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A Comparison of Flow Rates and Warming Capabilities of

the Level 1 and Rapid Infusion System with Various-Size

Intravenous Catheters

Sandra L. Barcelona, MD, DABA*, Fatima Vilich, MD, DABA, andCharles J. Cote, MD, DABA, FAAP*

*Department of Anesthesiology, Northwestern University, The Feinberg School of Medicine; and Department of PediatricAnesthesiology, Childrens Memorial Hospital, Chicago, Illinois

Cases involvingmassive bloodtransfusion may requirethe use of specialized blood warmers, such as the Level1 (L-1) (Level1 Technologies,Inc.,Rockland,MA) or theRapid Infusion System (RIS) (Haemonetics Corp.,Braintree, MA). In this in vitro study, we compared theinfusion and warming capabilities of the L-1 (model1000) versus theRIS using pediatric- andadult-sizedIVcatheters. The time to infuse 2 L of lactated Ringerssolution and the end temperature after infusionthrough 20-, 18-, 16-, and 14-gauge catheters, and 4-, 5-,6-, 7-, and 8.5-French catheters using both the L-1 andRIS were measured. The flow rates of both systems

were similar for 18- and 20-gauge catheters; however,the flow rates with the RIS were progressively fasterthantheL-1ascathetersizeincreasedto18gauge.Theheating capabilities of the RIS were superior to the L-1for all catheters 16 gauge. We conclude that the RISwassuperior to theL-1 forboth flow rates andwarmingcapacity for all IV catheters18 gauge, i.e., those usedfor cases with massive blood loss. The RIS provided noadvantage(withregard to heating andflow) when usedwith typical pediatric-sized catheters.

(Anesth Analg 2003;97:35863)

The Level 1 (L-1) (Level 1 Technologies, Inc., Rock-land, MA) and the Rapid Infusion System (RIS)(Haemonetics Corp., Braintree, MA) are fluid

warmers designed for rapid infusion and warming ofblood and crystalloids to adult as well as pediatricpatients. The specifications of the RIS suggest that upto 1500 mL/min can be delivered through an 8.5-French (F) sheath. However, no published data com-paring the capabilities of these devices with differentsize IV catheters exist. The purpose of this study wasto compare the heating and flow rate performance ofthe L-1 and RIS to determine which system would be

most effective with each size IV catheter. This infor-mation should help the clinician decide which systemwould be most appropriate for pediatric patients

based on the potential for massive blood loss and theIV access in place.

MethodsFlow and warming characteristics of the L-1 and RISwere examined with 9 different size IV catheters (20-,18-, 16-, and 14-gauge peripheral IV catheters [Jelco,Ethicon, Arlington, TX], 4, 5, and 6F large-volumeinfusion catheters [Cook Inc., Bloomington, IN], and 7and 8.5F introducer sheaths [Arrow International,Reading, PA]). Each catheters length was measured tothe closest millimeter using a standard ruler. The in-ternal radius of each catheter was obtained from themanufacturer.

Catheters were connected to a high-flow exten-sion set and stopcock (MS92133L; Medex Medical,Dublin, OH) and either the L-1 (model 1000) or RISstandard disposable infusion system. Each systemwas primed with room-temperature (23.8C) lac-tated Ringers (LR) solution. Both L-1 pressurechambers were used simultaneously at 300 mm Hg

This study was supported by the Childrens Memorial HospitalsDepartment of Anesthesiology research fund.

This study was presented in part at the American Society ofAnesthesiologists annual meeting, October 2000, San Francisco, CA.

FV was completing her fellowship at Childrens Memorial Hos-pital at the time this study was conducted; her current affiliation isDepartment of Anesthesiology, Loyola University, Maywood, IL.

Accepted for publication March 20, 2003.Address correspondence and reprint requests to Sandra L. Barce-

lona, MD, 2300 N. Childrens Plaza #19, Chicago, IL 60614. Addresse-mail to [email protected].

DOI: 10.1213/01.ANE.0000070235.67887.5C

2003 by the International Anesthesia Research Society358 Anesth Analg 2003;97:35863 0003-2999/03


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(maximal default setting). Because the RIS automat-ically slows its rate of infusion if the pressure ex-ceeds 300 mm Hg, it was not possible to fix theinfusion pressure exactly at 300 mm Hg. We there-fore determined the maximal flow rate allowed with

each catheter to maintain a constant infusion pres-sure of 280 295 mm Hg and then used that flow ratefor the study. Infused LR solution was collected andmeasured using a 2-L graduated cylinder (PyrexL*2982; Corning Inc., Corning, NY). The time takento infuse 1 and 2 L of LR solution (using 1-L bags)through each size catheter with both the L-1 and RISwas measured with a stopwatch. Each combinationof equipment was studied in duplicate and the re-sults were averaged. If a discrepancy 10% betweenthe two infusions existed, a third was performed,and the outlying infusion time discarded.

