Oxygenation concepts are topics you’ll start learning about in first semester and build on throughout your nursing school journey. In this article, we’ll talk about the basics of oxygenation, related concepts and some nursing interventions to apply to your care plans or in clinical.

Let’s first review some key terms related to oxygenation concepts. These are oxygenation, ventilation, diffusion and perfusion. 

  • Oxygenation is the process of supplying oxygen to the body’s cells. 
  • Ventilation is the process of exchanging oxygen and carbon dioxide, which is essentially breathing. Oxygen comes in to the body via the airway, it’s offloaded onto the red blood cells while carbon dioxide diffuses across the membrane into the alveoli and is then exhaled. You breathe in oxygen and exhale CO2.
  • Diffusion involves substances moving across concentration gradients from areas of higher concentration to areas of lower concentration. This is the process involved with gas exchange. 
  • Perfusion is the body process of supplying oxygenated blood to the cells and is reliant on adequate cardiac output in order to be optimal.

When everything is working as it should, you have what is considered a normal presentation, or an assessment that is WDL (within defined limits.) So what does this look like?

In a healthy adult with healthy lungs this looks like a patient who is breathing without any signs of distress. Their breathing is unlabored at around 12-20 breaths per minute. You don’t see any abnormal signs of increased respiratory effort such as nasal flaring or accessory muscle use. Their skin is a normal color for their race with no signs of pallor or cyanosis (blue-ish tinge to the skin). They are calm, not showing signs of anxiety, confusion or restlessness. When you listen to their lungs, their lung sounds are clear. Their voice is clear without signs of hoarseness and they are able to cough and swallow effectively. In other words, you don’t see any imminent risk for airway occlusion due to airway edema or dysphagia. 

Hypoxia and hypoxemia

Two other terms that you need to know as you are learning about oxygenation are hypoxia and hypoxemia. A lot of times you will hear these terms used interchangeably, though hypoxia refers to a low oxygen level in the tissues, whereas hypoxemia is low oxygen level in arterial blood. Hypoxia is a SpO2 < 90% as measured by pulse oximetry and hypoxemia is typically measured arterially and is a PaO2 below 80 mmHg. It is very important to understand that these two conditions are actually different AND do not always occur simultaneously. A patient can have hypoxemia without hypoxia if the body has had time and the ability to utilize compensatory mechanisms. Conversely, the patient can have hypoxia (low level in the tissues) without hypoxemia (low level in the blood) if the cells aren’t able to utilize oxygen effectively. Did I lose you there? I thought that might happen, so let’s take a little deeper dive into this one.

Let’s say you have a patient with acute hypoxemia (low PaO2) because they’ve gotten hit with a pretty good case of pneumonia. How likely is it that their tissues are getting adequate oxygen if the amount of oxygen in the arterial blood is low? If you said, “It’s probably not that likely” then you get a gold star! This patient will most probably show signs of hypoxia, which again is that low oxygen level at the tissues. 

But what if your patient has chronic hypoxemia because they’ve lived with COPD for the past five years? Do you think their body has possibly had time to compensate for this low arterial oxygen level? Is their tissue oxygen level possibly going to be within normal limits? It’s very possible and it’s all because of compensatory mechanisms. Remember that the body loves homeostasis and will go to great lengths to always keep things in balance. In the case of our patient with COPD, he has compensated for the lower arterial O2 by increasing oxygen delivery through increased RBC production or increased cardiac output, or by decreasing oxygen consumption at the tissue level. But what do you think would happen to this patient if he, for instance, developed left-sided heart failure or renal insufficiency? Would he compensate as well? Probably not.

On the other hand, patients who have a normal PaO2 level (meaning they are NOT hypoxemic) may actually be hypoxic if they have issues with oxygen delivery or their tissues are not able to utilize oxygen effectively. This can occur in cases such as mitochondrial disorders, metabolic derangements that occur in sepsis, and cyanide poisoning. But, in general, hypoxemia (low PaO2 level) is usually the cause of hypoxia.

So what does hypoxia look like? Patients who are hypoxic will likely be tachycardic as the cardiovascular system tries to compensate by increasing cardiac output. In addition, they may be anxious, confused or restless, and their SpO2 will be low. Pallor or cyanosis are later signs, so if you see those your patient is definitely in trouble. They may be showing signs of air hunger or exhibiting  increased work of breathing by gasping or gulping for air, using accessory muscles or breathing quickly (tachypnea). 

