Manipulation of the micro-circulation for free flap surgery

Abstract

Small vessel vasospasm during microvascular surgery imposes technical difficulties during microanastomosis which may compromise free flap transfer. Factors which tend to promote vasospasm are surgical manipulation, hypothermia, a reduced cardiac output and acid-base disturbance. Various anaesthetic regimes have been described to try to overcome these problems. Active and passive warming techniques to prevent hypothermia with consequent vasoconstriction are mandatory. In addition, specific techniques have been advocated to promote small vessel dilatation and flow which include epidural blockade, colloid infusion and the administration of alpha-blocking agents. Our experience has shown that these measures are not always successful in avoiding the vasospasm caused by local factors such as surgical manipulation or produced by the general factors which diminish tissue perfusion during long surgical procedures. A logical approach seeking to overcome the problems of vasospasm during free flap transfer, employing the directly-acting vasodilator, sodium nitroprusside (SNP) combined with intravenous fluid augmentation is used to reduce the haematocrit whilst increasing the cardiac output. In this context, unlike techniques that are designed to reduce operative haemorrhage, vasodilation with fluid augmentation leads to an increase in recipient site perfusion. The resultant increase in tissue flow provides good conditions for micro-surgical anastomosis. The use of SNP is logical as, unlike epidural blockade or many vasodilators previously tried, its action is independent of a non-functioning autonomic nervous system, a condition of the free flap. Its vascular smooth muscle relaxant properties also diminish vasospasm. Other factors influencing peripheral flow, such as temperature, acid-base disturbance, oedema and blood viscosity are strictly controlled.