Purpose: The photoplethysmogram (PPG) recorded using finger pulse oximeter estimates the  oxygen saturation. During out-of-hospital cardiac arrest (OHCA) the PPG waveform shows amplitude changes with chest compressions (CC. The aim of this study was to analyze the feasibility of using the finger PPG to provide feedback on CC rate during OHCA.

Materials and methods: Records of 46 patients were included, comprising the PPG and compression depth signals extracted from Zoll E-Series defibrillator files. They were acquired by the DFW Center for Resuscitation Research (UTSW, Dallas) and the Emergency Medical Services agencies from the Resuscitation Outcomes Consortium’s Portland site (OHSU). An automatic algorithm analyzed the PPG every 5s and detected useful PPG, presence of CCs and CC-rate. The compression depth signal (acquired by the CPR-pad-z) was used as the reference signal to simultaneously compute the rate and check for presence of CCs. The percentage of useful PPG, and sensitivity (SE)/positive predictive value (PPV) for detecting CCs were computed. The CC-rate error was assessed as mean(standard deviation) and 95% level of agreement (LOA, Bland-Altman). A feedback system on the CC-rate was implemented for the intervals where PPG was available, and evaluated in terms of SE, PPV and specificity (SP) to trigger alarms for CC-rates  out of the range 90-120 CC/min. 

Results: A total of 420 min (9.1±7.6 min per episode) were processed. A total of 4971 segments were analyzed, 4319 including CCs with rate 116 (15) CC/min. The PPG signal was not available 17% of the time. The SE/PPV to detect CCs were 86.2/95.4%, and the CC-rate error 2.4 (6.3) CC/min (see figure). The SE/SP/PPV for the feedback system to trigger alarms were 83.6/92.4/85.3% respectively.    

Conclusions: When available, the finger PPG signal reliably gives feedback on CC rate.

1 - Feasibility of the finger photoplethysmography to give feedback on chest compression rate