by Julie J. Martin, MS
Anatomy and Physiology
In order to live and function normally, humans need oxygen. When you breathe in, oxygen reaches your lungs, where it comes into contact with blood. Blood absorbs the oxygen and transports it to all parts of your body. This process is referred to as respiration.
Oxygen in the air reaches your lungs by first passing through your mouth or nose and into the throat, or pharynx. It then goes past your epiglottis, through your voice box, or larynx, and into your windpipe, or trachea. The trachea divides to become the left and right main bronchi, which enter the lungs.
Inside the lungs the main bronchi divide repeatedly and eventually become small tubes called bronchioles. At the end of the bronchioles are tiny air sacs called alveoli.
Oxygen in the alveoli is absorbed into nearby blood vessels called capillaries. At the same time, carbon dioxide, a gas in the blood that must be removed, passes into to the alveoli and back out through the airways. This process is called gas exchange.
The movement of oxygen into the lungs during inhalation occurs when the diaphragm, the intercostal muscles between the ribs, and other muscles nearby cause the chest cavity to expand. Gas rich in carbon dioxide is exhaled when the lung tissue passively returns to its original size. The process of moving air into and out of the lungs is referred to as ventilation.
Reasons for Procedure
Respiratory problems may occur when air cannot adequately move through the airways or when the alveoli cannot properly transport oxygen and carbon dioxide in and out of the blood. This may cause oxygen levels in the blood to be too low or the carbon dioxide levels to be too high. Either of these conditions can result in damage to the vital organs, including the heart and brain.
Some conditions that may lead to severe respiratory problems include: drowning, an obstruction in the trachea, such as a foreign object or tumor, obstructive pulmonary diseases such as asthma, chronic bronchitis, and emphysema, diseases such as pneumonia and acute respiratory distress syndrome, or ARDS, severe weakness of the muscles that control breathing, damage to the bones and tissues of the chest, under these circumstances, supplying a patient with additional oxygen, or supporting his or her efforts to breathe through mechanical ventilation, may become necessary.
While mechanical ventilation is often used in emergency situations, it is also performed for surgeries requiring general anesthesia. Mechanical ventilation is ideal for: delivering anesthetic drugs, preventing the aspiration of stomach contents into the lungs, closely controlling the levels of oxygen and carbon dioxide in the blood during surgery.
Oxygen therapy is a technique used to deliver extra oxygen through a facemask or by nasal prongs. If these delivery methods prove inadequate, mechanical ventilation may be required.
Mechanical ventilation is used to help patients who cannot adequately breathe on their own. A ventilator is a specially designed pump that aids respiration by delivering well- oxygenated air into the lungs and permitting carbon dioxide to escape from the lungs. Depending on the reason for mechanical ventilation, air may be forced into the airways under higher pressure than normal.
The first step in mechanical ventilation is called endotracheal intubation. This is the process of inserting one end of a tube, called an endotracheal tube, into the airway, which allows oxygen and carbon dioxide to pass freely. The other end of the tube is attached to a ventilator.
In the days leading up to an elective intubation and mechanical ventilation: your doctor may ask you to temporarily discontinue any medications, herbs, or dietary supplements that you regularly take. Do not start taking any new medication, herbs, or dietary supplements without consulting your doctor. The night before, eat a light meal and do not eat or drink anything after midnight. Your doctor will discuss with you any other special instruction related to your upcoming surgery. An intravenous line will be started and your doctor will give a medication through the IV to put you to sleep. As the medication takes effect, he or she will place an oxygen mask over your nose and mouth and ask you to breathe deeply. This will ensure that you have a reserve of oxygen in your system prior to the procedure.
Once you are asleep, your doctor will use an instrument called a laryngoscope to perform the intubation. A laryngoscope, which consists of a handle, light, and dull blade, helps guide the endotracheal tube to its proper position.
Your doctor will tilt your head back slightly and insert the laryngoscope through your mouth and down into your throat, taking special care to avoid contact with your teeth. Using the blade, your doctor will gently raise the epiglottis, which is a flap of tissue protecting your larynx. He or she will then advance the tip of the endotracheal tube into the trachea.
Once the endotracheal tube is in the trachea, your doctor will inflate a small balloon surrounding the tube to make sure it remains snuggly in place. Your doctor will remove the laryngoscope and tape the tube to the corner of your mouth to prevent it from being jostled out of position.
Your doctor will check to see that the tube is properly positioned in the lower part of the trachea by inflating your lungs with a special bag and listening for breath sounds on both sides. If the end of the tube is too low, both lungs will not receive the same amount of air. In some cases, an x-ray is taken immediately after intubation to confirm the tube' s placement.
Once the endotracheal tube is in the proper position, your doctor will attach it to the mechanical ventilator. Levels of oxygen and carbon dioxide will be closely monitored to confirm that the ventilator is working.
Risks and Benefits
Risks and complications associated with intubation and mechanical ventilation include: esophageal intubation, in which the tube is mistakenly inserted into the esophagus, which leads to the stomach instead of the lungs, movement of the tube down into one of the main bronchi, injured vocal cords, pneumonia, ruptured lungs, lung injury due to over-inflation of alveoli, broken teeth or bridgework, low blood pressure.
Benefits of intubation and mechanical ventilation include: lifesaving treatment for severe respiratory diseases, safe administration of general anesthesia, protection from aspiration of stomach contents into the lungs during surgery.
In intubation and mechanical ventilation, or any procedure, you and your doctor must carefully weigh the risks and benefits to determine whether it' s the most appropriate treatment choice for you.
After the Procedure
Before removing the endotracheal tube, your doctor will make sure you are able to safely breathe on your own by measuring how often you take a breath and how much air you breathe in and out with each breath.
After your breathing tube is removed, you can expect to have a mild sore throat and a raspy voice for a few days. Be sure to contact your doctor if your voice does not gradually recover or if you experience: worsening throat pain, signs of infection, such as fever and chills, difficulty breathing at any time, chest pain, choking on food or drink, and/or coughing up blood.
- Beers, Mark H., and Robert Berkow, eds. The Merck Manual of Diagnosis and Therapy, 17th ed. Merck Research Laboratories: Whitehouse Station, NJ. 1999.
- Braunwals, Eugene, Anthony S. Fauci, and Dennis L. Kaspers. Harrison's: Principles of Internal Medicine, 15th ed. McGraw- Hill: New York. 2001
- Tierney, Lawrance, M., Stephen J. McPhee, and Maxine A. Papadakis. Current Medical Diagnosis and Treatment. Lange Medical Books/McGraw- Hill: New York. 2004.
- Tobin, Martin J., ed. Principles and Practice of Mechanical Ventilation. McGraw- Hill: New York. 1994.
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