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Nutritional status of patients requiring cardiac surgery
Nutritional status of patients requiring cardiac surgery Nutritional studies were carried out on 47 randomly selected patients undergoing valve replacement. The total-body potassium was measured noninvasively . by use of a whole-body monitor with an accuracy of ±4 percent. This was used as an absolute index of nutritional status of the nonacidotic patient. The metabolic response to operation, as calculated from changes in total-body potassium, was a median loss of 11.1 Gm. or a mean loss of9.8 Gm. of nitrogen per day over 7 postoperative days, compared with a mean loss of 6.8 Gm. of nitrogen per day in the same patients as calculated by conventional nitrogen balance methods. Total-body water measured before operation was not significantly different from the predicted level (p > 0.05), and there was no difference between preoperative total-body water and that measured on the seventh postoperative day (p > 0.07). Twenty-three of the patients exhibited preoperative nutritional depletion (range,S to 30 percent) as assessed by loss of body cell mass from total-body potassium measurements. The well-nourished patients had a median postoperative hospital stay of 17 days (range, II to 25) compared with 27 days (range, 12 to 60) for those who had been nutritionally depleted (p < 0.01). None of the 21 normally nourished patients died. Nine of the 26 nutritionally depleted patients died and this difference is significant (Fisher's exact p = 0.009). In patients with a normal packed cell volume, who are clinically free of edema, there is a highly significant correlation between body cell mass measured by total-body potassium and fat-free mass measured by skinfold calipers (p < 0.01). This allows a better bedside measurement of the degree of preoperative nutritional depletion than derived from unreliable clinical impressions.
R. K. Walesby, M.B., M.Sc., F.R.C.S.,* A. W. Goode, F.R.C.S., M.D.,** T. J. Spinks, B.Sc., A. Herring, B.Sc., M.Sc., A. S. O. Ranicar, M.I.S.T., and H. H. Bentall, M.B., F.R.C.S., London, England
T
here has been a marked decrease in mortality and morbidity rates associated with cardiac surgery during the past decade. This is due in part to improvements in both cardiopulmonary bypass and surgical techniques, together with better management of complications arising from cardiac surgical procedures. It is well recognized that malnutrition is often associated with chronic congestive cardiac failure, I but to date there has been little direct assessment of either the nutritional depletion of patients requiring cardiac surgery or the nutriFrom the Departments of Cardiothoracic Surgery, Surgery, and Medical Physics and the M.R.C. Cyclotron Unit, Hammersmith Hospital and the Royal Postgraduate Medical School, London, England. Received for publication May 3, 1978.
Accepted for publication Oct. 1I, 1978. No reprints available. *Current address: Thoracic Surgical Unit, The Middlesex Hospital, Mortimer St., W.I, England. **Current address: Academic Surgical Unit, St. Mary's Hospital, London W.2, England.
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tional consequences of such surgical procedures. It is well documented that nutritional depletion results in increased morbidity after operation, irrespective of the technical excellence of the procedure," and that patients with an acute weight loss (more than 30 percent of desired weight) are unlikely to survive." Moore and associates" have proposed that body cell mass, the energy-utilizing component of the body, is the most accurate index of nutritional status and that this should be determined from the measurement of the total-body potassium. They used a whole-body monitor, thus allowing a noninvasive assessment of both preoperative nutritional depletion and the metabolic response to cardiac surgery, independent of changes in body weight that may be due to changes in hydration.
Patients and methods We studied 47 randomly selected patients undergoing cardiac surgery with cardiopulmonary bypass. There were 29 men and 18 women in the series and they underwent replacement of the mitral or aortic
0022-5223/79/040570+07$00.70/0 © 1979 The C. V. Mosby Co.
