Download Shock LO`s - PBL-J-2015

Learning Objectives
Blood on the Road
Blood on the Road
Weeks 1 and 2
Classify the causes of shock into broad functional groups?
Two classes of shock
1. Low Stroke Volume
a) Hypovolaemic, a reduction in blood volume, may be internal or external bleeding,
extreme water loss.
b) Cardiogenic; severe mechanical issues with heart, i.e. myocardial infarction.
c) Obstructive; obstruction to blood flow around the circulation. e.g. pulmonary embolism,
even a tension pneumothorax
2. Vasodilation
a) Septic/SIRS; infection or other causes of systemic inflammatory response
b) anaphylactic; inappropriate vasodilation caused by an allergen
c) Neurogenic; caused by injury to nervous system in the area that controls neurogenic
vasomotor control.
Identify the signs and symptoms of shock?
Clinical Features of Shock (Colledge et al. Davidson's Principles and
practice of Medicine)
Low-flow shock, e.g. hypovolaemia, cardiogenic shock
a) rapid, shallow respiration
b) Cold clammy skin
c) Tachycardia (>100/min)
d) Hypotension (systolic BP < 100 mmHg)
e) Drowsiness, confusion, irritability (late)
f) Oliguria
g) Multi-organ failure
Vasodilated shock, e.g. sepsis, anaphylaxis
a) Rapid shallow respiration (very early)
b) Warm peripheries
c) Tachycardia
d) Hypotension
e) Drowsiness, confusion, irritability (late)
f) Oliguria
g) Multi-organ failure
List the sequence of clinical signs that appear as a patient continues to bleed.
Circulatory failure and shock as a patient continues to bleed, as described on page 186, of
Davidson's Principles and Practice of Medicine.
• the reduction in levels of oxygen which fails to meet the metabolic requirements,
• The classical images of shock caused by hypovolaemic, cardiogenic and obstructive
circulatory failure is, cold extremities, reduced peripheral pulses, weak central pulses and
evidence of low cardiac output.
• Early haemorrhagic shock, a narrowed pulse pressure, idicates the combination of
hypocolaemia, and also activation of the sympathetic nervous system with noradrenaline
induced vasoconstriction raising the DBP.
Describe the time-line of the changes, in particular defining the compensatory
mechanisms appearing in progressive hypovolaemia and the change in signs as
compensation fails.
The Body responds to rapid blood loss by activation the heamatologic, cardiovascular,
renal and neuroendocrine systems.
Learning Objectives
Blood on the Road
Blood on the Road
Weeks 1 and 2
“The cardiovascular system initially responds to hypovolemic shock by increasing the heart
rate, increasing myocardial contractility, and constricting peripheral blood vessels. This
response occurs secondary to an increased release of norepinephrine and decreased
baseline vagal tone (regulated by the baroreceptors in the carotid arch, aortic arch, left
atrium, and pulmonary vessels). The cardiovascular system also responds by
redistributing blood to the brain, heart, and kidneys and away from skin, muscle, and GI
tract.” http://emedicine.medscape.com/article/760145-overview#a0104
Without fluid and blood resuscitation and/or correction of the underlying pathology causing
the hemorrhage, cardiac perfusion eventually diminishes, and multiple organ failure soon
follows.
Be aware of the positive feedback of progressive damage in irreversible shock
Describe the role of the autonomic nervous system in the body's response to shock.
“Do not rely on systolic BP as the main indicator of shock; this practice results in delayed
diagnosis. Compensatory mechanisms prevent a significant decrease in systolic BP until
the patient has lost 30% of the blood volume. More attention should be paid to the pulse,
respiratory rate, and skin perfusion. Also, patients taking beta-blockers may not present
with tachycardia, regardless of the degree of shock.”
http://emedicine.medscape.com/article/760145-clinical#a0217