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Management of Shock in Cats: They’re Not Just Small Dogs
Marie K. Holowaychuk, DVM, Diplomate ACVECC
[email protected]
Introduction
There are many aspects of critical care that are unique to the cat. The physiologic
response to shock, monitoring techniques used, and methods of resuscitation are different in
cats in comparison to dogs. Although the underlying etiologies and pathophysiology of shock
are similar in the two species, care must be taken to treat cats appropriately in order to
avoid life-threatening consequences.
Definition
The medical dictionary defines shock as “a medical emergency in which the organs
and tissues of the body are not receiving adequate blood flow, thus depriving them of oxygen
and allowing the buildup of waste products”. Essentially, shock occurs when the delivery of
oxygen to the tissues does not meet their oxygen requirement. The body compensates by
diverting blood flow to the heart and brain. Other organs including the gastrointestinal (GI)
tract, pancreas, kidneys, and lungs sustain ischemic injury as a result. Ultimately, there is
death of renal tubular cells resulting in kidney insufficiency, GI ischemia leading to bacterial
translocation, and acute lung injury and impaired pulmonary gas exchange. In cats, the
“shock organ” or organ that is most affected during shock is the lung. Thus, cats will often
present with signs localizing to the respiratory system including tachypnea, respiratory
distress, and pale or cyanotic mucous membranes. Cytokines (i.e., tumor necrosis factor-α,
interleukin-1) are also released and cause a systemic inflammatory response. Anaerobic
metabolism occurs leading to excess lactate production and subsequent metabolic acidosis.
If left untreated, eventually shock will lead to cellular dysfunction, organ failure, and
ultimately death.
Classification
There are several classification schemes used to categorize shock including those
based on underlying etiology (e.g., cardiogenic, hypovolemic, hemorrhagic, septic, traumatic,
anaphylactic), anatomic location affected (e.g., heart, blood [loss], vascular), and
identification of the hemodynamic defect (e.g., hypovolemic, cardiogenic, distributive,
obstructive). Classification by the hemodynamic defect (Table 1) is helpful to understand
the pathophysiologic mechanisms of shock and to consider therapies that will reverse the
dysfunctions. However, shock is complex and it is important to realize that most clinical
forms of shock have many underlying mechanisms affecting the animal simultaneously.
Therefore, there is no universal treatment for each category of shock that will suit every
patient.
Hypovolemic shock is a common cause of shock in cats. It occurs due to an actual
(absolute) or perceived loss (relative) of intravascular volume. Hemorrhage is considered
an absolute cause of hypovolemic shock because it involves an actual loss of intravascular
(blood) volume. Examples of clinical presentations for cats with absolute hypovolemic shock
due to hemorrhage include trauma, coagulopathies, or GI hemorrhage. Absolute
hypovolemic shock can also be caused by non-hemorrhagic events that involve a large loss in
plasma volume. Examples include severe dehydration, polyuria, vomiting/diarrhea, and
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third space losses (e.g., abdominal or pleural effusion). Anaphylaxis also has characteristics
of absolute hypovolemic shock as endothelial damage can enable the leakage of large
volumes of plasma from the intravascular to the interstitial spaces, resulting in peripheral
edema. Relative hypovolemic shock occurs when there is no loss of intravascular (blood or
plasma) volume; however, because of venous or arterial dilation, there is a relative
inadequacy of intravascular volume. This term is not used very commonly anymore as most
people categorize this type of shock as distributive.
Table 1: Common Causes of Shock in Cats
Hypovolemic
Cardiogenic
 Hemorrhage (trauma,
 Cardiomyopathy
coagulopathy)
(dilated,
 Profuse vomiting
hypertrophic,
and/or diarrhea
unclassified)
 Severe polyuria
 Severe arrhythmias
 Marked internal fluid
loss (pleural,
peritoneal, interstitial)
 Severe dehydration




Distributive
Sepsis
Pancreatitis
Severe tissue
trauma
Anaphylaxis



Obstructive
Pericardial
tamponade
Restrictive
pericarditis
Pulmonary
thrombo-embolism
Cardiogenic shock occurs due to a decrease in cardiac output and is most commonly
seen in cats with cardiomyopathy, arrhythmias, or other conditions that adversely affect
myocardial contractility. Many of these cats are concurrently in congestive heart failure.
Because of this, the presenting clinical signs are not just characteristic of shock, but can also
include additional signs such as pulmonary crackles, decreased lung/cardiac sounds due to
pleural effusion, jugular distension, or a heart murmur.
