Comparison of the FiO2 delivered by seven models of the self-inflating bag-mask system

Abstracts

JUSTIFICATIVA E OBJETIVOS: Devido ao fato dos reanimadores com sistema balão-máscara auto-infláveis fabricados e/ou comercializados no Brasil serem amplamente disponíveis e utilizados em serviços de saúde extra e intra-hospitalares, este estudo teve o objetivo de determinar as frações de O2 ofertadas por sete reanimadores recebendo diferentes fluxo de O2. MÉTODO: Sete reanimadores com sistema balão-máscara auto-infláveis foram testados na Unidade Respiratória do HC/UNICAMP. Um fluxômetro de O2 de parede foi conectado ao reanimador que recebia fluxo de O2 de 1, 5, 10 e 15 L.min-1, sendo estes conectados a um pulmão-teste. Os reanimadores que têm a capacidade de se conectar um reservatório de O2 foram testados com e sem esse acessório. Foram efetuadas 20 medidas consecutivas e determinada a média. RESULTADOS: Apenas um reanimador apresentou oferta de fração de O2 pouco abaixo do limite mínimo preconizado (0,80), quando utilizado com o reservatório de O2. Sem esse dispositivo acoplado todos os reanimadores atingiram o limite mínimo de fração de O2 preconizada (0,40). Os reanimadores que não apresentam a possibilidade de acoplar o reservatório de O2 apresentaram maior oferta de O2 em relação aos outros reanimadores. CONCLUSÕES: Todos os reanimadores que possuem a opção de acoplagem do reservatório de O2 forneceram maior concentração de O2 com esse acessório. Os reanimadores que não têm possibilidade de acoplar o reservatório de O2 apresentaram maior oferta de O2 em relação aos outros que podem ser acoplados ao reservatório quando usados sem esse acessório.

EQUIPAMENTOS

SCIENTIFIC ARTICLE

Comparison of the FiO₂ delivered by seven models of the self-inflating bag-mask system^*

Comparación de la FiO₂ suministrada por siete modelos de sistema balón-máscara autoinflable

Armando Carlos Franco de Godoy, M.D.^I; Ronan José Vieira, M.D.^II

^IProfessor Fisioterapeuta das Enfermarias de Emergência Clínica e Cirurgia do Trauma do HC/UNICAMP

^IIMédico Professor Doutor Coordenador da Enfermaria de Emergência Clínica do HC/UNICAMP; Coordenador da Disciplina de Emergência Clínica do Departamento de Ciências Médicas da Faculdade de Ciências Médicas da UNICAMP

Correspondence to

SUMMARY

BACKGROUND AND OBJECTIVES: Since resuscitators with self-inflating bag-mask systems manufactured and/or commercialized in Brazil are widely available and used in health services, both out- and intra-hospitals, the objective of this study was to determine the O₂ fractions delivered by seven resuscitators receiving different O₂ flows.

METHODS: Seven resuscitators with self-inflating bag-mask systems were tested at the Respiratory Unit of the HC/UNICAMP. A wall O₂ flowmeter was connected to the resuscitator that received an O₂ flow of 1, 5, 10, and 15 L.min^-1 and those were connected to a test lung. Resuscitators capable of being connected to an O₂ reservoir were tested with and without this accessory. Twenty consecutive measurements were performed and the mean determined.

RESULTS: Only one resuscitator delivered and O₂ fraction slightly below the accepted limit (0.80) when used with the O₂ reservoir. Without this device, all resuscitators achieved the minimal limit of O₂ fraction (0.40). Resuscitators not capable of being connected to an O₂ reservoir delivered a higher O₂.

CONCLUSIONS: All resuscitators capable of being connected to an O₂ reservoir delivered a higher O₂ concentration when connected to this device. Resuscitators that do not have this capability delivered a higher O₂ concentration than the ones that could be connected to this device but are used without it.

Key words: EQUIPMENT: Ventilator.

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: Debido al hecho de que los reanimadores con sistema balón -máscara autoinflables fabricados y/o comercializados en Brasil están ampliamente al alcance y que son utilizados en servicios de salud extra e intrahospitalarios, este estudio tuvo el objetivo de determinar las fracciones de O₂ ofertadas por siete reanimadores recibiendo diferentes flujos de O₂.

