Acta anaesth. scand. 1979, 23, 97-102
Warming of Blood Units in Water Bath and Cooling of Blood at Room Temperature K. LINKO and S. PALOSAARI Finnish Red Cross Blood Transfusion Service, Helsinki, and Department of Chemistry, Helsinki University of Technology, Espoo, Finland
Warming of whole blood units in a waterbath is considered too slow for emergencies and also results in a waste of blood. In this study the blood temperature was recorded continuously during warming in various kinds of baths. T h e warming of 5°C CPD blood units (500 g) in a bucket of water was considerably slower than in a stirred and thermostated ( + 39.5%) water bath, where the blood temperature reached +35"C in 13.4 min. Addition of continuous mechanical agitation of the blood unit raised the temperature to +32"C in 5.0 min, and to + 35°C in 6.6 min. This should be sufficient for most clinical situations. Agitation did not cause significant hemolysis when compared with units warmed without agitation. The cooling rate of warmed blood (+37"C) at room temperature (f21"C) was also studied experimentally. The temperature of the blood units fell 3°C in 5 min and 5°C in 15 min. Cooling of blood simultaneously in the bag, microfilter and transfusion set resulted in an infusion temperature of 32°C at the end of the transfusion with a flow rate of 85 g/min. Thus, blood units should be warmed immediately before use. Insulation of the transfusion set may also be practicable.
+
+
Received 28 June, accepted for publication 9 September 1978
I t is more convenient to warm blood units before transfusion than to use so-called in-line blood warmers when rapid blood replacement is needed (LINKO1979a,b). Electromagnetic blood warmers have been designed for this purpose. However, probably because of the high price of these devices and the complications reported with the microwave oven (ARENS& LEONARD 1971, STAPLES & GRINER1971, MCCULLOUGH et al. 1972, DALILI et al. 1973, DALILI & ADRIANI 1974), blood units are still commonly warmed in a bucket of hot water or in a stirred and thermostated water bath. This kind of warming is believed to be slow and to cause a considerable waste of blood, because all units warmed may not be transfused, and there is a risk of bacterial contamination. There is also a risk of the blood unit cooling before the transfusion when prewarmed blood is used. I n
addition, cooling occurs in the transfusion set, & especially a t low flow rates (MANNERS MILLS1968, RUSSELL1969). However, when blood units are warmed in a water bath there is no risk of local overheating (as with electromagnetic ovens), and damage to red cells should not occur if the bath temperature is below +45"C (HAMet al. 1948, CHALMERS & RUSSELL 1974). We have studied the warming rates of whole blood units in different kinds of water baths, and the possibilities for accelerating the warming process. We also examined the cooling rate of blood a t room temperature in the bag and during transfusion a t different flow rates.
BASIC T H E O R Y The mechanisms involved in the heat transfer from a water bath to blood are the following:
98
K . L I N K 0 A N D S. PALOSAAKl
I . Heat transfer in water by conduction and convection; 2. Heat transfcr from water to the outer surface of the bag; 3. Conduction through the wall of the bag; 4. Hcat transfer from the inner surface of the bag to blood ; 5. Heat transfer in blood by conduction and convection. A simple equation is obtained from the heat balance where the change in internal energy of the blood unit is equal to the net heat flow from the bath to the bag in onc time unit, as shown by KREITH (1966): T, = exp (--!)Ct
(1)
where t is time, T, is dimensionless temperature, and C , is the time constant. Thc quantities T, and C, are defincd as follows:
T- I.., T, = ~ - _ T,-T,
_
(2)
where T is the temperature of the blood unit, Tois the initial tempcrature of the unit, and T, is the final temperature, in this case the temperature of the water bath.
(3) where c = specific heat of the warming body, W/kg"C p = dcnsity of the warming body, kg/m3 V = volume of the warming body, m3 U = overall heat transfer coefficient, W/m2"C A = heat transfer surface, m2 If free convection is not important, the overall heat transfrr coefficient, U, in the above equation can be assumed to be independent of the temperature difference betwcrn the surface and the fluid. Then, if a single warming time, t, and the corresponding temperature, T, are determined experimentally, the quantity T, can be calculated from equation (2), which in turn enables the time constant, C,, to be solved from equation (1). After the time constant has been determined, it is possible to calculate the whole warming history of the blood unit for all initial and final temperatures as well as all volumes of the unit. However, several warming time and temperature measurements were made for each warming condition in order to calculate the time constarits more accurately.
