Prehospital Emergency Care Pathophysiology

Prehospital: Emergency Care
Eleventh Edition
Chapter 8
Pathophysiology
Copyright © 2018, 2014, 2010 Pearson Education, Inc. All Rights Reserved

Learning Readiness
• EMS Education Standards, text p. 177.
• Chapter Objectives, text p. 177.
• Key Terms, text p. 177-178.
• Purpose of lecture presentation versus textbook reading
assignments.

Setting the Stage
• Overview of Lesson Topics
– Cellular Metabolism
– Components Necessary for Adequate Perfusion

Case Study Introduction
EMTs Patty Mirabal and Gus Oakes are on the scene of a
52-year-old man who is complaining of difficulty breathing.
The patient is breathing shallowly and rapidly. He gasps,
“Need … help … can’t … breathe.”

Case Study (1 of 5)
• What purposes does breathing serve?
• In what ways does a problem with breathing affect the
body?

Introduction
• Oxygen and glucose are necessary for normal cell
function.
• Illnesses and injuries can disturb the delivery of oxygen
and glucose and removal of waste by-products.
• A fundamental purpose of emergency care is maintaining
adequate delivery of oxygen and glucose.

Cellular Metabolism (1 of 7)
• Cellular metabolism is the process in which the body
breaks down molecules of glucose to produce energy.
– Aerobic metabolism takes place when oxygen is
available.
– When there is a lack of oxygen, the body uses a less
effective process called anaerobic metabolism.

• Aerobic Metabolism
– The initial steps of cellular metabolism do not require
oxygen, but produce only small amounts of energy.
– Oxygen is required to complete the process of
extracting energy from glucose and removing the
wastes produced by the process.

AAerobic Metabolism. Glucose Broken Down in the
Presence of Oxygen Produces a Large Amount of
Energy (ATP)

• Aerobic metabolism
– The initial steps of cell metabolism take place in the
cytosol and are called glycolysis.
▪ Glycolysis produces a small amount of ATP.
▪ Then the process continues in the mitochondria,
where larger amounts of ATP are produced.

– By-products of aerobic metabolism include
▪ heat, carbon dioxide, and water.
– The majority of ATP is used by the sodium-potassium
pump.

The Sodium/Potassium Pump
Energy (ATP) is required to pump sodium molecules out of
the cell against the concentration gradient.

– By-products of aerobic metabolism include
▪ heat, carbon dioxide, and water.
– The majority of ATP is used by the sodium-potassium
pump.
– If the pump fails, the cell will die.

• Anaerobic Metabolism
– The first stage of cell metabolism is anaerobic.
▪ The waste product produced is pyruvic acid.
▪ Without oxygen, pyruvic acid is converted to lactic
acid.
▪ Accumulation of lactic acid is harmful to body
functions.

• Anaerobic Metabolism
– Sodium/Potassium Pump Failure
▪ In anaerobic metabolism, the combination of
inadequate energy production and accumulating
lactic acid result in failure of cell processes.

Anaerobic Metabolism
Glucose broken down without the presence of oxygen
produces pyruvic acid that converts to lactic acid and only a
small amount of energy (ATP).

Components Necessary for Adequate
Perfusion (1 of 52)
• Perfusion
– Delivery of oxygen, glucose, and other substances to
the cells and the elimination of waste products from
the cells.
– Requires interaction of multiple components.

Perfusion (2 of 52)
• Components
1. Composition of ambient air
2. Patency of the airway
3. Mechanics of ventilation
4. Ventilation/Perfusion ratio
5. Transport of O₂ and CO₂ by the blood

Perfusion (3 of 52)
• Components
6.Blood volume
7. Pump function of the myocardium
8. Systemic vascular resistance
9.Microcirculation
10.Blood pressure

Perfusion (4 of 52)
• Any alteration in the components may lead to poor
cellular perfusion.
• Inadequate perfusion can shift cells from aerobic to
anaerobic metabolism.
• Emergency care focuses on restoring and maintaining
the components.

Case Study (2 of 5)
Gus quickly moves next to the patient to better assess his
condition, while Patty unzips the airway kit and begins to
select equipment to begin patient care.

Case Study (3 of 5)
• What, specifically, will Gus be assessing to determine the
patient’s condition?
• How will Patty know what equipment and treatment the
patient needs?
• What is happening to the patient at the cellular level?
• What will happen if the EMTs do not intervene quickly?

