Effective methods of in-line intravenous fluid
`warming at low to moderate infusion rates
`
`Lt Col C. CARL BOSTEK, CRNA, MSN, USAF, NC
`Minot Air Force Base, North Dakota
`
`Three methods of warming intravenous (IV)
`fluids were examined. An in-line blood
`warmer was generally ineffective at flow rates
`of< 250 mL/hr but did produce temperatures
`of 80 to 310C at the catheter when the infusion
`rate was 500 to 1,000 mL/hr and the tubing was
`insulated. An in-line hot water bath
`- 30°C at flow rates
`produced temperatures of
`of200 to 1,000 mL/hr with uninsulated tubing.
`The addition of insulation maintained an
`infusate temperature of 30°C at a rate of
`100 mL/hr. Application of a K-Thermia®
`pad to the IV tubing close to the patient
`maintained an infusate temperature of 2 300 C
`at rates of 50 to 200 mL/hr. Warming at rates
`of 200 to 1,000 mL/hr is most effective with an
`in-line hot water bath. Warming at low
`infusion rates is best accomplished with a
`K-Thermia pad. The use of in-line blood
`warmers for routine fluid warming is
`ineffective.
`Key words: Hypothermia prevention,
`intravenous fluid temperature,
`intravenous fluid warming.
`
`Introduction
`The incidence of hypothermia has been reported
`to be as high as 60% during elective surgery.' De-
`creased oxygen delivery resulting from a left shift
`of the oxyhemoglobin dissociation curve, de-
`creased tissue perfusion secondary to vasoconstric-
`
`tion, an increased incidence of deep vein thrombo-
`sis and pulmonary embolism, increased plasma
`levels of catecholamines and thyroid hormones,
`coagulopathy, increases in oxygen consumption
`during light general anesthesia, increases in car-
`bon dioxide production and oxygen consumption
`up to 300% as a result of shivering, and, possibly,
`prolonged emergence and recovery from anesthe-
`sia are all potential sequelae of hypothermia.2.
`Causes of hypothermia in the operating room
`include the use of unwarmed intravenous (IV) and
`irrigation solutions, unheated dry gases, low room
`temperatures, and the administration of drugs
`which impair thermoregulation. The metabolic
`cost of heating unwarmed fluids is approximately
`16% of basal heat production when fluid require-
`ments reach 6 mL/kg per hour in a 70-kg patient.2
`This level is readily exceeded when infusion rates
`are increased to compensate for decreases in blood
`pressure or periods of increased blood loss. Thus,
`the body heat expended to warm IV fluids admin-
`istered at room temperature is a significant por-
`tion of basal heat production.
`Heat loss can be reduced by preheating IV
`fluids or by in-line warming during administra-
`tion. But neither method provides near body tem-
`perature infusate unless flow rates are - 1 L/hr.4-7
`Allowing for basal metabolic requirement, 6 mL/kg
`per hour for interstitial losses, and replacement of
`nothing by mouth induced fluid deficit over 3
`hours, the fluid requirement during the first 3
`hours of a major abdominal case will approximate
`850 mL/hr in a 70-kg patient. This infusion rate is
`
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`
`too slow to provide near body temperature infusate
`when using preheated fluids or an in-line blood
`warmer.
`The purpose of this study was to evaluate the
`effectiveness of two alternative in-line warming
`techniques at loss infusion rates. Warming was ac-
`complished by immersing IV tubing in a high-
`temperature water bath or by wrapping a K-Ther-
`mia® pad around the IV tubing close to the inser-
`tion site. Results of warming by these methods were
`compared with in-line warming using a common
`blood warmer.
