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Preventing hypothermia in trauma patients by microwave warming of IV fluids
TheJournalof Emergency Medicme. Vol. 3, pp. 4X-442. 1965 PrintedIn the USA ??Copyright 0 1966 PergamonJournalsLtd
PREVENTING HYPOTHERMIA IN TRAUMA PATIENTS BY MICROWAVE WARMING OF IV FLUIDS J. Antonio Aldrete,
MD, MS
Department of Anesthesiology, The University of Alabama at Btrmingham and Saint Anthony Hospital, Denver, Colorado Reprint address: J. Antonio Aldrete, MD, Department of Anesthesiology, School of Medicme, University of Alabama in Birmingham, Birmmgham, AL 35294
0 Abstract - Warming plastic bags containing intravenous solutions in a microwave oven (MWO) raised the temperature from 18°C to an average of 34.1”, 40.2”, and 42.8”C when treated for 120, 150, and 160 seconds, respectively. Fluids at 18”C, when passed through a blood warmer, resulted in temperatures at the distal end (DE) of about 27°C; but if the bags were priorly warmed to 42”C, fluids arrived at the DE at a temperature of about 30°C. Fluids heated by MWO to 42°C through a single short tubing 180 cm long arrived at the DE at a temperature of 33.7”C. Fluids administered at operating room ambient temperature of 18°C arrived to the DE with a temperature of about 19”C, thus most likely contributing to lowering the body temperature of traumatized patients treated with large volumes given at rapid flows. One group of 19 patients undergoing repair of injuries to extremities received infusions warmed by MWO to 42”, while other groups received them at about 20”. After an initial fall, average temperature in the former tended toward normal levels while in the latter, body temperature declined. The simple expedience of MWO wanning of the bags to 42”C, and flowing through shorter administration tubing, appears to ameliorate this complication and in some cases prevents it. 0 Keywords - IV fluids: hypothermia; microwave; warming
-
Introduction Inadvertent, undesired hypothermia is a common complication that may hamper the resuscitation of trauma victims.‘-4 Although a variety of procedures have been proposed to prevents-’ and treats-lo it, none of them appear to be completely effective; therefore, most of them are used in combination. One more method of slowing the rapid decline of body temperature during the fast infusion of cold intravenous (IV) solutions was studied-heating bags containing IV fluids in a microwave oven (MWO). Observations of fluid temperature changes were made in vitro and also in two groups of patients treated with and without this therapeutic modality.
Materials and Methods First, Viaflex (TravenoP) bags, with their plastic cover still on, containing 1000 mL of Ringer’s lactate solution were separately warmed, for various periods of time, in an ordinary Sears Kenmore microwave oven until the desired temperature was consistently achieved. Then, in an operating room
Original Contributions presents articles of interest to both academic and practicing physicians. This section of JEM is coordinated by John A. Marx, MD, of Denver General Hospital.
RECEIVED: 9
April 1985; ACCEPTED: 14 November 1985 435
0736-4679185 $3.00 + .OO
436
at 18°C of ambient temperature, the bags were hung from an IV pole, and conduit tubing of different lengths was connected. The fluid temperature was measured at the inferior pole of the bag and at the most distant rubber bulb of the tubing, (situated 2 cm before the distal end), recording the changes of temperature occurring at both points, as every 100 mL of fluid were drained. Two rates of infusion were studied, 100 mL/min and 20 mL/min, as determined by using a modified “IVAC 1500” perfusion pump. The lengths of the tubing varied as follows: (1) a 180-cm single tubing without extension, (2) a 230-cm composite including a single tubing, plus two extensions, and (3) a 375cm composite including a single tubing (180 cm) plus a bag to be used with a Goldman-Rupp model DW blood warmer, having an inlet tubing of 100 cm in length and an outlet tubing 95 cm long. When used, the blood warmer was kept at a constant temperature of 36°C. Experiments were conducted in sets of four, and the mean and their standard errors were calculated.
