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The lack of influence of hemodilution perfusion on alterations in total body potassium
The lack of influence of hemodilution perfusion on alterations in total body potassium Richard E. Clark, M.D., * Walter E. Beasley, Ill, Commander (MC) USN, ** Jonas Sode, Captain (MC) USN, and Mitchell Mills, Captain (MC) USN, Bethesda, Md.
Extracorporeal circulation, major surgery, and trauma are known to cause changes in total exchangeable potassium. i -« Recent reports have suggested that a large net potassium loss occurs as a consequence of hemodilution perfusions.:'- " Although others,'; who used radioisotopes, have reported losses of 120 to 266 mEq. of potassium in perfused patients, there has been no report on a simultaneously studied group of patients undergoing major surgical procedures without total body perfusion. A noninvasive method of measuring total body potassium was used in this study. A naturally occurring and constant form of a potassium isotope, "UK, was measured before and after thoracotomy and hemodilution perfusion. In addition, balance studies were conducted to examine the alteration of ionic potassium equilibrium imposed by hemodilution perfusion. This is a report of the findings. From the Thoracic-Cardiovascular Surgery Service, Naval Hospital, National Naval Medical Center, Bethesda, Md. 20014. The
opinions and assertions contained herein do not necessarily reflect the views of the Department of the Navy or the Naval Service at large.
Received for publication June 7, 1972.
* Present
address: Division of Cardiothoracic Surgery, Washington University School of Medicine, 51. Louis, Mo. 63110.
Methods Patient groups. Three groups were studied. The first was a mixed population of 23 normal, healthy persons ranging in age from 10 to 35 years, with a mean age of 18.2 ± 1.9 (S.E.)* years. In each individual, the total body potassium was determined by both the 4UK and the 4"K methods. Red cell mass was measured by the "'er method. These data provided a base against which patients with pulmonary, esophageal, and cardiac diseases could be compared. The second group consisted of II patients who underwent thoracotomy but did not have extracorporeal perfusion. The mean age of this group was 41.7 ± 3.8 (S.E.) years. The third group consisted of 19 patients with both congenital and acquired heart disease. All had extracorporeal hemodilution perfusion which lasted from 31 to 131 minutes (average 62 minutes). Hypothermia, between 28 and 32° c., was used in most cases. The characteristics of each group are given in Table I. Total body potassium. Total body potassium was determined by a 6-crystal, wholebody counter which measured emissions of the 4°K isotope. This natural isotope occurs
** Present
address: Thoracic-Cardiovascular Surgery Service, Naval Hospital, Philadelphia, Pa.
112
·S.E. is standard error of the mean.
Volume 65 Number 1 January, 1973
Hemodilution perfusion re total body potassium
113
Table I Variable
Total No. of patients Males Females Age (yr.) 10-20 21-40 41-50 51-60 61-70 Mean Acquired disease Congenital disease Preoperative weight (Kg.) Range Mean Body surface area (sq. M.) Range Mean
Healthy control group
Thoracotomy group
23 12 11
11 7 4
17 6
2 3 4 3
18.2 ± 9.2 (S.D.) ± 1.9 (S.E.)
41-97 8004 ± 39.0 (S.D.) ± 8.1 (S.E.) 1.42-2.40 1.70 ± 0.27 (S.D.) ± 0.06 (S.E.)
Perfusion group
19 8 11
41.7 ± 12.6 (S.D.) ± 3.8 (S.E.)
6 4 6 2 1 37.3 ± 14.2 (S.D.) ± 3.4 (S.E.)
10 1
12 7
48-87 67.8 ± 15.6 (S.D.) ± 4.7 (S.E.)
37-94 58.7 ± 14.5 (S.D.) ± 4.0 (S.E.)
1.37-2.08 1.77 ± 0.26 (S.D.) ± 0.08 (S.E.)
1.38-2.05 1.62 ± 0.25 (S.D.) ± 0.07 (S.E.)
Legend: S.D., Standard deviation. S.E., Standard error.
as a constant and amounts to 0.018 per cent of all potassium. The counting error ranged from 3 to 8.5 per cent and averaged a standard error of 6.1 per cent. The data were reproducible in the same patient within 2 to 3 per cent. Studies were performed on all but 30f the 30 patients in the thoracotomy and perfusion groups at least twice preoperatively. Postoperatively, counting was performed as early as the second day after operation and continued as late as the forty-seventh postoperative day. An average of 4.1 determinations per patient was made in the postoperative period. The total body potassium per patient was expressed as grams of potassium per square meter of body surface area. Variables studied preoperatively. Preoperatively, determinations of blood cell counts, serum osmolalities, arterial blood gases, serum electrolytes, blood urea nitrogen, creatinine, total protein, albumin, calcium, alkaline phosphatase, total bilirubin, glucose, serum glutamic oxaloacetic transaminase, lactic dehydrogenase, serum glutamic pyruvic transaminase, uric acid, 17ketosteroids, and 17-hydroxycorticosteroids
Table II. Pump prime analysis Components
Osmolality (mOsm.) Potassium (mEq./L.) Sodium (mEq./L.) Chloride (mEq./L.) Glucose (mg. %) Hematocrit (%) MCV (cu. p.) MCH (vv) MCHC (%) Blood (rnl.) Crystalloid (rnl.) Total volume (rnl.)
