Occurrence and extent of bruising according to duration of administration of subcutaneous Low-Molecular-Weight Heparin: a quasi-experimental case-crossover study

Abstract Background: Several authors have documented the role of Low-Molecular-Weight Heparin injection techniques in bruising. However, few researchers have measured the influence of injection duration on the occurrence and extent of bruising. Purpose: To evaluate the influence of different durations of subcutaneous heparin injection on the occurrence and extent of bruising. Methods: A quasi-experimental case-crossover study design was adopted in 2010. A consecutive serie of patients admitted to two orthopaedic units in a large (600 beds) teaching hospital located in northern Italy were eligible for enrolment. Injections were administered following a standard procedure: the manipulated variable was the duration of the injection, 10-seconds (Treatment ‘A’) and 30-seconds (Treatment ‘B’). The evaluation of bruise occurrence and extension performed after 48 hours and data analysis were conducted in a blinded fashion. Results: One hundred and fifty patients receiving their first and second subcutaneous heparin injections (300 injections) were enrolled. Eighty-seven bruises were observed out of 300 injections (29%): 57 out of 150 (38%) after subcutaneous Low-Molecular-Weight Heparin injections lasting 10 seconds, and 30 out of 150 (20%) after injections lasting 30 seconds [RR 1.50, CI95% 1.21 to 1.86; P = 0.00]. Of the 87 bruises that occurred, 69 (79.3%) were small (2–5 mm) and 18 (20.6%) were large (> 5 mm) with no difference in size between 10-second injections and 30-seconds injections (RR 0.91, CI 95% 0.39 to 2.12, P = 0.83). Conclusions: Low-Molecular-Weight Heparin injection should be administered at 30 seconds. Clinical Implications: There is a need to reflect on the feasibility of such a practice because injecting Low-Molecular-Weight Heparin at 30 seconds requires accuracy, a steady hand, the absence of tremor, a calm environment, and the ability to administer an infinitesimally small amount of liquid (e.g., 0.4 ml) per second. Key words: Low-Molecular-Weight Heparin, injection, duration, bruise, administration, case-crossover, quasi-experimental