Why flush peripheral intravenous cannulae used for intermittent intravenous injection?

We aimed to investigate whether regular flushing of peripheral intravenous cannulae used for intermittent injections with heparin-saline, in a unit for acute medicine for the elderly, reduced the incidence of complications necessitating cannula removal. We wanted to see if this could also prolong the time that cannulae may remain functional in situ. In a prospective, open study, 50 consecutively inserted cannulae were flushed regularly and a subsequent 50 consecutive cannulae were not flushed. The incidence of complications necessitating removal was not significantly different between the two groups (18% flushed, 22% unflushed). Overall, only 5% of cannulae were removed because of blockage. Heparin-saline flushes did not significantly increase the time that cannulae remained in situ. Antibiotic use was found to be associated with an increased rate of complications necessitating cannula removal. We found no significant advantage in heparin-saline flushing of peripheral intravenous cannulae used for intermittent administration of medications.