Clinical Observations Two groups of 19 adult patients each, with injuries to only the extremities, were given fluids from bags preheated to 42°C or from bags stored in the operating room with an ambient temperature of 20” f 1.3”C while having surgical procedures under general anesthesia. Esophageal temperatures were recorded 10 and 30 minutes after induction of anesthesia, and every 30 minutes thereafter, for the remainder of the anesthetic procedure. All anesthetics were administered by the same anesthesiologist, using the same technique. In group A patients, on entering the operating room, the IV solutions that were being given were replaced by Ringer’s lactate solution prewarmed to about 42”C, while in group B, the same solution was given but at room temperature. The vol-
J. Antonio Aldrete
Table 1. Temperatures of Fluid Contents After MWO Warming Warming Period
Temperature of Fluid
120 set 150 set 160 set
34.1% (*1.3) 40.2% (kO.9) 42.6% (h1.1)
Note: All bags of 1,000 mL were stored at 18% of ambient temperature. Figures in parentheses represent standard error of the mean from four bags warmed at each interval.
umes administered were dictated by the clinical circumstances and the anesthesiologist’s judgment. If more than two units of whole blood were necessary to replace blood loss, that case was eliminated from the study. All the blood units were given through a blood warmer.
Results When bags taken from storage in an operating room with ambient temperature of 18% were warmed in a microwave oven, the temperature increased, as shown in Table 1. The temperature changes noted in the fluid of bags heated for 120 seconds (to 34.4 f 1.2”C) between the bag (B) and the distal end (DE) of the tubing were produced by different rates of infusion (Figure 1). With the faster flow, the temperature gradient between (B) and (DE) was reduced from 10” to 5°C by the end of the infusion; with the slower flow rate, that gradient was 3.5”C. When the length of the tubing was altered, fluid contained in bags heated for 160 seconds, to about 41.5 f .26”C, arrived to the DE warmer when the shorter conduit was used, 33’C and colder if longer tubing was used (Figure 2). The use of the Goldman-Rupp blood warmer at 36”C, through which cold (about 20°C) fluid was passed, raised fluid temperatures at the distal end of the tubing (375 cm long) only to about 27”C, although it was not until 300 mL had been infused that the peak temperature was reached, re-
Warming IV Fluids
437
??
100 ml/min @ X
Bag
25
20
15
1
I
100 200
I
I
300
400
500
I
1
I
1
I
600
700
800
900
1000
Volume in ml Figure 1. The temperature of fluid contained in bags warmed in a MWO for 120 seconds reached about 34%. Draining the fluid at two different flow rates produced a greater decline of temperature at the bag (6) site and lower temperature at the distal end (DE).
maining at that level until the completion (1,000 mL) of the infusion (Figure 3). Prewarming of bags in MWO and passing that fluid through a blood warmer with a 375cm-long tubing ended in temperatures around 29°C at DE (Figure 4). Control observations were made as bags stored at 18°C remained at about the same temperature level at B and DE points (Figure 5).
Clinical Observations In 17 of the 19 patients treated with the prewarmed solutions, an initial fall of body temperature occurred followed by a rise, 30 to 60 minutes into the procedure. In two others, temperatures began to rise earlier. In contrast, those patients receiving cold fluids had a continuous and persistent decline of body temperature. The mean
changes noted in esophageal temperature and standard errors of the mean are shown for both groups in Figure 6. In group A, after 120 minutes, levels approached average initial temperature values.
Discussion Moderate to severe hypothermia is undesirable in trauma victims since it shifts the oxygen dissociation curve to the left, thus placing it in a disadvantageous position for the release of oxygen at the tissue level. It also makes monitoring and venous line access difficult,3 alters the coagulation process, and delays elimination of anesthetic and muscle-relaxant drugs from the body.2.3 Moreover, hypothermia results in peripheral vasoconstriction, hypoperfusion of certain vascular beds with resultant metabolic
J. Antonio Aldrete
438
40
-
39
-
36
.
