Oxygen delivery and return of spontaneous circulation with ventilation:compression ratio 2:30 versus chest compressions only CPR in pigs

Abstract

The need for rescue breathing during the initial management of sudden cardiac arrest is currently being debated and reevaluated. The present study was designed to compare cerebral oxygen delivery during basic life support (BLS) by chest compressions only with chest compressions plus ventilation in pigs with an obstructed airway mimicked by a valve hindering passive inhalation. Resuscitability was then studied during the subsequent advanced life support (ALS) period. After 3 min of untreated ventricular fibrillation (VF) BLS was started. The animals were randomised into two groups. One group received chest compressions only. The other group received ventilations and chest compressions with a ratio of 2:30. A gas mixture of 17% oxygen and 4% carbon dioxide was used for ventilation during BLS. After 10 min of BLS, ALS was provided. All six pigs ventilated during BLS attained a return of spontaneous circulation (ROSC) within the first 2 min of advanced cardiopulmonary resuscitation (CPR) compared with only one of six compressions-only pigs. While all except one compressions-only animal achieved ROSC before the experiment was terminated, the median time to ROSC was shorter in the ventilated group. With a ventilation:compression ratio of 2:30 the arterial oxygen content stayed at 2/3 of normal, but with compressions-only, the arterial blood was virtually desaturated with no arterio-venous oxygen difference within 1.5–2 min. Haemodynamic data did not differ between the groups. In this model of very ideal BLS, ventilation improved arterial oxygenation and the median time to ROSC was shorter. We believe that in cardiac arrest with an obstructed airway, pulmonary ventilation should still be strongly recommended.

Sumàrio

A necessidade de insuflações de emergência durante a fase inicial da abordagem da paragem cardı́aca súbita está actualmente em debate e a ser reavaliada. Este estudo foi desenhado para comparar o fornecimento cerebral de oxigénio durante o suporte básico de vida (BLS) só com compressões torácicas e com compressões torácicas e insuflações, em porcos com a via aérea obstruı́da através de uma válvula. A reanimabilidade era depois estudada no perı́odo subsequente de suporte avançado de vida (ALS). Após 3 minutos de fibrilhação ventricular iniciava-se BLS. Os animais eram distribuı́dos aleatoriamente em dois grupos. Um, recebia apenas compressões torácicas. O outro recebia ventilações e compressões à razão de 2:30. Usou-se uma mistura gasosa de 17% de oxigénio e 4% de dióxido de carbono para a ventilação durante o BLS. Ao fim de 10 min de BLS, iniciava-se o ALS. Os seis porcos ventilados durante o BLS atingiram um retorno de circulação espontânea (ROSC) nos primeiros 2 min de reanimação cardio-pulmonar avançada quando comparados com apenas um dos porcos dos que só receberam compressões. Só um dos animais do grupo apenas com compressões não conseguiu ROSC antes de terminar a experiência. O tempo médio até atingir ROSC era menor no grupo ventilado. Quando a razão ventilação: compressão era de 2:30 a concentração arterial de oxigénio permaneceu em 2/3 do normal, mas no grupo só com compressões, o sangue arterial estava virtualmente dessaturado, sem diferença artério-venosa de oxigénio ao fim de 1.5–2 min. Os dados hemodinâmicos não diferiram entre os grupos. Neste modelo de BLS ideal, a ventilação melhorou a oxigenação e o tempo médio para ROSC foi mais curto. Acreditamos que, na paragem cardı́aca com via aérea obstruı́da, a ventilação pulmonar deve continuar a ser fortemente recomendada.

Resumen

La necesidad de ventilaciones de rescate durante el manejo inicial de paro cardı́aco súbito está actualmente siendo debatido y reevaluado. El presente estudio fue diseñado para comparar la entrega de oxigeno cerebral durante el soporte vital básico (BLS) con aplicación solamente de compresiones o con compresiones y ventilaciones en cerdos con una vı́a aérea obstruida simulada con una válvula que evita la inhalación pasiva. La resucitabilidad fue entonces estudiada durante el perı́odo de soporte vital avanzado (ALS) subsecuente. Después de tres minutos de fibrilación ventricular(VF) sin tratamiento se inició BLS. Los animales fueron randomizados en dos grupos. Un grupo recibió solo compresiones torácicas. El otro grupo recibió ventilaciones y compresiones torácicas en una relación 2:30. Se uso una mezcla de gas con 17% de oxı́geno y 4% de dióxido de carbono durante el BLS. Después de 10 minutos en BLS, se proporcionó ALS. Los 6 cerdos ventilados durante el BLS alcanzaron retorno a circulación espontánea(ROSC) dentro de los primeros 2 minutos de reanimación cardiopulmonar (CPR) avanzada comparados con solo uno de seis de los cerdos manejados solo con compresiones. Mientras todos salvo un animal del grupo solo compresiones alcanzó ROSC antes de terminar el experimento, la mediana de tiempo a ROSC fue mas corta en el grupo ventilado. Con una relación ventilación : compresión de 2:30 el contenido arterial de oxı́geno se mantuvo en 2/3 de lo normal, pero solo con compresiones el contenido arterial de oxı́geno fue virtualmente desaturado, sin diferencia arteriovenosa de contenido de oxı́geno, al cabo de 1.5–2 minutos. Los datos hemodinámicos no difirieron entre los grupos. En este modelo de BLS muy ideal, la ventilación mejoró la oxigenación arterial y la media de tiempo a ROSC fue mas corta. Creemos que en el paro cardı́aco con vı́a aérea obstruida, la ventilación está fuertemente recomendada.

Introduction

Bystander cardiopulmonary resuscitation (CPR) improves the chances of successful resuscitation and survival [1], [2]. The presently recommended procedure for lay rescuer CPR includes a combination of two rescue breaths interposed after every 15th chest compression [3]. Over the past decade, the need for assisted ventilation in treatment of adult patients with primary cardiac arrest has been challenged and re-evaluated [4], [5], [6], [7]. One reason for this re-evaluation is the fact that both lay rescuers and professional medical providers are reluctant to perform mouth-to-mouth ventilation owing to concerns about transmission of infectious diseases [8], [9], [10]. In addition, the current basic CPR technique is a complex psychomotor task that is difficult to learn and perform without complications such as gastric inflation [11], [12], [13]. Finally, the relatively long pauses in chest compression required for ventilation interrupt the CPR-generated perfusion, potentially compromising the success of cardiac resuscitation [14], [15], [16].

On this basis, some investigators have begun to explore ventilation:compression ratios with much longer sequences of uninterrupted compressions [14], [17] or even chest compressions only CPR [7], [18], [19], [20].

Based on theoretical considerations Babbs and Kern [21] recently suggested that a ratio of 2:30 would be ideal during basic life support (BLS) with pauses in chest compressions of 2.5 s per breath, and in a previous study of different ventilation:compression ratios we found oxygen saturation data supporting that a ratio near 2:30 might be optimal for standard, guidelines specified, BLS [22].

The purpose of the present study was to compare BLS by compressions-only to a ventilation-compression ratio of 2:30 for 10 min followed by standard advanced life support (ALS) in a pig model of ventricular fibrillation (VF). The primary outcome variables were the calculated carotid and cerebrocortical oxygen delivery during BLS and time to return of spontaneous circulation in the ALS period.

It was our hypothesis that adequate oxygen delivery and favourable resuscitation outcome may be maintained with ventilation:compression ratio of 2:30 whilst compressions-only CPR would result in rapid arterial deoxygenation and compromised resuscitability.