Slow versus fast subcutaneous heparin injections for prevention of bruising and site pain intensity.

Background: Heparin is an anticoagulant medication that is usually injected subcutaneously. Subcutaneous administration of heparin may result in complications such as bruising, haematoma, and pain at the injection site. One of the factors that may affect pain, haematoma, and bruising is injection speed. Several studies have been carried out to determine if speed of injection affects the amount of pain and bruising where the injection is given; however, the results of these studies have differed, and study authors have not reached a clear final conclusion. This is the second update of a review first published in 2014.

Objectives: To assess the effects of duration (speed) of subcutaneous heparin injection on pain and bruising at the injection site in people admitted to hospitals or clinics who require treatment with unfractionated heparin (UFH) or low molecular weight heparin (LMWH). We also looked at haematoma at the injection site.

Search methods: The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL databases and the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 22 June 2020. We undertook reference checking of included studies to identify additional studies.

Selection criteria: We searched for randomised controlled trials (RCTs) comparing the effects of different durations of subcutaneous injection of heparin on pain, bruising, and haematoma at the injection site.

Data collection and analysis: For this update, two review authors independently selected studies and extracted data via Covidence software and assessed methodological quality using Cochrane's risk of bias tool. The primary outcomes of interest were pain intensity at injection site and size and incidence of bruising. The secondary outcomes of interest were size and incidence of haematoma at injection site. We calculated the odds ratio (OR), mean difference (MD), or standardised mean difference (SMD) with corresponding 95% confidence intervals (CIs). We assessed the certainty of the evidence using GRADE criteria.

Main results: We identified one new study for this update, resulting in a total of five included studies with 503 participants who received subcutaneous injections of LMWH into the abdomen. Given the nature of the intervention, it was not possible to blind participants and caregivers (personnel) in any of the included studies. Two studies described blinding of outcome assessors. Overall, the methodological quality of included studies was moderate. 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; meta-analysis showed no evidence of a difference in site pain intensity immediately after slow injection when compared to fast injection (MD -1.52, 95% CI -3.56 to 0.53; 140 participants; low-certainty evidence). Meta-analysis of three studies indicated that site pain intensity may be slightly reduced 48 hours after the slow heparin injection compared to fast injection (MD -1.60, 95% CI -2.69 to -0.51; 103 participants; low-certainty evidence). Five studies assessed bruise size at 48 hours, and two studies assessed bruise size at 60 hours. Meta-analysis showed there may be a reduction in bruise size 48 hours (SMD -0.54, 95% CI -1.05 to -0.02; 503 participants; 5 studies; very low-certainty evidence) and 60 hours (SMD -0.49, 95% CI -0.93 to -0.06; 84 participants; 2 studies; low-certainty evidence) after slow injection compared to fast injection. There was no evidence of a difference in bruise size 72 hours after slow injection compared to fast injection (SMD -0.27, 95% CI -0.61 to 0.06; 140 participants; 2 studies; low-certainty evidence). Three studies evaluated incidence of bruising and showed there may be a reduction in bruise incidence 48 hours (OR 0.39, 95% CI 0.26 to 0.60; 444 participants; low-certainty evidence) and 60 hours (OR 0.25, 95% CI 0.10 to 0.65; 84 participants; 2 studies; low-certainty evidence) after slow injection compared to fast injection. We downgraded the certainty of the evidence due to risk of bias concerns, imprecision, and inconsistency. None of the included studies measured size or incidence of haematoma.

Authors' conclusions: Administering medication safely and enhancing patient comfort are the main aims of clinical nurses. In this review, we identified five RCTs that evaluated the effect of subcutaneous heparin injection duration on pain intensity, bruise size and incidence. We found that pain may be slightly reduced 48 hours after slow injection. Similarly, there may be a reduction in bruise size and incidence after slow injection compared to fast injection 48 and 60 hours postinjection. We downgraded the certainty of the evidence for all outcomes to low or very low due to risk of bias concerns, imprecision, and inconsistency. Accordingly, new trials with a more robust design, more participants, and a focus on different injection speeds will be useful in strengthening the certainty of the available evidence.