Bag
X
Distal End
100
ml/mln
Room Temperature
co
37
-
36
-
35
-
34
-
33
-
32
-
1P C
MWO Bag Heated lor 160 8ec
4:
200
Tubing 150 cm long
X
Tubing 230 cm long
a
300
700
400
500
600
500
go0
1000
Volume in ml Figure 2. When the bags were warmed in a MWO for 160 seconds, bag temperatures reached about 41.4% and slowly decreased as the fluid was drained. Differences from B to the DE were greater when transported through a tubing 230 cm long than through a shorter tubing of 180 cm in length.
acidosis, and interference with the metabolism and excretion of certain drugs.g Below 29°C in addition to aggravating the already-mentioned physiologic variants, the danger of ventricular fibrillation occurring around temperatures of 28”C11-13is significant. Therefore it behooves us to prevent hypothermia and, even more so, to treat it when already present. Warming of blood transfusions has been recognized as a useful procedure that partially prevents lowering the patient’s temperature and allows for reentry of K’ ions into erythrocytes. 12~13 This has been accomplished by passing the blood tubing through coils immersed in water baths or heated by metal surfaces. Early experiences with microwave heating of blood brought about
concern regarding the potential harmful effect on erythrocyte integrity and denaturation of plasma proteins.14 These two possible objections are not valid in the case of crystalloid fluids, a therapeutic modality that can be applied not only to all trauma victims, but to nearly all patients undergoing anesthesia, major surgical procedures, and in whom reductions of temperature often occur.14,15 Our observations showed that fluids stored at ah-conditioned atmospheres (around 18’C) remain and enter the patient’s venous circulation cold, contributing to the lowering of the patient’s temperature (Figure 6). The body then needs to expend calories to warm and to bring the temperature back to its normal level. Depending on the total vol-
Warming IV Fluids
439
100 9
Bag
x
Distal End
ml/min
RoomTemperature 16’ sag at Room Temperature Passed
30
-
26
J.._ . . . . f-...-$
26
by Warmer
Tubing
-
375
at 36’
cm Ion9
.._.._4 _______ f. . . . . . . I . . . . . . . _7___..__ 1 -
,,’ /
16
-
14
-
12-
’ 100
) 200
’ 300
’ 400
’ 500
’ 600
’ 700
’ 600
’ 900
’ 1000
Volume in ml Figure 3. Fluids contained in bags stored in air-conditioned ambient-maintained temperatures in proximity of 19% in the bag: Passing them through a blood warmer raised the fluid temperature to only 27% at DE.
ume given and on its rate of administration, core temperatures begin to fall when one or both are in excess. Warming IV fluids by passing them through water baths, steam sterilization, autoclaving, and electric heat, although partially effective, are cumbersome and unpredictable. It must be remembered that containers with metal attachments cannot be used in a MWO. Since this method is limited to plastic bags, bottles with metal rings must be warmed by other methods. The observations reported here indicate that B-DE gradients remain smaller when the length of the IV tubing is shorter (Figure 2) and the flow rate is faster (Figure 1). This is in contrast to warming by the usual blood warmer method, which is more efficient at slower flow rates,16,” although not to the same degree. Interjecting a blood warmer is helpful if fluids at ambient room
temperature are infused; however, the warmer alone only raised DE temperatures to about 27°C (Figure 3), a probable result of the increase of the conduit to 375 cm in length. In combination with prewarming of the bag to approximately 42.8”C, blood warming raised the DE temperature to about 30°C (Figure 4). Without the blood warmer, higher DE temperature (about 32.7” f 0.4”C) resulted when shorter tubing was used. Since none of the variously warmed fluids studied approached body temperatures at DE, the potential for entering the circulation at greater than 42°C and harming blood constituent integrity did not appear to be a real risk. It must, however, be kept in mind that a warning has been given about faults in the integrity of plastic bagP.? that under high pressure, bags may rupture more readily at weak points.
J. Antonio Aldrete
440
40 -
30 -
100 mllmin
??
