Accuracy of Continuous Noninvasive Respiratory Rate Derived From Pulse Oximetry in Chronic Obstructive Pulmonary Disease Patients

Abstract

PURPOSE: A new method of analyzing a pulse oximeter waveform (RRoxi algorithm) allows continuous non-invasive respiratory rate monitoring. The RRoxi algorithm uses respiratory-induced modulations in the photoplethysmogram secondary to changes in hemodynamic and autonomic activity throughout the respiratory cycle. Patients with chronic obstructive pulmonary disease (COPD) may exhibit abnormal cardiorespiratory interactions that could influence the modulations used by RRoxi to extract respiratory rate. We therefore sought to determine the accuracy of RRoxi in patients with COPD. METHOD(S): With IRB approval and patient consent, we enrolled 22 non-intubated patients diagnosed with COPD (age: 61.8 A+/- 11.8 yr; BMI: 28.6 A+/- 7.7 kg/m2, 4 female/ 18 male). During an observational study period of ~20 min on the general care floor or in the ICU, photoplethysmogram data were acquired from an index finger using a pulse oximetry sensor. Nasal/oral capnography waveforms were acquired simultaneously to determine a reference respiratory rate. Respiratory rate values were computed offline by RRoxi. Accuracy was calculated as root mean square deviation (RMSD) between RRoxi and the reference respiratory rate, and Pearson correlation coefficients were computed to assess their relationship. RESULT(S): RRoxi determined a respiratory rate value 93% of the monitoring period, yielding a total of 4,917 paired observations (RRoxi values and the capnography-based reference). Mean and range of the reference respiratory rate were 17.6 A+/- 4.4 and 8.1 to 32 breaths per minute, respectively. The mean difference between the reference and RRoxi respiratory rate measurements was 0.7 A+/- 1.6 breaths per minute. The accuracy of RRoxi was 1.7 breaths per minute, as measured by RMSD and the agreement between RRoxi and the reference was R2=0.87. CONCLUSION(S): These results demonstrate that in patients with COPD, the RRoxi algorithm was accurate to within 1.7 breaths per minute (RMSD) and able to determine a respiratory rate value during 93% of the monitoring period.