Evaluation of Intravascular Monitoring of Partial PRessure of Oxygen for Neonatal intensiVE Care Patients

Inclusion Criteria: * Sick newborn infants where the clinical routine indicates use of an umbilical catheter. At least one of the criteria below should be fulfilled: * The infant needs invasive measurement of blood pressure. * The infant needs repetitive sampling of blood. * The infant needs prolonged infusion(s) \> 2 days. * The infant needs infusion of vessel irritating and potentially vessel harming solutions. * The infant is born extremely preterm (before 28+0 weeks gestational age). * A newborn infant with severe respiratory disorder, requiring oxygen treatment (more than 40% Fraction of inspired oxygen (FiO2)). * The infant is undergoing therapeutic hypothermia following asphyxia ("oxygen deficiency at birth"). * The infant has a severe infection/sepsis. * Signed informed consent form by both parents (or guardians), (if the infant has only one parent (or guardian) one informed consent is required). Exclusion criteria: * Gastroschisis * Omphalocele * Peritonitis * Necrotizing enterocolitis * Omphalitis