TRANSITION SERIESTRANSITION SERIES

Topics for the Advanced EMTTopics for the Advanced EMT

CHAPTERCHAPTER

Ambient Air, Airway, and Ambient Air, Airway, and Mechanics of VentilationMechanics of Ventilation

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ObjectivesObjectives

• 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)Objectives (cont’d)

• Discuss ventilation and cellular oxygenation.

• Discuss adequate and inadequate ventilation.

IntroductionIntroduction

• 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)Introduction (cont’d)

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

PhysiologyPhysiology

• 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)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)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)Physiology (cont’d)

• Mechanics of Ventilation– Factors affecting ventilation

Compliance issues Airway resistance issues

A normal bronchiole A constricted bronchiole

Physiology (cont’d)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)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)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)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)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)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)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 StudyCase 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)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)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)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)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)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)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)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)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)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)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)Case Study (cont’d)

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

SummarySummary

• 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.