Introduction

Iv delivery systems for rapid fluidresuscitation are composed of com­ponents that exhibit different resis­tances to the administered fluid.

Accordingly, previous investigationswere directed toward the evaluation ofthe total flow rate through N infusionsets that were composed of differentcomponents of various manufacturers.Most of the experiments were con­ducted in relatively simple bench mod-

drip chamber with a fine-mesh circularfilter (about 1.2 sq cm) at the bottom(referred to here as "AI"), tubing (3.2mm ID and 150 cm long), and a rubberflashback bulb. The roller clamp wasfully open. The drip chamber was par­tially filled with air, as in real infusion.The flow characteristics of the infusionset were measured while assembledwith an N catheter (Baxter; 14 and 18gauge; both 51 mm long).

To evaluate the interdependency of

a small-bore catheter 08 gauge) isused, the largest pressure drop is overthe N catheter. However, the resistanceof the drip chamber is of a similar orderof magnitude as the tubing and theflashback bulb. When the standard dripchamber (A}) is used along with alarge-bore catheter 04 gauge) or tub­ing, it becomes the flow-limiting com­ponent with the largest pressure drop.The flow rates (Q) for each of thesecases are summarized in Figure 1.

Hdrod namic Evaluationo INTRAV NOUS INFUSION SYSTEMS

David Elad, DSc • Uri Zaretsky, PhD • Ori Heller, MD

els, which were designed to measurethe flow rate of a given delivery sys­tem. The contribution of various com­ponents to the total flow resistance wasanalyzed by adding or removing certainparts of the N infusion set.

Materials and MethodsWe designed a simple experimental

setup in which the resistance of eachcomponent of a given N delivery sys­tem could be determined. A pressurizedreservoir in the inlet line was used tocontrol the fluid pressure upstream ofthe N infusion set. The N catheter wasinserted into a fluid-filled V-shaped elas­tic tube (parallel to the tube axis) tosimulate in vivo infusion into a vein.Fluid discharge was leveled with thepoint of inlet flow where pressure wasmeasured. The working fluid in thisstudy was distilled water, which alsowas filtered before entering the N set.

The overall driving pressure acrossthe N delivery set, as well as pressuredifferences across each of the compo­nents, was measured with a differentialpressure transducer, with hypodermicneedle ports 04 gauge), or with thinplastic tubes in a way that did notinduce flow disturbances.

The "basic set" for this study was adelivery system composed of a standard

various components of the N set, wemeasured pressure-flow characteristicsin the following combinations: 0) thebasic set, (2) a set similar to the basicset but with a coarser filter in the dripchamber (referred to here as "A2"), (3)a set similar to the basic set but with alarge-bore tube (6 mm ID, 150 cmlong), and (4) a set similar to the basicset but with an improved (in terms offlow rate) drip-filter chamber with alarge-area (about 19 sq cm) coarse fil­ter in the shape of an open cylinder(referred to here as "M").

Experiments were conducted forinfusion pressures ranging from 50 mmHg (gravity-driven infusion) to 400 mmHg (pressurized infusion). For a morecomprehensive analysis of the limits ofa given N infusion set, we also mea­sured separately the pressure-flowcharacteristics of each component.

ResultsPressure drops over each component

in a given N infusion set, as well asflow rates, were acquired for a range ofpressurized infusions. In all cases where

Excerptfrom an article originallypublished in the March 1994 issue

o/the Annals ofEmergencyMedictne.

The relationship between flow rateand infusion pressure is nonlinear forall cases. Measurements of flow rateversus pressure drop for each compo­nent of the IV set, including the IVcatheters, are summarized in Figure 2.These results clearly indicate the flow­limiting parts in a fluid delivery setting.

DiscussionThe purpose of this investigation was

to quantify the performance character­istics of N infusion sets for rapid fluiddelivery. A quick glance at the resultsof Figure 1 reveals that the N catheteris the major flow-limiting component,as reported in previous work. 1-9 It canbe seen that an N set with a 14 gaugecatheter rather than an 18 gauge cathe­ter may increase the flow rate twofoldor more, especially during pressurizedinfusion.

The standard drip chamber (A}),which has a fine-mesh filter, imposesthe largest resistance or consumes agreat deal of the driving force whenused with a large-bore catheter (14gauge). When a small-bore catheter08 gauge) is used, the relative resis­tance of the catheter is very large, andas much as 70% of the pressure dropis consumed to drive the infusatethrough the N catheter.

