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Original article
The effectiveness of Ambu neonatal self-inflating bag to provide consistent positive end-expiratory pressure
  1. Mark Tracy1,2,
  2. Dharmesh Shah1,3,
  3. Archana Priyadarshi1,3,
  4. Murray Hinder1,3
  1. 1 Neonatal Intensive Care, Westmead Hospital, Westmead, New South Wales, Australia
  2. 2Department of Paediatrics and Child Health, Sydney University, Westmead, New South Wales, Australia
  3. 3Sydney University, New South Wales, Australia
  1. Correspondence to Dr Mark Tracy, Department of Paediatrics and Child Health, Sydney University, P.O. Box 533, Wentworthville, NSW 2145, Australia; mark.tracy{at}sydney.edu.au

Abstract

Background The self-inflating bag (SIB) is the most common device used to resuscitate newborn infants worldwide. Delivering positive end-expiratory pressure (PEEP) may be important in infant resuscitation and limited research using one brand (Laerdal) SIB has led to international guidelines stating SIBs ‘often deliver inconsistent positive end-expiratory pressure’.

Aim To measure delivered PEEP using disposable and reusable Ambu SIBs fitted with Ambu PEEP valve and manometer comparing different rates of 20, 40 and 60 inflations per minute (IPM) and test lung compliance.

Design Three experienced neonatal medical staff provided positive pressure ventilation each using different disposable and reusable Ambu SIBs, targeting peak inflation pressure of 30–35 cm H2O at three different set PEEP levels of 5, 7.5 and 10 cm H2O on test lungs of compliance of 0.5 and 3.0 mL/cm H2O. Inflation data were captured with Florian Monitor and analysed by analysis of variance for repeated measures.

Results A total of 3265 inflations were analysed. The delivered PEEP was rate and lung compliance dependent. At set PEEP of 5 cm H2O, the adjusted measured PEEP was 3.6, 4.4 and 4.8 cm H2O at rates 20, 40 and 60 IPM, respectively, while at set PEEP of 10 cm H2O, the adjusted measured PEEP was 7.0, 8.8 and 9.8 cm H2O. The delivered PEEP was statistically higher with more compliant test lungs.

Conclusions The Ambu SIB with Ambu PEEP valve can deliver consistent mean levels of PEEP close to the operator set PEEP. The performance of SIB with PEEP valves is likely brand specific and requires further evaluation.

  • newborn
  • self-inflating bag
  • Resuscitation
  • PEEP
  • peak inspiratory pressure

https://doi.org/10.1136/archdischild-2015-308649

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    What is known on this topic

    • Previous studies on only one brand of self-inflating bag (SIB) (Laerdal) show inconsistent positive end-expiratory pressure (PEEP) delivery with PEEP valve.

    • There is a need for a cheap effective device to deliver PEEP during newborn resuscitation in resource-poor countries.

    • International Liaison Committee for Resuscitation (ILCOR) guidelines recommend provision of PEEP during resuscitation if suitable equipment is available.

    What this study adds

    • Ambu SIB (reusable and disposable) with Ambu PEEP valve can provide consistent levels of PEEP.

    • Ambu SIB with Ambu manometer fitted can provide adequate peak inflation pressure.

    • Delivery of PEEP via SIB may vary between brands depending on PEEP valve attachment design.

    Background

    Globally, approximately 10% of all newborn infants require stabilisation immediately following birth, with 5 to 8% requiring positive pressure ventilation to establish adequate respiration.1 ,2 A recent systematic review of neonatal resuscitation has estimated that there is a potential for 30% reduction in the rates of neonatal death due to prematurity worldwide with improved facility-based resuscitation.3 Establishing an adequate functional residual capacity (FRC) is an essential component of postpartum adaptation, which can be delayed in states of surfactant deficiency.4 Although positive end-expiratory pressure (PEEP) has been shown to be of benefit in the care of preterm infants with surfactant deficiency, the role of PEEP during resuscitation, particularly for term infants remains to be established.1 Birthing environments in high-resource countries have access to a variety of resuscitation methods (T-piece resuscitators (TPR), self-inflating bags (SIBs) and anaesthetic bags) and commonly access to blended air/oxygen medical gases. TPR have been shown to provide the most reliable PEEP,5 ,6 yet these systems are not available to most infants at need globally.

