Diagnostic dilemma: Low oxygen saturation during cardiac surgery

We report a case of rheumatic heart disease with severe mitral stenosis having cyanosis and low oxygen saturation on pulse oximetry. The findings of clinical examination and low values on pulse oximetry were inconsistent with the findings of normal partial pressure of oxygen and oxygen saturation on arterial blood gas analysis, leading to diagnostic dilemma. In such clinical scenario, the anesthesiologist should be aware and vigilant about the differential diagnosis of low oxygen saturation on pulse oximetry.