Objective: To determine the influence of digital clubbing on oxygen saturation by pulse oximetry measurements (SpO2) in Cystic Fibrosis patients.
Background: Measuring the arterial oxygen saturation at the fingertip by pulse-oximetry is commonly used in the management of CF patients. In these patients, clinical signs of hyperoxia are often observed with oxygen supplies based on digital oximetry readings. This suggests inaccuracies in the digital measurement method, which in its turn may be caused by digital clubbing. In order to study the influence of digital clubbing, measurements between fingertip and forehead sensor were compared in a clubbing and non-clubbing CF-population. The ear sensor measurements are used as a reference variable.
Methods: Two groups were examined. Group 1 consisted of 50 CF patients without digital clubbing (DPD/IPD ratio<1.00). Group 2 consisted of 50 CF patients with digital clubbing (DPD/IPD ratio>1.00). Patients were measured at rest before any treatment and with their daily oxygen supply, if applicable. Saturation was simultaneously measured with three Criticare SpO2 T pulse oximeters, using a fingertip sensor at the right index (transmission oximetry), a forehead sensor at the forehead (reflectance oximetry) and an ear sensor at the right ear.
Results: Using the Bland and Altman method no clear difference was found between the saturation measurements of right ear versus forehead sensor in the two groups. When the measurements of right ear versus fingertip sensor are compared there is still no difference for the non-clubbing group. On the contrary, for the clubbing group lower saturation scores were measured by the fingertip probe compared to the right ear measurement. The differences in saturation became greater as the saturation value at fingertip was lower.
Conclusion: Digital clubbing significantly influences the registrations of the SpO2 measurements by means of a fingertip probe, underestimating the saturation. It can be advised to use the ear sensor as good alternative for these patients.