Inclusion Criteria:  Preterm infants (< gw 37+0) who are in need for analgesic or sedative medication according to clinical judgment (scoring with pain assessment scales; ALPS-Neo and Comfort-Neo) Existing arterial or venous cannulas/catheters for repeated non-traumatic blood sampling Informed and written parental consent  Exclusion Criteria:  Hemodynamic instability (same as in clinical routine). Cardiac malformations in need for postnatal surgery. Any serious medical condition or ethical issues that could, in the Investigators opinion, interfere with the study procedures.