Simulation and educationMetronome improves compression and ventilation rates during CPR on a manikin in a randomized trial☆
Introduction
The importance of minimizing interruptions in chest compressions for successful resuscitation from cardiac arrest is now well recognized.1, 2, 3 Concerted efforts in many emergency medical services (EMS) systems have markedly decreased previously accepted compression interruptions such as checking for a pulse, reviewing the electrocardiogram, inserting a central intravenous line, providing rescue breaths, or performing endotracheal intubation.4, 5 The importance of delivering more than 80 chest compressions/min during CPR has been noted in both animal experimental studies,6 and clinical observations.7 Major changes in the CPR Guidelines were instituted in 2005 to provide more chest compressions, including the recommendation of a 30:2 chest compression to ventilation ratio.8
The use of an audible metronome for guiding chest compression rate is one strategy to improve the effectiveness of chest compressions. Previous studies of metronome guidance during CPR have shown better compliance with recommended chest compression rates.9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 Some of these studies did not show a difference in mean or median compression rate, but they did show a substantial reduction in standard deviation or interquartile range.13, 16 Some studies have shown increases in expired end-tidal carbon dioxide, an indirect marker of circulation during resuscitation.9, 10, 11 One study reported improved survival rates compared to a historical control group when metronomes were attached to ambulance defibrillators.18
Evidence suggests that excessive positive pressure ventilation during CPR can be detrimental to resuscitation haemodynamics and outcomes.20 Hyperventilation by professional rescuers is quite common in both in-hospital11, 21 and out-of-hospital resuscitations.20 Some have reported the use of audio feedback during CPR can improve ventilation timing and rate.22, 23
The use of a metronome for guiding both chest compressions and ventilations during CPR efforts by professional responders both before and after intubation had not been previously evaluated. We therefore performed a study using a CPR manikin to test professional emergency medical technicians (EMTs) for their ability to perform CPR according to the 2005 guidelines with and without metronome guidance.
Section snippets
Objectives
Our objective was to assess the effectiveness of a compression/ventilation metronome intended for use both before and after securing an advanced airway, for CPR done by two EMTs on a manikin. Consistent with 2005 American Heart Association (AHA) guidelines,8 the CPR metronome prompts for a 30:2 compression to ventilation ratio for CPR with a bag/valve/mask. It prompts for continuous chest compressions and a ventilation rate of 10 min−1 for CPR with an advanced airway, such as an endotracheal
Methods and statistics
The study used a prospective, randomized, parallel group design in which EMTs performed two-rescuer CPR on a manikin. Each pair of EMTs was randomly assigned to either the intervention (CPR metronome) group or the control group and performed two CPR sessions without crossing over to the other group. Each CPR session consisted of 2 min of CPR without an advanced airway, then placement of an endotracheal tube by study staff, then four more minutes of CPR. Six minutes of CPR was chosen to induce
Results
Sixty-eight firefighter EMTs volunteered from the Spokane Fire Department and Spokane Valley Fire Department (Spokane, Washington), allowing for 17 pairs for the intervention (CPR metronome) group and 17 pairs for the control group. Demographic data (available online as supplemental data) were similar for the two groups. In December 2007, in the Spokane Valley Fire Department's training classroom, each pair of EMTs performed two CPR sessions, switching roles between sessions, resulting in 34
Discussion
The current study is the first to methodically evaluate metronome guidance of both chest compressions and ventilation, both before and after endotracheal intubation. The combined tone and voice prompt audio guidance was effective at maintaining the target chest compression rate and avoiding the common problem of hyperventilation during cardiopulmonary resuscitation by professional rescuers.11, 20, 21
Without audible guidance chest compression rates varied widely from 75 to 160 min−1. Without
Conclusions
A unique combination tock and voice prompting metronome was effective with volunteer, paid EMTs at directing correct chest compression and ventilation rates both before and after intubation, thereby avoiding hyperventilation. The CPR metronome was well accepted by the EMTs. The effectiveness of this CPR metronome should be confirmed in clinical use.
Conflict of interest
Kern is on a medical advisory panel for Physio-Control. Stickney, Gallison and Smith are employed by Physio-Control. The CPR metronome used in this study was subsequently made commercially available in the LIFEPAK® 15 monitor/defibrillator (Physio-Control, Redmond, WA, USA).
Author contributions
Study concept and design: Kern, Stickney and Gallison. CPR metronome audio design: Smith and Stickney. Audio equipment design: Smith. Data collection: Gallison and Stickney. Data analysis: Stickney and Kern (CPR measurements) and Gallison (demographics and questionnaire). Manuscript writing and editing: all authors.
Acknowledgements
The authors thank the firefighter/EMTs from the Spokane and Spokane Valley Fire Departments who volunteered as subjects, and the Spokane Valley Fire Department for providing their training facility for data collection. The authors thank Joyce Szymanski, Jennifer Jensen and Ryan Finne, all employed by Physio-Control, for assisting the data collection by operating the manikin measurement software. Physio-Control provided the funds to compensate subjects for their time.
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2009.10.015.