Sudden cardiac arrest is one of the most important issues in healthcare and every year about 350 000 people die in Europe after such an event.1 Chest compressions are a cornerstone of the cardiopulmonary resuscitation procedure. The recently published European Resuscitation Council (ERC) Guidelines for Cardiopulmonary Resuscitation 2015 stated that ‘the routine use of mechanical chest compression devices is not recommended, but they are a reasonable alternative in situations wherein sustained high-quality manual chest compressions are impractical or compromise provider safety’.2 Moreover, the ERC guidelines describe the use of automated mechanical chest compression devices in cases where ventricular fibrillation/pulseless ventricular tachycardia persist, return of spontaneous circulation has not been achieved or transfer to a hospital under cardiopulmonary resuscitation is required.2,3 Other reasons for the use of automated mechanical chest compression devices are prolonged cardiopulmonary resuscitation (e.g. hypothermia, severe hyperkalaemia, anaphylaxis and pulmonary embolism), resuscitation at high altitude (as cardiopulmonary resuscitation is more exhausting for the rescuer than at sea level) and during percutaneous coronary intervention (e.g. to reduce the radiation burden of the personnel).2,3 The ERC guidelines highlight the importance of preflight preparation and use of automated mechanical chest compression devices on board Helicopter Emergency Medical Service and air ambulances if the patient is at risk of cardiac arrest during the flight.3
The ERC guidelines list adequate depth and rate, minimal interruptions and avoiding delay in defibrillation as the advantages of automated mechanical chest compression devices (within a structured, monitored programme including comprehensive competency-based training and regular opportunities to refresh skills).2
In the USA, data from the Cardiac Arrest Registry to Enhance Survival show that 45% of participating Emergency Medical Services use automated mechanical chest compression devices.8 In Europe, there has also been an increase in the use of automated mechanical chest compression devices. Therefore, problems with the use of automated mechanical chest compression devices have significant implications for patient safety and are of major interest for the scientific community.
At first sight, the three major studies on the use of automated mechanical chest compression devices, the LINC4 [LUCAS in cardiac arrest (LUCAS-2 compression device), n = 2589], the PARAMEDIC5 [prehospital randomised assessment of a mechanical compression device (LUCAS-2 compression device), n = 4471] and the CIRC6 (circulation improving resuscitation care (AutoPulse compression device), n = 4753] trial, raise no serious doubts about the safety of automated mechanical chest compression devices (Table 1). These three recently published studies included over 11 000 patients suffering from out-of-hospital cardiac arrest, 5051 patients treated with automated mechanical chest compression devices and 6240 patients treated with manual chest compressions. Although several meta-analyses and reviews (including two further automated mechanical chest compression device studies)10,11 did not show a benefit of automated mechanical chest compression devices over manual chest compressions in out-of-hospital cardiac arrest, they also did not reveal any profound risks or evidence of inferiority of automated mechanical chest compression devices.9,12
However, one major safety issue is not sufficiently assessed in these investigations: ventilation strategy and quality. In the LINC4 trial, in both groups, ventilation and drugs were given according to the 2005 ERC guidelines.14 Hence, no further information concerning the airway management, except the time to intubation [LUCAS-2, n = 852 vs. manual, n = 828 (median, interquartile range, 20 (15 to 25) vs. 18 (14 to 23) min)] was reported.4 In the PARAMEDIC trial,5 both the groups received a compression-to-ventilation ratio of 30 : 2 before intubation, and continuous uninterrupted chest compressions with asynchronous ventilation after intubation. The compression-to-ventilation ratio after insertion of a laryngeal mask airway or other supraglottic airway devices is not clearly depicted. Chest compressions and medications were given in accordance with the ERC guidelines from 2010.15 The airway was managed with either tracheal intubation (LUCAS-2, n = 749, 45% vs. manual, n = 1297, 46%) or with insertion of a laryngeal mask airway or other supraglottic airway device (LUCAS-2, n = 435, 26% vs. manual, n = 736, 26%). Interestingly, details regarding the airway management seem to be unknown in a large number of patients (LUCAS-2: 29% vs. manual: 28%). In the CIRC6 trial, for both groups, the compression-to-ventilation ratio before and after airway management was not reported. Treatment was rendered according to the American Heart Association guidelines for resuscitation from 2005.16 Data on the intubation rate or the use of a laryngeal mask airway or other supraglottic airway devices were not reported. The mean ± SD ventilation rate per minute during the first 10 min in the automated mechanical chest compression device group in comparison with the manual group was 7 ± 3 vs. 9 ± 5. Thus, the recommended ventilation rate of 10 ventilations/min according to the recently published guidelines was not achieved.2
All studies suffer from missing data regarding ventilation quality when automated mechanical chest compression devices are used. Surprisingly, in all three automated mechanical chest compression device trials mentioned earlier,4–6 detailed data on advanced airway management interventions (e.g. successful intubation of the trachea, successful insertion of a supraglottic airway device) are missing. In the PARAMEDIC trial, 39 vs. 38% of patients received ongoing cardiopulmonary resuscitation at hospital admission (LUCAS-2 vs. manual group). For both groups of patients, the proportion of patients ventilated via supraglottic airway devices is not known. In particular, there were no data presented on the ventilation quality and possible airway management problems. One would expect data for end-tidal carbon dioxide concentration or for oxygen saturation at hospital admission or any other time points during cardiopulmonary resuscitation or after return of a spontaneous circulation. Notably, the CIRC study protocol stated that the cardiopulmonary resuscitation quality was recorded in the trial database for each patient, including the variables ‘end-tidal carbon dioxide’ and ‘oxygen saturation’.7 However, no such data were reported in the subsequent publication.6
Beyond the three major automated mechanical chest compression device studies, a study by Tranberg et al.13 investigating the quality of cardiopulmonary resuscitation stated in the ‘Methods’ section that the prehospital critical care teams and the Helicopter Emergency Medical Service teams completed a separate study form regarding the end-tidal carbon dioxide concentration. This should serve as a surrogate parameter for cardiopulmonary resuscitation quality.21 Unfortunately, these results were not presented in the publication and the authors stated that they were unable to report the end-tidal carbon dioxide concentrations because of a lack of registered values/too many missing values.13
The guidelines do not address the ventilation problems with automated mechanical chest compression devices. The recommendations made in 2005, 2010 and 2015 by the ERC concerning the compression-to-ventilation ratio before and after advanced airway management are identical.2,14,15
- A compression-to-ventilation ratio of 30 : 2 before intubation/supraglottic airway device and uninterrupted chest compression after intubation or use of supraglottic airway device as airway strategy.