Temperature of the infusate was measured using a

digital thermistor from a cardiac bypass device (Elec-tromedics model TM-147T; Englewood, CO). The tipof the thermistor was secured adjacent to the tip of theIV catheter within an 8.5-mL test tube suspended atthe top of the graduated cylinder. The test tube wasused to assure that the true temperature of the infusateas it left the IV catheter was measured. If simplymeasured within the graduated cylinder, the coolingeffect of the surrounding room air decreased the re-corded temperature.

Statistical comparisons consisted of paired t-tests forwithin- and between-catheter comparisons. Regres-sion analysis using catheter radius and length as the

dependent variables was used to compare flow ratesand temperature. Spearman and Pearson correlationswere used to examine the relationship between cath-eter radius and fluid temperature.

ResultsThe difference between the maximal flow rates withthe L-1 versus RIS with 20- and 18-gauge catheterswas negligible. For catheters 16 gauge, the RIS be-came progressively more efficient than the L-1 at rap-idly infusing crystalloid (P 0.008); the largest differ-ence occurred with the 8.5F catheter (Fig. 1). For bothdevices, the flow rates of crystalloid were directlyrelated to catheter radius (L-1, P 0.02; RIS, P 0.001)(Table 1). Catheter length was an independent deter-minant of flow rate using the RIS (P 0.025) but notusing the L-1 (P 0.063). As catheter size incremen-tally increased to 14 gauge and larger, there wererelatively smaller increases in flow rates with the L-1than with the RIS (Fig. 2). The largest incrementalincrease in flow for both systems occurred when in-creasing from 18 to 16 gauge (Table 1).

An additional observation was that the infusion

rates of the L-1 were dependent on the amount of fluid

present in the bags. The time taken to infuse the sec-ond liter through the L-1 was universally longer thanthat to infuse the first liter (Table 2) (P 0.005); thiswas not true when comparing the first- and second-liter flow rates for the RIS (P 0.716).

There was also a difference between devices in theability to warm fluids (Table 3). The L-1 heated theinfusate more efficiently than the RIS with the 20-gauge catheter. The systems were identical whenusing 18-gauge catheters. However, with catheters16 gauge, the heating performance of the RIS was

better than that of the L-1. Pair-wise comparisonsshowed that the RIS demonstrated less change inend-temperature readings as flows increased (P 0.004, Fig. 3). Both Pearson and Spearman correla-tions demonstrated a significant negative relation-ship between catheter radius and lower final fluidtemperature for the L-1 (P 0.008) but not for theRIS (P 0.862). The heating capability of the L-1was inversely related to the flow rate (Fig. 3) ( r

0.807) whereas there was no relationship for the RIS

Figure 1. Percent difference in flow rates for the Rapid InfusionSystem (RIS) versus Level 1 for all catheter sizes. Note that the RIS

produces progressively greater incremental changes in flow forcatheters 16 gauge (g). F French.

Table 1. Flow Rate Comparison of L-1 Versus RIS

Catheter size

Internalradius(mm)

Length(mm)

Flow L-1(mL/min)

Flow RIS(mL/min)

20 gauge 0.423 33 140 14418 gauge 0.515 52 209 20516 gauge 0.705 55 368 41214 gauge 0.895 64 488 5844F 0.675 34 450 5165F 0.835 42 533 667

6F 1.00 75 548 7027F 1.175 110 564 7728.5F 1.43 112 596 857

L-1 Level 1, RIS Rapid Infusion System, F French.

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(r 0.022). The RIS was able to heat fluids to 37Cfor all flow rates studied, whereas L-1 infusate tem-peratures increased only to the 3435C range withthe largest catheters.

DiscussionOur study demonstrated that the L-1 system is asefficient as the RIS at transfusing crystalloid rapidlywhen used in conjunction with a 20- or 18-gauge

catheter. However, as catheter size is increased 18gauge, the infusion rates provided by the RIS be-come progressively greater than those of the L-1. Wecompared the systems by using only one arm of theRIS infusion set. It is likely that the RIS is capable ofeven more rapid fluid delivery if both arms of theinfusion set are used. Conversely, two L-1 systemscould be used at less of a cost than the RIS. This may

be adequate in pediatric patients who are not ofadult size.

