Hypertonic saline dextran--the fluid of choice in the resuscitation of haemorrhagic shock?

The crystalloid – colloid debate regarding the most effective intravenous fluid for resuscitation from haemorrhagic shock has been raging over the past 60 years, and still continues without a satisfactory resolution (1). Crystalloid solutions are essentially isotonic salt solutions (270-310 mOsm/L) and have been in use since the 1800s but their use became widespread during World War I. Normal saline or Ringer’s lactate solutions currently predominate over all other fluids for intravenous volume support. Colloids, on the other hand, are large macromolecules that remain in the circulation and exert a colloid osmotic or oncotic pressure due to their molecular weight. Their size also determines how long they remain osmotically active in the circulation. Albumen, separated from plasma by Cohn in 1942, was introduced as a colloid and was used extensively in World War II. Today macromolecular solutions of albumin, dextran, hetastarch and gelatin are used, with preferences determined more by cost and marketing than for clinical indications or efficacy. Colloid solutions are normally 3-10% macromolecules in an isotonic crystalloid to prevent haemolysis. Most colloid solutions have a colloid osmotic (oncotic) pressure similar to plasma (20-30 mmHg). A 6% solution of albumin is isooncotic and expands plasma volume by 80% of infused volume; 6% hetastarch is slightly hyperoncotic and 6% dextran 70 is markedly hyperoncotic (60-75 mmHg) and expands plasma volume by 20-50% more than the infused volume (2-4). The ensuing debate revolved around the physiological response to hypovolaemia. The advantage of colloids is that they are more efficient plasma expanders and cause less oedema in hypovolaemic shock, compared to crystalloids that distribute rapidly throughout the entire extracellular space with no preference for the vascular compartment. Since the extracellular space is 4-5 times larger than the plasma volume, only 10-20% of infused crystalloid remains in the circulation, requiring at least three units of crystalloid to replace each unit of shed blood – the “3:1 rule” (2,5). The two major disadvantages of colloids are cost and their potential complications (Table 1). While blood and blood products have remained the mainstays of massive transfusions, they are only available in the hospital environment and there is always the risk of infection and immunological reactions. Blood substitutes, such as haemoglobin solutions, liposome encapsulated haemoglobins and perfluorocarbons are still in development and remain some years away from routine use. Thus, in recent years, attention has turned to the potential benefits of other fluids for resuscitation, in particular, hypertonic saline solutions, alone or combined with a colloid for the treatment of haemorrhagic shock. At the same time, research has questioned the traditional management of haemorrhagic shock with aggressive fluid resuscitation (based on the Wiggers (6) and Shires (7) models of controlled haemorrhage) as set out in the Advanced Trauma Life Support manual (8). The introduction of an animal model of uncontrolled haemorrhage that more closely mimics the pre-hospital clinical scenario favours hypotensive resuscitation regimen prior to the definitive control of haemorrhage in the operating theatre (9). The concept of hypotensive resuscitation was subsequently examined in Bickell’s seminal clinical trial where delayed fluid resuscitation in hypotensive patients with penetrating torso injuries was found to improve outcome (10) This review will concentrate on the resuscitation of haemorrhagic shock with one such fluid, a combination of hypertonic saline (7.5%) and the hyperoncotic colloid dextran 70 (6%), called hypertonic saline dextran or HSD. This review aims to