The other key component to always be aware of is airway patency. An inflamed or swollen airway is going to be narrow, while occlusions can occur for a variety of reasons including mucus plugs, anatomical structures (tongue or tumor) and foreign bodies. 

What are you going to do about it? Let’s look at a few examples:

Bob, who has a history of COPD has presented to the emergency room with increasing shortness of breath. He is speaking in three word sentences and sitting leaned forward with his hands on his knees (tripod position). He feels warm to the touch and says he’s been coughing up thick, yellow-ish green sputum. What two vital signs do you want the most?

  • Spo2
  • Respiratory rate

Because you suspect Bob is dealing with a pneumonia, you want to get some information about his oxygenation status, and the fastest way to do that is to measure SpO2 via pulse oximetry and count respirations. You would also follow this with a full set of vital signs, perform a focused respiratory assessment, and anticipate the MD ordering a WBC, sputum culture and chest x-ray.

So is Bob’s problem ventilation or oxygenation? The fluid-filled alveoli are preventing adequate gas exchange, so Bob’s problem is oxygenation. You’ll anticipate supplying supplemental oxygen and administering ordered medications such as antibiotics and corticosteroids.

Let’s try another example:

Sally has been brought in by a family member who found her unresponsive on the bathroom floor. Why they didn’t call an ambulance is anyone’s guess, but here they are. You notice Sally is breathing only 7 times per minute. What other data do you want to obtain? 

  • SpO2
  • Glasgow Coma Scale score (GCS)
  • Other vital signs
  • Focused respiratory assessment

You hook Sally up to the monitor and notice that her SpO2 is 77% on RA. Her GCS is a 3, meaning she does not open her eyes or move her body in response to any stimulation (even painful stimuli) and makes no vocalizations at all. Her lungs sound clear, but her respirations are very shallow and slow.

What kind of problem is Sally most likely having…a problem with ventilation or a problem with oxygenation? Most likely Sally’s problem is with ventilation. Her respiratory rate and depth are just not adequate, leading to her decreased SpO2. If you were to obtain a PaO2 from an ABG, what would you expect it to be…normal or low? If you said low, you are probably right. Good job! So, now that we’ve determined that Sally’s problem is most likely due to poor ventilation, what do you immediately do next?

  • Perform assisted ventilation with a bag valve mask at oxygen running at 10-15 L/minute. 
  • Call for the MD and prepare to intubate

The family member has finally stopped panicking and has been able to tell one of the nurses that Sally has degenerative disc disease and wears a fentanyl patch to deal with the chronic pain. You quickly do a scan of Sally’s whole body and find not one, not two, not three, but four fentanyl patches in various places. NOW, what do you do?

  • Call for Narcan
  • Remove the fentanyl patches
  • Continue assisting ventilation with 100% FiO2 until Sally regains consciousness

The Narcan has been administered and Sally wakes up with guns a blazing…she’s agitated, in extreme pain and, happily, breathing on her own. What do you do next?

  1. Assess Sally for suicidal ideation then send her home when she states it was an accident
  2. Continue monitoring Sally for respiratory depression
  3. Send Sally to the Med/Surg floor while you wait for a psych consult
  4. Provide Sally with education about fentanyl patches before discharging her from the ER

Hopefully you chose B…continue monitoring Sally for respiratory depression. Though naloxone works great at reversing opioids, it doesn’t last very long. Without knowing how long the patches were on Sally’s skin, we really have no idea how much systemic fentanyl is still running through her system. We will monitor Sally for signs of respiratory depression and administer additional doses of Narcan until the fentanyl has cleared.  We would also want to ask Sally what other medications she may have taken and assess her for suicide risk. If this was an intentional act, she’ll need to be held and evaluated by a psychiatrist. If you answered C, you were probably correct in thinking Sally may very possibly be admitted while we get a psychiatrist on board. However, a Med/Surg floor would not be ideal as she needs to be closely monitored for respiratory depression during this time. If she is admitted, she’d go to the ICU, and possibly even on a continuous naloxone infusion.