`Methods and procedures
`In all groups, a Mon-a-therm® Model 6000
`(Mon-A-Therm, Inc., St. Louis, Missouri) with a
`specially modified skin sensor probe was used to
`measure temperature at the distal end of the IV
`extension tubing by threading the probe into an
`Extension Set with "T" (Abbott Hospitals, Inc.,
`North Chicago, Illinois) (Figure 1). Flow rates of
`50, 100, 150, 200, 250, 500, and 1,000 mL/hr were
`
`Figure I
`Distal end of infusion setup
`
`Modified skin temperature probe has been inserted under the
`rubber stopper into the T-piece to simulate measurement
`of infusate temperature at the catheter site. An extension tube
`was attached to the distal end of the T-piece to prevent
`evaporation of infusate at that point.
`
`achieved using an AVI GuardianTM 100 Infusion
`Pump (AVI, Inc., St. Paul, Minnesota) positioned
`between the IV bag and the heating device. A flow
`rate of 6,000 mL/hr was the maximum attained
`through unrestricted IV tubing.
`For Group I, fluids were warmed by passing
`them through a Pharmaseal® warming coil
`(Pharmaseal Co., Valencia, California) in a Phar-
`maseal DW 1000 Blood Warmer (Table I). In
`Group Ia, a single length of Pharmaseal K50L ex-
`tension tubing (capacity 3.3 mL, length 84 cm) and
`a Pharmaseal K52 extension tube with stopcock
`were attached to the distal end of the coil. In Group
`Ib, only a K52 was attached, and in Group Ic, a
`K52 was insulated with a strip of "egg crate" foam
`insulation (E.R. Carpenter Co., Medical Products
`Division, Russellville, Kentucky).
`In Group II, half the length of a K50L exten-
`sion tubing was coiled into a water bath (Marquest
`Medical Products, Inc., Englewood, Colorado)
`heated by an MR 430 Servo Controlled Heated Re-
`spiratory Humidifier set at 37 0 C (Isothermal/
`Fisher & Paykel, Ltd., Riverside, California). The
`actual temperature of the water was 650 C. Approx-
`imately 38 cm of the extension tube was distal to
`the water bath. In Group IIa, the tubing distal to
`the bath was exposed to room air, while in Group
`IIb, it was insulated with a strip of blue foam insu-
`lation. To test for the presence of plasticizer-the
`chemical responsible for the flexibility of IV bags
`and tubing-an extension tube was filled with
`preservative-free sterile water and heated for 8
`hours. The heated infusate was then spectrophoto-
`metrically scanned at wavelengths from 200 to
`750 nm.
`For Group III, a single length of K50L exten-
`sion tubing was coiled inside a 20 x 30-cm K-Ther-
`mia Pad heated by an Aquamatic K-Thermia
`Model RK-600 (Gorman-Rupp Industries, Bell-
`ville, Ohio) which had been folded in half along its
`length and again along its width to form a pad
`approximately 10 x 15 cm. In Group IIIa, the
`heater was set to 38 0 C, and the T-piece was left
`exposed to room air. In Group IIIb, the heater was
`set to 410 C, and the T-piece was again left exposed
`
`Table I
`Summary of warming methods and insulation used by groups and subgroups
`Group I
`Group II
`Warming method
`Pharmaseal warmer
`Water bath
`Subgroup
`a
`c
`b
`a
`b
`Tubing plus extensions K50/K52
`K52
`K52
`38 cm
`38 cm
`Insulation
`-
`-
`Foam
`-
`Foam
`
`Group III
`K-Thermia
`b
`at 41°C
`10 cm
`-
`
`a
`at 370C
`10 cm
`-
`
`c
`at 41°C
`10 cm
`Pad
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`
`to room air. In Group IIIc, the heater was set to
`41 0 C, but the T-piece was surrounded by the
`K-Thermia pad.
`In all groups, the IV solution had been stabi-
`lized overnight at room temperature, and in-line
`temperatures were allowed to stabilize for 5 to 10
`minutes after changes in flow rate. Five tempera-
`tures were recorded at 15-second intervals for each
`flow rate. Room and IV bag temperatures ranged
`from 21.3 to 23.10 C.
