Ambient Air, Airway, and Mechanics of Ventilation

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Ambient Air, Airway, and Mechanics of Ventilation
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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.

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Objectives (contd)

• Discuss ventilation and cellular oxygenation.
• Discuss adequate and inadequate ventilation.

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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.

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Introduction (contd)

• The first three components, ambient air, the
  airway, and ventilation are presented here.

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Physiology

• Composition of Ambient Air
• What is breathed in directly impacts the
  available oxygen for cellular use.

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Percentage and Partial Pressures of Gases in
Ambient Air at Sea Level
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Physiology (contd)

• 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

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Airway obstruction can occur at several levels of
the upper and lower airway, including the
nasopharynx, oropharynx, posterior pharynx,
epiglottis, larynx, trachea, and bronchi.
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Physiology (contd)

• 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

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Physiology (contd)

• Mechanics of Ventilation
• Factors affecting ventilation
• Compliance issues
• Airway resistance issues

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A normal bronchiole
A constricted bronchiole
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Physiology (contd)

• 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

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The pleural lining of the lung
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Physiology (contd)

• 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

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Physiology (contd)

• 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

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Physiology (contd)

• 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.

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Physiology (contd)

• 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.

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Physiology (contd)

• 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.

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Physiology (contd)

• 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.

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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.

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Case Study (contd)

• 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.

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Case Study (contd)

• 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

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Case Study (contd)

• 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?

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Case Study (contd)

• Primary Assessment Findings
• Patient responsive to verbal stimuli, AOx3
• 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

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Case Study (contd)

• 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?

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Case Study (contd)

• 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

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Case Study (contd)

• 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

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Case Study (contd)

• 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

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Case Study (contd)

• 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?

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Case Study (contd)

• 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

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Case Study (contd)

• Explain how the following interventions may help
  improve the patient's condition
• Oxygen administration
• Positive pressure ventilation
• Occlusive dressing placement

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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.