Volume 77
Nutrition in cardiac surgery
Number 4 April, 1979
valve or both. The mean age was 45.7 years (range, 22 to 76 years) and the mean body weight was 59.4 kilograms (range, 46 to 76 kilograms). Assessments were made before operation and on the seventh postoperative day by the following criteria: I. Total-body potassium was measured noninvasively by use of a whole-body counter' with an accuracy of ±4 percent. The method relies on measurement of the gamma emission from naturally radioactive potassium (4°K) present in the body as 0.012 percent of the stable isotopes of potassium 9 K and 4IK). As 98 percent of potassium is in the cells of the body cell mass in the nonacidotic patient, this measurement is an index of the lean tissue mass. The acid-base status of each patient was measured prior to each assessment of total-body potassium. The age, sex, height, and desired weight of the patient were recorded and the total-body potassium for good health was predicted from the regression formulas of Goode and Hawkins": Man: Total-body potassium (mmoles) = (30.84 x W) + (17.85 x H) - (8.14 x A) - 1,402, Woman: Total-body potassium (mmoles) = (23.80 x W) + (18.39 x H) - (1.72 x A) - 1.887, where W = weight in kilograms, H = height in centimeters, and A = age in years. The coefficient of variation for men is 6.9 percent and for women is 8.9 percent. The predicted values were compared with those obtained from the two prediction formulas of Boddy and colleagues," with weight included in the first calculation and excluded in the second. No significant difference in the predicted values of total-body potassium was calculated using the three methods (p > 0.4). The degree of preoperative depletion was calculated from the difference between the predicted and measured preoperative values, and the metabolic response to operation was calculated from the difference between the measured preoperative and postoperative total-body potassium levels. 2. Total-body fat was measured by use of Harpenden skinfold calipers according to the method of Durnin and Womersley. 8 The fat-free mass was calculated by subtraction of the total-body fat from body weight. 3. Total-body water was measured before operation and on the seventh postoperative day in the first 20 patients in our series. Nine of these patients required mitral valve operations, seven needed aortic valve replacement, and four underwent double-valve operations. An oral dose of 250 /LCi of tritiated water (3H 20 ) was administered before operation and 1,250 /LCi was administered after operation. Blood samples were taken within 3 to 6 hours of administration of the first dose
e
57 I
and an intermediate sample was taken prior to administration of the second dose, in order to measure the residual activity. Duplicate plasma samples were counted by liquid scintillation and these values were compared with a standard of known dilution. Counting efficiency corrections were carried out by internal standardization. Agreement in corrected counts between duplicate samples was better than 4 percent. Predicted total-body water was calculated from the formulas of Hume and Weyers." Before the preoperative and seventh day postoperative measurements, body weight was recorded, the patient was examined to exclude edema, the packed-cell volume was determined, and the acid-base status was checked. Over the seven postoperative days, all urine and drainage losses were collected to determine urea nitrogen levels, and from these nitrogen balance. Fecal and skin losses were ignored. The oral calorie and nitrogen intakes were determined. Bypass technique All patients underwent valve replacements using cardiopulmonary bypass, in which either a RyggKyvsgaard or a Harvey bubble oxygenator was used. A Harvey oxygenator was chosen only for use in operations in which the anticipated bypass time would exceed 90 minutes. The pump prime was entirely bloodless, comprising 1,800 C.c. of Hartmann's solution with 20 mmoles of sodium bicarbonate. The patients were perfused at 2.4 L. per square meter per minute, with cooling to 30° C. during perfusion. The mean bypass time was 102 minutes (range, 50 to 180 minutes). The perfusate was supplemented with Hartmann's solution at a volume of approximately 500 c.c. per lf2 hour of bypass time in order to maintain a constant perfusion volume.
Results The distribution of results of the total-body potassium measurements is shown in Fig. I as percentage ratios of predicted values. No patient showed a decreased potassium concentration in the fat-free mass, derived anthropometrically, outside the range of 63.1 ± 3.67 mmoles per I Kg. of fat-free mass for men and 60. I ± 4.9 mmoles per I Kg. of fat-free mass for women, as documented by Goode and Hawkins." Cellular potassium concentration was normal; therefore, the observed depletion was interpreted as a loss of lean tissue and not depletion of cellular potassium concentration. Twenty-one patients had measured values of total-body potassium in excess of the ninety-fifth percentile of that predicted from the formula of Goode
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W
10
Thoracic and Cardiovascular Surgery
n = 47
DEATHS
Boddy ( HI. Age. )
8
6 4 2 0 >-
n = 47
~IO
.... ::::l 0 ....
""u..
I-
z ....
I-
( HI. WI. Age)
Boddy
8
6 4 2 0 n • 47
10
Goode (HI. WI. Age)
8
6 4 2
o
'--.L<.LU-....JULL
-40 -35 -30 -25 -20 -15 -10 -5 +5 +10 +15 +20 +25 +30 PERCENTAGE RATIO OF MEASURED I PREDICTED TOTAL BODY POTASSIUM
Fig. 1. The relationship between fat-free mass calculated from anthropometric measurements and bodycell masscalculated from total-body potassium (r = 0.85; P < 0.01). The 95 percent confidence limits are shown for the line.
• •
70 60
""'"
50
40
:E
.....
..... ....
30
>c
20
n • 47
10
P <0.01
u 0
r • 0.85
."