Prime
338 3.8 123 87 484 3.1 76 30 35
Normal range
281-298 3.5-5.0 136-144 92-98 80-110 38-47 82-92 27-31 32-36 500 1,500 2,000
Legend: MCV, Mean corpuscular volume. MCH, Mean corpuscular hemoglobin. MCHC, Mean corpuscular hemoglobin concentration.
were made on patients who had perfusion. Determinations of the concentration of sodium, potassium, chloride, creatinine, and uric acid were performed on 24 hour urine samples. Potassium concentrations of intracellular erythrocytes were determined by the lysis-dilution technique. Coagulation studies consisted of determinations of the prothrombin time, clotting time (Lee-White
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Table III. The influence of operation on patients who had thoracotomy and hemodilution perfusion Patient Healthy control
Variable
Preoperative
80.4 ± 8.1 1.70 ± 0.06 100.67 ± 5.8 60.0 ± 2.8
Weight (Kg.) Body surface area (sq. M.) Total body potassium (Gm.) Total body potassium (Gm.z'sq. M.)
67.8 1.77 120.1 66.7
± 4.7
± 0.08 ± 10.8 ± 3.7
Legend: N.S., Not significant.
Table IV. Body potassium loss by operation Total loss Patient group
Grams
Thoracotomy Hemodilution perfusion
12.8 9.5
I equivalent Milli320 238
cent 1Perchange -10.7 - 9.2
J
Loss per square meter BSA Grams 5.8 4.8
Milli-
I equivalent 145 120
Per cent change -8.7 -6.8
Legend: BSA, Body surface area.
technique), and partial thromboplastin generation time. These variables were also measured frequently in the postoperative period. Blood volumes were determined by independent measurement of the red cell mass with 5ler and plasma volumes with 131 Itagged albumin. Perfusion and postoperative periods
Serum and urinary potassium were measured immediately prior to the induction of anesthesia, after the induction of anesthesia but before the operation was begun, and immediately prior to the start of perfusion. Serum and urinary electrolytes, osmolalities, blood gases, and pH were obtained for the first three 5 minute intervals after the start of bypass and every 15 minutes thereafter during the perfusion. At least one further measurement was made prior to the patient's exit from the operating room. Measurements of all variables were then performed on a rigid schedule at 6:00 A.M. and 6:00 P.M. for a minimum of 72 hours. The studies were performed again at least twice before discharge. Samples of all transfused blood and chest drainage were obtained for determinations of serum and intracellular erythrocytic potassium. The priming solution of the extracorporeal circuit, which included a Temptrol
bubble oxygenator and roller pumps, was analyzed after recirculation and immediately prior to bypass. The prime consisted of 2 L. of crystalloid solution, most of which was Ringer's lactate solution, and 500 ml. of 24 hour acid-cit rate-dextrose blood (Table II). Glucose, insulin, mannitol, sodium bicarbonate, calcium chloride, and heparin were added. Results Healthy control group. This group of 23 subjects had a mean body surface of 1.70 ± 0.06 (S.E.) sq. M. and an average weight of 8004 ± 8.1 (S.E.) kilograms. The exchangeable body potassium as determined by the 42K method was 95.4 ± 5.6 (S.E.) Gm. The mean value by the 4°K method was 100.7 ± 5.8 (S.E.) Gm. As a result, the ratio of total body 4°K to total body 42K was 1.057. There was a highly significant difference statistically between the two methods by the paired t test (p < 0.001). The total body potassium per square meter of body surface area was 60.0 ± 2.8 (S.E.). Thoracotomy group. No statistical differences were found by the t test for unpaired data between this group and the healthy control subjects except for age. However, significant statistical differences were found between the pre- and postoperative states
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January, 1973
(mean values ± standard error of the mean) group Hemodilution perfusion
Thoracotomy Postoperative 1-2 wk. 65.3 1.73 107.3 60.9
± ± ± ±
4.4 0.07 9.3 3.4
p value
Preoperative
< < < <
58.7 1.62 103.1 62.6
0.01 0.01 0.01 0.001
± 4.0 ± 0.07 ± 8.0 ± 2.8
Postoperative 1-2 wk. 57.6 1.60 93.6 57.8
± ± ± ±
p value
3.9 0.Q7 6.9 2.3
N.S. N.S. < 0.001 < 0.01
Table V. Hemodilution perfusion group Normal range
Parameters (mean values) Total body (~"K) (Gm./sq. M.) RBC-K (mEq./L.) Serum K (mEq./L.) Osmolality (mOsm./L.) Net Kloss (mEq./24 hr.) Base excess (+) or deficit (-) (mEq./L.)
