Mechanical ventilation amplifies intratracheal lipopolysaccharide-induced plasma and brainstem inflammation in preterm fetal sheep

Preterm newborns exposed to infection/inflammation in utero are at an increased risk of requiring respiratory support at birth, often in the form of mechanical ventilation. Mechanical ventilation and intrauterine inflammation independently cause inflammation in brainstem respiratory-related centres. However, the synergistic effect of intrauterine inflammation and mechanical ventilation on brainstem inflammation is unknown. We hypothesised that 24 hours of mechanical ventilation after intratracheal LPS exposure exacerbates inflammation in the brainstem respiratory-related centres of preterm fetal sheep. Preterm fetal sheep (110 ± 1 days’ gestation (d)) were surgically instrumented with catheters and tubing for in utero ventilation (VENT). At 115 ± 3 d, fetal sheep were randomly assigned to: 1) unventilated control + intratracheal (i.t.) saline (CONTSAL; n=6), 2) 24 h of VENT with i.t. saline (VENTSAL; n=7), 3) unventilated control with i.t. LPS (CONTLPS; n=7), or 4) 24 h VENT with i.t. LPS (VENTLPS; n=6). In utero ventilation was started 1 h after i.t. LPS/saline administration, targeting a tidal volume of 3-5 mL/kg for 24 h. Serial plasma samples and post-mortem CSF were assessed for systemic and central inflammation, respectively. At 24 h, brainstem tissue was collected for molecular and histological assessment of markers of inflammation and injury. Plasma interleukin (IL)-1β, IL-6, IL-10 and interferon-γ-induced protein-10 (IP-10) were significantly increased in VENTLPS fetuses compared to CONTSAL and VENTSAL (P<0.05). IL-6 was higher in the cerebrospinal fluid of VENTLPS groups compared to CONTLPS (P=0.0002). mRNA tumour necrosis factor (TNF) (P=0.035) and prostaglandin-endoperoxide synthase-2 (PTGS2) (P=0.011) were increased in the brainstems of VENTLPS fetuses compared to CONTLPS. LPS exposure increased the number of astrocytes, microglia and STAT3+ cells within key respiratory-related centres compared to CONTSAL and VENTSAL (P<0.01). Mechanical ventilation for 24 h after i.t. LPS amplifies markers of systemic and brainstem inflammation but does not further exacerbate histological inflammation or cell death in brainstem respiratory-related centres. The exacerbated inflammation suggests that mechanical ventilation preceded by intrauterine inflammation may impede cardiorespiratory control with adverse effects on spontaneous breathing and cardiovascular function in preterm infants.