Page 441 - Clinical Small Animal Internal Medicine

41 Approach to the Patient with Shock 409

Treatment traumatized or hemorrhaging patients and may be par­
VetBooks.ir If possible, the treatment of shock should be directed at ticularly useful for resuscitation of animals with head
trauma. Hypertonic saline recruits fluid from the intra­
cellular space to rapidly increase the intravascular vol­
the underlying cause and should be aggressive and com­
prehensive. Most patients in shock can be initially resus­ ume, providing much needed volume expansion while
citated in a similar or identical manner with a few notable minimizing the risk of overresuscitation and edema for­
exceptions. If the patient has an obvious cause of shock mation. Boluses of hypertonic saline can be administered
with tachycardia without significant heart disease pre­ over a shorter period of time than boluses of isotonic
sent or suspected, then fluid therapy is almost always crystalloid fluids due to the smaller volume required.
beneficial. In cases of hypovolemic, distributive, or Unfortunately, hypertonic saline behaves in a similar
obstructive shock, increasing intravascular volume often manner to replacement crystalloids, with rapid redistri­
results in significant improvement. The exception to bution of fluid into the interstitial space, and because of
fluid administration for shock is cardiogenic etiology. the high osmolarity of hypertonic saline and the absolute
The type and dose of fluid administered for shock are solute load, repeated dosing is not recommended due
among the most controversial topics in medicine. In to the risk of hypernatremia. Relative or absolute con­
most circumstances, isotonic crystalloids are as effective traindications to hypertonic saline include preexisting
or better, as safe or safer, and less expensive than any of dehydration, hypernatremia or hyperosmolar conditions
the other choices for the initial resuscitation of shock. (ex. hyperosmolar‐hyperglycemic diabetes mellitus). To
There are subtle nuances, with different resuscitative maintain the volume expansion derived from adminis­
fluid strategies for specific disease states, but in general tration of hypertonic saline, it is often combined with a
replacement crystalloid fluids are suitable choices. synthetic colloid such as hetastarch (10–20 mL/kg) and
The traditional dose of fluids for patients in shock for administered together.
dogs and cats respectively is 90 mL/kg and 60 mL/kg of Colloids have been used successfully in the resuscita­
crystalloid fluids. This represents approximately one tion of patients in shock for years. However, controlled
blood volume that is intended to be administered over a studies have not consistently shown that colloidal solu­
short period of time. Many patients do not require an tions are more effective at achieving resuscitation than
entire shock dose of fluids to be effectively resuscitated isotonic crystalloids. Theoretically, the use of a colloid
so the most utilized clinical approach is to divide the for resuscitation in patients with low serum protein or
dose into four equal parts and administer the aliquots those with edematous diseases may be preferred.
until endpoints of resuscitation are reached. Although Incremental doses of 5 mL/kg of hydroxyethyl starch is
effective at restoring circulating volume, the duration of a reasonable starting point, with a total shock dose
effect of replacement crystalloids is short due to rapid equaling 10 mL/kg and 20 mL/kg for cats and dogs
redistribution of bolus fluids into the interstitial space. respectively. Clinically, the primary utility of synthetic
For this reason, it may be necessary to administer subse­ colloids for resuscitation is to maintain the duration of
quent boluses to maintain the desired volume expansion. volume expansion achieved with isotonic crystalloids.
Unfortunately, overaggressive resuscitation can lead to Synthetic colloids are almost never used alone for
interstitial edema formation and dilutional coagulopa­ resuscitation of a patient. Rather, they are co‐adminis­
thy. Because of this risk, it is necessary to keep track of tered with either isotonic or hypertonic crystalloids. An
the total volume of replacement crystalloid administered effective resuscitation plan would include alternating
to a patient and to consider alternative methods of resus­ administration of isotonic crystalloid and colloid solu­
citation if initial crystalloid boluses do not result in last­ tions (1/4 volume aliquots of each) until resuscitation
ing resolution of shock. has been achieved. Significant debate exists regarding
Alternatives to replacement crystalloid fluids include the impact of synthetic colloids on coagulation and
hypertonic saline, blood products (i.e., fresh frozen platelet function. There is little debate that synthetic
plasma, fresh whole blood or packed red blood cells), colloids can impair platelet function in vitro, but the
synthetic colloid solutions (i.e., hydroxyethyl starches), clinical implications are less clear. Perhaps of more clin­
albumin‐based colloid solutions (human serum albumin ical import is the potential for synthetic colloids to
or lyophilized canine albumin), hemoglobin‐based oxy­ induce dilutional coagulopathy. For these reasons, syn­
gen carriers (HBOC), or combination of any of the above. thetic colloids should be used thoughtfully in patients
Of these, hypertonic saline and synthetic colloids are with thrombocytopenia/thrombocytopathia or docu­
used the most frequently. mented coagulopathy. Ultimately, the clinician should
Hypertonic saline has the advantage of being rela­ attempt resuscitation with the method they are most
tively inexpensive and having a long shelf‐life. Doses of comfortable with rather than attempting to use a resus­
4–6 mL/kg of 7.5% NaCl can be used in nondehydrated citation strategy that is unfamiliar.