User:Bron766/Arterial and venous blood gas/tutorial 1

Tutorial 1: Interpret the acid-base results of an Arterial Blood Gas.

Subject classification: this is a medicine resource.

This is a set of exercises for practising skills related to Arterial Blood Gas (ABG) acid-base interpretation. You can work through all of the exercises or jump to whichever one you like. The first 4 steps cover the basics of ABG acid-base interpretation. There are a number of more detailed interpretation steps hidden at the bottom of the page when you're ready for them.

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Step 1: Is the ABG normal or abnormal?

What is a normal v. abnormal pH range?

Explanation
Normal pH is between 7.35 and 7.45.

Quiz me!

You can use this quiz however you like. No marks are permanently recorded and there is no penalty for a wrong answer, so you may as well just have a go. You can skip questions or only answer one question. Press submit for feedback. 1 An arterial blood pH of 7.4 is Too low Normal Too high 2 An arterial blood pH of 6.9 is Too low Normal Too high 3 An arterial blood pH of 7.8 is Too low Normal Too high 4 An arterial blood pH of 7.37 is Too low Normal Too high 5 An arterial blood pH of 7.41 is Too low Normal Too high 6 Normal arterial blood pH values include: 7 7.42 3.5 7.50 7.36 7.35 7.45 7.46 7.4 7.44

What is an abnormal level of pCO₂ or [HCO₃^-]?

Explanation
Normal pCO2 is between 35 and 45 mmHg. Normal [HCO3-] is between 22 and 26 mEq/L.

Quiz me!

1 Question: What is the highest level that arterial blood pCO2 can reach and still be normal? mmHg What is the lowest level that arterial blood HCO3- can reach and still be normal? mEq/L 2 How would you interpret this ABG? pH = 7.25, pCO2 = 60, [HCO3-] = 26 pH is too low pH is normal pH is too high pCO2 is too low pCO2 is normal pCO2 is too high [HCO3-] is too low [HCO3-] is normal [HCO3-] is too high 3 How would you interpret this ABG? pH = 7.8, pCO2 = 25, [HCO3-] = 38 pH is too low pH is normal pH is too high pCO2 is too low pCO2 is normal pCO2 is too high [HCO3-] is too low [HCO3-] is normal [HCO3-] is too high

Step 2: Is the problem acidemia or alkalemia?

What is the difference between the terms acidosis, acidemia, alkalosis and alkalemia?

Explanation

Some acid-base terms are confusing! Acidemia means the overall pH is too low. Alkalemia means the overall pH is too high. But often things are complicated and there are multiple abnormal processes going on in the one patient. Each individual process may be pushing the pH in a different direction: Acidosis is a process that is lowering the pH. Alkalosis is a process that is raising the pH. The overall pH is the sum of all the different processes happening at once. So even if the overall pH is low (acidemia), there might be an underlying acidosis AND an alkalosis at work. Or there might be multiple different acidoses at work (read more on that later).

Quiz me!
1 A pH of 8 can be described as Acidemia Alkalemia 2 A pH of 7 can be described as Acidemia Alkalemia 3 True or false: A patient with a pH of 7.21 has at least one source of acidosis in their body. True False 4 True or false: A patient with a pH of 7.33 does not have an alkalosis. True False 5 True or false: A patient with a pH of 7.4 does not have any acidosis or alkalosis. True False

Step 3: Is the primary problem respiratory or metabolic?

Acidemia: is the cause respiratory or metabolic?

Explanation

Acidemia can be caused by: respiratory acidosis (high pCO2) and/or metabolic acidosis (low [HCO3-]) For example, poor lung ventilation causes CO2 to build up, eventually making the blood acidic. There can of course be more than one problem or abnormal acid/base process happening at once. For example, the primary problem can cause the body to compensate by increasing the opposite process to try and return the pH to normal.

Quiz me!

1 An acidemia with a high pCO2 is primarily caused by a Respiratory acidosis Metabolic acidosis 2 An acidemia with a pCO2 of 60 mmHg is primarily caused by a Respiratory acidosis Metabolic acidosis 3 An acidemia with a pCO2 of 40 mmHg and a [HCO3-] of 16 mEq/L is primarily caused by a Respiratory acidosis Metabolic acidosis 4 An acidemia with a pCO2 of 65 mmHg and a [HCO3-] of 16 mEq/L is Normal Caused by a respiratory acidosis Caused by a metabolic acidosis Caused by a mixed respiratory and metabolic acidosis 5 pH 7.26, pCO2 20 mmHg and [HCO3-] of 8.8 mEq/L is Normal Caused by a respiratory acidosis Caused by a metabolic acidosis Caused by a mixed respiratory and metabolic acidosis 6 pH 7.33, pCO2 25 mmHg and [HCO3-] of 13 mEq/L is Normal Caused by a respiratory acidosis Caused by a metabolic acidosis Caused by a mixed respiratory and metabolic acidosis

Alkalemia: is the cause respiratory or metabolic?

Explanation
Alkalemia can be caused by: respiratory alkalosis (low pCO2) and/or metabolic alkalosis (high [HCO3-])

Quiz me!

1 An alkalemia with a high [HCO3-] suggests a Respiratory alkalosis Metabolic alkalosis 2 An alkalemia with a pCO2 of 20 mmHg suggests a Respiratory alkalosis Metabolic alkalosis 3 An alkalemia with a pCO2 of 40 mmHg and a [HCO3-] of 30 mEq/L suggests a Respiratory alkalosis Metabolic alkalosis 4 pH 7.6, pCO2 20 mmHg and [HCO3-] of 19.4 mEq/L is Normal Caused by a respiratory alkalosis Caused by a metabolic alkalosis 5 pH 7.44, pCO2 26 mmHg and [HCO3-] of 17.4 mEq/L is Normal Caused by a respiratory alkalosis Caused by a metabolic alkalosis

Step 4: Is it compensated or uncompensated?

Respiratory acidosis/alkalosis: compensated or uncompensated?

Explanation
If a respiratory acidosis (with high pCO2) is compensated, the [HCO3-] is also high. If a respiratory alkalosis (with low pCO2) is compensated, the [HCO3-] is also low.

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Metabolic acidosis/alkalosis: compensated or uncompensated?

Explanation
If a metabolic acidosis (with low [HCO3-]) is compensated, the pCO2 is also low. If a metabolic alkalosis (with high [HCO3-]) is compensated, the pCO2 is high.

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More advanced steps: coming soon, click here for a preview

If it is metabolic acidosis, is it normal or high anion gap? Explanation Coming soon Quiz me! Coming soon If it is metabolic alkalosis, is it chloride responsive? Explanation Coming soon Quiz me! Coming soon Is it complete or partial compensation? Explanation Coming soon Quiz me! Coming soon Match the ABG results to the clinical situation Common causes of acid-base disorders Explanation Coming soon Quiz me! Coming soon Common signs of acid-base disorders Explanation Coming soon Quiz me! Coming soon Mixed acid-base disorders: Describe approximate guidelines for the expected change in pH with high pCO2 Describe approximate guidelines for the expected change in pH with change in [HCO3-] Describe approximate guidelines for the expected change in pCO2 with low [HCO3-] Interpret base excess results Calculate the percent difference ratio Use Winter's formula Calculate the delta ratio Calculate the corrected bicarbonate Calculate the strong Ion difference or stewart approach

http://www.youtube.com/watch?v=5wW2RYGUDV4 alternative method