a b s t r a c t

Background: Clinical investigations have shown improved outcomes with primary compression cardiopulmonary resuscitation strategies. It is unclear whether this is a result of passive ventilation via chest compressions, a low re- quirement for any ventilation during the early aspect of resuscitation or avoidance of inadvertent over-ventilation. Objectives: To quantify whether chest compressions with guideline-compliant depth (N2 in) produce measurable and substantial Ventilation volumes during emergency department resuscitation of out-of-hospital cardiac arrest. Methods: This was a prospective, convenience sampling of adult non-traumatic out-of-hospital cardiac arrest patients receiving on-going cardiopulmonary resuscitation in an academic emergency department from June 1, 2011 to July 30, 2013. Cardiopulmonary Resuscitation quality files were analyzed using R-Series defibrillator/monitors (ZOLL Medical) and ventilation data were measured using a Non-Invasive Cardiac Output monitor (Philips/Respironics, Wallingford, CT).

Results: cardiopulmonary resuscitation quality data were analyzed from 21 patients (17 males, median age 59). The median compression depth was 2.2 in (IQR = 1.9, 2.5) and the median chest compression fraction was 88.4% (IQR = 82.2, 94.1). We were able to discern 580 ventilations that occurred during compressions. The median passive tidal volume recorded during compressions was 7.5 ml (IQR 3.5, 12.6). While the highest volume re- corded was 45.8 ml, 81% of the measured tidal volumes were b20 ml.

Conclusion: Ventilation volume measurements during emergency department cardiopulmonary resuscitation after out-of-hospital cardiac arrest suggest that chest compressions alone, even those meeting current Guideline recommendations for depth, do not provide physiologically significant tidal volumes.

(C) 2018

Introduction

In this brief report, we sought to quantify ventilation volumes gener- ated during emergency department (ED) chest compressions with guideline-compliant depth to determine if volumes produced by com- pressions alone were measurable using a Novel method of measuring

Abbreviations: OHCA, out-of-hospital cardiac arrest; NICO, Non-Invasive Cardiac Output; CPR, cardiopulmonary resuscitation; ED, emergency department.

* Corresponding author.

E-mail addresses: [email protected] (R. McDannold), [email protected] (B.J. Bobrow), [email protected] (V. Chikani), [email protected] (A. Silver), [email protected] (D.W. Spaite), [email protected] (T. Vadeboncoeur).

ventilation volumes. Research has shown improved out-of-hospital cardiac arrest (OHCA) survival with bundled strategies designed to increase chest compression fraction, decrease compression pauses, and avoid excessive ventilation [1-7]. Whether improved outcomes are related to limiting interruptions to forward blood flow during car- diopulmonary resuscitation (CPR), avoiding harmful effects of excessive ventilation, or if compressions alone provide meaningful ventilation is not clear [1-3, 8, 9]. Aufderheide and colleagues demonstrated that high ventilation rates during out-of-hospital resuscitation are both common and harmful [10]. Similarly, hyperventilation during in- hospital resuscitation has been demonstrated [11]. Previous attempts to explore whether chest compressions alone produce meaningful ventilation volume did not examine compressions of current guideline quality and yielded conflicting results [12].

https://doi.org/10.1016/j.ajem.2018.06.057

0735-6757/(C) 2018

Material and methods

Setting

The (facility name removed) has approximately 55,000 ED patient visits annually and has an Accreditation Council for Graduate Medical Education (ACGME) approved emergency medicine residency training program. The hospital is a designated cardiac receiving center in the Arizona Department of Health Services (ADHS) sponsored Save Hearts in Arizona Registry and Education (SHARE) program. The SHARE pro- gram was implemented in 2005 by the Arizona Department of Health Services as a statewide quality improvement program in response to its declaration of OHCA as a major Public health problem in Arizona. SHARE includes a voluntary Utstein-style database with detailed OHCA data and linked hospital outcomes from 39 Arizona hospitals. As an ADHS-sponsored public health initiative, the Attorney General has determined that the program is exempt from the requirements of the Health Insurance Portability and Accountability Act . This allows linkage of EMS and hospital data, tracking of OHCA events, and evaluation of efforts to improve resuscitation care. The ADHS Human Subjects Review Board and the (institution name removed) Institutional Review Board have determined that, by virtue of being a public health initiative, neither the interventions nor their evaluation constitute Human Subjects Research and have approved the publication of de-identified data. Additionally, the (facility name removed) Institu- tional Review Board approved this study. The SHARE program has pre- viously been described in detail [1, 9, 13-15].

