Deadspace: A Potential Error in Concentration of Medication during Dilutional Process in Neonates

Objective: To evaluate the volume of deadspace (DS) and degree of errors in concentration of medications during medication dilution with needle removable syringe (NRS) compared to needle nonremovable syringe (NNRS). Material and Method: 300 syringes were tested and divided into 3 groups as follows: The first group was 100 syringes of needle removable insulin 1 ml syringe (NRIS) with a 27 gauge needle (Terumo®), the second group was 100 syringes of NRIS with a 27 gauge needle (Nipro®) and third group 3 was 100 syringes of needle non removable insulin syringe (NNRIS) with a 27 gauge needle (Terumo®). All syringes with needle sets (without needle cover) were weighed with a Mettler electronic balance. Volume of DS was measured and calculated using a standard method. 10 syringes of each group were randomly selected to test for degree of errors in concentration of medications during the dilutional process using standard insulin (310 micro unit per ml) as a medication for dilution. All specimens were collected by ejecting all diluents into collecting tubes and insulin concentrations were measured using radioimmunoassay technique (insulin-CT biointernational, France) twice in each sample. Concentration was then calculated back and the results were noted and analysed. Results: Means of DS in group 3 (2.4 ± 0.8 μl) was significantly less than group 1 (49.7 ± 00.9 μl) and group 2 (65.3 ± 0.7μl) (median = 2 microlitre). All three groups were significantly different from each other with the largest DS in group 2. After dilution, insulin concentrations from diluents in group 3 were still close to standard insulin (335 ± 28 vs 310 microunits/ml), whereas group 1 and 2 were significantly higher than group 3 (1.7 and 1.9 times) and standard insulin (1.8 and 2 times). Conclusions: DS in NRIS is not negligible and is considered a potential source of error in the concentration of medications when it is used to dilute parenteral medications in the neonatal intensive care unit (NICU).