Final answer:
The best indicator of respiratory depression in a post-surgery patient in the PACU is decreased oxygen saturation, measured non-invasively with a pulse oximeter.
Step-by-step explanation:
The best indicator of respiratory depression in a patient admitted to the postanesthesia care unit (PACU) after abdominal surgery is decreased oxygen saturation. This condition signals that the lungs are not effectively exchanging oxygen and carbon dioxide. Increased respiratory rate can sometimes indicate the body's attempt to compensate for hypoxemia or other issues, but it is not a direct measure of respiratory depression. Increased carbon dioxide pressure could indicate that the patient is retaining CO2 due to respiratory depression, but it requires blood gas analysis to determine, which is not always the immediate assessment tool available. Frequent premature ventricular contractions (PVCs) are more closely related to cardiac issues rather than an indicator of respiratory function. Therefore, a decreased oxygen saturation, which can be quickly and non-invasively measured by a pulse oximeter, is considered the most accurate and immediate clinical sign of respiratory depression in a postoperative patient.