In vitro measurement of flow rate variability in neonatal IV therapy with and without the use of check valves

Pressure-adjusted venting eliminates start-up delays and compensates for vertical position of syringe infusion pumps used for microinfusion

Microinfusions are commonly used for the administration of catecholamines, but start-up delays pose a problem for reliable and timely drug delivery. Recent findings show that venting of the syringe infusion pump with draining of fluid to ambient pressure before directing the flow towards the central venous catheter does not counteract start-up delays. With the aim to reduce start-up delays, this study compared fluid delivery during start-up of syringe infusion pumps without venting, with ambient pressure venting, and with central venous pressure (CVP)-adjusted venting. Start-up fluid delivery from syringe pumps using a microinfusion of 1 mL/h was assessed by means of liquid flow measurement at 10, 60, 180 and 360 s after opening the stopcock and starting the pump. Assessments were performed using no venting, ambient pressure venting or CVP-adjusted venting, with the pump placed either at zero, - 43 cm or + 43 cm level and exposed to a simulated CVP of 10 mmHg. Measured fluid delivery was closest to the calculated fluid delivery for CVP-adjusted venting (87% to 100% at the different timepoints). The largest deviations were found for ambient pressure venting (- 1151% to + 82%). At 360 s after start-up 72% to 92% of expected fluid volumes were delivered without venting, 46% to 82% with ambient pressure venting and 96% to 99% with CVP-adjusted venting. CVP-adjusted venting demonstrated consistent results across vertical pump placements (p = 0.485), whereas the other methods had significant variances (p < 0.001 for both). In conclusion, CVP-adjusted venting effectively eliminates imprecise drug delivery and start-up delays when using microinfusions.

Evaluation of the venting principle to reduce start-up delays in syringe infusion pumps used for microinfusions

Start-up delays of syringe pump assemblies can impede the timely commencement of an effective drug therapy when using microinfusions in hemodynamically unstable patients. The application of the venting principle has been proposed to eliminate start-up delays in syringe pump assemblies. However, effectively delivered infusion volumes using this strategy have so far not been measured. This invitro study used two experimental setups to measure the effect of the venting principle compared to a standard non-venting approach on delivered start-up infusion volumes at various timepoints, backflow volumes, flow inversion and zero drug delivery times by means of liquid flow measurements at flow rates of 0.5, 1.0 and 2.0 mL/h. Measured delivered initial start-up volumes were negative with all flow rates in the vented and non-vented setup. Maximum backflow volumes were 1.8 [95% CI 1.6 to 2.3] times larger in the vented setup compared to the non-vented setup (p < 0.0001). Conversely, times until flow inversion were 1.5 [95% CI 1.1 to 2.9] times shorter in the vented setup (p < 0.002). This led to comparable zero drug delivery times between the two setups (p = 0.294). Start-up times as defined by the achievement of at least 90% of steady state flow rate were achieved faster with the vented setup (p < 0.0001), but this was counteracted by the increased backflow volumes. The application of the venting principle to the start-up of microinfusions does not improve the timely delivery of drugs to the patient since the faster start-up times are counteracted by higher backflow volumes when opening the three-way stopcock.

Flow Rate Deviation in Infusion Pump: Infusion Set Defect Enables Pump Malfunction and Considerable Accuracy Deviation

Volumetric infusion pumps are used together with infusion sets to deliver medication to patients. Flow rate errors leading to overinfusion or underinfusion are known problems with these devices. Recently, numerous underinfusion flow rate errors were reported at a Swedish hospital. This experimental study reports on the investigation of these errors and specifically investigates the effect of operating the pump with a defective infusion set that has a visible elongation of the silicone segment of the set. Pump flow rate accuracy testing was performed using a gravimetric method. Experiments included a manipulated infusion set and a defective infusion set used in clinic. The use of a defective infusion set resulted in considerable accuracy deviations. The pump reported an infused amount greater than what was infused and did not provide any alarm or information indicating a reduced output. Using an elongated infusion set, the pump can be brought into an erroneous operating state where the infused amount delivered by the pump is considerably less than what has been programmed and what is shown on the pump display. This could put the patient at risk of not receiving the intended medication within the appropriate time.

