Wednesday, June 7, 2017

1920-1980: The evolution of oxygen delivery devices

By the mid 1920s many of the challenges of oxygen therapy had been tackled.  Oxygen could be easily produced, stored in tanks, and delivered to the patient.  There also existed the means of confirming oxygenation status of patients, and the effects of oxygen therapy.  So the stage was set for oxygen to be introduced to hospitals.

In 1922 John Haldane wrote about his research in "The Therapeutic Administration of Oxygen."
Soon thereafter oxygen tanks became more and more common at the patient bedside.  The tanks were stored in closets, and when needed were strapped by the patient bedside.

There were various devices available for providing oxygen, which included a metal nasal cannula, a nasal catheter, the oxygen chamber, the Haldane Apparatus, and the oxygen rebreather mask or mouthpiece and an oxygen tent.  For patients that were comatose, any device needed to provide therapeutic oxygenation could be used.  For awake and alert patients, the mask posed a claustrophobic feeling, and it was also hot.  The same was true with the oxygen tent.  So the physician would basically have to base what oxygen device he used on the patient.

One of my readers at my Respiratory Therapy Cave blog informed me that, the first practical oxygen tent was invented by Doctor Benjamin Eliasoph in 1921, at The Mount Sinai Hospital,New York, with rubberized fabric from the Goodyear Rubber Company, Aeronautical Division used for balloons such as the widely known Goodyear Blimp." 

This information is confirmed in a New York Times obituary for Dr. Benjamin Eliasoph, which notes: "Dr. Benjamin Eliasoph, a physician at Mount Sinai Hospital who was a pioneer in the design of the oxygen tent, died Sunday at the hospital. He was 70 years old."

The first mass producible oxygen tent was invented by Doctor Leonard Hill.  It consisted of a canopy with slots so the patient could see out that was placed over the bed and patient, and a machine was set at the bedside that blew oxygen into the tent and over the patient.

Dennis Glover, in his 2010 book "A History of Respiratory Therapy," said there was no means of cooling the atmosphere inside these tents, and being inside was almost unbearably hot and uncomfortable for many patients.

Glover said that the most common use for the oxygen tent was for patients presenting with cyanosis due to heart failure or pneumonia.  Some patients would beg to get out of the tents, Glover explained, yet once out they would became short of breath and they'd beg to get back in.  So it was sort of a double edged sword for the patient until the patient got better, if they got better.  Some critics complained such tents basically provided a tortuous method of ending a person's life, and petitioned for their demise.

In 1926 Alvin Barach invented an oxygen tent that blew air over ice chips to cool the temperature inside the tent.  This made it so being inside the tents was much more bearable.  Usually these they were reserved for patients with pneumonia and heart failure. (2)

In 1931 John Emerson invented an oxygen tent that had a cooling system.  Previous devices were prone to rust and failure.  (7)

The metal cannula was another device that was used.  It was a narrow metal pipe that was secured to the forehead by a strap that wrapped around the head, and at the lower end of the pipe were two prongs that were inserted into the nares.  I can imagine this may have felt awkward for the patient, but it may have been much nicer than having to lie inside an oxygen tent or having a rubber mask on your face.

The nasal catheter was introduced to the world by Lane in 1907, and introduced to the United States in 1931 by Waters and Wineland. (3)  Between 1920 and 1960 the nasal catheter was the most widely used method of delivering oxygen to patients. (8)

Glover explained that by the 1960s vinyl had been invented and this technology spread to the medical profession.  Masks, catheters, nasal cannulas and tubing were then made of this new material, and were much more comfortable for patients.  (2)
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Another benefit was the material was see through, and this allowed the caregivers to see right away if the mask was filling with secretions, vomit or pulmonary edema. This made the masks much safer. They were also disposable, so it removed the need to clean and sterilize between patients.

Vinyl nasal cannulas quickly became the preferred basic oxygenation device, and this slowly caused the demise of the nasal catheter.

The nonrebreather was also introduced during the 1920s.  For those not familiar with these, they involve placing a mask tightly over the patients face to prevent the entry of room air. A one way valve on the mask allows the patient to exhale, but it closes on inhalation. This forces the patient to inhale only oxygen, which enters the airway from tubing which is connected from the mask to an oxygen flow meter. A bag connected to the mask collects oxygen while the patient is exhaling. When the patient inhale, inhales oxygen that is stored in the bag.

It is called a nonrebreather because the patient is not rebreathing any exhaled air. The idea here is that, if there is that if the mask is sealed tightly around the patient's face, and the one way valves are working, then the patient should be inhaling 100% oxygen.

