Page 438 - Clinical Small Animal Internal Medicine

406 Section 5 Critical Care Medicine

blood pressure should always be used when available. heart and brain. This decrease in splanchnic blood flow
VetBooks.ir A systolic blood pressure of less than 90 mmHg or a has a significant impact on the mucosal integrity of the
GI tract, leading to the vomiting and hemorrhagic diar­
mean arterial pressure (MAP) of less than 60 mmHg
should be aggressively pursued.
ings associated with shock, GI signs are usually mild to
Numerous factors can confound the interpretation of rhea often seen in shock. As with most of the exam find­
pulses in clinical cases. Since the pulse that is palpated is absent in animals in the compensatory stages of shock
the difference between the systolic and diastolic pres­ and can be moderate to severe in animals that have pro­
sures, a small difference will cause the pulse to be weak or gressed to the later stages of decompensated shock.
thready and a large difference will cause the pulse to be The use of biomarkers for detection of shock and co‐
strong or bounding. None of these descriptions reflect morbidities has become widely accepted as standard of
the actual pressure within the vessel, and all of these pulse care in human medicine. These measurements (i.e., elec­
qualities can represent a patient in shock. An obstruction trolytes, blood glucose, creatinine) can provide impor­
to blood flow can also inhibit the detection of pulses, as is tant information regarding the underlying cause of shock
the case in aortic thromboembolism by causing an abso­ in addition to aiding in its recognition and diagnosis.
lute reduction in blood flow through the artery. Biochemical abnormalities can be prognostic or diag­
Patients in shock also frequently demonstrate tachyp­ nostic and can direct the clinician to appropriate thera­
nea as the body attempts to maximize oxygen delivery to peutic interventions. All patients in shock should have a
the alveoli and subsequently to the arterial blood. blood gas profile with lactate as a part of the initial and
Respiratory rates in excess of 40 breaths per minute for a ongoing evaluation of the patient whenever possible.
dog and 60 breaths per minute for a cat are consistent Lactate is an important marker of tissue perfusion and
with shock. In this instance, tachypnea must be differen­ has been the most widely used biomarker of shock in vet­
tiated from true dyspnea or respiratory distress, the erinary patients. Lactate is easily measured in clinical
presence of which may indicate an underlying etiology practice with a range of options from bench‐top blood
but does not lead to a diagnosis of shock. Tachypnea is gas analyzers to handheld monitors that have been vali­
also a common response to pain, which may confound dated in veterinary patients. Blood lactate concentra­
the use of respiratory rates for evaluation of possible tions greater than 2.5 mmol/L are indicative of significant
shock. Often, evaluating the respiratory rate after admin­ anaerobic metabolism and, in a patient with other signs
istration of analgesia provides a better representation of consistent with shock, should be considered to be diag­
the patient’s ventilatory status. nostic for failure of oxygen delivery.
Altered mentation is seen in patients in decompen­ The availability and use of ultrasound in veterinary
sated shock as blood flow and oxygen delivery to the medicine has become very common. While not particu­
brain are reduced. Since the brain has high demands for larly useful for the diagnosis of shock itself, ultrasound
energy and little reserve for energy production, cerebral has become especially useful because it allows identifica­
function and consciousness are affected early after tion of the etiology faster. The use of focused assessment
decompensation begins. The typical patient in compen­ with sonography for trauma (FAST) protocols for the
sated shock will appear bright and alert while the patient abdomen (AFAST) and thorax (TFAST) have been very
in early decompensated shock will be mildly to moder­ well described in veterinary medicine. These techniques
ately obtunded. As shock progresses so will mentation can be performed with minimal training and are quite
change and patients that find themselves in late decom­ effective at the identification of fluid in cavities as well as
pensated shock will appear severely obtunded to stupor­ the presence of a poorly contracting heart or pneumo­
ous. Pain can also affect a patient’s response to its thorax. If available, and as long as positioning and
environment and care should be taken to ensure that restraint will not be detrimental to the patient, ultra­
changes in behavior are in fact due to altered mentation sound should be used to evaluate patients in shock to
rather than pain. Evaluation of mentation is especially attempt to determine the underlying cause. A descrip­
relevant in cases with head trauma when the level of con­ tion of the FAST procedures is provided in Chapter 46.
sciousness can be used as a prognostic sign or metric of
the severity of injury. In these cases, shock and pain
should be addressed before those assessments are made Classification of Shock
or at the very least, they should be interpreted with these
facts in mind. The following provides a guide to the classification of
The GI tract is affected in almost all cases of shock as shock. The categorization of shock can be beneficial for
evidenced by the ubiquity of the term “shock gut.” Recall formulating a diagnostic and therapeutic approach to a
that the GI tract is one of the organ systems that is sacri­ patient. While clinically useful, it should be reiterated
ficed in order to divert the scarce blood flow toward the that a patient in shock might often have disease processes