Syringe pump assemblies and the natural history of clinical technology

Digital droplet infusion

Infusion pumps have been widely used in clinical settings for the administration of medications and fluids. We present the digital droplet infusion (DDI) device, a low-cost, high-precision digital infusion system, utilizing a microfluidic discretization unit to convert continuous flow into precisely delivered droplet aliquots and a valving unit to control the duration and frequency of flow discretization. The DDI device relies on a distinct capillarity-dominated process of coalescence and pinch-off of droplets for flow digitization, which is monitored by a pair of conductive electrodes located before and after the junction. The digital feedback-controlled flow rate can be employed to adjust a solenoid valve for refined infusion management. With this unique digital microfluidic approach, the DDI technology enables a simple yet powerful infusion system with an ultrahigh resolution of digital droplet transfer volume, as small as 57 nL, which is three orders of magnitude lower than that of clinical standard infusion pumps, as well as a wide range of digitally adjustable infusion rates ranging from 0.1 mL h^-1 to 10 mL h^-1, in addition to an array of programmable infusion profiles and safety features. Its modular design enables fast assembly using only off-the-shelf and 3D-printed components. Overall, benefiting from its simple device architecture and excellent infusion performance, the DDI technology has great potential to become the next-generation clinical standard for drug delivery with its high precision and ultimate portability at a low cost.

Performance of modern syringe infusion pump assemblies at low infusion rates in the perioperative setting

BACKGROUND

Syringe infusion pumps are used for the precise continuous administration of intravenous drugs. Their compliance and mechanical deficiencies have been found to cause considerable start-up delays, flow irregularities during vertical displacement, as well extensive delays of occlusion alarms at low infusion rates. The aim of this study was to evaluate the performance of several modern syringe infusion pumps at low infusion rates and the impact on drug concentration.

METHODS

Seven currently marketed syringe infusion pump assemblies were assessed in an in vitro study during start-up, vertical displacement manoeuvres, and infusion line occlusion at a set flow rate of 1 ml h^-1. The measured data were used as input for a pharmacokinetic simulation modelling plasma concentration during a standard neonatal continuous epinephrine infusion.

RESULTS

The mean time from starting the infusion pump to steady-state flow varied from 89 to 1622 s. The zero-drug delivery time after lowering the pump ranged from 145 to 335 s. In all assemblies tested, occlusion alarm delays and measured flow irregularities during vertical displacement manoeuvres resulted in relevant deviations in plasma epinephrine concentration (>25%) as calculated by the pharmacokinetic simulation model.

CONCLUSION

Problems with the performance of syringe infusion pump assemblies can have considerable impact on plasma drug concentration when highly concentrated short-acting cardiovascular drugs are administered at low flow rates. The problems, which affected all assemblies tested, are mainly related to the functional principle of syringe infusion pumps and will only partially be solved by incremental improvements of existing equipment.

Infusion system carrier flow perturbations and dead-volume: large effects on drug delivery in vitro and hemodynamic responses in a swine model

BACKGROUND

We have previously shown that, at constant carrier flow, drug infusion systems with large dead-volumes (V) slow the time to steady-state drug delivery in vitro and pharmacodynamic effect in vivo compared to those with smaller V. In this study, we tested whether clinically relevant alterations in carrier flow generate perturbations in drug delivery and pharmacodynamic effect, and how these might be magnified when V is large.

METHODS

Drug delivery in vitro or mean arterial blood pressure (MAP) and ventricular contractility (max dP/dt) in a swine model were quantified during an infusion of norepinephrine (fixed rate 3 mL/h) with a crystalloid carrier (10 mL/h). The carrier flow was transiently halted for either 10 minutes or 20 minutes and then restarted. In separate experiments, a second drug infusion (50 mL over 10 minutes) was introduced into the same catheter lumen used by a steady-state norepinephrine infusion. The resulting perturbations in drug delivery and biologic effect were compared between drug infusion systems with large and small V.

