The steady-state flow rates were normally distributed; thus, t tests were used to analyze steady-state flow rate data. The time intervals for steady-state flow rates ranged from 4 to 18 minutes. Overall, the steady-state flow rate for each trial in both groups was below the pump programmed flow rate. Figure 4 depicts the mean percent deviation from the programmed flow. This deviation was below 0 for each programmed flow rate (maximum deviation = −17.3% ± 5.8%), indicating that all flow rates were lower than the corresponding programmed flow rate. Table 3 depicts the mean steady-state flow rates for each trial. For the highest initial flow rate (1.0 mL/h), the steady-state flow rate attained was lower in the filter group than the control group for the initial rate (P = 0.04) and doubling of initial rate (P = 0.04) with a trend during the return to initial rate (P = 0.06). This effect was not observed when doubling the initial rate trials of 0.8 or 0.6 mL/h compared with the control group. There were no statistically significant differences in the steady-state flow rate between either group for any of the other flow rates (0.4, 0.6, or 0.8 mL/h), although the width for the 95% confidence intervals for these differences ranged from 0.08 to 0.73.
Flow Rate Variability
When the variance (the square of the SD) for the steady-state flow rate was compared between the filter and control groups, the only difference in rate variability (Table 1) was observed for the doubling of the flow rate to 1.2 mL/h (after initial flow rate of 0.6 mL/h) for that rate trial. This difference was not observed in any other trial (Table 3).
Time to Reach Steady-State Flow
Student t tests were used to analyze these data. The average time to reach steady-state flow from start of the infusion ranged from 1.3 to 3.8 minutes (Table 4) and did not differ statistically between the control and filter groups. In addition, the average time to reach steady-state flow after a flow rate change ranged from 0.8 to 5.5 minutes and also did not differ between the control and filter groups. The 95% confidence intervals for these differences were wide between both groups (see “Study Limitations”).
This study found that an in-line IV filter did not statistically significantly increase the amount of time from zero flow to initial flow (startup delay) and did not statistically significantly increase the amount of time to reach steady-state flow. Also, in-line IV filters did not have an effect on flow variability.
Our study revealed that, even with adherence to the syringe pump manufacturer’s recommendations, the steady-state flow rates for all experimental trials were lower than the syringe pump programmed flow rates (Table 3; Figure 4). Only for the initial flow rate of 1.0 mL/h were the steady-state flow rates lower in the filter group compared with the controls with statistical significance only present with the initial flow rate and doubling of initial flow rate and not maintained with the return to initial rate (initial rate, P = 0.04; doubling of initial rate, P = 0.04; and return to initial rate, P = 0.06). This same effect was not observed at the initial rate trials of 0.8 or 0.6 mL/h when doubling to rates >1.0 mL/h compared with the control groups. Also, there were no differences in the experimental trials with initial flow rates of 0.4, 0.6, and 0.8 mL/h. Therefore, the aforementioned observed effect may not be a sustained finding with further investigation.
Our results demonstrate that in-line IV filters did not affect startup delay under our study conditions with a mean startup delay of <1 minute across all trials. The preparatory trials (Appendix 1) determined that 2 mL of fluid delivered immediately before starting any experimental trials minimized startup delay because of mechanical factors of the syringe pump. All experimental trials were performed immediately after this 2 mL of fluid delivery from the syringe pump. Bartels et al.2 tested the same syringe pump as our study (Medfusion 3500) and illustrated the importance of immediately starting the syringe pump infusion after pump priming; their study revealed that a longer time interval between pump priming and the subsequent start of the infusion created a longer startup delay. The backflow observed during startup delay was also noted by Schmidt et al.1 In that study, the authors described transient decreases in weight measurements using gravimetric methods when a 50-mL syringe was used with a syringe infusion pump.
