Anatomy of the Respiratory System
The primary function of the respiratory system is gas exchange. Oxygen is absorbed by the body from inspired air, and carbon dioxide is removed from the body and released into the environment. Oxygen is used by every cell in the body for the production of energy, and carbon dioxide is a waste product of cellular metabolism that becomes dangerous if accumulated. The body can neither store oxygen nor tolerate elevated levels of carbon dioxide for a long period, so respiratory gas exchange must function continually to support life. The respiratory system’s anatomy can be subdivided into three sections: the airway, the lungs, and the muscles of respiration.
The Airway
The airway is the “A” of the ABC resuscitation mnemonic (Airway, Breathing, and Circulation) and is a passageway through which gases are exchanged. The airway can be further divided into two parts: the upper airway (nasal cavity, the oral cavity, the pharynx, and the larynx) and the lower airway (consisting of the tracheobronchial tree).
Nose, Mouth, and Throat
Air inhalation and exhalation can occur through either the nose or mouth and most frequently through both. Each nostril has three turbinates (shelves of cartilage) that filter, heat, and moisten air. Most conscious adults inspire through the nose.
The mouth is defined as the space between the lips, cheeks, tongue, hard and soft palates, and the throat. The throat, or pharynx, begins behind the nose and ends at the top of the trachea and esophagus ( Fig. 10.1 ). The nasopharynx is the area behind the nose, the oropharynx is the area behind the mouth, and the hypopharynx is the deeper (more caudal) part. At the caudal end of the hypopharynx is the beginning of two important structures: the esophagus (part of the gastrointestinal system) and the larynx (located anteriorly to the esophagus).
Larynx
The larynx, or “voice box,” serves two important functions. The first is a conduit for gas exchange, and the second is phonation (speech), which occurs when air passes through movable structures located in the larynx called vocal cords. In order to provide a range of sound, the larynx is relatively narrow at this point, so it can become obstructed in a variety of situations. During inspiration, the epiglottis (a flap of tissue above the larynx) opens like a trap door to allow air to freely pass into the lungs. However, during swallowing, the epiglottis folds back over the laryngeal opening to cover the larynx, preventing food aspiration into the lungs. The epiglottis is an important landmark during endotracheal intubation and can cause severe airway obstruction if it becomes inflamed (epiglottitis).
Lower Airway
Below the larynx is the trachea, a tubular structure supported by cartilage. The trachea splits into the two bronchi, one for each lung, in the upper part of the chest. The bronchi then divide into progressively smaller bronchi (called bronchioles), which terminate at structures called alveoli, where capillaries bring blood very close to the inspired air. There are hundreds of millions of alveoli in the lungs. The alveoli are thin-walled air sacs that look like tiny bunches of grapes. In these structures, oxygen is absorbed from the air, and carbon dioxide is released to be removed from the body by exhalation.
The Pleural Cavity
The lungs are encased in two thin membranes, called pleura, covering the outer surface of each lung and the inner surface of the chest wall including the muscles and ribs. These membranes are constantly sliding across one another during respiration and help maintain a slightly negative pressure within the chest cavity at rest that helps the lungs stay inflated.
The Muscles of Respiration
Chest Wall and Ribs
The chest wall is made up of 12 ribs on each side joined at the sternum anteriorly. The intercostal muscles lie between the ribs and pull the ribs together, making exhalation of air easier.
Diaphragm
The diaphragm is the dome-shaped muscle that separates the chest from the abdomen, and it is the main muscle of respiration. During breathing, the diaphragm moves downward until it is flat, creating negative pressure in the chest, which causes air to rush into the lungs. When it relaxes, it tents upward, which causes air to rush out of the lungs during exhalation. The nerve signals to the diaphragm via the phrenic nerve originate in the upper (cervical) spine, which is why upper cervical spinal cord injuries can lead to respiratory failure.
Respiratory Emergencies
Respiratory emergencies can be categorized as traumatic or nontraumatic, as well as by the location of the pathology to the upper or lower airway or the brain. This chapter will focus on nontraumatic causes. Although most patients in respiratory distress arrive by emergency medical services (EMS) and conduct much of the initial evaluation and initial treatment in the field, the following discussion assumes no prehospital care or evaluation.
Initial Evaluation
When evaluating a patient with a potential respiratory emergency, the emergency department (ED) technician (EDT) should evaluate the following:
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The patient’s general appearance and the pulse and blood pressure readings
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The natural position that the patient is assuming
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The respiratory rate
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The use of accessory muscles of respiration
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The pulse oximeter reading (or the presence of blueness on the nail beds or the lips, called cyanosis)
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The patient’s level of consciousness
The order of evaluation will vary with different clinical circumstances, but the initial actions that should be taken are placing the patient on a cardiac monitor, providing a source of supplemental oxygen, disrobing the patient as appropriate, and positioning the patient on the stretcher in the best possible position ( Table 10.1 ).
| Emergency Evaluation | Initial Tech Management | Additional Adjuncts (if appropriate) |
|---|---|---|
| Airway and Breathing |
|
|
| Circulation |
| 12-lead ECG |
| Exposure |
|
Respiratory Rate
The normal respiratory rate is about 12 to 18 times per minute. Most respiratory emergencies present with a rapid rate (>20 breaths/min). We most frequently estimate the rate, and as you gain more experience, you will become proficient at determining who is breathing very quickly (hyperventilation) without taking the time to precisely measure it. Conversely, patients who are breathing very slowly (hypoventilation) are either at an advanced stage of a variety of disease processes or have central nervous system (CNS) depression, often from an opioid overdose and occasionally from low blood sugar (hypoglycemia). Patients with severe hypoventilation should be taken to a “code” or resuscitation room, given supplemental oxygen, and have an intravenous (IV) line inserted. Except where CNS depression can be quickly reversed (e.g., naloxone for opioids, IV dextrose for hypoglycemia), these patients will need endotracheal intubation and mechanical ventilation.
