ABG analysis PDF

Preview

Summary

abg...

Description

ABG analysis Key components These components all have different normal values and represent different aspects of the blood gas.   

pH: 7.35-7.45 Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg Bicarbonate (HCO3): 22-28 mEq/L

How to Interpret an ABG The first value a nurse should look at is the pH to determine if the patient is in normal range, above, or below. If a patient’s pH > 7.45, the patient is alkalotic. If the pH < 7.35, then the patient is acidotic. Next, examine the PaCO2. This will determine if the changes in the blood gas are due to the respiratory system or metabolically driven. Below is a chart that contains the different values and factors that determine if the patient is suffering from a respiratory or a metabolic component. Remember, CO2 is the ACID component, HCO3 is the BICARB component. They compensate for each other! pH CO2 Respiratory acidosis Respiratory alkalosis Respiratory acidosis with metabolic compensation Respiratory alkalosis with metabolic compensation

↓

↑

↑ ↓ ↑

↓ ↑ ↓

HCO3 Normal Normal ↑ ↓

The acronym ROME is used to help nurses remember the relationship between pH and CO2 & pH and HCO3. Respiratory Opposite (the “arrow” that represents whether the CO2 value is high or low, will go in the OPPOSITE direction of the pH “arrow”). Ex: If your pH is 7.25 (arrow pointing down, because pH is low/acidic) then your CO2 “arrow” will point up-opposite the pH arrow, because the CO2 is high/there’s too much acid…respiratory acidosis. Respiratory alkalosis will be inverse. The pH arrow will point up (because the pH is higher than normal) and the CO2 will point down, because there isn’t enough acid. **See above red arrows. Metabolic Equal. The same ROME concept applies to metabolic acidosis/alkalosis. You’re just looking at the HCO3 instead of the CO2 & both of the “arrows” will point in the SAME direction. Ex: pH 7.25

(arrow points down because it’s low/acidic), HCO3 16 (arrow points down because this value is low when compared to the normal range). Both arrows point down, so it’s metabolic acidosis. REMEMBER…The CO2 is the respiratory component of the blood gas. When compared to the pH, these two values move in opposite directions, regardless if it’s acidosis or alkalosis. On the other hand, the HCO3 is the metabolic component of the blood gas. These two values move in the same direction.

How to determine compensation Once you determine the acid/base balance, you look at the opposite value to see if the body is compensating. Ex: if you determine that it is a respiratory (CO2) impairment, then you look at the bicarb (HCO3) to see if its value is doing what it needs to BALANCE the pH. For ex: in respiratory acidosis (pH low, CO2 high) the HCO3 will also be high because it’s trying to counterbalance some of the acid by increasing bicarb. In this situation, partial compensation would occur if the HCO3 is high. Full compensation occurs if the HCO3- is high AND the pH is back within normal range. No compensation if the HCO3 hadn’t moved and was still in the normal range. Anytime a patient loses fluid that’s acidic (ex: vomiting, GI suction) there will be a deficit in acid (which leaves an alkalotic state). Anytime a patient has diarrhea (which is high in bicarb) there will be a bicarb deficit (which leaves an acidotic state). In addition, a patient who overuses antacids will ingest excess bicarb (from the medication) and will develop metabolic alkalosis. Because vomiting, diarrhea, antacids, etc. have nothing to do with the lungs, this is clearly a metabolic issue which the lungs should compensate for. Anytime a person has a condition that allows for the retention of carbon dioxide (which we lose when we exhale) they may develop respiratory acidosis (retained CO2 causes acidosis). EX: impaired respiratory drive from overdose, impaired gas exchange from lung diseases such as COPD, pneumonia). On the contrary, a patient who hyperventilates (due to anxiety, excess pain, etc) will blow off too much CO2/acid which results in an alkalotic state. These are clearly lung related issues for which the kidneys should compensate. So…you’re either really confused now or maybe this makes sense. Know your values and which is acid and base, read it slow, & draw the arrows. And review pages 190-197. For those of you who had Abbi for clinical last quarter, she tells me these are the videos she showed you guys Interpretation Compensation...