0 10
20
30
40
50
60
70
80
FAT FREE MASS (Kg)
Fig. 2. The distribution of total-body potassium measurements as a percentage of thosepredicted by the regression equations of Boddy and his associates (height, age, sex, or height, weight, age, sex) and Goode and Hawkins (height, weight, age, sex).
and Hawkins." Twenty-six patients had total-body potassium measurements below the ninety-fifth percentile and we regarded these patients as being relatively potassium deficient and hence nutritionally depleted. The equivalence of the three predictive formulas was tested by assessing the differences between the various patient groups using each formula to see if conclusions were the same. This was the case. Each equation indicated that the mean values of measured/total-body potassium before operation were not significantly different between the groups (0.6 < p < 0.8). The metabolic response to cardiac surgery was measured as the difference between potassium levels preoperatively and on the seventh postoperative day. The loss of body cell mass in kilograms was calculated by the method of Goode and Hawkins," where 82 mmoles of potassium represent I Kg. of muscle tissue and I Gm. of nitrogen is equivalent to 6.25 Gm. of protein or 30 Gm. of muscle tissue. The loss of nitrogen in the patients was nonparametrically distributed, with a positive skew distribution. The median loss of body cell mass, as calculated from the total-body potassium loss and expressed in conventional terms of grams of nitrogen per day, resulted in a negative nitrogen balance of 11.1 Gm. of nitrogen per day (range, 1.34 to 25.1 Gm. per day). This result may also be obtained from the conversion factor of 2.45 mmoles of potassium per I Gm. of nitrogen, as derived in 115 normal subjects at our laboratories. The postoperative nitrogen balance was also calculated using the conventional methods of determining daily nitrogen intake and loss with an allowance of 1.5 Gm. of nitrogen per day for insensible loss in the feces and skin. The mean negative nitrogen balance was 6.8 Gm. of nitrogen each day (range, 2.1 to 7.4 Gm. per day). In the postoperative period, the nutritional requirements of the patients were met almost entirely by oral feeding according to standard clinical practice . Weighed amounts were analyzed for nitrogen and calorie content, and from this, the mean daily intake over the first 7 postoperative days was 3.97 ± 1.76 Gm. of nitrogen per day (range, 1.2 to 6.7 Gm.). The mean daily calorie intake over 7 days was 662 ± 297 (range, 226 to 1,178) kcal. per day. The loss of body cell mass was only partially reflected in the postoperative weight loss. The mean loss of weight was 1.86 ± 3.6 kilograms by the postoperative day 7, whereas the average loss of body cell mass was 2.058 Kg. (9.8 Gm. of nitrogen per day x30 Gm. of protoplasm per 1 Gm. of nitrogen x 7 days = 2.058 Kg. of protoplasm per week). The mean weight loss of the nutritionally normal patients was
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Table I. Measured preoperative and postoperative total-body water levels and predicted preoperative normal total-body water Patient No.
Predicted preop. TRW (L.)
Measured preop. TRW (L.)
Measured/predicted TRW (%)
I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18
29.1 32.6 32.1 37.6 39.5 25.8 28.6 41.8 39.8 37.8 26.0 44.0 35.3 34.8 41.2 28.6 35.1 28.9
29.1 39.7 36.8 35.2 51.2 28.9 33.5 47.0 41.4 45.7 30.3
100 121 116 96 130 112 114 112 104 121 117
40.6 39.3 50.3 39.0 35.1 29.5
115 113 122 135 100 102
19 20
35.1 40.1
39.6
113
*
*
Postop. change in TRW (L.)
28.7 35.3
*
-0.4 -4.4
49.7 47.0 21.5 31.6 53.8 43.5 51.1 27.0 44.4 37.9 38.1 47.8 38.5 34.0 33.4
+14.5 -4.2 -7.4 -1.9 +6.8 +2.1 +5.4 -3.3
28.7 45.7
-10.9
-2.7 -1.2 -2.5 -0.5 -1.1 +3.9
Operations performed AVR + MVR AVR + MVR MVR Open mitral valvotomy AVR MVR MVR AVR AVR + MVR AVR AVR AVR MVR MVR MV repair MV repair MV repair Aortic and mitral valvotomies AVR AVR
Legend: TBW. Total-body water. AYR. Aortic valve replacement. MVR, Mitral valve replacement. MV, Mitral valve.
'Technical error.
