IV fluids are widely used in intensive care units for resuscitation. There is emerging evidence that the type and dose of resuscitation fluid may affect patient-centered outcomes. The latest article in our Critical Care series reviews the various fluids available and how to choose among them.
Fluid resuscitation with colloid and crystalloid solutions is a ubiquitous intervention in acute medicine. The selection and use of resuscitation fluids is based on physiological principles, but clinical practice is determined largely by clinician preference, with marked regional variation. No ideal resuscitation fluid exists. There is emerging evidence that the type and dose of resuscitation fluid may affect patient-centered outcomes.
• How are resuscitation fluids categorized?
Resuscitation fluids are broadly categorized into colloid and crystalloid solutions. Colloid solutions are suspensions of molecules within a carrier solution that are relatively incapable of crossing the healthy semipermeable capillary membrane owing to the molecular weight of the molecules. Crystalloids are solutions of ions that are freely permeable but contain concentrations of sodium and chloride that determine the tonicity of the fluid. Proponents of colloid solutions have argued that colloids are more effective in expanding intravascular volume because they are retained within the intravascular space and help to maintain colloid oncotic pressure. The volume-sparing effect of colloids, as compared with crystalloids, is considered to be an advantage, which is conventionally described in a 1:3 ratio of colloids to crystalloids. Proponents of crystalloid solutions have argued that colloids, in particular human albumin, are expensive and impractical to use as resuscitation fluids, particularly under field-type conditions. Crystalloids are inexpensive and widely available and have an established, although unproven, role as first-line resuscitation fluids. However, the use of crystalloids has classically been associated with the development of clinically significant interstitial edema.
• What are the benefits and risks of the use of human albumin?
Human albumin (4 to 5%) in saline is considered to be the reference colloidal solution. It is an expensive solution to produce and distribute, and its availability is limited in low- and middle-income countries. Investigators in Australia and New Zealand conducted the Saline versus Albumin Fluid Evaluation (SAFE) study, a blinded, randomized, controlled trial, to examine the safety of albumin in 6997 adults in the ICU. Resuscitation with albumin was associated with a significant increase in the rate of death at 2 years among patients with traumatic brain injury (relative risk, 1.63; 95% CI, 1.17 to 2.26; P=0.003). This outcome has been attributed to increased intracranial pressure, particularly during the first week after injury. Resuscitation with albumin was associated with a decrease in the adjusted risk of death at 28 days in patients with severe sepsis (odds ratio, 0.71; 95% CI, 0.52 to 0.97; P=0.03), suggesting a potential, but unsubstantiated, benefit in patients with severe sepsis.
Morning Report Questions
Q: What are the risks of using hydroxyethyl starch (HES) as a replacement solution?
A: In a blinded, randomized, controlled trial involving 800 patients with severe sepsis in the ICU, Scandinavian investigators reported that the use of 6% HES (130/0.42), as compared with Ringer’s acetate, was associated with a significant increase in the rate of death at 90 days and a significant 35% relative increase in the rate of renal-replacement therapy. In a blinded, randomized, controlled study, called the Crystalloid versus Hydroxyethyl Starch Trial (CHEST), involving 7000 adults in the ICU, the use of 6% HES (130/0.4), as compared with saline, was not associated with a significant difference in the rate of death at 90 days. However, the use of HES was associated with a significant 21% relative increase in the rate of renal-replacement therapy. Both trials showed no significant difference in short-term hemodynamic resuscitation end points, apart from transient increases in central venous pressure and lower vasopressor requirements with HES in CHEST. In CHEST, the use of HES was associated with an increased use of blood products and an increased rate of adverse events, particularly pruritus.
Q: When are balanced salt solutions recommended as resuscitation fluids, and what are the associated risks?
A: Crystalloids with a chemical composition that approximates extracellular fluid have been termed “balanced” or “physiological” solutions and are derivatives of the original Hartmann’s and Ringer’s solutions. Balanced salt solutions are relatively hypotonic because they have a lower sodium concentration than extracellular fluid with associated anions such as chloride and bicarbonate. Excessive administration of balanced salt solutions may result in hyperlactatemia, metabolic alkalosis, and hypotonicity (with compounded sodium lactate) and cardiotoxicity (with acetate). Given the concern regarding an excess of sodium and chloride associated with normal saline, balanced salt solutions are increasingly recommended as first-line resuscitation fluids in patients undergoing surgery, patients with trauma, and patients with diabetic ketoacidosis. Resuscitation with balanced salt solutions is a key element in the initial treatment of patients with burns, although there is increasing concern about the adverse effects of fluid overload, and a strategy of “permissive hypovolemia” in such patients has been advocated.