Evaluation of an impedance threshold device in patients receiving active compression–decompression cardiopulmonary resuscitation for out of hospital cardiac arrest
Introduction
Most people die from cardiac arrest, despite receiving cardiopulmonary resuscitation (CPR). There are many reasons for the high mortality rates, notably the time to the start of CPR, and the inherent inefficiency of CPR itself. While time to initiation of CPR is dependant upon the overall efficiency of the emergency medical services, standard manual CPR is intrinsically inefficient as the chest compression promotes forward flow but there is little to promote the return of blood back into the heart. Indeed, standard CPR only provides 10–20% of normal blood flow to the heart and 20–30% of normal blood flow to the brain [1], [2], [3]. Many have tried to develop new CPR techniques [4], [5], [6], [7], [8], [9]. Most efforts have focused on means to increase systemic pressures directly during the compression phase of CPR. Two approaches have been recently discovered to increase venous return to the heart during the decompression phase, thereby priming the pump for each subsequent compression phase.
The first one is active compression–decompression (ACD) CPR [10], [11], [12], [13]. It is performed with a hand-held suction device fixed on the anterior chest wall. During the compression phase, the chest is compressed and blood is forced out of the heart to perfuse the vital organs. When actively pulling up with the device, a vacuum is created within the thorax, drawing more blood back into the heart. This technique is known to improve haemodynamics [3], [10] and, in some studies, survival rates in patients in cardiac arrest compared with patients receiving standard CPR [12], [13]. A second approach involves use of the impedance threshold device (ITD) during CPR [14], [15], [16]. It is a small (35 ml) valve with a silicone diaphragm that can be attached to the tracheal tube or face mask or laryngeal mask airway [16], [17] (see Fig. 1). When not actively ventilating the patient, the diaphragm is designed to selectively impede inspiratory airflow into the patient when the intrathoracic pressure is less than 0 atm, thereby increasing the degree of negative intrathoracic pressure with each chest decompression when compared with CPR alone. This creates and maintains a vacuum within the chest to improve venous return back to the heart further. During active ventilation by the rescuer, neither inspiratory nor expiratory gas exchange to the patient is impeded by the ITD. Similarly, with chest compression, there is no resistance to the movement of air out of the chest [15]. Should the patient gasp spontaneously, or begin to breathe on his or her own, then ventilation is possible through a side port safety check valve set to open at −21 cm H2O. The ITD is removed after there is a return of spontaneous circulation (ROSC).
Recently, animal studies have demonstrated that ITD improves vital organ blood flow and survival rate during standard and, to a greater degree, during ACD CPR because of the enhancement of the decrease in intrathoracic pressure with active chest wall decompression [1], [18], [19], [20]. Based upon the improvement in blood pressure and coronary perfusion pressure in patients treated with the combination of the ACD CPR and ITD [14], this device combination was given a Class IIb recommendation in the International CPR Guidelines 2000 (“acceptable alternative” to standard CPR) [21], [22].
Based upon these promising results, the present study was designed to determine if the combination of ACD CPR with the ITD would result in improved short-term survival rates when compared with ACD CPR alone.
Section snippets
Material and methods
This prospective multi-site clinical randomized blinded trial complies with the Declaration of Helsinki. It was approved by the Consultative Council for the Protection of Persons Volunteering for Biomedical Research of Lariboisière Saint-Louis University, Paris. This ethical committee waived the requirement for informed consent since it was not possible under the clinical circumstances and the committee felt that the study was justified based upon a previous haemodynamic study with the same
Results
A total of 618 emergency calls for cardiac arrests were recorded during the study period. Of these, 218 patients were excluded from enrollment and did not receive ALS. BLS was not provided in 57 patients because of irreversible death and in three patients with do-not-resuscitate orders. ALS was not provided in 56 patients with a terminal illness and in the 69 patients with a known time from collapse to initiation of basic CPR greater than 30 min. A total of 33 patients recovered following BLS
Discussion
The combination of ACD CPR with the ITD has been shown recently to improve coronary artery perfusion pressures and systemic blood pressures significantly in animals and patients in cardiac arrest when compared with ACD CPR alone [14], [16]. Results from the present study confirm that the haemodynamic benefit observed in previous studies translates to a direct increase in survival rates and improved neurological function. In the current study, the principal endpoint was 24 h survival. We observed
Conclusions
While rapid deployment of emergency response personnel is a key element to successful resuscitation, the advances made in circulation to the vital organs with the combination of ACD CPR and the ITD have been shown, for the first time in the current study, to translate directly into improvement in overall short-term survival rates when compared with ACD CPR alone. Brain function was at least as good in the survivors with the new technique compared with controls. Building upon the positive
Acknowledgments
This study was funded in part by Advanced Circulatory Systems Incorporated (formerly CPRx LLC) 7615 Golden Triangle Dr., Suite A, Technology Park, Eden Prairie, MN 55344, USA.
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