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Short report
A respiratory function monitor improves mask ventilation
  1. F E Wood1,
  2. C J Morley1,2,3,
  3. J A Dawson1,
  4. P G Davis1,2
  1. 1
    Division of Neonatal Services, Royal Women’s Hospital, Carlton, Victoria, Australia
  2. 2
    Departments of Obstetric and Gynaecology, University of Melbourne, Victoria, Australia
  3. 3
    Murdoch Children’s Research Institute, Melbourne, Victoria, Australia
  1. Professor C J Morley, Division of Neonatal Services, Royal Women’s Hospital, 132 Grattan Street, Carlton, Victoria 3053, Australia; colin.morley{at}rwh.org.au

Abstract

This study investigated whether the use of a respiratory monitor during simulated neonatal resuscitation reduced leak at the face mask. It showed the leak was more than halved, being reduced from 27% to 11% when 25 participants used the monitor to identify and correct the mask leak.

https://doi.org/10.1136/adc.2007.120097

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    In studies using a modified manikin, we investigated face masks during simulated neonatal resuscitation.1–4 We found mask leaks are large and variable, irrespective of mask design or the operator’s experience, with the mean (SD) leak being 55 (31)%.3 Operators were unaware of the magnitude of the leak.3 We showed that teaching techniques of holding face masks reduced the leak to 33 (26)%.4

    Inadequate tidal volumes as a result of mask leak may result in failure to resuscitate an infant, and high tidal volumes will cause lung injury. Accurate methods to identify and reduce mask leak are lacking.

    This study aimed to investigate whether observing a respiratory function monitor reduces face mask leak.

    METHODS

    The 25 staff who participated in the present study had taken part in the previous face mask studies3 4 and had received training to improve their face mask technique. All were experienced in the use of the Florian respiratory monitor (Acutronic Medical Systems, Ag, Switzerland).

    A Laerdal Resusci Baby manikin (Laerdal, Stavanger, Norway) was modified by replacing the original “lung” with a 50 ml test lung (Dräger, Lubeck, Germany) positioned so inflation caused chest rise, and connected to the mouth with an airtight seal.1 3 4 A size 0/1 Laerdal neonatal mask was used. The Neopuff Infant resuscitator (Fisher & Paykel Healthcare, Auckland, New Zealand) had a gas flow of 8 l/min. A pressure monitoring line was connected near the test lung.

    The flow sensor of a Florian respiratory monitor was placed between the T piece and face mask and used to measure inspiratory and expiratory tidal volumes at the mask. Volume was calibrated using a 10 ml syringe. Airway pressure was calibrated against a column of water. The screen showed 15 s of pressure and tidal volume waves, equivalent to about 10–15 inflations. Operators were taught to identify the face mask leak when the expired tidal volume was less than the inspired tidal volume (fig 1).

    Figure 1
    Figure 1 An example of the pressure and volume waves displayed on the Florian respiratory function monitor showing eight inflations. The inflation pressures are at the top and the tidal volumes at the bottom. The volume wave re-sets to zero at the end of each expiration. When the expired tidal volume is less than the inspired tidal volume, because there has been a leak at the face mask, the vertical component of the wave visually represents the volume of the mask leak. A: overlies an inspiratory tidal volume; B: overlies an expiratory tidal volume; and C overlies the leak.

    The Spectra physiological recording programme (Grove Medical, London, UK) acquired data from the Florian monitor onto a computer.

    Study protocol

    Participants were instructed to give positive pressure ventilation (PPV) at about 60/min with a peak inspiratory pressure (PIP) of 30 cm H2O and a positive end-expiratory pressure (PEEP) of 5 cm H2O for 1 min, ensuring good chest rise.

    Before any recordings were made, the participants familiarised themselves with the Florian and holding the face mask. A recording was made with the monitor covered, so that the participants could not see the display. They were then instructed to use the display to achieve minimal mask leak. The second recording started when participants indicated they were satisfied with the Florian display. A third recording was made with the Florian display re-masked. Between each recording the participants put down the ventilation equipment.

    Spectra software calculated the mean percentage leak, PIP and PEEP for each recording, excluding the first three inflations in each case.

    The sample size was calculated using the mean (SD) percentage leak of 55 (30)% from our first study.3 Twenty participants were required to detect a 20% difference in the mean leak with an α value of 0.05 and 80% power.

    Data were analysed using SPSS. Paired t tests were used to compare the leak differences. A p value of <0.05 was considered significant. Data are expressed as mean (SD) or percentage unless otherwise stated.

    RESULTS

    Participants and years of experience

    There were 25 participants including 9 consultants, 8 fellows (specialist registrar level) and 8 neonatal nurses. The median years of neonatal experience were: consultants 18.3, fellows 3.3 and neonatal nurses 10.8.

    Leak at the face mask

    Figure 2 shows a box plot of percentage mask leak before, during and after the use of the Florian monitor. The mean (SD) leak before, during and after using the Florian was 26.6 (24.3)%, 11.2 (13.1)% and 20.2 (18.3)%, respectively. Using the Florian reduced the leak by 15.4 percentage points (95% CI 6.2 to 24.4, p = 0.002). This was a 58% reduction in leak. When the Florian display was hidden again, the leak increased by 8.9 percentage points (95% CI 1.2 to 16.7, p = 0.025).

    Figure 2
    Figure 2 Percentage leak at the face mask before, during and after using the Florian respiratory monitor to identify the presence or absence of leak. The box plots show median values (solid black bar), interquartile range (margins of box), range of data, outliers (circles) and extreme values (*).

    The mean (SD) time participants practised with the Florian to minimise leak before the recording was 47.3 (58.4) s (minimum 5 s, maximum 259 s).

    Inflation pressures

    The mean PIP before, during and after using the Florian monitor was 29.4 (1.1) cm H2O, 29.6 (1.0) cm H2O and 29.6 (0.5) cm H2O, respectively. The mean PEEP was 4.2 (0.5) cm H2O, 4.1 (0.6) cm H2O and 4.1 (0.4) cm H2O, respectively. There were no significant differences between these values.

    DISCUSSION

    This study showed that seeing a respiratory function monitor significantly reduced mask leak during simulated neonatal resuscitation. When the display was covered, the mask leak increased. This suggests that seeing the tidal volume and mask leak enabled participants to improve their face mask ventilation technique. Participants’ previous training to optimise techniques of mask positioning and hold had already reduced their mean (SD) leak from 57 (29)% to 27 (24)%.4 If the Florian had been used with an untrained group a larger reduction of leak may have occurred.

    Neonatal staff are experienced in the interpretation of similar respiratory signals from ventilators. This technology has immediate application in resuscitation training and merits further evaluation in the delivery room.

    CONCLUSION

    Use of a respiratory function monitor reduced face mask leak in a model of neonatal resuscitation. This monitor may assist training in resuscitation and is worthy of further study in the delivery room.

    Acknowledgments

    We thank the staff of the Royal Women’s Hospital Melbourne for their participation.

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    Footnotes

    • Funding: Supported in part by an NHMRC Practitioner Fellowship PGD and The Australian National Health and Medical Research Council Program Grant number 384100.

    • Competing interests: None.