The quality of evidence is downgraded by inconsistency (statistical heterogeneity), and by imprecise results (few patients and wide confidence intervals).
A Cochrane review [Abstract] 1 included 5 studies with a total of 503 subjects who received subcutaneous injections of low molecular weight heparin (LMWH) into the abdomen. The duration of the fast injection was 10 seconds and the duration of the slow injection was 30 seconds in all included studies.
Four studies reported site pain intensity after each injection at different time points. Two studies assessed site pain intensity immediately after each injection, and meta-analysis (n=140) showed no clear difference in site pain intensity immediately post slow injection when compared to fast injection (MD -1.52, 95% CI -3.56 to 0.53, statistical heterogeneity I2 =73%). In contrast, meta-analysis of 3 studies (n=103) showed that 48 hours after the heparin injection, slow injection was associated with less pain intensity compared to fast injection (MD -1.60, 95% CI -2.69 to -0.51, statistical heterogeneity I2 =50%).
Five studies assessed bruise size at 48 hours, and 2 studies at 60 hours after each injection. Meta-analysis showed a reduction in bruise size after slow injection compared to fast injection at 48 hours (SMD -0.54, 95% CI -1.05 to -0.02; statistical heterogeneity I2 =81%; 5 studies, n=503) and at 60 hours (SMD −0.49, 95% CI −0.93 to −0.06; 2 studies, n=84). There was no difference in bruise size at 72 hours (SMD −0.27, 95% CI −0.61 to 0.06; 2 studies, n=140). Three was a reduction in bruise incidence 48 hours (OR 0.39, 95% CI 0.26 to 0.60; 3 studies, n=444) and 60 hours (OR 0.25, 95% CI 0.10 to 0.65; 2 studies, n=84) after slow injection compared to fast injection. None of the included studies measured size or incidence of haematoma.
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