Page 97 - Physiological based CPAP for preterm infants at birth Tessa Martherus

High-CPAP does not impede cardiovascular changes at birth in preterm sheep
Lambs received a lethal dose of sodium pentobarbitone (100 mg/kg intravenously, Virbac Pty Ltd., Peakhurst, Australia) after completing study duration (30 + 15 min) or earlier due to reaching an ethical endpoint, where it was assessed that intubation was considered necessary. Intubation was deemed necessary if lambs were hypoxic and did not initiate breathing, despite the use of tactile stimulation, 100% oxygen and the rescue interventions detailed above.
Outcome Measures
Physiological Data Measurement and Collection
P
PBF and CBF were measured using a flow meter (Transonics systems; Ithaca, NY, US), whereas brachial arterial (BAP), intrapleural, upper tracheal (UTP), and jugular venous pressures (JVP) were measured with pressure transducers (BP Transducer/Cable kit, ADInstruments, New South Wales Australia) and FiO2 was measured with a MX300-I Oxygen sensor (Teledyne Analytical instruments, CA, US). Physiological data was recorded continuously using LabChart 8 (ADInstruments, New South Wales Australia) and arterial blood gas status was measured every 3 min (ABL90 flex and ABL800 analyzer, Radiometer Medical ApS, Brønshøj, Denmark).
For physiological data, a mean was calculated over a 10 s epoch every 3 min, heart rate was 4 derived from PBF and alveolar to arterial differences in PO2 (AaDO2) was calculated as ((713*FiO2) -(PaCO2/0.8) -PaO2). To assess CBF stability, a mean CBF was calculated over each
15 s epochs and the CBF variability was calculated by measuring the coefficient of variation
of mean CBF values throughout the experiment; this was calculated as (standard deviation (CBF)/average (CBF)*100). Breathing rate (60/duration period*number of breaths) and inter-breath variability (standard deviation (duration breath)/average (duration breath)*100) were calculated in 30 s epochs. Expirations that involved distinct increases in intrapleural pressure above baseline were considered to be active expirations that involve the use of expiratory muscles.
Statistical Analysis
Data were analyzed using SPSS Statistics version 24.0 (IBM Software, Chicago, Illinois, US, 2018). Baseline characteristics were compared using Kruskal-Wallis test, Pearson Chi-Square test or Fishers exact test. Raw data are presented as median (Q1-Q3) or n (%). Statistical significance was accepted when p <0.05.
CPAP strategies were compared over time using linear mixed-effect regression models, accounting for the relation between multiple measurements of the same lamb with a first-order autoregressive covariance structure on residuals. Group, time and group*time interaction were included in the model as fixed factors and random effects. To ensure that the estimated value of the parameters remained between 0-100% and 21-100%, logit transformations were used on the SaO2 (Ln(X/(1-X))) and FiO2 (Ln(79/100*(X-0.21)/(1-
93
r