Bag
x
Distal
Tempwature 100 Bag Heated 160 S.C
ROQrn
End
36 -
Passed
by Warmer
Tubing
375
at 36’
cm long
34 -
CO 32 -
30 -
28 -
26 -
24 -
22 -
20’
a 100
’ 200
’ 300
I 400
a 500
’ 600
0 700
’ 800
I 900
’ 1000
Volume in ml Figure 4. Bags were warmed for 160 seconds in a MWO and their fluid content heated as it passed through a blood warmer kept at 36% produced fluid temperatures at the DE between 25 and 30.2%.
20 ml/min Room Temperature
18
’
17
-
18
-
Tubing
230
,
1
18”
C
cm long
OC Bag x Distal knd
??
15
14
-
’
I 100
1 200
I
I
,
300
400
500
800
700
800
900
1000
Volume in ml Figure 5. Fluid from bags stored at about lQ°C, passed a 230-cm-long tubing, resulted in DE temperatures of 19’C, while temperatures In the bag decreased about 1 OC.
Warming
441
IV Fluids
32
10
30
30
90
120
150
130
210
240
TIME IN MINUTES
Figure 6. Average body temperature changes and standard errors, in two groups of anesthetized patients undergoing emergency surgical procedures of the extremities. Group A received MWOwarmed fluids during surgery; group B wss given fluids at ambient temperature. The numbers in parentheses represent the number of patients in observation at any one time-a factor influenced by the duration of the operative procedure.
Warming by microwave oven may present some dangers when thawing frozen solutions;‘9 nevertheless, it does not appear to affect the viability of the solutions’ constituentP even when temperatures are kept about 40°C for up to two weeks.21 Nevertheless, other methods of rapidly warming solutions up to certain temperatures in a consistent and dependable fashion may also be used satisfactorily. In conclusion, a simple, readily available method of warming IV solutions contained in plastic bags is being proposed as a prevention and treatment of hypothermia. This may be especially useful in trauma victims or surgical patients in need of rapid administration of large volumes of parenteral so-
lutions, while being resuscitated, or operated on in cold ambient temperature facilities. Microwave warming of solutions contained in bags up to about 42°C and the administration of the warmed fluids through short IV tubing results in warmer temperatures in the fluids at the distal end of the sets. It must be recognized however, that this simple expediency is not enough to maintain normal body temperatures in extreme cases requiring administration of large volumes of parenteral fluids. In those instances, other maneuvers such as raising the ambient temperature plus a device to warm and moisten inhaled gases by a heated humidifier5 or using rebreathing in a closed circuit,6 as well as a reflecting blanket, would also be necessary.’
REFERENCES I. Walters FJM, Nott MR: The hazards of anesthesia in the injured patient. Br J Anaesth 1977; 49~707-720. 2. Booij LHDJ: Pitfalls in anaesthesia for multiply injured patients. Injury 1982; 14:81-88.
3. Weiskopf RD, Fairley HB: Anesthesia for major trauma. Surg Clin North Am 1982; 62:31-45. 4. Silva R, Moore EE, Bar-Or D, et al: The risk : benefit of autotransfusion-comparison to banked
J. Antonio Aldrete
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blood in a canine model. J Trauma 1984; 24:557564. 5. Chalon J, Ah M, Turndorf H, et al: New systems
designed to raise inspired humidity through the use of a common breathing tube, coaxial breathing tubes and the insertion of internal conduits of anesthetic gases. In Humidification of Anesthetic Gases. Springfield, Ill, CC Thomas, 1981, pp 8994. 6. Aldrete JA, Cubillos P, Sherrill D: Humidity and
temperature changes during low flow and closed system anaesthesia. Acta Anaesfh Stand 1981; 25: 312-314. 7. Bourke DL, Wurm H, Rosenberg M, et al: Intraoperative heat conservation using a reflecting blanket. Anesthesiology 1984; 60:151-154. 8. Wickstrom P, Ruiz E, Lilja GP, et al: Accidental hypothermia, core rewarming with partial bypass. Am J Surg 1976; 131:622-625. 9. Miller JW, Danzl DF, Thomas DM: Urban accidental hypothermia: 135 cases. Ann Emerg Med 1980; 9:456-461. 10. Patton JF, Doolittle WH: Core rewarming by peritoneal dialysis following induced hypothermia in dogs. J Appl Physiol 1972; 33:800-804. I 1. Benzinger TH: Heat regulation: Homeostasis of central temperature in main. Physiol Rev 1969; 49:671-759. 12. Dybkjaer E, Elkjaer P: The use of heated blood
in massive blood replacement. Acta Anaesth Stand 1964; 8:271-274. 13. Boyan CP: Cold or warmed blood for massive transfusion. Ann Surg 1964; 160:282-284.
