Download AEMT Transition - Unit 7 - Airway Physiology

TRANSITION SERIES
Topics for the Advanced EMT
CHAPTER
7
Ambient Air, Airway, and
Mechanics of Ventilation
Objectives
• Understand gas composition in the air
and the effects of imbalances on
metabolism.
• Discuss the structure and function of
the airway.
• Discuss determinants of alveolar
ventilation.
Objectives (cont’d)
• Discuss ventilation and cellular
oxygenation.
• Discuss adequate and inadequate
ventilation.
Introduction
• This chapter and the following two
chapters introduce pathophysiological
principles.
• The components associated with
perfusion must all function in unison if
an organism is to survive.
Introduction (cont’d)
• The first three components, ambient
air, the airway, and ventilation are
presented here.
Physiology
• Composition of Ambient Air
– What is breathed in directly impacts the
available oxygen for cellular use.
Percentage and Partial Pressures of Gases in Ambient Air at Sea Level
Physiology (cont’d)
• Patency of the Airway
– Maintaining an airway is one of the most
basic and important steps in prehospital
medicine
– Without an adequate airway, all other
interventions are doomed to fail
– Obstructions can occur at several
anatomic locations
 Upper and lower airway structures
Airway obstruction can occur at several levels of the upper and lower airway,
including the nasopharynx, oropharynx, posterior pharynx, epiglottis, larynx,
trachea, and bronchi.
Physiology (cont’d)
• Mechanics of Ventilation
– Inspiratory and expiratory muscles,
accessory muscles
– Change in intrathoracic pressure is what
creates airflow into and out of the lungs
– Intrathoracic pressure in relation to
atmospheric pressure
Physiology (cont’d)
• Mechanics of Ventilation
– Factors affecting ventilation
 Compliance issues
 Airway resistance issues
A normal bronchiole
A constricted bronchiole
Physiology (cont’d)
• Mechanics of Ventilation
– Pleural Space
 Visceral and parietal pleura envelop the
lungs
 Negative pressure between them
 Damage to either pleura: air or blood
may fill space and cause the lung to
collapse
The pleural lining of the lung
Physiology (cont’d)
• Mechanics of Ventilation
– Minute Ventilation
 Refers to amount of air moved into and
out of the lung in one minute
 Minute ventilation = tidal volume x
frequency
 Changes in tidal volume or frequency can
alter minute ventilation detrimentally
Physiology (cont’d)
• Mechanics of Ventilation
– Alveolar Ventilation
 Refers to the amount of air moved in and
out of the alveoli in one minute
 Takes into account dead space
 Alveoli are the last to be ventilated
during inhalation, and the first to suffer
from poor ventilation when the minute
ventilation drops
Physiology (cont’d)
• Mechanics of Ventilation
– Alveolar ventilation = tidal volume dead space.
– In an average-size adult patient, the
alveolar ventilation can be calculated:
 (500 mL – 150 mL) = 350 mL alveolar
ventilation
– If something causes a drop in tidal
volume, alveolar ventilation will change
before dead space.
Physiology (cont’d)
• Mechanics of Ventilation
– Alveolar Ventilation
 Although the patient may breathe faster
to improve his minute ventilation, the
amount of air available for gas exchange
in the alveoli may be insufficient if the
tidal volume is low.
Physiology (cont’d)
• Mechanics of Ventilation
– Alveolar Ventilation
 The dead space will fill first, regardless of
the volume of air breathed in.
 This means alveolar ventilation suffers.
 To improve gas exchange in the patient
with an inadequate tidal volume, you
must provide positive pressure
ventilation to increase tidal volume and
move more air into the alveoli.
Physiology (cont’d)
• Mechanics of Ventilation
– Alveolar Ventilation
 By placing a patient with a low tidal
volume on an oxygen mask, you will
enrich the air in the dead air space with
little getting to the alveoli; the patient
needs ventilation.
Case Study
• Just as you finish completing the
morning equipment list on the
ambulance, you get toned out for an
industrial accident. Upon your arrival,
you are met by a man who says his
buddy “got a big hole in his chest from
some scrap metal that flew outta the
thrashing machine.”
Case Study (cont’d)
• Although you are not familiar with
exactly what a “thrashing machine”
does, you do recognize that a hole in
the chest wall can create significant
problems.
• When you arrive at the patient's side,
there is blood on his shirt, and he looks
like he is struggling to breathe.
Case Study (cont’d)
• Scene Size-Up
– 45-year-old male patient
– BSI precautions are taken
– MOI is a traumatic injury
– There is only one patient
– Ingress and egress can occur without
difficulty from the site
Case Study (cont’d)
• What organs or tissues may be injured
due to this mechanism of injury?
• The patient's obvious dyspnea points to
an injury to what body system?
• What precautions for your safety should
you take?
Case Study (cont’d)
• Primary Assessment Findings
– Patient responsive to verbal stimuli,
A&Ox3
– Airway patent, no foreign bodies or fluid
– Labored breathing on inhalation, patient
speaking in 1-2 word sentences
– Respiratory rate is 28 times/minute
– Peripheral pulse is present, chest injury
is bleeding minimally
Case Study (cont’d)
• Is this patient a high or low priority?
Why?
• What care should be provided
immediately?
• If the penetration injury pierced the
right parietal pleura, what would you
expect breath sounds on that side to
be?
Case Study (cont’d)
• Medical History
– Patient shakes his head “no” when you
ask about medical problems
• Medications
– He states “vitamins” when you ask
about meds
• Allergies
– Patient denies any known allergies
Case Study (cont’d)
• Pertinent Secondary Assessment
Findings
– Pupils reactive to light, airway patent
– Penetration to 4 ICS on right anterior
chest
– Breath sounds absent on right side
– Pulse oximeter reads 90% on room air
Case Study (cont’d)
• Pertinent Secondary Assessment
Findings
– Muscle tone is noted to all extremities
– Patient denies traumatic fall or other
injury
– Skin cool and dry, color ashen
– B/P 110/78, Pulse 108, Respirations 26
Case Study (cont’d)
• Will you change your treatment based
on information you have now learned?
• How can the change in tidal volume
precipitate anaerobic metabolism?
• Why is the patient's tachypnea not
really helping his oxygenation status?
Case Study (cont’d)
• Care provided:
– Spinal precautions taken
– Occlusive dressing applied to injury
– PPV with high-flow oxygen provided
– Paramedic intercept initiated prior to
departure
– Patient packaged and transported by
ambulance
Case Study (cont’d)
• Explain how the following interventions
may help improve the patient's
condition:
– Oxygen administration
– Positive pressure ventilation
– Occlusive dressing placement
Summary
• The airway is considered to be the
“channel of life.” With no airway, the
patient cannot survive.
• Adequate oxygen levels in the inspired
air and a good ventilatory effort are
also integral to assuring adequate
oxygen levels for cellular metabolism.