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How do different brands of size 1 laryngeal mask airway compare with face mask ventilation in a dedicated laryngeal mask airway teaching manikin?
  1. Mark Brian Tracy1,2,
  2. Archana Priyadarshi1,2,
  3. Dimple Goel1,2,
  4. Krista Lowe1,
  5. Jacqueline Huvanandana3,
  6. Murray Hinder1,3
  1. 1 Westmead Hospital, Neonatal Intensive Care Westmead, Westmead, New South Wales, Australia
  2. 2 Department of Paediatrics and Child Health, Sydney University, Sydney, New South Wales, Australia
  3. 3 Faculty of Engineering and Information Technologies, BMET Institute, Sydney University, Sydney, New South Wales, Australia
  1. Correspondence to Dr Mark Brian Tracy, Paediatrics and Child Health, Sydney University, PO Box 533, Wentworthville, NSW 2145, Australia; mark.tracy{at}sydney.edu.au

Abstract

Background International neonatal resuscitation guidelines recommend the use of laryngeal mask airway (LMA) with newborn infants (≥34 weeks’ gestation or >2 kg weight) when bag-mask ventilation (BMV) or tracheal intubation is unsuccessful. Previous publications do not allow broad LMA device comparison.

Objective To compare delivered ventilation of seven brands of size 1 LMA devices with two brands of face mask using self-inflating bag (SIB).

Design 40 experienced neonatal staff provided inflation cycles using SIB with positive end expiratory pressure (PEEP) (5 cmH2O) to a specialised newborn/infant training manikin randomised for each LMA and face mask. All subjects received prior education in LMA insertion and BMV.

Results 12 415 recorded inflations for LMAs and face masks were analysed. Leak detected was lowest with i-gel brand, with a mean of 5.7% compared with face mask (triangular 42.7, round 35.7) and other LMAs (45.5–65.4) (p<0.001). Peak inspiratory pressure was higher with i-gel, with a mean of 28.9 cmH2O compared with face mask (triangular 22.8, round 25.8) and other LMAs (14.3–22.0) (p<0.001). PEEP was higher with i-gel, with a mean of 5.1 cmH2O compared with face mask (triangular 3.0, round 3.6) and other LMAs (0.6–2.6) (p<0.001). In contrast to other LMAs examined, i-gel had no insertion failures and all users found i-gel easy to use.

Conclusion This study has shown dramatic performance differences in delivered ventilation, mask leak and ease of use among seven different brands of LMA tested in a manikin model. This coupled with no partial or complete insertion failures and ease of use suggests i-gel LMA may have an expanded role with newborn resuscitation as a primary resuscitation device.

  • newborn
  • resuscitation
  • laryngeal mask airway
  • self inflating bag
  • manikin

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What is already known on this topic?

  • The International Liaison Committee on Resuscitation guidelines recommend use of LMA at newborn resuscitation if adequate face mask positive pressure ventilation or endotracheal intubation insertion cannot be accomplished.

  • Use of non-inflatable LMA in paediatric patients is beneficial due to possible cuff hyperinflation of inflatable cuff types.

  • Efficacy of LMA use during neonatal resuscitation remains unclear.

What this study adds?

  • Size 1 LMAs tested in this manikin study showed marked performance variation.

  • The i-gel brand LMA showed superior performance for provision of peak inspiratory pressure, positive end expiratory pressure and mask leak compared with other LMAs and face masks tested.

  • Inexperienced users of LMA showed higher proficiency in attaining adequate lung inflation and ease of insertion using i-gel brand LMA.

Introduction

Laryngeal mask airways (LMA) are listed in the International Liaison Committee on Resuscitation (ILCOR) neonatal resuscitation guidelines as a means of assisting positive pressure ventilation (PPV) during resuscitation of term and near-term infants where face mask PPV is not adequate and resuscitator skills to effect endotracheal intubation are insufficient.1 LMA may also be of assistance with newborn infants with rare significant craniofacial abnormalities such as Pierre Robin syndrome where upper airways obstruction is severe and endotracheal intubation even in expert hands may be very difficult. Simply put, the LMA may be a life-saving device when ‘you can’t ventilate and you can’t intubate’.2 3 Assessment of LMA for use by local birth attendants (physicians and midwives) in developing and developed countries in manikin models compared with face mask PPV showed the feasibility of training and use of LMA in these settings and recommended further evaluation.4–6

The 2005 Cochrane review on the use of LMA versus bag-mask ventilation or endotracheal intubation comments that evidence from observational studies suggests LMA can provide rescue airway and achieve effective PPV during newborn resuscitation if both bag-mask ventilation and intubation have been unsuccessful.7 Two recent prospective, unblinded, randomised, controlled trials comparing LMA to face mask ventilation for newborn ≥34 weeks’ gestation found there was less need for endotracheal intubation using LMA and it was more effective than face mask.8 9

