Care is required when adding heparin sodium to infusion solutions,especially in flexible containers.When heparin sodium was added to a flexible PVC container of sodium chloride 0.9% hanging in the use position,pooling of the heparin resulted;97% of the heparin was delivered in the first 30% of the solution.Repeated inversion and agitation of the containers to effect thorough mixing eliminates this pooling(and the danger of overdosage),yielding an even distribution and a constant delivery concentration