MATERIAL AND METHODS The blood: Outdated CPD whole blood in Fenwalm bags was used. T h r units were weighed to500k3 g (including the bag) and the hematocrit level was determined. One pool of 12 units of ABO and R h compatible blood was also prepared. The units were transferred to a 10-1 glass bottle and then aliquoted to empty bags during continuous mixing. The homogeneity of the
pool was controlled by a hematocrit determination at the beginning and at the end of preparing the aliquots. The bags thus obtained were divided alternately into two groups. Six of the units were warmed in test 1 and six in test 3. After warming, free plasma hemoglobin was determined from each unit in both tests (PAGE& CULVER1960). A sample taken from the pool before preparing the aliquots served as a control.
Water bath and temperature measurements: Blood units were warmed in a 15-1 water container with a thermostat and a stirrer (Julabo Paratherm 111, Juchheim Labortechnik). The temperatures within the blood unit were mca3ured in tests 1 and 3 by a thermistor (Implantable brain probe 532, Yellow Springs Instruments Go., Inc.) and a Tele-Thermometer (43TZ, YSI) connected to a paper recorder (Servogor RE 541, Goerz Electro) or by a mercury thermometer inserted in the blood bag (tests 2 and 4). Temperatures in the transfusion set (tests 5 and 6) were measured by a Hypodermic probe (524, YSI) and a Tele-Thermometer (41TB, YSI). Devices for temperature measurement were calibrated against a mercury thermometer. The room and water bath temperatures were recorded with mercury thermometers. Warming of the blood units A summary of the methods is given in Table 1. Test I . The water bath was warmed u p to +39.5"C. The blood bag ( +5.0"C) was placed in the bath in a holder and the temperature was recorded continuously from the middle of the unit. The bath was neither stirred nor thermostated. The temperature of the water bath was measured at the end of each test (30.0 min) . Test 2. The blood unit (+5.OoC) was immersed in a stirred and thermostated water bath (f39.5"C) for 5.0 min, then taken out and mixed for 30 s by hand. The temperature was determined (0.5"C: precision) and the unit was cooled again. The same procedure was repeated with 10.0- and 15.0-min immersions. l e s t 3. Blood units were placed in a metal frame in the bath ( +39.5"Cl) and the temperature elevation was recorded continuously while a mechanical shaker moved the frame 1 cm to and fro at a frequency of 200 min-' in the direction of the width of the unit. Cooling o f warmed blood at room temperature, -+ 2 I . O T Test 4. Warmed (+37.OoC) blood units were allowcd to cool at room temperature. The blood temperature was determined as in test 2.
Test 5. Warm blood ( +37.0"C) was transfused at six different flow rates through a microfilter and transfusion
WARMING AND COOLING OF BLOOD UNITS
set (Ultipor@SQ40KL, Pall Biomedical Ltd.). The temperature of blood was recorded at the distal end of the set. Test 6. Blood units (+37.0"C) were attached to the microfilter and transfusion set (Ultipor) and inserted in a pressure infusor (Fenwalw). Each unit was transfused under a different infusor pressure. The flow rates and the highest and lowest temperatures at the distal end of the set were determined.
RESULTS Warming o f blood units Warming in a bucket of water was simulated in test 1. It took 16 min for the core of the units to reach +32.0°C (Fig. 1). The temperature of the water "bucket" at the end of the test varied from +35.6 to +35.8"C.
99
Continuous agitation of the blood unit during warming caused a 50% reduction of warming times from those obtained in test 2 (Fig. 1). The temperature of +32.0°C was reached in 5.0 min, and of +35.0°C in 6.6 min. Hemolysis caused by warming. Free plasma hemoglobin was 333-456 mg/l when units (6) were agitated continuously during warming, and 345-450 mg/l when units (6)were warmed in a similar bath without agitation. The control value obtained from the pool was 330 mdl. Cooling of blood at room temperature The cooling of whole blood units (test 4 ) is illustrated in Figure 1. The +37.0°C blood units cooled 2.9"C in 5.0 min at room temperature and down to + 3 1.9"C in 15.0 min.