Training for use of LMA in newborn resuscitation requires leak-free manikins with anatomically correct pharyngeal structures to apply LMA cushion to seal. Size 1 LMA brands differ substantially in stiffness of angled tube, the angle of the tube, tube internal diameter, and the size, shape and type of mask cushion (inflatable with a syringe, auto inflate with PPV or non-inflatable contoured gel) (figure 1). This suggests the potential for variation in performance characteristics. Studies to date of comparisons between LMA brands have been limited to up to three LMA model comparisons.10–15 Clinical studies of LMA use in infancy by anaesthetists have been conducted in more controlled clinical situations of elective surgery with stable patients; brand comparisons have focused on ease of use, time to insert and inflation pressure at which audible leak occurs.10–12 The neonatal resuscitation focus on sufficient tidal volume (TV) with least peak inflation pressure, in newborn infants with significant lung disease, has dictated the search for devices and methods to reduce face mask leak. There is a need to guide clinicians how a range of different LMA devices perform in dedicated LMA training manikins and clinical practice at birth.

Figure 1

Laryngeal mask airway tested, physical characteristics: (1) Ultimate, (2) PRO-Breathe, (3) Supreme, (4) Unique, (5) air-Q, (6) AuroOnce and (7) i-gel.

We aimed to examine delivered ventilation and airway leak to an anatomically correct manikin head designed specifically to train in LMA use attached to a neonatal test lung. This crossover study was designed to test seven size 1 LMAs compared with two face masks (round and triangular). Our null hypothesis was that there would be no differences between face mask and brands of LMA in the rate of successful insertion (LMA), delivered ventilation, maximal inflation pressure, mask leak and particularly the ability to achieve targeted positive end expiratory pressures (PEEP). Primary outcomes were the delivered ventilation to the manikin, and the secondary outcomes were the insertion failure tally and subjective assessment of ease of LMA insertion.

Methods

Forty clinicians in a busy tertiary neonatal intensive care unit (9 consultants/fellows, 13 registrars and 18 nurses) agreed to participate in this study. All were experienced in bag-mask ventilation and variably less experienced with LMA use. A new AirSim Baby manikin head (JR10001, TruCorp, Belfast, Ireland) was modified by changing the supplied lung bag to a test lung (SmartLung Infant, IMT Medical, Buchs, Switzerland) with a static compliance of 2 mL/cmH2O and resistance of 50 cmH2O/L/s, simulating a near-term infant (figure 2). Seven internationally available size 1 LMA single-use devices were examined: (1) Ultimate (Ultimate Medical, Tianjin Medis, China), (2) PRO-Breathe (Well Lead Medical, China), (3) LMA Supreme (The Laryngeal Mask, Seychelles), (4) Unique LMA (The Laryngeal Mask), (5) air-Qsp (Cookgas, Malaysia), (6) AuroOnce (Ambu A/S, Ballerup, Denmark) and (7) i-gel (Intersurgical, Wokingham, Berkshire, UK).

Figure 2

Manikin/lung test set-up.

Two face mask devices were compared with LMA: (1) Ambu (Ambu A/S) triangular size infant (Part No 252 052) and (2) Laerdal (Stavanger, Norway) round size 1 (Part No 851600). PPV was supplied using an Ambu self-inflating bag (SIB) (SPUR II Part No 335 102 000) with Ambu manometer and PEEP valve (0–20 cmH2O, Part No 199 102 001). Two neonatal respiratory function monitors (RFM) (Florian, Hirzel, Acutronics, Switzerland, and Cosmo Novametrix) were used to determine the TV, flow and inflation pressures at two points. At point 1, the pneumotach of the Florian RFM was sited between the SIB and the proximal end of the device under test (LMA or face mask). At point 2, the pneumotach of the Cosmo RFM was sited between the test lung and the manikin head. Both RFMs were calibrated with an external syringe of known volume and pressure/flow via a traceable reference ventilator analyser (PF300, IMT Medical). Participants were blinded to both RFM displays. The manikin head was assessed for system leak and leak points at the base of the head where airway bifurcates and the corner of the lip was sealed with silicone. Test lung, manikin head and measurement system (RFM pneumotach’s proximal pressure lines) were pressurised to a static pressure of 50 cmH2O, and over 120 s there was no fall in pressure, indicating the system was leak-free.

A PowerLab data acquisition system (Part No ML880, ADInstruments, Sydney, Australia) with a sample rate of 200 Hz and a laptop computer collected analogue signals for volume, airflow and airway pressure from both RFMs. Respiratory parameters from each RFM (peak inspiratory pressure (PIP), PEEP, TV), for each breath, were determined by a customised program software algorithm (Python Software Foundation).

