The Histamine Reaction: A Useful Adjunct for Monitoring Free Flaps

Abstract

Sir: Regular observation in the immediate postoperative period following free tissue transfer is imperative to flap survival.1–4 Free flaps are most vulnerable until the reepithelialization of the anastomosis.2,3 Clinical vigilance and careful monitoring are essential during this period to ensure successful outcomes. Survival rates of greater than 50 percent can be expected in salvaged flaps, with survival being inversely proportional to both the delay in detecting compromised perfusion and the subsequent delay in surgical exploration.1–5 Flap monitoring is therefore a crucial prerequisite to successful flap salvage. A commonly used method of monitoring is capillary refill measurement, which involves digital pressure on the skin for 3 seconds and then release. The skin blanches temporarily but returns to normal skin color within 2 seconds. A prolonged capillary refill time indicates inadequate flap perfusion, whereas a brisk return may represent compromised venous drainage of the flap.2,3,5 However, assessment of capillary return in, for example, perforator flaps can be challenging on account of the difficulty of eliciting a blanching response on application of digital pressure because of paleness of flaps. Histamine and serotonin are the primary mediators released in inflammatory reactions. These preformed mediators are found in mast cells, basophils, and platelets, and their release leads to an increase in vascular permeability, resulting in local tissue edema. The senior author (M.S.K.) often induces a histamine flare onto the cutaneous surface of pale free flaps postoperatively (Fig. 1). Typically, this is achieved by gently scratching the surface of the flap with a handle of a pair of Adson's forceps. This mechanical irritation of the epidermis results in histaminergic activation with local angioedema characterized by a wheal and flare.4 This flare can be used as a landmark to subsequently assess capillary refill. Histamine is directly released from cutaneous mast cells in response to mechanical stimuli, although eicosanoids, in addition to other cytokines, may also have a role to play in this immunoglobulin E–mediated process.Fig. 1.: (Above, left) Free flap before scratch test. The flap perfusion status is difficult to determine accurately, as the flap is pale. (Above, right) Primed flap following scratch. A transverse strip of hyperemic skin is visible along the flap. (Below, left) Assessment of capillary refill of primed free flap by gentle compression with the handle of a pair of tenotomy scissors. (Below, right) A blanched area corresponding to the scissors handle is readily visible, thus allowing an accurate assessment of the capillary refill time.The authors propose the histamine reaction scratch test to surmount the assessment difficulties of pale flaps. This method of augmenting the innate capillary return greatly improves the ability to undertake accurate flap observations in pale free flaps. The limitation to the histamine scratch test is its duration of action, which we estimate to be on the order of 2 to 6 hours. The test can be readily repeated at the bedside until the flap observation period has ceased. It is common practice to assess flap perfusion by using a hypodermic needle to scratch or prick the cutaneous portion of the flap to induce capillary bleeding; indeed, in certain situations, such as head and neck reconstruction, a small portion of the flap may be deepithelialized to facilitate direct observation of capillary bleeding on repeated occasions. We have used these techniques in our unit; however, we are cognizant of the attendant risks of infection, hematoma formation, and potential iatrogenic injury to the pedicle itself. The histamine scratch test all but obviates these risks, as the epidermis is not breached. This response occurs independently of the sympathetic and parasympathetic nervous systems. We have shown that scratching a pale flap is a good, reliable, and safe way of monitoring a free flap. Although physiologically this assessment works in clinical practice, the response does not last long enough for the flap to be monitored for sustained periods of time. Assessment of capillary return in pale flaps (such as the deep inferior epigastric perforator and anterolateral thigh flaps) can be problematic on account of the difficulty of eliciting a blanching response on application of digital pressure. The authors feel that this test is a technically straightforward, noninvasive, bedside test that aids in informing the clinician of the underlying flap perfusion status. The test is therefore an invaluable adjunct in the monitoring of pale free flaps. Zeeshan Ahmad, M.R.C.S. Marc C. Swan, D.Phil. Department of Plastic and Reconstructive Surgery and Burns Matthew Flynn, F.R.C.Path. Department of Histopathology Mansoor S. Khan, F.R.C.S.(Plast.) Department of Plastic and Reconstructive Surgery and Burns Salisbury District Hospital Salisbury, Wiltshire, United Kingdom DISCLOSURE No funding was received in the production of this article. There is no conflict of interest.