12 "VAC Sum mer I 9 9 9

Introduction

Iv delivery systems for rapid fluidresuscitation are composed of com­ponents that exhibit different resis­tances to the administered fluid.

Accordingly, previous investigationswere directed toward the evaluation ofthe total flow rate through N infusionsets that were composed of differentcomponents of various manufacturers.Most of the experiments were con­ducted in relatively simple bench mod-

drip chamber with a fine-mesh circularfilter (about 1.2 sq cm) at the bottom(referred to here as "AI"), tubing (3.2mm ID and 150 cm long), and a rubberflashback bulb. The roller clamp wasfully open. The drip chamber was par­tially filled with air, as in real infusion.The flow characteristics of the infusionset were measured while assembledwith an N catheter (Baxter; 14 and 18gauge; both 51 mm long).

To evaluate the interdependency of

a small-bore catheter 08 gauge) isused, the largest pressure drop is overthe N catheter. However, the resistanceof the drip chamber is of a similar orderof magnitude as the tubing and theflashback bulb. When the standard dripchamber (A}) is used along with alarge-bore catheter 04 gauge) or tub­ing, it becomes the flow-limiting com­ponent with the largest pressure drop.The flow rates (Q) for each of thesecases are summarized in Figure 1.

Hdrod namic Evaluationo INTRAV NOUS INFUSION SYSTEMS

David Elad, DSc • Uri Zaretsky, PhD • Ori Heller, MD

els, which were designed to measurethe flow rate of a given delivery sys­tem. The contribution of various com­ponents to the total flow resistance wasanalyzed by adding or removing certainparts of the N infusion set.

Materials and MethodsWe designed a simple experimental

setup in which the resistance of eachcomponent of a given N delivery sys­tem could be determined. A pressurizedreservoir in the inlet line was used tocontrol the fluid pressure upstream ofthe N infusion set. The N catheter wasinserted into a fluid-filled V-shaped elas­tic tube (parallel to the tube axis) tosimulate in vivo infusion into a vein.Fluid discharge was leveled with thepoint of inlet flow where pressure wasmeasured. The working fluid in thisstudy was distilled water, which alsowas filtered before entering the N set.

The overall driving pressure acrossthe N delivery set, as well as pressuredifferences across each of the compo­nents, was measured with a differentialpressure transducer, with hypodermicneedle ports 04 gauge), or with thinplastic tubes in a way that did notinduce flow disturbances.

The "basic set" for this study was adelivery system composed of a standard

various components of the N set, wemeasured pressure-flow characteristicsin the following combinations: 0) thebasic set, (2) a set similar to the basicset but with a coarser filter in the dripchamber (referred to here as "A2"), (3)a set similar to the basic set but with alarge-bore tube (6 mm ID, 150 cmlong), and (4) a set similar to the basicset but with an improved (in terms offlow rate) drip-filter chamber with alarge-area (about 19 sq cm) coarse fil­ter in the shape of an open cylinder(referred to here as "M").

Experiments were conducted forinfusion pressures ranging from 50 mmHg (gravity-driven infusion) to 400 mmHg (pressurized infusion). For a morecomprehensive analysis of the limits ofa given N infusion set, we also mea­sured separately the pressure-flowcharacteristics of each component.

ResultsPressure drops over each component

in a given N infusion set, as well asflow rates, were acquired for a range ofpressurized infusions. In all cases where

Excerptfrom an article originallypublished in the March 1994 issue

o/the Annals qfEmergencyMedictne.

The relationship between flow rateand infusion pressure is nonlinear forall cases. Measurements of flow rateversus pressure drop for each compo­nent of the IV set, including the IVcatheters, are summarized in Figure 2.These results clearly indicate the flow­limiting parts in a fluid delivery setting.

DiscussionThe purpose of this investigation was

to quantify the performance character­istics of N infusion sets for rapid fluiddelivery. A quick glance at the resultsof Figure 1 reveals that the N catheteris the major flow-limiting component,as reported in previous work. 1-9 It canbe seen that an N set with a 14 gaugecatheter rather than an 18 gauge cathe­ter may increase the flow rate twofoldor more, especially during pressurizedinfusion.

The standard drip chamber (A}),which has a fine-mesh filter, imposesthe largest resistance or consumes agreat deal of the driving force whenused with a large-bore catheter (14gauge). When a small-bore catheter08 gauge) is used, the relative resis­tance of the catheter is very large, andas much as 70% of the pressure dropis consumed to drive the infusatethrough the N catheter.

12 "VAC Sum mer I 9 9 9

400

~I.

