Crystalloids requirements

Rapid fluid resuscitation with a crystalloid or a colloid if hypotensive (large volumes may be required)... 

Initial fluid resuscitation consists of isotonic crystalloid (0.9% sodium chloride or lariated Ringer s solution), colloid (5% Plasmanate or albumin, 6% hetastarch), or whole blood. Choice of solution is based on 02-carrying capacity (e.g., hemoglobin, hematocrit), cause of hypovolemic shock, accompanying disease states, degree of fluid loss, and required speed of fluid delivery. 

Most clinicians agree that crystalloids should be the initial therapy of circulatory insufficiency. Crystalloids are preferred over colloids as initial therapy for burn patients because they are less likely to cause interstitial fluid accumulation. If volume resuscitation is suboptimal following several liters of crystalloid, colloids should be considered. Some patients may require blood products to assure maintenance of 02-carrying capacity, as well as clotting factors and platelets for blood hemostasis. 

The use of colloids has recently been advocated for the resuscitation of hypovolemic horses and for the treatment of severe hypoproteinemia (McFarlane 1999). Colloids have two advantages over crystalloids that makes them attractive for fluid therapy. Firstly, because of their persistence in the circulation, a three to six times lower volume of a colloid solution is required to produce the same resuscitative effect as a crystalloid solution (Rackow et al 1987). This is particularly useful in acute resuscitation of severely dehydrated horses or in the field where large amounts of crystalloids may be difficult to transport. Secondly, the administration of colloids can increase colloidal oncotic pressure, in contrast to the administration of large volumes of crystalloids, which decreases the colloidal oncotic pressure (Jones et al 1997,2001). 

The resuscitation phase aims to restore circulating volume. There are two ways to think about the treatment of hypovolemia, both of which result in similar treatment patterns. Hypovolemic horses typically require 20-80 ml/kg of crystalloid fluids acutely. 

The "shock dose" concept is borrowed from small animal medicine. The shock dose for adult horses and neonatal foals is 50-80ml/kg crystalloid fluids. Depending on the perceived degree of hypovolemia, one-quarter to one-half of the shock dose is given as rapidly as possible (in less than 20 min) and the horse is reassessed. If the horse requires further fluid, another quarter of the shock dose is given and again the horse is reassessed. The final quarter of the shock dose is only given to severely hypovolemic horses. 

Hypokalemia is treated with i.v. potassium chloride solution. The rate of administration is more important than the amoimt. Normally the rate should not exceed 0.5mEq/kg/h and should never exceed 1 mEq/kg/h (Schaer 1999). The addition of 40mEq/l potassium chloride to crystalloid fluids is safe at infusion rates of up to lOml/kg/h (51/h for a 500 kg horse). This amount is usually only required in severe hypokalemia (<2.7mEq/l) and smaller disturbances can often be treated successfully with 20mEq/l. If hypokalemia does not respond to potassium chloride admirustration, magnesium should be supplemented (Hamill-Ruth McGory 1996). 

Patients suffering from mild or moderate exposures may only require supportive care and observation (8,21). More severe exposures necessitate basic life support, including mechanical ventilation, 100% oxygen, circulatory support with crystalloid and vasopressor agents, sodium bicarbonate for correction of the metabolic acidosis and seizure control with benzodiazepines (7,21). 

Maintain adequate cardiovascular function—-intravenous crystalloid solutions and vasopressors (e.g., dopamine, norepinephrine) if required. 

Significant fluid leaks from the vasculature occur with sepsis, and administration of large volumes of crystalloid solution such as normal saline is required. 

Isotonic crystalloids, such as 0.9% sodium chloride (normal saline) or lactated Ringer s solution, are used commonly for fluid resuscitation. A patient in septic shock typically requires up to 10 L of crystalloid solution during the first 24-hour period. These solutions distribute into the extracellular compartment. Approximately 25% of the infused volume of crystalloid remains in the intravascular space, whereas the balance distributes to extravascular spaces. Although this could impair diffusion of oxygen to tissues, clinical impact is unproven. 

Although crystalloid solutions require two to four times more volume than colloids, they are generally recommended for fluid resuscitation owing to the lower cost. However, colloids may be preferred, especially when the serum albumin concentration is less than 2.0 g/dL. 

The intrinsic double refraction expresses the essentially anisotropic or internally crystalloidal character of the aligned particles themselves. Since formalin-treated fibers show positive intrinsic double refraction relative to the fiber axis (curve A of Fig. 29) this is probably the normal condition. Because of colloidal variabiUty of native collagen fibers the analysis of form and intrinsic components by means of immersion methods requires prior fixation. 

Treatment of shock (see p 16) may require large amounts of crystalloid fluids, possibly blood (to replace loss from hemorrhagic gastroenteritis), and pressor agents such as dopamine (p 438). 

Replace fluid and electrolyte losses with intravenous saline or other crystalloid solutions (patients with mild illness may tolerate oral rehydration). Patients with hypotension may require large-volume intravenous fluid resuscitation (see p 16). 

In addition, the proportionality between vapor pressure and concentration (Raoult s law) and that between osmotic pressure and concentration (van t Hoff s law) had to be satisfied. Both requirements were adequately fulfilled within the limits of experimental error by the covalent crystalloids then studied, but not by the colloids. This error concerning the two laws made the high molar masses of the colloids also seem suspect. However, we know today that both laws are only limiting laws for infinite dilution. A molar mass apparently dependent on concentrations, i.e., calculated from the limiting laws, is also the rule rather than the exception for low-molar-mass substances. This effect, dependent on the interaction between the molecules in the solution, was known as early as 1900 from ebullioscopic measurements by Nastukoff, who also proposed an extrapolation to zero solute concentration. Caspari obtained a molar mass of 100 000 g/mol for rubber using osmotic measurements by a similar extrapolation procedure. 

Surface tension of liquids can be measured by either of the two methods static and dynamic. The static methods are based on the assumption that the liquid has attained surface equilibrium. For pure liquids and solutions of crystalloids the process of attainment of equilibrium is very fast and the static methods are best suitable. But for colloidal solutions a considerable time is required to reach the equilibrium state and therefore the dynamic methods of measuring surfacf tension are preferred. The dynanJc methods measure the tension of a liquid before the surface film has had time to form. TTiere are other methods too which fall between the static and the dynamic methods. Among the static methods, the most commonly used ones are (0 the capillary rise method, (ip the du Nouy ring method, (Up the Wilhelmy balance method, and (iv) the drop-weight method.,... 

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