`Results
`SPSS 4.0 (Statistical Package for Social Sci-
`ences, version 4.0) on a DEC VAX/VMS was used
`for statistical analysis. Analysis of variance revealed
`statistically significant differences among the
`groups at the .05 level. The Tukey-B procedure
`was used for pairwise comparisons. Statistically sig-
`nificant differences are summarized in Table II. In
`the following discussion, temperature measure-
`ments are reported as means plus or minus (±) one
`standard deviation.
`In Group I, the most effective warming oc-
`curred when a single extension tube was used and
`insulation was applied from the warming coil to
`the insertion site (Figure 2). Fluid temperatures at
`the catheter when using the Pharmaseal blood
`warmer with insulation and a single extension tube
`were never above 30 0C at low or moderate flow
`rates. At a rate of 1 L/hr, the infusate temperature
`at the catheter was 30.72 ± .22 0 C with two exten-
`sion tubes and no insulation, 30.66 ± .110 C with
`an uninsulated K52 extension, and 30.54 ± .060 C
`with an insulated K52 extension. Increasing the
`flow rate through the blood warmer to 6 L/hr pro-
`duced infusate temperatures at the catheter of
`33.64 ± .060C with two extension tubes and no in-
`sulation, 33.68 ± .130 C with an uninsulated K52
`extension tube, and 34.54 ± .11 0C with an insu-
`lated K52 extension. Except for flow rates of 50,
`100, and 1,000 mL/hr, the use of insulation with
`only a K52 extension tube provided significantly
`greater warming (P< .05).
`In Group II,
`the most effective heating oc-
`curred when insulation was applied to the exten-
`sion tube leading from the water bath (Figure 3).
`Infusate temperatures 2 30 0C at the catheter were
`achieved with the water bath and uninsulated tub-
`
`Figure 2
`Mean (± 1 standard deviation) temperatures of
`intravenous infusate at the catheter site after warming
`with an in-line blood warmer
`Temperature (°C)
`32
`
`30
`
`28
`
`26
`
`22-
`
`24
`
`--
`--
`
`Group la
`-- Group lb
`Group Ic
`
`20
`
`,
`,
`0 100 200 300 400 500 600 700 800 900 1000 1100
`Flow rates (mL/hr)
`Group la-Two extension tubes and a T-piece
`Group Ib-One extension tube and a T-piece
`Group Ic-Insulation added to one extension tube and
`T-piece
`
`ing at flow rates of 200 to 1,000 mL/hr. When the
`30 0 C were
`tubing was insulated, temperatures -
`achieved with flow rates of 100 to 1,000 mL/hr. The
`warmest temperature attained was 38 ± .040 C at a
`flow of 500 mL/hr. The use of insulation provided
`significantly greater heat retention at all flow rates
`from 50 to 500 mL/hr (P< .05).
`In Group III, warming was most effective
`when the K-Thermia pad completely covered the
`extension tube and insertion site (Figure 4). The
`lowest flows provided the most effective warming:
`infusate temperature was 38.4 ± .040 C at 50 mL/hr,
`.04 0 C at 100 mL/hr, 32.1 ±
`.070 C at
`34.2 ±
`150 mL/hr, and 30.1 ± .07 0C at 200 mL/hr. The use
`of a warming temperature of 41 0 C with the exten-
`sion tube provided significantly greater warming
`at rates of 50, 100, and 150 mL/hr (P< .05).
`Discussion
`Warming of IV fluids is traditionally accom-
`plished by preheating the bottles in warming cabi-
`
`Table II
`ANOVA showed these warming methods to be significantly different at the .05 level at the Infusion rates Indicated.