Distributive shock occurs when there is dysfunction of the microcirculation due to
inappropriate arterial or venous dilation resulting in abnormal blood flow. Most often
vasodilation is a consequence of inflammatory mediators that are released and lead to the
production of nitric oxide, a potent vasodilator. This can occur in cats with systemic
inflammatory response syndrome (SIRS), sepsis, or severe pancreatitis. Conversely,
anaphylaxis is another cause of distributive shock resulting in the IgE-mediated release of
vasoactive substances (e.g., histamine, amine, tumor necrosis factor-α, prostaglandin,
leukotriene) from mast cells, which cause massive vasodilation.
Obstructive shock happens when there is an obstruction of blood flow from the heart
or returning to the heart. Clinical examples of obstructive shock include pericardial
tamponade due to pericardial effusion or pulmonary or aortic thromboembolism. The
clinical signs associated with obstructive shock vary depending on the location of
obstruction. For instance, pericardial tamponade can cause pulses paradoxus (i.e., a weaker
pulse on inspiration and a stronger pulse on expiration), whereas aortic thromboembolism
can result in an absence of femoral pulses.
Clinical Stages and Signs
Shock has been traditionally separated into three clinical stages that illustrate the
progression: compensatory, early decompensatory, and decompensatory shock. Cats are
different than dogs in that they rarely present with signs of compensatory shock, but are
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much more likely to show signs of early decompensatory or decompensatory shock. During
the compensatory stage of shock, the body is able to maintain adequate cardiac output
despite a mild to moderate loss of intravascular volume. However, the compensatory stage
cannot last indefinitely without treatment and ultimately systemic vascular resistance will
decrease, cardiac dysfunction will occur, and decompensation begins. Eventually, complete
circulatory collapse occurs and death can occur.
Compensatory stage: The signs of compensatory shock are often overlooked or
mistaken as “normal”. These signs include a normal to mildly increased heart and
respiratory rate, injected (bright pink to reddish) mucous membranes, shortened capillary
refill time (< 1 sec), normal mentation, normal blood pressure, and normal to increased
(bounding) pulses. Injected mucous membranes and increased pulse pressure are rarely
detected in cats as opposed to dogs.
Early decompensatory stage: Cats and dogs most commonly present during the early
decompensated stages of shock. Signs noted during this stage include tachycardia, normal to
decreased pulse pressure, hypotension, pale mucous membranes, prolonged capillary refill
time, decreased mentation, and decreased body temperature. Tachycardia does not occur in
cats as often as dogs during this stage and should not be an expected finding. Cats that have
all of the other signs should be considered in shock and treated accordingly.
Decompensatory (terminal) stage: Clinical signs of decompensatory shock include a
low heart rate, severe hypotension, pale or grey mucous membranes, absent capillary refill,
weak or absent pulses, decreased heart sounds, low body temperature, stuporous or
comatose mentation, and decreased or absent urine production. If aggressive resuscitation
is not provided, cardiopulmonary arrest and death will occur.
Cats typically present with a trilogy of signs during shock regardless of the stage that
include hypothermia, hypotension, and bradycardia. It is important to note that a heart
rate < 160 bpm in a visibly sick cat is a concerning finding and the possibility of shock should be
considered, especially if other signs of shock are seen.
Monitoring and Quick Diagnostic Tests
Thorough and frequent physical examinations focusing on perfusion parameters are
important when monitoring patients during resuscitation from shock. Monitoring cats can
be particularly difficult given that changes in their physical perfusion parameters (i.e., pulse
quality, capillary refill time, mucous membrane color, extremity temperature) are often
subtle compared to those in dogs. For example, while femoral and dorsal pedal pulses are
easily detected in most dogs, dorsal pedal pulses can be difficult to palpate even in normal
healthy cats. Likewise, detecting subtle changes in femoral pulse quality is a skill that only
those with excellent tactile sensation possess. Nevertheless, it is important that attempts be
made to palpate both dorsal pedal and femoral pulses in cats during shock resuscitation. A
change in pulse strength or an absence or gain of a pulse can help to gauge response to
resuscitation efforts. Similarly, vital signs and other perfusion parameters should be
monitored frequently to ensure an appropriate response to resuscitation (Table 2).