I

Figure I 15

814..... JoI_

1410 "."

-.4 u

GI11 ..

-. pup ..Ju EGI.. ......

..J(1

E • 0 Ilr1>~AI.-'ll_......(1 TV 1lr1>~11,-'11...

• 0 Ilr1>a.-AI.-.I.O.... Figure :2 0• I:> 1lr1>a.-A2.-'U'" P (mm Hg) 200

00 P (mm Hg) 300 400

An important result is obtained forgravity infusion with 50 mm Hg, whichis relevant when the fluid bag is placedabout 65 cm above the patient. In thesecases (Figure 1), the flow rate depen­dency of the catheter size (18 or 14gauge) or the tube diameter (3.2 mm or6 mm ID) is relatively weak. This hassome practical implication concerningthe choices available to increase flowrate of the administered fluid. For agiven N set, and based on the availablemethod of fluid delivery, flow rate maybe increased by using two or more infu­sion sites rather than one port with alarge-bore tube or N catheter.

Previous studies have shown that Ncatheters largely reduce the flow rate ofinfusion sets. We demonstrated thischaracteristic by measuring the pressure­flow relationships of each componentover the range of infusion pressure (Fig­ure 2). The catheter with the largestbore that we measured (14 gauge) willlimit the flow rate to about 10 rnVsec at

300 mm Hg. For the 18-gauge catheter,this value is about 3.5 rnVsec. A givenN delivery system also includes othercomponents (as required by interna­tional standards) that have resistance toflow, and accordingly, the actual flowrate will be smaller. Thus, infusion at300 mm Hg with the basic set and a 14­guage catheter yields a flow rate of 5.3rnVsec (Figure 1).

ConclusionA simple experimental method has

been presented for a comprehensivequantitative evaluation of N fluid deliv­ery systems. It has been demonstratedthat a low-resistance drip chamber canlargely increase the delivered flow rate,even at gravity-driven infusion. How­ever, N catheters remain the rate-limit­ing components of infusion sets. Theflow-through catheters become turbu­lent at relatively low delivery pressures,and thus their resistance increases withdelivery pressure.

The conclusions can be divided arbi­trarily into gravity and pressurized infu­sion. At gravity-delivered pressures (50and 100 mm Hg), the only effectiveway of increasing flow rate (more thantwofold) is to use a more efficient(low-resistance) drip chamber or to usetwo infusion sites. At pressurized deliv­ery pressures (more than 200 mm Hg),increasing catheter size from 18 to 14gauge would be more effective thandoubling the number of infusion sets.Also, a more efficient drip chamberadds an important advantage. Finally,increasing the tubing diameter addsonly minimal benefit. •

Elad, E, U Zaretsky, and 0 Heller.''Hydrodynamic evaluation of intra­venous infUSion systems." Ann EmergMed 1994; 23: 457-463. (c)1994 byAmerican College ofEmergency Physi­cians. Reprinted with permission ofMashy-Year Book, Inc., St Louis, Missouri.

REFERENCES

1. Mateer, JR, et al. Rapid fluid resuscita­tion with central venous catheter. Ann

Emerg Med 12: 149-152; 1983.2. Mateer, JR, et al. Effects of rapid infusion

with high pressure and large-bore IVtubing on red blood cell lysis and wann­ing. Ann Emerg Med 14: 966-969; 1985.

3. Millikan, J5, 11. Cain, and J Hans­brough. Rapid volume resuscitation forhypovolemic shock: a comparison oftechniques and equipment. ] Trauma

24: 428-431; 1984.4. 5adler, R, et al. Comparative flow rates

of intravenous catheters. Military Med

149: 415-416; 1984.5. Iserson, KV, AK Reeter, and E Criss.

Comparison of flow rates for standardand large-bore blood tubing. West]

Med 143: 183-185; 1985.6. Hoelzer, MF. Recent advances in intra­

venous therapy. Emerg Med Clin North

Am 4: 487-500; 1986.

7. Dutky, PA, 5L 5tevens, and KI Maull.Factors affecting rapid fluid resuscita­tion with large-bore introducer cathe­ters. ] Trauma 29: 856-860; 1989.

8. Landow, L and A 5hahnarlan. Efficacy oflarge-bore intravenous fluid administra­tion sets designed for rapid volume resus­

citation. Crlt CareMed 18: 540-543; 1990.9. Rottman, 5J, B Lannon, and T Manix.

Rapid volume infusion in prehospital care.Prehosp Disast Med 5: 225-230; 1990.

