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Lesson 2
Physiology of Life and Death
Maintenance of Life
• Body systems
– Interrelated
– Interdependent
• Every cell and
every organ
work together to:
– Sustain cellular energy production
– Maintain vital metabolic processes
Energy
• Energy powers all body functions
– Energy sustains cellular and organ functions
• Cells make energy from oxygen and
glucose
• Energy is stored in the form of adenosine
triphosphate (ATP) molecules
• Without energy, cellular functions cease
• The goal is to help ensure that the
patient’s body maintains energy
production
Systems and Components
(1 of 2)
• Airway
– Must be patent
• Breathing (lungs)
– Adequate oxygen must:
• Reach alveoli
• Cross alveolar/capillary wall
• Enter the circulation
– Carbon dioxide (CO2) must be removed
Systems and Components
(2 of 2)
• Circulation
– Distributes red blood cells (RBCs)
– Ensures adequate number of RBCs
– Transports oxygen to every cell in every organ
Airway (1 of 3)
• An open airway is
essential to deliver
air (oxygen) to the
alveoli
Airway (2 of 3)
• Normal air movement
– Inhalation results from negative intrathoracic
pressure as the chest expands
• Air fills the alveoli
Airway (3 of 3)
• Normal air movement (cont’d)
– Exhalation results from increased
intrathoracic pressure as the chest relaxes
• Forces air out of the alveoli
Breathing (Lungs) (1 of 2)
• When air reaches the
alveoli:
– Oxygen crosses the
alveolar–capillary
membrane
• Oxygen
– Enters the RBCs
– Attaches to hemoglobin
for transport
Breathing (Lungs) (2 of 2)
• CO2 in the plasma and cells
– A by-product of aerobic metabolism and
energy production
– Crosses the alveolar–capillary membrane into
the alveoli
– Is removed
during exhalation
Circulation (1 of 2)
• Oxygen-enriched
RBCs are pumped
through the blood
vessels of the body
to deliver oxygen to
target organs
Circulation (2 of 2)
• Oxygen is then
off-loaded from the
RBCs to fuel the
metabolic processes
of the cell
• CO2 is transferred
from the cells to the
plasma for
elimination via the
lungs
Cellular Metabolism — Aerobic
(1 of 3)
• Aerobic metabolism
– Most efficient method of energy production
– Uses oxygen and glucose to produce energy
via chemical reactions known as glycolysis
and the Krebs cycle
– Produces large amounts of energy
– Waste products
• Carbon dioxide
• Water
Cellular Metabolism — Aerobic
(2 of 3)
• Aerobic metabolism is dependent upon:
– Adequate and continuous supply of oxygen
– Patent airway
– Functioning lungs (pulmonary system)
– Functional heart
• Pump blood to the cells
Cellular Metabolism — Aerobic
(3 of 3)
• Aerobic metabolism is dependent upon
(cont’d):
– Intact vascular system
– Adequate supply of RBCs
• Carry and transport oxygen
• Remove waste
Aerobic Metabolism
Cellular Metabolism —
Anaerobic (1 of 2)
• An injury that affects any of these three
components of the oxygen delivery system
will affect energy production
• Anaerobic metabolism is a metabolic
process that functions in the absence of
oxygen
Cellular Metabolism —
Anaerobic (2 of 2)
• Metabolism without adequate oxygen
• Uses stored glucose in the form of
glycogen for energy production
• Capable of sustaining energy
requirements only for a short time
• Produces only small amounts of energy
– 19-fold decrease in energy
– Increased lactic acid as a by-product
Anaerobic Metabolism
Shock
• Inadequate energy production required to
sustain life
• Change from aerobic to anaerobic
metabolism
– Secondary to hypoperfusion
– Delivery of oxygen is inadequate to meet
metabolic demands
– Decreased energy production
• Cellular and organ death
Consequences of
Hypoperfusion (1 of 4)
• Cellular hypoxia
• Decreased ATP (energy) production
• Cell dysfunction
– Lactic acid buildup
– Low pH
Consequences of
Hypoperfusion (2 of 4)
• Cell dysfunction (cont’d)
– Autodigestion of cells
• Leads to cellular death and organ failure
– Entry of sodium and water into the cell
• Cellular edema (swelling) worsens with
overhydration
– Continuation of cycle
• Unless oxygenated red blood cells reach the
capillaries
– If further loss of intravascular (blood) volume
• The cycle continues
Consequences of
Hypoperfusion (3 of 4)
• Inadequate ATP
• Cells and organs do not function properly
– Hypothermia
• Decreased heat production
Consequences of
Hypoperfusion (4 of 4)
• Cells and organs do not function properly
– Acidosis
• What little ATP is being produced is used to shiver
• Lactic acid production increases
– Coagulopathy
• As body temperature drops, blood clotting
becomes impaired
Triangle of Death
Cascade of Death
Types of Shock
• Shock is any condition that causes
decreased cellular energy production
• Hypovolemic
– Dehydration
– Hemorrhage
• Distributive
– Neurogenic
– Septic
– Anaphylactic
– Psychogenic
• Cardiogenic
– Pump failure (intrinsic versus extrinsic)
Trauma-Related Types of
Shock
• Hypovolemic
– Dehydration