99 4.1 2!!7
105 3.8 338
102 3.1 292
o
o
-1.2
90.1 3.7 286 72 +4.3
56.5
56.7
57.8
54.8- 66.9
92.3 4.0 285 55
91.8 3.9 276
95.0 4.6 284
88.2-101 3.5- 5.0 281 -298
Legend: RBC-K. Red blood cell potassium.
(p < 0.0 I all cases) for weight, body surface area, total body potassium, and total body potassium per square meter (Tables III and IV). There was a mean weight loss of 2.5 kilograms, a small reduction in body surface area of 0.04 sq. M., and a 12.8 Gm. potassium loss or 320 mEq. (l0.7 per cent). The total body potassium per square meter decreased 5.8 Gm. (p < 0.001) or 145 mEq. per square meter (8.7 per cent). Perfusion group. Preoperatively, total body potassium in the perfusion group was not statistically different from that of the healthy control group or the thoracotomy group. There was no significant difference in any variable studied between the thoracotomy and perfusion groups in either the preoperative or postoperative periods. The mean values of the serum potassium, osmolality, and concentrations of intracellular erythrocyte potassium were all normal preoperatively. At the time of surgery and perfusion, however, significant changes occurred (Table V). First, the arterial Pco, was decreased to a mean value of 27 ± 0.8 (S.E.) mm. Hg immediately prior to perfusion by hyperventilation. No base excess
or deficit was incurred during this period. Second, the serum potassium changed from 4.1 to 2.7 ± 0.07 (S.E.) mEq. per liter within the first 15 to 30 minutes and then gradually increased thereafter. The mean value for the serum potassium during all perfusions was 3.1 ± 0.07 (S.E.) mEq. per liter. By the second postoperative week all patients had lost weight, but the difference was insignificant statistically as was the small decrease in body surface area. There was a mean loss of 9.5 Gm. or 238 mEq. of potassium, representing a 9.2 per cent decrease which was significant (p < 0.001). However, there was no difference in the amount of potassium lost between this group and the thoracotomy group. The potassium balance studies accounted for an average net loss of 127 ± 3.1 mEq. during the first 72 hours after operation. This was 53.3 per cent of the total loss as determined by total body counting of 4f'K during the 7 to 14 day period. Two other significant changes occurred. First, metabolic alkalosis was present during the first 24 hours after operation, resulting in a base excess of 4.3 ± 0.10 mEq. per
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Clark et al.
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Surgery
liter. Second, the serum osmolality decreased (p < 0.05) during the 4 to 7 day period. Concomitantly, there was a small decrease in erythrocytic intracellular potassium, but this was not statistically significant. The serum potassium concentration changed little during the postoperative period. No patient in the perfusion group developed a postoperative ventricular arrhythmia. Discussion
Body potassium is primarily contained within cells. Correlative studies performed on the control group of healthy subjects demonstrated a linear relationship between red cell mass and total body potassium. However, the red cell mass constitutes less than 10 per cent of total body potassium. There are approximately 8 Gm. of potassium per 5 L. of normal whole blood. Therefore, although deficits in red cell mass and total blood volume may be expected after major surgical procedures," these changes should not have a marked influence on alterations in total body potassium. The major loss may be related to loss of lean body mass which was not reflected by the weight measurements. A loss of 1 Gm. of I"K per square meter corresponds to a loss of 0.4 kilogram per square meter of lean body mass. If normal preoperative and postoperative blood volumes are assumed for both surgical groups, the thoracotomy group would have lost 2.32 kilograms per square meter or 4.0 kilograms of lean body mass and the perfusion group 1.9 kilograms per square meter or 3 kilograms, respectively. These large and significant changes of lean body mass 1 to 2 weeks after operation were not accurately reflected in the weight loss of each group. This may be explained by an increase in total body water. If such were the case, it was not reflected in the serum concentrations of any ion or variable measured in this group of patients 7 to 14 days after operation. The serum osmolality and the red cell intracellular potassium 7 or more days after operation were normal. The continuing and careful work of Kirklin with respect to body compartmental and compositional changes as a result of heart
disease and extracorporeal circulation is pertinent to the data in this study. Measurements of radioactive bromide and mean insulin space have demonstrated an increase of 3.4 and 4.0 L., respectively, in the extracellular fluid space 24 hours after hemodilution perfusion.' These changes persist 2 to 4 weeks after operation as demonstrated by an 8.2 per cent increase in total body water and a 15 per cent increase in intracellular water." A calculation of lean body mass for the perfusion group reported here, based on the formula Jean body weight
=
grams total body potassium 2.46
,
yields values of 41.9 and 38.1 kilograms for the preoperative and postoperative periods, respectively. Normally, total body water is approximately 73 per cent of lean body mass," resulting in a preoperative value of 30.6 L. If this value were increased in the postoperative period by 8.2 per cent, as demonstrated by Pacifico's group," then a 2.5 L. increment in total body water was incurred by operation and perfusion. Thus the discrepancies between the small weight changes in the perfusion group and the large equivalent calculated loss of lean body weight as determined by counting of total body potassium can be explained in large part by an increase of total body water. Another explanation is that, during starvation, the lean body mass is depleted of potassium to a far greater extent initially than of protein. I" This could be partly responsible for the difference in the amount of potassium accountable by weight shifts of 4.9 and 2.0 grams for the thoracotomy and perfusion groups, respectively, and for the difference measured by the total body counting method of 12.8 and 9.5 Gm. in these two groups. Thus the potassium loss can be explained best in terms of a disproportionate loss of intracellular potassium compared to protein in response to trauma and starvation, a small blood volume deficit, and a moderate loss of lean body mass. The changes during perfusion were unexpected. The osmolality of the prime averaged 338 mOsm. and returned to the nor-
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Hemodilution perfusion re total body potassium
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January, 1973
mal range within 5 minutes after the onset of perfusion. The serum potassium of the prime was in the low normal range, but on initiation of bypass it decreased from 4.1 to 2.7 mEq. per liter within the first 15 to 30 minutes. In the presence of glucose, insulin, hypothermia, and a high flow (2.5 L. per minute per square meter) and low pressure state characteristic of hemodilution perfusion, potassium must have been lost to an interstitial space not in equilibrium with the perfusion and/or have been driven to the intracellular space. The return toward the preoperative value in the second 30 minutes represents the consequences of rewarming and a gradual return toward equilibrium. The amount of potassium in a hyperosmolar prime apparently does not influence potassium loss in the postoperative period."
