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  • Title: Impact of conventional breath inspiratory time during high-frequency jet ventilation in preterm lambs.
    Author: Musk GC, Polglase GR, Song Y, Pillow JJ.
    Journal: Neonatology; 2012; 101(4):267-73. PubMed ID: 22248665.
    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 H(2)O, PIP(HFJV) 40 cm H(2)O, FiO(2) 0.4) with superimposed CMV breaths (PIP(CMV) 25 cm H(2)O, rate 5 breaths/min) was commenced after delivery and continued for 2 h. CMV breath inspiratory time (t(I)) was either 0.5 s (HFJV+CMV(0.5); n = 8) or 2.0 s (HFJV+CMV(2.0); n = 8). Age-matched unventilated controls (UVC) were included for comparison. RESULTS: Serial arterial blood gas analyses were performed. PIP(HFJV) was adjusted to target a PaCO(2) of 45-55 mm Hg. FiO(2) was adjusted to target SpO(2) 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+CMV(0.5) and HFJV+CMV(2.0). 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+CMV(2.0) 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 t(I) suggest greater risk of injury.
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