Leak during PPV was determined as (TV proximal (SIB) − TV distal (test lung))/TV proximal (SIB)×100.

Each subject received extensive instruction and practice with both face mask and LMA insertion/cuff inflation with each brand using the manikin head over several sessions. Competency with each method was assessed in the training phase by the instructor determining adequate test lung inflation and lack of audible leak.

Participants were asked to deliver 2 min of PPV aiming to achieve adequate test lung inflation for each randomised device; a 2 min rest period was provided between each test sequence. If the LMA device required cuff inflation, a volume of 4 mL was used, reflecting recommended maximum inflation volume. If the subject judged test lung inflation inadequate or there was no test lung movement, this was noted as an unsuccessful attempt; a second placement of the device was allowed, and two unsuccessful attempts were noted as a complete failure. Successful PPV following the second insertion was judged a partial failure (table 1). PEEP valve was set at 5 cmH2O and PIP was not specified beyond adequate test lung inflation. The inflation rate (40–60) is as per ILCOR guidelines.1 At the end of each sequence the subjects were instructed to provide four inflations of maximum SIB compression to determine if delivery of PIP up to the SIB overpressure value of 40 cmH2O (+/−5 cmH2O) could be achieved, simulating the need to increase PIP during PPV at resuscitation.3 16

Table 1

Delivered test lung respiratory data, device insertion failures and device insertion rating

Data analysis

The analysis using Stata V.14 examined the mean and SD for PIP, PEEP, TV and mask leak. Analysis of variance for repeated measures was used to determine differences between device types, with estimated means reported with their SEs (table 1) with p values-adjusted F test using Box’s conservative epsilon. p Values of <0.05 were considered significant. Pairwise comparisons between groups were assessed with Bonferroni correction. LMA insertion attempts were grouped as frequency counts of subjects (no failure, partial or complete failure), and participant impression of ease of insertion (dichotomised to easy or difficult) per device was examined by Fisher’s exact test.

Results

There were 12 415 inflations recorded and analysed. The i-gel LMA consistently and statistically outperformed all other devices tested (table 1). Box and whisker plots demonstrate the median and spread of values for primary outcomes (PEEP in figure 3 and leak in figure 4).

Figure 3

Box and whisker plot: test lung delivered positive end expiratory pressure. The median of 25–75th centile for box and whiskers is 1.5× IQR (above and below), which gives the upper and lower adjacent values. PEEP, positive end expiratory pressure.

Figure 4

Box and whisker plot: mask leak. The median of 25–75th centile for box and whiskers is 1.5× IQR (above and below), which gives the upper and lower adjacent values.

Primary outcomes

The mask leak observed with i-gel LMA of 5.7% was dramatically lower than all other devices observed, including face mask (ranging from 37.5% to 65.4%, p<0.001) (table 1 and figure 4). The i-gel LMA provided the highest mean PIP of 28.9 cmH2O compared with the other devices (ranging between 16.3 and 25.5 cmH2O, p<0.001) (table 1). The i-gel delivered PEEP was closest to the set value of 5.0 cmH2O, with others ranging from 0.6 cmH2O to 3.6 cmH2O (p<0.001) (table 1 and figure 3). Comparing the maximal average PIP for the four inflations targeting the highest peak inflation pressure possible, the i-gel LMA delivered a significantly higher mean value of 38.4 cmH2O compared with other devices, ranging from 18.5 cmH2O to 32 cmH2O (p<0.001) (table 1).

Secondary outcomes

The i-gel LMA was regarded by all 40 (100%) subjects as easy to insert, which compared with the range of subjective ratings for the other LMA from 16 (40%) with AuroOnce LMA to 38 (95%) with the Supreme LMA. All subjects were able to insert the i-gel LMA the first time with minimal leak. All other LMAs had at least one first insertion failure and four LMA brands had two failures recorded for subjects ranging from 1 to 5 in total.

Discussion

We believe this is the first comprehensive study in a dedicated LMA manikin model looking at the performance of several brands (n>3) of size 1 single-use LMA devices compared with face mask PPV. The laryngeal structure of the AirSim Baby manikin head is modelled on CT scans of anatomically normal infants aged 2 months (TruCorp, personal communication 2017). Anatomically correct laryngeal structure is vital to train LMA use and allow assessment of LMA cushion leak. During the design phase, the RFM pneumotach positioned between the SIB and the LMA tube connector frequently indicated 100% leak with some brands of LMA when the test lung was clearly moving. Thus, a single point pneumotach measurement at the delivery device (SIB) may not account for differing leak characteristics during inspiratory and expiratory flow past the LMA seal. A second pneumotach sited at the test lung was required to assess system leak relative to TV (figure 2).