Summary The first study of total body potassium measured by a noninvasive whole body 4°K counting method on patients who had thoracotomy or hemodilution perfusion is reported. Fifty-three patients in three groups were studied. Twenty-three healthy control subjects had a mean value for total body potassium of 60.0 ± 2.8 (S.E.) Gm. of potassium per square meter. Eleven patients who had a thoracotomy and 19 patients who had hemodilution perfusion for acquired and congenital heart disease had preoperative total body potassium values of 66.7 ± 3.7 and 62.6 ± 2.8 Gm. of potassium per square meter, respectively. There was no significant difference between groups. Postoperatively, the total body potassium values were 60.9 ± 3.4 (thoracotomy) and 57.8 ± 2.3 (hemodilution perfusion). No difference in loss of potassium between the two groups was found. The net loss for the thoracotomy group was 12.8 Gm. (l0.7 per cent) or 320 mEq. The loss for the hemodilution perfusion group was 9.5 Gm. (9.2 per cent) or 238 mEq. These losses represented 145 and 120 mEq. per square meter for the two groups. Significant metabolic alkalosis occurred in the first 24 hours after operation,
and a hypoosmolar state developed 4 to 7 days postoperatively. No significant changes were found in the erythrocyte intracellular or serum potassium concentrations. This study has demonstrated that hemodilution perfusion does not decrease total body stores of potassium to any greater degree than does thoracotomy alone. The metabolic alkalosis following hemodilution perfusion is best recognized by frequent determinations of the base excess from bloodgas data and measurement of the urine volume and potassium concentrations in the initial postoperative period. REFERENCES 1 Clark, R. E., Beasley, W. E., Sode, J., and Mills, M.: Influence of Hemodilution Perfusion on Total Body Potassium and Intracellular Potassium: Critical Prospective Study, Surg, Forum 20:40, 1969. 2 Moore, F. D., and Ball, M. R.: The Metabolic Response to Surgery, Springfield, III., 1952, Charles C Thomas, Publisher. 3 Moore, F. D., Olesen, K H., McMurrey, 1. D., Parker, H. V., Ball, M. R., and Boyden, C. M.: The Body Cell Mass and Its Supporting Environment: Body Composition in Health and Disease, Philadelphia, 1963, W. B. Saunders Company, p. 523. 4 Neville, W. E., and Tal so, P. 1.: Postperfusion Compartmental Fluid Alterations, Surgery 63: 220, 1968. 5 Krohn, B. G., Urquhart, R. R., Magidson, 0., Tsuji, H. K, Redington, 1. V., and Kay, J. H.: Metabolic Alkalosis Following Heart Surgery, 1. THORAC. CARDIOVASC. SURG. 56: 732, 1968. 6 Breckenridge, I. M., Deverall, P. B., Kirklin, J. W., and Digerness, S. B.: Potassium Intake and Balance After Open Intracardiac Operations, J. THORAC. CARDIOVASC. SURG. 63: 305, 1972. 7 Breckenridge, I. M., Digerness, S. B., and Kirklin, J. W.: Increased Extracellular Fluid After Open Intracardiac Operation, Surg. GynecoI. Obstet. 131: 53, 1970. 8 Pacifico, A. D., Digerness, S. B., and Kirklin, J. W.: Regression of Body Compositional Abnormalities of Heart Failure After Intracardiac Operations, Circulation 42: 999, 1970. 9 Oberhausen, E., and Onstead, C. 0.: Relationship of Potassium Content of Man With Age and Sex, in Radioactivity in Man, Springfield, III., 1965, Charles C Thomas, Publisher, p. 179. 10 Drenick, E. J.: Obesity, Weight Reduction and Body Composition, Ann. Intern. Med. 64: 1148, 1966.
