Abstract
Background:
Pulse oximetry is used to measure oxygen in blood. It uses either transmittance on fingers or reflectance on the forehead. Practitioners often assume equal readings between sites, and will switch probes and locations to obtain SpO2. Accurate estimation of patient's oxygen status is critical during patient care and testing to assess oxygen needs. This study evaluated the finger probe to the forehead probe to determine which has greater accuracy when compared to the arterial blood gas-the gold standard for determining the actual amount of oxygen circulating in blood. We hypothesized the finger probe was more accurate than the forehead probe when compared to arterial blood gas due to clinical experiences of the staff.
Methods:
50 patients were consented following IRB approval. Inclusion criteria included, a practitioner ordered arterial blood gas (ABG), age greater than or equal to 18 years old, and good hand circulation as assessed by temperature and color. Once the patient was consented, the forehead and finger probes were placed simultaneously, ensuring a regular pulse waveform prior to blood draw. The respiratory therapist then drew the blood sample and at that time, the oxygen saturations were recorded. After the sample was analyzed, the fraction of oxygen attached to hemoglobin (FO2Hb) was also recorded. Data analysis included student's t-tests comparing the finger probe to FO2Hb, forehead probe to FO2Hb, and finger probe and forehead probe to each other as well as calculations of percent difference from standard device error.
Results:
The t-tests showed that each comparison (finger probe vs. blood gas, forehead probe vs. blood gas, and finger probe vs. forehead probe) was statistically significant (p-values of 0.00073, 2.9*10-9, and 0.0022 respectively). Due to the p-values being below the standard 0.05 p-value we chose, the p-values indicate the finger probe and forehead probe differ significantly from the blood gas and from each other.
Conclusions:
There was statistical significance in the difference found between each probe and the blood gas, when compared to the forehead probe. The relatively low percentage of error greater than 2% for the finger probe combined with the precision of the finger probe seems to indicate that the finger probe is clinically superior to the forehead probe in the outpatient setting. Therefore, the finger probe should be used over the forehead probe.
Masimo reports a possible +/- 2% error without motion with the finger oximeter, and +/- 3.5% without motion with the forehead oximeter. View all access options for this article.Percentage of time probe was outside Masimo's reported accuracy
Probe type
Number of times probe was less accurate
Total number of subjects
Percentage of time probe was less accurate
Finger probe
24
50
48%
Head probe
34
50
68%
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