Study design

This was a prospective, convenience sampling of adult non- traumatic OHCA patients receiving continued CPR in the ED from June 11, 2011, to July 6, 2013.

Data collection

Ventilation data and CPR metrics were collected on patients under- going resuscitation. Patients who had both a defibrillator-monitor data file and ventilation data were included in the study. Fig. 1 describes case inclusion and exclusion. The study ED uses monitor defibrillators

(R Series, ZOLL Medical) with U.S. Food and Drug Administration- approved accelerometer-based technology that allow for measurement of multiple CPR quality metrics, including compression depth, compres- sion rate and compression fraction. It was standard ED practice to collect defibrillator-based CPR quality data during the study period. Data files were downloaded and reviewed using Code Review software (ZOLL Medical, Chelmsford, MA). This study also involved detailed ventilation monitoring on a convenience sampling of patients using the novel Non-Invasive Cardiac Output (NICO) Monitor (Philips/Respironics, Wallingford, CT). The NICO monitor uses a CO2/flow sensor placed at the endotracheal tube. NICO waveform and breath-by-breath data were captured using LabView (National Instruments Corporation, Austin, TX).

Demographic and patient care information was obtained from several sources. ED data were entered into the Save Hearts in Arizona Registry and Education (SHARE) database maintained on a secure server at the (facility name removed) [13]. Patient medical records were obtained as part of an ongoing series of research projects at the (facility name removed). cardiac arrest treatment details were extracted from both the hospital electronic medical record and CPR Flow sheets created by the American Heart Association. All records were de-identified of all protected health information. Fig. 2 includes information on the data collection process.

Data analysis

Data from NICO download files were obtained and a master spread- sheet of usable NICO data was created. A novel Matlab (MathWorks, Na- tick, Massachusetts) script translated the exported NICO waveform files into continuous flow integration. This allowed for visualization of peaks in the volume integral that were associated with compressions. Active ventilations were observed to occur during regular intervals and with significantly higher volumes. Measures were taken of the start of the rise in volume and the peak volume during a given compression. Subtracting the starting measure from the peak volume gave the pas- sively inhaled volume. A sample of at least 1 ventilation volume was taken during compressions identified in each downloaded NICO file. Be- cause each case was of a different duration and because there were not always a large number of readable volumes, we took a sample of quality ventilations rather than attempting to include every tracing in each

Case Inclusion/ Exclusion

88 Cases with CPR

Quality data

21 Cases with CPR Quality

data and NICO Data

4 NICO files with no Zoll file or hospital record match

66 Cases with no NICO data file and 1 with unusable data

53 Cases with no Zoll file

141 Hospital OHCA cases in Database

Fig. 1. Case inclusion/exclusion. OHCA: out-of-hospital cardiac arrest, NICO: Non-Invasive Cardiac Output, CPR: cardiopulmonary resuscitation.

Fig. 2. Data collection and analysis. ED: emergency department, SHARE: Save Hearts in Arizona Registry and Education, OHCA: out-of-hospital cardiac arrest, NICO: Non-Invasive Cardiac Output, CPR: cardiopulmonary resuscitation.

