Inaccuracy of fluid container volume markings

Abstract

During an emergency neurosurgical procedure, a patient was given 250 ml mannitol 20%. The volume was estimated visually according to the gradations marked on either side of the 500-ml fluid bag, but there was a suspicion that these did not correlate closely with the volume infused. Postoperatively, the residual volume of mannitol was drawn off using a 50-ml syringe, and found to measure 270 ml. On withdrawing 100-ml aliquots from suspended bags of mannitol 20% and saline 0.9% (both Baxter, Thetford, UK) using a 50-ml syringe (BD Plastipak, BD, Oxford, UK), sequential meniscus levels were found to differ considerably from their isovolumetric bag markings (Figs 7a and 7b). It is clear that the fluid bag gradations do not represent the remaining volume. As mis-information is less desirable than no information, I suggest these markings are removed. An alternative would of course be accurate placement of the same.