- Once a supraglottic airway device has been inserted, uninterrupted chest compressions should be attempted; if excessive gas leakage causes inadequate ventilation, chest compressions should be interrupted to enable ventilation (using a compression-to-ventilation ratio of 30 : 2).
Similarly, the American Heart Association guideline 2005 did not differ from the recommendation for the compression-to-ventilation ratio of 30 : 2 until an advanced airway is in place.16 Notably, and not surprisingly, given the general lack of evidence, no special recommendations were made regarding the use of supraglottic airway devices during mechanical chest compressions.
There is a lack of data to support the safety and effectiveness of the recommendation for uninterrupted chest compression using automated mechanical chest compression devices and ventilation via supraglottic airway devices. There is insufficient or missing evidence for the effectiveness of any ventilation strategy and the use of automated mechanical chest compression devices. To the best of our knowledge, there are no clinical studies that focus on effective oxygenation and elimination of carbon dioxide in patients suffering from cardiac arrest who are being treated with automated mechanical chest compression devices. Furthermore, there is a notable lack of data on upper airway pressure limits (e.g. avoidance of barotrauma) during manual chest compressions. During automated mechanical chest compression device use, airway pressure may exceed 20 cmH2O, which can make ventilation using supraglottic airway devices ineffective. Ventilation problems might occur in the setting of supraglottic airway devices and automated mechanical chest compression device use.
In the authors’ clinical experience, automated mechanical chest compression devices make continuous high-quality ventilation difficult and sometimes impossible. None of the available automated mechanical chest compression devices were constructed with particular regard to effective and safe ventilation. In general, the use of a supraglottic airway device itself can be complicated by numerous problems that lead to inadequate ventilation, hypoxaemia and hypercapnia (e.g. displacement, incorrect placement and tongue/pharyngeal swelling).17,18 As chest compressions alone without oxygenation and ventilation are recommended only for the brief time period of basic life support performed by laypersons (compression-only cardiopulmonary resuscitation), a safe strategy for airway management and ventilation is an integral part of any resuscitative measures. After the arrival of healthcare professionals (e.g. paramedics and Emergency Medical Service physicians) and during advanced life support, ensuring oxygenation and elimination of carbon dioxide is crucial – even if the optimal strategy for managing the airway has not been determined yet.19 High-quality chest compressions only, with and without automated mechanical chest compression devices, will remain unsuccessful without oxygenation and decarboxylation of the blood. Desaturated blood does not contribute to myocardial and cerebral oxygenation, and hypercapnia may be detrimental (e.g. acidosis and cardiodepressive effects).20
During ventilation with supraglottic airway devices – perceived as an unsecured airway – while using automated mechanical chest compression devices, there is considerable potential for ineffective ventilation with continuous and uninterrupted mechanical chest compression. Thus, it is conceivable that the results of the three major automated mechanical chest compression device trials (LINC, PARAMEDIC and CIRC) may reveal a significant difference between the study arms if patients ventilated with a bag-valve-mask or supraglottic airway device were excluded from the analysis. We presume that, particularly with supraglottic airway devices and continuous automated mechanical chest compression, ventilation is ineffective and a significant confounder in the three major automated mechanical chest compression device studies. This may be particularly important for patients transported to a hospital with prolonged and ongoing cardiopulmonary resuscitation during transport. Therefore, we suggest an extended raw data analysis of the three major automated mechanical chest compression device trials with regard to the impact of automated mechanical chest compression devices on effective ventilation. We hope that this will lead to better recommendations on safe and effective airway management strategies during the use of automated mechanical chest compression devices, regarding, in particular, the use of supraglottic airway devices in these patients.
Acknowledgements relating to the article
Assistance with the editorial: none.
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Conflict of interest: none.
Comment from the Editor: this Editorial was checked and accepted by the Editors, but was not sent for external peer-review. BB is an associate editor of the European Journal of Anaesthesiology.
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