Can you give some examples of a clinically indicated need for BiPAP/CPAP?
CPAP (Continuous Positive Airway Pressure) is a therapy in which a machine delivers a continuous stream of pressurized air through a mask strapped tightly over the mouth and nose. This pressurized air holds the airway (particularly the throat and tiny air sacs in the lungs called alveoli) open in situations where the patient may not be able to maintain their airway on their own, allowing them to breathe uninterrupted.
1. Obstructive Sleep Apnea: CPAP's most well known use is for obstructive sleep apnea, a condition in which the upper airway (throat) collapses when a person sleeps, causing the patient to briefly (10-30 seconds at a time) but frequently (up to 400 times per night) stop breathing. While not immediately life threatening, sleep apnea causes extremely poor quality sleep, extreme fatigue during the day, and contributes to other health problems like high blood pressure, diabetes, and stroke. The CPAP machine, worn while sleeping, holds these patients’ airways open and allows them to breathe normally through the night.
2. Pulmonary Edema: Pulmonary edema is a fancy word for swelling in the lungs. This can be caused by many problems, including heart failure, infections (pneumonia), poisons (irritants), high altitude (HAPE, a medical emergency where ascending to a high altitude without proper adjustment periods causes a fast-onset pulmonary edema), allergic reactions (causing inflammation in the lung passages), and injuries to the lung tissue.
You can think of the lungs as made of sponge-like tissue, filled with passages that split many times into smaller and smaller tubes that ultimately end in tiny air sacs called alveoli. It is in the alveoli that tiny blood vessels pick up oxygen from the air we breathe and release carbon dioxide to be breathed out (a process called gas exchange). In pulmonary edema, swelling in the lung passages and alveoli make it incredibly difficult to get air all the way to the blood vessels. The hardest part of this is re-opening the alveoli with each breath. The pressurized air pushed in by a CPAP machine can help keep these passages and alveoli open and decrease the work of breathing.
3. Chest Trauma: We breathe in when our diaphragm (a muscle that covers the bottom part of our ribcage) pulls downward, creating extra space within the ribcage that is filled by air entering the lungs. This process requires a mostly-intact ribcage. If the ribcage is significantly damaged (say, flail chest or badly broken ribs), the lungs may not inflate completely, or may not inflate in certain areas. If the lung passages do not inflate fully, not only is the patient not getting all the oxygen/carbon dioxide exchange they might need, but those areas are at risk for developing pneumonia. A CPAP can again keep these passages open and decrease the need for an intact chest while the chest ribcage heals.
Now let’s talk about NIV:
NIV (Non-Invasive Ventilation, sometimes known by the trade name BiPAP) is a therapy that is similar to a CPAP, but instead of a constant flow of pressurized air into the person’s airway, it alternates between two different pressures over the course of a breath- The pressure is higher when the person breathes in and lower when the person breathes out.
Like CPAP, this pressure (both high and low), can “splint” the airway open, decreasing the work of breathing. Unlike CPAP, however, NIV can also monitor a person’s breathing and force them to take a breath if they go too long without taking one themselves. In this way, it is similar to a ventilator (in fact, most ventilators have an NIV setting)- the breaths are just delivered through a mask worn on the face or a full-head “helmet” instead of a tube that goes down the person’s throat.
1. Prior to/weaning from an endotracheal (ET) tube: The least amount of time a patient has an ET tube in their throat, the better off they will be. Tubes are extremely uncomfortable, require a lot of medication to make them tolerable for patients, require the patient to be immobilized which leads to increasing muscle weakness the longer the patient goes without moving, and they can cause sores and other injuries to the airway.
NIV can be used to support breathing until a patient absolutely needs an ET tube, and it can be used when the patient no longer needs the tube but still needs support breathing. Both of these decrease the total amount of time the person needs a tube down their throat, which hopefully makes their outcome better. NIV can also be used (to a limited degree) as an alternative for people who refuse an ET tube but still need breathing support.
2. CO2 buildup/respiratory failure not responding to CPAP: If a person can’t get rid of enough CO2 (for example, in a COPD exacerbation or acute respiratory failure) a CPAP and medication alone might not be enough to correct this problem. In this case, CO2 builds up in the blood, causing it to become acidic, which can quickly become dangerous. Since NIV has a lower pressure when breathing out, it can help encourage the patient to “blow off” some of the excess CO2 when they exhale and return their CO2 levels to normal.
3. Neuromuscular diseases: Some people have diseases that cause their breathing muscles to be too weak to breathe adequately, or have had an accident that left them paralyzed and unable to breathe enough to support themselves. In this case, they may wear an NIV mask constantly or while sleeping to support or take over the work of breathing.
4. Central sleep apnea: Unlike obstructive sleep apnea (OSA), which is a problem with the airway, central sleep apnea is a problem where the brain doesn’t always correctly send signals to the breathing muscles during sleep. It manifests similarly to OSA (excessive daytime fatigue, increased risk for various chronic illnesses) but instead of a device that just keeps the airway open, central sleep apnea also requires a device that can initiate breaths if the patient doesn’t take them on their own.
