Studies of manikins and infants reveal large leaks from face masks.1^–3 Available masks are either round or anatomically shaped.4 Cushioned rimmed masks were advocated,2 however the silicone Laerdal “round” (LR) mask (Laerdal, Stavanger, Norway) is the most widely used.1 2 4 A new round mask (Fisher & Paykel Healthcare, Auckland, New Zealand) is claimed to be more effective. We investigated whether leak between the mask and face during simulated neonatal resuscitation differed between these two masks.

METHODOLOGY

Setting and participants

Neonatal medical, nursing staff and midwives of the Royal Women’s Hospital, Melbourne, Australia participated. All had received training in neonatal resuscitation.

Face masks

The LR mask is the only design in routine use at our hospital. The size 0/1 Laerdal mask and the Fisher & Paykel (FP) 60 mm round mask were the appropriate sizes for the manikin (fig 1). No participant had previously used the FP mask.

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Figure 1 Photograph showing the Laerdal round mask (left) and the new Fisher & Paykel neonatal resuscitation mask (right).

Manual ventilation device

The Neopuff Infant Resuscitator (Fisher & Paykel Healthcare, Auckland, New Zealand) is a pressure limited T-piece device where the peak inspiratory pressure (PIP) and positive end expiratory pressure (PEEP) are set and displayed. All participants were experienced in its use. The hospital protocol suggested a gas flow of 8 l/min, a PEEP of 5 cm H₂O and a PIP of 30 cm H₂O.

Modified manikin

A Laerdal Resusci baby manikin (Laerdal, Stavanger, Norway) was modified by removing the lung and stomach bags, and positioning a 50 ml test lung (Dräger, Lubeck, Germany) into the chest so chest excursion mimicked that of an unaltered training manikin.2 5 The test lung was connected by non-distensible tubing to the mouth with an airtight seal. A pressure monitoring line was connected to the airway. The system compliance when pressurised to 30 cm H₂O was 0.5 ml/cm H₂O, with a maximal lung volume of 65 ml.

Respiratory monitor, recording equipment and values measured

A Florian respiratory monitor (Acutronic Medical Systems, Ag, Switzerland) measured inflating pressures and gas flow through the mask. Airway pressure was calibrated against a column of water; a 10 ml syringe was used to calibrate volume measurement. The flow sensor was placed between the T-piece and mask; tidal volume was calculated by integration of the flow signal. Percentage leak at the face mask was the difference between the inspired and expired tidal volumes, expressed as a percentage of the inspired tidal volume. O’Donnell et al showed this system provides a good estimate of the tidal volumes and leak.5

Spectra software (Grove Medical, London, UK) was used to acquire the output from the Florian monitor through an A:D converter to a computer. Neither screen was visible to participants.

Study protocol

Participants ventilated the manikin for 2 minutes at a rate of 40–60 breaths per minute according to the hospital protocol, ensuring chest rise. They knew we were recording tidal volume, mask leak and inflation pressures.

The mean ventilation rate, PIP, PEEP, inspired and expired tidal volumes and percentage leak were measured for a 2 minute period of ventilation with each mask, excluding the first five inflations.

Observations and participant survey

Mask placement and hold techniques, including the use of jaw lift were recorded. Participants were asked “Do you think your average mask leak was large or small?” (five-point Likert scale).

Randomisation, primary outcome and power calculation

The order of assessment of the masks was randomised. The sample size was calculated using the mean percentage leak of 70% (SD 30%) for the Laerdal mask.2 To detect a 15% difference in mean leak with an alpha value of 0.05 and power of 80%, 34 participants were required.

Statistical analysis

Data were analysed using SPSS. A paired t test compared leak between the two masks, p<0.05 was considered significant. One-way ANOVA assessed the influence of placement-and-hold technique on mask leak.

RESULTS

Participants and years of experience

There were 10 participants in each of the professional categories. The median years of experience were: consultants 18.5 years, fellows (SpR grade) 3.3 years, registrars (SHO grade) 0.1 years, neonatal nurses 9.5 years and midwives 3.5 years. A total of 10 084 inflations were recorded.

Techniques of mask application and holds used to form a seal with the face

Participants held the masks in four ways: (1) stem hold, the thumb and index finger gripping the stem; (2) two-point top hold, applying pressure to two points of the top flat portion of the mask; (3) rim hold, encircling much of the rim of the upper flat portion of the mask; (4) any other hold.

LR mask

Frequencies were: stem hold 24%, two-point top hold 46%, rim hold 28% and other 2%. The mask was rolled onto the face by 14% and the remaining 86% placed the mask directly onto the face. Jaw lift was applied by 50%.

FP mask

Frequencies were: stem hold 26%, two-point top hold 44%, rim hold 28% and other 2%. The mask was rolled onto the face by 10%, with 90% directly placing the mask. Jaw lift was applied by 58%.

PIP, PEEP and ventilation rate

There were no significant differences in PIP, PEEP and ventilation rates between the two masks.

Percentage leak at the face mask

The mean (SD) leak for the LR mask was 55% (31) and FP mask was 57% (25), there was no significant difference between the devices.

Figure 2 shows a box-plot where percentage leak is grouped by professional category for each mask. A large variation in leak was found for all categories. One-way ANOVA analysis showed no significant difference in leak for either mask when grouped by mask hold, placement technique or use of jaw lift.

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Figure 2 Percentage leak at the face mask for each mask design (LR dark shading, FP light shading) and professional group. Box-plots show median values (solid lines), interquartile range (margins of box), range of data and any outliers (circles).

Participant assessment of mask leak compared with actual leak

Figure 3 shows box-plots for LR and FP percentage leak grouped by self assessed leak for each mask. There was wide variation of actual leak in nearly all of the self-assessed leak categories for both masks. No one thought they had a very large leak with the LR mask, despite many with leaks of 80 to 100%. For either mask, no one who said they had a very small/nil leak had a leak less than 20%.

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Figure 3 Participant assessment of face mask leak of the Laerdal round mask (left) and the Fisher & Paykel mask (right) compared with actual leak. Box-plots show median values (solid black lines), interquartile range (margins of box), range of data and any outliers (circle).

DISCUSSION

We found mask leak varied widely with both masks from almost zero to 100% with no significant difference between the two masks.

Palme et al1 studied face mask efficiency by measuring leak indirectly. They reported that the Laerdal mask “leaked” least, suggesting that the other designs must have had considerable leaks.

The techniques of holding the mask on the face, the way the mask was placed on the manikin’s face and the use of jaw lift showed considerable variation, with three distinct hold techniques being used. The technique used made no significant difference to the mask leak.

The set PIP could be achieved despite very large mean leaks (data not shown). This is consistent with findings by O’Donnell et al.2 6 Overall, the participants were unable to accurately self-assess their leak.

CONCLUSION

We compared a new mask with an established design and found no difference in leak. On average the mask leak was >50% irrespective of operator experience or technique. Many operators were unaware of the magnitude of the leak.

Further studies of mask techniques, particularly directed towards detecting and reducing leak, are required to improve effectiveness of PPV.