Effect of vertical pump position on start-up fluid delivery of syringe pumps used for microinfusion

BACKGROUND

Connection and opening a syringe infusion pump to a central venous line can lead to acute anterograde or retrograde fluid shifts depending on the level of central venous pressure. This may lead to bolus events or to prolonged lag times of intravenous drug delivery, being particularly relevant when administering vasoactive or inotropic drugs in critically ill patients using microinfusion. The aim of this study was to assess the effect of syringe pump positioning at different vertical heights on start-up fluid delivery before versus after purging and connection the pump to the central venous catheter.

METHODS

This in vitro study measured ante- and retrograde infusion volumes delivered to the central venous line after starting the syringe pump at a set infusion rate of 1 mL/h. In setup one, the pump was first positioned to vertical levels of +43 cm or -43 cm and then purged and connected to a central venous catheter. In setup two, the pump was first purged and connected at zero level and secondarily positioned to a vertical level of +43 cm or -43 cm. Central venous pressure was adjusted to 10 mmHg in both setups.

RESULTS

Positioning of the pump prior to purging and connection to the central venous catheter resulted in a better start-up performance with delivered fluid closer to programmed and expected infusion volumes when compared to the pump first purged, connected, and then positioned. Significant backflow volumes were observed with the pump purged and connected first and then positioned below zero level. No backflow was measured with the pump positioned first below zero level and then purged and connected.

CONCLUSIONS

Syringe infusion pump assemblies should be positioned prior to purging and connection to a central venous catheter line when starting a new drug, particularly when administering highly concentrated vasoactive or inotropic drugs delivered at low flow rates.

Effect of central venous pressure on fluid delivery during start-up of syringe infusion pumps for microinfusion

BACKGROUND

Intravenous administration of highly concentrated and potent drugs at low flow rates is common practice, particularly in critically ill children. Drug delivery during infusion start-up can be considerably delayed by intrinsic factors of syringe infusion pump assemblies. The impact of central venous pressures on the course of start-up fluid delivery of such microinfusions remains unknown.

METHODS

Infusion volumes delivered after activation of the start button in a conventional 50 mL syringe infusion pump assembly equilibrated (representing classical in vitro testing) and not equilibrated (representing real clinical conditions) to central venous pressure levels of 0, 10 and 20 mmHg at a set infusion flow rate of 1 mL/h were measured using a fluidic flow sensor.

RESULTS

The experimental setup mimicking real life conditions demonstrated considerable differences in fluid delivery during pump start-up depending on central venous pressure. A central venous pressure of 0 mmHg resulted in massive fluid delivery at infusion start-up, while central venous pressure levels of 10 and 20 mmHg resulted in retrograde flows with related mean (95% CI) zero-drug delivery times of 3.22 (2.98-3.46) min and 4.51 (4.33-4.69) min, respectively (p < .0001).

CONCLUSION

Depending on central venous pressure level, connection and starting a new syringe pump can result in significant antegrade or retrograde fluid volumes. In clinical practice, this can lead to hemodynamic instability and hence requires clinical alertness. Further research and methods to improve start-up performance in syringe infusion pump systems are desirable.

Effect of non-return valves on the time-of-arrival of new medication in a patient after syringe exchange in an infusion set-up

The presence of a non-return valve in an infusion set-up is expected to affect the time-of-arrival of new medication in a patient after syringe exchange. Using Computational Fluid Dynamics (CFD) we have studied the flow through a typical non-return valve, focusing on two separate effects: (A) the overall delay in the time-of-arrival, and (B) timing effects due to the distortion of the Poiseuille flow profile in the non-return valve. The results show that (A) the additional delay in time-of-arrival of new medication, caused by the non-return valve alone, corresponds to the delay that would be caused by 11.2 cm of extra infusion line instead of the valve, and that (B) the non-Poiseuille flow profile inside the non-return valve gives rise to an extra slow wash-out of the last portion of the remnant fluid of the old medication. We conclude that awareness of these extra delays may be important for clinicians in certain time-critical situations.

[Infusion sets in neonatology: What practices in France?]

OBJECTIVES

Therapeutic management of ill newborns can require complex infusion practices using medical devices (MD). Currently, there does not exist any recommendations concerning these infusion practices. The objective of this work was to study and characterise French infusion methods neonatal and neonatal intensive care units.