– Hemorrhage
• Distributive
– Neurogenic
– Septic
– Anaphylactic
– Psychogenic
• Cardiogenic
– Pump failure (intrinsic versus extrinsic)
Hemorrhagic Shock
• Most common cause of hypoperfusion
after trauma
• Internal or external blood loss
• Classes of shock
Neurogenic “Shock”
• Associated with spinal cord injury
• Interruption of the sympathetic nervous
system resulting in vasodilation
• Patient has normal blood volume but
vascular container has enlarged, thus
decreasing blood pressure
Cardiogenic Shock — Extrinsic
• Results from external compression of the
heart
• Ventricles cannot fully expand
– Less blood is ejected with each contraction
• Blood return to the heart is decreased
• Causes from trauma include:
– Pericardial tamponade
– Tension pneumothorax
Pathophysiology of Shock
(1 of 6)
• Shock is progressive
• Changes in shock include:
– Hemodynamic
– Cellular (metabolic)
– Microvascular
• Compensatory mechanisms
– Short-term
– Will fail without interventions
Pathophysiology of Shock
(2 of 6)
• The heart must be an effective pump
– Primed by return of blood through the vena
cavae
• Starling’s Law
• Stroke volume (SV)
– Amount of blood ejected with each contraction
– Depends on adequate return of blood
– If blood volume decreases
• SV will decrease
• Cardiac output (CO) will decrease unless the heart
rate (HR) increases
CO = SV × HR
Pathophysiology of Shock
(3 of 6)
• Adequate blood pressure
– Required to maintain cellular perfusion
• CO is one factor in maintaining blood
pressure (BP)
• If CO falls
– Vasoconstriction occurs
– Systemic vascular resistance (SVR) increases
in an attempt to maintain BP
BP = CO × SVR
Pathophysiology of Shock
(4 of 6)
• Vasoconstriction leads to the ischemic
phase of shock
• Microvascular changes
– Early
• Precapillary and postcapillary sphincters constrict
• Resulting in ischemia in the tissues
• Must then produce energy anaerobically
Pathophysiology of Shock
(5 of 6)
– As acidosis increases:
• The precapillary sphincters relax
• The postcapillary sphincters remain
constricted
• This results in stagnation of blood in the
capillary bed
Pathophysiology of Shock
(6 of 6)
– Finally:
• The postcapillary sphincters relax
• Results in washout
• Releases microemboli
• Aggravates acidosis
• Causes infarction of organs by microemboli
Signs Associated with Types
of Shock
Organ System Failure Due to
Shock
• If not recognized and promptly corrected,
shock will lead to organ dysfunction:
– First in oxygen-sensitive organs
– Then in other less oxygen-sensitive organs
• This cascading effect will lead to
multi-organ dysfunction syndrome and
patient death
– Failure of one major organ system
• Mortality rate of approximately 40%
– As additional organ systems fail, mortality
approaches 100%
Organ Sensitivity to Hypoxia
• Extremely sensitive
– Brain, heart, lungs
• Moderately sensitive
– Kidneys, liver,
gastrointestinal tract
• Least sensitive
– Muscle, bone, skin
Organ System Failure Due to
Shock (1 of 4)
• Acute renal failure
– May result if oxygen delivery is impaired for
more than 45–60 minutes
– Will result in:
• Decreased renal output
• Reduced clearing of toxic products
Organ System Failure Due to
Shock (2 of 4)
• Acute respiratory distress syndrome
(ARDS)
– Results from:
• Damage to the alveolar cells
• Hyper-resuscitation (fluid overload)
– Results in:
• Leakage of fluid into the interstitial spaces and
alveoli
Organ System Failure Due to
Shock (3 of 4)
• Hematologic failure
– Impaired clotting cascade
• May result from:
– Hypothermia
– Dilution of clotting factors from fluid administration
– Depletion of clotting factors
Organ System Failure Due to
Shock (4 of 4)
• Hepatic failure
– Results from prolonged shock
• Overwhelming infection
– Results from decreased function of the
immune system due to ischemia and loss of
energy production
Summary (1 of 3)
• Cellular function depends on adequate
energy production
• Adequate energy production depends on a
continuous and adequate supply of oxygen
• A continuous and adequate supply of
oxygen depends on:
– Patent airway
– Functioning lungs
– Functioning heart
– Intact circulation
Summary (2 of 3)
• Interruption of the oxygen supply for any
reason will lead to anaerobic metabolism
• Anaerobic metabolism provides insufficient
energy to sustain cellular function for any
length of time
• This leads to cellular dysfunction and cell
death, organ dysfunction and organ death,
and ultimately patient death
Summary (3 of 3)
• Knowledge, understanding, and early
recognition of impaired energy production
resulting from airway compromise,
pulmonary injury, and impaired circulation
are key to early recognition of shock.
• Prompt intervention by prehospital care
providers to correct these conditions can
prevent the cascade of cellular dysfunction
that leads to organ death.
• This will improve the survival rate for
victims of traumatic injury.
Questions?