RESULTS

Halting carrier flow immediately decreased drug delivery in vitro, and MAP and max dP/dt. These returned to steady state before restarting carrier flow with the small, but not the large, V. Resuming carrier flow after 10 minutes resulted in a transient increase in drug delivery in vitro and max dP/dt in vivo, which were of longer duration and greater area under the curve (AUC) for larger V. MAP also increased for longer duration for larger V. Resuming the carrier flow after 20 minutes resulted in greater AUCs for drug delivery, MAP, and max dP/dt for the larger V. Adding a second infusion to a steady-state norepinephrine plus carrier flow initially resulted in a drug bolus in vitro and augmented contractility response in vivo, both greater with a larger V. Steady-state drug delivery resumed before the secondary infusion finished. After the end of the secondary infusion drug delivery, MAP and max dP/dt decreased over minutes. Drug delivery and max dP/dt returned to steady state more quickly with the small V.

CONCLUSIONS

Stopping and resuming a carrier flow, or introducing a second medication infusion, impacts drug delivery in vitro and biologic response in vivo. Infusion systems with small dead-volumes minimize these perturbations and dampen the resulting hemodynamic instability. Alterations in carrier flow impact drug delivery, resulting in substantial effects on physiologic responses. Therefore, infusion systems for vasoactive drugs should be configured with small V when possible.

Drug infusion system manifold dead-volume impacts the delivery response time to changes in infused medication doses in vitro and also in vivo in anesthetized swine

BACKGROUND

IV infusion systems can be configured with manifolds connecting multiple drug infusion lines to transcutaneous catheters. Prior in vitro studies suggest that there may be significant lag times for drug delivery to reflect changes in infusion rates set at the pump, especially with low drug and carrier flows and larger infusion system dead-volumes. Drug manifolds allow multiple infusions to connect to a single catheter port but add dead-volume. We hypothesized that the time course of physiological responses to drug infusion in vivo reflects the impact of dead-volume on drug delivery.

METHODS

The kinetic response to starting and stopping epinephrine infusion ([3 mL/h] with constant carrier flow [10 mL/h]) was compared for high- and low-dead-volume manifolds in vitro and in vivo. A manifold consisting of 4 sequential stopcocks with drug entering at the most upstream port was contrasted with a novel design comprising a tube with separate coaxial channels meeting at the downstream connector to the catheter, which virtually eliminates the manifold contribution to the dead-volume. The time to 50% (T50) and 90% (T90) increase or decrease in drug delivery in vitro or contractile response in a swine model in vivo were calculated for initiation and cessation of drug infusion.

RESULTS

The time to steady state after initiation and cessation of drug infusion both in vitro and in vivo was much less with the coaxial low-dead-volume manifold than with the high-volume design. Drug delivery after initiation in vitro reached 50% and 90% of steady state in 1.4 ± 0.12 and 2.2 ± 0.42 minutes with the low-dead-volume manifold and in 7.1 ± 0.58 and 9.8 ± 1.6 minutes with the high-dead-volume manifold, respectively. The contractility in vivo reached 50% and 90% of the full response after drug initiation in 4.3 ± 1.3 and 9.9 ± 3.9 minutes with the low-dead-volume manifold and 11 ± 1.2 and 17 ± 2.6 minutes with the high-dead-volume manifold, respectively. Drug delivery in vitro decreased by 50% and 90% after drug cessation in 1.9 ± 0.17 and 3.5 ± 0.61 minutes with the low-dead-volume manifold and 10.0 ± 1.0 and 17.0 ± 2.8 minutes with the high-dead-volume manifold, respectively. The contractility in vivo decreased by 50% and 90% with drug cessation in 4.1 ± 1.1 and 14 ± 5.2 with the low-dead-volume manifold and 12 ± 2.7 and 23 ± 5.6 minutes with the high-dead-volume manifold, respectively.

