Question

Three days ago Ms. X fractured several ribs in an auto accident, and her breathing has been shallow since then. Her arterial blood pH is 7.29, PCO₂ is 50mm Hg and HCO³⁻ is 30 mEq./L. Her acid base imbalance will most likely be:

a. Respiratory acidosis
b. Respiratory alkalosis
c. Metabolic acidosis
d. Metabolic alkalosis

Answer 1

Ms. X's blood pH of 7.29 with elevated PCO₂ and HCO₃⁻ suggests respiratory acidosis with compensatory increased bicarbonate levels. Shallow breathing due to fractured ribs is likely impairing CO₂ removal, leading to respiratory acidosis.

Step-by-step explanation:

The student's question is about acidosis or alkalosis and determining whether it is metabolic or respiratory in nature. Ms. X's arterial blood pH is 7.29, indicating acidosis as a blood pH less than 7.35 is considered acidic.

The elevated PCO₂ level at 50 mm Hg suggests there is an accumulation of CO₂ in the blood due to shallow breathing. Meanwhile, an HCO₃⁻ level of 30 mEq/L is higher than normal, which indicates a compensatory mechanism to counteract the acidosis. The presence of respiratory acidosis is further suggested by the consistent pattern of increased PCO₂ leading to acidosis and the elevated bicarbonate level as a compensatory mechanism attempting to buffer the increased acidity.

Respiratory acidosis is problematic because excess CO₂ is present in the blood. Initially, bicarbonate levels would be normal, but as compensation occurs, bicarbonate levels increase in an attempt to reestablish the proper ratio of bicarbonate and carbonic acid/CO₂. This mechanism is in line with Ms. X's condition where shallow breathing due to rib fractures has likely impaired her ability to remove CO₂ effectively, leading to the observed lab values.