Imaging the Respiratory Transition at Birth: Unraveling the Complexities of the First Breaths of Life.

Rationale: The transition to air breathing at birth is a seminal respiratory event common to all humans, but the intrathoracic processes remain poorly understood. Objectives: The objectives of this prospective, observational study were to describe the spatiotemporal gas flow, aeration, and ventilation patterns within the lung in term neonates undergoing successful respiratory transition. Methods: Electrical impedance tomography was used to image intrathoracic volume patterns for every breath until 6 minutes from birth in neonates born by elective cesearean section and not needing resuscitation. Breaths were classified by video data, and measures of lung aeration, tidal flow conditions, and intrathoracic volume distribution calculated for each inflation. Measurements and Main Results: A total of 1,401 breaths from 17 neonates met all eligibility and data analysis criteria. Stable FRC was obtained by median (interquartile range) 43 (21-77) breaths. Breathing patterns changed from predominantly crying (80.9% first min) to tidal breathing (65.3% sixth min). From birth, tidal ventilation was not uniform within the lung, favoring the right and nondependent regions; P < 0.001 versus left and dependent regions (mixed-effects model). Initial crying created a unique volumetric pattern with delayed midexpiratory gas flow associated with intrathoracic volume redistribution (pendelluft flow) within the lung. This preserved FRC, especially within the dorsal and right regions. Conclusions: The commencement of air breathing at birth generates unique flow and volume states associated with marked spatiotemporal ventilation inhomogeneity not seen elsewhere in respiratory physiology. At birth, neonates innately brake expiratory flow to defend FRC gains and redistribute gas to less aerated regions.

Regional ventilation characteristics during non-invasive respiratory support in preterm infants.

OBJECTIVES: To determine the regional ventilation characteristics during non-invasive ventilation (NIV) in stable preterm infants. The secondary aim was to explore the relationship between indicators of ventilation homogeneity and other clinical measures of respiratory status. DESIGN: Prospective observational study. SETTING: Two tertiary neonatal intensive care units. PATIENTS: Forty stable preterm infants born <30 weeks of gestation receiving either continuous positive airway pressure (n=32) or high-flow nasal cannulae (n=8) at least 24 hours after extubation at time of study. INTERVENTIONS: Continuous electrical impedance tomography imaging of regional ventilation during 60 min of quiet breathing on clinician-determined non-invasive settings. MAIN OUTCOME MEASURES: Gravity-dependent and right-left centre of ventilation (CoV), percentage of whole lung tidal volume (VT) by lung region and percentage of lung unventilated were determined for 120 artefact-free breaths/infant (4770 breaths included). Oxygen saturation, heart and respiratory rates were also measured. RESULTS: Ventilation was greater in the right lung (mean 69.1 (SD 14.9)%) total VT and the gravity-non-dependent (ND) lung; ideal-actual CoV 1.4 (4.5)%. The central third of the lung received the most VT, followed by the non-dependent and dependent regions (p<0.0001 repeated-measure analysis of variance). Ventilation inhomogeneity was associated with worse peripheral capillary oxygen saturation (SpO2)/fraction of inspired oxygen (FiO2) (p=0.031, r2 0.12; linear regression). In those infants that later developed bronchopulmonary dysplasia (n=25), SpO2/FiO2 was worse and non-dependent ventilation inhomogeneity was greater than in those that did not (both p<0.05, t-test Welch correction). CONCLUSIONS: There is high breath-by-breath variability in regional ventilation patterns during NIV in preterm infants. Ventilation favoured the ND lung, with ventilation inhomogeneity associated with worse oxygenation.

Surgery and magnetic resonance imaging increase the risk of hypothermia in infants.

AIM: Maintaining normothermia is a tenet of neonatal care. However, neonatal thermal care guidelines applicable to intra-hospital transport beyond the neonatal intensive care unit (NICU) and during surgery or magnetic resonance imaging (MRI) are lacking. The aim of this study is to determine the proportion of infants normothermic (36.5-37.5°C) on return to NICU after management during surgery and MRI, and during standard clinical care in both environments. METHODS: Sixty-two newborns requiring either surgery in the operating theatre (OT) (n = 41) or an MRI scan (n = 21) at the Royal Children's Hospital (Melbourne) NICU were prospectively studied. Core temperature, along with cardiorespiratory parameters, was continuously measured from 15 min prior to leaving the NICU until 60 min after returning. Passive and active warming (intra-operatively) was at clinician discretion. RESULTS: The study reported 90% of infants were normothermic before leaving NICU: 86% (MRI) and 93% (OT). Only 52% of infants were normothermic on return to NICU (relative risk (RR) 1.75; 95% confidence interval (CI) 1.39-2.31; number needed to harm (NNH) 2.6). Between departure from the NICU and commencement of surgery, core temperature decreased by mean 0.81°C (95% CI 0.30-1.33; P = 0.0001, analysis of variance), with only 24% of infants normothermic when surgery began (P < 0.0001; RR 3.80 (95% CI 2.33-6.74); NNH 1.5). After an MRI, infants were a mean 0.41°C (95% CI 0.16-0.67) colder than immediately before entering the scanner (P = 0.001, analysis of variance), with only 43% being normothermic (P = 0.003; RR 2.11 (95% CI 1.35-3.74); NNH 2.1). CONCLUSION: Unintentional hypothermia is a common occurrence during surgery in the OT and MRI in neonates, indicating that evidence-based warming strategies to prevent hypothermia should be developed.

Volume guaranteed? Accuracy of a volume-targeted ventilation mode in infants.

OBJECTIVES: Volume-targeted ventilation (VTV) is widely used and may reduce lung injury, but this assumes the clinically set tidal volume (VTset) is accurately delivered. This prospective observational study aimed to determine the relationship between VTset, expiratory VT (VTe) and endotracheal tube leak in a modern neonatal -volume-targeted ventilator (VTV) and the resultant partial arterial pressure of carbon dioxide (PaCO2) relationship with and without VTV. DESIGN: Continuous inflations were recorded for 24 hours in 100 infants, mean (SD) 34 (4) weeks gestation and 2483 (985) g birth weight, receiving synchronised mechanical ventilation (SLE5000, SLE, UK) with or without VTV and either the manufacturer's V4 (n=50) or newer V5 (n=50) VTV algorithm. The VTset, VTe and leak were determined for each inflation (maximum 90 000/infant). If PaCO2 was sampled (maximum of 2 per infant), this was compared with the average VTe data from the preceding 15 min. RESULTS: A total of 7 497 137 inflations were analysed. With VTV enabled (77 infants), the VTset-VTe bias (95% CI) was 0.03 (-0.12 to 0.19) mL/kg, with a median of 80% of VTe being ±1.0 mL/kg of VTset. Endotracheal tube leak up to 30% influenced VTset-VTe bias with the V4 (r2=-0.64, p<0.0001; linear regression) but not V5 algorithm (r2=0.04, p=0.21). There was an inverse linear relationship between VTe and PaCO2 without VTV (r2=0.26, p=0.004), but not with VTV (r2=0.04, p=0.10), and less PaCO2 within 40-60 mm Hg, 53% versus 72%, relative risk (95% CI) 1.7 (1.0 to 2.9). CONCLUSION: VTV was accurate and reliable even with moderate leak and PaCO2 more stable. VTV algorithm differences may exist in other devices.