Evaluation of LUCAS, a new device for automatic mechanical compression and active decompression resuscitation
Introduction
Cardiac arrest, either as asystole or as ventricular fibrillation (VF), is the most dramatic situation in medicine. Since Kouwenhoven and coworkers published their landmark article in 1960 [1], manual closed-chest compressions (combined with mouth-to-mouth ventilation) has been established as the initial treatment of choice for circulatory arrest, followed by defibrillation as soon as the equipment is available, if VF is the cause of the collapse. With proper training, anyone, anywhere can initiate cardio-pulmonary resuscitation (CPR). However, due to fatigue, manual CPR cannot be given for more than a few minutes before it becomes ineffective [2], and it cannot be given effectively at all during transport [3]. Most cardiac arrests occur out-of-hospital and the survival rates are very poor; in most published reports the 1-year survival rate is less than 5%. In a randomized study, Plaisance and coworkers [4] compared standard manual CPR (n=377 patients) with active compression/decompression CPR performed manually with the CardioPump (AMBU, Copenhagen, Denmark) (n=373 patients). The 1-year survival rate was very poor in both groups, 2 versus 5% (P=0.03); all resuscitation efforts with either method were performed only at the scene of the cardiac arrest, and only if they were successfully resuscitated at the scene were the patients transported to hospital. To prevent fatigue, the rescuers were instructed to alternate after each 3 min of CPR. The study of Plaisance et al. demonstrates the need for a mechanical device giving adequate compressions/decompressions continuously until the patient can be delivered to a hospital with all facilities for the treatment of heart disease, including direct PTCA and heart surgery.
Most devices for mechanical chest compression in use today have operational limitations because they take too long to apply, they are cumbersome to install and operate, they are unstable on the chest, heavy, and expensive to purchase [5]. Therefore, no mechanical device for chest compression/decompression currently is used routinely in clinical practice, in spite of the obvious limitations of manual CPR. Recently, a new device named LUCAS, has been made commercially available (Fig. 1, Fig. 2). It is designed to give automatic mechanical chest compression and active decompression. It is portable and works during transport both on stretchers and in ambulances.
The aim of the present investigation was to compare the efficacy of LUCAS with that of manual compressions on an artificial thorax model allowing exact analysis of pressure- and flow-curves, and on a pig model in which relevant physiological variables could be registered. In an earlier study using the same pig model we studied the effects of adrenaline (epinephrine) and noradrenaline (norepinephrine) on end-tidal CO2, coronary perfusion pressure and cardiac output during cardiopulmonary resuscitation [6]. In the present study we decided to eliminate all drug therapy in order to elucidate the effects of chest compressions per se. Data from the first clinical pilot study with LUCAS are also presented.
Section snippets
The artificial thorax model
A 25 l plastic drum made of polyvinyl chloride (PVC) was used as an artificial thorax (Fig. 3). A soft plastic bag (150 ml), simulating a heart, was included in the drum. Pressure (P) was continuously measured in the bag. By means of a stiff tube penetrating the tight cork of the drum, the soft bag was connected to an artificial circulatory system including two artificial heart valves for flow direction. The plastic drum was filled with 20 l water and 5 l air, and regained its original shape
Manual CPR vs. LUCAS-CPR in the artificial thorax model
Typical pressure-flow curves for the artificial thorax model are presented in Fig. 6; in the left panel the rescuer performs manual CPR as he would have done in a clinical situation, and in the middle panel his performance during 5 s of maximal effort is shown. As seen in the right panel, LUCAS-CPR creates pressure-flow curves quite different from those seen during manual CPR, i.e. the area under the curves produced by LUCAS is greater, with a corresponding increase in mean pressure and flow.
Discussion
The animal experiments in this study were performed and reported according to the Utstein guidelines for laboratory CPR research [7]. These recommend use of swine weighing 20–25 kg. The anteroposterior chest diameter of pigs this size will be similar to that of average sized adult humans. Our measurements of 65 adult humans confirmed this. Swine have the advantage of being uniform in size and shape at similar ages and weights and there are many similarities in metabolic and cardiovascular
Acknowledgements
This study was supported by grants from the University Hospital of Lund, the Swedish Heart Lung Foundation, and the Swedish Medical Research Council (Project no. K2002-71X-12648-05C).
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