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Original article
Neopuff T-piece resuscitator: does device design affect delivered ventilation?
  1. Murray Hinder1,2,
  2. Pranav Jani1,3,
  3. Archana Priyadarshi1,3,
  4. Alistair McEwan2,
  5. Mark Tracy1,3
  1. 1Neonatal Intensive Care, Westmead Hospital, Westmead, New South Wales, Australia
  2. 2Faculty of Engineering and Information Technologies, BMET Institute, Sydney University, Sydney, New South Wales, Australia
  3. 3Department of Paediatrics and Child Health, Sydney University, Westmead, New South Wales, Australia
  1. Correspondence to Dr Mark Tracy, Department of Paediatrics and Child Health, Sydney University, PO Box 533, Wentworthville, NSW 2145, Australia; mark.tracy{at}sydney.edu.au

Abstract

Background The T-piece resuscitator (TPR) is in common use worldwide to deliver positive pressure ventilation during resuscitation of infants <10 kg. Ease of use, ability to provide positive end-expiratory pressure (PEEP), availability of devices inbuilt into resuscitaires and cheaper disposable options have increased its popularity as a first-line device for term infant resuscitation. Research into its ventilation performance is limited to preterm infant and animal studies. Efficacy of providing PEEP and the use of TPR during term infant resuscitation are not established.

Aim The aim of this study is to determine if delivered ventilation with the Neopuff brand TPR varied with differing (preterm to term) test lung compliances (Crs) and set peak inspiratory pressures (PIP).

Design A single operator experienced in newborn resuscitation provided positive pressure ventilation in a randomised sequence to three different Crs models (0.5, 1 and 3 mL/cmH2O) at three different set PIP (20, 30 and 40 cmH2O). Set PEEP (5 cmH2O), gas flow rate and inflation rate were the same for each sequence.

Results A total of 1087 inflations were analysed. The delivered mean PEEP was Crs dependent across set PIP range, rising from 4.9 to 8.2 cmH2O. At set PIP 40 cmH2O and Crs 3 mL/cmH2O, the delivered mean PIP was significantly lower at 35.3 cmH2O.

Conclusions As Crs increases, the Neopuff TPR can produce clinically significant levels of auto-PEEP and thus may not be optimal for the resuscitation of term infants with healthy lungs.

  • Resuscitation
  • Neopuff
  • T-piece
  • Newborn
  • auto PEEP

https://doi.org/10.1136/archdischild-2016-311164

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    What is already known on this topic?

    • Neopuff T-piece resuscitator performance has been reported in preterm infants and low compliance lung models.

    • Use of Neopuff in resuscitation of term infants with normal lung compliance has increased.

    What this study adds?

    • When using Neopuff T-piece resuscitator in a lung model, as lung compliance increases, the delivered positive end-expiratory pressure (PEEP) may increase from the set PEEP value and peak inspiratory pressures may be less than intended.

    • Clinicians using T-piece devices to resuscitate term infants should be aware of an unintended rise in PEEP that may be mitigated by reducing inflation rate.

    Background

    The T-piece resuscitator (TPR) is a device widely used to provide positive pressure ventilation during resuscitation of infants ≤10 kg.1 The device requires an interface to the patient via face mask, laryngeal mask airway or endotracheal tube (ETT). The Neopuff (Fisher & Paykel New Zealand) TPR is a gas flow-dependent resuscitator consisting of three operator-adjusted valves. These are set with the aid of a built-in manometer to the desired level for peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP) and safety pressure limit required to provide intermittent positive pressure ventilation (IPPV). Driving gas of 5–15 L per minute (LPM) is provided by blended gas, air or oxygen flowmeter.

    Two control dials located on the Neopuff provide adjustable ranges for PIP of 2–75 cmH2O and safety pressure limit of 40–80 cmH2O. PEEP is adjusted by changing a variable orifice flow resistor located at the distal end of the patient circuit. The adjustable PEEP pressure range is 1–25 cmH2O.

    Setting delivery pressures must be carried out in the correct sequence stated in manufacturer documentation; otherwise, delivery of adequate ventilation will not be successful.1 ,2 Any alteration to the gas inflow rate after the initial setting and start of IPPV requires recalibration by the user, which requires disconnection from the patient.2 ,3 Hawkes et al4 showed that adjustment of circuit gas inflow from 5 to 15 LPM without recalibrating the delivery pressures resulted in an inadvertent increase in PEEP (300%), PIP (40%) and safety over pressure (33%) from the initial set value.

    IPPV is started by occluding the gas outlet located on the PEEP valve assembly. The operator determines inflation rate and inspiratory:expiratory ratio (I:E ratio). If IPPV is not initiated and circuit seal is maintained, a continuous positive airway pressure is delivered to the patient at the same set PEEP value.

