Pulse oximetry measures pulse rate and hemoglobin saturation (normal values, >95%). Similar to capnometry, pulse oximetry relies on cardiac output to generate an adequate signal. However, because hemoglobin saturation values are usually located far right on the flat part of the oxygen-hemoglobin dissociation curve, pulse oximetry is not always sensitive in detecting hypoxemia when administering 100% oxygen (eg, during inhalant anesthesia).
During induction and recovery, when inhaled oxygen levels are less than 100% (and are closer to room air, ~21%), pulse oximetry may quickly determine deficiencies in oxygenation because patients are closer to the sloped portion of the curve (ie, further to the left), where small changes in oxygenation greatly affect hemoglobin saturation.