Extracorporeal circulation, major surgery, and trauma are known to cause changes in total exchangeable potassium. i -« Recent reports have suggested that a large net potassium loss occurs as a consequence of hemodilution perfusions.:'- " Although others,'; who used radioisotopes, have reported losses of 120 to 266 mEq. of potassium in perfused patients, there has been no report on a simultaneously studied group of patients undergoing major surgical procedures without total body perfusion. A noninvasive method of measuring total body potassium was used in this study. A naturally occurring and constant form of a potassium isotope, "UK, was measured before and after thoracotomy and hemodilution perfusion. In addition, balance studies were conducted to examine the alteration of ionic potassium equilibrium imposed by hemodilution perfusion. This is a report of the findings. From the Thoracic-Cardiovascular Surgery Service, Naval Hospital, National Naval Medical Center, Bethesda, Md. 20014. The
opinions and assertions contained herein do not necessarily reflect the views of the Department of the Navy or the Naval Service at large.
Received for publication June 7, 1972.
* Present
address: Division of Cardiothoracic Surgery, Washington University School of Medicine, 51. Louis, Mo. 63110.
Methods Patient groups. Three groups were studied. The first was a mixed population of 23 normal, healthy persons ranging in age from 10 to 35 years, with a mean age of 18.2 ± 1.9 (S.E.)* years. In each individual, the total body potassium was determined by both the 4UK and the 4"K methods. Red cell mass was measured by the "'er method. These data provided a base against which patients with pulmonary, esophageal, and cardiac diseases could be compared. The second group consisted of II patients who underwent thoracotomy but did not have extracorporeal perfusion. The mean age of this group was 41.7 ± 3.8 (S.E.) years. The third group consisted of 19 patients with both congenital and acquired heart disease. All had extracorporeal hemodilution perfusion which lasted from 31 to 131 minutes (average 62 minutes). Hypothermia, between 28 and 32° c., was used in most cases. The characteristics of each group are given in Table I. Total body potassium. Total body potassium was determined by a 6-crystal, wholebody counter which measured emissions of the 4°K isotope. This natural isotope occurs
** Present
address: Thoracic-Cardiovascular Surgery Service, Naval Hospital, Philadelphia, Pa.
112
·S.E. is standard error of the mean.
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Hemodilution perfusion re total body potassium
113
Table I Variable
Total No. of patients Males Females Age (yr.) 10-20 21-40 41-50 51-60 61-70 Mean Acquired disease Congenital disease Preoperative weight (Kg.) Range Mean Body surface area (sq. M.) Range Mean
Healthy control group
Thoracotomy group
23 12 11
11 7 4
17 6
2 3 4 3
18.2 ± 9.2 (S.D.) ± 1.9 (S.E.)
41-97 8004 ± 39.0 (S.D.) ± 8.1 (S.E.) 1.42-2.40 1.70 ± 0.27 (S.D.) ± 0.06 (S.E.)
Perfusion group
19 8 11
41.7 ± 12.6 (S.D.) ± 3.8 (S.E.)
6 4 6 2 1 37.3 ± 14.2 (S.D.) ± 3.4 (S.E.)
10 1
12 7
48-87 67.8 ± 15.6 (S.D.) ± 4.7 (S.E.)
37-94 58.7 ± 14.5 (S.D.) ± 4.0 (S.E.)
1.37-2.08 1.77 ± 0.26 (S.D.) ± 0.08 (S.E.)
1.38-2.05 1.62 ± 0.25 (S.D.) ± 0.07 (S.E.)
Legend: S.D., Standard deviation. S.E., Standard error.
as a constant and amounts to 0.018 per cent of all potassium. The counting error ranged from 3 to 8.5 per cent and averaged a standard error of 6.1 per cent. The data were reproducible in the same patient within 2 to 3 per cent. Studies were performed on all but 30f the 30 patients in the thoracotomy and perfusion groups at least twice preoperatively. Postoperatively, counting was performed as early as the second day after operation and continued as late as the forty-seventh postoperative day. An average of 4.1 determinations per patient was made in the postoperative period. The total body potassium per patient was expressed as grams of potassium per square meter of body surface area. Variables studied preoperatively. Preoperatively, determinations of blood cell counts, serum osmolalities, arterial blood gases, serum electrolytes, blood urea nitrogen, creatinine, total protein, albumin, calcium, alkaline phosphatase, total bilirubin, glucose, serum glutamic oxaloacetic transaminase, lactic dehydrogenase, serum glutamic pyruvic transaminase, uric acid, 17ketosteroids, and 17-hydroxycorticosteroids
Table II. Pump prime analysis Components
Osmolality (mOsm.) Potassium (mEq./L.) Sodium (mEq./L.) Chloride (mEq./L.) Glucose (mg. %) Hematocrit (%) MCV (cu. p.) MCH (vv) MCHC (%) Blood (rnl.) Crystalloid (rnl.) Total volume (rnl.)