Table 2: Perfusion Parameters and the Desired Change during Resuscitation
Parameter
During Shock
Desired Change
Presence of pulse/quality
Absent, poor/weak
Present, normal
Heart rate
< 160 bpm
> 160 bpm
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Respiratory rate
Extremity temperature
Blood pressure
Mucous membrane colour
Capillary refill time
Rectal temperature
Urine production
Mentation
Lactate
Tachypneic
Cool
Systolic < 90 mmHg
Pale/grey/white
Prolonged or absent
< 37oC
Minimal or absent
Depressed, stupor, coma
> 2 mmol/L
Normal
Normal
Systolic > 110 mmHg
Pale pink or pink
1-2 seconds
> 37oC
Normal (1-2 mL/kg/hour)
Alert and responsive
< 2 mmol/L
Blood pressure monitoring should be used to confirm the physical examination
findings. It is important when measuring blood pressure using either Doppler or
Oscillometric devices to ensure that the cuff size is appropriate (width 30-40% of limb
circumference) as small cuffs might over-estimate blood pressure and large cuffs might
under-estimate blood pressure. Normal pressure is 120/80 mmHg (mean arterial pressure
[MAP] 90 mmHg) and hypotension is typically defined as a systolic blood pressure [SBP] 
90 mmHg or a MAP  70 mmHg. Doppler ultrasonographic blood pressure devices measure
the systolic blood pressure when the inflated cuff is released and blood flow and arterial wall
motion occur creating the characteristic “whooshing” sound. Research studies have shown
that in anaesthetized cats Doppler measurements more closely reflect the mean arterial
blood pressure; however, this is debatable in awake or ill cats. A study investigating Doppler
blood pressure in critically ill cats revealed that cats with an increase in Doppler blood
pressure ≥ 20 mmHg were more likely to survive. Oscillometric blood pressure devices
detect pulsatile arterial wall vibrations by an automatically inflating/deflating cuff. The cuff
is inflated until no vascular vibrations (oscillations) are detected and then deflated.
Throughout the deflation cycle, the average oscillations and corresponding cuff pressures
are computer analyzed to determine the systolic, diastolic, and mean arterial pressures.
Oscillometric devices are most appropriate for monitoring trends (they can be set to
measure every 1-30 minutes). Oscillometric devices generally underestimate systolic blood
pressure in cats but are fairly accurate for mean and diastolic blood pressures.
Unfortunately, their accuracy in measuring blood pressure in small or hypotensive animals is
decreased. Therefore, they are most accurate in large cats (> 5 kg) but may not be as
accurate with tachycardia, rapidly changing heart rates, or shock/vasoconstricted states.
Lactate: When perfusion and oxygen delivery are inadequate, anaerobic metabolism
increases resulting in increased lactate production and a metabolic acidosis. Normal blood
lactate levels are < 2 mmol/L. Mild hyperlactatemia is 2-4 mmol/L, moderate
hyperlactatemia is 5-8 mmol/L, and severe hyperlactatemia is > 8 mmol/L. Lactate
measurements can also be trended over time to assess the adequacy of fluid resuscitation or
improvement in oxygen delivery during treatment for shock. Blood lactate can be easily
measured in practice by the use of an iSTAT® or other handheld devices. When handheld
devices were compared to standard laboratory analyzers using blood samples from cats, the
iSTAT® and LactatePro® (http://www.vetlab.com/Lactate%20Pro.htm) were found to be
the most accurate.
ECG monitors are becoming more frequently used in small animal practice. Many
blood pressure and pulse oximetry machines have an ECG as well. An ECG is helpful for
assessing cats with bradycardia, tachycardia, pulse deficits, or a history of heart disease, and
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for enabling moment-to-moment monitoring of heart rate during resuscitation from shock.
If hyperkalemia is measured or suspected (e.g., urethral obstruction, uroabdomen, kidney
failure), an ECG should be performed to assess for associated conduction disturbances such
as small to absent P-waves, tall T-waves, or a widened QRS complex. Severe bradycardia (HR
< 140 bpm) in critically ill cats is an emergency that requires immediate intervention.
Pulse oximetry is a non-invasive method for assessing oxygenation in cats with shock
and respiratory signs. It measures the peripheral oxygen saturation (SpO 2), which is an
indirect measure of SaO2 and thus PaO2 using the oxygen-hemoglobin dissociation curve. A
SpO2 of 90% corresponds to a PaO 2 of 60 mmHg (severe hypoxemia) and a SpO2 of 95%
corresponds to a PaO2 of 80 mmHg (normal).
Electrolyte and Glucose Measurements: Electrolytes can be measured on a chemistry
analyzer or blood gas machine to rule out severe abnormalities (potassium < 3.0 or > 6.0
mEq/L, sodium < 140 or > 170 mEq/L, ionized calcium < 1.0 mmol/L). A blood glucose
measurement should always be measured for cats in shock using a chemistry machine or
glucometer. Hyperglycemia is common in cats due to the stress of hospitalization or illness;
however, hypoglycemia can occur in cats with shock. A blood glucose measurement < 80
mg/dL (< 4.5 mmol/L) in a cat in shock necessitates treatment with dextrose
supplementation.
