Page 392 - Clinical Small Animal Internal Medicine

360 Section 5 Critical Care Medicine

The last class of synthetic colloid is the gelatins – can be administered over a specific amount of time (for
VetBooks.ir polydisperse molecules derived from bovine collagen. example, a 250 mL bolus of 0.9%NaCl over 10 minutes),
or in profoundly compromised patients as rapidly as pos-
These solutions have a mean molecular weight of 35 000
daltons and are rapidly excreted upon infusion. As a
result, they are far less effective than the hydroxyethyl sible. Frequently, one‐quarter of the calculated shock
bolus is administered as a starting point for resuscita-
starches or dextrans for sustained volume expansion. In tion. After the bolus is complete, the animal is reassessed.
addition, the gelatins are associated with the highest rate If their perfusion parameters have not responded ade-
of anaphylactoid reactions among the synthetic colloids. quately, additional fluid therapy is indicated. It should be
As a class, gelatins are not available in the United States. remembered that when using an isotonic crystalloid for
rapid volume expansion, that crystalloid should be
devoid of fluid additives such as supplemental dextrose,
Albumin
potassium chloride or magnesium sulfate.
Physiologically speaking, albumin is an extremely impor- Synthetic colloids such as Hespan® or Vetstarch® can
tant protein. It contributes roughly 80% of the COP also be used for rapid volume expansion. Because syn-
within the vascular space. In addition to its osmotic thetic colloids are osmotically active, they promote the
activity, albumin has many other roles in the body and movement of water from the interstitium into the vascu-
functions as a carrier for a variety of substances, includ- lar space. This movement of fluid between body fluid
ing bilirubin, as well as many different drugs. Albumin compartments as well as the volume of colloid adminis-
also plays a role in platelet function and in the scaveng- tered collectively results in the expansion of the ECV. An
ing of free radicals. The ability of albumin to create initial shock bolus of synthetic colloid would be 5 mL/kg
colloid osmotic pressure is enhanced by its negative administered over 10–15 minutes.The total shock dose is
charge as well as the Gibbs–Donnan effect that describes equal to the recommended total daily dose of 20 mL/kg
how charged molecules may not be equally dispersed in the dog. In the cat, the total daily dose is somewhat
across a semipermeable membrane due to the relative lower at 10 mL/kg. Rapid administration of hydroxyethyl
permeability of the membrane. starch has been associated with nausea and vomiting in
the cat. Again, reassessment of the patient following
completion of the bolus will guide further fluid therapy.
Indications for Fluid Therapy If the response to therapy has not been adequate, addi-
tional fluids should be administered until the animal has
Rapid Volume Expansion been stabilized. If the animal is unstable but is deemed to
be volume replete, other therapies such as inotropes or
The rapid administration of IV fluids is indicated for the vasopressors may be needed. It should be remembered
treatment of hypoperfusion. Rapid volume expansion is not that synthetic colloids are potent osmotic agents so over-
appropriate if hypotension is the result of forward cardiac zealous administration can result in volume overload as
failure for any reason other than cardiac tamponade. The well as dilutional coagulopathy.
goal of rapid volume expansion is to restore the effective Hypertonic saline can also be used for rapid volume
circulating volume (ECV) to levels that permit adequate expansion. Hypertonic saline is commonly supplied as a
perfusion and thus tissue oxygenation. Serial monitoring of 7–7.5% NaCl solution. The initial shock bolus is 4–6 mL/
perfusion parameters is used to guide therapy during rapid kg over 10–15 minutes. Hypertonic saline should not be
volume expansion. Parameters that are commonly moni- administered at a rate exceeding 1 mL/kg/min as vagally
tored include physical examination parameters such as mediated bradycardia, hypotension, and bronchocon-
heart rate, pulse rate, pulse quality, mucous membrane striction may be seen with too rapid administration. If
color, and capillary refill time (CRT). In addition, monitor- needed, this initial bolus can be repeated once; further
ing may also include toe‐web to core body temperature gra- administration of hypertonic saline can result in serious
dient, urine output, central venous pressure, and blood complications such as hypernatremia and hyperchlori-
lactate measurements. A full discussion of end‐points of demia. Hypertonic saline administered alone will not
resuscitation can be found in Chapter 37. expand the vascular space for much time, and is usually
The dosing of IV fluids for the treatment of shock var- combined with a synthetic colloid to prolong its volume‐
ies with the type of fluid chosen for resuscitation as well expanding effects. Hypotonic crystalloids such as 0.45%
as the patient’s response to therapy. The most common NaCl are not appropriate for rapid volume expansion.
fluid types used for rapid volume expansion are isotonic In certain situations, fluid resuscitation with whole
crystalloids. Classically, a full “shock” bolus is considered blood or blood component therapy may be indicated.
to be 90 mL/kg in the dog and 45–60 mL/kg in the cat. This fluid choice not only provides volume expansion
These amounts approximate one blood volume. Boluses but, in the case of whole blood or packed red blood cells,