Microdialysis to Monitor Scalp Flap Viability

Dear Sir,

We welcome Setala and colleagues[1] recent work on the use of microdialysis as a method of assessing the viability of skin flaps. Intracerebral microdialysis is already established as a useful minitor in the field of neurocritical care,[2] with evidence for clinical benefit in patients with traumatic brain injury and subarachnoid hemorrhage.

Recently, we have applied microdialysis to monitor scalp flap viability in a patient with a cerebral abscess and large, infected basal cell carcinoma of the scalp. After draining the abscess and debriding the bone, a free latissimus dorsi myocutaneous flap was used to repair the skin defect. This flap was monitored with microdialysis (Fig. [1]). Unfortunately, the flap became necrotic and had to be removed. A second free latissimus dorsi flap was used to fill the defect and was again monitored with microdialysis. This flap remained viable and the patient made a very good recovery.

Figure 1 Monitoring of two scalp flaps with microdialysis.

Concurring with Setala and colleagues, our first failed flap showed a marked decrease in glucose and rise in lactate, whereas the second successful flap showed none of these changes. We also plotted the lactate-pyruvate ratio (LPR), which is now recognised as the fundamental marker of ischemia in cerebral tissue (see Fig. [1]). The threshold for a raised LPR is 25. In the first flap, there was a steady rise in LPR, although there was a slight temporary decrease after leeches were placed on the flap. However, overall the LPR ratio continued to rise and the flap failed. The LPR in the second viable flap remained low for the duration of the monitoring.

The LPR is a more sensitive marker than lactate per se (which may be elevated in conjunction with pyruvate in states of hyperglycolysis) and we therefore commend the use of the LPR in further studies of microdialysis in assessing flap viability. Whether microdialysis becomes as clinically useful in plastic surgery as it has in neurosurgery remains to be seen.

REFERENCES

• 1 Setala L, Papp A, Romppanen E L, Mustonen P, Berg L, Harma M. Microdialysis detects postoperative perfusion failure in microvascular flaps.  J Reconstr Microsurg. 2006;  22 87-96
• 2 Bellander B M, Cantais E, Enblad P et al.. Consensus meeting on microdialysis in neurointensive care.  Intensive Care Med. 2004;  30 2166-2169 , Epub 2004 Nov 10