Prime
338 3.8 123 87 484 3.1 76 30 35
Normal range
281-298 3.5-5.0 136-144 92-98 80-110 38-47 82-92 27-31 32-36 500 1,500 2,000
Legend: MCV, Mean corpuscular volume. MCH, Mean corpuscular hemoglobin. MCHC, Mean corpuscular hemoglobin concentration.
were made on patients who had perfusion. Determinations of the concentration of sodium, potassium, chloride, creatinine, and uric acid were performed on 24 hour urine samples. Potassium concentrations of intracellular erythrocytes were determined by the lysis-dilution technique. Coagulation studies consisted of determinations of the prothrombin time, clotting time (Lee-White
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Thoracic and Cardiovascular Surgery
Table III. The influence of operation on patients who had thoracotomy and hemodilution perfusion Patient Healthy control
Variable
Preoperative
80.4 ± 8.1 1.70 ± 0.06 100.67 ± 5.8 60.0 ± 2.8
Weight (Kg.) Body surface area (sq. M.) Total body potassium (Gm.) Total body potassium (Gm.z'sq. M.)
67.8 1.77 120.1 66.7
± 4.7
± 0.08 ± 10.8 ± 3.7
Legend: N.S., Not significant.
Table IV. Body potassium loss by operation Total loss Patient group
Grams
Thoracotomy Hemodilution perfusion
12.8 9.5
I equivalent Milli320 238
cent 1Perchange -10.7 - 9.2
J
Loss per square meter BSA Grams 5.8 4.8
Milli-
I equivalent 145 120
Per cent change -8.7 -6.8
Legend: BSA, Body surface area.
technique), and partial thromboplastin generation time. These variables were also measured frequently in the postoperative period. Blood volumes were determined by independent measurement of the red cell mass with 5ler and plasma volumes with 131 Itagged albumin. Perfusion and postoperative periods
Serum and urinary potassium were measured immediately prior to the induction of anesthesia, after the induction of anesthesia but before the operation was begun, and immediately prior to the start of perfusion. Serum and urinary electrolytes, osmolalities, blood gases, and pH were obtained for the first three 5 minute intervals after the start of bypass and every 15 minutes thereafter during the perfusion. At least one further measurement was made prior to the patient's exit from the operating room. Measurements of all variables were then performed on a rigid schedule at 6:00 A.M. and 6:00 P.M. for a minimum of 72 hours. The studies were performed again at least twice before discharge. Samples of all transfused blood and chest drainage were obtained for determinations of serum and intracellular erythrocytic potassium. The priming solution of the extracorporeal circuit, which included a Temptrol
bubble oxygenator and roller pumps, was analyzed after recirculation and immediately prior to bypass. The prime consisted of 2 L. of crystalloid solution, most of which was Ringer's lactate solution, and 500 ml. of 24 hour acid-cit rate-dextrose blood (Table II). Glucose, insulin, mannitol, sodium bicarbonate, calcium chloride, and heparin were added. Results Healthy control group. This group of 23 subjects had a mean body surface of 1.70 ± 0.06 (S.E.) sq. M. and an average weight of 8004 ± 8.1 (S.E.) kilograms. The exchangeable body potassium as determined by the 42K method was 95.4 ± 5.6 (S.E.) Gm. The mean value by the 4°K method was 100.7 ± 5.8 (S.E.) Gm. As a result, the ratio of total body 4°K to total body 42K was 1.057. There was a highly significant difference statistically between the two methods by the paired t test (p < 0.001). The total body potassium per square meter of body surface area was 60.0 ± 2.8 (S.E.). Thoracotomy group. No statistical differences were found by the t test for unpaired data between this group and the healthy control subjects except for age. However, significant statistical differences were found between the pre- and postoperative states
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Hemodilution perfusion re total body potassium
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January, 1973
(mean values ± standard error of the mean) group Hemodilution perfusion
Thoracotomy Postoperative 1-2 wk. 65.3 1.73 107.3 60.9
± ± ± ±
4.4 0.07 9.3 3.4
p value
Preoperative
< < < <
58.7 1.62 103.1 62.6
0.01 0.01 0.01 0.001
± 4.0 ± 0.07 ± 8.0 ± 2.8
Postoperative 1-2 wk. 57.6 1.60 93.6 57.8
± ± ± ±
p value
3.9 0.Q7 6.9 2.3
N.S. N.S. < 0.001 < 0.01
Table V. Hemodilution perfusion group Normal range
Parameters (mean values) Total body (~"K) (Gm./sq. M.) RBC-K (mEq./L.) Serum K (mEq./L.) Osmolality (mOsm./L.) Net Kloss (mEq./24 hr.) Base excess (+) or deficit (-) (mEq./L.)
99 4.1 2!!7
105 3.8 338
102 3.1 292
o
o
-1.2
90.1 3.7 286 72 +4.3
56.5
56.7
57.8
54.8- 66.9
92.3 4.0 285 55
91.8 3.9 276
95.0 4.6 284
88.2-101 3.5- 5.0 281 -298
Legend: RBC-K. Red blood cell potassium.
