How Does Intra-operative Hypothermia Affect Peri-operative Outcomes in Hip Fracture Surgery?

AIMS AND BACKGROUND: Intra-operative hypothermia is a potentially modifiable peri-operative risk factor of uncertain clinical significance in hip fracture surgery. This study examines whether intra-operative hypothermia is associated with adverse peri-operative and mortality outcomes, and whether the nature of that association differs when hypothermia is quantified using a conventional binary threshold (core temperature <36.0 °C) vs a continuous cumulative burden metric [area under the curve (AUC) below 36.0 °C, expressed as °C·minutes].

MATERIALS AND METHODS: We conducted a retrospective cohort study of patients aged 55-89 years undergoing operative fixation or arthroplasty for hip fracture at a Level I Trauma Centre (2018-2025). Patients were classified by binary intra-operative hypothermia status, with 102 hypothermic patients and 102 randomly selected normothermic controls. Continuous intra-operative core temperature data were used to calculate hypothermia burden (AUC < 36.0 °C, °C·minutes). Outcomes included intra-operative blood transfusion (primary), estimated blood loss (EBL), surgical site infection (SSI), length of stay (LOS), 30 days readmission and mortality, and 1 year mortality. Associations were evaluated using logistic and linear regression models.

RESULTS: Among 204 patients (mean age 73.4 ± 8.7 years; 58.8% female), binary hypothermia was associated with increased intra-operative transfusion [17.6 vs 5.9%; odds ratio (OR) 3.43, 95% confidence interval (CI): 1.30-9.04; p = 0.013]. Although transfused patients exhibited higher mean hypothermia burden (31.6 vs 17.5 °C·minutes), continuous modelling demonstrated no statistically significant association between hypothermia burden and transfusion (OR 1.08 per 10 °C·minutes; p = 0.097) or any secondary outcome. Hypothermia burden correlated modestly with longer operative duration and lower pre-operative haemoglobin but not with clinical endpoints.

CONCLUSIONS: An association between binary hypothermia and intra-operative transfusion was observed, but this association was not robust when hypothermia was quantified as a continuous cumulative burden. The relationship between intra-operative hypothermia and transfusion risk in hip fracture surgery therefore remains uncertain, and may reflect operative complexity or confounding rather than a direct causal effect. Studies with larger event numbers and prospective design are needed to clarify this relationship.

CLINICAL SIGNIFICANCE: These findings highlight a nuanced relationship between intra-operative hypothermia and transfusion risk in hip fracture surgery. The divergence between binary and continuous analyses may reflect the non-linear nature of thermal effects, limited statistical power for rare events, or confounding by operative complexity. Hypothermia remains an important peri-operative consideration for trauma surgeons and anaesthesiologists, but whether it acts as an independent modifiable driver of adverse outcomes or primarily as a marker of surgical complexity warrants further investigation. Continuous AUC-based quantification offers an alternative metric of hypothermia exposure and may improve cross-study comparability in future research.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.