Summer 1999 ~VAD 13

10

15 ,...------------.,....----,.,.--,Figure I

14......

4-.uCII

11 ..-. ...... ..Ju ECII.. --

..J 0E • 0 ~~"I._.U---0 ... v ~~K,-,U_

• 0 ~~"I._.I.O""" Figure :2 0.to A ~~A2._'U"""

P (mm Hg) 200 40000 P (mm Hg) 300 400

8

An important result is obtained forgravity infusion with 50 mm Hg, whichis relevant when the fluid bag is placedabout 65 cm above the patient. In thesecases (Figure 1), the flow rate depen­dency of the catheter size (18 or 14gauge) or the tube diameter (3.2 mm or6 mm ID) is relatively weak. This hassome practical implication concerningthe choices available to increase flowrate of the administered fluid. For agiven IV set, and based on the availablemethod of fluid delivery, flow rate maybe increased by using two or more infu­sion sites rather than one port with alarge-bore tube or IV catheter.

Previous studies have shown that IVcatheters largely reduce the flow rate ofinfusion sets. We demonstrated thischaracteristic by measuring the pressure­flow relationships of each componentover the range of infusion pressure (Fig­ure 2). The catheter with the largestbore that we measured (14 gauge) willlimit the flow rate to about 10 mVsec at

300 mm Hg. For the 18-gauge catheter,this value is about 3.5 mVsec. A givenIV delivery system also includes othercomponents (as required by interna­tional standards) that have resistance toflow, and accordingly, the actual flowrate will be smaller. Thus, infusion at300 mm Hg with the basic set and a 14­guage catheter yields a flow rate of 5.3mVsec (Figure 1).

ConclusionA Simple experimental method has

been presented for a comprehenSivequantitative evaluation of IV fluid deliv­ery systems. It has been demonstratedthat a low-resistance drip chamber canlargely increase the delivered flow rate,even at gravity-driven infusion. How­ever, IV catheters remain the rate-limit­ing components of infusion sets. Theflow-through catheters become turbu­lent at relatively low delivery pressures,and thus their resistance increases withdelivery pressure.

The conclusions can be divided arbi­trarily into gravity and pressurized infu­sion. At gravity-delivered pressures (50and 100 mm Hg), the only effectiveway of increasing flow rate (more thantwofold) is to use a more efficientOow-resistance) drip chamber or to usetwo infusion sites. At pressurized deliv­ery pressures (more than 200 mm Hg),increasing catheter size from 18 to 14gauge would be more effective thandoubling the number of infusion sets.Also, a more efficient drip chamberadds an important advantage. Finally,increasing the tubing diameter addsonly minimal benefit. •

Elad, E, U Zaretsky, and 0 Heller.''Hydrodynamic evaluation of intra­venous infUSion systems." Ann EmergMed 1994; 23: 457-463. (c)1994 byAmerican College ofEmergency Physi­cians. Reprinted with permission ofMashy-Year Book, Inc., St Louis, Missouri.

REFERENCES

1. Mateer, JR, et al. Rapid fluid resuscita­tion with central venous catheter. Ann

Emerg Med 12: 149-152; 1983.2. Mateer, JR, et al. Effects of rapid infusion

with high pressure and large-bore IVtubing on red blood cell lysis and warm­ing. Ann Emerg Med 14: 966-969; 1985.

3. MilIikan, ]S, 11. Cain, and ] Hans­brough. Rapid volume resuscitation forhypovolemic shock: a comparison oftechniques and equipment. ] Trauma

24: 428-431; 1984.4. Sadler, R, et al. Comparative flow rates

of intravenous catheters. Military Med149: 415-416; 1984.

5. Iserson, KV, AK Reeter, and E Criss.Comparison of flow rates for standardand large-bore blood tubing. West]

Med 143: 183-185; 1985.6. Hoelzer, MF. Recent advances in intra­

venous therapy. Emerg Med Clin NorthAm 4: 487-500; 1986.

7. Dutky, PA, SL Stevens, and KI Maull.Factors affecting rapid fluid resuscita­tion with large-bore introducer cathe­ters. ] Trauma 29: 856-860; 1989.

8. Landow, L and A Shahnarian. Efficacy oflarge-bore intravenous fluid administra­tion sets designed for rapid volume resus­citation. Crit Care Med 18: 540-543; 1990.

9. Rottman, S], B Larmon, and T Manix.Rapid volume infusion in prehospital care.Prehosp Disast Med 5: 225-230; 1990.

Summer 1999 '"'VAC 13