Elsevier

Resuscitation

Volume 54, Issue 2, 1 August 2002, Pages 167-173
Resuscitation

Effects of decreasing inspiratory flow rate during simulated basic life support ventilation of a cardiac arrest patient on lung and stomach tidal volumes

https://doi.org/10.1016/S0300-9572(02)00110-7Get rights and content

Abstract

If the airway of a cardiac arrest patient is unprotected, basic life support with low rather than high inspiratory flow rates may reduce stomach inflation. Further, if the inspiratory flow rate is fixed such as with a resuscitator performance may improve; especially when used by less experienced rescuers. The purpose of the present study was to assess the effect of limited flow ventilation on respiratory variables, and lung and stomach volumes, when compared with a bag valve device. After institutional review board approval, and written informed consent was obtained, 20 critical care unit registered nurses volunteered to ventilate a bench model simulating a cardiac arrest patient with an unprotected airway consisting of a face mask, manikin head, training lung [with lung compliance, 50 ml/0.098 kPa (50 ml/cmH2O); airway resistance, 0.39 kPa/l/s (4 cmH2O/l/s)] oesophagus [lower oesophageal sphincter pressure, 0.49 kPa (5 cmH2O)] and simulated stomach. Each volunteer ventilated the model with a self-inflating bag (Ambu, Glostrup, Denmark; max. volume, 1500 ml), and a resuscitator providing limited fixed flow (Oxylator EM 100, CPR Medical devices Inc., Toronto, Canada) for 2 min; study endpoints were measured with 2 pneumotachometers. The self-inflating bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes (945±104 vs. 921±250 ml), significantly (P<0.05) higher peak inspiratory flow rates (111±27 vs. 45±21 l/min), and peak inspiratory pressure (1.2±0.47 vs. 78±0.07 kPa), but significantly shorter inspiratory times (1.1±0.29 vs. 1.6±0.35 s). Lung tidal volumes were comparable (337±120 vs. 309±61 ml), but stomach tidal volumes were significantly (P<0.05) higher (200±95 vs. 140±51 ml) with the self-inflating bag. In conclusion, simulated ventilation of an unintubated cardiac arrest patient using a resuscitator resulted in decreased peak flow rates and therefore, in decreased peak airway pressures when compared with a self-inflating bag. Limited flow ventilation using the resuscitator decreased stomach inflation, although lung tidal volumes were comparable between groups.

Sumàrio

Se a via aérea de um doente em paragem cardı&#x0301;aca não estiver protegida, o suporte básico de vida com fluxos inspiratórios baixos em vez de altos pode reduzir a insuflação gástrica. Adicionalmente, se o fluxo inspiratório for constante, tal como ocorre num ventilador, o desempenho pode melhorar, principalmente quando usado por socorristas menos experientes. O objectivo deste estudo foi verificar o efeito da ventilação com fluxos limitados nas variáveis respiratórias e nos volumes pulmonar e gástrico quando comparado com um sistema de reservatório-valvula (autoinsuflador). Depois da aprovação da administração da instituição e da obtenção do consentimento informado, 20 enfermeiras de cuidados intensivos foram voluntárias para ventilar um modelo de doente em paragem cardı&#x0301;aca com a via aérea não protegida e que consistia numa máscara facial, cabeça de manequim, pulmão de treino [com compliance de 50 ml/0.098 KPa (50 ml/cmH2O); resistência das vias aéreas de 0.39 KPa/l/s (4 cmH2O/l/s)], esófago [pressão esfincter esofágico inferior de 0.49 KPa (5 cmH2O)] e estomago simulado. Cada voluntário ventilou o modelo com um auto-insuflador (Ambu, Glostrup, Dinamarca; vol máx 1500 ml) e um ventilador que fornecia um fluxo fixo limitado (Oxylator EM 100, CPR Medical devices Inc, Toronto, Canada) durante 2 minutos; as variáveis do estudo foram medidas com 2 pneumotacometros. A comparação do auto-insuflador vs. ventilador gerou volumes correntes médios±SD da máscara comparáveis (945±104 vs. 921±250 ml), fluxos no pico inspiratório significativamente mais elevados (P<0.05, 111±27 vs. 45±21 l/min), e pressão inspiratória de pico também com diferença significativa (1.2±0.47 vs. 78±0.07 KPa), mas tempos inspiratórios significativamente mais curtos (1.1±0.29 vs. 1.6±0.35 s). Os volumes correntes pulmonares foram comparáveis (337±120 vs. 309±61 ml), mas os volumes correntes gástricos foram significativamente (P<0.05) mais elevados (200±95 vs. 140±51 ml) com o auto-insuflador. Em conclusão, a ventilação simulada de um doente em paragem cardı&#x0301;aca não intubado, utilizando um ventilador, resultou numa diminuição dos fluxos de pico e, por conseguinte, em diminuição das pressões de pico das vias aéreas quando comparado com a utilização de um auto-insuflador. A ventilação com fluxos limitados utilizando um ventilador, diminuiu a insuflação gástrica apesar de os volumes correntes pulmonares serem comparáveis em ambos os grupos.

