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Chapter 13: Shock
Comprehensive, easily digestible, & aesthetically pleasing notes on Chapter 13: Shock from Jones & Bartlett Emergency Care and Transportation of the Sick and Injured, Twelfth Edition
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Chapter 13 Shock Notes* Introduction
- Shock (hypoperfusion) is defined as inadequate cellular perfusion
- Any compromise in perfusion can lead to cellular injury or death
- In the early stages of shock, the body attempts to maintain homeostasis; however, as shock progresses, from tissues &
organs to organ systems & the whole body, blood circulation slows & eventually ceases
* Pathophysiology
* Perfusion
- The circulation of blood to the tissues in adequate amounts to meet the cell’s needs
- This includes delivery of oxygen & removal of toxic waste products
-Diffusion:
- A passive process in which molecules move from an area with a higher concentration of molecules to an area of lower
concentration
- This is how oxygen & carbon dioxide cross the walls of the alveoli
- The majority of oxygen is carried to the tissues attached to hemoglobin
- Carbon dioxide can be transported in the blood from tissues back to the lungs in three ways:
- Dissolved in the plasma
- Combined with water in the form of bicarbonate
- Attached to hemoglobin
- Carbon dioxide waste products released from cells can combine with water in the bloodstream to form bicarbonate
- Once it reaches the lungs, the bicarbonate breaks back down into carbon dioxide & water & the carbon dioxide is
exhaled
- In cases of poor perfusion (shock):
- Transportation of carbon dioxide out of the tissues will become impaired
- This results in a dangerous buildup of waste products, which may cause cellular damage
- Shock refers to a state of collapse & failure of the cardiovascular system that leads to inadequate circulation (Early recognition
can save lives but requires immediate recognition & rapid transport)
- To protect vital organs, the body directs blood flow from organs that are more tolerant of low flow (such as the skin &
intestines) to organs that cannot tolerate low blood flow (such as the heart, brain, & lungs)
- The cardiovascular system consists of three parts known as the
“perfusion triangle):
- The heart (Pump)
- Blood vessels (Container)
- The blood (Contents)
(When a patient is in shock, one of these three a components are not
working properly)
- Blood pressure is the pressure of blood within the vessels at any moment in time
- Systolic pressure: The peak arterial pressure (Pressure generated every time the heart contracts)
- Diastolic pressure: The pressure maintained within the arteries while the heart rests between beats
- Pulse Pressure is the difference between systolic & diastolic pressures (systolic - diastolic = pulse pressure)
- It signifies the amount of force the heart generates with each contraction
(A pulse pressure less than 25 mm Hg may be seen in patients with shock)
- Blood flow through the capillary beds is regulated by the capillary sphincters (Circular muscular walls that constrict & dilate)
- These sphincters are under the control of the autonomic nervous system, which regulates involuntary functions
- Capillary sphincters also respond to other stimuli, such as:
- Heat
- Cold
- The need for oxygen
- The need for waste removal
(Regulation of blood flow is determined by cellular needs)
, - Perfusion also requires adequate:
- Oxygen exchange in the lungs
- Nutrients in the form of glucose in the blood
- Waste removal, primarily though the lungs
- Mechanisms are in place to help support the respiratory & cardiovascular systems when the need for perfusion of vital organs is
increased (This includes the autonomic nervous system & hormones)
- The sympathetic side of the autonomic nervous system, which is responsible for the fight or flight response, will assume more
control of the body’s functions during a state of shock (This response by the autonomic nervous system causes the release of hormones
such as epinephrine & norepinephrine)
- Hormones are triggered when the body senses pressure falling
- This can cause an increase in:
- Heart rate
- Strength of cardiac contractions
- Peripheral vasoconstriction (vasoconstriction in nonessential areas, primarily the skin & GI tract)
(This response causes all the signs & symptoms of shock in a patient)
* Causes of Shock
- Many different socks result from three basic causes:
- Pump failure
- Poor vessel function
- Low fluid volume
* Types of Shock
* Cardiogenic Shock
- Caused by inadequate function of the heart (pump failure)
- A major effect is the backup of blood into the pulmonary vessels
- The resulting building forces fluid out of the capillary beds that surround the alveoli, leading to what’s known as pulmonary edema
- Cardiogenic shock develops when the heart can’t maintain sufficient output to meet the demands of the body
- Cardiac output is the volume of blood that the heart can pump per minute, & is dependent on several factors:
- The heart must have adequate strength, which is largely determined by the ability of the heart muscle to contract
(myocardial contractility)
- The heart must receive adequate blood to pump (preload)
- The resistance of flow in the peripheral circulation must be appropriate (afterload)
* Obstructive Shock
- Caused by a mechanical obstruction that prevents an adequate volume of blood from filling the heart chambers
- Three of the most common examples of obstructive shock are:
- Cardiac tamponade (pericardial tamponade):
- Collection of fluid between the pericardial sac & the myocardium (pericardial effusion) becomes large enough to prevent
ventricles form filling with blood
- Caused by blunt or penetrating trauma that causes hemorrhage around the heart
- Signs & symptoms are known as Beck triad:
- Presence of jugular vein distention
- Muffled heart sounds
- Narrowing pulse pressure where the systolic & diastolic pressures start to merge
- Tension pneumothorax:
- Cause by damage to lung tissue
- Air normally held within the lung escapes into the chest cavity
- The lung collapses, & if the pneumothorax is left untreated, air will accumulate in the chest cavity & apply pressure to the
organs, including the heart & the great vessels
- Pulmonary embolism:
- A blood clot that occurs in the pulmonary circulation that blocks blood flow through the pulmonary vessels
- If massive:
- Can result in complete backup of blood in the right ventricle
- Leads to catastrophic obstructive shock & complete pump failure
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