Warming in a stirred and thermostated bath (test 2 ) . By agitating the blood prior to measuring, an The injuence of bloodjow on cooling in the microeven temperature was achieved in the units. I t filter and transfusion set (test 5) is demontook 10.0 min to warm a unit from +5.0°C to strated in Figure 2. At room temperature, +32.0°C and 13.4 min to +35.0°C. blood cooled about 1.5"C at a flow of 150 Table 1 Summary of the methods used in this study, the number of the units used and the hematocrit range in each test.
Test
1 2
3
4 5
6
Method
Warming No stirrer, no thermostat. Stirred and thermostated bath; temperature determined after mixing of blood. Stirred and thermostated bath; continuous agitation of blood units during warming.
Cooling +37"C blood units at room temperature; temperature determined after mixing of blood. Cooling of +37"C blood in the microfilter and transfusion set (Ultipor@)at room temperature using different flow rates. Cooling of +37"C blood at room temperature within the bag and in the microfilter and transfusion set simultaneously using different flow rates. Infusion temperature range registered a t the distal end of the transfusion set.
No. of bIood units used
Hematocrit range
6 10
0.40 0.35-0.42
10
0.40
6
0.44-0.45
6
0.39-0.41
4
0.38-0.41
100
K . LINK0 AND S. PALOSAARI
5
lb
15
20
25
30
WARMING TIME, MINUTES
Fig. 1. Temperature of the blood unit as a function of time. Curve 1 (A ---A): Blood hag in a stagnant water batli-not agitated. Curve 2 (0-0): Blood hag in a stirred and thermostated water bath-- not agitated (time constant 6.59 min). Curve 3 (0-0) : Blood bag agitated in a stirred and thcrmostated water bath (time constant 3.26 min). Curve 4 (X - - - X) : Blood bag cooling at room temperatnre, + 2 1.0"C:. The solid lines were calculated by the use of equation ( 1 ) (see text) aftrr the time constant had been determined from the measured values shown in the figure. The dotted lines were madr by connecting the measured values by visual smoothing. 'The points indicating the experiments are mean values of 10 temperature determinations in tests 2 and 3 and six determinations in tests 1 and 4.
g/min, 1.8"C: at 100 g/min and 3.0"C at 50 g/min.
A clinical situation was simulated in test 6 where prewarmed blood cooled in room air simultaneously in the bag and in the microfilter and transfusion set (Fig. 2). The +37.0°C blood cooled down to +32"C at a flow rate of 70-80 g/min. At a flow of 160 g/min the highest infusion temperature registered was 35.0"C.
+
DISCUSSION The warming history of the units in tests 2 and
3 can be well described by a time constant. This indicates that the heat transfer coefficient is not a function of a temperature difference anywhere in the system, and furthermore, that it is possible to predict the warming time by the use of equations ( l ) , (2), and (3) for all initial temperatures of the bag and for all temperatures of the water bath. Thus, the warming times needed to raise the temperature to +35.0°C are 9.0, 6.6, and 5.4 min at the water bath temperatures of $37.0, +39.5 and +42.0°C:, respectively, when the blood units are agitated effectively during warming. Thus, shorter times are attained at higher temperatures of the water bath. However, the highest acceptable water bath temperature is limited by the temperature that causes damage to blood. Equation (3) shows that the heating time is directly proportional to the mass of the blood unit when the surface area remains the same. Thus a 1076 increase in bag volume causes a 10% increase in heating time. Warming of refrigerated blood units in a bucket ofwarm water (test 1) was found to be very slow. Addition of an effective stirrer and thermostat accelerated the heat transfer to the units considerably, but resulted in warming times too long for massive transfusions. Continuous mechanical agitation of the blood unit during warming reduced the warming times by 50% compared to those obtained without agitation (Fig. 1) by decreasing the time constant. Unfortunately the time constant as a function of agitation frequency could not be calculated because of resonances that occurred in the shaking mechanism at lower agitation frequencies. The warming times obtained with the shaking mechanism used should be satisfactory for most clinical situations. However, electromagnetic blood warming devices are even faster and should be used if very rapid transfusions are needed. Warming of stored blood in a water bath should not cause hemolysis at temperatures below +45"C. I n this study, however, some of the units warmed in a +39.5"C bath
WARMING AND COOLING OF BLOOD UNITS
101
Fig. 2. T h e infusion temperature of blood with different transfusion rates. Curve No. 5 gives the temperature of blood at the distal end after it has passed through the transfusion line, leaving the bag at $37.0 0
L. 1
The curves denoted by No 6. are otherwise similarly obtained, but the blood bag was at room temperature having been at +37.O0C before the trst was started. T h e hatchcd area shows the fall of the temperature with time. These curves simulate an actual transfusion situation. All points given represent one
u
" , cc
5:
p
E 9
m
32
temperature determination.
