most critically ill patients will require volume expansion at some juncture during their stay in the intensive care unit ( icu ) . common indications for fluid administration in the icu include trauma , haemorrhage , dehydration and sepsis . an array of additional clinical situations may also prompt fluid administration ; for instance , in burn victims , hypoproteinaemic patients , cirrhotic patients with ascites undergoing therapeutic paracentesis , and so on . the pathophysiologic mechanisms of fluid imbalance and the optimal approaches to fluid management continue to be actively investigated in both clinical and preclinical studies . further light is also being shed on fluid management issues by recent meta - analyses . the meta - analytic findings are provocative ; however , many questions have been raised regarding their implications for clinical practice . one such question is the appropriateness of relying on mortality as the primary outcome measure , since choice of fluid may exert a relatively minor impact on this particular endpoint . also , the manner in which the skilled clinician implements a fluid management strategy may have a greater bearing on outcome than the type of fluid administered . the appropriate basis for adopting a particular fluid management strategy hypovolaemia can lead to reduced circulating blood volume , diminished venous return and , in severe cases , arterial hypotension . the aims of fluid management are to preserve intravascular fluid volume , adequate blood pressure and tissue oxygenation . in the hypovolaemic patient with normal pulmonary function , the use of colloids to maintain colloid osmotic pressure can limit the development of pulmonary oedema under conditions of elevated hydrostatic pressure . this approach may be of more limited value during states of increased lung capillary permeability ; however , since the permeability barrier generally remains at least partially intact , colloid administration may still be useful . there is growing appreciation that hypovolaemia may also precipitate localized microcirculatory disorders , in which tissue perfusion is locally compromised despite apparent systemic normovolaemia . the appropriate roles for colloids and crystalloids continue to be a major focus of clinical investigation . these two fluid categories appear to be largely indistinguishable in terms of their effects on preload recruitable stroke volume or oxygen delivery . however , because of their propensity for leakage into the extravascular space , crystalloids need to be administered in volumes approximately three - fold greater than those of colloids in order to achieve comparable resuscitation endpoints . colloids , in contrast , are retained to a greater degree in the intravascular space , and hence smaller infused volumes are needed to attain haemodynamic endpoints . based on limited data , colloids may offer the advantage of enhancing oxygen consumption to a greater extent than crystalloids . crystalloids are generally regarded as first - line fluids for the haemodynamically stable patient and , in the typical scenario , colloids are administered in addition to rather than in lieu of crystalloids . however , when the patient is haemodynamically compromised , colloids are preferred by many clinicians including authorities in the field of critical care medicine . the comparative advantages and limitations of natural and artificial colloids are also a topic of contention . advantages of the natural colloid albumin vis -  - vis artificial colloids include a less limited recommended dose range , reduced risk of haemostatic complications , clearance without tissue deposition , and lower incidence of anaphylactoid reactions . albumin is also readily monitored on a routine basis , so that there is diminished potential for excessive administration of this colloid and consequent hyperalbuminaemia , although this risk is remote . artificial colloids are less expensive per unit dose and have not been subject to the same periodic supply shortages as albumin . clinical investigations into the pathophysiology of fluid imbalance have become increasingly sophisticated with the availability of monitoring tools such as intrathoracic blood volume measurement , mercury plethysmography and labelled erythrocytes , plasma or albumin . suitable models of multiple organ failure and of acute respiratory distress syndrome ( ards ) , for example , have proven elusive . nevertheless , many models are available that can potentially reproduce a particular state of fluid imbalance and allow the effects of therapeutic interventions to be meaningfully assessed . animal models can aid in the justification and design of clinical trials and are also well suited for investigating pathophysiologic mechanisms . intriguing new clinical data are now emerging in the area of acute lung injury ( ali ) and ards . transit of large molecules into the interstitial space may be increased due to capillary leakage in these inflammatory conditions . nonetheless , the permeability barrier to large molecules is usually not entirely abolished , and therefore osmotic pressure may also play a role . a preliminary report has appeared describing the results of a randomized controlled trial employing combination therapy with albumin and furosemide in ali patients . this therapy increased serum albumin and total serum protein levels , promoted weight loss , increased acute oxygenation and improved long - term haemodynamic stability without clinically important adverse effects . if these observations are confirmed in larger - scale trials , this fluid management approach could potentially provide a welcome option for these high - risk patients . although cost has long been a major concern in fluid management , the available data on which to base clinical decisions are highly limited . rigorous pharmacoeconomic data are needed that address the comparative total costs of care between different fluid management regimens in particular clinical indications . specifically , the costs incurred as a result of fluid - associated morbidity , mortality and differences in length of icu or hospital stay also need to be taken into account . the optimal types of fluids and administration regimens for particular indications remain far from resolved . fluid management controversies are long standing , especially concerning the comparative merits of colloids and crystalloids . nevertheless , numerous studies are continuing to elucidate further the effectiveness and safety of differing fluid management approaches . as a consequence ,
fluid management strategies need to be guided by an understanding of the pathophysiologic mechanisms underlying fluid imbalance . in the hypovolaemic patient , 
 reduced circulating blood volume and venous return and , in severe cases , altered tissue perfusion may initiate a cascade of pathophysiologic processes culminating in multiple organ failure . 
 the objectives of fluid management are to maintain adequate blood pressure , tissue oxygenation and intravascular fluid volume . 
 both crystalloids and colloids can be useful for these purposes . in the hypovolaemic patient with normal pulmonary function , the use of colloids to maintain colloid osmotic pressure can limit the development of peripheral as well as pulmonary oedema . however , choice of fluid is less important in states of increased lung capillary permeability . 
 further evidence is needed to broaden understanding of the optimal roles for particular fluid management strategies . 
 experimental models can make an important contribution in gathering such evidence . 
 rigorous pharmacoeconomic studies are also needed to define the benefits and costs of differing fluid regimens .