One more case study before you go:

James has been brought in by ambulance (BIBA) for increased shortness of breath and extreme fatigue for three days. His wife states she has noticed some “black, tar-like” stools but thought it was related to something he ate. Your first impression of James is that he is incredibly pale, lethargic and has a weak, thready and rapid pulse. He’s telling you he just can’t catch his breath and he’s beginning to get a bit confused. What other information would you like to have?

  • SpO2
  • Blood pressure
  • CBC (especially hemoglobin and hematocrit)

James is exhibiting some pretty classic signs of a patient who has had a substantial GI bleed (the black, tarry stools are the big hint here) and is now suffering from respiratory distress and hypovolemia. You check James’ vital signs and notice that his SpO2 is 88% on room air, his heart rate is 123 and his blood pressure is 83/52. While you wait for the CBC, the MD orders a fluid bolus to address the low BP and oxygen to maintain levels above 92%. What do you grab first? The oxygen mask or the fluid bolus? 

If you answered “the oxygen mask” then you get another gold star! While both are important, prioritization often falls down to which item can be done more quickly. An O2 mask is easy to apply, while the fluid bolus is going to take at least 5 to 10 minutes to infuse. So, you get the mask on James and start the 500 ml fluid bolus. While it is infusing, the lab calls and tells you James has a critically low hemoglobin level. Now, what do you think Jame’s core problem is? He’s breathing fine, but he simply doesn’t have enough hemoglobin to transport oxygen around his system. So while oxygen may help in his situation, what’s REALLY going to help is a blood transfusion. You get two units of packed RBCs into James, who “pinks up”, starts breathing more easily and states he feels “so much better.” He gets admitted to the ICU for close monitoring and the doc orders a GI consult with plans for an EGD in the morning.

Three cases of oxygenation problems, three different reasons

So there are three different examples of patients who presented in respiratory distress for three very different reasons.

  • Bob had pneumonia. He was ventilating fine, but oxygenation across the alveolar membrane was suffering. He got supplemental O2 and treatment for his infection.
  • Sally had opioid-induced respiratory depression. Her lungs were in great shape, but her respiratory effort was weak. She got assisted ventilation with the BVM, and would have gotten intubated if we hadn’t discovered the cause and all those darn fentanyl patches. A dose or two of Narcan and Sally improved dramatically!
  • James had shortness of breath due to severe anemia. We supported his oxygenation with some supplemental O2 and two units of packed RBCs. Good job!

So, what are you going to do about it?

When your patient is having respiratory difficulties, the causes can be quite varied. With that said, there are some general interventions you can do as the nurse:

  • If the patient is lying down, sitting them more upright often helps dramatically. Lung expansion is often a lot easier in an upright position, especially if the patient is obese or has pulmonary edema or CHF.
  • If the patient is unconscious and occluding their airway, a simple jaw thrust or chin-lift maneuver may be all it takes to restore airway patency. 
  • If oxygen levels are low-ish and the patient can cooperate, having them cough and take some deep breaths is sometimes very effective. Coughing clears lungs of secretions that could be inhibiting gas exchange. 
  • If the patient has restrictive airway disease such as COPD, a technique called “pursed-lip breathing” helps increase intra-airway pressure to keep those alveoli open longer (and make them more available for gas exchange).
  • Most patients will have orders for oxygen as needed to maintain a certain oxygen saturation level (often > 90 or 92%). Which oxygen delivery system you choose will depend on the severity of the respiratory distress and the patient’s condition. Read more about oxygen delivery systems and when to intubate.

Looking for more oxygenation concepts? 

Learn about ventilators here.
Learn about ARDS here.
Want to learn when you might intubate your patient?
What’s a P/F ratio anyway?

Get this on audio in podcast episode 89.


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Sarkar, M., Niranjan, N., & Banyal, P. (2017). Mechanisms of hypoxemia. Lung India : Official Organ of Indian Chest Society, 34(1), 47–60. https://doi.org/10.4103/0970-2113.197116

Stern, A., Skalsky, K., Avni, T., Carrara, E., Leibovici, L., & Paul, M. (2017). Corticosteroids for pneumonia. The Cochrane Database of Systematic Reviews, 2017(12). https://doi.org/10.1002/14651858.CD007720.pub3