showed higher values of free plasma hemoglobin than the control sample taken from the pool. I t seems obvious that this hemolysis was due to the destruction of outdated RBC during the mixing of the pool and transfer of the blood into the bags, and that it was not caused by the warming. Agitation of the blood units did not cause significant mechanical destruction of RBC when compared with the units warmed without agitation. Since blood units were found to cool quite rapidly, it seems reasonable that they should be warmed immediately before use. I n practice, however, blood also has time to cool during transfusion, both in the bag and in the microfilter and transfusion set. The degree of cooling depends on the flow rate used, as shown in Figure 2. Because cooling in the transfusion set is rapid, insulation of the set would be of practical value, as was also proposed by RUSSELL (1969). Our data show that it is possible to accelerate considerably the warming of blood units in a water bath by agitating the units mechanically during the warming process. A bath temperature of +39--42°C seems to be suitable for rapid warming and to compensate for cooling of blood during the transfusion.
50
100
150
200
FLOW RATE g/mm
REFERENCES ARENS,J. F. & LEONARD, G. Id. (1971) Danger of overwarming blood by microwave, 3. Amer. med. Ass. 218, 1045. C. & RUSSELL, W. J. (1974) When does CHALMERS, blood hemolyse? A temperature study. Brit. J . Ariaesth. 46, 742. DALILI,H., ADRIANI, J., WU, W.T. & SAhIUELS, M.S. (1973) Radiowave and microwave blood warmers: Comparison with water bath blood warming units. Sth. med. 3. 66, 1254. DALILI,H. & ADRIANI,J. (1974) Effects of various blood warmers on the components of bank blood. Anesth. Analg. 53, 125. HAM,T.H., SHEN, S.C., FLEMING, E.M. & CASTLE, W.B. (1948) Studies on the destruction of red blood cells. IV Thermal injury: Action of heat in causing increased spheroidicity, osmotic and mechanical fragilities and hemolysis of erythrocytes: Observations on the mechanism of destruction of such erythrocytes in dogs and in a patient with a fatal thermal burn. Blood 3,373. KPEITH, F. (1966) PririLip1t.s o f Heat Transfer. International Textbook Company, Scranton, Pennsylvania, p. 129. LINKO,K. (1979a) In-line blood warming and microfiltration devices. I. Testing of flow and warming properties by pressure transfusion of aggregate-free blood. Acta anaestti. scand. 23, 40. LINKO,K. (197913) In-line blood warming and microfiltration devices. 11. Influence of blood temperature on flow rate and hemolysis during pressure transfusion through microfilters and transfusion sets. Acta afiaesth. scand. 23, 46.
102
K. LINK0 AND S. PALOSAARI
MANNERS, J. M. & MILLS,K. L. M. (1968) Another blood warmer. Anaesthesia 23, 646. MCCULLOUGH, J., POLESKY, H. F., NELSON,C. & HOFF,T. (1972) Iatrogenic hemolysis: A complication of blood warmed by a microwave device. Anaesth. Analg. 51, 102. PAGE,L. & CULVER, P. (1960) A Syllabus of Laboratory Examination in Clinical Diagnosis. Harvard University Press, Cambridge, p. 116. RUSSELL, W.J. (1969) A discussion of the problems of heat exchange blood warming devices. Brit. 3. Amesth. 41, 345.
STAPLES, P.J. & GRINER, P. F. (1971) Extracorporeal hemolysis of blood in a microwave blood warmer. N e w En&. 3. Med. 285, 3 17.
