Acid- Base Imbalances and ABGs

 Acid- Base Imbalances and ABGs

All cellular processes require a normal serum pH level.  pH is the concentration of hydrogen ions (H+) present in the blood. pH is normal between 7.35 and 7.45 when the ratio of acid to base in the body is 1:20. 

Base exists as bicarbonate or HCO3. HCO3 is a metabolic parameter. 

Acid exists as carbonic acid or H2CO3. Water and carbon dioxide can combine to make carbonic acid, CO2 is a respiratory parameter.

When too much base HCO3 or not enough carbonic acid is present, the 1:20 ratio of acid to base is thrown off, resulting in alkalosis (pH will be elevated). Too few hydrogen ions are present.

When too much carbonic acid (H2CO3) is present or not enough bicarbonate, the 1:20 ratio of acid to base is thrown off, resulting in acidosis (pH is low)). Too many hydrogen ions are present. 

When the 1:20 ratio of acid-base balance is thrown off, the kidneys and lungs can compensate. The kidneys compensate by reabsorbing HCO3 or increasing HCO3 excretion. The kidney can also excrete hydrogen ions as ammonia. Metabolic compensation is slow.

The pulmonary system compensates by retaining CO2 (by decreasing respiratory rate and ventilation) or increasing CO2 elimination (by increasing respiratory rate and ventilation). Respiratory compensation is rapid.

Arterial blood gas analysis is used to assess acid-base balance and imbalance. 

An abnormal pH reflects acidosis (low pH) or alkalosis (high pH).

If HCO3 (base) is abnormal and follows the direction of the pH, then the imbalance is metabolic in origin.

If the PaCO2 (acid) is abnormal and opposite the pH, then the imbalance is respiratory in origin. 

Remember RO-ME Respiratory is opposite, metabolic is equal or follows the direction of the pH. 

If there is a respiratory imbalance, but the HCO3 is normal, then there is no compensation. 

If there is a metabolic imbalance, but the PaCO2 is normal, then there is no compensation.

If there is a respiratory imbalance, if the bicarbonate level is abnormal then partial compensation exists.

If there is a metabolic imbalance, if the PaCO2 is abnormal then there is partial compensation. 

If both HCO3 and PaO2 are acidotic and pH is low, then the imbalance is combined respiratory and metabolic acidosis.

If both HCO3 and PaCO2 are alkalotic and pH is high, then the imbalance is combined respiratory and metabolic alkalosis.

If pH is normal, and both HCO3 and paCO2 are abnormal, full compensation is present. 

PaCO2 moves opposite the direction of the pH, If the PaCO2 is high and the pH is low, there is respiratory acidosis.

If the PaCO2 is low and the pH is high, there is respiratory alkalosis. 

HCO3 moves in the same direction as the pH. If the pH and HCO3 are high there is metabolic alkalosis. If the pH and HCO3 are low, there is metabolic acidosis. 

See table below:

Let's practice reading ABGs. Fill in the imbalance in the table below: (write a comment for the correct answers)