Impedance monitoring for subcutaneous free flap transfers. 
The assessment of thoracic blood flow by electrical impedance is a well-established technique.  In an application of this a small electrode array has been developed in which an alternating electric current is passed through a subcutaneous free flap and the induced voltage across a small volume measured.  A graphical display of this changing voltage illustrates the pulsatile flow through the flap, allowing continuous assessment of perfusion on a beat by beat basis.  The electrode array is such that it can be placed in close contact with muscle without interface problems and can assess its viability.  It is non-invasive and easily removed.  We have found this accurate, easily interpreted by inexperienced staff, and a considerable reassurance in the postoperative period.