14. Roizen MF, Sohn YJ, L’Hommedieu CS, et al: Operating room temperature prior to surgical draping; effect on patient temperature in recovery room. Anesth Analg 1980; 59:852-855. 15. Holdcroft A, Hall GM: Heat loss during anaesthesia. Br J Anaesth 1978; 50:157-164. 16. Dula DJ, Muller HA, Donovan JW: Flow rate variance of commonly used IV infusion techniques. J Trauma 1981; 21:480-482. 17. Philip BK, Raemer DB, Philip JH: Large-volume
fluid resuscitation: Prediction of flow capability. Anesthesiology
1982; 57:A107. 18. Schwartz AJ, Jobes DR, Ellison N: Rupture of pressurized plastic bags. Anesth Analg 1980; 59: 226. 19. Kana M: Microwave oven explosion. Hosp Pharmacol 1980; 15:104-106. 20. Holmes CJ, Ausman RK, Walter CW, et al: Ac-
tivity of antibiotic admixtures subjected to different freeze-thaw treatments. Drug Intell C/in Phar 1980; 14:353-355. 21. Potterton D: Stability of IV additives subjected to different freeze-thaw techniques. Br J Pharm Pratt 1980; Vol 15-16.
PREVENTING HYPOTHERMIA IN TRAUMA PATIENTS BY MICROWAVE WARMING OF IV FLUIDS J. Antonio Aldrete,
MD, MS
Department of Anesthesiology, The University of Alabama at Btrmingham and Saint Anthony Hospital, Denver, Colorado Reprint address: J. Antonio Aldrete, MD, Department of Anesthesiology, School of Medicme, University of Alabama in Birmingham, Birmmgham, AL 35294
0 Abstract - Warming plastic bags containing intravenous solutions in a microwave oven (MWO) raised the temperature from 18°C to an average of 34.1”, 40.2”, and 42.8”C when treated for 120, 150, and 160 seconds, respectively. Fluids at 18”C, when passed through a blood warmer, resulted in temperatures at the distal end (DE) of about 27°C; but if the bags were priorly warmed to 42”C, fluids arrived at the DE at a temperature of about 30°C. Fluids heated by MWO to 42°C through a single short tubing 180 cm long arrived at the DE at a temperature of 33.7”C. Fluids administered at operating room ambient temperature of 18°C arrived to the DE with a temperature of about 19”C, thus most likely contributing to lowering the body temperature of traumatized patients treated with large volumes given at rapid flows. One group of 19 patients undergoing repair of injuries to extremities received infusions warmed by MWO to 42”, while other groups received them at about 20”. After an initial fall, average temperature in the former tended toward normal levels while in the latter, body temperature declined. The simple expedience of MWO wanning of the bags to 42”C, and flowing through shorter administration tubing, appears to ameliorate this complication and in some cases prevents it. 0 Keywords - IV fluids: hypothermia; microwave; warming
-
Introduction Inadvertent, undesired hypothermia is a common complication that may hamper the resuscitation of trauma victims.‘-4 Although a variety of procedures have been proposed to prevents-’ and treats-lo it, none of them appear to be completely effective; therefore, most of them are used in combination. One more method of slowing the rapid decline of body temperature during the fast infusion of cold intravenous (IV) solutions was studied-heating bags containing IV fluids in a microwave oven (MWO). Observations of fluid temperature changes were made in vitro and also in two groups of patients treated with and without this therapeutic modality.
