2025 – PAGE 370 – ACID-BASE DISORDERS

RESPIRATORY ACIDOSIS

A respiratory acidosis can be caused by anything that causes bradypnea (a decrease in respiratory rate) or a defect in ventilation perfusion exchange of carbon dioxide. The list includes, but is not limited to, several neurologic and neuromuscular disorders, late asthma (obstruction,) and pulmonary emboli.

• (DOUBLE TAKE) PEARL: If you are given an ABG and you diagnose an overarching respiratory acidosis, ALWAYS calculate for metabolic compensation. You do this by looking at the increase in pCO2 from the baseline of 40, and checking to see if the compensatory increase in bicarbonate (com­pensatory metabolic alkalosis via bicarb retention) is appropriate. If the bicarbonate level is lower than expected, then you have an additional primary metabolic acidosis. If it’s higher than expected, then there is an additional primary metabolic alkalosis. Keep in mind that the compensatory increase in bicarbonate could be from 1 to 3.5mmol/L for every 10 mmHg increase in pCO2, depending on whether you are dealing with an acute or chronic respiratory acidosis. Consider acute to be anything that’s happened within 3 days.
  • ACUTE respiratory acidosis compensation: 1 mmol of bicarb per 10 mmHg of pCO2
  • CHRONIC respiratory acidosis compensation: 5 mmol of bicarb per 10 mmHg of pCO2

RESPIRATORY ALKALOSIS

A respiratory alkalosis can be caused by basically anything that causes tachypnea. Sometimes this is due to hypoxia. The list includes, but is not limited to, early asthma, pneumonia, one of the aspirin phases, high altitude, fever, and anxiety/hyperventilation.

• (DOUBLE TAKE) PEARL: If you are given an ABG and you diagnose an overarching respiratory alkalosis, ALWAYS calculate for metabolic compensation. You do this by looking at the decrease in pCO2 from the baseline of 40, and checking to see if the compensatory decrease in bicarbonate (compensatory non-anion gap metabolic acidosis via bicarb excretion) is appropriate. If the bicarbonate level is lower than expected, then you have an additional primary metabolic acidosis on top of the compensatory acidosis. If it’s higher than expected, then there is an additional primary metabolic alkalosis. Keep in mind that the compensatory decrease in bicarbonate could be from 2 to 5 mmol/L for every 10mmHg decrease in pCO2, depending on whether you are dealing with an acute or chronic respiratory alkalosis. Consider acute to be anything that’s happened within 3 days.
  • ACUTE respiratory alkalosis compensation: 2 mmol of bicarb per 10 mmHg of pCO2
  • CHRONIC respiratory alkalosis compensation: 5 mmol of bicarb per 10 mmHg of pCO2