    The use of the Neopuff for preterm resuscitation is well published.5–7 Although it is widely used for resuscitation in term infants,8 limited data support its use in infants with weight 3.5–10 kg. We tested the hypothesis that the delivered ventilation of the Neopuff TPR is not different between low and normal newborn lung compliance (Crs) (0.5–3.0 mL/cmH2O).9

    The aim of this study was to determine whether the delivered ventilation with the Neopuff TPR varied with differing test Crs (0.5, 1 and 3 mL/cmH2O) and different set PIPs (20, 30 and 40 cmH2O).

    Methods and design

    A single Neopuff TPR (Part Number: RD900AEU) and delivery circuit (Part Number RD 1300-10) with a measured compliance of 0.4 mL/cmH2O and tubing flow resistance of 6 cmH2O/L/s at 30 LPM were used in this bench study.

    Two different leak-free test lungs were used (1) a 50 mL Draeger test lung (Draeger, Lubeck, Germany) with measured compliance of 0.5 mL/cmH2O; resistance 50 cmH2O/L/s and (2) a 200 mL IMT newborn test lung (Smart Lung Infant, IMT medical, Buchs, Switzerland) with adjustable measured compliances of 1.0 and 3.0 mL/cmH2O; resistance 50 cmH2O/L/s. A Florian respiratory function monitor (RFM) (Accutronics, Medical Systems AG, Zug, Switzerland) was connected via the hot wire pneumotach and pressure sensor line sited between the Neopuff TPR and the test lung. The Florian monitor was calibrated with an external syringe of known volume and pressure/flow via a traceable reference ventilator analyser (PF300, IMT Medical, Buchs, Switzerland). The analogue signals output from the RFM 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 cmH2O and over 120 s, there was no fall in pressure indicating the system was leak free.

    A single operator experienced in neonatal resuscitation was asked to deliver 2 min of IPPV in a randomised sequence to each of the Crs models (0.5, 1, and 3 mL/H2O) at the predefined PIP levels (20, 30 and 40 cmH2O).

    The RFM pneumotach was rezeroed and the TPR settings for circuit gas inflow 10 LPM air, PEEP 5 cmH2O and over pressure 50 cmH2O were reset and checked with ventilation analyser at the start of each randomised sequence. An inflation rate of 60 inflations per minute (IPM) guided by metronome was used across all Crs and inflation pressure combinations. Operator was blinded to RFM waveform display, only Neopuff manometer was visible to operator. We have previously shown no difference in delivered mask ventilation with operators guided by either the Neopuff pressure dial or the manikin chest rise.10 Finger dwell of <2 mm above PEEP valve orifice was observed to impede gas output flow and increase PEEP during passive deflation of the test lung. Thus, the operator was instructed to ensure finger distance from valve orifice during deflation was >2 mm. PEEP valve set position was marked and checked after each sequence to ensure no operator induced change occurred in adjusted valve position during IPPV.11 ,12

    Data analysis

    Analysis was conducted using Stata (V.13 MP, StataCorp, College Station, Texas, USA). The measured parameters included the mean, minimum and maximum PIP, PEEP and tidal volume (Vt). Analysis of variance (ANOVA) for repeated measures was used to determine differences between test Crs at different set PIP 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. Table 1 provides measured mean PIP, PEEP and Vt with IQR and SD for each Crs and set PIP with p values calculated with ANOVA for repeated measures.

    View this table:
    Table 1

    Measured respiratory parameters with differing set peak inspiratory pressures (PIP) and test lung compliance

    Results

    A total of 1087 inflations were analysed. Inspiratory times were statistically different across all sequences (mean=0.53, SD=0.04 s p≤0.001) but not considered clinically significant.

    The measured PIP as a percentage of set PIP ranged from 100% to 101% with Crs of 0.5 and 1 mL/cmH2O, which were not significantly different and was lowest at 88% with set PIP of 40 cmH2O and Crs 3 mL/cmH2O (p<0.001) (table 1, figure 1). The measured PEEP as a percentage of set PEEP ranged from 98% to 106% for Crs of 0.5 mL/cmH2O, 106% to 110% for Cl of 1 mL/cmH2O and 122% to 164% for Crs of 3 mL/cmH2O across set PIP range (p<0.001), this was highest at set PIP of 40 cmH2O and Crs of 3 mL/cmH2O (table 1, figure 2). The mean delivered Vt increased significantly with increasing Crs for each set PIP level, ranging from 8.5 mL (Cl 0.5 mL/cmH2O at set PIP 20 cmH2O) to 66 mL (Crs 3 mL/cmH2O at set PIP 40 cmH2O) (p<0.001) (table 1, figure 3).

    Figure 1
    Figure 1

    Measured peak inspiratory pressure (PIP).

    Figure 2
    Figure 2

    Measured positive end-expiratory pressure (PEEP).

    Figure 3
    Figure 3

    Measured inflation volume.

    Discussion

    The results of this bench study show when using Neopuff TPR to provide IPPV, there is a significant difference between set and delivered pressures as Crs increases. The unintended rise in delivered PEEP (auto-PEEP) at compliance of 3.0 mL/cmH2O was clinically important.

