Thursday May 20, 2010
Insulin in TPN - a bad idea?

Adding insulin to the TPN bag itself - this is chemically compatible and has been done for years. The debate comes in when we start to discuss how much actually makes it to the patient. Study results have been variable. The amount of insulin adsorbed (i.e. stuck to) the glass bottle, plastic bag, or plastic IV tubing can be as high as 80%. Some factors affecting this adsorption include type of container, solution, administration set, previous exposure of tubing to insulin, etc. The binding appears to happen within the first 30-60 minutes. Some in vitro studies have been conducted to assess the effect of "priming" the line with a dilute insulin solution. Priming the tubing with a dilute solution or running through and wasting the first aliquot of the insulin-containing solution increases delivery of insulin from 38% to 85% at 2 hours. Once the priming is done, the amount of insulin delivered remains pretty constant.

Other options - although costly and controversial, adding albumin in small concentrations may help deliver higher amount of insulin by decreasing the amount of insulin available to bind to the container and/or tubing. Adding 0.3 gram/100ml seems to decrease adsorption. Flushing the tubing with the insulin-containing solution two hours before administration seems to saturate the binding sites and minimizes further adsorption. Giving the insulin as a separate IV infusion is another delivery option but adsorption should be considered in this setup as well.