Crystalloids Versus Colloids for the Critical Care/Itu Patient

Crystalloids versus Colloids for the Critical Care/ITU Patient
Introduction: Fluid Balance, Resuscitation, and the Crystalloid-Colloid Debate
Fluid imbalance in the critical care patient may result from several conditions including hypovolemia, normovolemia with maldistribution of fluid and hypervolemia (Kreimeier, 2000, p. 4). Hypovolemia is a common cause of fluid imbalance and may be induced by blood loss from trauma, or by dehydration due to fluid loss via gastrointestinal illness, fever, complications of diabetes mellitus, or renal dysfunction (Kreimeier, 2000). The resultant decrease in circulating blood volume may lead to decreased venous return, and in severe cases, to arterial hypotension (Kreimeier, 2000, p. 4). In addition, catecholamines are released systemically, leading to peripheral vasoconstriction, increased myocardial contractility and tachycardia, thereby attempting to maintain a stable blood pressure in the face of hypovolemia (Kreimeier, 2000, p. 4). In extreme cases, heart failure may ensue due to the tachycardia coupled with increased oxygen demand by the heart. In later stages, anaerobic metabolism occurs and may lead to acidosis. The combination of myocardial dysfunction and acidosis can, in turn, lead to multi-organ system failure (Kreimeier, 2000, p. 4). Thus, fluid resuscitation in the hypovolemic critical care patient is an important aspect of care.
The body has several mechanisms for controlling the distribution of fluids among the intravascular (including intracellular and extracellular) and the interstitial spaces (van Wissen & Breton, 2004, p. 304). These mechanisms include fluid mechanics, vasodilatation and vasoconstriction, and sympathetic and hormonal responses (van Wissen & Breton, 2004, p. 304). Fluid mechanics includes oncotic and hydrostatic pressure. It is via oncotic pressure that colloids and hypertonic solutions help maintain vascular volume by attracting fluid into the vascular space by osmosis—attraction of fluid...