Risk factors and outcomes of unplanned PICU postoperative admissions: a nested case-control study.BACKGROUND:  Although unplanned postoperative admission to PICUs (unplanned intensive care admission [UIA]) is uncommon, it might be associated with increased costs, morbidity, and mortality. However, detailed knowledge of risk factors and outcomes after UIA in children is still lacking. OBJECTIVES:  To determine prevalence, risk factors, and outcomes of UIA patients compared with non-UIA patients. DESIGN:  Case-control study. SETTING:  A tertiary university-affiliated hospital. PATIENTS:  All postoperative children admitted to the PICU were monitored for UIA. About 28 cases and 88 controls were included. INTERVENTIONS:  none. MEASUREMENTS AND MAIN RESULTS:  The overall prevalence of UIA was 2.6%. About 28 patients (24.1%) of 116 had unplanned admission. Multiple logistic regression revealed that factors predicting UIA were airway abnormality (odds ratio 16.2, 95% confidence interval 2.65-99.6), anesthetic factors (odds ratio 5.8, 95% confidence interval 1.06-32.2), and hypoxia intraoperative (odds ratio 7.4, 95% confidence interval 1.21-46.24). Procedures on abdomen, emergency surgery, combined anesthesia, and occurrence of intraoperative adverse events were also risk factors for an UIA. Patients with UIA had longer duration of mechanical ventilation than non-UIA patients (4.5 vs. 2 days, p = 0.01), but there were no differences in length of PICU and hospital stays. Preventable adverse events were detected in 25% of UIA children. CONCLUSIONS:  Airway abnormality, anesthetic factors, and hypoxia intraoperative were risk factors associated with UIA. Although preventable events contribute significantly to unplanned PICU admissions, they constitute a room of opportunity in quality improvement programs.