Factors predicting prolonged mechanical ventilation in critically injured patients: Introducing a simplified quantitative risk score

Our objective was to identify a set of readily available and easily obtainable parameters that would predict prolonged mechanical ventilation in the critically injured patient. A surgical intensive care unit of an academic Level 1 trauma center. Prospectively collected data were retrospectively analyzed on all critically injured patients receiving mechanical ventilation for more than 2 days between January and December 1994. Prolonged mechanical ventilation (PMV) was defined as the need for mechanical ventilatory support for more than 7 days. One hundred and nineteen patients entered the final analysis. Of these, 63 remained on the ventilator for 7 days or less and 56 for more than 7 days. The Injury Severity Score (ISS), partial arterial oxygen tension (PaO₂)/inspired fraction of oxygen (FiO₂), net fluid balance, and use of Swan-Ganz were significantly different between the two groups when calculated 48 hours after surgical intensive care unit admission. Furthermore, we dichotomized these four variables across cutpoints that were determined by statistical analysis (ISS more or less than 20, PaO₂/FiO₂ more or less than 250, fluid retention more or less than 2000 cc, and presence or absence of Swan-Ganz). Again, significantly more patients required PMV if they had any one of the following: Swan-Ganz, ISS more than 20, PaO₂/FiO₂ less than 250, or fluid retention more than 2000 cc at 48 hours. An easily calculated five-point risk score (0-4 points) for predicting PMV based on these four variables was developed. Among the 35 patients at the extremes of the risk score (0 or 4 points), 33 (94.3%) were correctly prognosticated as to their needs for PMV. The need for an easily calculated score, which is derived from readily available parameters and can reliably identify patients with prolonged needs for ventilatory support, is obvious in the trauma setting. We describe a five-point risk score by which we can predict the need for PMV early in the course of the disease. Resource utilization and personnel allocation issues, as well as important therapeutic procedures, can be planned based on this score.