The superiority of the i-gel LMA to deliver ventilation compared with the other LMAs and face mask tested was unexpected given the group of experienced neonatal resuscitators. The ease of use of the i-gel LMA coupled with no insertion failures indicates the physical structure of the LMA does significantly influence performance at least in this manikin model. Many of the LMAs tested in our study were rated by the users as difficult to insert. This paralleled the higher rates of partial or complete failure to establish a useable laryngeal seal. The provision of an effective PEEP may well be desirable in preterm infants, with some degree of surfactant deficiency and abnormally low lung compliance. Intubation with endotracheal tubes is frequently associated with many adverse physiological changes including hypoxia, bradycardia and raised blood pressure (cerebral and arterial).17 The use of LMAs to provide PPV may mitigate some of these unwanted and potentially harmful physiological effects associated with intubation.

Recent interest in delivering surfactant via LMA18–20 has led to its experimental use below ILCOR recommended weight (>2000 g) or gestation (>34 weeks)1 in multicentre RCT in the USA, with results awaited.21 The LMA used in this multicentre RCT, the Unique LMA in our study, did not provide adequate PEEP (2.3 cmH2O) and had a lower mean and maximal achievable PIP of 20.7 and 25 cmH2O compared with the i-gel LMA mean and maximal achievable PIP of 28.9 and 38.4 cmH2O. Inability to achieve PIP higher than 24 cmH2O with size 1 LMAs has been reported in other manikin studies.22 This may be relevant as preterm infants who are surfactant-deficient may require rapid escalation of peak inflation pressures and adequate PEEP during resuscitation.3

Limitations are as with any manikin study in generalising device performance to human subjects. The AirSim Baby JR1001 (TruCorp) is designed for training airway management in infants 0–6 months of age. Our results may not be generalisable to other brands of LMA not tested in particular reusable devices or use with other brands of manikin. Visualisation of test lung movement by participants may not be the same as assessment of chest wall movement in a human or a full body newborn infant manikin.

Results in this dedicated manikin model concur with findings of recent two brand LMA prospective studies comparing i-gel conducted in infants and children undergoing elective surgery.10–12 23 However one study by Drake-Brockman et al 24 found the PRO-Breathe LMA superior to i-gel LMA in a wide age range of children (0–16 years) with LMA size range of 1.5–3. A study by Lee et al 25 in a lower age range of infants (10 months–5 years) found the Classic LMA had similar leak pressure to the i-gel LMA but longer insertion time.

A further important aspect not explored in this study nor in other studies we are aware of is the use of a flow-dependent t-piece resuscitator with an LMA device. T-piece resuscitators, in particular the Neopuff Resuscitator (NPR), have become a very popular device to resuscitate preterm newborns and infants with the provision of PEEP.1 26 27 Previous work has shown the NPR is slower to adjust up the PIP during resuscitation than with SIBs.16 28 29 The ability to quickly adjust the inflation pressure to respond to inadequate clinical response most likely due to mask leak may be important with the use of LMA devices given the variance of ventilation performance seen in this study. The clear superiority of the i-gel LMA with dramatically less leak and stable PEEP levels, compared with the traditional face mask SIB in this study, was unexpected. In our view, this warrants human studies to confirm this finding. Our group is currently examining the comparative performance of SIB and NPR with LMA devices, and beginning human infant studies to compare leak with face mask and i-gel LMA in the resuscitation of moderately preterm infants.

The emergency use of LMA devices during resuscitation of newborn infants is a time-critical procedure. We did not examine the additional time required for manual cuff inflation. We speculate devices that do not require manual inflation (i-gel with a solid gel cushion and the auto inflate cuff with the air-Qsp LMA) may allow shorter time to PPV and be simpler to use overall. This may be important with less experienced LMA users in the clinical setting of delivery suite or home birth.

Conclusion

This study has shown dramatic performance differences in delivered ventilation, mask leak and ease of use among seven different brands of LMA tested. PPV with the i-gel LMA with a solid gel laryngeal cushion had superior performance characteristics than the triangular or round face mask. This coupled with no partial or complete insertion failures and ease of use suggests i-gel LMA may have an expanded role with newborn resuscitation as a primary resuscitation device.

Acknowledgments

We thank staff at Westmead Neonatal Intensive Care Unit for their participation.

We also acknowledge and thank LMA and SIB suppliers for supply of devices to examine in this study, and Dr Peter Gibson paediatric anaesthetist for education and training assistance in the use of LMA.

References

Footnotes

  • Contributors MBT is primary researcher responsible for study design, statistical analysis, writing of manuscript and review. AP contributed to participant education, data collection, analysis, interpretation, manuscript construction and review. KL contributed to participant education, data collection and manuscript review. DG contributed to manuscript construction and review. JH contributed to programming of a customised respiratory data extraction algorithm, data interpretation and manuscript review. MH contributed by assisting in design, data collection, data analysis, writing the manuscript and review.

  • Competing interests None declared.

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

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