Perfusion (5 of 52)
• Composition of Ambient Air
– The concentration of oxygen in the ambient air
influences oxygen that ends up in the alveoli for gas
exchange.
– Ambient air contains approximately 79 percent
nitrogen, 21 percent oxygen, and trace amounts of
argon and carbon dioxide.

Table 8-1 Partial Pressure of Gases in
Ambient Atmosphere at Sea Level
Gas % Partial Pressure
Oxygen 20.95 159.2 mmHg
Nitrogen 78.08 593.4 mmetreHg
Argon 0.93 7.1 mmHg
Carbon Dioxide 0.03 0.2 mmHg
99.99% 759.9 mmH

Perfusion (6 of 52)
• Composition of Ambient Air
– FiO₂ is the fraction of inspired oxygen.
– FDO₂ is the fraction of delivered oxygen.
– One way to improve cellular oxygenation is to provide
supplemental oxygen.

Perfusion (7 of 52)
• Patency of the Airway
– A patent airway is open and not obstructed by any
substance.
– Establishing an open airway is one of the first steps in
emergency care.
– Failure to establish or maintain a patent airway leads
to cellular hypoxia and patient death.

Perfusion (8 of 52)
• Patency of the Airway
– Locations of airway obstructions
▪ Nasopharynx
▪ Oropharynx
▪ Epiglottis
▪ Larynx
▪ Trachea
▪ Bronchi and bronchioles

Airway Obstruction Can Occur at Several
Levels of the Upper and Lower Airway
Including the nasopharynx, oropharynx, posterior pharynx,
epiglottis, larynx, trachea, and bronchi.

Perfusion (9 of 52)
• Mechanics of Ventilation
– An intact thoracic cavity is integral to normal
ventilation.
– Boyle’s Law defines and illustrates how ventilation
occurs in the body.

Perfusion (10 of 52)
– Pleural linings
▪ Visceral pleura
▪ Parietal pleura
– Damage to one or both pleural linings can disrupt
normal ventilations.

Click on the Event that Occurs Just Prior to the
Movement of Air into the Lungs on Inhalation
A. The diaphragm relaxes.
B. The size of the chest cavity decreases.
C. Pressure within the chest decreases.
D. The intercostal muscles relax.

– Accessory muscles
▪ Used when extra effort is needed for inhalation or
exhalation
– Indication of a heighted ventilatory effort
– Requires more energy

Table 8-2 Accessory Muscles (1 of 2)
Accessory Muscles of Inhalation
The following accessory muscles of inhalation are used to
increase the size of the thoracic cavity and generate a
greater negative pressure, increasing the flow of air into the
lungs.
• Sternocleidomastoid muscles lift the sternum upward.
• Scalene muscles elevate ribs 1 and 2.
• Pectoralis minor muscles elevate ribs 3 to 5.

Table 8-2 Accessory Muscles (2 of 2)
Accessory Muscles of Exhalation
The following accessory muscles of exhalation are used to
decrease the size of the thoracic cavity and to create a
more positive pressure, forcing air out of the lungs.
• Abdominal muscles contract and increase the pressure
inside the abdominal cavity, forcing the diaphragm to
move higher against the lungs.
• Internal intercostal muscles contract and pull the
sternum and ribs downward.

– Airway Compliance and Resistance
▪ High resistance and low compliance increase the
effort needed to breathe and lead to hypoxia.
▪ Compliance disorders make it hard for the lung
tissue to inflate.
▪ Resistance disorders result from constriction of
small airways.

– Pleural Space
▪ Negative pressure is maintained in the pleural
space or cavity.
▪ An injury to the chest wall or lung that opens the
space can draw air, by way of negative pressure,
into the space.
▪ The lung may collapse from the air accumulation.

– Minute Ventilation
▪ The amount of air moved in and out of the lungs in
one minute.
▪ Minute volume = tidal volume × frequency of
ventilation.
▪ To ensure adequate ventilation, both the tidal
volume and respiratory rate must be adequate.

– A decrease in tidal volume decreases the minute
volume.
– A decrease in respiratory rate decreases the minute
volume.
– A decrease in minute volume reduces the air
available for gas exchange in the alveoli.

– Alveolar ventilation
▪ The amount of air moved in and out of the alveoli
in one minute.
▪ Dead space air does not reach the alveoli during
breathing.
▪ An average of 350 mL of a 500 mL tidal volume
reaches the alveoli.

