Clinical PaperQuantitative relationship between end-tidal carbon dioxide and CPR quality during both in-hospital and out-of-hospital cardiac arrest☆
Introduction
The administration of cardiopulmonary resuscitation (CPR) is currently based on a uniform approach for all adult patients. Specifically, international resuscitation guidelines recommend that chest compressions (CC) should be delivered at a rate of at least 100 min−1 and a depth of at least 50 mm (2 in) for all victims.1 Although these recommendations are intended to optimize blood flow during cardiac arrest, the guidelines do not suggest titration of CC performance to individual patient circumstances or to measures of blood flow resulting from CC delivery.2 It is plausible that certain patient characteristics, such as varying chest size/body mass index (BMI) and underlying arrest physiology, might require tailoring of CPR to maximize therapeutic response.3, 4 To guide such titration, tools to assess blood flow during CPR in real-time require evaluation and standardization. The relationship between specific CPR performance metrics and subsequently generated blood flow in actual clinical practice is poorly understood.
End-tidal carbon dioxide (ETCO2), as measured by waveform capnography, is considered a physiologic measure of cardiac output in low-flow states, and has been proposed in the 2010 consensus resuscitation guidelines as a possible real-time metric to assess the impact of CPR quality.5 In low-flow states such as during CPR, delivery of CO2 to the alveolar vascular bed becomes a rate-limiting determinant of ETCO2, and thus ETCO2 has a direct correlation with cardiac output.6, 7, 8, 9 Waveform capnography is an attractive potential metric to measure output during resuscitation care, given its wide availability and non-invasive application. A number of laboratory studies support the notion that ETCO2 could be used as an indicator of blood flow during CPR and suggest that ETCO2 may be sensitive to variations in CPR performance, yet little evidence exists from the clinical setting to support this concept.6, 7, 10, 11 We sought to assess the relationship between ETCO2 and actual CPR delivery in a time-based quantitative fashion. We hypothesized that ETCO2 would be sensitive to CPR performance characteristics such as CC depth and rate as well as ventilation rate in real-time during both in-hospital and out-of-hospital cardiac arrest. We further hypothesized that CC depth would exhibit the most significant relationship to ETCO2, as suggested by previous laboratory studies.
Section snippets
Methods
In this multicenter cohort study, quantitative CPR performance and time-synchronized ETCO2 data were collected from in-hospital and out-of-hospital cardiac arrest events between 4/2006 and 5/2013. The prospective collection of these data and subsequent analyses were approved by the Institutional Review Boards at the University of Pennsylvania and the University of Chicago for in-hospital cardiac arrest data collection, and at the University of Texas Southwestern Medical Center and Oregon Health
Data collection
Data were captured via CPR-recording defibrillators (MRx QCPR, Philips Healthcare, Andover, MA) equipped with continuous sidestream CO2 recording capabilities connected in conjunction with an advanced airway (e.g., endotracheal tube or laryngeal mask airway) during resuscitation events. These CPR-recording defibrillators provide real-time audiovisual feedback to rescuers regarding CPR quality during resuscitation.12, 13 In-hospital data were collected from the Hospital of the University of
CPR data inclusion and processing
All cardiac arrest events during the investigational time period that involved the provision of CPR, regardless of arrest etiology or initial rhythm, were considered for analysis. Only cardiac arrest events that contained ≥2 min of time synchronized CC and ETCO2 data were included for analysis to allow for meaningful assessment of changes over time; events with duration <2 min or without both ETCO2 and CC data were excluded. Using a computational algorithm developed by a member of the
Statistical analysis
Descriptive statistics and histograms were used to describe the ETCO2, CC rate, CC depth and ventilation rate in the sample overall and separately for each site, among cases that achieved return of spontaneous circulation (ROSC) and among those who did not achieve ROSC, and among those who survived to discharge and those who did not survive to discharge. Initially, CC rate and depth as measured over the epochs were each reclassified into an ordinal variable using quintiles (i.e., from slow to
Results
Of the 790 cardiac arrest events from the study sites, 583 met the study inclusion criteria, such that 29,028 CC and ETCO2 containing epochs were processed for analysis. Of the 207 cases excluded from analysis, 77 (37%) cases were excluded due to the absence of overlapping ETCO2 and CC data, 104 (50%) cases were excluded for containing less than 2 min of either ETCO2 or CC data, and 26 (13%) cases were excluded due to technical reasons such as corrupted data files or missing identifiers. Of the
Discussion
In this multicenter study of CPR quality and its quantitative association with ETCO2, we found that increased CC depth was associated with increased ETCO2 in a statistically significant fashion; this relationship is similar during CPR delivery in both IHCA and OHCA events. These data represent the largest clinical study of physiologic output during actual CPR performance to date, and provide quantitative support for the potential role of waveform capnography to monitor the quality of
Conclusions
In a multicenter analysis of CPR quality and waveform capnography from both IHCA and OHCA events, we found significant correlation of deeper CCs with higher ETCO2 values but did not find a correlation of CC rate with ETCO2 (over the dynamic range of CC rates that were actually delivered). These relationships were consistent during both in-hospital and out-of-hospital resuscitation efforts. This work highlights the physiologic importance of CC depth in particular, and suggests that physiologic
Conflict of interest statement
Dr. Abella reports research funding from the Medtronic Foundation, the National Heart, Lung and Blood Institute, the Travelers Foundation, and Stryker Medical. He also reports honoraria from Medivance Corporation, equity in Resuscor LLC and consulting from HeartSine Technologies Ltd. Ms. Leary reports research funding from the American Heart Association and equity in Resuscor LLC. Dr. Babaeizadeh reports Philips Healthcare as his full-time employer and is a stockholder in Philips Healthcare.
Acknowledgements
We thank the prehospital and inpatient healthcare providers who delivered resuscitation care and enabled the collection of CPR performance data at each site. We are grateful for administrative assistance from Eileen McDonnell and statistical advice from Anne Grossestreuer. This work was supported by the NCRP Winter 2014 Mentored Clinical & Population Research Award from the American Heart Association (14CRP19990024) to Ms. Leary and Dr. Abella, and NIH funding via the ROC consortium to both Dr.
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2015.01.026.