Page 569 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 23

Shock Syndromes

Kate Hopper, Deborah Silverstein, and Shane Bateman

Shock is perhaps one of the most common clinical conditions. The underlying problem or inciting event
conditions that veterinarians treat. It is also one of the for all causes of shock is a relative insufficiency of intracel­
least well understood. Although often thought of as a dis­ lular energy production. Most often this is caused by a
ease of the cardiovascular system, shock takes place within decrease in effective blood flow and oxygen delivery to
cells and results from inadequate production of intracel­ tissues that results in failure to meet the demands of
lular energy. This most commonly occurs because of inad­ the tissues. Stated differently, this form of shock is “the
equate delivery of oxygen and nutrients to tissues by an state in which profound and widespread reduction of
impaired cardiovascular system. It may also occur when effective tissue perfusion leads first to reversible and then,
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intracellular metabolic derangements prevent appropriate if prolonged, to irreversible cellular injury. ” The
cellular energy production (e.g., cyanide preventing decrease in effective perfusion can occur by many
mitochondrial energy production). Shock represents mechanisms, either cardiac or vascular in nature.
the final common pathway to death in many critical care In some cases, the inadequate cellular energy produc­
patients in veterinary and human medicine. Veterinary tion cannot be attributed to dysfunction of the cardiovas­
patients can be presented with shock, develop shock cular system, but rather to defects in oxygen loading or
during the diagnosis and treatment of a wide variety of unloading from the red blood cell, or to defects in gas
medical and surgical diseases, or develop shock during exchange in the lungs. Alternatively, mitochondrial dys­
the perioperative period. All of the shock syndromes in function or intracellular metabolic problems can also be
veterinary medicine can result in high morbidity and the source of inadequate cellular energy production.
mortality if not recognized and treated immediately. Regardless of the cause, inadequate production of intra­
Advances in our knowledge of all aspects of shock and cellular energy initiates a complex series of events that can
shock syndromes and innovative noninvasive and invasive result in altered cellular metabolism, cellular death, organ
monitoring techniques have resulted in the ability to failure, or ultimately the death of the animal.
anticipate, recognize, and treat shock syndromes more
effectively. Although we have learned a great deal about CLASSIFICATION OF SHOCK
the pathophysiology of this devastating condition, much SYNDROMES
work remains to be completed. Clinical trials in veterinary
medicine are badly needed to evaluate novel therapies Historically, shock has been classified into various
for veterinary patients, and potentially document the categories and causes to assist in understanding this com­
utility of promising therapies that might then be used plex disorder. Numerous classification schemes have been
to treat humans. presented to assist in understanding the clinical
syndromes of shock. Many classification schemes are
DEFINITION OF SHOCK aimed at simplifying a complex disorder of the cardiovas­
cular system into isolated components either on an ana­
A true understanding of shock syndromes must begin tomic or functional basis.
with the definition of shock. Shock is not defined by In this chapter classification of shock syndromes will be
tachycardia, hypotension, circulatory collapse, stupor, divided into circulatory causes, hypoxemic causes, and
coma, pale mucous membranes, or dehydration. These metabolic causes. Circulatory causes can be further divided
clinical signs may be associated with shock and are easily into hypovolemic causes, cardiogenic causes, and distribu­
recognized, but they are common to many other tive causes. Table 23-1 lists examples of each classification.

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