(p < 0.0 I all cases) for weight, body surface area, total body potassium, and total body potassium per square meter (Tables III and IV). There was a mean weight loss of 2.5 kilograms, a small reduction in body surface area of 0.04 sq. M., and a 12.8 Gm. potassium loss or 320 mEq. (l0.7 per cent). The total body potassium per square meter decreased 5.8 Gm. (p < 0.001) or 145 mEq. per square meter (8.7 per cent). Perfusion group. Preoperatively, total body potassium in the perfusion group was not statistically different from that of the healthy control group or the thoracotomy group. There was no significant difference in any variable studied between the thoracotomy and perfusion groups in either the preoperative or postoperative periods. The mean values of the serum potassium, osmolality, and concentrations of intracellular erythrocyte potassium were all normal preoperatively. At the time of surgery and perfusion, however, significant changes occurred (Table V). First, the arterial Pco, was decreased to a mean value of 27 ± 0.8 (S.E.) mm. Hg immediately prior to perfusion by hyperventilation. No base excess
or deficit was incurred during this period. Second, the serum potassium changed from 4.1 to 2.7 ± 0.07 (S.E.) mEq. per liter within the first 15 to 30 minutes and then gradually increased thereafter. The mean value for the serum potassium during all perfusions was 3.1 ± 0.07 (S.E.) mEq. per liter. By the second postoperative week all patients had lost weight, but the difference was insignificant statistically as was the small decrease in body surface area. There was a mean loss of 9.5 Gm. or 238 mEq. of potassium, representing a 9.2 per cent decrease which was significant (p < 0.001). However, there was no difference in the amount of potassium lost between this group and the thoracotomy group. The potassium balance studies accounted for an average net loss of 127 ± 3.1 mEq. during the first 72 hours after operation. This was 53.3 per cent of the total loss as determined by total body counting of 4f'K during the 7 to 14 day period. Two other significant changes occurred. First, metabolic alkalosis was present during the first 24 hours after operation, resulting in a base excess of 4.3 ± 0.10 mEq. per
The Journal af
1 16
Clark et al.
Thoracic and Cardiovascular
Surgery
liter. Second, the serum osmolality decreased (p < 0.05) during the 4 to 7 day period. Concomitantly, there was a small decrease in erythrocytic intracellular potassium, but this was not statistically significant. The serum potassium concentration changed little during the postoperative period. No patient in the perfusion group developed a postoperative ventricular arrhythmia. Discussion
Body potassium is primarily contained within cells. Correlative studies performed on the control group of healthy subjects demonstrated a linear relationship between red cell mass and total body potassium. However, the red cell mass constitutes less than 10 per cent of total body potassium. There are approximately 8 Gm. of potassium per 5 L. of normal whole blood. Therefore, although deficits in red cell mass and total blood volume may be expected after major surgical procedures," these changes should not have a marked influence on alterations in total body potassium. The major loss may be related to loss of lean body mass which was not reflected by the weight measurements. A loss of 1 Gm. of I"K per square meter corresponds to a loss of 0.4 kilogram per square meter of lean body mass. If normal preoperative and postoperative blood volumes are assumed for both surgical groups, the thoracotomy group would have lost 2.32 kilograms per square meter or 4.0 kilograms of lean body mass and the perfusion group 1.9 kilograms per square meter or 3 kilograms, respectively. These large and significant changes of lean body mass 1 to 2 weeks after operation were not accurately reflected in the weight loss of each group. This may be explained by an increase in total body water. If such were the case, it was not reflected in the serum concentrations of any ion or variable measured in this group of patients 7 to 14 days after operation. The serum osmolality and the red cell intracellular potassium 7 or more days after operation were normal. The continuing and careful work of Kirklin with respect to body compartmental and compositional changes as a result of heart
disease and extracorporeal circulation is pertinent to the data in this study. Measurements of radioactive bromide and mean insulin space have demonstrated an increase of 3.4 and 4.0 L., respectively, in the extracellular fluid space 24 hours after hemodilution perfusion.' These changes persist 2 to 4 weeks after operation as demonstrated by an 8.2 per cent increase in total body water and a 15 per cent increase in intracellular water." A calculation of lean body mass for the perfusion group reported here, based on the formula Jean body weight
=
grams total body potassium 2.46
,
yields values of 41.9 and 38.1 kilograms for the preoperative and postoperative periods, respectively. Normally, total body water is approximately 73 per cent of lean body mass," resulting in a preoperative value of 30.6 L. If this value were increased in the postoperative period by 8.2 per cent, as demonstrated by Pacifico's group," then a 2.5 L. increment in total body water was incurred by operation and perfusion. Thus the discrepancies between the small weight changes in the perfusion group and the large equivalent calculated loss of lean body weight as determined by counting of total body potassium can be explained in large part by an increase of total body water. Another explanation is that, during starvation, the lean body mass is depleted of potassium to a far greater extent initially than of protein. I" This could be partly responsible for the difference in the amount of potassium accountable by weight shifts of 4.9 and 2.0 grams for the thoracotomy and perfusion groups, respectively, and for the difference measured by the total body counting method of 12.8 and 9.5 Gm. in these two groups. Thus the potassium loss can be explained best in terms of a disproportionate loss of intracellular potassium compared to protein in response to trauma and starvation, a small blood volume deficit, and a moderate loss of lean body mass. The changes during perfusion were unexpected. The osmolality of the prime averaged 338 mOsm. and returned to the nor-
Volume 65 Number 1
Hemodilution perfusion re total body potassium
117
January, 1973
mal range within 5 minutes after the onset of perfusion. The serum potassium of the prime was in the low normal range, but on initiation of bypass it decreased from 4.1 to 2.7 mEq. per liter within the first 15 to 30 minutes. In the presence of glucose, insulin, hypothermia, and a high flow (2.5 L. per minute per square meter) and low pressure state characteristic of hemodilution perfusion, potassium must have been lost to an interstitial space not in equilibrium with the perfusion and/or have been driven to the intracellular space. The return toward the preoperative value in the second 30 minutes represents the consequences of rewarming and a gradual return toward equilibrium. The amount of potassium in a hyperosmolar prime apparently does not influence potassium loss in the postoperative period."