Focused Assessment Using Sonography for Trauma (FAST): Abdominal FAST is a
simple and rapid ultrasound examination that can be performed emergently in cats to detect
intra-abdominal free fluid suggestive of hemorrhage or organ rupture (e.g., uroabdomen).
Veterinarians with limited previous ultrasound experience can perform a FAST examination in
less than five minutes. It can be used with a scoring system (score 0-4) to evaluate for the
presence of fluid (anechoic) in four areas. With the cat in lateral recumbency (preferably
right lateral), use the ultrasound probe to assess for fluid: 1) just caudal to the xiphoid
process, 2) on the midline over the urinary bladder, and at the 3) left and 4) right flank regions.
During the FAST examination, the urinary bladder and gallbladder can also be visualized. Note
that even though an organ may be seen on radiographs or ultrasound and appear intact,
organ rupture (e.g., urinary bladder, urethra, gallbladder) can still be present. FAST can be
performed on initial presentation and serially thereafter to monitor for the presence of
abdominal fluid.
If abdominal fluid is found, an abdominocentesis can be performed to obtain a sample of
fluid for analysis. If the sample appears bloody, place it in a red top blood tube to ensure that it
does not clot. If the fluid sample clots, it is possible that a blood vessel or organ (e.g., spleen)
was inadvertently aspirated. Otherwise, perform a PCV and TS on the fluid; a PCV > 10% is
suggestive of hemorrhage. If uroabdomen is suspected, measure the potassium or creatinine
concentration of the fluid and compare it to the periphery (serum). A fluid:serum ratio of
potassium > 1.4:1 or creatinine > 2:1 is consistent with a uroabdomen.
Thoracic FAST can also be performed in cats presenting in shock with increased
respiratory effort or respiratory distress, to quickly determine if fluid is present in the thoracic
cavity. Differentials for the fluid will depend on the history and presenting complaint, but could
range from hemorrhage (i.e., traumatic shock) to pyothorax (i.e., septic shock) or chylothorax
(i.e., cardiogenic shock). PCV and TS (if bloody) or fluid cytology will be helpful if a sample of
fluid can be obtained for analysis.
Treatment
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Early recognition and resuscitation are very important for the successful treatment of
shock in cats. There are many facets of the treatment of shock in cats that are unlike that for
dogs. Cats can be difficult to resuscitate and often require more conservative management
to avoid complications such as fluid overload or pulmonary edema.
Fluid Resuscitation: Vascular access is a must when providing appropriate fluid
resuscitation to cats in shock. Subcutaneous fluids are NOT appropriate in cats with
evidence of shock and poor perfusion. Vascular access can be obtained via the cephalic or
medial saphenous veins. The volume of fluid required for treating shock is based on the cat’s
weight and estimated blood volume. If crystalloid fluids are used, one full blood volume
might need to be administered over one hour. The blood volume of cats is estimated to be
45-60 mL/kg and is less than that of dogs. The response to fluid resuscitation should
determine the volume of fluid that is administered. The recommended regimen for fluid
resuscitation during shock is to divide the total volume to be given over one hour into
smaller volumes and use frequent monitoring to assess the cat’s status. Divide the total fluid
volume into four aliquots (10-15 mL/kg) and recheck the cat’s perfusion parameters every
15 minutes to determine the response. Not all cats in shock will require replacement of a full
blood volume to treat their shock. If the clinical signs of shock resolve after the first 15
minutes, there is no need to proceed with another bolus of fluid. Consider giving a fluid
bolus by drawing the amount of fluid up into a syringe and manually “pushing” it into the cat
over 10-15 minutes. Conversely, a fluid pump can be set to deliver the volume over 15
minutes. Balanced electrolyte solutions (i.e., LRS, Plasmalyte-148, Plasmalyte-A) are
preferred over normal saline (0.9% NaCl); however, any isotonic fluid that is available can be
used. Because cats in shock are typically hypothermic, it is beneficial to warm fluids prior to
administration if possible.