Resumen

Si la vı&#x0301;a aérea de un paciente no está protegida, el soporte vital básico usando flujos inspiratorios bajos en lugar de altos, puede reducir la insuflación gástrica. Mas aún, si el flujo inspiratorio está fijado, como al ventilar con el resucitador, el desempeño de la ventilación puede mejorar; especialmente cuando es usado por reanimadores menos experimentados. El propósito de este estudio fue evaluar el efecto de la ventilación con flujo limitado sobre las variables respiratorias y sobre los volúmenes pulmonares y gástrico, comparandolo con el de ventilación con dispositivo de bolsa con válvula. Después de la aprobación de la junta institucional de revisión, y de obtener un consentimiento informado escrito, 20 enfermeras registradas de cuidados intensivos se ofrecieron de voluntarias para ventilar un modelo que simula de paro cardı&#x0301;aco con vı&#x0301;a aérea sin proteger, consistente en una máscara facial, una cabeza de maniquı&#x0301;, un pulmón de entrenamiento [con compliance pulmonar de 50 ml/0.098 kPa (50 ml/cmH2O); resistencia de la vı&#x0301;a aérea 0.39 kPa/l/s (4 cm H2O/l/s)], esófago [presión del esfı&#x0301;nter esofágico inferior, 0.49kPa (5cm H2O)], y un estómago simulado. Cada voluntario ventiló el modelo con un dispositivo mascara-bolsa autoinflable con válvula, (Ambu, Glostrup, Denmark; volumen máximo, 1500 ml), y con un resucitador que proporciona un flujo fijo limitado (Oxilator EM 100, CPR Medical devices Inc., Toronto, Canada) por 2 minutos; Las metas del estudio se midieron con 2 neumotacómetros. La comparación bolsa autoinflable versus el resucitador mostró volúmenes corrientes promedio comparables ± SD (945±104 vs. 921±250 ml), flujo inspiratorio máximo (111±27 vs. 45±21 l/min) y presión inspiratoria máxima (1.2±0.47 vs. 78±0.07 kPa) significativamente mayores (P<0.05), pero con tiempos inspiratorios significativamente mas cortos (1.1±0.29 vs.1.6±0.35 s.). Los volúmenes corrientes pulmonares fueron comparables (337±120 vs. 309±61 ml), pero los volúmenes corrientes del estómago (200±95 vs 140±51) fueron significativamente mayores con la bolsa autoinflable (P<0.05). En conclusión, la ventilación simulada de un paciente en paro cardı&#x0301;aco no intubado, usando un resucitador resulta en un flujo inspiratorio máximo disminuido, y por lo tanto, en presiones de vı&#x0301;a aérea máxima disminuidas, cuando se compara con bolsa manual autoinflable. El flujo ventilatorio limitado usando el resucitador disminuyó la insuflación gástrica, aunque los volúmenes corrientes pulmonares fueron comparables entre ambos grupos.