Summary The first study of total body potassium measured by a noninvasive whole body 4°K counting method on patients who had thoracotomy or hemodilution perfusion is reported. Fifty-three patients in three groups were studied. Twenty-three healthy control subjects had a mean value for total body potassium of 60.0 ± 2.8 (S.E.) Gm. of potassium per square meter. Eleven patients who had a thoracotomy and 19 patients who had hemodilution perfusion for acquired and congenital heart disease had preoperative total body potassium values of 66.7 ± 3.7 and 62.6 ± 2.8 Gm. of potassium per square meter, respectively. There was no significant difference between groups. Postoperatively, the total body potassium values were 60.9 ± 3.4 (thoracotomy) and 57.8 ± 2.3 (hemodilution perfusion). No difference in loss of potassium between the two groups was found. The net loss for the thoracotomy group was 12.8 Gm. (l0.7 per cent) or 320 mEq. The loss for the hemodilution perfusion group was 9.5 Gm. (9.2 per cent) or 238 mEq. These losses represented 145 and 120 mEq. per square meter for the two groups. Significant metabolic alkalosis occurred in the first 24 hours after operation,
and a hypoosmolar state developed 4 to 7 days postoperatively. No significant changes were found in the erythrocyte intracellular or serum potassium concentrations. This study has demonstrated that hemodilution perfusion does not decrease total body stores of potassium to any greater degree than does thoracotomy alone. The metabolic alkalosis following hemodilution perfusion is best recognized by frequent determinations of the base excess from bloodgas data and measurement of the urine volume and potassium concentrations in the initial postoperative period. REFERENCES 1 Clark, R. E., Beasley, W. E., Sode, J., and Mills, M.: Influence of Hemodilution Perfusion on Total Body Potassium and Intracellular Potassium: Critical Prospective Study, Surg, Forum 20:40, 1969. 2 Moore, F. D., and Ball, M. R.: The Metabolic Response to Surgery, Springfield, III., 1952, Charles C Thomas, Publisher. 3 Moore, F. D., Olesen, K H., McMurrey, 1. D., Parker, H. V., Ball, M. R., and Boyden, C. M.: The Body Cell Mass and Its Supporting Environment: Body Composition in Health and Disease, Philadelphia, 1963, W. B. Saunders Company, p. 523. 4 Neville, W. E., and Tal so, P. 1.: Postperfusion Compartmental Fluid Alterations, Surgery 63: 220, 1968. 5 Krohn, B. G., Urquhart, R. R., Magidson, 0., Tsuji, H. K, Redington, 1. V., and Kay, J. H.: Metabolic Alkalosis Following Heart Surgery, 1. THORAC. CARDIOVASC. SURG. 56: 732, 1968. 6 Breckenridge, I. M., Deverall, P. B., Kirklin, J. W., and Digerness, S. B.: Potassium Intake and Balance After Open Intracardiac Operations, J. THORAC. CARDIOVASC. SURG. 63: 305, 1972. 7 Breckenridge, I. M., Digerness, S. B., and Kirklin, J. W.: Increased Extracellular Fluid After Open Intracardiac Operation, Surg. GynecoI. Obstet. 131: 53, 1970. 8 Pacifico, A. D., Digerness, S. B., and Kirklin, J. W.: Regression of Body Compositional Abnormalities of Heart Failure After Intracardiac Operations, Circulation 42: 999, 1970. 9 Oberhausen, E., and Onstead, C. 0.: Relationship of Potassium Content of Man With Age and Sex, in Radioactivity in Man, Springfield, III., 1965, Charles C Thomas, Publisher, p. 179. 10 Drenick, E. J.: Obesity, Weight Reduction and Body Composition, Ann. Intern. Med. 64: 1148, 1966.