Why must plastic containers of the Baxter Healthcare Ltd product Sodium Chloride 0.18% and Glucose 4% Solution for Infusion BP not be connected in series?

Plastic containers of the Baxter Healthcare Ltd product Sodium Chloride 0.18% and Glucose 4% Solution for Infusion BP must not be connected in series because residual air drawn from the primary container before fluid administration from the secondary container is completed could cause air embolism.