Patient Positioning
Patients with respiratory compromise arriving by EMS will often be sitting up as erect as possible. This will allow for the best diaphragmatic excursion, which will help with pulmonary mechanics and optimize air exchange. Patients with upper airway obstruction may assume the “sniffing position,” in which the neck is extended to maximize the airflow through the upper airway.
Accessory Muscles
Although the diaphragm is the main muscle of respiration, the muscles between the ribs (intercostal muscles) and some of the neck muscles will be engaged to facilitate respiration during stress from a variety of conditions. Noting whether the patient is engaging these muscles or not may help establish the seriousness of a complaint of shortness of breath.
Pulse Oximeter
Oxygen saturation is often called the fifth vital sign. A pulse oximeter determines the oxygen saturation of hemoglobin by measuring how certain wavelengths of light are reflected by the capillary beds in the ear or the fingernail. When the amount of oxygen in the lungs drops, there is less oxygen for hemoglobin to capture and distribute to the tissues, and the hemoglobin actually changes color (becoming bluer and reflecting light differently than does fully oxygenated hemoglobin). The pulse oximeter is most often placed on the nail bed and gives a continuous update on the hemoglobin saturation, allowing the clinician to know when the patient is getting worse and also to help regulate the amount of supplemental oxygen provided.
Mental Status
Increasing confusion in a patient with apparent breathing difficulties is often an ominous sign. It can represent either low blood flow to the brain (hypotension), low oxygen in the blood (hypoxia), elevated amounts of carbon dioxide in the blood (hypercarbia), or some combination of all three. Hypotension and hypoxia will be apparent from bedside measurements, but a lab test is necessary to confirm elevated carbon dioxide levels.
As mentioned, the critical first steps for any patient with respiratory complaints in the ED are placing the patient on both cardiac and continuous pulse oximetry monitors. Supplemental oxygen should also be provided, if needed. A nasal cannula may be applied to patients with mildly increased work of breathing and mild oxygen desaturation. For patients presenting with significantly increased work of breathing or more profound hypoxia, or for any patient who appears to be in distress, a nonrebreather mask may first be applied with maximal oxygen flow (>15 L/min). If there is ever a question of degree of airway assistance needed, place a nonrebreather mask on the patient, as this can always be replaced with a nasal cannula once the patient has been evaluated and stabilized.
Airway Adjuncts
Breathing is a two-part process involving both ventilation and respiration. Ventilation is the process of moving air in and out of the lungs, whereas respiration refers to the gas exchange process occurring in the alveoli that oxygenates the blood and supplies oxygen to the cells of the body. If either respiration or ventilation is inadequate, the patient can quickly become hypoxic. Performing additional maneuvers and administering oxygen to the patient can be a lifesaving measure.
The goal of any additional airway maneuvers or application of adjuncts is to maintain airway patency. These techniques are often temporary while awaiting a change in patient’s clinical condition or while preparing for a more definitive airway (e.g., intubation).
Opening the Airway
Head-tilt, chin-lift: The head-tilt, chin-lift maneuver is used to quickly open the airway of a patient with no suspected cervical spine injuries. The maneuver must be constantly maintained manually or with an adjunct throughout ventilation.
Procedure
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Place one hand on the patient’s forehead and the other under the jaw.
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Gently apply backward pressure to the patient’s forehead while simultaneously lifting the patient’s jaw with your other hand. Be careful to only apply pressure to the bony part of the chin. Compressing the soft space under the jaw could create an airway obstruction.
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Hold the jaw so that the patient’s teeth are not touching. It may be necessary to slightly retract the lower lip to keep the airway open.
Jaw-thrust: The jaw-thrust is the preferred method for opening the airway of a patient with a suspected cervical spine injury since it does not require any movement of the cervical spine. Additionally, it may be all that is required to maintain airway patency by moving the tongue forward to decrease airway obstruction.
Procedure
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Position yourself at the head of the gurney or bed with the patient in the supine position. Place your forearms on either side of the patient’s head.
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Use your index and middle fingers to apply pressure to the angle and back of the jaw (mandible) to push the mandible up. It may be necessary to slightly retract the lower lip with your thumb to maintain an open airway
Nasopharyngeal airway (NPA): The NPA ( Fig. 10.2 ) is an important airway adjunct in patients with altered mental status and an intact gag reflex or in patients with a clenched jaw. The NPA is a flexible tube that is inserted into one of the nares with the distal tip ending in the nasopharynx, ensuring rescue breaths have a patent path of travel. It is contraindicated in patients with significant facial trauma, especially nasal trauma (See , Basic Airway Adjuncts).
