Passive Leg Raise (PLR) During Cardiopulmonary Resuscitation (CPR): a Randomised Study of Survival in Out-of-hospital Cardiac Arrest (OHCA)

1. Background The majority of sudden death cases have a cardiac origin and occur unexpectedly, often outside hospital. Attwood et al.[1] estimated the incidence of and survival from EMS-treated OHCA in Europe and found, for "all-rhythm" CA, an incidence of 37.72 per 100,000 person-years. Survival was 10.7% in "all-rhythm" CA. If these results were applied to the European population, approximately 275,000 persons would experience an all-rhythm, EMS-treated OHCA, with 29,000 persons surviving to hospital discharge[1].

To resuscitate a person, without neurological damage, various efforts, which are described as the four links in the chain of survival (early call, early CPR, early defibrillation and early advanced life support), have to be optimal[2]. During the last decade, the quality and continuity of chest compressions have been increasingly highlighted[3]. The reason is that blood flow and coronary perfusion during cardiac arrest are related to the quality and continuity of chest compressions[4]. A coronary perfusion pressure (CPP) above 15mmHg, at defibrillation, also appears to be necessary for the return of spontaneous circulation (ROSC)[5]. Consequently, different methods and devices to improve blood flow to the heart (coronary perfusion) and brain during CPR, such as different types of mechanical compressor and impedance threshold device[6-9], have been studied.

The initial CPR guidelines[10-12] stated that the "elevation of the lower extremities may promote venous return and augment artificial circulation during external cardiac compression". However, in the 1992 guidelines[13], this statement was removed. The reason for this decision was a lack of clinical evidence. During the last five years, the debate on how PLR may improve the outcomes of the resuscitation manoeuvres in CPR has been re-opened.

According to Préau et al.[14], the effect of PLR is equivalent to a rapid intravenous volume expander by shifting blood from the lower extremities towards the intra-thoracic compartment. A 45° leg elevation for four minutes increases right and left ventricular preload and, by definition, the stroke volume, if the heart is preload dependent[15]. This makes PLR predictive of fluid responsiveness among patients with circulatory failure, e.g. sepsis and acute pancreatitis[14-17], and it has been recommended as part of haemodynamic monitoring in recent international recommendations[18]. Other researchers have also shown the benefit of using PLR to increase resistance to blood flow[19], thereby shifting fluid from the lower extremities to the central circulation[20, 21].

The present study design is based on a pilot study recently conducted in Gothenburg, Sweden. This pilot study concluded that a 20° leg elevation during CPR improved the levels of end-tidal carbon dioxide (EtCO2) during CPR[22]. It has previously been concluded that EtCO2 correlates well with blood flow and that PLR induces an increase in descending aortic blood flow of at least 10% or in echocardiographic sub-aortic flow of at least 12%[23-26]. In other studies, EtCO2 has been shown to be quantitatively predictive of stroke volumes[27]. EtCO2 has also been described as an important value for predicting ROSC and CPR quality[22, 28, 29]. The resuscitation in the Gothenburg pilot study was performed using both manual and mechanical compressions made by LUCAS TM 2 (Lund University Cardiac Assist System), but the effect of PLR appeared to be greater during manual compressions. It was only possible to speculate on the reason for this, but the EtCO2 value started from a higher level in the mechanical group. The possible reason for this could be the "active decompression" creating a larger preload.