How should a subarachnoid hemorrhage grading scale be determined? A combinatorial approach based solely on the Glasgow Coma Scale

Object. The purpose of this study was to present a combinatorial approach u sed to develop a subarachnoid hemorrhage (SAH) grading scale based on the p atient's preoperative Glasgow Coma Scale (GCS) score. Methods. There are 4094 different combinations that can be used to compress the 13 scores of the CCS into two to 12 grades. Break points, the position s in the scale in which two adjacent scores connote a significantly differe nt out; come, are obtained by a direct comparison of the GCS and the Glasgo w Outcome Scale (GOS). Guided by the break points, the number of combinatio ns to be considered can be limited. All possible combinations are statistic ally analyzed with respect to intergrade differences in outcome. Single com binations, with the maximum number of grades having maximum intergrade outc ome differences for each corresponding set of adjacent grades, must be sele cted. The authors verified the validity of this combinatorial approach by r etrospectively analyzing 1398 consecutive patients with aneurysmal SAH who underwent surgery within 7 days of the last hemorrhage episode. The patient s' GCS scores were assessed just before surgery and their GOS scores were e stimated 6 months post-SAM. The combinatorial approach yields only one acce ptable grading scale: I (GCS Score 15); II (GCS Scores 11-14); III (GCS Sco res 8-10); IV (GCS Scores 4-7); and V (GCS Score 3). Conclusions. The combinatorial approach, guided by the break points, is so simple and systematic that it can be used again in the future when revision of the grading scale becomes necessary after development of new and effect ive treatment modalities that improve patients' overall outcome.