Restoring and maintaining normoglycemia by intensified insulin therapy in critically ill patients
is a matter of ongoing debate since the risk of hypoglycemia may outweigh positive effects on morbidity and mortality. In
this context, adsorption of insulin to different catheter materials may contribute to instability of glucose control. We
studied the adsorption of insulin to different tubing materials in vitro and the effects on glycemic control in vivo.
Materials and Methods:
In vitro experiments: A syringe pump was filled with 50 IU insulin diluted to 50 ml saline. A
flow of 2 ml/h was perfused through polyethylene (PET) or polyurethane (PUR) tubing. Insulin concentrations were
measured at the end of the tube for 24 hours using Bradford´s protein assay. In vivo study: In a randomized doubleblinded
cross-over design, 10 intensive care patients received insulin via PET and PUR tubes for 24 hours each, targeting
blood glucose levels of 80-150 mg/dl. We measured blood glucose levels, the insulin dose required to maintain target
levels, and serum insulin and C-peptide levels.
In vitro experiments: After the start of the insulin infusion, only 20% (median, IQR 20-27) (PET) and 22% (IQR
16-27) (PUR) of the prepared insulin concentration were measured at the end of the 2 meter tubing. Using PET, after one
hour infusion the concentration increased to 34% (IQR 29-36) and did not increase significantly during the next 24 hours
(39% (IQR 39-40)). Using PUR, higher concentrations were detected than for PET at every measurement from 1 hour
(82% (IQR 70-86)) to 24 hours (79% (IQR 64-87)). In vivo study: Glycemic control was effective and not different
between groups. Significantly higher volumes of insulin solution had to be infused with PET compared to PUR (median
PET 70.0 (IQR 56-82) ml vs. PUR 42 (IQR 31-63) ml; p=0.0015). Serum insulin concentrations did not decrease
significantly one hour after changing to PET or PUR tubing.
Polyurethane tubing systems allow application of insulin with significantly lower adsorption rates than
polyethylene tubing systems. As a consequence, less insulin solution has to be infused to patients for effective blood
glucose control. Tubing material of the insulin infusion may be crucial for safe and effective glycemic control in critically