Factors affecting delivery of drug through extension tubing.

A theoretical laminar flow model of drug delivery via extension sets (1250 mm long) was developed and tested experimentally by tracer studies. Despite discrepancies between theory and experiment (which are discussed in the text), when the infusion was allowed to run normally it was confirmed that there was a hyperbolic relationship between the flow rate of the infusion and the time of delivery of a given percentage of the injected drug. Even with the drip chamber (15 drops ml-1) running as a continuous stream, it can take up to almost 3 min for 90% of a 1-ml or 3-ml injection to enter the patient's vein. An alternative method of flushing the drug in with a syringe of saline produced a non-laminar flow regimen which was more efficient in terms of both the volume and the time required for a given percentage drug delivery.