Investigating High Flow Oxygen For Pneumothorax

Depiction of high flow nasal cannula.
Image taken from Google Images. 

We respiratory therapists are often skeptical. Recently, many doctors are prescribing high flow nasal cannula's (HFNC) for pneumothoraces. A common question is: Does this treatment do any good? Let's investigate.

What is a pneumothorax?

As we all know (or should know), a pneumothorax is a collapsed lung. It's when air seeps into the the space between the lungs and chest wall. It is air that seeps into the pleural space. This air pushes on the lungs to make them collapse. An entire lobe may collapse or just a small portion of it.^1-2

A small pneumothorax may cause no symptoms. It may resolve on it's own. A larger pneumothorax may cause symptoms. These include low oxygen levels and shortness of breath. They may also include sharp chest pains, rapid breathing, and rapid heart rate. 

They are either spontaneous or iatrogenic. 

• Spontaneous (Primary). This means they occur in otherwise healthy individuals.  The cause usually remains inexplicable. Those most likely to develop them are of the tall and lean type. Others at risk may include smoking tobacco or marijuana. 
• Iatrogenic (Secondary). This means they are secondary to treatment for a disease process. A good example here is secondary to a thorocentesis. The doctor inserts the needle too far and it pierces the lungs. Severe asthma, sarcoidosis, cystic fibrosis, pulmonary fibrosis, and emphysema are also potential secondary causes. Another cause may be barotrauma due to using high pressures during mechanical ventilation  ^2-4

How do they resolve?

They resolve as air is reabsorbed into nearby tissues. A small pneumothorax may cause no symptoms. These may also resolve on their own. Treatment here is observation. 

A larger pneumothorax may cause some symptoms. In these cases some treatment is probably needed. What to do is dependent on what guidelines you are referring to. Some recommend a needle aspiration to relieve the pneumo. Others recommend insertion of a chest tube. I think here in the U.S. a chest tube is recommended. ³

Oxygen also seems to help. A study in 1983 showed that higher oxygen levels increased the speed of pneumothorax resolution. Previous studies had patients inhaling room air. So, those study results were already known to the researchers. So, their goal was to see if higher oxygen concentrations (i.e. greater than 28%) improved the speed of pneumothorax resolution. ¹

Here's what the researchers reported: 

"6 patients with pneumothoraces of less than 30% showed a mean resolution rate of 4.2% per day with reduction to one-third original size in the first 72 h. This was more than three times the rate of resolution (1.25% per day) previously reported with breathing room air alone. In 2 patients who initially received a lower concentration of inspired oxygen via nasal cannula, the rate of absorption increased after placing them on a partial rebreathing mask." ¹

They concluded that high flow oxygen speeds up the pneumothorax resolution process. The theory is that oxygen washes out alveolar nitrogen. This in turn lowers the partial pressure of nitrogen. This is good because nitrogen slows absorption of air. So, it's not so much the oxygen that speeds up re absorption, it's the lowered partial pressure of nitrogen that speeds it up. 

At least that's the theory.

Is this theory credible?

This theory seems credible. It was during the 1960s that it was suspected. This was when it was learned that the partial pressure in the capillaries and venous system was the same as atmospheric pressure. However, this changed when 100% oxygen was administered.

With 100% oxygen nitrogen is washed out of alveoli. In the 1960s, it was observed that this effect causes a drop in the partial pressure of alveolar nitrogen from 573 to zero. This is a result of the partial pressure of arterial oxygen increasing from 100 to 640 mmHg. This in effect causes a change in the partial pressure of alveolar oxygen. This in turn changes the partial pressure of oxygen in capillaries.⁵

While inhaling room air, the partial pressure of capillary oxygen is It's 706 mmHg. While inhaling 100% oxygen, this decreases to 146 mmHg. This is important, as the flow of air travels to areas of higher pressure to lower pressures. So, this change in pressure causes an increased rate of reabsorption of air from the pleural space.⁵

What are the risks?

The potential risks always have to be weighed against potential benefits. Potential benefits in the case of pneumothorax is recovery. Although, one might speculate this would happen with or without high flow oxygen. Still, high flow oxygen speeds up the process. So, this is definitely a benefit. 

One study showed that wearing a nonrebreather for as little as three hours increased the risk for developing certain cancers. More recent studies link long-term low flow supplemental oxygen use with lung cancer. A common theory explaining this phenomenon is oxidative stress.^6-8 

Another risk is hypercarbia. John Haldane (1860-1936) described how oxygen has a higher affinity for hemoglobin than carbon dioxide. So, inhaling 100% FiO2 causes lots of oxygen molecules to enter arterial blood. These oxygen molecules push carbon dioxide off hemoglobin. These carbon dioxide molecules increase the partial pressure of arterial blood. This effect can be toxic to some people with COPD. This theory makes more sense than the hypoxic drive hoax.

So, these are two risks worthy of consideration.

What to make of this?

There is ample evidence supporting oxygen use for treating pneumothorax patients. The goal is to exceed 28% FiO2, although higher FiO2s seem to prove beneficial for these patients. I have yet to see any studies of HFNCs for these patients. So, at the present time, it's my conclusion that HFNCs are recommended mainly due to patient comfort. They allow delivery of high oxygen levels without having to wear an uncomfortable mask. If you are aware of any such studies please let me know in the comments below. As we learn more we will be sure to keep you posted. 

References.

1. Chadha T.S., Chon M.A., "Noninvasive Treatment of Pneumothorax with Oxygen Inhalation," Respiration, 1983, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600088/, accessed 8/18/19
2. Currie, et al, "Pneumothorax: An Update," Postgraduate medical Journal, 2007, July, https://www.mayoclinic.org/diseases-conditions/pneumothorax/symptoms-causes/syc-20350367, accessed 8/18/19
3.  Choi, Won-II, "Pneumothorax," Tuberculosis And Respiratory Disease (Seoul), 2014, March, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3982243/, accessed 8/18/19
4. Johnson, Jon, "Pneumothorax: Causes, Symptoms, And Treatment," 2017, June, https://www.medicalnewstoday.com/articles/318110.php, accessed 8/18/19
5. Northfield, T.C., "Oxygen Therapy for Spontaneous Pneumothorax," British Medical Journal, 1971, https://pdfs.semanticscholar.org/48ec/cf2353788a28b02355a31a23844a298cf618.pdf, accessed 8/18/19
6. Garcia, et al., "Lung Cancer in COPD patients on Home Oxygen Therapy, European Respiratory Journal, 2016, https://erj.ersjournals.com/content/48/suppl_60/PA2794, accessed 8/18/19
7. Valavanidis, et al., "Pulmonary oxidative stress, inflammation and cancer: respirable particulate matter, fibrous dusts and ozone as major causes of lung carcinogenesis through reactive oxygen species mechanisms," International Journal of Environmental Research and Public Health, 2013, August 27, https://www.ncbi.nlm.nih.gov/pubmed/23985773, accessed 8/18/19
8. "Can Inhaled Oxygen Cause Cancer," Science Daily, 2015, January 13, https://www.sciencedaily.com/releases/2015/01/150113090550.htm, accessed 8/18/19