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Effect of bowel exposure on body temperature during surgical operations
Effect of Bowel Exposure on Body Temperature during Surgical Operations C. FRANCIS
One of the more constant effects of anesthesia and surgical operation is a fall in body temperature which, in the adult, amounts to an average of 0.8” c (1.4” F) [I]. The deleterious aftereffects of this mild hypothermia include a large increase in postoperative ventilation and oxygen consumption, together with major changes in peripheral vascular tone [Z]. The causes of intraoperative hypothermia are numerous and include reduction of heat production by the body during anesthesia, exposure of the body to the cold operating room environment, preparation of the skin with volatile cleaning agents, and intravenous infusion of cold blood or other intravenous fluid. Another cause of intraoperative fall in body temperature which has been postulated but not documented is heat loss from the exposed bowel during abdominal operation. This loss might be expected to occur by the operation of two mechanisms: radiative heat loss from the warm surface of the bowel, and evaporative heat loss by evaporation of water from the moist serous surfaces. This study was designed to document the effect of bowel exposure on the body temperature under general anesthesia. Material and Methods Twelve New Zealand white rabbits weighing between 1,000 and 2,000 gm (average 1,300 gm) were used. General anesthesia was attained by intravenous administration of NembutaP, 30 mg per kg. Rectal temperatures (T,) were measured with an electronic thermometer (Brookline Instrument Company) checked for accuracy against a National Bureau of Standards-certified mercury thermometer. Bowel temperatures were measured with a Barnes infrared radiometer, checked for accuracy against electrically heated constant temperature metal blocks. This instrument has the advantage of measuring the temperature of solid objects without the necessity for physical con-
ROE, MB, ChB, New Haven,
Connecticut
tact. Body weight, changes were measured on a beam balance with a sensitivity of 0.5 gm. The accuracy of the scale ws19checked with National Bureau of Standards-certified test weights. The experiments were conducted in a laboratory where the ambient temperature was maintained at 25.5”~. The experiments were divided into three groups. In Group I, six animals were anesthetized under conditions exactly similar to the other groups. Rectal temperatures were taken at five minute intervals for one hour. The animals were allowed to recover and were used again several days later for the other parts of the investigation. Group II rabbits were anesthetized, part of the abdomen was shaved, and impermeable adhesive plastic drapes (steridrape) were applied. The abdomen then was opened through a 11/2inch upper midline incision and the small and large bowels were eviscerated. The steridrape was then wrapped around the bowels to form an impermeable extra-abdominal bag for them. The animal was quickly placed on the scale, and bowel temperature (through the plastic bag), rectal temperature, and weight. loss were recorded at. ten minute intervals for one hour, after which time the bowels were returned to the abdominal cavity and the incision was closed. The third group underwent substantially the same procedure except that the bowel was exteriorized and exposed to the air for the duration of the experiment. Total body heat loss was calculated from the formula : H = AT, X M x 0.9 where H = total body heat loss, AT, = the difference between starting and final rectal temperature, M = weight of animal, and 0.9 = estimated specific heat of the animal. Evaporative heat loss was estimated from the formula : E = M x 0.6 where E = evaporative heat loss, M = change in body weight (gm) during experiment, and 0.6 = latent heat of vaporization of water in Kcals (that is, 1 cc of water requires 0.6 Kcals of heat to convert it to water vapor). Heat loss from bowel was estimated from the formula :
Fromthe
Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut 06510.
Volume
122, July 1971
Hb
=
ATb x Mb x 0.9
13
0
-I
-2
ATR
ATR *C
%
-3
-4 1 -5
1
I
I
I
1
1
I
10
20
30
40
50
60
TIME
-5 10
(minutes)
20
30
TIME
Figure 1. Group 1. Average fall in rectal temperature of six anesthetized animals. No operations were performed in this group.
