We invited neonatal consultants, fellows, senior registrars and neonatal nurses with at least five years of newborn resuscitation experience to participate, 28 of whom consented. All worked in the neonatal intensive care unit (NICU) and were involved with delivery room resuscitation. The study was conducted at Westmead Hospital NICU, which is one of the largest tertiary referral centre for the state of New South Wales, Australia, with over 5000 deliveries annually and more than 1600 admissions to the newborn nursery. The study was approved by the Sydney West Area Health Service Human Research and Ethics Committee (LNR/11/WMEAD/288). Informed written consent was obtained from all study participants.
Devices And Model Used
We used a Laerdal 240-ml self-inflating bag (SIB) with a Laerdal 0/1 round mask (Laerdal Medical, NY, USA) to provide PPV. This SIB has a pop-off pressure release valve set at 35 cm H2O. A Laerdal® Advanced Life Support (ALS) baby™ manikin model, equivalent to a 3 kg infant. The manikin contains two separate lungs and a stomach with no intended leak. The “oesophageal tube” and “stomach” bag were blocked. The Laerdal manikin has a hinged mandible which allows the jaw-thrust manoeuvre . Prior to each study we measured the static compliance of the model, which was 3.9 ml/cm H2O. A Florian respiratory function monitor (Acutronics Medical Systems, Zurich, Switzerland) was used to measure the percentage mask leak. A pneumotach was placed between the Laerdal mask and the SIB. Mask leak was defined as: tidal volume inflation (VTi) - tidal volume exhalation (VTe)/(VTi) x 100. MV was then calculated. The manikin was modified with an optical pressure switch attached inside the chest to detect the chest compression. The pressure switch was activated when at least one-third of the antero-posterior diameter of the chest was compressed. This was to ensure that adequate CC was achieved. The signal was collected into the Grove Spectra software (Grove Medical, London, UK) via an analogue signal. Other respiratory mechanics parameters calculated were peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP), mean airway pressure (MAP), inhalation time (Ti) and exhalation time (Te).
Data Recording System
Data from the Florian monitor were collected at 200 Hz via an analogue to digital converting device, using Spectra software. The Florian monitor was calibrated with an external syringe of known volume and pressure/flow via a ventilator calibration analyser. Pressure resolution was 0.1 cm H2O with pressure accuracy of ± 0.5%, and flow calibration resolution of 0.1L/min with accuracy of ± 1% (RT-200; Timeter Instrument, Allied Healthcare Products, St Louis, MO, USA). An example of decoupled C:V ratio with ventilation is shown in Fig. 1.
The study participants were randomly assigned to a two-person team. They had extensive skills in neonatal resuscitation and demonstrated proficiency in the locally run newborn resuscitation course, based on the Australian Resuscitation Council (ARC) guideline . Participants were instructed to provide PPV and chest compressions for two minutes with a ratio of one inflation to three compression resulting in 90 CC per minute. Digital clock was used to time the PPV and compressions. After a two-minute rest, the study participants reversed the roles and repeated the same sequence. A standardised one-person mask (two-point top hold) technique was used . Further sequences included performing decoupled CC for two minutes each, which comprised 60 breaths per minute and 120 chest compressions per minute without any pause. The CC rate of 120 was performed based on the mathematical model by Babbs et al which suggested higher rates up to 180/min was needed to provide maximal systemic perfusion . As rate was 180/min was unachievable we performed 120/min.
Data for all studies were extracted from the Spectra software and analysed using Stata® 14 (Stata Corp, College Station, TX, USA). The first five inflations were excluded from the analysis. Analysis of variance was used to examine the differences between PPV with synchronous CC with decoupled CC. Non-normally distributed data were tested with Wilcoxon matched pairs analysis. Mean differences were calculated with 95% confidence interval (95% CI). Differences with a p-value of < 0.05 were considered significant.