Hypoxemia: Oxygen Therapy and Ventilation/Perfusion (VQ) Mismatches

Hypoxemia is an abnormally low concentration of oxygen in the blood which can lead to dire consequences when left unmanaged. In most patients with hypoxemia, the application of supplemental oxygen is a quick bandaid therapy that is often applied to counteract the problem. However, have you ever applied supplemental oxygen to a patient experiencing hypoxemia and there has been a minimal effect? Have you ever wondered why the application of supplemental oxygen works in some patients but not others? It all comes down to what is causing the hypoxemia and understanding the pathophysiology behind a ventilation/perfusion (VQ) mismatch.

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The Hypoxic Drive Theory…DEBUNKED!

breathing hypoxic drive

We’ve all heard it at some point or another: “Don’t give that COPD patient too much oxygen”. It has led us to believe that oxygen is a REALLY bad thing in patients with chronic obstructive pulmonary disease (COPD). This has caused nurses to be afraid to put oxygen on a COPD patient with low oxygen saturations (SpO2); yes, even in patients with SEVERE hypoxia! Why? Because of a little something known as the hypoxic drive… Continue reading

Chest X-Ray Interpretation in 7 Easy Steps!

chest xray analysis

It is important to understand that when a chest x-ray is taken, light is absorbed according to the density of what it passes. We have different densities within our bodies ranging from bone, to tissue, to fluid, to air. This results in a monochrome display ranging between white to black. There are three distinct things you should look for on a chest x-ray and they all rhyme: Continue reading

Oxygen Flow Rate and FiO2: Understand the Relationship!

Oxygen, we all need it! We do not need a lot of it under normal circumstances, with 0.21 being the fraction of inspired oxygen (FiO2) of room air. FiO2 is defined as the concentration of oxygen that a person inhales.  The air that we inhale on a day to day basis is made up of 21% of oxygen, 78% of nitrogen and 1% of trace elements such as argon, carbon dioxide, neon, helium and methane. For the purposes of this article, fractions and percentages will be used interchangeably for ease of explanation.  Continue reading

Diagnose ANY Arterial Blood Gas in 5 Easy Steps: Get it Right, Every Single Time!

It is important to understand that the pH in our bodies likes to stay within the very narrow range of 7.35 – 7.45. In the physiologically functioning body, this is achieved by the respiratory system maintaining a carbon dioxide (CO2) level between 35 – 45 mmHg and the metabolic system maintaining a bicarbonate level between 22 – 26 mEq/L.

When a pathophysiological process causes the CO2 or bicarbonate levels in our body to move outside of their normal ranges, the pH is affected and also moves outside of it’s normal range. Continue reading

Respiratory Failure: Type 1 or Type 2?

To recap the last blog post about oxygen saturations versus PaO2:

  • Respiration is the process of gas exchange, both at the alveoli to blood interface and blood to cellular tissue interface
  • Oxygen has to bind to haemoglobin in order to be effectively transported around the body, but must dissociate from the haemoglobin prior to be taken up by the cells
  • The amount of haemoglobin in the body that has oxygen attached is measured via oxygen saturations while the amount of oxygen freely floating in the blood unattached to haemoglobin is measured via PaO2
  • When we experience a failure to oxygenate, we have a problem with our oxygen
  • A decrease in oxygen saturations below 90% will cause the body to increase it’s ventilatory effort as a compensatory mechanism
  • A failure to oxygenate is known as type 1 respiratory failure, defined as a decreased PaO2 with a normal carbon dioxide level

In this blog post, we are going to discuss type 1 and type 2 respiratory failure in detail and explore which pathophysiological respiratory conditions lead to which type of failure. Continue reading

Oxygen Saturations Versus PaO2

To recap the last blog post about the importance of counting respiratory rate:

  • Ventilation is the physical movement of air in and out of the lungs
  • In a normal person, it is an elevated carbon dioxide level in our bodies that causes the respiratory centre in our brain to initiate a breath
  • When we experience a failure to ventilate, we have a problem with our carbon dioxide
  • A decrease in oxygen saturations only occurs at the point of decompensation when the patient can no longer keep up the ventilation effort/work of breathing to clear their carbon dioxide
  • A failure to ventilate is known as type 2 respiratory failure, defined as elevated carbon dioxide levels and low oxygen levels
  • Low oxygen levels in a patient failing to ventilate is a late sign and deterioration should be picked up earlier by monitoring the trend of the respiratory rate and work of breathing

In this blog post, we are going to discuss respiration and the relationship between oxygen saturations and the partial pressure of oxygen (PaO2) in our bodies when we are experiencing a failure to oxygenate (type 1 respiratory failure). Continue reading

The Importance of Counting Respiratory Rate

Having attended numerous MET calls and code blues over the years, there is a trend that becomes quite noticeable. Despite the blood pressure, heart rate and oxygen saturations trending up or down; the respiratory rate predominantly stays the same right up to the point just before the MET call or code blue is called. Continue reading