When discussing this topic, understanding the relationship between oxygenation and ventilation is the most important aspect. We will discuss the movement of oxygen therapy from nasal cannula to non-rebreather and the use of NPPV (Noninvasive Positive Pressure Ventilation) and will briefly discuss mechanical ventilation.
- Oxygenation: movement of oxygen from the alveoli to the bloodstream for cellular use and occurs throughout the body.
- Ventilation: simply the movement of air, but we will focus on it being the movement of carbon dioxide from the blood to the alveoli, removed as a waste product from the lungs.
Before we discuss how these factors are incorporated into oxygen therapy, let us go through terms that are typically used when discussing this topic.
- pH (acidity or base of blood): range between 7.35 – 7.45, where less than 7.35 is acidosis whereas above 7.45 is alkalotic.
- PaO2 (Partial Pressure of Arterial Oxygen): range between 80 – 100 mmHg, allows us to determine severity of hypoxemia or oxygen toxicity.
- PaCO2 (Partial Pressure of Carbon Dioxide): range between 35 – 45 mmHg, where hypoventilation (retention of carbon dioxide – higher CO2) and hyperventilation (loss of carbon dioxide – lower CO2).
- SPO2 (Saturation of Arterial Oxygen) – range between 90 -100% and determined by amount of light that passes from one part of the pulse oximeter to the other (secret fact!).
- HCO3- (Bicarbonate) – range between 22 – 28 mEq/L , where elevated HCO3 (leads to pH > 7.45 or alkalosis) & where decreased HCO3- (leads to pH < 7.35 or acidosis).
Now that we have all those upper- and lower-case letters done, we can talk about how to simplify what to use and WHEN to use it, and we will tie those words into these topics.
1. Oxygenation
When changes to oxygenation occur the major values, you want to monitor are the following pH, PaO2 and SPO2. These are important because they tell us how well oxygen is being delivered and utilized, which are two different concepts.
Delivery can be understood as the hemoglobin’s ability to carry oxygen (four oxygen molecules per hemoglobin) and utilization is the tissue’s ability to use that oxygen in aerobic metabolism.
When comparing these two concepts to practice when we have a delivery issue, we will expect to see a decreased SPO2 (less than 90% on the monitor – usually that blue number) and a decreased PaO2 (less than 80 mmHg).
Presentation wise our patient will be “air hungry” they can have tachypnea, accessory muscle use, and deep respiratory patterns. This is due to them wanting to get as much oxygen as they can into their lungs. This means that they can be described as.
- Hypoxia; decreased amount of oxygen to the tissues
- Hypoxemia; decreased amount of oxygen in the blood
When faced with this issue the treatment is getting more oxygen which means increasing their FIO2 (Fraction of Inspired Oxygen).
This value ranges from 21% which we know as room air to 100% which instead of a mixture of oxygen, nitrogen and other gases they are receiving complete oxygen through their device.
- Standard Nasal Cannula: 24 – 35% FiO2 at a flow of 1 – 4L/Min.
- Simple Face Mask: 40 – 60% FiO2 at a flow of 5L/Min.
- Nonrebreather Mask: >60% FiO2 at a flow of 15L.
- Venturi Mask: 24 – 60% FiO2 (suitable for patients with risk for hypercapnic respiratory failure).
- High Flow Nasal Cannula (heated and non-heated): 21 – 100 % FiO2 at 2 – 80 L/Min.
- CPAP (Continuous Positive Airway Pressure): occurs during the entire oxygen cycle where their CPAP level is set typically 5 – 10 cmH20, allowing for alveolar recruitment leading to increased surface area for diffusion.
When noticing that your patient is deteriorating in terms of oxygenation, movement through these forms of therapy is imperative to reduce poor outcomes. DO NOT fear throwing someone on a nonrebreather if they begin to spiral, because if they recuperate rapidly then reduce their FiO2 and device and if they do not well good luck CHARLIE!
2. Ventilation
When discussing ventilation, the main parameter we will be discussing is PCO2 (Partial Pressure of Carbon Dioxide). This is an unusual way to think about this concept, but it will allow you to make quick changes.
Deciding to use NPPV or Noninvasive Positive Pressure Ventilation is imperative in two main situations when the patient has an increased work of breathing and when carbon dioxide removal is the objective. When comparing CPAP (Continuous Positive Airway Pressure) and BIPAP (Bilevel Inspiratory Positive Pressure), there is just the difference between either one main setting or two.
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CPAP (Continuous Positive Airway Pressure): occurs during the entire oxygen cycle where their CPAP level is set typically 5 – 10 cm H20, allowing for alveolar recruitment leading to increased surface area for diffusion.
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BIPAP (Bilevel Inspiratory Positive Pressure): occurs when there are two levels being:
- EPAP (Expiratory Positive Airway Pressure) which is like CPAP in the sense that it activates during expiration and is a continuous pressure that allows for alveolar recruitment thus increased surface area for oxygenation. With a normal range from 5 – 12 cm H20.
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IPAP (Inspiratory Positive Airway Pressure) which occurs during inspiration and allows a patient’s work of breathing to decrease while overcoming the resistance seen in certain disease processes (e.g., pneumonia, pleural effusion, pulmonary edema), and the tubing of the BIPAP machine. With a normal range from 5 –20 cm H20.
The BIPAP machine is beneficial because if our PaO2 is decreased and our patient’s SPO2 is decreased we can increase FIO2 or EPAP (remember this helps with opening the alveoli leading to increased gas exchange).
Another function is if we have an elevated PaCO2, we can increase our tidal volume (the size of the breath), respiratory rate (the speed we are breathing at) and IPAP (the pressure at inspiration to improve breathing).
Overall, below I have listed situations where a BIPAP machine would be appropriate intervention.
- ABG (Arterial Blood Gas) or VBG (Venous Blood Gas) has an elevated PaCO2; increase respiratory rate, tidal volume or IPAP.
- ABG (Arterial Blood Gas) or VBG (Venous Blood Gas) has decreased PaO2; increase FiO2 or EPAP (remember that we can use typical oxygen therapies to help first).
- Patient has an increased work of breathing (e.g., tachypneic, accessory use, nasal flaring).
3. Combining Concepts
When our patients have reached their maxed settings on the listed devices, worsening diagnostic, or laboratory findings (e.g., ABG or VBG), exhibit altered mental status or presentation, or cannot protect their airway. It is imperative that we take over their respiratory system and use an artificial airway and ventilators to their condition through resting, exercising, and healing their lungs.
These are some of the indications and the usefulness of mechanical ventilation. It allows you to use multiple settings, and modes to manipulate a patient’s respiratory system to hopefully improve their outcomes.