    There is an urgent need for SIB devices with functional PEEP valve systems for newborn resuscitation in low-resource settings. However, the 2010 International Liaison Committee for Resuscitation (ILCOR) recommendations for newborn resuscitation suggests SIBs with PEEP valves ‘often deliver inconsistent end-expiratory pressures’.1 This is based on findings from two small studies examining the ability of one brand of SIB (Laerdal) fitted with a PEEP valve.7 ,8

    The Laerdal SIB is unusual in comparison with most SIBs, in that to provide PEEP a clip-on adaptor is placed over the head section of the SIB to allow the PEEP valve to be attached. Morley and colleagues examined one disposable and one reusable Laerdal 240 mL SIB and examined manual inflations at rates of 20, 40 and 60/min at peak inflation pressures (PIPs) of 30–35 cm H2O and differing PEEP levels of 5, 7 and 10 cm H2O. Morley et al8 concluded the Laerdal SIB with a PEEP valve cannot provide continuous positive airway pressure (CPAP) and PEEP rapidly falls from the set values. Kelm and colleagues examined one resuscitator using 11 Ambu PEEP valves sequentially attached to one new Laerdal SIB aiming to deliver 5 cm H2O. They found six Ambu valves delivered median PEEP levels of over 4 cm H2O and five Ambu valves delivered PEEP <3 cm H2O.7 Kelm and colleagues reported in detail their findings of the lack of consistent PEEP and followed up with an alert to the German regulator.7

    Most other SIB manufacturers have either SIBs that are designed with an integrated PEEP valve connector in the SIB moulding or have a design that precludes fitting a PEEP valve and so cannot deliver PEEP. They may perform differently. The ability of SIBs to provide PEEP particularly in resource-poor countries with limited resuscitation facilities requires further evaluation.

    The aim of this study was to assess the delivered end-expiratory pressures from the Ambu disposable PEEP valve attached to Ambu neonatal SIBs across a range of set PEEP values. The test structure was designed to examine if there were differences between two test lungs with differing compliance, three inflation rates and two device types (Ambu SIB disposable compared with reusable). We used the Ambu Mark IV Baby (reusable) and Ambu SPUR-II (disposable) SIBs fitted with the Ambu single-use disposable PEEP valve 0–20 cm H2O (Part Number 199 102 001).9

    Methods

    Our sample included the Ambu reusable and single-use disposable SIB models both fitted with a moulded expiratory diverter (figure 1). Both were fitted with Ambu disposable manometer and PEEP valves. The Ambu PEEP valve is spring loaded with scales marked in 5 cm major ticks. The PEEP dial is screwed inwards towards the centre of the SIB to increase the set PEEP. One revolution of the valve knob produced a PEEP increase of approximately 5 cm H2O. The user checks delivered PEEP with the attached manometer, as instructed in the manufacturer's product insert.9

    Figure 1
    Figure 1

    Test set-up.

    Three operators each tested two different devices (disposable and reusable) at combinations of three different inflations per minute (IPM) (20, 40 and 60 IPM); three PEEP valve settings (5, 7.5 and 10 cm H2O) and two lung compliances (0.5 and 3 mL/cm H2O). Approximately 30 inflations were recorded for each combination totalling 3265 inflations.

    The two different leak-free test lungs used were (1) a 50 mL Draeger test lung (Draeger, Lubeck, Germany) with measured compliance of 0.5 mL/cm H2O and (2) a 200 mL IMT newborn test lung (Smart Lung Infant, IMT medical, Buchs, Switzerland) with measured compliance of 3.0 mL/cm H2O. A Florian Respiratory Function Monitor (Accutronics, Medical Systems AG, Zug, Switzerland) was connected via the hot wire pneumotach and pressure sensor line sited between the SIB and the test lung (figure 1). The Florian Monitor was calibrated with an external syringe of known volume and pressure/flow via a ventilator calibration analyser with pressure resolution of 0.1 cm H2O with pressure accuracy of ±0.5% and flow calibration with resolution of 0.1 L/min with accuracy of ±1% (RT-200; Timeter Instrument, Allied Healthcare Products, St Louis, Missouri, USA). The analogue signals output from the Florian Monitor were collected and digitised at 200 Hz with analysis software (Grove Medical, London, UK). The test lungs and monitoring system were pressurised to static pressure of 50 cm H2O and over 60 s there was no fall in pressure indicating the system was leak free.

