American Board of Surgery Qualifying Exam (ABS QE) Practice Test

An O2 saturation of less than 85% during an apnea test is indeed suggestive of hypoxia. This test is often used to evaluate the respiratory drive and the ability of the lungs to oxygenate blood when ventilation is temporarily ceased. When oxygen saturation falls below 85%, it indicates that the body is not adequately oxygenating its tissues, which is a direct indication of hypoxia.

While methemoglobinemia can lead to decreased oxygen saturation, it typically presents with saturation levels that might remain at around 85% or higher due to the inability of the hemoglobin to effectively bind oxygen rather than a direct hypoxic state. Hypercapnia refers to elevated levels of carbon dioxide and would not primarily cause a drop in oxygen saturation unless associated with very severe respiratory failure. Acidosis may result from various metabolic or respiratory processes but is not directly indicated by a specific O2 saturation level in this context, making hypoxia the most fitting interpretation of reduced saturation in the apnea test.