The lungs are the organ that allows oxygen to enter the body and carbon dioxide to leave the body. They accomplish this by permitting gas to enter small sacs called alveoli. These sacs allow the exchange of gas across their membrane. The alveoli stay open through the use of a surfactant. In an infection, it can travel to the lungs and cause a potentially fatal condition called acute respiratory distress syndrome (ARDS). In ARDS, the alveoli fill with a fluid that is essentially pus, which diminishes the lungs’ ability to provide vital organs with enough oxygen. There are ways that we can fight that.
If the patient is conscious and able to keep their own airway open, we can put them on CPAP or BiPAP, which is a mask that pressurizes the air that the person is breathing. This extra pressure forces the fluid out of the alveoli and back into the bloodstream. If a person can’t maintain their own airway, they will be intubated and placed on a ventilator. That ventilator will provide pressurized oxygen, and this is called PEEP. You can see it at work here, where a mechanical ventilator is working on a set of pig lungs as a demonstration:
As doctors have gained more experience treating patients with COVID-19, they’ve found that many can avoid ventilation—or do better while on ventilators—when they are turned over to lie on their stomachs. This is called prone positioning, or proning. Because of how the lungs are positioned, this lets you use parts of your lungs that aren’t being used when you are on your back, because it reduces pressure from the heart and diaphragm on the lungs, which allows them to inflate more easily.
If we are talking about emergency intubations (IOW not for procedural reasons), the only people who get intubated and placed on a vent are really sick. People colloquially refer to this as “being on life support.” Anyone can tell you that a person who isn’t adequately breathing on their own is pretty sick. So, for starters, anyone who is being intubated is a pretty sick puppy.
The most common complications in COVID-19 infections are bilateral pneumonia which may progressed to ARDS, sepsis and septic shock, acute kidney injury and others such as acute cardiac injury, coagulopathy, hyponatremia (low sodium levels in the blood) and acidosis (blood Ph too low). Complications are more likely in serious sickness versus non-extreme illness.
On top of that, there are risks for mechanical ventilation: overinflating the lungs, oxygen toxicity, and other issues are possible complications. These complications are more likely in people with ARDS, diabetes, high blood pressure, chronic heart or lung disease, and obesity all are at higher risk of complications from mechanical ventilation. You will recall that these same risk factors also make a patient more susceptible to COVID.
If your COVID infection is bad enough that it is collapsing your alveoli, you likely have problems with other organs as well- specifically the liver, heart, and kidneys. Remember- the same cytokine storm that is damaging the lungs is also damaging other organs as well. This can cause the development of something called MODS (multiple organ dysfunction syndrome). What causes about 20% of COVID deaths is MODS, and is not due to the use of a ventilator. Three quarters of the people who developed MODS already had underlying problems like kidney or heart disease, diabetes, or were morbidly obese.
The simple fact is that we in health care are using other methods for treating low blood oxygen caused by COVID, such as high flow devices (up to 60 liters of oxygen per minute) to try and delay or put off the need to mechanically ventilate a patient, but once you are sick enough from COVID to need a ventilator, you are really sick and your likelihood for surviving is low.