Association between posttraumatic hypothermia onset and in-hospital mortality among patients with severe trauma: a retrospective cohort study

Abstract Hypothermia following severe trauma is a well-established predictor of poor outcomes; however, most previous studies have examined hypothermia only during the initial phase of trauma care. This study aimed to investigate the association between hypothermia occurring before or after intensive care unit (ICU) admission and in-hospital mortality among patients with severe trauma. We conducted a retrospective cohort study using data from the Japanese nationwide trauma registry, spanning from 2004 to 2022. The study was conducted at 302 emergency medical centers across Japan. Inclusion criteria were patients aged ≥ 16 years with blunt or penetrating trauma, Injury Severity Score ≥ 16, and ICU admission. Patients were classified into four body temperature groups: normothermia (no hypothermia), initial hypothermia (hypothermia at emergency department), persisting hypothermia (hypothermia at emergency department and ICU), and late-onset hypothermia (hypothermia after ICU admission). The primary outcome was in-hospital mortality. Among 89,774 patients, (median [interquartile range] age, 63 [43–76] years; 63,216 [70.5%] men), 61,658 were in the normothermia group, 27,564 in the initial hypothermia group, 466 in the persisting hypothermia group, and 86 in the late-onset hypothermia group. Overall mortality was 12,111/87,790 (13.8%). Compared with normothermia, initial, persisting, and late-onset hypothermia were independently associated with in-hospital mortality. Among the three hypothermia groups, the odds ratios [ORs] for hypothermia occurring after ICU admission (persisting and late-onset hypothermia) were higher than those for initial hypothermia (OR 1.15; 95% confidence interval [CI], 1.09–1.21; OR 1.61; 95% CI 1.24–2.09; and OR 2.46; 95% CI 1.40–4.33, respectively). In this nationwide cohort study, distinct patterns of hypothermia, particularly those occurring after ICU admission, were associated with increased in-hospital mortality among patients with severe trauma. Strategies to maintain normothermia throughout trauma care warrant further investigation.