Repeatedly measured biomarkers may provide additional prognostic information, as was for instance shown for delta BNP measurements during the SBT and BNP driven fluid-management to wean from mechanical ventilation.8,9,12, -14 Common causes of extubation failure are new (due to infection) or ongoing inflammation, fluid overload, and impaired cardiac function due to ischemia or congestive heart failure.12,15, -17 These processes are dynamic and biomarkers reflecting these processes are subjected to biological variation. This evidence concerns the gene NPPB and infection.