    The testing sequence involved each operator squeezing the SIB aiming to achieve a PIP between 30 and 35 cm H2O using the Ambu disposable manometer. For each sequence, the PEEP valve was adjusted to one of the three predefined PEEP levels (5, 7.5 and 10 cm H2O) using the Ambu manometer. Each operator was asked to provide 2 min bagging at rates of 20, 40 and 60 IPM, which were randomly sequenced. The first five inflations were discarded and the following 30 inflations were analysed. A 2 min rest period occurred between each sequence. This was repeated for the two different compliance test lungs. Morley et al8 demonstrated no difference with or without gas inflow into SIBs testing PEEP and thus no gas inflow was used in this study. Operator inflation rates were timed with audible metronome.

    Data analysis

    Analysis was conducted using Stata (V.12 MP, StataCorp, College Station, Texas, USA). The measured parameters included the mean, minimum and maximum PIP and PEEP at end expiration. ANOVA for repeated measures was used to determine differences between rates, device types and test lung compliance at different set PEEP levels. Differences between means determined by ANOVA were reported with p values adjusted F test using Box's conservative epsilon. p Values of <0.05 were considered significant. The ANOVA for repeated measures allows a valid statistical comparison between different rates, devices and lung compliance delivered by the same individual when the repeat measurements between individuals are not independent. Table 1 details the measured mean PEEP values with IQR and SD for each parameter with p values calculated with ANOVA for repeated measures. Predicted mean PEEP levels were reported graphically in figures 2⇓–4 with 95% CI adjusted for explanatory variables in the model.

    View this table:
    Table 1

    Measured positive end-expiratory pressure (PEEP) values with differing rates, device types and test lung compliance

    Figure 2
    Figure 2

    Rates, predicted mean positive end-expiratory pressure (PEEP) with 95% CI adjusted for self-inflating bag type and test lung compliance.

    Figure 3
    Figure 3

    Device types, predicted mean positive end-expiratory pressure (PEEP) with 95% CI adjusted for inflation rate and test lung compliance.

    Figure 4
    Figure 4

    Compliance, predicted mean with 95% CI adjusted for self-inflating bag type and inflation rate.

    Results

    Six Ambu devices were tested of which three were disposable single-use devices and three reusable systems. A total of 3265 inflations were analysed; 1636 with disposable and 1629 with reusable Ambu SIBs. Operators were able to accurately deliver the desired PIP over the range of set PEEPs with a mean (SD) PIP at set PEEP 5 cm H2O of 33.8 (1.04) cm H2O and at set PEEP 7.5 cm H2O of 34.4 (1.5) cm H2O and 33.7 (1.1) cm H2O. These PIPs were not statistically different. Figure 5 shows representative airway pressure waveforms for one subject for each set PEEP level (5, 7.5 and 10 cm H2O) at 20 IPM (figure 5A–C) and at 60 IPM (figure 5D–F) to demonstrate the decay in pressure between inflations.

    Figure 5
    Figure 5

    Recordings of airway pressure waveforms for each set positive end-expiratory pressure level (5, 7.5 and 10 cm H2O) at 20 inflations per minute (IPM) (A–C) and 60 IPM (D–F).

    Rate

    The measured PEEP as a percentage of set PEEP ranged from 70% to 72% at a rate of 20 IPM, 88–89% at 40 IPM and 96–98% at 60 IPM (table 1 and figure 2). These differences were statistically different (p<0.001).

    Device type

    Disposable Ambu SIB with PEEP valve had statistically higher measured PEEP at set PEEP valves adjusted for covariates at 7.5 and 10 cm H2O (p<0.01) (table 1 and figure 3). There was no statistical difference at set PEEP of 5 cm H2O. At 7.5 cm H2O, the mean measured PEEP was 15% higher with disposable compared with reusable. There was a smaller difference at set PEEP of 10 cm H2O (8% measured to set PEEP).

    Lung compliance

    The measured PEEP as a percentage of set PEEP ranged from 79% to 84% with test lung compliance of 0.5 mL/cm H2O and from 90% to 93% with test lung compliance of 3.0 mL/cm H2O (p<0.005) (table 1 and figure 4).