Another difference was that the end temperatureachieved with the L-1 was inversely proportional toflow rate whereas end temperatures using the RISwere more consistent over a wide range of flowrates. The end temperatures achieved with the RISwere consistently 36C for all flow rates. The endtemperature obtained with the L-1 was 36C onlyfor flows 400 mL/min. The end temperaturesachieved by the RIS using the smallest catheters(i.e., longest infusion times) (20- and 18-gauge) werelower than with many of the larger catheters. Thisprobably occurred secondary to cooling of the fluidas it traversed the nonheated extension tubing to thegraduated cylinder (1). Because blood products areoften cold when being infused, the end tempera-

tures achieved with either device when infusing

blood would likely be lower than what we mea-sured using room-temperature crystalloid.

An additional observation that may be clinically rele-vant was the incremental increase in infusion capacity ofsuccessively larger IV catheters. Of the catheters tested, a

16- versus an 18-gauge catheter provided the largestincremental increase in maximal flow (with both the L-1and RIS) than any other sequential increase in cathetersize. This is a function of the increase in the radius of thecatheter lumen; the radius of the 16-gauge catheter is37% larger than the 18-gauge catheter. As dictated byPoiseuilles Law, the radius is the most important factordetermining maximal flow of a given fluid. Flow (P1 P2) r 4/8L describes this relationship where P1 andP2 are pressures at the proximal and distal ends of thetubing, r is the radius of the tubing, is viscosity of thefluid, and L is length of tubing (2). The additional im-portance of catheter length is demonstrated when com-

paring the flows through the 14-gauge and 5F catheters.Although the radius of the 5F is smaller than that of the14 gauge, its flows are faster with both the L-1 and theRIS (the length of the 5F is 52% less than the 14-gaugecatheter). Although Poiseuilles Law demonstrates im-portant factors, the actual flow of fluid under pressure isdescribed as a quadratic equation because of the devel-opment of turbulence (3). This explains in part why evenlarger-bore catheters are not capable of delivering theflows predicted using only Poiseuilles Law (4).

In the United States, peripheral IV catheters areconventionally sized in terms of gauge whereascentral venous catheters are described in F sizes.

The gauge system was designed in the 19th centuryfor use in wire manufacturing and uses arbitrarymultiples of 0.0010 in. in inverse rank ordering ofsizes (5). The F system, also developed in the 19thcentury, is based on uniform incremental measure-ments of 0.333 mm and was originally used forsizing urologic and other medical devices (6). Dif-ferences in wall thickness and rounding of the sizesaccount for the actual measurements not being strictmultiples of the above-stated increments. The over-lap between these measurement systems is demon-strated in Table 1. The catheters for which this over-lap occurs are the larger-gauge IV catheters andsmaller-size F catheters (16- and 14-gauge and 4 and5F). Central lines of this caliber are more likely to beplaced in children than adults. These internal-diameter measurements may provide some guid-ance as to which catheters (i.e., larger peripheralversus smaller central lines) should allow more flowin a given patient regardless of which type of infu-sion system is being used in conjunction with them.

Our study also found that the RIS allows a constantrate of infusion over a large volume whereas the L-1flows slow down as the IV bags empty. Despite using

both L-1 pressure chambers simultaneously, it consis-

tently took longer to infuse the second liter of fluid

Figure 2. Flow rate and catheter size for the Rapid Infusion Systemversus Level 1 (L-1). Note that there is a minimal change in flow

capacity with the L-1 device for all catheters 14 gauge (g). *P 0.05; F French.

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than the first. Although a constant amount of pressure(300 mm Hg) is applied to the bag within the pressurechamber, the additional hydrostatic pressure exerted

by the column of fluid within the bag may have someeffect. As the bag empties, the smaller column of fluidexerts less force upon the infusion and thus it slows. It

may also relate in part to changes in the configuration

of applied pressure as the bags empty. This phenom-enon does not occur when using the RIS because ituses a roller pump mechanism and does not depend atall on gravity or compression of the bag. Although aconsistent observation, this is likely of minimal clinicalimportance.

