On Ventilation

Mammals, or humans in particular as it relates to this post, need to exchange gases. We take in oxygen and get rid of carbon dioxide. The process that we use to do that is breathing. There are two components to that process: ventilation, and respiration.

Ventilation is the mechanical process of moving air (or other gases) into and out of the lungs. Ventilation requires a functioning respiratory drive (provided by the CNS and portions of the PNS), an intact and functioning chest wall, the airways, and lung tissue that is functioning properly. Being a mechanical process, there are things that can affect it: physical blockages of the airway through trauma, inflammation, or even a failure to maintain open air passages because of dysfunction in the nervous system.

Respiration is the actual exchange of gases, first across the alveolar membranes, then into the blood, into the tissues of the body, then back to the blood and across the alveolar membranes to be expelled from the body. This process depends upon the relative pressures of the gases involved. Things like partial pressure, electrochemical gradient, pH, and other factors play a huge role in the moving of gases into and out of the lungs.

Entire textbooks are written on how this process works, so this limited post won’t be an exhaustive treatise on the function of the respiratory system. I want to mention mechanical ventilation and why intubating a patient and placing them on a ventilator is so important.

There are times when a patient’s respiration doesn’t function as it should. Perhaps the process of gas exchange has been disrupted because another gas has more affinity for the chemical reactions that are taking place, as is the case with hemoglobin’s stronger affinity for carbon monoxide than oxygen. Maybe the pH of the blood is shifting, causing gas exchange in the alveoli to cease. There are a lot of reasons why this can stop working as it should, and these can be addressed through multiple means. The simplest of these is simply putting a nasal cannula in place to deliver oxygen at a slightly higher partial pressure. Still, there are times when these tricks don’t work and respiration breaks down.

Once the breakdown in the processes of ventilation and respiration take place, a person will begin to struggle to breathe. The work of breathing increases, and the patient has to put in more and more effort to get a breath. This is extremely tiring. Sooner or later, the person becomes too exhausted to breathe, and slips into what is called respiratory failure. When this sets in, there are again numerous things that can be done to assist the person in breathing. BiPAP and CPAP are two ways to do this. However, if these measures don’t work, or if the person can’t breathe on their own, then someone or something has to breathe for them.

In the short term, a device called a bag valve mask allows medical personnel to breathe for the patient, but this isn’t a long term solution, nor is it very useful for delivering higher levels of pressure to the gases involved.

Ultimately, a person who is not breathing well on their own will wind up with a tube down their throat and a machine called a ventilator doing their breathing for them. This can be done because the person can’t keep their airways open when they are unconscious, like during surgery. It can be done because they have significant damage to the nervous system, for example a broken neck has damaged their phrenic nerve, are simply too tired to breathe, like during an asthma attack, and for a host of other reasons.

Here is a recent, real-life example. Steve is a known IV drug user who was found in his backyard by EMS. He is breathing with grunting, low volume respirations that are clearly ineffective. EMS tried giving him Narcan, but it had no effect, so they began ventilating him with a bag valve mask. Since he still had a gag reflex, they were unable to intubate the patient.

The doctor in the emergency room decides that he needs to be intubated and placed on a ventilator because he is simply incapable of maintaining and protecting his own airway. The staff gives him etomidate to sedate him, rocuronium to paralyze him, then the doctor inserts the tube before a respiratory therapist places him on a ventilator. The process is fast, taking less than 5 minutes.

The drugs used to place the tube will wear off in just a few minutes, so the patient needs to be sedated to keep him from fighting against the ventilator. Drugs like Versed, Propofol, Ketamine, and Fentanyl are used to keep the patient sedated. Of course, those drugs cause side effects that must also be dealt with. It becomes a delicate process of keep the patient sedated to the correct level while also maintaining the other parameters, as well as dealing with the drug overdose and the issues that it caused.

In the above case, the patient had rhabdomyolysis, liver failure, kidney failure, and a host of other issues that had to be dealt with. Dealing with those issues takes time, but unless a patient is breathing, time is what you don’t have. Ventilation buys you that time to deal with it.

There are COVID (as well as influenza and pneumonia) who get intubated to this day. Some make it, some do not. It’s not the ventilation that kills those patients, it’s the sepsis and the immune system’s response to it that kills them. In some patients’ cases, ventilation does more harm than good, but overall, mechanical ventilation is a process that saves thousands of lives per year.