`Water bath
`Warmer
`---, 100,150, 200, 250, 500,1000, 6000
`50, 100,150, 200, 250, 500
`
`Water bath
`K-Thermia
`
`50, 100, --, 200, 250, 500
`
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`
`Figure 3
`Mean (± 1 standard deviation) temperatures of
`intravenous infusate at the catheter site after warming
`with an in-line hot water bath
`Temperature (°C)
`40
`
`Figure 4
`Mean (± 1 standard deviation) temperatures of
`intravenous Infusate at the catheter site after warming
`with a K-Thermla pad
`Temperature (°C)
`40
`
`38
`
`36
`
`34
`
`32
`
`30
`
`28
`
`26
`
`24-
`
`22
`
`----
`
`Group Ila
`S---- Group lb
`
`38
`
`36
`
`34
`
`32
`
`30
`
`28
`
`26
`
`24
`
`22
`
`-
`
`--
`
`---
`
`-
`
`-
`--
`
`Group Ilia
`Group IIIb
`Group llic
`
`0
`
`100 200 300 400 500 600 700 800 900 1000 1100
`Flow rates (mL/hr)
`Approximately 40 cm of the first extension tube was
`threaded into the hot water bath. The remaining tubing
`was long enough to reach from the bath to a patient.
`Group la-One extension tube plus T-piece
`Group Ib-lnsulation added to one extension tube
`plus T-piece
`
`nets or running the IV tubing through an in-line
`blood warmer. Neither of these methods has
`proven completely satisfactory. This study exam-
`ined the effectiveness of insulating the tubing be-
`tween an in-line blood warmer, use of a hot water
`bath with minimal tubing between the bath and
`the patient, and use of a K-Thermia pad to pro-
`duce near body temperature infusate at the cathe-
`ter. Norman, Ahmad, and Zeig warmed bags of
`crystalloid in warming cabinets to 500 C and found
`that, over 1 hour, the temperature of infusate at the
`catheter decreased linearly from 37 to 310 C when
`the infusion was run at 1,000 mL/hr. Solution that
`was heated initially to 60 0 C decreased in tempera-
`ture at the catheter from 36.5 to 310 C after 1 hour
`and 27 0 C after 2 hours when run at 500 mL/hr.
`The tubing length was 275 cm, infusion pumps
`were not used, and the ambient room temperature
`was 23 to 250 C.5
`
`20
`
`0
`100
`200
`300
`400
`500
`600
`Flow rates (mL/hr)
`Group Illa-Heater set to 380C with the T-piece exposed
`to room air
`Group Illb-Heater set to 41 °C with the T-piece exposed
`to room air
`Group Illc-Heater was set to 41 °C but the T-piece was
`surrounded by the pad
`
`Skrivanek and Hein infused crystalloid solu-
`tions through a Pharmaseal blood warmer at rates
`of 1 to 12 L/hr. Ambient room temperature was
`20.4 to 20.90C. The temperature at the catheter site
`was 260 C when the infusion rate was 1 L/hr, 32.5 0 C
`at 2.4 L/hr, 29 0 C at 6 L/hr, and 26°C at 12 L/hr
`with two extension tubes attached to the IV tubing.
`With no extension tubes, the temperatures at the
`infusion site were 27.5 0 C, 310 C, 32 0 C, and 270C,
`respectively. An attempt to prevent heat loss by
`wrapping the IV tubing between the blood warmer
`and catheter with aluminum foil failed to increase
`infusate temperatures.6
`Aldrete also investigated the effect of infusion
`rate and tubing length on the temperature of
`infusate at the catheter site. The temperature of
`infusate at the catheter remained approximately
`250°C throughout the infusion period when the bag
`was warmed initially to 34.4 0 C and the infusion
`
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`rate was set to 100 mL/min (6 L/hr) using an IVAC
`pump. When infused at 20 mL/min (1.2 L/hr), the
`temperature at the catheter remained approxi-
`mately 23°C. Warming the bags to 41.4°C provided
`an infusate temperature of 33.5°C at the catheter
`(100 mL/min) when the IV tubing was 180 cm long.
