 Blood copeptin will be measured during the routine treatment of neonates, children and adolescents on the Intensive Care Unit of the University Childrens Hospital Zurich at different time points admission, 12, 24, 48, 96, 168 hours after admission. These values will be primarily analysed for their variability and their association with arterial hypotension. Blood samples will be drawn together with otherwise medically indicated blood withdrawals to avoid extra harm. Further, copeptin values will be compared to clinical and vital parameters, all of them open-label available during clinical routine. Copeptins predictive value for patients outcome will be analysed as secondary outcome. 