Address :
Kai Linko, M.D. Finnish Red Cross Blood Transfusion Service Kivihaantie 7 SF-003 10 Helsinki 31 Finland
Warming of Blood Units in Water Bath and Cooling of Blood at Room Temperature K. LINKO and S. PALOSAARI Finnish Red Cross Blood Transfusion Service, Helsinki, and Department of Chemistry, Helsinki University of Technology, Espoo, Finland
Warming of whole blood units in a waterbath is considered too slow for emergencies and also results in a waste of blood. In this study the blood temperature was recorded continuously during warming in various kinds of baths. T h e warming of 5°C CPD blood units (500 g) in a bucket of water was considerably slower than in a stirred and thermostated ( + 39.5%) water bath, where the blood temperature reached +35"C in 13.4 min. Addition of continuous mechanical agitation of the blood unit raised the temperature to +32"C in 5.0 min, and to + 35°C in 6.6 min. This should be sufficient for most clinical situations. Agitation did not cause significant hemolysis when compared with units warmed without agitation. The cooling rate of warmed blood (+37"C) at room temperature (f21"C) was also studied experimentally. The temperature of the blood units fell 3°C in 5 min and 5°C in 15 min. Cooling of blood simultaneously in the bag, microfilter and transfusion set resulted in an infusion temperature of 32°C at the end of the transfusion with a flow rate of 85 g/min. Thus, blood units should be warmed immediately before use. Insulation of the transfusion set may also be practicable.
+
+
Received 28 June, accepted for publication 9 September 1978
I t is more convenient to warm blood units before transfusion than to use so-called in-line blood warmers when rapid blood replacement is needed (LINKO1979a,b). Electromagnetic blood warmers have been designed for this purpose. However, probably because of the high price of these devices and the complications reported with the microwave oven (ARENS& LEONARD 1971, STAPLES & GRINER1971, MCCULLOUGH et al. 1972, DALILI et al. 1973, DALILI & ADRIANI 1974), blood units are still commonly warmed in a bucket of hot water or in a stirred and thermostated water bath. This kind of warming is believed to be slow and to cause a considerable waste of blood, because all units warmed may not be transfused, and there is a risk of bacterial contamination. There is also a risk of the blood unit cooling before the transfusion when prewarmed blood is used. I n
addition, cooling occurs in the transfusion set, & especially a t low flow rates (MANNERS MILLS1968, RUSSELL1969). However, when blood units are warmed in a water bath there is no risk of local overheating (as with electromagnetic ovens), and damage to red cells should not occur if the bath temperature is below +45"C (HAMet al. 1948, CHALMERS & RUSSELL 1974). We have studied the warming rates of whole blood units in different kinds of water baths, and the possibilities for accelerating the warming process. We also examined the cooling rate of blood a t room temperature in the bag and during transfusion a t different flow rates.
BASIC T H E O R Y The mechanisms involved in the heat transfer from a water bath to blood are the following:
98
K . L I N K 0 A N D S. PALOSAAKl
I . Heat transfer in water by conduction and convection; 2. Heat transfcr from water to the outer surface of the bag; 3. Conduction through the wall of the bag; 4. Hcat transfer from the inner surface of the bag to blood ; 5. Heat transfer in blood by conduction and convection. A simple equation is obtained from the heat balance where the change in internal energy of the blood unit is equal to the net heat flow from the bath to the bag in onc time unit, as shown by KREITH (1966): T, = exp (--!)Ct
(1)
where t is time, T, is dimensionless temperature, and C , is the time constant. Thc quantities T, and C, are defincd as follows:
T- I.., T, = ~ - _ T,-T,
_
(2)
where T is the temperature of the blood unit, Tois the initial tempcrature of the unit, and T, is the final temperature, in this case the temperature of the water bath.
(3) where c = specific heat of the warming body, W/kg"C p = dcnsity of the warming body, kg/m3 V = volume of the warming body, m3 U = overall heat transfer coefficient, W/m2"C A = heat transfer surface, m2 If free convection is not important, the overall heat transfrr coefficient, U, in the above equation can be assumed to be independent of the temperature difference betwcrn the surface and the fluid. Then, if a single warming time, t, and the corresponding temperature, T, are determined experimentally, the quantity T, can be calculated from equation (2), which in turn enables the time constant, C,, to be solved from equation (1). After the time constant has been determined, it is possible to calculate the whole warming history of the blood unit for all initial and final temperatures as well as all volumes of the unit. However, several warming time and temperature measurements were made for each warming condition in order to calculate the time constarits more accurately.