Materials and Methods First, Viaflex (TravenoP) bags, with their plastic cover still on, containing 1000 mL of Ringer’s lactate solution were separately warmed, for various periods of time, in an ordinary Sears Kenmore microwave oven until the desired temperature was consistently achieved. Then, in an operating room
Original Contributions presents articles of interest to both academic and practicing physicians. This section of JEM is coordinated by John A. Marx, MD, of Denver General Hospital.
RECEIVED: 9
April 1985; ACCEPTED: 14 November 1985 435
0736-4679185 $3.00 + .OO
436
at 18°C of ambient temperature, the bags were hung from an IV pole, and conduit tubing of different lengths was connected. The fluid temperature was measured at the inferior pole of the bag and at the most distant rubber bulb of the tubing, (situated 2 cm before the distal end), recording the changes of temperature occurring at both points, as every 100 mL of fluid were drained. Two rates of infusion were studied, 100 mL/min and 20 mL/min, as determined by using a modified “IVAC 1500” perfusion pump. The lengths of the tubing varied as follows: (1) a 180-cm single tubing without extension, (2) a 230-cm composite including a single tubing, plus two extensions, and (3) a 375cm composite including a single tubing (180 cm) plus a bag to be used with a Goldman-Rupp model DW blood warmer, having an inlet tubing of 100 cm in length and an outlet tubing 95 cm long. When used, the blood warmer was kept at a constant temperature of 36°C. Experiments were conducted in sets of four, and the mean and their standard errors were calculated.
Clinical Observations Two groups of 19 adult patients each, with injuries to only the extremities, were given fluids from bags preheated to 42°C or from bags stored in the operating room with an ambient temperature of 20” f 1.3”C while having surgical procedures under general anesthesia. Esophageal temperatures were recorded 10 and 30 minutes after induction of anesthesia, and every 30 minutes thereafter, for the remainder of the anesthetic procedure. All anesthetics were administered by the same anesthesiologist, using the same technique. In group A patients, on entering the operating room, the IV solutions that were being given were replaced by Ringer’s lactate solution prewarmed to about 42”C, while in group B, the same solution was given but at room temperature. The vol-
J. Antonio Aldrete
Table 1. Temperatures of Fluid Contents After MWO Warming Warming Period
Temperature of Fluid
120 set 150 set 160 set
34.1% (*1.3) 40.2% (kO.9) 42.6% (h1.1)
Note: All bags of 1,000 mL were stored at 18% of ambient temperature. Figures in parentheses represent standard error of the mean from four bags warmed at each interval.
umes administered were dictated by the clinical circumstances and the anesthesiologist’s judgment. If more than two units of whole blood were necessary to replace blood loss, that case was eliminated from the study. All the blood units were given through a blood warmer.
Results When bags taken from storage in an operating room with ambient temperature of 18% were warmed in a microwave oven, the temperature increased, as shown in Table 1. The temperature changes noted in the fluid of bags heated for 120 seconds (to 34.4 f 1.2”C) between the bag (B) and the distal end (DE) of the tubing were produced by different rates of infusion (Figure 1). With the faster flow, the temperature gradient between (B) and (DE) was reduced from 10” to 5°C by the end of the infusion; with the slower flow rate, that gradient was 3.5”C. When the length of the tubing was altered, fluid contained in bags heated for 160 seconds, to about 41.5 f .26”C, arrived to the DE warmer when the shorter conduit was used, 33’C and colder if longer tubing was used (Figure 2). The use of the Goldman-Rupp blood warmer at 36”C, through which cold (about 20°C) fluid was passed, raised fluid temperatures at the distal end of the tubing (375 cm long) only to about 27”C, although it was not until 300 mL had been infused that the peak temperature was reached, re-
Warming IV Fluids
437
??
