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Arterial Blood Gas Interpretation

ABGs are another one of those things that at first glance can seem a bit overwhelming. The good news is that they are really not as complicated as they first appear! The following sections break down some elements of ABG interpretation. 

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Understanding Respiratory Acidosis and Alkalosis


When we talk about respiratory acidosis or Alkalosis were also talking about Carbon dioxide (CO2), and the effort the lungs are making to clear it from the body.

It's not a good idea to hang on to too much CO2 in your blood, it combines with water and turns into an acid! But equally we don't want remove to much CO2 either as that will lead to alkalosis! 

There is only one way of getting CO2 out of our blood and that's through our lungs. We expel it when we breath out (on expiration), the more effort we put into breathing, the more co2 that will be cleared from out systems. 

Blood Gas Basics: Respiratory Acidosis & Alkalosis (Physiology & Interpretation made simple)

Blood Gas Basics: Respiratory Acidosis & Alkalosis (Physiology & Interpretation made simple)

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If we breath more rapidly we clear more CO2 from our systems. If we take bigger deeper breaths then we will also clear more CO2. 

Normally our bodies are very good at regulating our work of breathing to ensure that our blood CO2 levels, and therefore our blood pH levels, are within normal range. When our bodies 

IF the body is unable to expire enough CO2 through the lungs then the body may enter a respiratory acidosis. For example, to much opiate (eg. morphine) can suppress the respiratory centres of the brain leading to reduced respiratory effort and the build up of CO2 in the blood. A respiratory alkalis occurs when the lungs work to hard, clearing to much CO2 from our bodies. For example, someone having a panic attack may begin to hyperventilate leading to a lowering of their blood co2 levels.

resp acidoisi

Metabolic and  Respiratory Compensation 

I think this is one of the better videos I've made, so far as my aim is to present complex processes simply via graphics. However visually, it's not the most excitinging........ Try and stick with it as it does quite a good job of explaining what can be a quite confusing concept.  


Broadly speaking we have two components that can affect our blood pH. The respiratory component, and the metabolic component. However, these two components do not operate in isolation, the pH of the blood will be affected by respiratory and metabolic factors simultaneously


To put it very simply, an acidosis and an alkalosis can cancel each other out!

Let's look at an example

Your patient develops sepsis resulting in the excess production of lactic acid (a metabolic acidosis). The respiratory system can respond

Respiratory and Metabolic affects on blood pH (including compensation). ABG basics made Easy!

Respiratory and Metabolic affects on blood pH (including compensation). ABG basics made Easy!

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by making the patient breathe more rapidly and more deeply. They will blow off more CO2 sending them into a respiratory alkalosis. The net result is the patient returns to a neutral pH. The respiratory system has 'compensated' for the metabolic acidosis. 

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