetry as a guide to early division of pedicled flaps.  J R Coll Surg Edinb. 1997;  42 187-188
• 4 Angel M F, Mellow C G, Knight K R, O'Brien B M. Secondary ischemia time in rodents: contrasting complete pedicle interruption with venous obstruction.  Plast Reconstr Surg. 1990;  85 789-793 discussion 794-795
• 5 Hölzle F, Loeffelbein D J, Nolte D, Wolff K D. Free flap monitoring using simultaneous non-invasive laser Doppler flowmetry and tissue spectrophotometry.  J Craniomaxillofac Surg. 2006;  34 25-33
• 6 Knobloch K, Tomaszek S, Busch K H, Vogt P M. Palmar microcirculation does not deteriorate 2 years after radial artery harvesting - implications for reconstructive free forearm flap transfer.  Langenbecks Arch Surg. 2007;  392 315-322