Mechanical ventilation amplifies intratracheal lipopolysaccharide-induced plasma and brainstem inflammation in preterm foetal 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 hypothesized that 24†h of mechanical ventilation after intratracheal LPS exposure exacerbates inflammation in the brainstem respiratory-related centres of preterm foetal sheep. Preterm foetal sheep (110 ± 1 days' gestation) were surgically instrumented with catheters and tubing for in utero ventilation (VENT). At 115 ± 3 days, foetal sheep were randomly assigned to: (i) unventilated control + intratracheal (i.t.) saline (CONT(SAL); n = 6), (ii) 24†h of VENT with i.t. saline (VENT(SAL); n = 7), (iii) unventilated control with i.t. LPS (CONT(LPS); n = 7) or (iv) 24†h VENT with i.t. LPS (VENT(LPS); 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 VENT(LPS) foetuses compared to CONT(SAL) and VENT(SAL) (P < 0.05). IL-6 was higher in the cerebrospinal fluid of VENT(LPS) groups compared to CONT(LPS) (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 VENT(LPS) foetuses compared to CONT(LPS). LPS exposure increased the number of astrocytes, microglia and STAT3+ cells within key respiratory-related centres compared to CONT(SAL) and VENT(SAL) (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.