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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.59 no.1 Campinas Jan./Feb. 2009
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
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
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
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.
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.
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.
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.
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.
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 mL12-15, 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.
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Correspondence to: Submitted em 18
de setembro de 2007 *
Received from Enfermaria de Emergência Clínica e Cirurgia do Trauma
do Hospital de Clínicas da Universidade Estadual de Campinas (HC/UNICAMP),
Dr. Armando Carlos Franco de Godoy
Rua Hercules Florence, 100/23
13020-170 Campinas, SP
Accepted para publicação em 21 de outubro de 2008
Submitted em 18
de setembro de 2007
* Received from Enfermaria de Emergência Clínica e Cirurgia do Trauma do Hospital de Clínicas da Universidade Estadual de Campinas (HC/UNICAMP), SP