Management of shock in trauma

Abstract

Shock is a state of acute circulatory failure, with inadequate tissue perfusion causing cellular hypoxia. Hypovolaemia from haemorrhage is the most common cause after trauma, but other mechanisms must be excluded. Initially, sympathetic and neurohumoral mechanisms compensate for the reduced pre-load, but eventually, negatively inotropic products of anaerobic metabolism, have direct cytotoxic effects, leading to failure of membrane pumps and the initiation of the inflammatory cascade. The final common pathway is arteriolar vasodilatation, refractory to further fluids or catecholamines. The priorities are to ensure adequate ventilation and oxygenation, to stop further blood loss and to restore the circulating volume with warmed fluids. There is no evidence to support the use of one fluid over another, provided they are given in sufficient quantity. Adequacy of fluid repletion can initially be judged by simple physiological measures, guided by the base deficit and plasma lactate. In the critical care setting, transoesophageal Doppler or continuous cardiac output monitors can provide additional valuable information on volume status and the requirement for inotropes. Isotonic crystalloids are cheap, but poor volume expanders, which need to be given in repeated boluses, often leading to tissue oedema with gut and pulmonary dysfunction. Colloids give better plasma expansion at smaller doses with good volume-stabilizing abilities. However, they are expensive and side-effects include hypersensitivity reactions, coagulopathies and storage lesions. A novel approach is low volume resuscitation using a combination of colloid and hypertonic saline. These solutions lead to rapid improvement in cardiac output and mean arterial pressure with increased capillary blood flow and reduced cellular oedema; however, there are side-effects. Permissive hypotension is a resuscitation technique designed to prevent further blood loss by limiting fluid boluses to a target systolic blood pressure of 80, until haemostasis has been achieved. The risk and benefits of tissue perfusion against further bleeding have to be assessed for each patient. This technique is best suited to young patients without co-morbidities, but is contraindicated in the presence of traumatic brain injury. It is possible that developments in blood substitutes, will enable low volume resuscitation while allowing for increased oxygen delivery.