MATERIAL AND METHODS The blood: Outdated CPD whole blood in Fenwalm bags was used. T h r units were weighed to500k3 g (including the bag) and the hematocrit level was determined. One pool of 12 units of ABO and R h compatible blood was also prepared. The units were transferred to a 10-1 glass bottle and then aliquoted to empty bags during continuous mixing. The homogeneity of the
pool was controlled by a hematocrit determination at the beginning and at the end of preparing the aliquots. The bags thus obtained were divided alternately into two groups. Six of the units were warmed in test 1 and six in test 3. After warming, free plasma hemoglobin was determined from each unit in both tests (PAGE& CULVER1960). A sample taken from the pool before preparing the aliquots served as a control.
Water bath and temperature measurements: Blood units were warmed in a 15-1 water container with a thermostat and a stirrer (Julabo Paratherm 111, Juchheim Labortechnik). The temperatures within the blood unit were mca3ured in tests 1 and 3 by a thermistor (Implantable brain probe 532, Yellow Springs Instruments Go., Inc.) and a Tele-Thermometer (43TZ, YSI) connected to a paper recorder (Servogor RE 541, Goerz Electro) or by a mercury thermometer inserted in the blood bag (tests 2 and 4). Temperatures in the transfusion set (tests 5 and 6) were measured by a Hypodermic probe (524, YSI) and a Tele-Thermometer (41TB, YSI). Devices for temperature measurement were calibrated against a mercury thermometer. The room and water bath temperatures were recorded with mercury thermometers. Warming of the blood units A summary of the methods is given in Table 1. Test I . The water bath was warmed u p to +39.5"C. The blood bag ( +5.0"C) was placed in the bath in a holder and the temperature was recorded continuously from the middle of the unit. The bath was neither stirred nor thermostated. The temperature of the water bath was measured at the end of each test (30.0 min) . Test 2. The blood unit (+5.OoC) was immersed in a stirred and thermostated water bath (f39.5"C) for 5.0 min, then taken out and mixed for 30 s by hand. The temperature was determined (0.5"C: precision) and the unit was cooled again. The same procedure was repeated with 10.0- and 15.0-min immersions. l e s t 3. Blood units were placed in a metal frame in the bath ( +39.5"Cl) and the temperature elevation was recorded continuously while a mechanical shaker moved the frame 1 cm to and fro at a frequency of 200 min-' in the direction of the width of the unit. Cooling o f warmed blood at room temperature, -+ 2 I . O T Test 4. Warmed (+37.OoC) blood units were allowcd to cool at room temperature. The blood temperature was determined as in test 2.
Test 5. Warm blood ( +37.0"C) was transfused at six different flow rates through a microfilter and transfusion
WARMING AND COOLING OF BLOOD UNITS
set (Ultipor@SQ40KL, Pall Biomedical Ltd.). The temperature of blood was recorded at the distal end of the set. Test 6. Blood units (+37.0"C) were attached to the microfilter and transfusion set (Ultipor) and inserted in a pressure infusor (Fenwalw). Each unit was transfused under a different infusor pressure. The flow rates and the highest and lowest temperatures at the distal end of the set were determined.
RESULTS Warming o f blood units Warming in a bucket of water was simulated in test 1. It took 16 min for the core of the units to reach +32.0°C (Fig. 1). The temperature of the water "bucket" at the end of the test varied from +35.6 to +35.8"C.
99
Continuous agitation of the blood unit during warming caused a 50% reduction of warming times from those obtained in test 2 (Fig. 1). The temperature of +32.0°C was reached in 5.0 min, and of +35.0°C in 6.6 min. Hemolysis caused by warming. Free plasma hemoglobin was 333-456 mg/l when units (6) were agitated continuously during warming, and 345-450 mg/l when units (6)were warmed in a similar bath without agitation. The control value obtained from the pool was 330 mdl. Cooling of blood at room temperature The cooling of whole blood units (test 4 ) is illustrated in Figure 1. The +37.0°C blood units cooled 2.9"C in 5.0 min at room temperature and down to + 3 1.9"C in 15.0 min.
