Danish study links mechanical restraint to increased blood clot risk
Research spanning 22 years suggests that mechanical restraints increase the risk of venous thromboembolism compared to chemical restraints.
Danish study links mechanical restraint to increased blood clot risk
A comprehensive observational study from Denmark has identified a correlation between the use of mechanical restraint in psychiatric hospitals and a slight increase in the short-term risk of venous thromboembolism (VTE), the medical term for blood clots. Published in The BMJ, the research analyzed data from all Danish psychiatric hospitals over a 22-year period from 2000 to 2022.
Mechanical restraint involves the use of devices such as ankle straps, wrist straps, or waist belts to physically restrict a patient's movement. While these measures are often utilized as emergency interventions to prevent imminent harm to patients or staff, the study found they can contribute to the formation of life-threatening clots.
Quantifying the Risk
The research cohort consisted of 24,423 adults aged 18 and older who underwent either chemical restraint — the use of sedative pharmacological agents — or mechanical restraint. A subset of 10,208 individuals experienced mechanical restraint, with males making up 68% of that group and a median age of 40 years.
The findings revealed that within a 30-day window following the intervention, the incidence rate of VTE was approximately double for those in mechanical restraints compared to those given chemical restraints. The specific rates were:
| Restraint Type | VTE Incidence Rate (per 1,000 patients) |
|---|---|
| Mechanical Restraint | 3.5 |
| Chemical Restraint | 1.7 |
Despite the relative increase, the absolute risk remains low. The authors calculated that for every 548 patients subjected to mechanical restraint, there is one excess VTE event, provided a direct causal relationship exists.
Pathophysiological Mechanisms
The immobilization caused by belts and straps reduces venous blood flow, which can foster the formation of clots in the deep veins, typically located in the legs. These clots may subsequently embolize to critical organs, such as the lungs. The study notes that these biological changes align with Virchow’s triad, a framework for thrombogenesis involving endothelial dysfunction, hypercoagulability, and impaired venous return.
Psychiatric inpatients may already possess a baseline predisposition to thrombotic events due to obesity, smoking, chronic inactivity, and coexisting physical health comorbidities. Furthermore, external compression from straps may compound venous stasis.
Impact on Adolescents and Vulnerable Groups
While the Danish study focused on adults, other reports highlight risks in younger populations. In one reported case from Germany, a 17-year-old female patient with borderline personality disorder developed a massive pulmonary embolism after 12 hours in five-point restraints. This patient had several risk factors, including a body mass index greater than 30 kg/m2, smoking, and the use of quetiapine.
Medical literature suggests that DVT risks in adolescent psychiatric patients are often unrecognized. Because acutely ill psychiatric patients may have impaired communication abilities, early symptoms like leg pain are difficult to detect, and respiratory distress may be misinterpreted as psychosis or anxiety.
Determinants of Restraint Use
Separate research indicates that the application and duration of restraints vary by patient characteristics and environment. A descriptive study in Barcelona, Spain, conducted in 2018, found that 25.6% of patients in acute psychiatric units required mechanical restraint, with a median duration of 16.4 hours.
That study identified two primary factors associated with a higher risk of restraint: a diagnosis of psychotic disorder and the presence of a language barrier. male sex was the only variable significantly associated with a longer duration of restraint.
In China, a retrospective analysis of patients in open psychiatric wards between 2016 and 2021 found that 36.5% of restrained patients experienced multiple episodes. These patients typically had a prolonged hospital stay and higher serum creatine kinase levels at admission compared to those who had a single episode.
Clinical Recommendations and Next Steps
Because the Danish study was observational, causality cannot be definitively established, and some factors, such as body mass index and smoking status, were not captured in the dataset. However, the results suggest a need for refined care protocols.
The authors and accompanying editorials suggest several risk-mitigation strategies:
- Implementing pharmacological thromboprophylaxis in select high-risk cases.
- Enhancing staff training in de-escalation techniques to reduce reliance on restraints.
- Utilizing comprehensive risk assessment protocols, such as the Padua or Caprini models, though these are currently designed for medical and surgical patients rather than psychiatric ones.
- Vigilant monitoring for early signs of VTE.
Future research is sought to establish more precise absolute and relative risks through prospective designs and larger cohorts. Clinicians are urged to balance the necessity of restraints as safety tools against their potential to cause vascular morbidity.