– Hypoxia can occur from:
▪ A low tidal volume.
▪ A slow ventilatory rate.
▪ A fast ventilatory rate.
– Typically pulmonary illnesses and trauma affect
the tidal volume more significantly.

• Regulation of Ventilation
– Breathing is an involuntary process controlled by
the ANS.
▪ Receptors measure oxygen (O₂), carbon
dioxide (CO₂), and hydrogen ions (pH).
▪ Receptors send signals to the brain to adjust
the rate and depth of respiration.

– Chemoreceptors
▪ Central
▪ Peripheral
– Hypercapnic Drive
– Hypoxic Drive

– COPD patients have a tendency to retain CO₂.
▪ They become insensitive to small changes in CO₂.
▪ Their respirations are controlled by decreased
oxygen levels; this is called the hypoxic drive.

Respiration is Controlled by the Autonomic
Nervous System
Receptors within the body measure oxygen, carbon dioxide, and hydrogen ions
and send signals to the brain to adjust the rate and depth of respiration.

• Control of Ventilation
– Lung Receptors
▪ Three types of receptors within the lungs provide
impulses to help regulate respiration:
1. Irritant receptors
2. Stretch receptors
3. J-receptors

– Respiratory Centers in the Brainstem
1. Ventral respiratory group
2. Dorsal respiratory group
3. Pontine respiratory center

Case Study (4 of 5)
The patient is working hard to breathe, and has pale, moist
skin. He is using accessory muscles to breathe, but seems
to be moving very little air. The patient appears sleepy as if
on the verge of exhaustion.
Patty selects a bag-mask device to assist the patient’s
ventilations, and connects it to supplemental oxygen.

Case Study (5 of 5)
• What medical problems could lead a patient to have such
severe difficulty breathing?

• Ventilation/Perfusion Ratio (V/Q)
– V/Q ratio is the relationship between alveolar
ventilation and perfusion of the alveolar capillaries.
▪ The relationship influences gas exchange.
▪ Can be used to explain causes of hypoxemia.

Overview of Ventilation and Perfusion

– In an ideal state the amount of ventilation is equally
matched to the amount of perfusion.
▪ However, a perfect match does not actually occur.
▪ Overall, perfusion exceeds ventilation, but the
situation is highly functional.

– When ventilation is better than perfusion, there is
wasted ventilation.
– When perfusion is better than ventilation, there is
wasted perfusion.

Possible Causes of Ventilation Disturbances

– Pressure Imbalance
▪ If the air pressure in an alveolus exceeds the blood
pressure in the capillary bed, blood flow through
the capillary stops.
– Occurs normally in the apex of the lungs.
– Occurs when the systemic blood pressure
decreases.

– Ventilatory Disturbances
▪ A condition that decreases the amount of air
reaching the alveoli, such as asthma, results in
wasted perfusion.
– Hypoxemia and hypoxia result.
– Treatment is aimed at increasing lung
ventilation.

– Perfusion Disturbances
▪ Ventilation is normal, or even increased, but blood
flow through the lungs is decreased.
▪ There is wasted ventilation, leading to hypoxemia
and hypoxia.
▪ Administering oxygen may help, but the perfusion
disturbance must be corrected.

• Transport of O₂ and CO₂ by the Blood
– Oxygen must be continuously delivered by the blood
to the cells.
– Carbon dioxide must be carried back to the lungs to
be blown off in exhalation.
– A disturbance in the transport system may lead to
cellular hypoxia and hypercarbia.

– Gases move from areas of higher concentration to
areas of lower concentration.

– Oxygen Transport
▪ O₂ is transported in the blood in two ways.
– 1.5 to 3 percent is dissolved in plasma.
– 97 to 98.5 percent is attached to hemoglobin
molecules.

– Oxygen Transport
▪ Role of hemoglobin
– A protein molecule that contains iron.
– There are four iron sites per hemoglobin.

– Carbon Dioxide
▪ Transported in the blood in three ways.
– 7 percent is dissolved in plasma.
– 23 percent is attached to hemoglobin in RBCs.
– 70 percent is transported by the lungs in the
form of bicarbonate.

Oxygen is Transported in the Blood Two
Ways
Attached to hemoglobin and dissolved in plasma. Carbon
dioxide is transported in the blood three ways: as
bicarbonate, attached to hemoglobin, and dissolved in
plasma.