Warming in a stirred and thermostated bath (test 2 ) . By agitating the blood prior to measuring, an The injuence of bloodjow on cooling in the microeven temperature was achieved in the units. I t filter and transfusion set (test 5) is demontook 10.0 min to warm a unit from +5.0°C to strated in Figure 2. At room temperature, +32.0°C and 13.4 min to +35.0°C. blood cooled about 1.5"C at a flow of 150 Table 1 Summary of the methods used in this study, the number of the units used and the hematocrit range in each test.
Test
1 2
3
4 5
6
Method
Warming No stirrer, no thermostat. Stirred and thermostated bath; temperature determined after mixing of blood. Stirred and thermostated bath; continuous agitation of blood units during warming.
Cooling +37"C blood units at room temperature; temperature determined after mixing of blood. Cooling of +37"C blood in the microfilter and transfusion set (Ultipor@)at room temperature using different flow rates. Cooling of +37"C blood at room temperature within the bag and in the microfilter and transfusion set simultaneously using different flow rates. Infusion temperature range registered a t the distal end of the transfusion set.
No. of bIood units used
Hematocrit range
6 10
0.40 0.35-0.42
10
0.40
6
0.44-0.45
6
0.39-0.41
4
0.38-0.41
100
K . LINK0 AND S. PALOSAARI
5
lb
15
20
25
30
WARMING TIME, MINUTES
Fig. 1. Temperature of the blood unit as a function of time. Curve 1 (A ---A): Blood hag in a stagnant water batli-not agitated. Curve 2 (0-0): Blood hag in a stirred and thermostated water bath-- not agitated (time constant 6.59 min). Curve 3 (0-0) : Blood bag agitated in a stirred and thcrmostated water bath (time constant 3.26 min). Curve 4 (X - - - X) : Blood bag cooling at room temperatnre, + 2 1.0"C:. The solid lines were calculated by the use of equation ( 1 ) (see text) aftrr the time constant had been determined from the measured values shown in the figure. The dotted lines were madr by connecting the measured values by visual smoothing. 'The points indicating the experiments are mean values of 10 temperature determinations in tests 2 and 3 and six determinations in tests 1 and 4.
g/min, 1.8"C: at 100 g/min and 3.0"C at 50 g/min.
A clinical situation was simulated in test 6 where prewarmed blood cooled in room air simultaneously in the bag and in the microfilter and transfusion set (Fig. 2). The +37.0°C blood cooled down to +32"C at a flow rate of 70-80 g/min. At a flow of 160 g/min the highest infusion temperature registered was 35.0"C.
+
DISCUSSION The warming history of the units in tests 2 and
3 can be well described by a time constant. This indicates that the heat transfer coefficient is not a function of a temperature difference anywhere in the system, and furthermore, that it is possible to predict the warming time by the use of equations ( l ) , (2), and (3) for all initial temperatures of the bag and for all temperatures of the water bath. Thus, the warming times needed to raise the temperature to +35.0°C are 9.0, 6.6, and 5.4 min at the water bath temperatures of $37.0, +39.5 and +42.0°C:, respectively, when the blood units are agitated effectively during warming. Thus, shorter times are attained at higher temperatures of the water bath. However, the highest acceptable water bath temperature is limited by the temperature that causes damage to blood. Equation (3) shows that the heating time is directly proportional to the mass of the blood unit when the surface area remains the same. Thus a 1076 increase in bag volume causes a 10% increase in heating time. Warming of refrigerated blood units in a bucket ofwarm water (test 1) was found to be very slow. Addition of an effective stirrer and thermostat accelerated the heat transfer to the units considerably, but resulted in warming times too long for massive transfusions. Continuous mechanical agitation of the blood unit during warming reduced the warming times by 50% compared to those obtained without agitation (Fig. 1) by decreasing the time constant. Unfortunately the time constant as a function of agitation frequency could not be calculated because of resonances that occurred in the shaking mechanism at lower agitation frequencies. The warming times obtained with the shaking mechanism used should be satisfactory for most clinical situations. However, electromagnetic blood warming devices are even faster and should be used if very rapid transfusions are needed. Warming of stored blood in a water bath should not cause hemolysis at temperatures below +45"C. I n this study, however, some of the units warmed in a +39.5"C bath
WARMING AND COOLING OF BLOOD UNITS
101
Fig. 2. T h e infusion temperature of blood with different transfusion rates. Curve No. 5 gives the temperature of blood at the distal end after it has passed through the transfusion line, leaving the bag at $37.0 0
L. 1
The curves denoted by No 6. are otherwise similarly obtained, but the blood bag was at room temperature having been at +37.O0C before the trst was started. T h e hatchcd area shows the fall of the temperature with time. These curves simulate an actual transfusion situation. All points given represent one
u
" , cc
5:
p
E 9
m
32
temperature determination.