CONCLUSIONS

The architecture of the manifold impacts the in vivo biologic response, and the drug delivery rate, to changes in drug infusion rate set at the pump.

Delay and stability of central venous administration of norepinephrine in children: a bench study

In children, because of the dead volume of the central venous catheter (CVC) and the low flow rate of norepinephrine (NE) infusion, the delay between start-up and effective administration can be adversely long. A theoretical calculation enables to estimate the delay and variations of effective administration. However, numerous factors can hinder this theoretical approach. Herein, we measured via bench testing the actual delay and stability of NE administration kinetics. Using an assembly reproducing our currently-implemented catecholamine administration protocol, diluted NE (200 μg ml(-1)) was infused at an initial rate of 2 ml h(-1) (theoretically 6.67 μg min(-1)) for a period of 24 h. An assay measuring the amount of NE (μg) exiting the CVC was conducted by high-pressure liquid chromatography with colorimetric detection. The theoretical calculation of the delay in administered NE, taking into account a CVC dead volume of 0.3 ml, was 9 min. The measured percentage of the administered dose as a function of time in minutes (M) was M0-M3 (0 %), M3-M6 (0 %), M6-M9 (13 %), M9-M12 (28 %), M12-M15 (70 %), and M15-M18 (100 %) The amount of NE (μg) at fixed rate (2 ml h(-1)) was established at 6.9 ± 0.4 μg min(-1) during the 24 h.

CONCLUSION

Continuous NE infusion via a CVC at low rate is stable. In children, because of CVC dead volume and low flow rate infusion, the delay in achieving intended dose delivery is significantly longer than that estimated by theoretical calculation. New modalities of initiation of catecholamine infusion adapted to the child are warranted.

In-line filter included into the syringe infusion pump assembly reduces flow irregularities

PURPOSE

To evaluate whether an in-line filter inserted in the syringe pump infusion line assembly influences start-up times and flow irregularities during vertical pump displacement at low infusion rates.

METHODS

Fluid delivery after syringe pump start-up and after vertical displacement of the syringe pump by -50 cm was determined gravimetrically at flow rates of 0.5, 1.0 and 2.0 ml h(-1). Measurements were repeated for each flow rate four times with two different syringe pumps with and without an in-line filter incorporated. Data are shown as median and range.

RESULTS

Start-up times were reduced by an in-line filter at 0.5 ml h(-1) flow rate from 355.5 s (0-660) to 115 s (0-320), whereas the effect was attenuated at higher flow rates. Pooling of fluid into the infusion system after lowering the infusion syringe pump was halved in all flow rates tested. Amount of infusion bolus after elevating the syringe pump by 50 cm was not affected by an in-line filter.

CONCLUSION

In the evaluated model in-line filters help to reduce flow irregularities and delay in drug delivery of syringe pumps at low flow rates and represent an option to optimize continuous administration of highly concentrated short-acting drugs at very small infusion rates.

The Delivery of Drugs to Patients by Continuous Intravenous Infusion: Modeling Predicts Potential Dose Fluctuations Depending on Flow Rates and Infusion System Dead Volume

IV drug infusion has the potential for dosing errors, which arise from complex interactions between carrier flows and the infusion set dead volume. We computed the steady-state mass of drug stored in the infusion set dead volume, using phenylephrine as a model compound. The mass of drug in the dead volume increases with stock drug concentration and desired dose but decreases with carrier flow rate. We also modeled the dynamic perturbations in drug delivery when a carrier is abruptly stopped. Rapid initial carrier flow rates lead to greater depression in drug delivery rate after carrier flow ceases. Rapid drug infusion rates lead to faster restoration of desired drug delivery. Finally, the time to reach a new steady-state after a change in drug delivery or carrier rate was computed. This time is longest for large stock-drug concentrations, larger dead volumes, and slower final carrier rates. These computations illustrate that (a) the dead volume may contain a large mass of drug available for inadvertent bolus, (b) cessation of carrier flow can profoundly reduce drug delivery, and (c) after a change in carrier flow or drug dosing, a significant lag is possible before drug delivery achieves steady state. Although computed for phenylephrine, the concepts are generic and valid for any drug administered by IV infusion.