MÉTODO: Siete reanimadores con sistema balón-máscara autoinflables fueron probados en la Unidad Respiratoria del HC/UNICAMP. Un fluxómetro de O₂ de pared fue conectado al reanimador que recibía flujo de O₂ de 1, 5, 10 y 15 L.min^-1, siendo que ellos se conectaron a un pulmón test. Los reanimadores que poseen la capacidad de conectarse a un reservorio de O₂ se probaron con y sin ese accesorio. Se efectuaron 20 medidas consecutivas y se determinó el promedio.

RESULTADOS: Apenas un reanimador presentó oferta de fracción de O₂ poco por debajo del límite mínimo preconizado (0,80), cuando se usó con el reservorio de O₂. Sin ese dispositivo acoplado, todos los reanimadores alcanzaron el límite mínimo de fracción de O₂ preconizada (0,40). Los reanimadores que no presentaron la posibilidad de acoplar el reservorio de O₂ presentaron una mayor oferta de O₂ con relación a los otros reanimadores.

CONCLUSIONES: Todos los reanimadores que poseen la opción de acoplamiento del reservorio de O₂, suministraron una mayor concentración de O₂ con ese accesorio. Los reanimadores que no tienen la posibilidad de acoplar el reservorio de O₂ presentaron una mayor oferta de O₂ con relación a los otros que sí pueden ser acoplados al reservorio cuando se usan sin ese accesorio.

INTRODUCTION

Resuscitators with self-inflating bag-mask systems are used to ventilate patients who need ventilatory support in situations such as extra- and intra-hospital transportation and cardiopulmonary reanimation ¹. Those devices can be divided in two parts: compressible unit and patient connector, but some models have the option to be connected to an O₂ reservoir (Figure 1). The compressible unit is the segment of the device that is supposed to be compressed by the operator to deliver a volume of air to the patient and, in the back, one might find the connection for the O₂ reservoir and entrance of the O₂ flow. The connector to the patient is where the face mask or endotracheal tube is attached.

Several studies have demonstrated that different models of self-inflating bag-mask systems ^1-3 might show differences in the fraction of O₂ delivered (FiO₂), since it is influenced by the shape and type of material of the compressible unit⁴, tidal volume delivered ³, the use or lack of the O₂ reservoir ¹, and flow of O₂ delivered to the compressible unit ^2-5, among others.

The objective of this study was to determine the FiO₂ of seven different brands of self-inflating bag-mask systems manufactured or commercialized in Brazil when they received O₂ at 1, 5, 10, and 15 L.min^-1, were manipulated with both hands at 12 breaths per minute with or without O₂ reservoir.

METHODS

The data was collected at the Respiratory Unit of the Hospital de Clínicas da Universidade Estadual de Campinas Unicamp, from January to March 2007.

The material used in the study included: a Vent Aid TTL-49504 Michigan Instruments test lung, a Newport Medical Instruments OM-100 O₂ analyzer, a BD wall O₂ flowmeter, an Oxigel 953 flowmeter, and a Bird T-tube with directional valve. The seven self-inflating bag-mask systems used could be classified into two groups, one group in which an O₂ reservoir could be attached: Oxigel^® model B, CE Reanimadores^®, Protec^® vinyl, and Missouri^®; and those that could not be connected to an O₂ reservoir: Oxigel model A^®, Axmed^®, and Narcosul^®.

To test the FiO₂ (Figure 2), the wall O₂ flowmeter was connected to another flowmeter which was connected to the port of O₂ entry in the device. The connector to the patient was coupled to the O₂ analyzer, which was connected to the T-tube with a directional valve leading the flow to the surrounding environment, and a T-tube was connected to the test lung.

The test lung was ventilated by the device, with one or both hands, 12 incursions per minute, receiving flows of O₂ of 1, 5, 10, and 15 L.min^-1. Systems that allowed the connection of O₂ reservoirs were tested with and without it. After two minutes of ventilation with each flow, the FiO₂ delivered by each device on the O₂ flowmeter connected to the system was recorded. During the study, the test lung remained with a resistance of 20 cmH₂O.L^-1.sec^-1 and a complacency of 0.05 L. cmH₂O^-1, the self-inflating bag-mask systems were operated by the same person, and the flows of O₂ delivered to the RAMI were measured and controlled by the devices of the system.

