What is shock?
- Inadequate oxygen delivery to the tissues
- A condition of severe hemodynamic and metabolic dysfunction characterized by reduced tissue perfusion, impaired oxygen delivery and inadequate cellular energy production.
10 clinical Signs of Shock
(5 to do with specifics, 5 to do with circulation)
1. Reduced level of mentation (head)
2. Increased respiratory rate and effort (lungs)
3. Tachycardia (or bradycardia in cats) (heart) + ionotropy
4. Decreased GI blood flow/ GI ulceration (gut)
5. Decreas
Where are epinephrine (adrenaline) & norepinephrine is released from?
adrenal glands & vasomotor endplates
Epinephrine and norepinephrine stimulate an increase in:
- Heart rate
- Cardiac contractility (ionotropy)
- Vasoconstriction (except distributive shock)
- Endocrine response to conserve water - not making much pee!!!
3 major endocrine responses to shock
1. Epinephrine and norepinephrine released from the adrenal glands & vasomotor endplates
- Immediate response
2. Antidiuretic hormone released from the pituitary
- To conserve water
- Response within minutes
3. Renin-Angiotensin-Aldosterone (RAS) system
-
Shock is associated with what two general things?
Increased sympathetic output
Increased endocrine response
Angiotensin
A normal blood protein produced by the liver, angiotensin is converted to angiotensin I by renin (secreted by kidney when blood pressure falls). Angiotensin I is further converted to angiotensin II by ACE (angiotensin converting enzyme). Angiotensin II is
Ace inhibitor
Drug that causes dilation of blood vessels and lowers blood pressure, prevents heart attacks, strokes, and congestive heart failure. ACE stands for angiotensin-converting enzyme, which normally constricts blood vessels. (e.g. benazepril)
What are the 3 stages of shock?
1. Early Compensatory Shock
2. Early Decompensatory Shock
3. Late Decompensatory Shock
Describe Early Compensatory Shock
� Appropriate cardiovascular compensation; physiologic responses successfully maintain normal (or exaggerated) blood pressure
�Clinical signs:
- Tachycardia, normal or elevated BP, normal or increased pulses, hyperemic mm, CRT< 1 sec
� Easily missed, anim
baroreceptor reflex
reflex that maintains appropriate blood pressure; responds to changes in pressure in the aorta and carotid arteries
Describe Early Decompensatory Shock
�The compensatory mechanisms have difficulty keeping up
�Associated with clinical signs of shock:
-Tachycardia, tachypnea, poor peripheral pulses, hypotension, prolonged CRT, pale mm, hypothermia, depressed mentation
�Redistribution of blood flow:
-Decrea
Describe Terminal Shock; irreversible
� Intrinsic compensatory mechanisms no longer provide oxygen delivery
� Clinical signs:
- Slowed heart rate (relative), pale cyanotic mm, absent CRT, weak / absent pulses, severe hypotension, hypothermia, mentally unresponsive / coma, no urine production.
What are the 4 broad categories of shock? (Based on pathophysiologic mechanisms)
�
� Cardiogenic
� Hypovolemic
� Obstrucitve
� Distributive = vasodilatory = hyperdynamic
A patient can suffer from more than one category
Cardiogenic Shock
� Inadequate ventricular pump function
� May be due to:
-Arrhythmias
-Myocardial failure (ie. Cardiomyopathy)
-Valvular dysfunction (ie. Severe mitral valve disease)
Describe Hypovolemic Shock
�Profound decrease in intravascular (blood) volume
-Loss of 30-40% of circulating blood volume
OR
-10-15% dehydration
�Inadequate blood volume to deliver to vital organs
�Hypoperfusion
Etiology
-Blood loss / hemorrhage
�Internal
�External
-Dehydration
�Po
How much blood loss will result in clinical signs of shock?
Expect at least 30% blood loss for clinical signs of shock to be present
Describe Non-Cardiogenic, Obstructive Shock
-Diminished cardiac output secondary to compression on the vascular system or obstruction to blood flow
-Blood can't get to the heart, therefore blood can't be ejected from the heart!
-Examples
�Gastric dilation volvolus
�Tension pneumothorax
�Pericardial
Describe Distributive (Vasodilatory) Shock
-A fundamental maldistribution of blood flow; and an inability of tissues to extract oxygen
-Failure of the vascular smooth muscle to constrict
�Vasodilatory shock
�Normally 70% of blood volume is in the venous system
�Massive vasodilation leads to
-Massi
How do the clinical Signs of Shock change when the shock is distributive?
(all circulatory signs of shock are opposite)
warm extremities
bounding peripheral pulses
injected mucous membranes (brick red)
Rapid capillary refill time (< 1 sec)
But:
- Normal to increased CO
What are some common causes for distributive (vasodilatory) shock?
-Sepsis (Endotoxemia)
-Anaphylaxis
-Drug reactions
-Massive trauma
-> But...final common pathway for decompensatory shock of any cause
How does sepsis cause vasodilatory shock?
There is a proinflammatory and procoagulant response to invading pathogens (bacteria) causing vasodilation
What are some proposed mechanisms for vascular failure?
-Vascular cell death due to prolonged hypotension
-Inadequate oxygen extraction by the tissues
-Increased prostaglandin vasodilatory activity
-Activation of Nitric Oxide
-Deficiency in ADH (vasopressin)
Nitric Oxide
A biologic effector molecule with a broad range of activities that, in macrophages, function as a potent microbicidal agent that kills ingested organisms. It is also a vasodilator, and is released by many small neurons; alters blood flow as well as neuron
Decompensation in distributive shock
� Decreased cardiac contractility
� Decreased CO
� Poor peripheral pulses
� Hypotension
� Pale mm
� Prolonged CRT > 2-3 seconds
At what point do you have severe hypotension? (without anesthesia)
- Systolic < 90 mmHg
- MAP <60 mmHg
Femoral pulses are absent once systolic BP gets how low?
< 40 mmHg
Peripheral pulses are absent once systolic BP gets how low?
Peripheral pulses (dorsal pedal, radial) are absent when systolic BP < 60 - 70 mmHg
What are good things to monitor when an animal is showing signs of shock?
Heart Rate & Rhythm
- pulse quality
- auscultate
- recommend an EKG
MM Colour and CRT
Blood pressure
Urine output (urine = good)
PCV & total solids (Baseline; 15minutes; 30-60 minutes)
Lactate production (< 2)
Blood gas analysis
Blood glucose/BUN
Central
Describe Central venous pressure
� Normal CVP is 0-5 cmH2O
� The measurement is determined by venous return and right ventricular compliance
� CVP should be regarded as a trend. It is conventional to volume load an under-resuscitated patient to a target CVP of 8 - 10 cmH2O
What are 7 possible consequences of shock?
- GI hemorrhage / ulceration
- Acute renal failure
- Bacterial translocation
- Endotoxemia / sepsis
- Disseminated intravascular coagulation
(DIC) (Blood clotting abnormalities)
- Respiratory failure (ARDS)
- Multiple organ failure