100 ml/min @ X
Bag
25
20
15
1
I
100 200
I
I
300
400
500
I
1
I
1
I
600
700
800
900
1000
Volume in ml Figure 1. The temperature of fluid contained in bags warmed in a MWO for 120 seconds reached about 34%. Draining the fluid at two different flow rates produced a greater decline of temperature at the bag (6) site and lower temperature at the distal end (DE).
maining at that level until the completion (1,000 mL) of the infusion (Figure 3). Prewarming of bags in MWO and passing that fluid through a blood warmer with a 375cm-long tubing ended in temperatures around 29°C at DE (Figure 4). Control observations were made as bags stored at 18°C remained at about the same temperature level at B and DE points (Figure 5).
Clinical Observations In 17 of the 19 patients treated with the prewarmed solutions, an initial fall of body temperature occurred followed by a rise, 30 to 60 minutes into the procedure. In two others, temperatures began to rise earlier. In contrast, those patients receiving cold fluids had a continuous and persistent decline of body temperature. The mean
changes noted in esophageal temperature and standard errors of the mean are shown for both groups in Figure 6. In group A, after 120 minutes, levels approached average initial temperature values.
Discussion Moderate to severe hypothermia is undesirable in trauma victims since it shifts the oxygen dissociation curve to the left, thus placing it in a disadvantageous position for the release of oxygen at the tissue level. It also makes monitoring and venous line access difficult,3 alters the coagulation process, and delays elimination of anesthetic and muscle-relaxant drugs from the body.2.3 Moreover, hypothermia results in peripheral vasoconstriction, hypoperfusion of certain vascular beds with resultant metabolic
J. Antonio Aldrete
438
40
-
39
-
36
.
Bag
X
Distal End
100
ml/mln
Room Temperature
co
37
-
36
-
35
-
34
-
33
-
32
-
1P C
MWO Bag Heated lor 160 8ec
4:
200
Tubing 150 cm long
X
Tubing 230 cm long
a
300
700
400
500
600
500
go0
1000
Volume in ml Figure 2. When the bags were warmed in a MWO for 160 seconds, bag temperatures reached about 41.4% and slowly decreased as the fluid was drained. Differences from B to the DE were greater when transported through a tubing 230 cm long than through a shorter tubing of 180 cm in length.
acidosis, and interference with the metabolism and excretion of certain drugs.g Below 29°C in addition to aggravating the already-mentioned physiologic variants, the danger of ventricular fibrillation occurring around temperatures of 28”C11-13is significant. Therefore it behooves us to prevent hypothermia and, even more so, to treat it when already present. Warming of blood transfusions has been recognized as a useful procedure that partially prevents lowering the patient’s temperature and allows for reentry of K’ ions into erythrocytes. 12~13 This has been accomplished by passing the blood tubing through coils immersed in water baths or heated by metal surfaces. Early experiences with microwave heating of blood brought about
concern regarding the potential harmful effect on erythrocyte integrity and denaturation of plasma proteins.14 These two possible objections are not valid in the case of crystalloid fluids, a therapeutic modality that can be applied not only to all trauma victims, but to nearly all patients undergoing anesthesia, major surgical procedures, and in whom reductions of temperature often occur.14,15 Our observations showed that fluids stored at ah-conditioned atmospheres (around 18’C) remain and enter the patient’s venous circulation cold, contributing to the lowering of the patient’s temperature (Figure 6). The body then needs to expend calories to warm and to bring the temperature back to its normal level. Depending on the total vol-
Warming IV Fluids
439
100 9
Bag
x
Distal End
ml/min
RoomTemperature 16’ sag at Room Temperature Passed
30
-
26
J.._ . . . . f-...-$
26
by Warmer
Tubing
-
375
at 36’
cm Ion9
.._.._4 _______ f. . . . . . . I . . . . . . . _7___..__ 1 -
,,’ /
16
-
14
-
12-
’ 100
) 200
’ 300
’ 400
’ 500
’ 600
’ 700
’ 600
’ 900
’ 1000
Volume in ml Figure 3. Fluids contained in bags stored in air-conditioned ambient-maintained temperatures in proximity of 19% in the bag: Passing them through a blood warmer raised the fluid temperature to only 27% at DE.
