Dynamic positive end-expiratory pressure strategies using time and pressure recruitment at birth reduce early expression of lung injury in preterm lambs.

Positive end-expiratory pressure (PEEP) is critical to the preterm lung at birth, but the optimal PEEP level remains uncertain. The objective of this study was to determine the effect of maximum PEEP levels at birth on the physiological and injury response in preterm lambs. Steroid-exposed preterm lambs (124-127 days gestation; n = 65) were randomly assigned from birth to either 1) positive pressure ventilation (PPV) at 8 cmH2O PEEP or 3-min dynamic stepwise PEEP strategy (DynPEEP), with either 2) 20 cmH2O maximum PEEP (10 PEEP second steps) or 3) 14 cmH2O maximum PEEP (20-s steps), all followed by standardized PPV for 90 min. Lung mechanics, gas exchange, regional ventilation and aeration (electrical impedance tomography), and histological and molecular measures of lung injury were compared between groups. Dynamic compliance was greatest using a maximum 20 cmH2O (DynPEEP). There were no differences in gas exchange, end-expiratory volume, and ventilator requirements. Regional ventilation became more uniform with time following all PEEP strategies. For all groups, gene expression of markers of early lung injury was greater in the gravity nondependent lung, and inversely related to the magnitude of PEEP, being lowest in the 20 cmH2O DynPEEP group overall. PEEP levels had no impact on lung injury in the dependent lung. Transient high maximum PEEP levels using dynamic PEEP strategies may confer more lung protection at birth.

Synchronized Inflations Generate Greater Gravity-Dependent Lung Ventilation in Neonates.

OBJECTIVE: To describe the regional distribution patterns of tidal ventilation within the lung during mechanical ventilation that is synchronous or asynchronous with an infant's own breathing effort. STUDY DESIGN: Intubated infants receiving synchronized mechanical ventilation at The Royal Children's Hospital neonatal intensive care unit were studied. During four 10-minute periods of routine care, regional distribution of tidal volume (VT; electrical impedance tomography), delivered pressure, and airway flow (Florian Respiratory Monitor) were measured for every inflation. Post hoc, each inflation was then classified as synchronous or asynchronous from video data of the ventilator screen, and the distribution of absolute VT and delivered ventilation characteristics determined. RESULTS: In total, 2749 inflations (2462 synchronous) were analyzed in 19 infants; mean (SD) age 28 (30) days, gestational age 35 (5) weeks. Synchronous inflations were associated with a shorter respiratory cycle (P = .004) and more homogenous VT (center of ventilation) along the right (0%) to left (100%) lung plane; 45.3 (8.6)% vs 48.8 (9.4)% (uniform ventilation 46%). The gravity-dependent center of ventilation was a mean (95% CI) 2.1 (-0.5, 4.6)% toward the dependent lung during synchronous inflations. Tidal ventilation relative to anatomical lung size was more homogenous during synchronized inflations in the dependent lung. CONCLUSIONS: Synchronous mechanical ventilator lung inflations generate more gravity-dependent lung ventilation and more uniform right-to-left ventilation than asynchronous inflations.

Skin-to-skin care alters regional ventilation in stable neonates.

OBJECTIVE: Skin-to-skin care (SSC) has proven psychological benefits; however, the physiological effects are less clearly defined. Regional ventilation patterns during SSC have not previously been reported. This study aimed to compare regional ventilation indices and other cardiorespiratory parameters during prone SSC with supine and prone position cot-nursing. DESIGN: Prospective observational study. SETTING: Single quaternary neonatal intensive care unit in Australia. PATIENTS: 20 infants spontaneously breathing (n=17) or on non-invasive ventilation (n=3), with mean (SD) gestational age at birth of 33 (5) weeks. INTERVENTIONS: Thirty-minute episodes of care in each position: supine cot care, prone SSC and prone cot care preceding a 10 min period of continuous electrical impedance tomography measurements of regional ventilation. MAIN OUTCOME MEASURES: In each position, ventral-dorsal and right-left centre of ventilation (CoV), percentage of whole lung ventilation by region and percentage of apparent unventilated lung regions were determined. Heart and respiratory rates, oxygen saturation and axillary temperature were also measured. RESULTS: Heart and respiratory rates, oxygen saturation, temperature and right-left lung ventilation did not differ between the three positions (mixed-effects model). Ventilation generally favoured the dorsal lung, but the mean (95% CI) ventrodorsal CoV was -2.0 (-0.4 to -3.6)% more dorsal during SSC compared with prone. Supine position resulted in 5.0 (1.5 to 5.3)% and 4.5 (3.9 to 5.1)% less apparently unventilated lung regions compared with SSC and prone, respectively. CONCLUSIONS: In clinically stable infants, SSC generates a distinct regional ventilation pattern that is independent of prone position and results in greater distribution of ventilation towards the dorsal lung.