Concerning pulse oximetry true is: (A) Oxyhemoglobin and deoxyhemoglobin light absorption is equal at the isobestic point of 660nm, (B) Measurements are accurate in the presence of high levels of bilirubin, (C) Measurements are accurate in presence of carboxyhaemoglobin, (D) Measurements are accurate in presence of pigmented skin.
Answer is D. Light absorption of both oxy and deoxy haemoglobin is equal at isobestic point of 805 nm. Bilirubin, carboxyhemoglobin and methaemoglobin can affect the reading of pulse oximeter. Pigmented skin doesn’t influence the reading.