Unproven clinical evidence in mechanical ventilation. 
To describe the management principles that have not been verified or tested but nonetheless successfully guide the logic of everyday practice at the bedside.  The importance of physiologic data integration, timing, and careful patient selection has been emphasized by reanalyses of recent clinical trials that individually have led to controversial conclusions and recommendations.  The practitioner of intensive care often has no choice but to make difficult decisions and to select a course of treatment that remains unguided by specific, scenario-specific evidence from observational studies and clinical trials.  Experience gathered over many prior encounters combined with solid physiologic understanding helps to develop guiding principles and unproven rules of management that serve well in confronting complex, ever changing problems of acute illness.  Although some element of trial and error is unavoidable, careful monitoring, short loop feedback, and mid-course corrections render many logic-driven and experience-driven decisions relatively safe to implement and often effective in an uncertain, high-stakes environment.