An 80-year-old woman fell on the ice and fractured her femur. After several hour

Question

An 80-year-old woman fell on the ice and fractured her femur. After several hours, when she arrives at the emergency department, she was anxious, panting, and complaining of severe chest pain and not being able to breath. Her pulse was rapid (tachycardia) as was her respiration rate (tachypnea). Blood gases were drawn with the following results:

   pH       7.31

   pCO2       27 mmHg

   pO2       62 mmHg

   HCO3       12 mmol/L

   SO2       78% (calculated, reference range >95%)

What is the patient’s acid-base status? (Acidemia or alkalemia? Metabolic or respiratory?) How do you know?

Why is the HCO3 level so low?

What caused the acid-base imbalance?

Explanation / Answer

The normal blood pH ranges between 7.35 to 7.45. Here, the pH of blood is 7.31.

The patient is tachypneic. So, she is hyperventilating and carbon dioxide is washed out. Therefore, her pCO2 levels are lower than the normal value of 40 mm Hg. The bicarbonate levels are also lower to compensate for the increased loss of carbondioxide. The acid-base imbalance is caused by alterations in the normal functioning of lungs and kidneys.

Therefore, the acid base status of the patient is respiratory alkalosis with compensated metabolic acidosis.

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