GROUP
2
40
50
60
I
,
I
I
10
20
30
40
Iminuted
TIME
Figure 2. Group II. Average fall in rectal temperature in animals in which bowels were exteriorized but protected from evaporative heat loss by enclosing them in plastic steridrape.
,
50’
60
hinuted
Figure 3. Group Ill. Average fall in rectal temperature in animals whose bowels were exteriorized and exposed to the air.
GROUP I
I
I
-2
GROUP II
GROUP II
GROUP II
-4 ‘&IS
3 -6
4t
\
*C
GROUP 111
-6 GROUP 111 6l
' 10
'
'
'
'
'
20
30
40
50
60
TIME
(minutw1
Average total body heat loss Figure 4. in each group. Evisceration of the bowel causes a slightly increased heat loss even when protected by impermeable plastic bag. Heat loss is greatly accelerated when the bowel is exposed to the air.
-12’
’ 10
’ 20
’ 30
TIME
(minuted
’ 50
’ 60
Figure 5. Change in body weight during experiment. High rate of weight loss in group III is caused by evaporation of water from exposed bowel surface.
where H, = heat loss from bowel, AT, = change in av-
erage bowel temperature during experiment, and MMb = average weight of exposed bowel. Results The rectal temperature started to fall promptly with the animals under anesthesia. Figure 1 shows the average fall in T, in the six animals in group I amounting to 1.6”~ in one hour. In group II (bowels exteriorized but protected from evaporative water loss) and group III (bowels exteriorized and exposed to the air), the average fall in T, was 2.0% and 3.5”~ respectively. (Figures 2 and 3.) The average heat losses represented by these falls in temperature are shown for all three groups in Figure 4, and were 1.75 Kcals, 2.34 Kcals, and 4.10 Kcals, respectively. The change in body weight during the experiments is shown in Figure 5. Significant changes in weight probably resulted from evaporation of water from the bowel surface since unoperated upon rabbits showed negligible (<0.5 gm) insen-
14
’ 40
GROUP 111
-10
-14
I 10
,
I
20
30
TIME
(minuted
1 40
I 50
60
Figure 6. Changes in exteriorized bowel temperatures. 0 on the ordinate represents the initial temperature in each animal.
sible weight loss in a sixty minute period. Animals in group II showed an average weight loss of 1 gm per hour, probably reflecting small amounts of fluid loss around the steridrape. Group III showed an average weight loss of 8 gm per hour. The heat loss by evaporation in group II was therefore 0.6 Kcals and in group III was 4.8 Kcals. In these animals, with an average weight of 1.3 kg, 1 Kcal heat loss would produce a fall in body temperature of 0.7” c beyond the fall in temperature of the animals in group I. In group III loss of 4.8 Kcals would similarly be expected to cause a fall in body temperature of 3.3” c beyond the fall seen in group I. Thus, there is an obvious discrepancy in the results since the average measured fall in rectal temperature of the animals in group III was only 1.9” C more than those in group I. Thus, 2.0 Kcals of evaporative heat loss were unaccounted for, the reason being that the exteriorized bowel cooled to a much lower temperature than the rest of the body, an average of 6.5” c below the rectal temperature. Since the average weight of the exposed
The American
Journal
of Surgery
Bowel Exposure
bowel was 300 gm, this factor accounted for 1.8 Kcals. The small remaining discrepancy could be accounted for by a small amount of fluid evaporating from the surface of the steridrape, causing loss of weight but not heat from the animal. This residual amount is only 5 per cent of the average total water loss in the animals in group III. Comments
In this series of experiments, exposure of most of the small and large bowel to the air had a substantial effect on the heat loss sustained during anesthesia and operation. The intraoperative fall in body temperature in animals with bowel exposed was more than double that of the unoperated upon animals, and almost double that of animals whose bowels were eviscerated but not exposed to the air. The difference in rectal temperatures between animals in group I (anesthetized, unoperated upon) and those in group II (eviscerated, unexposed) was due to the radiative heat loss from the warm exteriorized bowel, and the difference between those in group II and group III (eviscerated, exposed) was due to the evaporative heat loss from the