Five Hours After an Uneventful Knee Surgery, a Conscious 50-Year-Old $\mathrm { pH } = 7.30$

Five hours after an uneventful knee surgery, a conscious 50-year-old woman has minor heart pain and a decrease in systolic blood pressure from 110 to 90 mm Hg. Arterial blood gas analysis on her breathing room air shows: * $\mathrm { pH } = 7.30$
* $\mathrm { pCO } _ { 2 } = 52 \mathrm {~mm} \mathrm { Hg }$
* $\mathrm { pO } _ { 2 } = 58 \mathrm {~mm} \mathrm { Hg }$ Which of the following is the most likely cause of these findings?

A) Alveolar hypoventilation
B) Cardiac failure
C) Hypoxia due to anesthetic gases
D) Pulmonary hypertension