Airway Management, Oxygenation, and Ventilation

1

What is the point of airway management in the prehospital setting?

The point is the same regardless of setting: to ensure adequate oxygenation and ventilation while protecting the patient from aspiration.

Oxygenation is the process of oxygen diffusing to cells down a concentration gradient, while ventilation is the process of gas movement down a pressure gradient. It is possible to have oxygenation without ventilation (passive or apneic oxygenation) and to have ventilation without oxygenation (movement of oxygen-depleted gas). Both are critical. Likewise, oxygenation and ventilation are both dependent on an unobstructed path from the exterior environment to the alveoli. If that path is obstructed by vomitus, blood, excessive secretions, teeth, or the tongue, neither oxygenation nor ventilation can occur.

2

What are the indications for providing airway management?

Interruptions in oxygenation or ventilation, i.e., some type of respiratory failure, or the need to protect the patient’s airway from obstruction.

Acute respiratory failure can roughly be broken into two groups: hypoxic and hypercapnic. If a patient is not maintaining sufficient oxygenation, increased inspired oxygen must be provided. If the patient is not moving sufficient gas to remove carbon dioxide, ventilatory support must be provided. Often, these two overlap, but it is helpful to think of why a patient needs airway support.

3

How can oxygenation and ventilation be assessed?

There are direct and indirect approaches to assessing oxygenation and ventilation. The direct approach involves measurement. Pulse oximetry (SpO ₂ ) uses infrared light projecting through a tissue bed to measure the oxygen saturation of hemoglobin, while end-tidal carbon dioxide (EtCO ₂ ) measures the partial pressure of expired CO ₂ . SpO ₂ directly measures oxygenation and EtCO ₂ measures ventilation.

Indirectly, oxygenation should be assessed through the patient’s mental status (oxygen is required for proper cognitive function), skin color, work of breathing, and degree of dyspnea (the sensation of not being able to breathe). Ventilation can be assessed by estimating the patient’s tidal volume (V _t ). V _t is the volume of air moved in a single breath. It can be assessed by looking at chest rise and fall and, roughly, at the amplitude of the EtCO ₂ waveform. Minute volume (V _m ) is the amount of gas moved in a minute and is calculated by multiplying the V _t by the respiratory rate. If the respiratory rate is too slow, there will be inadequate gas exchange.

Respiratory rate is under complex physiologic control. Tachypnea (rapid respiratory rate) is often a response to hypoxia or increased metabolic need for either more oxygen or more CO ₂ off-loading.

Auscultation of breath sounds can provide useful information about ventilation. The presence of wheezing can indicate bronchospasm of the small airways, crackles can indicate increased interstitial fluid seen in pulmonary edema or presence of pneumonia, while the absence or decreased breath sounds can indicate obstruction of the airways or collapse of the lung.