Hypertonic saline (3-7%) is another fluid that can be considered during fluid
resuscitation of shock. It is not commonly used in cats because they are small enough that
isotonic fluids can be given rapidly and in large enough volumes to achieve the desired effect
of intravascular volume expansion. However, hypertonic saline has other benefits including
the reduction of intracranial pressure in cats with head trauma. In that case, a dose of 2-4
mL/kg is recommended over 15-20 minutes. Care should be taken not to administer
hypertonic saline too quickly as it can cause bronchoconstriction. Hydroxyethyl starch
(HES) solutions (e.g., Voluven®, Vetstarch®) are tetrastarch colloid solutions containing
hydrolyzed amylopectin dissolved in a crystalloid solution (typically NaCl 0.9%). They are
administered for volume resuscitation in patients with hypoalbuminemia secondary to
sepsis or trauma that are not responsive to crystalloid therapy alone. Potential
complications of HES solution administration include volume overload, kidney injury, and
coagulopathies. Typically, boluses are given in 2.5-5 mL/kg volumes over 10-15 minutes,
not exceeding a total daily dose of 20-40 mL/kg/day. Cats are especially sensitive to boluses
of HES solutions and will vomit if they are given too quickly.
Blood Transfusions: Cats in shock due to traumatic episodes might be anemic and
hypoproteinemic secondary to blood loss. If the cat is indeed in hypovolemic shock due to
hemorrhage and cannot be stabilized with fluid resuscitation alone, a whole blood
transfusion might be necessary. Remember that cats MUST be blood typed (or cross
matched) prior to receiving a blood transfusion of any kind, as type A-B incompatibilities in
cats can result in lethal transfusion reaction.
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Analgesia: Providing adequate pain relief to cats that are in shock is also extremely
important. Cats that are in shock will not be able to elicit the same signs of pain that are
recognized in otherwise normal cats (e.g., tachycardia, restlessness, irritability, withdrawn
demeanor). Therefore, if the cat has experienced a traumatic event (e.g., dog attack, HBC) it
must be assumed that the cat is painful and its pain should be treated accordingly. Ideally,
reversible opioid medications should be used, but it is best to titrate them to effect. If
additional pain relievers are needed, ketamine (IV) or gabapentin (PO) can be considered.
Non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided in cats with shock due to
the risk of kidney injury.
Table 3: Suggested Analgesics
Pain-relieving Medication
Fentanyl
Hydromorphone
Buprenorphine
Ketamine
Dose
1-2 mcg/kg IV bolus followed by 2-5
mcg/kg/hr IV continuous rate infusion
0.02-0.05 mg/kg IV or IM every 4-6 hours
0.005-0.02 mg/kg IV or IM every 6-8 hours
0.5-1.0 mg/kg IV bolus followed by 0.1-1.0
mg/kg/hr IV continuous rate infusion
Heat Support: It is very common for cats in shock to be hypothermic. The low body
temperature is often exacerbated by the low heart rate and subsequent low cardiac output.
Unfortunately, the hypothermia will also heighten the bradycardia by depressing the sinus
node. Therefore, it is very important that attempts be made to warm cats during shock
resuscitation. This can be effectively achieved by applying external warming sources such as
a circulating war water blanket, warm air blower, or heated towel to the cat. Additionally,
administering warmed (rather than room temperature) intravenous fluids can be helpful.
Oxygen Therapy: Oxygen supplementation should also be administered to cats that
are in shock and whose SpO2 is < 95%. This will help to improve oxygen delivery to tissues.
It should be provided in such a way that does not cause stress to the cat. The easiest
methods during the resuscitation period are flow-by (blow-by) or mask oxygen. Mask
oxygen will enable a higher concentration of oxygen to be provided to the cat; however, not
all cats will tolerate the mask. In those cases, directing the oxygen flow toward or near the
cat’s nose and mouth is sufficient. If the cat is being housed in a cage during its resuscitation,
an oxygen cage or oxygen hood may be used if available.
Electrolyte and Blood Glucose Disturbances: Hypoglycemia should be immediately
treated with an IV bolus of dextrose. Dilute 0.5-1 mL/kg of 50% dextrose to a concentration
of 12.5-25% and administer it over 2-3 minutes. Recheck the blood glucose 10-15 minutes
after the bolus to ensure that it is normal. If it is low again, administer another IV bolus and
add 2.5-5% dextrose to the IV fluids. Calcium gluconate 10% 0.5-1 mL/kg IV should be
administered over 10-15 minutes in cats with ionized hypocalcemia or hyperkalemia with
associated ECG abnormalities. Hyperkalemia should also be treated with IV dextrose (as
above), as well as sodium bicarbonate (1 mL/kg IV over 10-15 minutes) or regular insulin
(0.5 U/kg) and IV dextrose 50% (2 mL/kg) concurrently.
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