Although insertion of an intravenous cannula is technically easy and usually causes the patient only mild distress, occasionally the procedure can be difficult, requiring significant professional time and resulting in patient discomfort. Patient distress and the degree of difficulty rise with repeated attempts because of the activation of the sympathetic nervous system; thus, success at the first attempt is important. Lenhardt and colleagues studied the effect of warming the hand and lower arm on ease of venous cannulation.

They studied the effect of a warming mitt designed to warm the hand and lower arm on 100 neurosurgical and 40 chemotherapy patients. The mitt wrapped around the limb, leaving one side open for cannula insertion. Patients were randomly assigned to active warming (mitt warmed to 52°C [125.6°F]) or passive warming (mitt not heated). In the neurosurgical patient group, the mitt was applied for 15 minutes before a nurse anesthetist, who was blinded to the patient assignment and the study hypothesis, attempted to insert an 18-gauge cannula into a vein on the back of the left hand. In the chemotherapy patient group, the mitt was applied for 10 minutes, and the assignment to active or passive warming was alternated at consecutive visits. Success in cannulation was ascertained by administration of a crystalloid solution without any signs of infiltration. Time to completion of cannula insertion was measured, and patients were asked about discomfort from the mitt.

In the neurosurgical patient group, the success rate in cannula insertion was 94 percent when active warming was used, compared with a 72 percent rate with passive warming. In addition to this significant difference, cannula insertion times were reduced by one half (36 versus 62 seconds). No discomfort was reported, and no skin irritation was observed. Similar results were obtained in the chemotherapy patients, who acted as their own control subjects. In this group, the success rate changed from 73 to 95 percent with warming, and the time to successful insertion was reduced by 20 seconds.

The authors conclude that simple warming of the limb improves success rates in inserting cannulas and reduces the time to complete the procedure without any obvious adverse effects.