    Discussion

    Our study shows Ambu SIBs fitted with Ambu disposable manometers and PEEP valves provide consistent mean delivered PEEP close to set PEEP at all rates tested. Our results indicate delivered PEEP is significantly closer to set PEEP at higher rates. An interesting finding not previously examined is the impact of compliance of the test lung. The delivered PEEP was statistically higher in the compliance lung model of similar values to a normal term lung (4.5 cm H2O compared with 4.0 cm H2O adjusted for covariates p=0.002). PEEP delivered during resuscitation has defined benefits of improved FRC and oxygenation in preterm animal models with surfactant deficiency.4 ,10–12 CPAP in non-intubated infants and end-expiratory pressure in intubated infants are routine and well-evidenced methods in the treatment of respiratory distress. However, a recent randomised trial comparing T-piece resuscitators and SIB in resuscitation of preterm newborns in delivery suite failed to demonstrate any difference in the primary outcome of oxygenation at 5 min after birth.13 Our study differs from Morley et al8 who examined two Laerdal SIBs, one reusable and the other disposable and found much lower PEEP values (36% of set PEEP value at 5 cm H2O and rate of 20 IPM) at each rate examined. The Laerdal SIB system has a separate flow diverter which needs to be positioned over the patient valve assembly (Part Number 851250) on the SIB to allow a PEEP valve to be connected. Other brands we have examined provide a SIB either for use with PEEP valve where an integrated moulded port in the patient valve assembly allows connection to the PEEP valve or not. Unpublished research from our group indicates a significant leak from the Laerdal disposable flow diverter packaged with the disposable PEEP valve (Part Number 845040) and the reusable flow diverter (Part Number 845080) that is independent of the PEEP valve. If the flow diverter is installed incorrectly (not completely clipped on) or is moved during use, further loss of PEEP will occur and will be undetected if a manometer is not connected. We believe this may account for most of the differences found between our results and those of Morley et al and Kelm et al. The Cochrane review on the resuscitation at term stated there were no trials meeting the defined search criteria to examine the effect of PEEP in this group.14 Although there are not sufficient research data to currently recommend the use of PEEP in term resuscitation, a recent resuscitation practice survey in 2011 of UK's lead paediatricians (n=180) at 212 hospitals with newborn units showed that between 65.9% and 82.8% target PEEP (4–6 cm H2O) during resuscitation of term babies and between 4.9% and 7.2% of practitioners use SIB with PEEP valves.15 These survey data would suggest that our study findings of Ambu SIB fitted with PEEP valve can consistently provide delivered mean PEEP in the range of PEEP commonly targeted by clinicians in the UK for rates 40 and 60 IPM. This is in contrast to the findings of Morley et al8 and Klem et al7 using the Laerdal SIB with clip on PEEP adaptor. Our results also indicate it is possible to consistently deliver a required PIP using an Ambu disposable manometer.

    Conclusion

    Disposable and reusable Ambu SIB with Ambu PEEP valve attached can provide and maintain consistent mean delivered PEEP at inflation rates examined (20, 40 and 60 IPM). Our study indicated that the Ambu SIB used with the Ambu manometer allows accurate targeting of desired PIP, which is in contrast to the findings of others examining Laerdal SIB.16 ,17 Delivered PEEP is closer to set value with normal compliance test lung suggesting establishing an FRC in a term baby resuscitation using an Ambu SIB with PEEP valve is in line with current clinician's practice.15 Further research is warranted to examine other brands of SIB that offer PEEP valves to determine their effectiveness in delivering PEEP.

    Acknowledgments

    We thank Professor Sally Tracy and Dr Jan Klimek for their helpful comments and suggestions. We also acknowledge and thank Ambu Australia for supply of devices to examine in this study.

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    Footnotes

    • Contributors MT is primary researcher responsible for conceiving, designing, analysing and writing manuscript. MH contributed by assisting design, data collection, analysis, manuscript writing and review. AP, DS contributed data collection, analysis, interpretation, manuscript construction.

    • Funding This study was researcher generated and conducted with no external funding required.

    • Competing interests None declared.

    • Ethics approval This study was approved by the Western Sydney Local Health District human research ethics committee approval number SAC2014/5/6.8 (3998).

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement Raw data waveforms for each data collection collected from Florian Respiratory Monitor to Grove Spectra.