Extremely premature-born animals were cared for in humidified, heated incubators (Drägerwerk) as outlined in Fig. 1A. In brief, PC-CMV was continuously adapted to maintain paO2 between 7.3 and 9.3 kPa (55-70 mmHg) and paCO2 between 6.0 and 7.3 kPa (45-55 mmHg). Ketamine and midazolam (Akorn) were provided as required. Heparinized, sodium- and pH-adapted maintenance fluids (normal saline, half-normal saline, or sodium acetate with 1 U/mL unfractionated heparin—all from Hospira) and an individually prepared, amino acid-rich, electrolyte, and glucose-adapted total parenteral nutrition were infused alongside intravenous lipids. Maintenance fluid rates were adapted to maintain mean arterial pressures> >25 mmHg. If hypotensive, a maximum of 2 boluses (10 mL/kg) normal saline was given and escalated to inotropic therapy if required with dopamine ± dobutamine (both from Hospira) up to doses of 20 µg/kg/min, respectively. If hypotension persisted, hydrocortisone at 1 mg/kg every 12 hours was initiated and tapered as soon as possible. Acidosis was buffered with sodium bicarbonate (Hospira) at 1 mmol/kg. Animals were transfused with stored placental or maternal packed blood cells at 10 mL/kg if hematocrits persisted below 30%. To prevent sepsis, preemptive ampicillin (50 mg/kg), gentamicin (2.5 mg/kg) and vancomycin (15 mg/kg, all from Hospira) were given (Fig. 1A). Whole-body anteroposterior X-ray films were taken every 24 hours to assess the lung, heart, intestines and evaluate the position of the endotracheal tube and the intravascular catheters. Echocardiographic studies were performed daily by a pediatric cardiologist; an open ductus arteriosus was neither treated medically, nor surgically.