Henna paste and pulse oximetry: Effect of different methods of application

Various factors affect the accuracy of pulse oximeters. Objective of our study was to evaluate the accuracy of pulse oximetry if finger was coloured with Lawsonia Inermis (henna). Sixty ASA I and II females, aged between twenty and forty-five years were randomly assigned to two groups to have either the nail of the left thumb (group I) or the entire distal phalynx of the left thumb (group II) stained with henna. Next morning, two pulse oximeters of similar make were applied to the thumbs of both hands of each individual (study digit and control digit). Thirty readings were recorded at one-minute interval for each subject per digit. Results showed no statistically significant difference among the readings of the two groups between the control digits. No significant difference was observed between the study and control digit readings in group I. A statistically significant difference was observed between the study and control digit reading in group II. On comparing study digit readings between the two groups the arterial oxygen saturation in group II was significantly lower. Thus the method of application of henna dye has an effect on readings obtained by pulse oximetry and alternative sites should be used to monitor arterial oxygen saturation if possible.