showed higher values of free plasma hemoglobin than the control sample taken from the pool. I t seems obvious that this hemolysis was due to the destruction of outdated RBC during the mixing of the pool and transfer of the blood into the bags, and that it was not caused by the warming. Agitation of the blood units did not cause significant mechanical destruction of RBC when compared with the units warmed without agitation. Since blood units were found to cool quite rapidly, it seems reasonable that they should be warmed immediately before use. I n practice, however, blood also has time to cool during transfusion, both in the bag and in the microfilter and transfusion set. The degree of cooling depends on the flow rate used, as shown in Figure 2. Because cooling in the transfusion set is rapid, insulation of the set would be of practical value, as was also proposed by RUSSELL (1969). Our data show that it is possible to accelerate considerably the warming of blood units in a water bath by agitating the units mechanically during the warming process. A bath temperature of +39--42°C seems to be suitable for rapid warming and to compensate for cooling of blood during the transfusion.
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FLOW RATE g/mm
REFERENCES ARENS,J. F. & LEONARD, G. Id. (1971) Danger of overwarming blood by microwave, 3. Amer. med. Ass. 218, 1045. C. & RUSSELL, W. J. (1974) When does CHALMERS, blood hemolyse? A temperature study. Brit. J . Ariaesth. 46, 742. DALILI,H., ADRIANI, J., WU, W.T. & SAhIUELS, M.S. (1973) Radiowave and microwave blood warmers: Comparison with water bath blood warming units. Sth. med. 3. 66, 1254. DALILI,H. & ADRIANI,J. (1974) Effects of various blood warmers on the components of bank blood. Anesth. Analg. 53, 125. HAM,T.H., SHEN, S.C., FLEMING, E.M. & CASTLE, W.B. (1948) Studies on the destruction of red blood cells. IV Thermal injury: Action of heat in causing increased spheroidicity, osmotic and mechanical fragilities and hemolysis of erythrocytes: Observations on the mechanism of destruction of such erythrocytes in dogs and in a patient with a fatal thermal burn. Blood 3,373. KPEITH, F. (1966) PririLip1t.s o f Heat Transfer. International Textbook Company, Scranton, Pennsylvania, p. 129. LINKO,K. (1979a) In-line blood warming and microfiltration devices. I. Testing of flow and warming properties by pressure transfusion of aggregate-free blood. Acta anaestti. scand. 23, 40. LINKO,K. (197913) In-line blood warming and microfiltration devices. 11. Influence of blood temperature on flow rate and hemolysis during pressure transfusion through microfilters and transfusion sets. Acta afiaesth. scand. 23, 46.
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MANNERS, J. M. & MILLS,K. L. M. (1968) Another blood warmer. Anaesthesia 23, 646. MCCULLOUGH, J., POLESKY, H. F., NELSON,C. & HOFF,T. (1972) Iatrogenic hemolysis: A complication of blood warmed by a microwave device. Anaesth. Analg. 51, 102. PAGE,L. & CULVER, P. (1960) A Syllabus of Laboratory Examination in Clinical Diagnosis. Harvard University Press, Cambridge, p. 116. RUSSELL, W.J. (1969) A discussion of the problems of heat exchange blood warming devices. Brit. 3. Amesth. 41, 345.
STAPLES, P.J. & GRINER, P. F. (1971) Extracorporeal hemolysis of blood in a microwave blood warmer. N e w En&. 3. Med. 285, 3 17.
Address :
Kai Linko, M.D. Finnish Red Cross Blood Transfusion Service Kivihaantie 7 SF-003 10 Helsinki 31 Finland