Of course a problem with this system is that there were no surefire methods of knowing how much oxygen was left in an oxygen tank. So when a tank became empty, the patient had not oxygen to inhale, and would die of asphyxia. Learning this the hard way must have given quite a fright to some early orderlies, nurses and doctors.

The remedy to this problem was to remove one of the one way valves to assure that, if the oxygen tanks to run empty, that the patient can still inhale some room air. This is how most nonrebreather masks are produced today. So, while some people still report that nonrebreathers give patients 100% oxygen, the actual percentage is estimated to be between

Nonrebreathers of today aren't even nonrebreathers at all: they are partial rebreathers. Still, it is very common for them to be called nonrebreathers. They aren't generally referred to as partial nonrebreathers until both one way flaps are removed. With both flaps removed, the patient's estimated FiO2 is about 50-60%.

This represents one of the medical conundrums in medicine.

Early masks were also not see through, so if a patient vomited you might not know right away. Newer masks are made of disposable material that is see through, eliminating some of the older complications from these masks.

Regardless, nonrebreathers were good devices for oxygenating patients suffering from acute anoxia.

The next evolutionary breakthrough in oxygen delivery devices came as a result of observations made during the 1950s that some patients given 100% oxygen were becoming lethargic. It was soon realized that these were patients with emphysema and chronic bronchitis, or what we now refer to as chronic obstructive pulmonary disease (COPD).

This was where the hypoxic drive theory was derived from. You can learn about this theory in my post, "Hypoxic Drive Theory: A History of the Myth."  Essentially, this theory postulates that giving too much oxygen to some COPD patients might blunt their drive to breathe. So this resulted in the market for a better oxygen delivery device, and the invention of the Venturi Mask.

The new masks were based on the Venturi Principle, and allowed physicians the opportunity to provide accurate oxygen levels up to 50%. Nasal catheters, and later cannulas, were the preferred method of oxygenating these patients. However, because these devices are low flow devices, changes in the rate and depth of breathing make these less effective. Venturi masks were nice because they guaranteed the patient would get the desired oxygen level.

This was because the masks were based on the Venturi Principle. An adjustable opening allowed the caregiver to determine how much air was being inhaled. The larger the opening, the more air was inhaled and the less oxygen inhaled. The smaller the opening the less air was inhaled and the more oxygen was inhaled. So oxygen could now be set at between 28 and 50%, and this would not be affected by changes in rate or depth of breathing. It was a nice concept, especially for COPD patients.

These masks are still used today as a nice option for patients who are in respiratory distress, or who need a little more oxygen than a nasal cannula can provide, but don't quite need anything higher than 50%. They are generally only made as a temporary oxygen device, although some patients with terminal lung diseases (such as lung cancer) may occasionally use one at home.

By the 1980s plastic had been invented, and during this decade most respiratory therapy devices were slowly replaced by plastic.  Plastic nasal cannulas, masks, and nebulizers were introduced in the early 1980s and slowly phased into various hospitals through assimilation.

The earliest oxygen humidifiers were either made of metal or glass.  Until plastic was invented, none of the equipment here was disposable, and needed to be washed, sterilized, dried, and restocked on the shelves before being set up on the patient. So cleaning respiratory therapy equipment became sort of a secondary job for therapists until this aspect was phased out by turn of the 21st century.

References:
  1. Hess, Dean,  Neil MacIntyre, Shelley Misha,"Respiratory Care:  Principles and Practice," page 281
  2. Glover, Dennis, "History of Respiratory therapy: discovery and evolution, ," 2010, Indiana, page 94
  3. Wyka, Kenneth A., Paul J. Mathews, John Rutkowski, editors, "Foundations of Respiratory Care," 2012, U.S., Delmar, page 9
  4. Hess, Dean,  Neil MacIntyre, Shelley Misha,"Respiratory Care:  Principles and Practice," page 281
  5. Barach, Alvin L., "The Therapeutic Use of Oxygen," The Journal of the American Medical Association, Vol 79, No. 9, Chicago, October 26, 1922, page 693-699
  6. Barach, Alvin L, Margaret Woodwell, "Studies in oxygen therapy with determinations of blood gases," Archives of Internal Medicine, Vol. 28, 1921, Chicago, American Medical Association, pages 367-393
  7. Branson, Richard D, "Jack Emerson:  Notes on his life and contributions to Respiratory Care," Respiratory Care, July 1998, vol. 43, no. 7, pages 567-71
Further Reading:

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