`Increasing the tubing length to 230 cm decreased
`the temperature of the infusate to approximately
`31.8°C. When bags were heated to 42.8°C and the
`fluid passed through a blood warmer at 36°C, the
`temperature of infusate at the catheter was 28 to
`30°C. Significant heat was lost from the IV fluid,
`since the blood warmer was cooler than the
`infusate.7
`Regardless of the method, preheating IV
`fluids only provides infusate temperatures - 30°C
`when the initial fluid temperature is ? 40°C
`and flow rates exceed 500 mL/hr. This occurs be-
`cause the large surface area of IV tubing allows
`rapid cooling of warm fluids. And since surface
`area varies directly with tubing length, the use of
`extensions will speed cooling. Furthermore, blood
`warmers are generally ineffective in providing
`body temperature infusate at the catheter because
`of the distance between the warmer outlet and the
`catheter site and because the warmer only reaches
`a temperature of approximately 37°C. The use of
`foam insulation slows heat loss from tubing, but
`this is of no clinical significance at low rates.
`The K-Thermia pad warms the air surround-
`ing the IV tubing. The heat in the air is conducted
`across the tubing to the fluid, making for an ineffi-
`cient warming system. The pad provides good
`warming at low rates if there is no exposed tubing,
`because low flows allow plenty of time for the
`infusate to warm. At higher flows, the pad is inef-
`fective, largely because of the poor heat conduc-
`tion.
`The water bath is the most efficient warming
`system studied, because of the high temperature of
`the bath and the excellent heat conduction between
`the water and the tubing. It provides for near body
`temperature infusate over the widest range of tem-
`peratures (Figure 5). However, a potential problem
`with this technique was recognized when the IV
`tubing in the bath was seen to become opaque with
`prolonged heating, raising the possibility that plas-
`ticizer would diffuse into the IV fluid.
`Plasticizers are important components of many
`plastic articles used in medical practice because
`they provide flexibility. Plasticizers, especially the
`phthalates, have been tested extensively in animal
`models and have been found safe when ingested
`orally. Phthalate plasticizers, however, will kill
`myocardial cells in tissue culture and can induce
`acute respiratory distress when injected IV at doses
`
`Figure 5
`Comparison of mean (± 1 standard deviation)
`temperatures of intravenous infusate at the catheter
`site after warming with the most effective method
`from each group
`Temperature (°C)
`39-
`
`37
`
`35
`
`33
`
`31
`
`29
`
`27
`
`25
`
`23
`
`21 1.
`
`-----
`
`Group Ic at 20°C
`SGroup Ilb at 20°C
`Group Illc at 20°C
`
`19
`
`0 100 200 300 400 500 600 700 800 900 1000 1100
`Flow rates (mL/hr)
`In-line blood warmer with one extension
`Group Ic-
`tube plus T-piece, insulated.
`Group lib-In-line hot water bath, one extension tube
`plus T-piece, insulated.
`Group Illc-K-Thermia pad covering all tubing and set
`to 41°C.
`
`of 200 mg/kg of body weight.'!' Blood and plasma
`proteins will leach plasticizer from intravenous
`bags and tubing made from polyvinyl chloride
`(PVC), but crystalloid solutions will not."10- 2 Fur-
`thermore, microwave warming of plastic IV bags
`containing crystalloid solutions shows no increase
`in plasticizer concentration when compared to con-
`trol fluids at room temperature. ':
`In this study, IV tubing filled with sterile water
`was heated in the water bath for 8 hours. Spectro-
`photometric analysis showed no change in optical
`density of the heated solution when compared with
`sterile water that was not heated in IV tubing. This
`observation, though not definitive, makes it seem
`unlikely that leaching of plasticizer into heated IV
`tubing is a major problem.
`No single method of warming IV fluids can
`provide body temperature infusate at the catheter
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`at all flow rates. Flow rates in excess of 1 L/hr are
`common in resuscitation efforts, and the infusion
`of fluids prewarmed to 500 C effectively provides
`infusate temperatures near 370C at the catheter.'
`But flow rates of 200 to 600 mL/hr are more com-
`mon during major elective surgery in adults, while
`even lower flows are associated with pediatric
`patients.
`
`Conclusions
`1. There is no single method for warming IV
`fluids that will provide near body temperature
`infusate at all flow rates.
