Elsevier

Resuscitation

Volume 61, Issue 1, April 2004, Pages 75-82
Resuscitation

Reducing ventilation frequency combined with an inspiratory impedance device improves CPR efficiency in swine model of cardiac arrest

https://doi.org/10.1016/j.resuscitation.2003.12.006Get rights and content

Abstract

Background: The basic premise that frequent ventilations during cardiopulmonary resuscitation (CPR) are a necessity for tissue oxygenation has recently been challenged. An inspiratory impedance threshold device (ITD) recently has also been shown to increase CPR efficiency, principally by augmenting circulation with little impact on ventilation. The optimal compression to ventilation (C/V) is not known for this new device. The purpose of this study was to compare the currently recommended C/V ratio of 5:1 with a 10:1 ratio, ± the ITD, to optimize circulation and oxygenation during CPR. Methods: Thirty-two adult pigs weighing 26–31 kg were randomized to CPR with varying C/V ratios ± the ITD as follows: A=5:1, B=5:1+ITD, C=10:1, D=10:1+ITD. After 6 min of untreated ventricular fibrillation (VF), closed-chest standard CPR was performed with an automatic piston device that does not impede passive chest wall recoil, at a continuous compression rate of 100 min−1. Synchronous breaths were given every 5 or 10 compressions during the decompression phase depending on the group. CPR was performed for 6 min and physiological variables were measured throughout the experimental protocol. Results: A reduction in the frequency of ventilation from 5:1 to 10:1 resulted in significantly improved arterial and coronary perfusion pressure in a pig model of cardiac arrest. Addition of an ITD resulted in further increases in arterial and coronary perfusion pressures with both 5:1 and 10:1 C/V ratios, without compromising oxygenation. Conclusion: CPR efficiency can be optimized by changing the compression: ventilation ratio from 5:1 to 10:1 and with concurrent use of the inspiratory threshold device.

Sumàrio

Contexto: O conceito de que durante a reanimação cardio-pulmonar (CPR), são necessárias ventilações frequentes para a assegurar a oxigenação tecidular tem sido desafiada recentemente. Um aparelho de limiar de impedância inspiratória (ITD) também mostrou recentemente aumentar a eficiência da CPR, principalmente aumentando a circulação e com pouco impacto na ventilação. A razão compressão para ventilação (C/V) optimizada para este aparelho não é conhecida. O objectivo deste estudo foi comparar as recomendações actuais da relação C/V de 5:1 com 10:1, ± o ITD, para optimizar a oxigenação e a circulação durante a CPR. Método: Foram aleatorizados 32 porcos adultos com peso 26–31 kg para CPR com C/V variáveis ± ITD da seguinte forma: A = 5:1, B = 5:1 + ITD; C = 10:1, D = 10:1 + ITD. AO fim de 6 minutos de fibrilhação ventricular (VF) não tratada era efectuada CPR externa com um aparelho de piston automático que não impede a recolha elástica da parede torácica, a uma frequência de compressões constante de 100 min−1. Efectuaram-se insuflações sı́ncronas a cada 5 ou 10 compressões durante a fase de descompressão, dependendo do grupo. A CPR foi efectuada durante 6 minutos e os parâmetros fisiológicos foram medidos durante o protocolo experimental. Resultados: A redução da frequência de ventilação de 5:1 para 10:1 resultou numa pressão de perfusão arterial e coronária significativamente melhoradas num modelo de paragem cardı́aca em porcos. A adição do ITD resultou em melhoria adicional nas pressões de perfusão arterial e coronária em ambas as relações de C/V, 5:1 ou 10:1, sem comprometer a oxigenação. Conclusão: A eficiência da CPR pode ser optimizada pela alteração da relação compressão: ventilação de 5:1 para 10:1 e com o uso concomitante do aparelho de limiar inspiratório.

Resumen

Antecedentes: La premisa básica que dice que ventilaciones frecuentes durante la reanimación cardiopulmonar (CPR) son una necesidad para la oxigenación tisular ha sido recientemente desafiada. Recientemente se ha mostrado que un dispositivo de umbral impedancia inspiratoria (ITD)mejora la eficiencia de la CPR, principalmente aumentando la circulación con muy poco impacto en la ventilación. No se conoce aun la relación ventilación compresión (C/V) óptima para este dispositivo. El propósito de este estudio fue comparar la relación C/V de 5 :1 actualmente recomendada con una relación 10:1, ± el ITD, para optimizar la oxigenación y circulación durante la CPR. Métodos: Se usaron 32 cerdos adultos que pesaban 26–31 kg, randomizados a CPR variando la relación C/V ± el ITD de la siguiente manera: A = 5:1, B = 5:1 + ITD, C = 10:1, D = 10:1 + ITD. Después de 6 minutos de fibrilación ventricular (VF) sin tratamiento, se realizó CPR estándar a tórax cerrado con un dispositivo de pistón automático que no impide la recuperación pasiva del tórax, a una frecuencia de compresión continua de 100 por minuto. Se dieron ventilaciones sincronizadas cada 5 o 10 compresiones durante la fase de descompresión dependiendo del grupo. Se realizó CPR por 6 minutos y se midieron los parámetros fisiológicos a lo largo del protocolo del experimento. Resultados: Una reducción en la frecuencia de ventilación de 5:1 a 10:1 resultó en presiones arteriales y de perfusión coronaria significativamente aumentadas en un modelo porcino de paro cardı́aco. La adición del ITD resulto en ulteriores aumentos en presiones arteriales y de perfusión coronaria con ambas relaciones 5:1 y 10:1, sin comprometer la oxigenación. Conclusión: La eficiencia de la CPR puede ser optimizada cambiando la relación ventilación compresión de 5:1 a 10:1 y con el uso del dispositivo de umbral de impedancia inspiratoria.

