Air administration for patients requiring pressure assistance or increased oxygen is one area where the medical community leaves caregivers guessing and confused. As caregivers, we need a firm understanding of the fundamentals.
Confuse them with medical speak
A doctor, nurse, or respiratory therapist walks into a patient’s room on oxygen support or a ventilator; as the professional opens their mouth, a gush of what I call “medical speak” rushes out, washing away anything you thought you knew about the situation. They talk about upping this and reducing this, and it all gets REALLY confusing. I don’t know if this is intentional (my personal belief is that it makes RTs with a certificate feel superior) with doctors and nurses. It just happens. They have their own language. A language we lay people don’t speak. It has nothing to do with our intelligence or our desire to learn. But is it too much trouble to explain it to those of us responsible for the care of others?
I hope that by explaining some of the terms and giving examples of use cases, you will better understand your loved one’s breathing process.
Terminology Quickies
- Oxygen – This is the life-sustaining element that we require to exist. Some geeky information: It has an atomic number of 8, its symbol is O, and it’s labeled as O2. Note: Oxygen is highly toxic. At normal atmospheric pressure, 21% O2 is considered safe. As O2 concentration increases, the side effects of oxygen toxicity can begin to appear. These include coughing, trouble with breathing, chest pain, convulsions, blurred or near-sighted vision, muscle twitching, and mild throat irritation. Additionally, many of the chemical breakdowns that occur around us are caused by oxidation (rust), and within the body, free radical O2 molecules interact in non-conventual ways with some cells that can lead to cancer, arthritis, aging, autoimmune disorders, cardiovascular and neurodegenerative diseases.
- Room Air – There is nothing magic about this; it is simply a reference to the air we breathe daily. It consists of about 21% Oxygen (O2).
- Flow Rate – is how fast (time) a measured unit (volume) moves through a space (think tubing). The most common rate in medicine is Liters per Minute (l/min).
- High Flow – There is some argument about the level at which a high l/min becomes “High Flow”. Some say anything above 4 l/min of O2 should be considered high-flow treatment. Most hospitals in the Atlanta area consider High Flow to be 15 -60 l/min of oxygen-rich, heated, and humidified air. High flow does not necessitate high oxygen levels, although the values often travel together.
- Concentration – the percentage of an element in a mixture. In the rest of this article, we will reference the concentration of O2 in the airflow delivered to a patient.
- Saturation – the measure of how much hemoglobin is currently bound to oxygen compared to how much hemoglobin remains unbound. That was a mouthful. It’s the number that you get when you put your finger in the little machine, and it returns a percentage. %100 perfect, 95-99% normal and healthy, 90-95% is acceptable if overexerting or getting over a cold, 85-90% is considered ok for those with COPD, but a bit more serious might need to see a doctor. Below 85%, you should be talking to medical personnel. As the saturation drops off, some body areas begin to work overtime to compensate. Hands and fingers/toes get cold, and a spiral begins. The brain begins to shut down organs and limbs to protect itself, hoarding any O2 for itself. When it shuts down the heart, no new O2 is being circulated.
- FiO2 – the fraction of inspired oxygen or oxygen concentration in the gas mixture. More often than not, this value is expressed as a decimal versus a percentage. Again, a layman’s view of this should be the potential mix at the point the patient inspires or breathes in the mixture, whether at a trach collar or a nasal cannula.
Lesson 1 – Healthy on Room Air
So you are sitting quietly in a chair using a pulse oximeter, or pulse ox, to measure your blood oxygen saturation and pulse rate. As you breathe in, you are inspiring room air with a concentration of 21% O2. Flow rate could be calculated. But again, for us lay folks, think of the flow as passive, in that no other force outside of atmospheric pressure is operating to force air into our system. We draw the air mixture into our lungs. All things being equal, we would consider the FiO2, available O2 at the point you inspire, to be .21.
Lesson 2 – Small Boost on bottled oxygen
We have seen athletes run to the sidelines and take a “hit of oxygen” from a bottle. These are professionals with well-tuned bodies. In their circumstance, they have over-exerted themselves for their operating conditions. Heavy use of muscles requires increased oxygen use, which requires greater inspiration of oxygen. A rapid depletion of blood oxygen requires a balanced increase in oxygen intake to keep saturation at a safe level. Now is also a time to mention atmospheric pressure and weather conditions. I mentioned that 21% O2 is the normal, healthy concentration in room air. That number comes from being at sea level, or 1 earth atmosphere. An athlete who has trained at sea level will find that to get the same 21% O2 when playing in Denver will have to breathe faster (RR – respiratory rate) and deeper. The air in Denver still has a 21% concentration of O2, and there is just less air around you due to the elevations. That player may need a boost of 2-3 l/min of 100% concentrated oxygen to bring his body back into equilibrium.
