The consequences of fluid therapy and optimal fluid balance in relation to open-heart surgery are important. Extracorporeal circulation changes several of the transcapillary Starling forces, resulting in fluid retention and interstitial oedema, which can influence cardiorespiratory function and postoperative recovery. 1 Cumulative intraoperative fluid balances after cardiopulmonary bypass (CPB) of several litres are common, 2 and Breckenridge et al. 3 found postoperative fluid accumulation due to CPB was equal to one-third of the entire extracellular fluid space.

Recently, there has been interest in the use of small volume hypertonic saline (HS) solutions for volume resuscitations. Velasco et al. 4 demonstrated successful resuscitation of severely haemorrhaged dogs by infusing HS (2400mOsm NaCl) in a volume equal to only 10% of lost blood. One of the main effects of HS is the hydration of the intravascular space by rapid mobilization of fluid from the intracellular to the extracellular compartment. 5 The addition of colloids such as dextran or hetastarch prolong the volume expansion and improves cardiovascular function. 6 The initial intravascular volume expansion of such a combined hyperosmotic NaCl and hyperoncotic colloid is equal to up to four times the infused volume, with most of the expansion occurring as the solution is