The pulse oximeter is a noninvasive instrument that uses light absorption to assess hemoglobin configuration as a proxy for blood oxygen levels. The number generated by this device guides care in clinics and hospitals worldwide. Yet the technology has a known flaw: patients with darker skin are more likely to yield readings that are falsely elevated. This discrepancy, known as hidden hypoxemia, is defined as hypoxemia as measured by the arterial blood gas (SaO2) that is not detected on pulse oximetry (SpO2). While the technical limitations of the pulse oximeter have been recognized for more than 30 years, investigations into clinical implications of hidden hypoxemia in patients with darker skin have been relatively (and distressingly) recent.1