Twenty consecutive measurements of the FiO₂ were recorded for each flow in each brand of the self-inflating bag-mask system and the person who recorded the data did not know the objective and methodological procedure of the study. The program BioEstat 3.0 for Windows was used for the statistical analysis using means and standard deviation.

RESULTS

Figure 3 shows the FiO₂ delivered by the seven different brands of systems manufactured or commercialized in Brazil when they received a flow of O₂ 1, 5, 10, and 15 L.min^-1, were manipulated with both hands with a frequency of 12 incursions per minute, and with and without an O₂ reservoir.

DISCUSSION

The Guidelines of the European Resuscitation Council 2000 on Advanced Adult Life Suppport, 2000 ⁶ and the Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, 2000 ⁷ emphasize that it is essential to administer oxygen at the highest concentration possible during resuscitation maneuvers, stating that high oxygen concentrations are toxic only when administered for a prolonged period. Some authors consider that the FiO₂ delivered is the most important parameter to be considered regarding its performance.

Since most of the time hospitalized patients who need self-inflating bag-mask systems are already receiving supplemental oxygen, the ideal resuscitator should deliver FiO₂ as closer to 1.0 as possible ^2,9.

ISO 1997 ¹⁰ and ASTM 1999 ¹¹ recommend that those systems should delivered a FiO₂ of at least 0.40 without an O₂ reservoir and 0.80 with this accessory, receiving a maximal O₂ flow of 15 L.min^{-1 2,8}.

Contrary to other authors who stipulated a fixed tidal volume of 600 mL^12-15, in the present study a fixed tidal volume was not stipulated because in daily practice one cannot maintain it unchanged since it depends on the size and compression force of the operator's hand, presence or absence of pressure-limiting valves at the connector to the patient, and the type of material, design, and size of the compressible unit ^2,5,16. Thus, each device delivered the tidal volume that its design allowed.

In the present study, the test system was adapted with a T-tube with directional valve (Figure 2: 5, 6) to eliminate the air ejected from the test lung to the environment preventing, therefore, return of the O₂ to the compressible unit in case of failure of the seal of the patient's valve. Failure of the seal could lead to a false increase in the FiO₂ delivered by the equipment. Although the function of this mechanism for ejection of the air is pertinent, we did not find studies using it in the literature. Several authors used a hole between the self-inflating bag-mask system and the test lung ^2,12-15; therefore, whenever the compressible unit was squeezed, this hole was simultaneously closed by the finger of the operator, and when the compressible unit return to its normal size the hole was uncovered.

During the FiO₂ test, the respiratory rate was maintained at 12 incursions per minute with one or both hands, since this is how ventilation with those devices is done more often¹⁷.

The FiO₂ delivered was influenced by the flow of O₂ and its dislocation to the compressible unit and the use, or lack, of the O₂ reservoir.

All self-inflating bag-mask systems that could be connected to an O₂ reservoir, Oxigel model B^®, Missouri^®, CE Renimadores^®, and Protec^® vinyl, delivered a higher FiO₂ when this accessory was connected to the compressible unit, but CE Reanimadores^® delivered a FiO₂ slightly below the minimal limit of 0,80 recommended by ISO, 1997 ¹⁰ and ASTM, 1999 ¹¹, i.e., 0.74 (0.6).

All self-inflating bag-mask systems that could be connected to an O₂ reservoir delivered a FiO₂ of 0.40 or more with an O₂ flow of at least 10 L.min^-1 when used without his accessory. When the O₂ reservoir was not used, the FiO₂ delivered was lower because the oxygen that reaches the resuscitator is dissolved in the room air near the compressible unit (Figure 1) and it is partially aspirated by the resuscitator. Devices in which an O₂ reservoir could not be attached to, delivered higher amounts of O₂ than the other resuscitators in all O₂ flows.

REFERENCES

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*

Recebido da Enfermaria de Emergência Clínica e Cirurgia do Trauma do Hospital de Clínicas da Universidade Estadual de Campinas (HC/UNICAMP), SP

Publication Dates

• Publication in this collection
  16 Feb 2009
• Date of issue
  Feb 2009

History

• Accepted
  21 Oct 2008
• Received
  18 Sept 2007