moist bowel. Another effect of this evaporative heat loss was to reduce markedly the bowel temperature to a point at which it was much colder than the rest of the body. (Figure 6.) This phenomenon gave rise to another aspect of this experiment. In the animals whose bowels were exposed to the air, the rectal temperatures did not correctly reflect the total amount of heat which was being lost. The rectal temperature “read high” because it did not reflect the low temperature of the exposed bowel. When the cold bowel was returned to the abdomen, however, the cooling effect on the whole body resulted in a brisk fall in rectal temperature. This
Volume
122,
July
1971
and Body Temperature
at Surgery
offers an explanation for the not uncommon finding of a sudden drop in rectal temperature at the end of an operation after the abdomen has been closed. These experiments suggest some practical points in the management of abdominal operations. When it is important to maintain the body temperature during operations such as those in infants and elderly or sick patients, exposure of the bowel should be avoided as much as possible since this will minimize heat loss from this source. If the bowel must be exteriorized, it should be enclosed in a plastic bag designed for that purpose. If this is not possible, and the bowel has been exposed and thus cooled, the abdominal cavity should be irrigated repeatedly with warm (40” C) saline solution to rewarm the cold bowel after it has been returned to the abdominal cavity. This, if done adequately, will prevent the fall in temperature which would otherwise occur at the end of operation. Summary
Exposure of bowel causes increased evaporative heat loss which can, in experimental animals, cause a pronounced fall in body temperature. Return of the cold exposed bowel to the abdominal cavity causes a further fall in body temperature. These problems can be avoided by enclosing the bowel in a plastic envelope and irrigating the abdominal cavity with warm saline solution after the bowel has been returned to the abdominal cavity. References 1. Goldberg MJ, Roe CF: Temperature
changes during anesthesia. Arch Surg 93: 365, 1966. 2. Roe CF, Goldberg MJ, Blair CS, Kinney JM: The influence of body temperature on early postoperative oxygen consumption. Surgery 120: 85, 1966.
15
One of the more constant effects of anesthesia and surgical operation is a fall in body temperature which, in the adult, amounts to an average of 0.8” c (1.4” F) [I]. The deleterious aftereffects of this mild hypothermia include a large increase in postoperative ventilation and oxygen consumption, together with major changes in peripheral vascular tone [Z]. The causes of intraoperative hypothermia are numerous and include reduction of heat production by the body during anesthesia, exposure of the body to the cold operating room environment, preparation of the skin with volatile cleaning agents, and intravenous infusion of cold blood or other intravenous fluid. Another cause of intraoperative fall in body temperature which has been postulated but not documented is heat loss from the exposed bowel during abdominal operation. This loss might be expected to occur by the operation of two mechanisms: radiative heat loss from the warm surface of the bowel, and evaporative heat loss by evaporation of water from the moist serous surfaces. This study was designed to document the effect of bowel exposure on the body temperature under general anesthesia. Material and Methods Twelve New Zealand white rabbits weighing between 1,000 and 2,000 gm (average 1,300 gm) were used. General anesthesia was attained by intravenous administration of NembutaP, 30 mg per kg. Rectal temperatures (T,) were measured with an electronic thermometer (Brookline Instrument Company) checked for accuracy against a National Bureau of Standards-certified mercury thermometer. Bowel temperatures were measured with a Barnes infrared radiometer, checked for accuracy against electrically heated constant temperature metal blocks. This instrument has the advantage of measuring the temperature of solid objects without the necessity for physical con-
ROE, MB, ChB, New Haven,
Connecticut