Time to Reach Steady-State Flow
In our study, the use of in-line IV filters did not significantly affect the time to reach steady-state flow with our time measurements ranging from 1.3 to 3.8 minutes, although the confidence limits for differences between filter and control groups were wide. After a rate change, the time to reach steady-state flow ranged from 0.8 to 5.5 minutes at all flow rates. Neff et al.3 found that infusate delivery was significantly influenced by the syringe size and the programmed flow rate; lower pump programmed flow rates and larger syringe sizes used for delivery from the syringe pump significantly prolonged the time to reach steady-state flow. In another study, the programmed flow rate of 1.0 mL/h was not achieved before 60 minutes when a 50-mL syringe connected to the syringe pump was used for delivery.1
Steady-State Flow Rates Compared with Pump Programmed Flow Rates
Delivered steady-state flow rates were lower compared with programmed flow rates whether a filter was present or not. Although syringe infusion pumps represent the most accurate device for delivery at low flow rates, pump performance may be compromised4,5 when operational limits are approached (eg, with very low flow rates). Some of these operational limitations involve the pumps’ components and can lead to startup delays and a longer time to reach steady-state flow.1,3,6–10
To evaluate the effect of filters on syringe pump performance, Jonckers et al.11 compared the effect of in-line IV filters (0.2-μm size) with controls without a filter on the in-line pressures. When in-line pressures exceed a preset limit, this would cause the syringe pump to alert the user to a possible occluded syringe pump delivery system. A filter added to the system was associated with higher in-line pressures11 that Jonckers’ group hypothesized was because of increased resistance from the clogging of filter pores. Under our study conditions, steady-state flow rates were maintained after the addition of a filter, although at the highest flow rate of 1.0 mL/h, the steady-state flow rate attained was lower in the filter than the control group for the initial rate (P = 0.04) and doubling of initial rate (P = 0.04) with a trend during the return to initial rate (P = 0.06). Because this effect was not observed when doubling the initial rate trials of 0.8 or 0.6 mL/h compared with the control group, it brings into question the validity of these findings.
Flow Rate Variability
Flow rate variability was similar in the filter and control groups in all conditions except for the doubling of the flow rate to 1.2 mL/h (after initial flow rate of 0.6 mL/h), which showed decreased variability (Table 3). These results were not sustained across the entire trial and raise questions about their reliability.
Transient and random flow rate alterations were observed during some of the trials (Figure 3, A and C). Each measurement was graphically displayed in real time after input into the database, allowing the study investigators to search for contributing factors present during the experimental trials. No factors were noted that could explain the rate alterations seen (eg, sudden changes in laboratory environment). Further investigation would be required to examine other internal or external factors that might influence the syringe infusion pump system delivery profile. These yet-to-be-determined factors may be present in patient care areas that use syringe infusion pumps.
Clinical Impact of IV In-Line Filters
Filters may lead to decreased complication rates, lengths of stay, and organ dysfunction in pediatric intensive care unit patients12,13 and may significantly reduce overall complication rates in sick newborns.14 A 2015 Cochrane analysis involving 704 preterm infants and neonates15 revealed a nonsignificant reduction in individual complications (eg, sepsis) and may have been underpowered to detect low incidence complications. The 2015 Cochrane analysis15 concluded that there was “insufficient evidence to recommend the use of IV in-line filters to prevent mortality and morbidity in neonates.”
The American Society for Parenteral and Enteral Nutrition, the British Pharmaceutical Nutrition Group Working Party, and the U.S. Food and Drug Administration recommend IV filter use for parenteral nutrition to avoid the potential hazards of precipitation, particulate matter, air, and micro-organisms.16,17 The 0.2-μm size filter is recommended for nonlipid-containing admixtures, whereas the 1.2-μm size filter is recommended for lipid-containing solutions.
In our study, the following factors were controlled to minimize confounding variables: (1) a 10-mL syringe was used for all experimental trials to minimize effects related to syringe size differences; (2) the IV infusion system was standardized; (3) new IV infusion system parts and filters were used for each experimental trial with the exception of the single-lumen central line; (4) assembly and priming methods of the IV infusion system, and all experimental techniques, were standardized; (5) the syringe pump was positioned at the same height as the distal tip of the single-lumen catheter; and (6) environmental conditions were consistently maintained (eg, evaporation was negligible). Limitations of our study include analyzing only 1 syringe infusion pump brand and 1 size (0.2 μm) filter. In addition, this study may have been underpowered to detect smaller differences in time to reach steady state.
Syringe Pump Infusion System Performance
Strategies to optimize pump performance have been described.7 Improving recognition of the limitations, safety issues, and other factors that impact syringe pump performances are a key strategy in the U.S. Food and Drug Administration’s Infusion Pump Improvement Initiative.c Syringe infusion pumps and in-line IV filters are 2 parts of the continuous IV drug delivery system for complex surgical and critically ill pediatric patients. Infusion system dynamics are complex with the potential for greater clinical impact in these very ill and low-body-weight pediatric patients. For instance, the very low body weight of the patient may result in limited IV access and restricted total daily fluid. Lovich et al.18–25 have extensively investigated drug delivery kinetics and the dynamics of continuous infusion therapy. Relevant factors influencing continuous drug delivery include the specific architecture of the connectors, the manifold design for multiple infusions, the selection of the infusion connecting port, the dead volume of the system, the presence of a carrier fluid, alterations in the infusate and carrier flow rates, and coinfusion interactions.18–25 Health care providers should be educated regarding syringe pump devices and limitations within their own patient care areas to enable the best clinical decisions for delivery of medications to complex surgical and critically ill pediatric patients.
