Invited Discussion

The success of re-exploration and salvage of the free flap is inversely related to a time interval between the onset of flap ischemia and its clinical recognition. Therefore, a reliable technique for postoperative monitoring of free-tissue transfers, to allow immediate detection or at least early recognition of impaired flap perfusion, is of critical importance. Many techniques of postoperative monitoring of free-tissue transfers have been developed; however, there is still no consensus on a standard accepted method.

Tissue pO₂ is one of the parameters of metabolism that can be measured following free-tissue transfer.[1] In this paper, Dr. Kamolz and colleagues report their experience with the use of the Licox catheter pO₂ probe for continuous monitoring of tissue pO2 in 60 free-tissue transfers over a period of 3 years. The probe has been used mainly in the field of neurosurgery to measure brain-tissue pO₂.[2] The use of this system for free-flap monitoring was first reported by Wechselberger et al. in 1997.[3]

In this paper, the authors report a modification in the use of the Licox catheter system with an on-line alarm system, which informs the medical staff at the time when the Licox software detects a fall in the pO₂ level in the free-flap tissue. A standard microcatheter pO2 probe is inserted into the flap at the end of the operation. The tissue pO₂ measurements are performed continuously and are then sent to a linked laptop and, in the case of significant decrease, the physician on duty is notified. The authors recommend re-exploration of the flap, if the tissue pO2 level drops below 10 mmHg or if relative tissue pO₂ level decreases 10 mmHg over one-half hour. Rapid decrease is an indication that there is an arterial thrombosis and, with a venous problem, the tissue pO2 level decreases more gradually. Of 60 free-tissue transfers, eight flaps required re-exploration. Two of the eight flaps were explored for arterial thrombosis, and both flaps could be salvaged. Six of the eight flaps were re-explored for venous thrombosis: four out of six flaps were salvaged, and two flaps were not salvageable.

Even with this continuous monitoring of the flap with the Licox system, two of six flaps that were re-explored due to venous thrombosis, were unable to be salvaged, indicating that the timing of the re-exploration may not have been soon enough. It would be interesting to know if any of these tissue pO₂ level drops correlated with clinical changes in the flap. Were flaps re-explored solely based on the changes in the tissue pO2 level, even though clinically there was no evidence of arterial or venous thrombosis?

Dr. Kamolz and his colleagues are to be congratulated for this clever modification of the Licox system with attachment to a compact on-line alarm system, which allows an on-line and staff-independent free-flap monitoring. This has the potential for saving time, especially in a setting in which experienced clinical staff for monitoring of the flap is limited. However, like all other flap-monitoring techniques, there are pitfalls to this method as well. They may include the fluctuation of the tissue pO₂ level due to micromovements at the tip of the probe, local regulatory changes in the microcirculation, the distance of the probe from the pedicle, and dislodgment of the probe. Continuous tissue pO2 measurement can be a useful tool for flap observation; however, it must be used in conjunction with accurate clinical assessment.

REFERENCES

• 1 Achauer B M, Black K S, Litke D K. Transcutaneous pO₂ in flaps: a new method of survival prediction.  Plast Reconstr Surg . 1980;  656 738
• 2 Dings J S, Meixensberger J, Jager A, Roosen K. Clinical experience with 118 brain tissue oxygen partial pressure catheter probes.  Neurosurgery . 1998;  43 1082
• 3 Wechselberger G, Rumer A, Schoeller T. Free flap monitoring with tissue oxygen measurement.  J Reconstr Microsurg . 1997;  13 125