tact. Body weight, changes were measured on a beam balance with a sensitivity of 0.5 gm. The accuracy of the scale ws19checked with National Bureau of Standards-certified test weights. The experiments were conducted in a laboratory where the ambient temperature was maintained at 25.5”~. The experiments were divided into three groups. In Group I, six animals were anesthetized under conditions exactly similar to the other groups. Rectal temperatures were taken at five minute intervals for one hour. The animals were allowed to recover and were used again several days later for the other parts of the investigation. Group II rabbits were anesthetized, part of the abdomen was shaved, and impermeable adhesive plastic drapes (steridrape) were applied. The abdomen then was opened through a 11/2inch upper midline incision and the small and large bowels were eviscerated. The steridrape was then wrapped around the bowels to form an impermeable extra-abdominal bag for them. The animal was quickly placed on the scale, and bowel temperature (through the plastic bag), rectal temperature, and weight. loss were recorded at. ten minute intervals for one hour, after which time the bowels were returned to the abdominal cavity and the incision was closed. The third group underwent substantially the same procedure except that the bowel was exteriorized and exposed to the air for the duration of the experiment. Total body heat loss was calculated from the formula : H = AT, X M x 0.9 where H = total body heat loss, AT, = the difference between starting and final rectal temperature, M = weight of animal, and 0.9 = estimated specific heat of the animal. Evaporative heat loss was estimated from the formula : E = M x 0.6 where E = evaporative heat loss, M = change in body weight (gm) during experiment, and 0.6 = latent heat of vaporization of water in Kcals (that is, 1 cc of water requires 0.6 Kcals of heat to convert it to water vapor). Heat loss from bowel was estimated from the formula :
Fromthe
Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut 06510.
Volume
122, July 1971
Hb
=
ATb x Mb x 0.9
13
0
-I
-2
ATR
ATR *C
%
-3
-4 1 -5
1
I
I
I
1
1
I
10
20
30
40
50
60
TIME
-5 10
(minutes)
20
30
TIME
Figure 1. Group 1. Average fall in rectal temperature of six anesthetized animals. No operations were performed in this group.
GROUP
2
40
50
60
I
,
I
I
10
20
30
40
Iminuted
TIME
Figure 2. Group II. Average fall in rectal temperature in animals in which bowels were exteriorized but protected from evaporative heat loss by enclosing them in plastic steridrape.
,
50’
60
hinuted
Figure 3. Group Ill. Average fall in rectal temperature in animals whose bowels were exteriorized and exposed to the air.
GROUP I
I
I
-2
GROUP II
GROUP II
GROUP II
-4 ‘&IS
3 -6
4t
\
*C
GROUP 111
-6 GROUP 111 6l
' 10
'
'
'
'
'
20
30
40
50
60
TIME
(minutw1
Average total body heat loss Figure 4. in each group. Evisceration of the bowel causes a slightly increased heat loss even when protected by impermeable plastic bag. Heat loss is greatly accelerated when the bowel is exposed to the air.
-12’
’ 10
’ 20
’ 30
TIME
(minuted
’ 50
’ 60
Figure 5. Change in body weight during experiment. High rate of weight loss in group III is caused by evaporation of water from exposed bowel surface.
where H, = heat loss from bowel, AT, = change in av-
erage bowel temperature during experiment, and MMb = average weight of exposed bowel. Results The rectal temperature started to fall promptly with the animals under anesthesia. Figure 1 shows the average fall in T, in the six animals in group I amounting to 1.6”~ in one hour. In group II (bowels exteriorized but protected from evaporative water loss) and group III (bowels exteriorized and exposed to the air), the average fall in T, was 2.0% and 3.5”~ respectively. (Figures 2 and 3.) The average heat losses represented by these falls in temperature are shown for all three groups in Figure 4, and were 1.75 Kcals, 2.34 Kcals, and 4.10 Kcals, respectively. The change in body weight during the experiments is shown in Figure 5. Significant changes in weight probably resulted from evaporation of water from the bowel surface since unoperated upon rabbits showed negligible (<0.5 gm) insen-
14
’ 40
GROUP 111
-10
-14
I 10
,
I
20
30
TIME
(minuted
1 40
I 50
60
Figure 6. Changes in exteriorized bowel temperatures. 0 on the ordinate represents the initial temperature in each animal.