MATERIALS AND METHODS

The study was performed in 2019, during 6 months. French hospitals possessing high (type 3) or medium (type 2B) grade maternity ward were contacted and asked to complete a 5 part online survey, to gather general information about the hospital/ward, infusion methods (overall and detailed), and detailed information about the medications and MD used.

RESULTS

The participation level was of 19.6 % Type 3 maternities use overall two-times more MD than those of type 2B. The vascular access device most commonly used was a single lumen catheter (80.6 % of infusion methods). 100 % of the hospitals having answered used multi-access devices (three-way tap, multiport infusion manifold, Y-extension lines) and 93.5 % used a pump-infusor. Lipidic filters for parenteral nutrition were used in 78.6 % of the hospitals. Two general standard of infusion methods were isolated: a simple version with two access points (type 2B hospitals), and a complex one with five access points (from hospitals with type 3 maternities).

CONCLUSIONS

Neonatal infusion practices in France are very heterogeneous, thus exposing the patients to a degree of variability during their therapeutic management. This work is a first step forwards to help analyse and anticipate the risks of content/container interactions caused by infusion practices.

Accuracy of low-weight versus standard syringe infusion pump devices depending on altitude

Background

Intravenous drug infusions in critically ill patients require accurate syringe infusion pumps (SIPs). This is particularly important during transportation of critically ill patients by helicopter emergency medical services (HEMS), where altitude may influence device performance. Because weight is a real concern in HEMS, new low-weight devices are very appealing.

The aim of this study was to compare infusion flow rates delivered by low-weight versus standard SIP devices, in the prehospital emergency medicine setting, at different altitudes.

Methods

We conducted a comparative bench study involving five SIP devices (two standard and three low-weight models) at 300, 1700 and 3000 m altitude. The primary endpoint was the flow rate delivered by SIPs for prespecified values. We used two methods to measure flow. The normative method consisted in measuring weight (method A) and the alternate method consisted in measuring instantaneous flow (method B).

Results

Using method A, no significant differences were found in median flow rates and interquartile range depending on device and altitude for a prespecified 10-mL/h flow. However, method B showed that low-weight SIPs delivered multiple sequential boluses with substantial variations (1.2–15.8 mL/h) rather than a prespecified continuous 5-mL/h flow. At 1700 m altitude, the interquartile range of delivered flows increased only for low-weight devices (p for interaction< 0.001).

Conclusions

Despite satisfactory normative tests, low-weight SIPs deliver discontinuous flow with potential clinical implications for critically ill patients receiving vasoactive drugs. This study also highlights a thus far unknown negative impact of altitude on SIP function. We believe that normative requirements for SIP approval should be revised accordingly.

Analytical method for calculation of deviations from intended dosages during multi-infusion

BACKGROUND

In this paper, a new method is presented that combines mechanical compliance effects with Poiseuille flow and push-out effects ("dead volume") in one single mathematical framework for calculating dosing errors in multi-infusion set-ups. In contrast to existing numerical methods, our method produces explicit expressions that illustrate the mathematical dependencies of the dosing errors on hardware parameters and pump flow rate settings.

METHODS

Our new approach uses the Z-transform to model the contents of the catheter, and after implementation in Mathematica (Wolfram), explicit expressions are produced automatically. Consistency of the resulting analytical expressions has been examined for limiting cases, and three types of in-vitro measurements have been performed to obtain a first experimental test of the validity of the theoretical results.

RESULTS

The relative contribution of various factors affecting the dosing errors, such as the Poiseuille flow profile, resistance and internal volume of the catheter, mechanical compliance of the syringes and the various pump flow rate settings, can now be discerned clearly in the structure of the expressions generated by our method. The in-vitro experiments showed a standard deviation between theory and experiment of 14% for the delay time in the catheter, and of 13% for the time duration of the dosing error bolus.

CONCLUSIONS

Our method provides insight and predictability in a large range of possible situations involving many variables and dependencies, which is potentially very useful for e.g. the development of a fast, bed-side tool ("calculator") that provides the clinician with a precise prediction of dosing errors and delay times interactively for many scenario's. The interactive nature of such a device has now been made feasible by the fact that, using our method, explicit expressions are available for these situations, as opposed to conventional time-consuming numerical simulations.