Figure 4. Identifying Intracranial Pressure (ICP) Thresholds as Robust Factors Associated With Outcome.

Elastic net regression was used to determine the most robust threshold associated with outcome. Elastic net regression plots show a single ICP threshold (19 mm Hg) performed better than all other thresholds tested in an analysis of all patients, with the regression coefficient for the 19 mm Hg threshold remaining most resistant to shrinkage from ridge regression penalties of 1.0 (A, selected model) and 0.1 (B, optimal model). C, To test how this single threshold compared with other factors, an optimal scaling regression model was used and revealed that the 19 mm Hg ICP threshold performs as well as age and injury type in a predictive model of Glasgow Outcome Scale outcome at discharge. The threshold of 19 mm Hg was robust because it was also strongly associated with outcome when patients with traumatic brain injury, and those who underwent a craniectomy were analyzed with separate elastic net regressions (not shown).