`2. The Pharmaseal DW 1000 blood warmer is
`ineffective in providing near body temperature
`infusate when used with long extension tubing.
`3. A hot water bath located close to the infu-
`sion site is the most effective means of providing
`near body temperature infusate at flow rates of
`100 to 1,000 mL/hr if exposed tubing is insulated
`with foam. Warming is effective at rates from
`250 to 1,000 mL/hr when exposed tubing is not
`insulated.
`4. A K-Thermia pad applied around the tub-
`ing and close to the insertion site provides near
`body temperature infusate at or below 100 mL/hr.
`
`Clinical recommendations
`1. The first bottle of IV fluid given when a
`patient comes to surgery should be prewarmed,
`since that bottle is usually infused in less than 1
`hour.
`2. Loss of body temperature from the infusion
`of cold IV fluids will be minimized by using a
`single intravenous site for administration of
`
`warmed maintenance fluids while keeping veins
`open at other available sites.
`REFERENCES
`(1) Vaughan MS, Vaughan RW, Cork RC. Postoperative hypothermia
`in adults: Relationship of age, anesthesia, and shivering to rewarming.
`AnesthAnalg. 1981;60:746-751.
`(2) FlackeJW, Flacke WE. Inadvertent hypothermia: Frequent, insidi-
`ous, and often serious. Seminars in Anesthesia. 1983;2:183-196.
`(3) Reed HL, Chernow B, Lake CR, et al. Alterations in sympathetic
`nervous system activity with intraoperative hypothermia during coro-
`nary artery bypass surgery. Chest. 1989;95:616-622.
`(4) Leaman PL, Martyak GG. Microwave warming of resuscitation
`fluids. Ann Emerg Med. 1985;14:876-879.
`(5) Norman EA, Ahmad I, Zeig NJ. Delivery temperature of heated
`and cooled intravenous solutions. Anesth Analg. 1986;65:693-699.
`(6) Skrivanek GD, Hein HAT. Fluid warming: Effectiveness with ex-
`tension tubing. Anesthesiology. 1986;65:A126. Abstract.
`(7) Aldrete JA. Preventing hypothermia in trauma patients by micro-
`wave warming of IV fluids. JEmerg Med. 1985;3:435-442.
`Jaeger RJ, Rubin RJ. Some pharmacologic and toxicologic effects
`(8)
`of di-2-ethylhexyl phthalate (DEHP) and other plasticizers. Environ
`Health Perspect. 1973;3:53-59.
`(9) Schulz CO, Rubin RJ, Hutchins GM. Acute pulmonary pathology
`and sudden death in rats following the intravenous administration of
`the plasticizer, di(2-ethylhexyl) phthalate, solubilized with Tween sur-
`factant. NASA. 1975;Cr-143803.
`Jaeger RJ, Rubin RJ. Migration of a phthalate ester plasticizer
`(11)
`from polyvinyl chloride blood bags into stored human blood and its
`localization in human tissues. NEnglJ Med. 1972;287:1114-1118.
`Jaeger RJ, Rubin RJ. Extraction, localization, and metabolism of
`(12)
`di-2-ethylhexyl phthalate from PVC plastic medical devices. Environ
`Health Perspect. 1973;3:95-102.
`(13) Gong V. Microwave warming of IV fluids in management of
`hypothermia. Ann Emerg Med. 1984;13:645. Letter.
`AUTHOR
`Lt Col C. Carl Bostek, CRNA, MSN, USAF, NC, is a senior anes-
`thetist at Minot AFB, North Dakota. He holds a BA from St. John's
`College, Santa Fe, New Mexico; a BSN from the University of Texas at
`Houston; and an MS in Physiology from the Medical College of Vir-
`ginia. He graduated from the U.S. Army Anesthesia School in 1979.
`The opinions stated in this article are solely those of the author
`and do not reflect the official opinions of the U.S. Air Force or the
`Department of Defense.
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