OH Please
Help the light come !!!!!!Acid / Base
OH Please
Help the light come !!!!!!
Watch this review on electrolytes (click on the electrolytes tutorial)
Good site explaining electrolytes
The interactive Oxyhemoglobin Dissociation Curve
Excellent site for Acid / Base
www.nurseshift.com/ABG/tutor3.htm
www.rnceus.com/abgs/abgframe.html: A great review and interactive.
Good lab values to memorize
Many nurses have difficulty interpreting arterial blood gases (ABGs). Confusion often results when too many pieces of information are analyzed at the same time. Therefore, it is helpful to separate the components of ABGs and categorize the information that they provide.
When ABGs are divided into their major components (acid/base balance and oxygenation), they become much easier to understand.
The pH tells us if the patient is acidotic or alkalotic. The pCO2 and HCO3 tell us where the acid/base abnormality comes from and whether there is compensation. Finally the pO2 and O2 saturation tell us about oxygenation.
To break this process down further use the six simple steps below:
Review these ABGs to see if you agree with the results:
ACUTE WORKSHEET
| ABG # | pH | PaC02 (torr) | HC03 (mEq/L | Pa02 torr |
| 1 | 7.23 | 55 | 23 | 55 |
| 2 | 7.01 | 43 | 17 | 88 |
| 3 | 6.98 | 88 | 23 | 47 |
| 4 | 7.45 | 35 | 22.5 | 94 |
| 5 | 7.47 | 33 | 26 | 83 |
| 6 | 7.55 | 38 | 29 | 58 |
| 7 | 7.60 | 42 | 32 | 43 |
| 8 | 7.00 | 61 | 23.4 | 37 |
| 9 | 7.13 | 54 | 23 | 64 |
| 10 | 7.34 | 39 | 21 | 75 |
See below for answers
| ABG # | Acid-base Interpretation | Oxygenation Interpretation |
| 1 | acute respiratory acidosis | moderate hypoxemia |
| 2 | acute metabolic acidosis | no hypoxemia |
| 3 | acute respiratory acidosis | moderate hypoxemia |
| 4 | Normal !!!! | no hypoxemia |
| 5 | acute respiratory alkalosis | no hypoxemia |
| 6 | acute metabolic alkalosis | moderate hypoxemia |
| 7 | acute metabolic alkalosis | severe hypoxemia |
| 8 | acute respiratory acidosis | severe hypoxemia |
| 9 | acute respiratory acidosis | mild hypoxemia |
| 10 | acute metabolic acidosis | mild hypoxemia |
Welcome to Partial Compensation!
This is the step in acid-base imbalance which occurs after the acute stage, considering the acute stage has not been reversed.
After hours of an acid-base imbalance, the lungs or kidneys now try to help bring the pH back toward normal. The tip here is that ALL parameters are outside normal limits!
Example: Acute respiratory acidosis -
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.22 | 55 | 24 |
If left untreated for a few hours, the blood gas will change to this:
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.25 | 55 | 28 |
Note the parameters that changed! The KIDNEYS tried to help out a respiratory problem by retaining a buffer (bicarb) and the pH is moving toward normal, but is not yet there. Try another:
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.04 | 30 | 18 |
This is the opposite of the former example. This is a partially compensated, metabolic acidosis.
What HAS tried to help this abnormality out?
Lungs, YES! The patient is hyperventilating, trying to get rid of C02, a potential acid. The pH acutely, was probably lower.
Try these exercises:
| ABG # | pH | PaC02 (torr) | HC03 (mEq/L) |
| 1 | 6.99 | 57 | 33 |
| 2 | 7.56 | 23 | 17 |
| 3 | 7.47 | 50 | 32 |
| 4 | 7.32 | 23 | 19 |
| 5 | 7.28 | 66 | 29 |
Answers: (pc = partially compensated)
| ABG # | Interpretation |
| 1 | (pc)respiratory acidosis |
| 2 | (pc)respiratory alkalosis |
| 3 | (pc)metabolic alkalosis |
| 4 | (pc)metabolic acidosis |
| 5 | (pc)respiratory acidosis |
Welcome to the last stage of acid-base imbalance: COMPENSATION!
We started with the acute phase which appeared instantly:
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.56 | 23 | 24 |
If left untreated for hours, it moved to partial compensation:
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.53 | 23 | 19 |
NOW, after days or months of untreated acid-base imbalance, the pH will now be in normal limits, but the other parameters will be abnormal. Example:
| pH | PaC02 (torr) | HC03 (mEq/L) |
| 7.44 | 23 | 17 |
So the only parameter that will be normal after FULL compensation, is the pH!
| ABG # | pH | PaC02 (torr) | HC03 (mEq/L) |
| 1 | 7.35 | 47 | 28 |
| 2 | 7.44 | 25 | 20 |
| 3 | 7.43 | 48 | 28 |
| 4 | 7.38 | 54 | 32 |
| 5 | 7.37 | 29 | 19 |
| ABG # | Interpretation (FC = fully compensated) |
| 1 | fc respiratory acidosis |
| 2 | fc respiratory alkalosis |
| 3 | fc metabolic alkalosis |
| 4 | fc respiratory acidosis |
| 5 | fc metabolic acidosis |
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