The results of this study demonstrate that IV filters do not have statistically significant effects on syringe pump performance in the delivery of infusate at the low flow rates that are commonly used in the pediatric intensive care unit or in the operating room for a complex pediatric surgical patient as it relates to startup delay, time to steady-state flow, and flow rate variability. The overall flow rate was lower than the programmed flow rate with or without a filter.
Before full implementation of the experimental trial protocol involving the control and the filter groups, a series of separate preparatory trials were performed to establish the steps required to assure optimal syringe pump performance under reproducible conditions. These preparatory trials were designed to minimize the startup delay component attributable to the mechanical properties of the syringe pump (eg, engaging of the gears in the mechanical drive of the specific syringe pumps) used in this study. Filters were not used during any of these preparatory trials. Startup delay was defined as the time after initiation of the infusion from zero flow to initial fluid flow at the distal tip of the catheter (see the graphical representation in Figure A1). By using a flow rate of 1.0 mL/h, 6 preparatory trials were performed. Three of these experimental trials, “trials without pump priming,” involved manually priming the IV infusion system with NS and the syringe pump only used for infusion delivery at 1.0 mL/h per preparatory trial protocol. In the other 3 experimental trials, “trials with pump priming,” the IV infusion system was manually primed with NS followed by the additional step of “pump priming” before starting the infusion delivery at 1.0 mL/h. Pump priming followed the manufacturer’s instructions of using the syringe pump at a preset rate of 300 mL/h while observing for fluid movement at the distal end of the single-lumen catheter. A pump priming volume of 2 mL was used for each experimental trial. For all 6 experimental trials, the infusion was started at a programmed flow rate of 1.0 mL/h until steady-state flow was reached.
Weight measurements were obtained at the start of the 1.0-mL/h infusion flow rate and then every 2 minutes thereafter. For each time interval, the increase in the measured weight was converted to volume by multiplying by 1 g/mL (the density of NS at 22°C is 1.0046 g/mL, which was rounded to 1 g/mL). The flow rate was then calculated by dividing the volume by the time for each interval. These flow rates were graphed against the time elapsed in real time.
Data were collected every 2 minutes with a graph generated in real time that plotted the delivered flow rate of fluid per unit time. Steady-state flow was defined as being achieved when 4 consecutive graphical data points 2 minutes apart stabilized around a flow rate value with at least 1 data point above and 1 below this value. The first of these 4 data points was used to identify the start of the steady-state flow (Figure A1).
We examined differences between preparatory experimental trials comparing trials “without pump priming” and trials “with pump priming” (Figure A2). Startup delay was significantly greater in the trials “without pump priming” (4.7 ± 1.2 minutes) compared with the trials “with pump priming” (0 ± 0 minute; P = 0.02). The preparatory trials “with pump priming” did not have any startup delay (0 ± 0 min), whereas every trial “without pump priming” had a startup delay with concomitant backflow (mean backflow = −0.11 g/mL ± 0.05).
The mean time to steady-state flow was lower in the group “with pump priming” (3.3 ± 1.2 minutes), achieving steady-state flow within 5 minutes after the start of the infusion. In contrast, the trials “without pump priming” had longer mean times to steady-state flow (12.7 ± 3.1 minutes; P = 0.02), requiring up to 15 minutes to achieve steady-state flow.
Name: Destiny F. Chau, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Name: Terrie Vasilopoulos, PhD.
Contribution: This author helped statistical analysis, comparison of the data, and write the manuscript.
Name: Miriam Schoepf, MD.
Contribution: This author helped to analyze the data and write the manuscript.
Name: Christina Zhang.
Contribution: This author helped conduct the study and write the manuscript.
Name: Brenda G. Fahy, MD, MCCM.
Contribution: This author helped design the study, analyze the data, and write the manuscript.
This manuscript was handled by: James A. DiNardo, MD.
a The Medicines and Healthcare products Regulatory Agency. Infusion systems. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/403420/Infusion_systems.pdf. Accessed October 6, 2015.
b U.S. Department of Health and Human Services, Food and Drug Administration. Infusion Pumps Total Product Life Cycle-Guidance for Industry and FDA Staff. Available at: http://www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/UCM209337.pdf. Accessed October 6, 2015.
c U.S. Department of Health and Human Services, Food and Drug Administration. Infusion Pump Improvement Initiative. Available at: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/GeneralHospitalDevicesandSupplies/InfusionPumps/ucm202501.htm. Accessed October 6, 2015.
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© 2016 International Anesthesia Research Society
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