Lesson 3 – Understanding the Oxygen Concentrator
If you or the person you provide care for has an oxygen concentrator, then your doctor has decided that there is a need for some supplementing of oxygen to maintain healthy levels. A common large concentrator is the Philips Respironics EverFlo. The device comes in 2 primary home-use configurations. The most common is the 5 l/min variety, and the less common is the 10 l/min model. For many doctors, a need for more than 5 l/min in a normally healthy person should require a visit by EMS and a visit to the doctor. Higher flow rates and concentrations become the norm for patients with tracheostomies or with COPD or other long-term lung damage.
Oxygen concentrators draw in room air containing 21% O2, compressing, isolating, and separating the O2. The O2 output concentration of a fully maintained and optimized concentrator will only be 95-99%. The flow rate will max at around 5 l/min. Measure a concentrator that has aged and been in use for a while, and you will frequently find that the concentration is below 95%, and the flow rate will be significantly less than indicated on the machine gauge.
Lesson 4 – Emergency Boost of Bottle Oxygen
Frequently, with an onset of pneumonia, severe bronchitis, or an asthma attack, the exchange of gases within the lungs does not occur optimally in room air. This may also be caused by long-term lung damage. Most of us recognize the classic E bottle, now called an M-24. These bottles contain 100% pure O2. Assuming they are pressurized to 2200 psi, they will contain 680 liters of O2. (Please, no more statistics!)
These statistics are important to know. If your loved one only needs 5 l/min, a full M-24 will last you ~ 136m. If your patient begins to desaturate and you need 10 l/min for transport, that same M-24, if full, will only last you 68m. 15 l/min is the highest flow rate for non-institutional usage. If you are at 15 l/min, that’s “high flow” in many hospitals, and your patient requires medical care NOW. A full M-24 only has 45m of run time. 136, 68, and 45 minutes may seem like rather long times, but that time flies by in a crisis.
Lesson 5 – You don’t want to be here!
In the past 8 years, a situation occurred simply due to a not-so-comedic series of events. Our 5 l/min concentrator died at the beginning of a pneumonia recovery cycle over a holiday. There was a delay in signing the Letter of Necessity for Home Oxygen as the DME hadn’t sent it to the pulmonologist. Cold and and flu were rampant in the local ERs, and taking this patient, already susceptible to airway infections, into that environment didn’t seem like a great idea.
Now, if you have bottle A pushing 10 l/min through a system to a nasal cannula, and you connect a T and add bottle B pushing 10 l/min into the same system. What is the l/min at the exit point? Yes, 20 l/min. At home you could achieve 20 l/min for 68 minutes with 2 full M-24 bottles.
Bringing it together
You are in the hospital, and the RT walks in for the first visit of her shift, and she mutters that the machine reads 45 and 29. You try to get her attention, but a call about cake in the break room makes her run off. What does 45/29 actually mean? The flow rate is 45 l/min, and the oxygen concentration within that flow is only 30%. Your patient doesn’t need much oxygen support; they need flow or pressure support. Once the oxygen mix gets to the Alveoli in the lungs, they seem to be doing an ‘ok’ job getting it into the bloodstream. But a weak body may be taking shallower breaths, a hurt rib cage, or post-op open heart surgery makes it hard to take a deep breath to pull that mixture in, so the 30% is being pushed at a rate of 45 l/min. I used 30% concentration for a reason:
Each liter per minute increases FiO2 by roughly 4%.
Room air (21%) + 2 l/min of O2 gives us 29% FiO2.
The 30% above is really close to only 2 l/min.
Does this help you understand how serious or NOT serious the numbers can be?
It is important to understand the distinction here. High Concentration at high Flow Rates indicates a body in great need of help, a point at which a ventilator most likely comes into play. The body can’t keep the airways open enough to bring the mixture in, and at the same time, the lungs don’t seem to be working efficiently.
Ventilators, waveforms, and volumes will be left for a different article.