ED/Hospital PCRs

Spreadsheet of patient information completed with CPR data

Sent to University Research staff

CPR data analyzed and exported

Matched to records in SHARE database

Matched to SHARE database

Uploaded to Hospital Server and sent to University Research Staff

Uploaded to Hospital Server and sent to University Research Staff

NICO monitor files

Matched to SHARE

database

NICO ventilation waveforms analyzed

case. The number of measurable ventilation volumes taken during each case for this project varied. Only the largest and most clear ventilations were measured in order to avoid including artifact in the sampling and because the smallest clearly did not provide adequate ventilation.

A median of 20 measures were taken in each case (IQR 16, 20). A total of 580 compression-associated ventilation volumes were mea- sured. Fig. 3 is a representation of one measured volume.

Data analysis was carried out using SAS v9.3 (SAS Institute, Inc., Cary, NC). Univariate analysis was conducted to describe the compression depth, rate and fraction. Results were reported as median and inter- quartile range (IQR).

Results

A total of 141 patients were treated during the study period. NICO data were collected on 22 patients; one case had unusable data. Patient demographics and baseline characteristics are described in Table 1. Most were male (17, 73%) and the median age was 59.2 years (IQR 47, 72). The majority of patients had a presumed cardiac cause as the underlying reason for cardiac arrest (17, 81%). Two cases had respiratory causes, one was a presumed drug overdose, and one was

determined to be either due to cardiac cause or pulmonary embolism. Twenty-nine percent of patients had an initial prehospital shockable cardiac rhythm (Table 2). Seven patients were intubated in the emer- gency department and 14 were intubated in the field. One patient in this analysis survived to hospital discharge.

The median compression depth for the cases was 2.2 in (IQR = 1.9, 2.5) and the median compression rate was 126.1 compressions per minute (cpm, IQR = 122.1, 129.7). We measured 580 discernible ventilation volumes that occurred during compressions from the NICO data files of the 21 patients. The median passive tidal volume occurring during compressions was 7.5 ml (IQR 3.5, 12.6) (Table 3). The highest observed value was 45.8 ml and 81% of the measured tidal volumes were b20 ml.

Discussion

CPR quality and the physiological response to CPR have been the focus of numerous clinical and animal studies over the last few decades but the ideal timing, rate, and volume of ventilation remain unknown [16]. Locations that have implemented CPR improvement strategies

Zoll monitor files

Fig. 3. Ventilation volume.

Table 1

Patient baseline characteristics.

Patient baseline characteristics (n = 21)

Gender Males	17
Females	4
Age	59.2 (IQR 47, 72)
Presumed cause of CA Cardiac	17 (81%)
Respiratory	2 (10%)
Overdose	1 (5%)
Cardiac or pulmonary embolism	1 (5%)
Patients intubated Where	20
Prehospital	13
ED	7

CA: cardiac arrest, IQR: interquartile range, ED: emergency department.

Table 2

Cardiac rhythm.

Prehospital

Ventricular tachycardia/ventricular fibrillation 29%

Asystole 24%

Pulseless electrical activity 24%

Bradycardic 10%

Idioventricular

Unknown/not noted 14%

Cardiac

Ventricular tachycardia/ventricular fibrillation 33%

Asystole 24%

Pulseless electrical activity 33%

Bradycardic 5%

Idioventricular

Unknown/not noted 5%

which minimize interruptions to chest compressions by de-emphasizing ventilations have seen subsequent improvements in survival rates [9, 17]. There are numerous plausible explanations for improved out- comes. Whether improved outcomes are from limiting interruptions to forward blood flow during CPR, avoiding harmful effects of excessive ventilation, or if early in cardiac arrest it is the circulation of oxygenated blood rather than ventilation that is most needed remains unknown. It has been postulated that improved outcomes from initiatives that avoid positive pressure ventilation are made possible by compressions them- selves producing meaningful ventilation.

