Assessment of respiratory patients, like most medical patients, involves an understanding of the anatomy and physiology which functions behind the scenes and how changes in those processes affect patient presentation. Particular changes in a patient’s body will manifest as specific findings during assessment. Airway patency, mechanics of ventilation and ventilation/perfusion ratio are important components of the life support chain for patient survival.
Airway patency
Patent means open and free from obstruction. The term patent or patency is used frequently in the practice of medicine. When referring to a patient’s airway, patent means that air is able to move easily throughout the length of airway. This means that the nose and mouth, trachea and the bronchi and alveoli are open, free of constriction from spasm, like in asthma, and clear of foreign body or secretions, like in pneumonia or CHF.
Airway patency is important because the ability to transport gases into (oxygen) and out of the body (carbon dioxide) represents a core function in maintaining homeostasis. Put simply, if a patient does not maintain a patent airway their body will not function for long.
Mechanics of ventilation
Breathing is actually a two-step process. Though sometimes (and incorrectly) used interchangeably the terms ventilation and respiration make up those steps. Ventilation is the act of moving air in and out of the body. Respiration is the exchange of gases at the cellular level.
The diaphragm is a flat sheet of muscle which divides the chest cavity from the abdominal cavity. When a patient breathes in, the diaphragm flattens out and the rib cage lifts increasing the amount of space in the chest cavity. This decreases the pressure in the chest which causes air to rush into the lungs. The pressure difference between the chest cavity and the outside environment maintains a patient’s ability to ventilate. An inability to ventilate means that a patient will not be able to exchange gases in the lungs and the remainder of the chain of life support will fail.
Ventilation/perfusion ratio
Once oxygen reaches the alveoli at the end of the airway it diffuses into the blood in the capillaries because the blood has a lower concentration of oxygen than the air the patient inhaled. In the same way, carbon dioxide leaves the blood for the alveoli to be expelled from the body.
In order for this exchange of gases to occur, there must be a match in the amount of air moving into the lungs and the amount of blood circulating around the lungs. A decrease in the amount of oxygen, like in a hypoxic environment, keeps the blood from being fully saturated. A decrease in blood flow to the lungs, like in a pulmonary embolus, will keep the available oxygen in the lungs from being fully absorbed.
What is a pneumothorax?
In the chest cavity, the lungs are surrounded by a thin membrane which forms two layers called pleura. The inner layer surrounds the lungs and their support structures while the outer layer attaches to the inside of the chest wall. The two layers are essentially in contact with each other with just a small amount of fluid in between.
A pneumothorax is a condition in which the two pleural layers have air between them. In the setting of trauma a pneumothorax occurs from a puncture wound. The pressure of air from the outside, which would normally fill the lung through the airway, pushes into the pleural space causing the pneumothorax to grow.
A pneumothorax can still occur without trauma, however. A spontaneous pneumothorax is one which occurs in the absence of external trauma. In these cases, a rupture of lung tissue allows air to escape through the inner plural membrane and into the plural space. A history of smoking places a patient at increased risk for spontaneous pneumothorax.
A progressing pneumothorax
If untreated, a basic pneumothorax, also called simple, can progress into a tension pneumothorax. Air is able to enter the pneumothorax but is unable to escape.
As the size of the pneumothorax increases the lung on the affected side has less space in which to expand. In an attempt to compensate the body increases the volume and rate of breathing, gradually increasing the size of the pneumothorax. Left untreated, a tension pneumothorax can be fatal.
A pneumothorax affects both the mechanics of ventilation and the ventilation/perfusion ratio. The mechanics are impacted when the diaphragm contracts and the lung expands in response to a decrease in pressure in the chest cavity. If the patient has a pneumothorax the space the lung ordinarily fills is occupied, reducing the volume of each breath in the affected lung. This decrease in volume also affects the ventilation/perfusion ratio. A normal amount of blood is entering the lungs but with less air volume available blood leaves the lungs without becoming fully saturated.
Treatment options for pneumothorax, both simple and tension, are largely limited for basic level providers to supportive care. If allowed in your system for your level of licensure, needle decompression or chest tube placement are the preferred prehospital treatment for a tension pneumothorax. A simple pneumothorax generally only requires supportive therapy which is transporting the patient in a position of best breathing and comfort and administering oxygen if the patient has signs of hypoxia.
Additional respiratory assessment options
In addition to the standard medical assessments for respiratory complaints, all EMS providers can use end-tidal capnography to obtain a clearer picture of the patient’s status. Because capnography measures exhaled carbon dioxide it gives the provider a perspective on the patient’s airway patency, ventilation quality and ability to exchange gases both in the lungs and throughout the body. In order to obtain a normal waveform the patient’s body has to take in oxygen, circulate it, turn the oxygen into carbon dioxide and then reverse the whole process to exhale the CO2.
Conclusion
After gathering Jeff’s history and assessing him you determine that he is at risk for a spontaneous pneumothorax as a smoker with a recent illness and cough. This differential diagnosis is further supported by Jeff’s low pulse oximetry reading and the decreased lung sounds on his left side. Since he does not appear to have a tension pneumothorax, however, you elect simply to provide oxygen and continue to assess him until the ALS transport unit arrives.
At the hospital, Jeff is confirmed to have a pneumothorax by X-ray. He has a chest tube placed and is admitted for observation. He is expected to make a full recovery.