– Alveolar/capillary gas exchange
▪ After inhalation, the alveolar air is high in O₂ and
low in CO₂.
▪ Venous blood in the capillaries surrounding the
alveoli is low in O₂ and high in CO₂.

Click on the Mechanism by Which Most of
the Oxygen in Blood is Transported
A. Bound to hemoglobin
B. In the form of bicarbonate
C. Dissolved in plasma
D. Carried by white blood cells

• Blood Volume
– A determinant of blood pressure and perfusion is
blood volume.
▪ Adults have 70 mL of blood/kg of body weight.
▪ A 70-kilog adult has 4,900 mL (4.9 L) of blood.

• Blood Volume
– Blood Composition
▪ 45 percent formed elements
▪ 55 percent plasma
– Blood Distribution
▪ Majority of blood in the venous system
▪ Minority of blood in the arterial system

Table 8-3 Distribution of Blood in the
Cardiovascular System
Blood is distributed in the various components of the
cardiovascular system as follows.
Venous 64%
Arterial 13%
Pulmonary vessels 9%
Capillaries 7%
Heart 7%

• Blood Volume
– Hydrostatic Pressure
▪ Force inside the vessel or capillary bed generated
by the contraction of the heart and the blood
pressure.
▪ Hydrostatic pressure exerts a “push” inside the
vessel or capillary.

• Blood Volume
– Plasma oncotic pressure
▪ Keeps fluid inside the vessels to oppose
hydrostatic pressure.
▪ The large plasma proteins have the effect of
“pulling” water into the capillaries.

Hydrostatic Pressure Pushes Water out of the
Capillary. Plasma Oncotic Pressure Pulls Water into
the Capillary

• Pump Function of the Myocardium
– The myocardium must be an effective pump to
maintain perfusion.
▪ Cardiac output (CO) is the amount of blood ejected
from the heart in one minute.
▪ CO = heart rate × stroke volume.

maintain perfusion.
▪ Heart Rate
– Sympathetic
– Parasympathetic

maintain perfusion.
▪ Stroke Volume
– Preload
– Contractility
– Afterload

Effect of Preload on Stroke Volume

Effect of Contractility on Stroke Volume

– Factors that increase cardiac output
▪ Increased heart rate (to a point)
▪ Increased blood volume
▪ Increased myocardial contractility
▪ Sympathetic nervous system stimulation
▪ Beta1 stimulation from epinephrine
▪ Lower diastolic BP

– Factors that decrease cardiac output
▪ Decreased heart rate
▪ Decreased blood volume
▪ Decreased myocardial contractility
▪ Parasympathetic nervous stimulation
▪ Beta1 blockade (beta blockers)
▪ Higher diastolic BP over time

• Systemic Vascular Resistance (SVR)
– SVR is the resistance to blood flow through a vessel.
– Vasoconstriction increases SVR, increased SVR
increases BP.
– Vasodilation decreases SVR, decreased SVR
decreases BP.

Effects of Vasoconstriction and Vasodilation
on Systemic Vascular Resistance

• Systemic Vascular Resistance Effect on Blood Pressure
– Pulse pressure is the difference between the systolic
and the diastolic BP readings.
▪ Systolic BP is a rough indicator of CO.
▪ Diastolic BP is a rough indicator of SVR.

• Microcirculation
– Refers to the flow of blood through the arterioles,
capillaries, and venules

Microcirculation is the Flow of Blood through the
Smallest Blood Vessels: Arterioles, Capillaries, and
Venules
Precapillary sphincters control the flow of blood through the
capillaries.

• Microcirculation
– Precapillary sphincters
▪ Regulatory influences on sphincters
1. Local factors
2. Neural factors
3. Hormonal factors

• Blood Pressure (BP)
– Blood pressure = CO × SVR
▪ Relationship of SV & HR on CO
– Increased SV increases CO.
– Decreased SV decreases CO.
– Increased HR increases CO.
– Decreased HR decreases CO.

• Blood Pressure (BP)
– Blood pressure = CO × SVR
▪ Relationship of CO & SVR on BP
– Increased CO increases BP.
– Decreased CO decreases BP.
– Increased SVR increases BP.
– Decreased SVR decreases BP.