The aim of the present feasibility study was to characterize the vol- ume of ventilation with compressions of adequate depth. While several studies have analyzed ventilation volumes associated with compres- sions in animal models, and one analyzED volumes associated with compressions delivered by mechanical device, this is the first clinical analysis of passive ventilations during Manual compressions by clini- cians in an ED setting. We found that chest compressions meeting cur- rent ILCOR guidelines for depth did not result in meaningful ventilation volume in cardiac arrest patients with prolonged CPR. Tidal volume was consistently low and far less than the average anatomical dead space (130 to 180 ml, depending on body morphology) for all subjects, sug- gesting that passive ventilation is unlikely to provide meaningful Gas exchange in the later minutes of resuscitation.

Previous animal studies have assessed tidal volumes associated with chest compressions [18-20]. A paper by Chandra et al., describes venti- lation in compression-only CPR performed in dogs. The authors found that there was significant gas-exchange generated by compressions in the earliest minutes of CPR (b4 min) [18]. Noc et al. similarly found that during the first 8 min of CPR performed in a rat model, precordial compressions were able to produce tidal volumes that were sufficient to maintain adequate gas exchange [20]. On the contrary, research by Geddes et al. demonstrated that compression-only CPR was unable to generate meaningful gas exchange in a porcine model [19]. One previ- ous research study found that compressions delivered by mechanical compression device in human subjects did not generate enough tidal volume for passive ventilation [12]. The prevailing theory as to why chest compressions produce adequate ventilations in some animals but not humans (and other animals) has to do with differences in the shape of the thoracic cavity [12]. During compressions on animals in

Table 3

Ventilation volumes, n = 580.

Statistical measure	ml
Median	7.5
75% quartile	12.6
25% quartile	3.5
Mean	11.4
Standard deviation	11.8

the supine position, compressions occur on the major access of the el- lipse which initially increases the thoracic volume and creates negative intrathoracic pressure until the major axis is equivalent to the minor ac- cess. In humans, sternal compressions are along the minor axis creating only positive pressure during the compression phase of CPR [21]. Addi- tionally, in humans the amount of air forced out of the lungs by com- pressions is extremely limited by air trapping [22].

Our study and previous literature suggest that improved outcomes reported with programs that minimize interruptions to chest compres- sions during professional CPR are unlikely to be a result of passive ven- tilations produced by chest compressions. As mentioned, numerous other possibilities exist. It is also possible that CPR with active ventila- tion is ideal, but that the complexity of CPR with ventilations results in poor CPR performance (hyperventilation and a low CC-fraction) which offsets potential benefits [23]. Nichol et al. have demonstrated that OHCA with continuous compressions did not result in improved out- comes compared to CPR with interruptions, but the Quality of CPR was higher than has been previously reported. It remains unknown how a minimally interrupted CPR protocol would perform against standard CPR in a typical community with limited training and resources. Because hyperventilation and pauses in chest compressions are common in the prehospital and hospital setting, it remains important to determine op- timal timing, volumes, and ventilation rates in order to avoid the detri- mental effects of excessive ventilation and pauses.

There are limitations to our study. We analyzed a relatively small convenience sample and it is possible that a larger sample of cardiac ar- rest patients with differing anatomies, etiology of arrest, and physiol- ogies would provide even greater detail on ventilation volumes with compressions alone. Additional subjects would allow analyses stratified by initial rhythm, witnessed arrest, age and the length of time in cardiac arrest. While this study sought to describe ventilation volumes, future work could potentially include the effect on outcomes. Any future out- come study would need to consider potential confounders, such as type of ventilation, gasping, blood pressure, initial rhythm, and quality and type of CPR performed in the prehospital setting [24,25]. The Matlab script created for this analysis is novel and will require future validation. Because the ventilation measurement system is not portable, ventila- tion measurements were made inside the emergency department after patients had received prehospital resuscitation attempts. Chest re- modeling and changes in lung compliance do occur after the initial rounds of compressions, however all physiological data was recorded after patients had received CPR in the field [26].

Conclusion

We found that ventilation volumes measured during chest compres- sions of guideline-compliant depth during emergency department resuscitation of out-of-hospital cardiac arrests did not provide tidal vol- umes consistent with physiologic ventilation.

Acknowledgments

Funding: His research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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