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Impact of Conventional Breath Inspiratory Time during High-Frequency Jet Ventilation in Preterm Lambs

Musk G.C.a · Polglase G.R.a, c · Song Y.a, b · Pillow J.J.a, b, d
aSchool of Women’s and Infants’ Health and bCentre for Neonatal Research and Education, The University of Western Australia, Crawley, W.A., cRitchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash Medical Centre, Clayton, Vic., and dNCCU, King Edward Memorial and Princess Margaret Hospitals, Subiaco, W.A., Australia Neonatology 2012;101:267–273 (DOI:10.1159/000334828)

Abstract

Background: Conventional mechanical ventilator (CMV) breaths during high-frequency jet ventilation (HFJV) are advocated to recruit and stabilize alveoli. Objectives: To establish if CMV breath duration delivered during HFJV influences gas exchange, lung mechanics and lung injury. Methods: Preterm lambs at 128 days gestational age were studied. HFJV (7 Hz, PEEP 8 cm H2O, PIPHFJV 40 cm H2O, FiO2 0.4) with superimposed CMV breaths (PIPCMV 25 cm H2O, rate 5 breaths/min) was commenced after delivery and continued for 2 h. CMV breath inspiratory time (tI) was either 0.5 s (HFJV+CMV0.5; n = 8) or 2.0 s (HFJV+CMV2.0; n = 8). Age-matched unventilated controls (UVC) were included for comparison. Results: Serial arterial blood gas analyses were performed. PIPHFJV was adjusted to target a PaCO2 of 45–55 mm Hg. FiO2 was adjusted to target SpO2 90–95%. Pressure-volume curves, broncho-alveolar lavage (BAL) and lung tissue samples were obtained postmortem. Gas exchange, ventilation parameters, static lung compliance and BAL inflammatory markers were not different between HFJV+CMV0.5 and HFJV+CMV2.0. Both ventilation groups had higher BAL inflammatory markers and increased iNOS-positive cells on histology compared to UVC, whilst lung tissue IL-1β and IL-6 mRNA expression was higher in the HFJV+CMV2.0 group compared to the UVC group. Conclusions: Preterm lambs were ventilated effectively with HFJV and 5 CMV breaths/min. CMV breath duration did not alter blood gas exchange, ventilation parameters, ex vivo static lung mechanics or markers of lung injury over a 2-hour study, although consistent trends towards increased inflammatory markers with the longer tI suggest greater risk of injury.

 

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