When caring for infants and toddlers in the periop-erative setting, neither the L-1 nor RIS is typicallynecessary to meet transfusion requirements unlessmassive hemorrhage occurs. Manual methods for de-livering fluids have traditionally been used for thesesmall patients. For small-bore IV catheters (22- and24-gauge), rapid withdrawal and injection of fluidswith a syringe and stopcock is more efficient than

pressure pump chamber compression and is most ef-ficient when performed with a 10-mL syringe (7). In-flatable pressure bags can also deliver fluids morerapidly than manual compression of drip chambers,

but will be rate limited if used with conventionalblood warmers that require fluids to traverse coiledtubing within a heating plate (8,9). This additionallength of coiled tubing provides considerable resis-tance and requires a long contact time with the heatingplate to allow adequate warming. Conversely, the L-1and RIS provide superior heating and flow of fluids byusing counter-current heat exchangers and heated wa-

ter baths to avoid the increased resistance of coiled

Table 2. L-1 Versus RIS Infusion Times for 1 and 2 L of Crystalloid

Cathetersize

Time (s) L-1 Time (s) RIS

1st L 2nd L 2 L total 1st L 2nd L 2 L total

20 gauge 408.5 449 857.5 419 415 834

18 gauge 268 306.5 574.5 285.5 299.5 58516 gauge 154.5 171.5 326 147.5 144 291.514 gauge 118 128 246 102.5 103 205.54F 127 139.5 266.5 116 116.5 232.55F 110.5 114.5 225 90 90 1806F 106 119 225 86.5 84.5 1717F 102 110 212 77.5 78 155.58.5F 96 105.5 201.5 70 70 140

L-1 Level 1, RIS Rapid Infusion System, 1st L first liter, 2nd L second liter, F French.

Table 3. End-Temperature Differences of L-1 Versus RIS

Catheter sizeL-1 end temperature

(C)RIS end temperature

(C)End-temperature difference

(C) RIS versus L-1

20 gauge 38.5 37.3 1.218 gauge 38.1 38.1 016 gauge 36.4 39.0 2.614 gauge 35.4 38.8 3.44F 35.6 38.8 3.25F 34.8 38.5 3.76F 35.1 38.8 3.77F 35.4 38.0 2.68.5F 34.6 37.6 3.1

L-1 Level 1, RIS Rapid Infusion System, F French.

Figure 3. Mean temperature at the end of 2 2-L infusions of crystalloidfor Level 1 (L-1) versus the Rapid Infusion System. Note that bothdevices are equivalent with flow rates of200 mL/min but that thereis markedly less warming capacity with the L-1 at higher flow rates.



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tubing used in heating-plate-type blood warmers(10,11). They provide superior flow rates to manualmethods and help to free anesthesiologists hands dur-ing times of rapid transfusion. Because of these ad-vantages, their use should be considered in situations

of massive transfusion in patients of all sizes.The differences in capabilities of the L-1 and the RISfound in this study may be partially explained bydifferences in their design. The L-1 is smaller and lesstechnically complex. It consists of a simple disposableinfusion set of large-bore IV tubing which can beconnected to two infusion bags (i.e., crystalloid or

blood product). Each infusion bag may be placedwithin a pressure chamber and infused under 300 mmHg of pressure or may simply flow by gravity. Fluid iswarmed in the heat exchanger as described above. Asingle air filter and vent are located distal to the heatexchanger. The L-1 disposable infusion set is easy to

install, and costs approximately 20 times less than thatof the RIS (approximately $20 United States dollars[USD] for L-1 versus approximately $440 for RIS). Theinitial purchase cost of the L-1 infusion device is alsomuch less than the RIS (approximately $5500 versusapproximately $51,700 USD). Disadvantages of the L-1system are its lack of low-fluid indicator and its infe-rior air-removal capabilities. Despite its air filter, fatalair embolism has been reported with the use of theL-1, and thus all air must be removed from fluid bags

before placing them into the pressure chamber forinfusion (12,13). The necessity for manual removal ofair adds time to the changeover of fluid bags. This

may be suboptimal during an emergent situation.The RIS uses a similar strategy for warming as the

L-1. However, the RIS also uses the principles of car-diopulmonary bypass, allowing rapid transfusion offluids and increasing safety. It uses a 3-L reservoir anda roller-pump mechanism for transfusing fluids. Lowreservoir alarms with automatic flow shut-off, two airdetectors, as well as a debubbling filter are incorpo-rated to help prevent air embolism and increase thesafety of rapid transfusion. The RIS also has an over-pressure alarm to prohibit high-pressure delivery offluid into a nonvascular space or to alert the clinicianof an obstruction or kink in the catheter or tubing. Theamount of fluid given, the current flow rate, temper-ature, and infusate pressures are provided by digitaldisplay. The anesthesiologist has the capability ofchanging the flow rate to a precise amount between 0and 1500 mL/min. A one-step mechanism by which todeliver a 100- or 500-mL fluid bolus may aid theoperator in fluid management as well. These featuresdemonstrate how the RIS is more technically ad-vanced than the L-1. The main disadvantages of theRIS are its expensive cost, the complexity of the set-up,and its larger footprint. Another theoretical disadvan-tage is that the large reservoir requires priming with

multiple units of blood products that may result in

unnecessary exposure of the patient, i.e., partial infu-sion of multiple combined units. The RIS set-up re-quires a series of specific steps that may be time con-suming for the occasional user.