sible weight loss in a sixty minute period. Animals in group II showed an average weight loss of 1 gm per hour, probably reflecting small amounts of fluid loss around the steridrape. Group III showed an average weight loss of 8 gm per hour. The heat loss by evaporation in group II was therefore 0.6 Kcals and in group III was 4.8 Kcals. In these animals, with an average weight of 1.3 kg, 1 Kcal heat loss would produce a fall in body temperature of 0.7” c beyond the fall in temperature of the animals in group I. In group III loss of 4.8 Kcals would similarly be expected to cause a fall in body temperature of 3.3” c beyond the fall seen in group I. Thus, there is an obvious discrepancy in the results since the average measured fall in rectal temperature of the animals in group III was only 1.9” C more than those in group I. Thus, 2.0 Kcals of evaporative heat loss were unaccounted for, the reason being that the exteriorized bowel cooled to a much lower temperature than the rest of the body, an average of 6.5” c below the rectal temperature. Since the average weight of the exposed
The American
Journal
of Surgery
Bowel Exposure
bowel was 300 gm, this factor accounted for 1.8 Kcals. The small remaining discrepancy could be accounted for by a small amount of fluid evaporating from the surface of the steridrape, causing loss of weight but not heat from the animal. This residual amount is only 5 per cent of the average total water loss in the animals in group III. Comments
In this series of experiments, exposure of most of the small and large bowel to the air had a substantial effect on the heat loss sustained during anesthesia and operation. The intraoperative fall in body temperature in animals with bowel exposed was more than double that of the unoperated upon animals, and almost double that of animals whose bowels were eviscerated but not exposed to the air. The difference in rectal temperatures between animals in group I (anesthetized, unoperated upon) and those in group II (eviscerated, unexposed) was due to the radiative heat loss from the warm exteriorized bowel, and the difference between those in group II and group III (eviscerated, exposed) was due to the evaporative heat loss from the moist bowel. Another effect of this evaporative heat loss was to reduce markedly the bowel temperature to a point at which it was much colder than the rest of the body. (Figure 6.) This phenomenon gave rise to another aspect of this experiment. In the animals whose bowels were exposed to the air, the rectal temperatures did not correctly reflect the total amount of heat which was being lost. The rectal temperature “read high” because it did not reflect the low temperature of the exposed bowel. When the cold bowel was returned to the abdomen, however, the cooling effect on the whole body resulted in a brisk fall in rectal temperature. This
Volume
122,
July
1971
and Body Temperature
at Surgery
offers an explanation for the not uncommon finding of a sudden drop in rectal temperature at the end of an operation after the abdomen has been closed. These experiments suggest some practical points in the management of abdominal operations. When it is important to maintain the body temperature during operations such as those in infants and elderly or sick patients, exposure of the bowel should be avoided as much as possible since this will minimize heat loss from this source. If the bowel must be exteriorized, it should be enclosed in a plastic bag designed for that purpose. If this is not possible, and the bowel has been exposed and thus cooled, the abdominal cavity should be irrigated repeatedly with warm (40” C) saline solution to rewarm the cold bowel after it has been returned to the abdominal cavity. This, if done adequately, will prevent the fall in temperature which would otherwise occur at the end of operation. Summary
Exposure of bowel causes increased evaporative heat loss which can, in experimental animals, cause a pronounced fall in body temperature. Return of the cold exposed bowel to the abdominal cavity causes a further fall in body temperature. These problems can be avoided by enclosing the bowel in a plastic envelope and irrigating the abdominal cavity with warm saline solution after the bowel has been returned to the abdominal cavity. References 1. Goldberg MJ, Roe CF: Temperature
changes during anesthesia. Arch Surg 93: 365, 1966. 2. Roe CF, Goldberg MJ, Blair CS, Kinney JM: The influence of body temperature on early postoperative oxygen consumption. Surgery 120: 85, 1966.
15