Oxygen Therapy Made Easy: 3rd Edition

If a patient is unable to oxygenate appropriately on room air, supplemental oxygen is indicated. This Course will help you decide what oxygen equipment is available. It will also help you determine how much supplemental oxygen a patient needs.

BASIC DEFINITIONS

Supplemental oxygen: It is when you inhale more oxygen than what is supplied in room air. This can be accomplished by using the various equipment described below.

PaO2: This is the partial pressure of arterial oxygen. It the level of oxygen in your arterial blood. It is obtained by drawing blood from an artery. The normal ranges are as follows:

• Normal: 80-100
• Mild Hypoxemia: 60-79
• Moderate Hypoxemia: 40-59
• Severe Hypoxemia: 39 or less

SpO2: It's a measure of how saturated hemoglobin are with oxygen. It is essentially a measure of what percentage of the oxygen you inhale makes it to your arterial blood. Normal ranges are as follows.

• Normal: 95-98%
• Acceptable: 90% or better, and sometimes 88% or better with some disease conditions.
• CMS will not pay for home oxygen unless the SpO2 is 88% or lower on room air at rest
• SpO2 decreases with age, while sleeping, and with some disease processes.

4-5-6-7-8-9-Rule. 

Allows you to use SpO2 to estimate PaO2.

• SpO2 70% = PO2 of 40 (supplemental oxygen is essential on any patient in this range)
• SpO2 80% = PO2 of 50 (some COPD patients may live in this range
• SpO2 90% = PO2 of 60 (This is what you want to maintain for most patients)

Fraction of Inspired Oxygen (FiO2): This is the percent of oxygen a patient is inhaling. Room air FiO2 is 21%. By applying supplemental oxygen, we allow patients to inhale greater than 21% FiO2. In the hospital setting, we have the equipment to allow a person to inhale anywhere from 22-100% FiO2.

Indications for Oxygen Therapy:

• To correct hypoxemia
• To reduce oxygen demand on the heart
• Suspected or acute myocardial infarction (MI)
• Severe trauma
• Post anesthesia recovery

How much oxygen does a patient need?

Spectrum Health’s protocol calls for maintaining an oxygen saturation of 90% or greater or as specified by a physician. Our COVID-19 oxygen protocol calls for maintaining an oxygen saturation of 88% or greater.

How to determine if oxygen therapy is working:

You know oxygen therapy is working when:

• SpO2 improves to acceptable levels as determined by protocol or physician
• Respiratory rate decreases to the normal range.
• Tidal volume are not erratic
• Patient notes improved work of breathing
• Pulse is normal or improving
• Blood pressure is improved or improving
• Underlying condition is improving, or whatever occurred to cause the hypoxemia

LOW FLOW OXYGEN DEVICES. These are oxygen devices where room air will be entrained. Because of this, the exact FiO2 cannot be calculated. You can, however, estimate the FiO2. How much FiO2 is delivered to the patient is dependent on:

• Liter flow set at the flowmeter
• Respiratory rate and pattern of the patient
• Equipment reservoir (stores oxygen)

The following are low flow oxygen devices:

1. Nasal Cannula: The nasal cannula is the most common oxygen device used and the most convenient for the patient. A nasal cannula at 2lpm is usually a good place to start.

You may at times need to estimate the FiO2. How do you estimate the FiO2 on a nasal cannula? For every liter per minute, the FiO2 increases by 4% as per the chart below:

• 1 lpm = 24%
• 2 lpm = 28%
• 3 lpm = 32%
• 4 lpm = 36%
• 5 lpm = 40%
•  6 lpm = 44%

The liter flow on a nasal cannula should never exceed 6lpm, as studies show doing so is of no added benefit to the patient. Also note that the prongs of a nasal cannula should face down. A bubbler can be added to humidify the nose to prevent nasal drying and bleeds. This is automatically set up at flows greater than 5lpm, or as ordered by physician. You may also add a bubbler for any patient you think may benefit from it. Setting up and managing nasal cannulas is a shared responsibility of nurses and respiratory therapists.

2. Non-Rebreather Mask (NRB): This is a mask that ideally will bring in 100% Fio2 so long as the liter flow is 15 and there is a good seal between the mask and the patient's face. And all three one-way valves are on the mask to prevent air entrainment. The bag acts as a reservoir for oxygen for storing oxygen. So, when you inhale, you will be getting 100% Fio2.

For legal purposes, however, one flap is always removed just in case the oxygen gets shut off. And therefore the highest FiO2 you can get from an NRB is estimated to be around 75%.

3. Partial Rebreather Mask (PRB): This is basically an NRB with both one-way valves removed from the mask. The estimated FiO2 is 60-65%. Flow should be set at 6-15 LPM. Note: The flow should never be set lower than 6LPM. This is because flows less than this may not be enough to flush CO2 out of the system, and may cause the patients PaCO2 to rise. Now that we have high flow devices, PRBs are rarely indicated today. So, in the 4th edition this section may be deleted. 

3. Intermediary High flow Nasal Cannulas. These allow the patient to inhale flows up to 15 LPM by nasal cannula. The tubing is thicker. They also come with a bubbler to prevent nasal drying and bleeding.

HIGH FLOW OXYGEN DEVICES

These are oxygen delivery devices that meet the inspiratory flow demand of the patient. These devices will allow you to give an exact FiO2 to the patient. Respiratory rate and tidal volume of the patient have no effect on FiO2 delivered.

Ideally, the larger the entrainment port on the device the lower the FiO2, and the smaller the entrainment port the higher the FiO2. A major disadvantage is a mask is required, and this may be a bit more uncomfortable than a nasal cannula.

1. Venturi Mask: These masks are ideal for patients with high respiratory rates. They allow you to deliver anywhere from 28-50% FiO2. These masks have various caps that connect to the mask and oxygen tubing. Each cap has a different color and a different size air entrainment port. Basically, the smaller the entrainment port the higher the FiO2. At most hospitals, each cap will have on them what the FiO2 will be delivered and what flow to set the flowmeter at. The flow can be higher than this. But it must never be lower in order to assure CO2 is being adequately cleared from the mask. These masks are ideal for patients with COPD who are in respiratory distress. The most common settings used are 40% and 50%.

2. Aerosol set-up: These devices will deliver anywhere from 21-100% FiO2. An adjustable air entrainment device sits on top of a water bottle. This is connected to a flowmeter. The entrainment device can be adjusted to the desired FiO2. The desired flow to set the device at a given FiO2 is written on the side of the bottle. Wide bore tubing from the entrainment device is connected to a mask.

These are ideal for patients with tracheotomies. This is because the wide bore tubing connects nicely to trach collars. They are nice because they allow us to easily make sure they are getting adequate humidification and oxygenation.

3. High flow nasal cannula: These are machines that allow us to deliver flows up to 60 LPM. They are connected to heat and humidity so the patient’s nose does not become irritated.

4. CPAP and BiPAP Machines. Home devices allow for oxygen tubing to be bleed into the system. This allows the patient to inhale low amounts of oxygen at home. Hospital devices allow us to deliver anywhere from 21-100% FiO2.

5. Ventilators. These also allow us to deliver 21-100% FiO2.