What We’re Reading: Pump Position Greatly Affects Insulin Delivery

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Although insulin pumps can be a convenient and precise method for managing diabetes, something so simple as where the pump is in relation to the infusion site can greatly affect how accurately the pump delivers insulin.

In a clinical study at the Sansum Diabetes Research Institute and the University of California, Santa Barbara, researchers compared the positioning of conventional insulin pumps to that of tubing-free pumps. The most pronounced effects of pump positioning were seen at low basal infusion rates. When the conventional pumps were extended to the full length of their tubing above or below their infusion sites, the results were drastic: at the 1 unit per hour rate, pumps below the infusion sites delivered only 74.5% of the expected dose. When the pumps were above the infusion sites, they delivered 123.3% of the expected dose. At the 1.5 unit per hour rate, pump delivery was 86.7% below the infusion site and 117.0% above the infusion site. In comparison, the tubeless system was able to maintain accuracy within 2% to 3% of the expected delivery in the same positions and at the same basal delivery levels.

Researchers attribute this effect to hydrostatic pressure, or how the weight of the fluid in the tubing exerts pressure on the fluid below it, which results in less accurate delivery than if the pump and tubing were perfectly level to the infusion site. Given that insulin pumps can often move during normal daily use, it may be valuable to keep these fluctuations in mind to ensure most accurate management. These unintended fluctuations “can increase blood glucose variability, a risk factor for the progression of complications of diabetes,” according to Dr. Howard Zisser, the study’s lead investigator. Further, he adds, “these findings may be particularly important for pediatric patients, who often use insulin pumps at low basal rates.”

This blog entry was written by Web Intern Helen Zhu.

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