Crystalloids vs Colloids
Based on current evidence, and relative to mortality as the primary outcome, there is no clearly superior fluid in a heterogeneous population of critically ill patients.
It is concluded that:
1. Hydroxyethyl starch (HES) does increase the need for renal replacement therapy (RRT), but does not increase mortality.
2. Saline fluid is the fuid of choice in head injury.
3. Balanced salt solutions should be of choice when there is risk of renal injury.
What is Known About Fluid Choice?
COLLOIDS
In large - sacale randomized controlled trials, short - term physiological gains associated with specific colloids hane not translated into longer - term improvements in patient - centred outcomes. Accordingly, the goal is to minimize toxicity. Clinical context should determine choice in specific situations. Albumin is either not widely available or is expensive in most countries and the Saline versus Albumin Fluid Evaluation study (SAFE) specifically examined safety among nearly 7000 adults in the intensive care unit. With respect to mortality or the development of new organ failure, effects of resuscitation with 4% albumin were not significantly different from resuscitation with 0.9% saline. However, albumin therapy increased the risk of death in a prespecified subgroup with traumatic brain injury. Precise mechanisms are unclear, but the increase in intracranial pressure among patients in the albumin group may be related to the relatively hypotonic and hypo-osmolar nature of the 4% albumin. In contrast, resuscitation with albumin has been associated with a decrease in the adjusted risk of death among patients with severe sepsis. Contrary to recommendations in clinical guidelines, fluid boluses in the resuscitation of septic patients may have potential adverse effects and confer significant risks regardless of the fluid type. Mechanisms for harm related to the rate of administration are unclear but may involve a lack of compensatory neurohormonal responses. The safety of HES has been under scrutiny for many years, with reviews noting increased risks, especially with older high molecular weight hyperoncotic HES. Modern tetrastarch (6% HES) may have been considered preferable with faster plasma clearance. However as seen in large investigator - initiated randomized controlled trials, risks of impaired kidney function with HES appear to be persistent, generic, and dose dependent. It is unclear if these results are generalizable to other semisynthetic colloids, like gelatin or polygeline preparations, as these have not been studied in high - quality. A recent observational study similarly raisen concern about the risk of acute kidney injury with the use of gelatin. In the ligt of current evidence, it is difficult to support the use of semisynthetic colloids during resuscitation in critically ill patients. The clinical use of HES solutions has been significantly restricted by regulatory authorities via warnings on the potential for adverse effects.
CRYSTALLOIDS
Animal and human experiments have shown that infusions of moderate to large volumes of 0.9% saline can cause a hyperchloraemic acidosis and can also cause greater interstitial oedema than balanced crystalloids (which are similar to huyman plasma in their composition, strong ion difference, and do not produce hyperchloraemia and acidosis). Hyperchloraemia can cause renal vasoconstriction, decreased renal artery flow velocity, blood flow, and cortical tissue perfusion, and reduced glomerular filtration rate, leading to salt and water retention, when compared with balanced crystalloids. However, review of the literature fails to reveal a single large randomized study showing 0.9% saline to be clinically superor to the more physiological balanced crystalloids. The absence of studies demonstrating better clinical outcomes with balanced crystalloids has led to the continued use of 0.9% saline in most areas of practice. Two early perioperative studies and one in the resuscitation setting suggested that the hyperchloraemic acidosis could be given a false pathological significance and could also exacerbate an acidosis resulting from an actual pathological state. In addition, two relatively small studies in humans comparing 0.9% saline vs Ringer;s lactate in the perioperative period showed that 0.9% saline cause more undesirable side - effects. In the first study, involving patients undergoing abdominal aortic aneurysmorrhaphy, those receiving saline needed more packed red blood cells, platelets, and bicarbonate therapy. Postoperative pH was significantly lower and chloride concentration significantly higher in the saline group, but this hyperchloraemic acidosis did not result in an apparent change in outcome other than the requirement of larger amounts of bicarbonate to achieve predetermined measurements of base deficit and the use of larger amounts of blood products. The other study involving patients undergoing renal transplantation had to be stopped prematurely because 19% of patients in the saline group had to be treated for hyperkalaemia and 31% for metabolic acidosis compared with none in those receiving Ringer;s lactate. There was no statistically significant difference in postoperative renal function. As both these studies were relatively small, it is quite possible that the lack of difference in clinical outcome measures may represent a type II error. Three recent large observational studies have also suggested that the high chloride content of 0.9% saline may cause harm, especially to the kideny. Using a validated and quality assured database, evaluation of outcomes in 30994 adult patients undergoing major open abdominal surgery showed that unadjusted in -hospital mortality and the percentage of patients developing complications were significantly greater in the 0.9% saline group when compared with the group receiving a balanced crystalloid. Patients receiving 0.9% saline had significantly greater blood transfusion requirements, more infectious complications, and were more likely to require dialysis than those receiving balanced crystalloids. These studies suggest that it may be time to reconsider the use of 0.9% saline as the default crystalloid of choice and restrict its use to specific situations.
