Discrepancy between finger probe SPO2 readings when placed on finger vs forehead

ABSTRACT

Case Report A 25 year old woman, G3P2 at 23w6d presented to the Emergency Department for one week of progressive cough and shortness of breath. Patient was febrile, tachypnic, with oxygen desaturation to 88% with minimal exertion. Chest radiograph showed bilateral airspace disease consistent with viral pneumonia. The Patient was diagnosed with covid- 19 and admitted for acute hypoxic respiratory failure secondary and started on dexamethasone and remdesivir. The patient subsequently had escalating oxygen requirements and was stepped up to the ICU on BIPAP on hospital day two. Her oxygen requirements gradually improved, and she was stepped down to the floor on day 8 of admission on highflow nasal cannula. The following day, the patient was noted to have oxygen saturation of 97% on room air with a disposable finger probe applied to the forehead. Placement of the finger probe on the forehead is an uncommon practice reserved for use when unable to obtain adequate wave-form on the finger. A separate evaluation that day using a disposable finger probe on the finger revealed markedly different oxygen saturation in the low 90's. Confirmatory ABG showed pH 7.46, pCO2 31, O2 48, and HCO3 22. After determining hypoxemia, we placed disposable finger probes on both the finger and forehead at the same time using two separate machines. The probe on the forehead showed an spO2 consistently 10% higher than the reading on the finger. The probe connectors were switched and continued to show a 10% higher reading on the probe attached to the forehead. Discussion Given the hypoxemia confirmed on ABG, we concluded that the disposable finger probe used on the forehead provided a falsely elevated spO2 reading. One small study comparing disposable finger probes on the finger vs the forehead showed a discrepancy of >5% in over half of the patients. Critical management decisions are made based on the spO2, and inaccurate readings pose significant risk to the patient. Use of disposable finger probes on the forehead should be avoided.