ABG Practice Answers – Part 2

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What ABG lab values would you expect to find given the symptoms in the scenario?

Example:  Patient has been nauseous & vomiting.  What ABG values might you expect, and why?

Metabolic Alkalosis pH: high(alkaline)   PaCO2: normal or increasing     HCO3: high   Puking rids the body of stomach acid, decreasing the total amount of acid in the body.    So acid would decrease, which causes the pH to increase (become more alkaline).  Reduced amounts of acid means that more free bicarb will be available, which makes the HCO3 value higher.  Since the problem is found in the GI system and HCO3 is the abnormal value, then this imbalance is considered a Metabolic type.  The PaCO2 would be normal because there is not a respiratory cause, or it might begin increasing (trying to make the body more acidic) if the respiratory system is starting to compensate.  

1) Client is in Acute Renal Failure due to prolonged hypovolemia. What ABG values might you expect, and why?

Metabolic Acidosis pH: low (acidic) PaCO2: normal or decreasing   HCO3: low     Normally, the kidneys resorb bicarbonate and excrete acid.  Since the kidneys are in failure, they can’t do either job effectively, especially resorbing bicarb.  With the kidneys losing bicarb, we can expect the HCO3 to be low, which also lowers pH and makes the body more acidic.  Since the problem is in the kidneys and the Imbalance s primarily r/t bicarb, then this imbalance is considered Metabolic.  The PaCO2 would be normal because there is not a respiratory cause, or it might begin decreasing (trying to make the body more alkaline) if the respiratory system is starting to compensate.   

2) Client reports that he ate some really spicy hot wings last night, and has been having diarrhea ever since. What ABG values might you expect, and why?

Metabolic Acidosis pH: low (acidosis)   PaCO2: normal or decreasing   HCO3: low       The pH would be acidosis because diarrhea makes you lose bicarbonate, making the body become more acidic.  So the HCO3 would be low.   Since the problem is in the GI system and the imbalance is r/t the HCO3, then cause of the imbalance is considered Metabolic.  The PaCO2 would be normal because this is not a respiratory cause, or it might begin decreasing (trying to make the body more alkaline) if the respiratory system is starting to compensate.  

3) You realize that the mechanical ventilation for a comatose client has been set at too high a rate. What ABG values might you want to check for, and why?

Respiratory Alkalosis pH: high (alkalosis)  PaCO2: low   HCO3: normal or decreasing     The client is breathing too fast (the equivalent of hyperventilation) and therefore is “blowing off” too much Carbon Dioxide (CO2), so the PaCO2 will be low.  Acid “follows” the carbon dioxide, so acid is also leaving the body, making the pH high (more basic/alkaline).  Since the cause of the imbalance is in the airway and r/t the PaCO2 level, then this imbalance is considered Respiratory.  The HCO3 would be normal because this imbalance does not have a metabolic cause, or it might begin decreasing if the metabolic system is starting to compensate.  

4) Client has COPD. What ABG values might you want to watch for, and why?

Respiratory Acidosis  pH:low (acidosis) PaCO2: high   HCO3: normal or increasing    Clients with COPD tend to “trap” carbon dioxide (CO2) in the lungs.  Since acid follows carbon dioxide, this causes the body’s pH to decrease and become more acidic.  Since the cause of this imbalance is in the lungs, and the PaCO2 level is abnormal, then it is considered a Respiratory imbalance.  The HCO3 would be normal because this imbalance does not have a metabolic cause, or it might begin increasing if the metabolic system is starting to compensate for the extra acid in the body. 

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