The intravenous administration of fluids in shock is life saving. However, there is increasing controversy as to the rationale for the normalisation of blood pressure in the treatment of shock with either colloids or crystalloids. Increasing the blood pressure by either the administration of colloids or crystalloids may also impair the formation of new blood clots and also dislodge existing ones and thus contribute to ongoing haemorrhage. The main aim of this thesis was to investigate the intrinsic and volumetric effect that these different intravenous resuscitation fluids have on the haemostatic process and bleeding. A variety of studies including in vitro mechanistic investigations, electron microscopy, randomised trials, randomised and double blinded trials were carried out. These were supported by epidemiological and systematic literature reviews to clarify the controversy.