Fluid therapy: Finding the best options for perfusion, oxygen supply - DVM
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Fluid therapy: Finding the best options for perfusion, oxygen supply


The answer to this question is an emphatic, "No."

Appropriate fluid therapy — combined with frequent patient evaluation, periodic cardiovascular and blood-chemical monitoring techniques — can produce astounding and at times miraculous results.

The message of clinical importance is that fixed fluid regimens (i.e., lactated Ringer's), fixed volumes (ml/lb, ml/kg) and rules of thumb are in many instances outdated, inappropriate and oftentimes inadequate. Stated another way, fluid therapy is a dynamic process, which must be reassessed at frequent intervals and adjusted in order to obtain the maximum results (i.e., optimal tissue perfusion).

Understanding options

Table 3: Evaluation of body fluid status
What, then, are the best fluids, fluid-therapy regimens and monitoring techniques needed to maximize tissue perfusion and oxygen delivery to tissues? (See Table 3.)

There are four types of fluids that can be used for the treatment of shock:

  • Those that deliver water (5 percent dextrose),
  • Electrolytes (crystalloids: lactated or acetated Ringer's),
  • Colloids (fluids that exert a colloid osmotic pressure and which expand the plasma volume)
  • Oxygen-carrying solutions (Oxyglobin®; see Table 3).

Although relatively popular in the past, the administration of a large volume of 0.9 percent saline (NaCl) or 5 percent dextrose in water is not recommended for fluid replacement due to dilutional (decreased potassium, total protein, packed cell volume; NaCl, 5 percent dextrose) and acidifying effects (NaCl).

Large amounts of normal saline can potentiate or precipitate hypokalemic, hyperchloremic metabolic (non-respiratory) acidosis.

Balanced electrolyte solutions (Ringer's) containing either acetate or lactate as base replacements are preferred as initial therapy for the treatment of hypovolemia from all forms of shock.

Although these solutions dilute blood components (protein, red-blood cells, etc.), they do not induce or worsen electrolyte or acid-base abnormalities. Providing the packed-cell volume can be maintained above 20 percent and the total protein above 3.5 g/dl, Ringer's solutions help a patient maintain vascular volume and peripheral perfusion.

Small volumes (3 to 5 ml/kg) of hypertonic saline solutions (3-14 percent) administered alone or in combination with colloidal solutions (6 percent dextran 70; hetastarch) are superior to crystalloids for the treatment of shock, including septic shock. The administration of 7 percent NaCl (approximately 2,400 mOsm/L) with colloids draws fluid from the interstitial fluid compartment into the vascular space.

Indeed, the administration of hypertonic solutions and colloids reduces the amount of crystalloid needed. Most plasma or blood-volume deficits are effectively replaced with two to four times less colloid than crystalloid.

Because fluid is drawn from the interstitial compartment into the vascular space, the potential for the development of peripheral or pulmonary edema is reduced. More specifically, cardiac filling pressures, cardiac output, cardiac stroke volume, arterial blood pressure and rates of oxygen delivery and oxygen consumption are improved. This improvement, however, is relatively short-lived (less than 30 minutes in some instances) when hypertonic saline is administered alone, suggesting that they are more effective when administered with colloids.


Source: DVM360 MAGAZINE,
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