Objective: To investigate the relationship between Therapeutic Intervention Scoring System (TISS), length of ICU stay and severity of illness.
Design: Prospective study lasting 1 year.
Setting: Two 4-bed surgical-medical ICU.
Patients: All consecutively ICU admitted patients.
Methods: Every day TISS of each patient during the last 24 h was computed. Age, sex, type of admission, SAPS II and APACHE II, length of ICU stay and hospital outcome were recorded. Out of 446 admissions, 14 were excluded since the ICU stay was < 16 h. Severity of illness was considered in 405 of the remaining 432; total TISS of readmitted patients resulted from all ICU admissions during the same hospital stay.
Results: Median TISS on day 1 was 24 (range 3-58, CI 95% 0.57) and median TISS +/- CI 95% during the first 10 ICU days ranged from 20 to 26. Spearman's correlation coefficient between TISS total and length of stay in ICU was 0.962. Total TISS increased with risk of hospital death predicted by both SAPS II and APACHE II. Total TISS of non surviving patients was significantly (p < 0.001) higher than that of the surviving up to probability of death of 20%.
Conclusions: Intensity of treatment is essentially steady and total TISS is well related to length of ICU stay. Total TISS increases with increasing risk of hospital death predicted by SAPS II and APACHE II, but it is high especially in non surviving patients with low probability of hospital mortality at the admission.