    Auto-PEEP can impair the reduction in pulmonary vascular resistance important to circulatory adaptation immediately after birth13 and increase risk of air leaks in term infants with meconium aspiration syndrome. We suspect the auto-PEEP observed in our study is due to circuit-imposed expiratory resistance of the Neopuff PEEP valve and delivery circuit compliance, increasing the system time constant, thus increasing lung deflation time. Similarly, the observed inability to attain set PIP of 40 cmH2O at Crs of 3 mL/cmH2O during inspiration may be due to insufficient fill time at the circuit inflow rate of 10 LPM and inflation rate of 60 IPM (figure 4). The compliance setting that we chose for our term lung model of 3 mL/cmH2O may be typical of a term infant of 3500 g birth weight,9 a recent human study by McEvoy et al14 suggests higher term infant values of 4–5 mL/cmH2O.

    Figure 4  
    Figure 4  

    Pressure waveforms for lung compliance 3 mL/cmH2O at set peak inspiratory pressures 20 cmH2O (A), 30 cmH2O (B), 40 cmH2O (C) and positive end-expiratory pressure 5 cmH2O.

    The development of auto-PEEP is tied to the time constant of the lung and airway. The lung time constant is proportional to the product of airway resistance (RAW) and Crs.

    Increasing RAW for a given Crs and volume results in a longer time for gas to exit the lung. Similarly, for a given RAW and airways pressure increasing Crs will also result in longer time for gas to exit the lung.15 Imposed resistance due to ventilator device design has been shown to increase patient work of breathing16–18 and change the overall respiratory system time constant.18 ,19 Wald et al17 showed that the expiratory resistance of the Neopuff TPR varied with gas in flow rate from 40.1 cmH2O/L/s at 15 LPM to 104.8 cmH2O/L/s at 6 LPM.

    Finer et al detailed eight occurrences in a 12-month period (n=120) of inadvertent increase in PEEP using TPR device from set 5 cmH2O (min 6.7; max 15.8 cmH2O), IPM <60 during resuscitation of infants <1000 g which he attributed to possible movement of the PEEP control knob. It is notable that both the recordings of actual resuscitations illustrated have a starting PIP of 40 cmH2O. Circuit gas inflow rate was not reported, Finer concluded ‘the Neopuff has the potential to cause an inadvertent and potentially toxic increase of PEEP which might not be noticed by the operator’.11 We have excluded PEEP valve positional changes contributing to rise in PEEP in our study by checking there was no change in a marker point on the PEEP valve during the experiment. Bennett et al examined increasing PIPs with the Neopuff TPR in a manikin model to 40 cmH2O as escalation to these levels may be required with diseased or immature lungs.20 ,21

    Limitations of our study are shared with other manikin and test lung studies of the ability to generalise to actual human resuscitations at birth. Changes in inflation rate and circuit gas flow rate were not examined in this study and may contribute to the level of device imposed auto-PEEP. The performance of other brands of TPR's may be different.

    Preliminary data by our group in a piglet study22 (n=10) comparing self-inflating bag (SIB) and Neopuff TPR delivered ventilation has confirmed our bench test results that the TPR device can contribute to the production of clinically significant auto PEEP during IPPV compared SIB with PEEP valve.

    Adaptive changes in pulmonary and circulatory physiology and establishment of a functional residual capacity of the lung during birth are complex. Detecting and adjusting for Crs changes during resuscitation with either SIB or TPR devices is difficult.23–25 The presence of leak during mask resuscitation is common and can also influence Neopuff performance.26 Mask leak that may be variable might obscure TPR generated auto-PEEP by providing a path of least resistance for expired gas. Mask ventilation by more experienced clinicians,27 using improved mask techniques28–30 or the presence of ETT may provide a patient/device interface that is closer to leak free, increasing device imposed auto PEEP from TPR devices.

    The efficacy of the T-piece device for term resuscitation is not established, and terms describing the device as the ‘gold-standard’31 should be viewed with caution. Our data suggest that in contrast to previous studies using Neopuff TPR in preterm lung models,32 delivered pressures are not consistent and vary from those preset as Crs increases.

    Conclusion

    We have shown in a test lung with compliance similar to that of a term infant that use of Neopuff TPR may result in increasing auto PEEP and decreasing PIP values. This is likely to be greater with higher Crs and higher inflation rates. Lower inflation rates may mitigate this effect. Operator finger position over PEEP valve orifice during lung deflation may also contribute to unintended PEEP. Clinicians using Neopuff to resuscitate term infants should be alert to these potential consequences.

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    Footnotes

    • Contributors MH is the primary researcher responsible for conceiving, designing, data collection, statistical analysis and writing manuscript. PJ contributed to data collection, interpretation, manuscript construction and review. AP and AM contributed to interpretation, manuscript construction and review. MT contributed by assisting design, statistical analysis, manuscript writing and review.

    • Competing interests None declared.

    • Ethics approval This study was approved by the Western Sydney Local Health District Human Ethics and Scientific committee approval number SAC2014/5/6.9(3999)QA.

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