OBJECTIVE: To examine the short term risk of venous thromboembolism (VTE) after mechanical restraint among inpatients at psychiatric hospitals.

DESIGN: Population based cohort and self-controlled case series study.

SETTING: Psychiatric hospitals in Denmark, from 1 January 2000 to 30 September 2022.

PARTICIPANTS: 24 423 inpatients (aged =18 years) exposed to mechanical or chemical restraint at psychiatric hospitals. The self-controlled case series included 1285 patients with incident VTE occurring during or shortly after a stay in a psychiatric hospital.

MAIN OUTCOME MEASURES: Cumulative incidence of VTE, weighted by propensity, and risk ratios or differences (including number needed to harm) in the cohort study. Incidence rate ratios in predefined risk periods after restraint were used in the self-controlled case series.

RESULTS: At 30 days after restraint, the cumulative incidence of VTE was 3.5 per 1000 patients (95% confidence interval (CI) 2.5 to 4.7) in the mechanical restraint group and 1.7 per 1000 patients (1.0 to 2.6) in the chemical restraint group, corresponding to a risk ratio of 2.07 (1.25 to 3.71), a risk difference of 1.8 per 1000 patients (0.5 to 3.2), and a number needed to harm of 548 (311 to 1912). In the self-controlled case series, the incidence rate ratio was 4.49 (3.09 to 6.54) in the 14 days after mechanical restraint compared with baseline periods.

CONCLUSIONS: Mechanical restraint was associated with an elevated risk of VTE. Although the absolute risk was low, these findings highlight the importance of preventive strategies to reduce the risk of VTE in patients exposed to mechanical restraint.

Psychiatry rater

This interesting paper shows that MR in psychiatric inpatients is associated with roughly a twofold higher 30-day risk of venous thromboembolism compared with chemical restraint, and about a fourfold increase in the first 14 days. Although the absolute risk is low, the data are methodologically robust and support systematic consideration of VTE prevention and tailoring thromboprophylaxis around episodes of MR. For most front-line psychiatrists, this is likely not yet familiar, but directly actionable for inpatient practice and guideline discussions.

Psychiatry rater

Confounding by indication and standing oral medications could not be neglected in this retrospective analysis.