Introduction

When ventilating an unintubated patient, the distribution of gas between lungs and stomach depends on the patient's lower oesophageal sphincter pressure (LESP) [1], respiratory mechanics such as respiratory system compliance [2] and degree of airway obstruction [3]. Moreover, the technique of the rescuer performing basic life support (BLS) may influence inspiratory flow rate, peak airway pressure, and tidal volume [4]. Stomach inflation during BLS is a complex problem that may cause regurgitation [5], aspiration [6], pneumonia, and possibly, death [7]. Stomach inflation may also elevate intragastric pressure [8], push up the diaphragm, restrict lung movements, and thereby decrease the respiratory system compliance [9]. A decreased respiratory system compliance may force even more gas into the stomach, thereby inducing a respiratory vicious cycle with each tidal volume of increasing stomach inflation, and decreasing lung ventilation [10].

In order to prevent stomach inflation, managing peak airway pressure is therefore of fundamental importance during BLS ventilation of unintubated patients in respiratory and/or cardiac arrest. When experienced healthcare professionals perform bag-valve-mask ventilation, it was observed that respiratory rates were ∼40 instead of ∼15/min [11], and inspiratory times ∼0.5 instead of ∼1.5 s [12], indicating that emergency ventilation is a more complex psychomotor manoeuvre than previously thought. We have previously shown that one strategy of decreasing peak airway pressure during bag-valve-mask ventilation is simply to decrease tidal volume from 1000 to 500 ml [13]; limitation of inspiratory flow rate may be another, possibly even more effective approach. If the inspiratory flow rate is fixed, BLS ventilation may have a built-in safety margin, and ventilation quality may improve, especially when used by less experienced rescuers. Based on this concept, a flow-limited resuscitator (Oxylator EM 100, CPR Medical Devices Inc., Toronto, Canada) has been developed. (Fig. 1). Accordingly, the purpose of the present study was to assess the effects of a self inflating bag compared to this resuscitator with fixed inspiratory flow rates on respiratory variables, tidal lung and stomach volumes in a simulated unintubated cardiac arrest patient. Our hypothesis was that there would be no difference in study endpoints between groups.

Section snippets

Materials and methods

The experimental protocol of this study was approved by the institutional review board of the study institution. Twenty critical care unit registered nurses certified in BLS volunteered as participants for the study. The participants were instructed to treat an experimental model as an adult cardiac arrest patient, and ventilate the manikin via a facemask with an adult self-inflating bag (maximal volume, 1.5 l) or with the resuscitator until the chest clearly rose.

In the experimental model

Results

Twenty critical care unit registered nurses (10 women, 10 men) performed bag-mask ventilation with an adult self-inflating bag, or with a resuscitator. The self-inflating bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes, significantly (P<0.05) higher peak inspiratory flow rates, and peak inspiratory pressure, but significantly shorter inspiratory times. Lung tidal volumes were comparable, but stomach tidal volumes were significantly (P<0.05) higher with the self-inflating

Discussion

In our study, we found that the self-inflatable bag vs. resuscitator resulted in comparable mean±SD mask tidal volumes, significantly (P<0.05) higher peak inspiratory flow rates and peak inspiratory pressure, but significantly shorter inspiratory times. Lung tidal volumes were comparable, but stomach tidal volumes were significantly (P<0.05) higher with the self-inflating bag.

In order to examine the effects of a resuscitator providing a decreased peak flow rate (Fig. 2) during simulated BLS

Acknowledgements

This project was supported, in part, by the Austrian Science Foundation Grant P14169-MED, Vienna, Austria; a Founders Grant of the Society of Critical Care Medicine, Anaheim, CA; and departmental funds. No author has a conflict of interest in regards of airway devices being discussed in this experiment.

References (20)

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