In our pediatric institution, in situations of potential

massive blood loss, it is common practice to use 1 or 2L-1 devices for children under 30 kg. We considerusing the RIS for children larger than 30 kg in whomsurgical pathology, coagulopathy, or re-do surgeryplaces the patient at additional risk. Our data regard-ing flow rates confirm that this is likely to be a rea-sonable transition point because peripheral IV cathe-ters 16 gauge and central venous catheters 5F arelikely to be placed in patients of this size. Although a10% (16 gauge) to 25% (5F) advantage in flow with theuse of the RIS compared with the L-1 may not seemclinically important, considering RIS use in these

larger pediatric patients has allowed us to maintainour skills and familiarity with the device.The findings of our study are somewhat limited

because, in clinical situations, the rates achieved witheither system would probably be less because of ve-nous resistance and increased turbulence (14). Addi-tionally, in massive transfusion situations, crystalloidsare only part of the resuscitation process. Transfusionof blood products would be slower because of theirincreased viscosity (15). We chose to study crystalloidsrather than blood products because of the ease ofobtaining large quantities and as a means of establish-ing some of the differences between the two transfu-

sion systems.The RIS has proven life-saving in situations of

adult-sized pediatric patients with massive hemor-rhage, e.g., liver transplantation, trauma, and livertumor resection. We recently cared for a 12-yr-old,60-kg patient undergoing hepatoma resection inwhich the advantages of the RIS were clearly demon-strated. The patient suddenly developed massive,rapid intraoperative hemorrhage, which 4 anesthesi-ologists and 2 L-1 devices could not match. The pa-tient became hemodynamically unstable and the he-moglobin level decreased to 1 g/dL. Switching to the

RIS enabled us to transfuse 50 L of blood productsand crystalloid through 2 7F introducers in 1 hourwhile surgical control over bleeding was obtained andthe patient was stabilized. The total transfusion for thecase was 46 L of crystalloid, 55 U of packed red bloodcells, 30 U of fresh frozen plasma, and multiple phere-sis units of platelets. Despite all of this, the childs coretemperature never decreased to 34.5C. Accordingto our data for crystalloid, the RIS is capable of deliv-ering 25 L more fluid than the L-1 with these sizecatheters over 60 minutes. Although the increasedviscosity of blood products and patients venous re-

sistance may limit the in vivo amount of fluid able to

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be given, the difference between the devices capabil-ities as demonstrated in our patient can be clinicallyimportant.

In conclusion, both devices offer advantages anddisadvantages and each clinician and each hospital

must decide which equipment is most appropriatefor their surgical population. In infants and smallerpediatric patients, the added cost and complexity ofthe RIS cannot be justified. Nor can its use be justi-fied for use with catheters smaller than 16 gauge.Although the RIS has superior warming capabilities,other methods of warming the patient, e.g., forced-air warming blankets, must be considered. How-ever, larger pediatric patients, like adults, may ben-efit from the use of the RIS. The decision to use theRIS instead of the L-1 is based on the rate andduration of massive bleeding. For example, even

though there may only be a 20% difference in flowper minute through a 14-gauge IV catheter, thismeans double the transfused volume every 5 min-utes. The differences become even greater with cath-eters 5F, and the RIS also offers the advantage ofnot having to vent air from bags of crystalloid or

blood products before infusion. When decidingwhich device may be most useful in a particularpediatric patient, one must consider the size of thepatient, the size of available venous access, the po-tential for rapid bleeding, and likelihood ofhypothermia.

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3. Philip BK, Philip JH. Characterization of flow in intravenousinfusion systems. IEEE Trans Biomed Eng 1983;30:7027.

4. Idris A, Melker RJ. High-flow sheaths for pediatric fluidresuscitation: a comparison of flow rates with standard pediat-ric catheters. Pediatr Emerg Care 1992;8:119 22.

5. Iserson KV. The origins of the gauge system for medical equip-ment. J Emerg Med 1987;5:45 8.

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a blood warmer that utilizes a 40 degrees C heat exchanger.Transfusion 1990;30:710.

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