The impact of carrier flow rate and infusion set dead-volume on the dynamics of intravenous drug delivery

The dynamics of IV drug delivery resulting from drug infusions connected to main-line crystalloid carriers can be complex and depend on infusion set dead-volume, drug flow rate, and carrier flow rate. While the concept of dead-volume is intuitive, a lack of appreciation of the interaction with the carrier and drug flow rates can lead to unintended clinical effects resulting from large variations in the delivery rate of potent drugs. We derived mathematical models to quantify these interactions. Experimental simulation with methylene blue infusions tested these predictions. The models predict a lag in response time to changes in carrier or drug flow, which is proportional to the dead-volume and inversely related to the total flow rate. Increasing the carrier rate provides an acute drug bolus. Temporary reduction or cessation of carrier flow decreases the rate of drug delivery, potentially for prolonged periods. Furthermore, a drug bolus results from restoration of the carrier flow. The method of connecting an infusion to a carrier and the use history affects the dynamics of drug delivery. Thus, although complex, the impact of infusion set architecture and changes in carrier and drug flow rates are predictable. These quantitative studies may help optimize the safe use of IV drug infusion systems.

Accurate continuous drug delivery at low infusion rate with a novel microvolumetric infusion pump (MVIP): pump design, evaluation and comparison to the current standard

Infusion devices for continuous and precise drug administration are indispensable tools in anaesthesia and critical care medicine. Problems such as start-up delays, non-continuous flow and susceptibility to hydrostatic pressure changes at low infusion rates resulting in accidental bolus release or prolonged flow interruption are inherent to current infusion technology. In order to improve precise drug delivery, an innovative technical concept has been realised in a novel microvolumetric infusion pump (MVIP) device. The MVIP principle includes repeated filling and emptying of a non-compliant microsyringe without the use of valves. The performance of the MVIP prototype has been evaluated and compared with standard syringe infusion pump assemblies. The novel MVIP concept has thereby proven to eliminate most problems during infusion start-up, steady state flow and vertical pump displacement, and has the potential of revolutionising infusion technology and setting a new dimension in patient safety.

The Panomat P-10 micro-volumetric infusion pump is suitable for continuous drug administration at minimal flow rates

PURPOSE

To evaluate the performance of the Panomat P-10 micro-volumetric infusion pump for its use in drug administration at minimal flow rates (microL x hr(-1); e.g., intrathecal application).

METHODS

Fluid delivery at steady state conditions, and after vertical displacement of the syringe pump by -50 cm was determined gravimetrically. The Panomat P-10 infusion pump was evaluated at 4, 10, 20, 50 and 100 microL x hr(-1), and compared to a conventional syringe pump assembly at 100, 200, 500 and 1000 microL x hr(-1). Measurements were repeated twice with two different devices of each syringe pump system, and with two syringes. Data are reported as mean +/- SD.

RESULTS

Steady state fluid delivery of the Panomat P-10 infusion pump revealed less than 5% deviation to set flow rate at 10, 20, 50 and 100 microL x hr(-1), and 12% deviation at 4 microL x hr(-1). Mean zero-drug delivery time (ZDDT) after lowering the pump by 50 cm at 4 microL x hr(-1) flow rate was 38.4 +/- 7.3 min. At 100 microL x hr(-1) and with original infusion line ZDDT was almost 20 times shorter when compared to the conventional syringe pump assembly (1.5 +/- 0.5 min vs 28.5 +/- 5.0 min).

CONCLUSION

The tested Panomat P-10 micro-volumetric pump shows an acceptable flow accuracy as well as a low susceptibility to vertical displacement, and is therefore suitable for continuous drug administration at minimal flow rates. The technology used in this pump carries potential implications for a new generation of syringe pumps.