Introduction

The basic premise that frequent ventilations are a necessity to maintain tissue oxygenation during cardiopulmonary resuscitation (CPR) has been challenged by recent animal and human studies [1], [2], [3], [4], [5], [12], [13]. These new investigations have shown that adequate oxygenation can be maintained with chest compressions alone without ventilation for some limited period of time and that there is no haemodynamic compromise with that approach. When chest compressions are stopped to deliver a breath, coronary perfusion is interrupted and consequently falls until the next series of compressions [17]. An additional cause and explanation for the negative hemodynamic consequences of ventilation is that frequent positive pressure ventilations may result in higher intrathoracic pressures and thereby impede venous return to the heart during the decompression phase of CPR. As such, the frequency of ventilation preventing venous return of blood to the heart during the chest wall decompression phase directly may alter coronary perfusion pressure (CPP) and cardiac output during CPR [8].

The importance of changes in intrathoracic pressure during CPR recently has been highlighted by studies of a new device called an inspiratory impedance threshold device (ITD). This helps to pump more blood back to the heart during cardiac arrest by enhancing negative intrathoracic pressure during the decompression phase of CPR, thereby enhancing blood return [6], [9], [10], [11], [14], [15]. In view of the increased efficiency of CPR with the ITD, we hypothesized that the cardiopulmonary interactions associated with blood flow and ventilation may be improved further by reducing the frequency of ventilations when using the ITD. A reduction in the ventilation frequency would result in less overall positive intrathoracic pressure, enable more time for venous blood flow back to the heart and provide more time per minute for the ITD to increase circulation [6], [7], [10].

To test the hypothesis we investigated the effects of two different compression: ventilation ratios, with and without an ITD, on the coronary perfusion pressure, mean arterial pressure (MAP), and oxygenation. Compressions were performed continuously at a rate of 100 min−1. The delivery of each breath was initiated during the decompression phase of CPR. To ensure that the chest wall was allowed to recoil fully during the decompression phase, an automatic compression-release device was used. The results support the hypothesis that fewer ventilations per minute improved hemodynamics during CPR. The physiological benefits of fewer ventilations per minute can be further enhanced using the ITD, without compromising oxygen delivery.

Section snippets

Materials and methods

The study was approved by the Committee of Animal Experimentation at the University of Minnesota. The animals received care in compliance with the 1996 Guide for the Care and Use of Laboratory Animals by the National Research Council in a facility that was accredited by the American Association for Accreditation of Laboratory Animal Care. Anaesthesia was used in all surgical interventions to avoid all unnecessary suffering. Experiments were performed by a qualified team. The study was performed

Results

A total of 32 pigs randomized to four equal groups: group A received CPR with a compression:ventilation (C/V) ratio of 5:1, group B with a C/V ratio of 5:1 plus the ITD, group C with a C/V ratio of 10:1 and group D with a C/V ratio of 10:1 plus the ITD. Before induction of cardiac arrest, there were no statistically significant differences in weight, temperature, hemodynamic variables and arterial blood gases between the groups (Table 1).

Intrathoracic pressures during the decompression phase

Discussion

Cardiopulmonary interactions during CPR are influenced by the ratio of chest compressions to ventilations and the degree of negative intrathoracic pressure achieved during chest wall recoil. The results of this study demonstrate that both a reduction in the frequency of ventilation and use of an ITD enhance the decompression phase vacuum created by the chest wall recoil. This results in a significant improvement in the efficiency of CPR and in survival rates [10], [14].

At present, the

Conclusions

This study supports the hypothesis that the efficiency of cardiopulmonary resuscitative measures can be improved by optimizing the cardiopulmonary interactions that regulate vital organ blood flow during CPR. A reduction in the frequency of ventilations resulted in a lower intrathoracic pressure during CPR and this contributed to the increase in arterial and coronary perfusion pressures. Addition of an inspiratory impedance device resulted in a further decrease in intrathoracic pressures during

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