Experimental model for transcutaneous electrical nerve stimulation on ischemic random skin flap in rats 1

The objective of this paper was to develop an experimental model to be used in the study of Transcutaneous Electrical Nerve Stimulation (TENS) on viability of random skin flap in rats. The sample was 15 Wistar-EPM rats. The random skin flap measured 10x4 cm and a plastic barrier was placed between the flap and the donnor site. The animals were submited to TENS for 1 hour immediately after the surgery and on the two subsequent days. On the seventh postoperative day, the percentage of necrotic area was measured and calculated. The experimental model proved to be reliable to be used in the study of effects of Transcutaneous Electrical Nerve Stimulation in random skin flap in rats.


Introduction
Skin flaps are largely used in all fields of plastic surgery, especially in reconstructives 1 .They have been utilizated for centuries and, during this time, one preoccupation has been to develop techniques to provide more assurance in skin flap realization.The research of skin flaps survival mechanisms and your possibles curate factors have been motive for publications. 2,3,4But in spite of all of these studies related with random skin flap survival, little progress was gotten in this field in the last 50 years. 5t is know that one of main complications that occur in the creation of the flap is ischemia, which, in a large number of cases, develops to tissue necrosis taking a failure in proposed treatment. 2Due to that complication, a considerable amount of research has been done with the aim of improving the blood flow in flaps, decreasing ischemic conditions and preventing necrosis 3,6 In the literature, there have been publications about several types of drugs, such as vasodilators, calcium channel blockers, prostagalndin inhibitors, anticoagulants, antiadrenergics and antioxidants. 3,7,8,9However, many of those present undesirable adverse effects, which makes their use in clinical practice unviable. 3Therefore, a new research field using nonpharmacological agents such as acupuncture and electroacupuncture 10,11 , pulsed electromagnetic energy 12 , low-power lasers 13,14,15 , polarized low frequency electrical currents 16,17 and nonpolarized currents 18,19 has emerged.
Among these resources, the transcutaneous electrical nerve stimulation has deserved detach due to its low cost and application facility, begining to be studied as possible method in the treatment of ischemic skin flaps.

Electrostimulator
The device used in this study was the Orion Tens® [Orion Aparelhos para Fisioterapia LTDA; serie number 00849], digital e controlled by microprocessor.The emitted pulses are rectangulars, biphasics and simmetricals.With electrical stimulator, it was used a cable, two silicone electrodes (4,2 x 1,5 cm), gel and adhesive tape for fix the electrodes.

Operation technique
In animals, it was realized a random skin flap with cranial base, measuring 10 cm length and 4 cm width.The animals were anesthestized with sodium thiopental (50 mg/kg) intraperitoneally during the operatory procedure and during electrostimulation sessions.After anesthesia induction, the rats were positioned in a plane surface with members extended and it was performed a digital tricotomy in their backs.
Then it was done the planning of the flap through a plastic mould [film F-1 (poliester + poliethilene)], cut out in pattern sizes (10x4 cm) in the backs of animals, taking as limits the inferior angles of the scapulae and the superior bones of pelvis (Figure 1).The random skin flap with cranial base was cut by scalpel and elevated through deep fascia, including the superficial fascia, panniculus carnosus, the subcutaneous tissue and skin 20,9 (Figure 2).After flap elevation a plastic barrier (film F1), with same dimensions (10x4 cm), was placed between it and the donnor site. 7The suture was realized with simple nylon 4-0 stitches (Figure 3). 9

Method for estimate percentage of necrotic area in distal portion of flaps
The percentage of skin flap necrosis area was calculated on the seventh postoperative day via the paper template method.The limit between viable tissue characterized by soft skin, rosy, warm and with hair and necrotic tissue (stiff skin, dark, cool and without hair) was demarcated in the animals.A mould of entire flap was drawn and cut in transparent paper, being checked in a precision balance (+/-0,001g error).It was cut from this fragment just the correspondent area to flap necrosis that was also checked.After that, it was used the following formule:

FIGURE 4 -
FIGURE 4 -Electrodes were placed at the base of the flap for the transcutaneous electrical nerve stimulation.