Intensive care utilization and outcomes after high-risk surgery in Scotland: a population-based cohort study

Background. The optimal perioperative use of intensive care unit (ICU) resources is not yet defined. We sought to determine the effect of ICU admission on perioperative (30 day) and long-term mortality. Methods. This was an observational study of all surgical patients in Scotland during 2005-7 followed up until 2012. Patient, operative, and care process factors were extracted. The primary outcome was perioperative mortality; secondary outcomes were 1 and 4 yr mortality. Multivariable regression was used to construct a risk prediction model to allow standard-risk and high-risk groups to be defined based on deciles of predicted perioperative mortality risk, and to determine the effect of ICU admission (direct from theatre; indirect after initial care on ward; no ICU admission) on outcome adjusted for confounders. Results. There were 572 598 patients included. The risk model performed well (c-index 0.92). Perioperative mortality occurred in 1125 (0.2%) in the standard-risk group (n = 510 979) and in 3636 (6.4%) in the high-risk group (n = 56 785). Patients with no ICU admission within 7 days of surgery had the lowest perioperative mortality (whole cohort 0.7%; high-risk cohort 5.3%). Indirect ICU admission was associated with a higher risk of perioperative mortality when compared with direct admission for the whole cohort (20.9 vs 12.1%; adjusted odds ratio 2.39, 95% confidence interval 2.01-2.84; P<0.01) and for high-risk patients (26.2 vs 17.8%; adjusted odds ratio 1.64, 95% confidence interval 1.37-1.96; P<0.01). Compared with direct ICU admission, indirectly admitted patients had higher severity of illness on admission, required more organ support, and had an increased duration of ICU stay. Conclusions. Indirect ICU admission was associated with increased mortality and increased requirement for organ support. Trial registration. UKCRN registry no. 15761.