• Blood Pressure
– The general effect of blood pressure on perfusion is:
▪ Increased BP increases cellular perfusion.
▪ Decreased BP decreases cellular perfusion.

• Blood Pressure
– Regulation of BP by Baroreceptors.
▪ Baroreceptors located in the aortic arch and
carotid sinuses detect changes in blood pressure.
▪ Signals are sent to the vasomotor and
cardioregulatory centers in the brainstem.

Baroreceptor Function and Influence on
Blood Pressure

• Blood Pressure
– Regulation of BP by Chemoreceptors
▪ A decrease in blood oxygen level stimulates the
sympathetic nervous system.
▪ Heart rate increases and blood vessels constrict.
▪ Hypoxia can present with pale, cool skin, and
increased heart rate.

Chemoreceptor Function and Influence on
Blood Pressure

Review of Aerobic Metabolism
Components (1 of 4)
1. Oxygen content in ambient air
2. Patency of the airway
3. Minute ventilation
– Ventilatory rate
– Tidal volume
4. Alveolar ventilation
– Ventilatory rate
– Tidal volume

Components (2 of 4)
5. Perfusion in the Pulmonary Capillaries
– Venous volume
– Right ventricular pump function
6. Gas Exchange Between the Capillaries and the Alveoli
7. Content of blood
– Red blood cells and Hemoglobin
– Plasma

Components (3 of 4)
8. Cardiac Output and Determinants
– Heart rate
– Preload
– Stroke volume
– Myocardial contractility
– Afterload

Review of Aerobic Metabolism Components
(4 of 4)
9. Systemic Vascular Resistance
– Sympathetic nervous system stimulation
– Parasympathetic nervous system stimulation
10.Gas Exchange Between the Capillaries and the Cells

Case Study Conclusion (1 of 2)
The patient has a history of chronic obstructive lung
disease and heart failure. He has been increasingly short of
breath for two days, with a sudden worsening today.
With the assistance of an engine crew, Patty and Gus
continue assisting the patient’s ventilations and providing
supplemental oxygen.

Case Study Conclusion (2 of 2)
The crew recognizes the seriousness of the patient’s
condition and is prepared to take further measures, if
needed, to maintain the patient's airway.
Gus calls in a report to the receiving hospital. When they
arrive at the ED, a physician, nurse, and respiratory
therapist are waiting to continue the patient’s care.

Lesson Summary
• Cells require oxygen and glucose to produce energy and
perform work.
• Without adequate ventilation and perfusion, cells engage
in anaerobic metabolism, which produces less energy
and more waste.
• A fundamental purpose of emergency care is to restore
and maintain cell perfusion.

Correct! (1 of 3)
• Your answer is supported by two principles of physics.
– First, according to Boyle’s law, the pressure of a gas
varies inversely with its volume.
– Second, air (a mixture of gases) moves from areas of
higher pressure to areas of lower pressure.

Correct! (2 of 3)
• When the diaphragm and intercostal muscles contract,
the thoracic cavity increases in volume, which lowers the
pressure in the thorax and lungs. Air flows from the
higher atmospheric pressure into the area of lower
pressure within the lungs.
Click here to continue the program.

Incorrect (1 of 4)
• When the diaphragm relaxes, it rises into the chest
cavity, making it smaller, which promotes exhalation.
Click here to return to the quiz.

Incorrect (2 of 4)
• According to Boyle’s law, when the volume of a gas
decreases, such as happens to the gas within the thorax
when the size of the thorax decreases, the pressure of
the gas increases. In the case of ventilation, this action
promotes exhalation.

Incorrect (3 of 4)
• When the intercostal muscles relax, the volume of the
thoracic cavity decreases in size, which increases the
pressure within thorax. This action promotes exhalation.

Correct
• Most oxygen transported in the blood is carried by
hemoglobin. Each molecule of hemoglobin contains iron,
to which the oxygen can bind. Each hemoglobin molecule
provides four binding sites, which allow it to carry up to
four molecules of oxygen.

Correct! (3 of 3)
• The loss of hemoglobin-containing red blood cells, such
as through hemorrhage, is a loss of oxygen-carrying
capacity. Controlling bleeding is a critical way to help
preserve a patient’s ability to deliver oxygen to his cells.
Click here to continue the program.

Incorrect (4 of 4)
• This is not the way most oxygen is transported in the
blood. Return to the quiz to try again.

Copyright

Prehospital Emergency Care Pathophysiology

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