The most common types of medication error in pediatric anesthesiology are wrong dose and syringe swap. Another source of medication error is syringe dead space, which is defined as residual volume left between the plunger and syringe tip after the total dose is given. A previous study showed potential for insulin dosing errors in neonates due to dead space.
Technical data from syringe manufacturer Becton Dickinson (USA) specifies dead space (percentage of total syringe capacity) in their 10-ml and 1-ml Luer-Lock syringes as follows: 0.1 ml (1%) and 0.07 ml (7%), respectively.
Dead space becomes important when administering small volumes of high-concentration medications. If a 1-month-old, 5-kg patient is to receive 2.5 μg (0.5 μg/kg) of IV fentanyl, the unit dose is 0.05 ml (50 μg/mL). If fentanyl is drawn up to the 0.05-ml mark (fig. 1) and the same syringe is used to flush the medication in-line using the push-pull method, the dose administered would be 0.07 ml + 0.05 ml = 0.12 ml, or 6 μg, which is more than twice the intended dose.
Best practice is to administer the dose and use a separate normal saline syringe to flush the IV line. Alternatively, dilution may mitigate the effect of dead space error by increasing the volume of the unit dose. Having anesthesiology and pharmacy devise a clinical plan to have prediluted medications readily available for clinical use is one solution, particularly where institutional policy prohibits dilution of medications outside of pharmacy.