ume given and on its rate of administration, core temperatures begin to fall when one or both are in excess. Warming IV fluids by passing them through water baths, steam sterilization, autoclaving, and electric heat, although partially effective, are cumbersome and unpredictable. It must be remembered that containers with metal attachments cannot be used in a MWO. Since this method is limited to plastic bags, bottles with metal rings must be warmed by other methods. The observations reported here indicate that B-DE gradients remain smaller when the length of the IV tubing is shorter (Figure 2) and the flow rate is faster (Figure 1). This is in contrast to warming by the usual blood warmer method, which is more efficient at slower flow rates,16,” although not to the same degree. Interjecting a blood warmer is helpful if fluids at ambient room
temperature are infused; however, the warmer alone only raised DE temperatures to about 27°C (Figure 3), a probable result of the increase of the conduit to 375 cm in length. In combination with prewarming of the bag to approximately 42.8”C, blood warming raised the DE temperature to about 30°C (Figure 4). Without the blood warmer, higher DE temperature (about 32.7” f 0.4”C) resulted when shorter tubing was used. Since none of the variously warmed fluids studied approached body temperatures at DE, the potential for entering the circulation at greater than 42°C and harming blood constituent integrity did not appear to be a real risk. It must, however, be kept in mind that a warning has been given about faults in the integrity of plastic bagP.? that under high pressure, bags may rupture more readily at weak points.
J. Antonio Aldrete
440
40 -
30 -
100 mllmin
??
Bag
x
Distal
Tempwature 100 Bag Heated 160 S.C
ROQrn
End
36 -
Passed
by Warmer
Tubing
375
at 36’
cm long
34 -
CO 32 -
30 -
28 -
26 -
24 -
22 -
20’
a 100
’ 200
’ 300
I 400
a 500
’ 600
0 700
’ 800
I 900
’ 1000
Volume in ml Figure 4. Bags were warmed for 160 seconds in a MWO and their fluid content heated as it passed through a blood warmer kept at 36% produced fluid temperatures at the DE between 25 and 30.2%.
20 ml/min Room Temperature
18
’
17
-
18
-
Tubing
230
,
1
18”
C
cm long
OC Bag x Distal knd
??
15
14
-
’
I 100
1 200
I
I
,
300
400
500
800
700
800
900
1000
Volume in ml Figure 5. Fluid from bags stored at about lQ°C, passed a 230-cm-long tubing, resulted in DE temperatures of 19’C, while temperatures In the bag decreased about 1 OC.
Warming
441
IV Fluids
32
10
30
30
90
120
150
130
210
240
TIME IN MINUTES
Figure 6. Average body temperature changes and standard errors, in two groups of anesthetized patients undergoing emergency surgical procedures of the extremities. Group A received MWOwarmed fluids during surgery; group B wss given fluids at ambient temperature. The numbers in parentheses represent the number of patients in observation at any one time-a factor influenced by the duration of the operative procedure.
Warming by microwave oven may present some dangers when thawing frozen solutions;‘9 nevertheless, it does not appear to affect the viability of the solutions’ constituentP even when temperatures are kept about 40°C for up to two weeks.21 Nevertheless, other methods of rapidly warming solutions up to certain temperatures in a consistent and dependable fashion may also be used satisfactorily. In conclusion, a simple, readily available method of warming IV solutions contained in plastic bags is being proposed as a prevention and treatment of hypothermia. This may be especially useful in trauma victims or surgical patients in need of rapid administration of large volumes of parenteral so-
lutions, while being resuscitated, or operated on in cold ambient temperature facilities. Microwave warming of solutions contained in bags up to about 42°C and the administration of the warmed fluids through short IV tubing results in warmer temperatures in the fluids at the distal end of the sets. It must be recognized however, that this simple expediency is not enough to maintain normal body temperatures in extreme cases requiring administration of large volumes of parenteral fluids. In those instances, other maneuvers such as raising the ambient temperature plus a device to warm and moisten inhaled gases by a heated humidifier5 or using rebreathing in a closed circuit,6 as well as a reflecting blanket, would also be necessary.’
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