2.1 ± 2.9 kilograms by the seventh postoperative day and that of the depleted patients 1.4 ± 1.7 kilograms by the seventh day. This difference is not statistically significant but it is in keeping with the concept that previously depleted patients lose less protoplasm than previously unstressed subjects when subjected to the stress of surgery. 4 The results of the total-body water measurements are shown in Table I. Taken as a group they show a mean preoperative overhydration of 13.6 percent (range, 0 to 35 percent). A chi-square test showed that with regard to total-body water before operation, the predicted distribution did not differ significantly from the observed one. Both a paired t test and a Wilcoxon rank sum test indicate no significant difference between preoperative total-body water and that measured on the seventh postoperati ve day. In three patients there was a technical error in the analysis. These patients were excluded from the statistical analysis. No patient was clinically edematous either before or after operation. The packed-cell volume was within the normal range for each patient. Fig. 2 shows a comparison of the preoperative values, for each patient, of lean body mass derived from total-body potassium measurement and fat-free mass derived anthropometrically using Harpenden skinfold calipers. The agreement between the two
methods of determining body cell mass was highly significant (p < 0.01, r = 0.85). The perfusion data were analyzed according to Student's t test in order to calculate the probability that values for the depleted patients were the same as those of patients requiring loss perfusions. No such postulate was substantiated (p > 0.5). Fourteen patients underwent aortic valve replacement alone, and in this group there were two deaths during the postoperative hospital stay. Twenty-five patients underwent mitral valve operations, of whom seven had mitral valve repairs and two died in the postoperative period. Eighteen patients underwent prosthetic mitral valve replacement; two died in the postoperative hospitalization period. In addition three patients with mitral valve replacements, although they came off bypass, died in the operating room and were shown to have had severe coronary artery disease at postmortem examination. Eight patients had doublevalve operations; five with double-valve replacements, two with aortic valve replacements with an open mitral valvotomy, and one with open aortic and open mitral valvotomies. There were no deaths in this group. Of the six patients who died in low-output cardiac failure in the postoperative period (5 to 30 days), two had had aortic valve replacements, two mitral valve replacements, and two mitral valve repairs. All
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deaths occurred in the nutritionally depleted group of patients, and this striking difference in mortality rate, zero in nondepleted patients and nine out of 23 in depleted patients, is significant (Fisher's exact p = 0.009). Thirty-eight (81 percent) of our patients who had valve replacement left the hospital, and we used the duration of the postoperative hospital stay as an index of morbidity. Since this index is nonparametrically distributed, the data were analyzed according to a Wilcoxon ranked sum test. The mean stay of the 21 nutritionally normal patients was 17 days (range, II to 25) while that of the nutritionally depleted patients was 27 (range, 12 to 60). The difference is significant (p < 0.01). We have recently learned that since the study (June, 1976, to December, 1977) there have been two further late deaths, both in severely depleted patients (88 and 79 percent), at 4 and IO months, respectively. Details of the causes of death are currently unavailable. Discussion Clinically, malnutrition is a common feature in patients requiring cardiac surgery. Although cardiac cachexia is generally associated with end-stage mitral valve disease, in our group of 26 malnourished patients there were 18 with mitral valve disease for whom the operative mortality rate was approximately 39 percent; there were eight patients in the depleted group with aortic valve disease, two of whom died; and there were four who required double-valve replacement, all of whom survived. The overall unit mortality rate for valve replacement was 8 percent during the period of the study, so it is difficult to account for an 18 percent rate in the study group and a 50 percent incidence of quantifiable malnutrition. We feel that the subselection may be biased due to II patients, nine of whom were depleted, who were referred from a distant source in the United Kingdom, who had been given late medical treatment for rheumatic valve disease, and who were prematurely admitted to the hospital for preoperative catheter studies. Twelve patients were non-British Europeans who also had a longer-than-normal preoperative hospitalization period. They were more accessible for a study for a longer period before operation, allowing whole-body counts, so the series represented an atypical sample. The degree of malnutrition associated with cardiac valve disease has been difficult to quantitate, as the normal criteria of change in body weight or measurement of skinfold thickness may be unreliable because of an unknown degree of fluid retention. Moore and
Thoracic and Cardiovascular Surgery
colleagues" have documented that loss of body cell mass, clinically seen as muscle wasting, is associated with a decreased ability to utilize energy and support vital body functions. Total-body potassium measured noninvasively with a whole-body monitor has been used as an absolute index of the body cell mass. Some of the patients had been treated with diuretics preoperatively, but a recent study by Davidson and his co-workers 10 has shown that long-term diuretic therapy is not associated with a depletion of potassium concentration in the body cell mass. Similarly, Goode, Hawkins, and Feggetter" have shown that in the immediate postoperative period furosemide therapy is also unassociated with a reduction of total-body potassium in the body cell mass. A reduction in the amount of potassium in the body cell mass without a proportional loss of nitrogen could be accounted for by the loss of muscle and liver glycogen, by oxidative deamination of amino acids, which is inversely related to liver glycogen content and is an immediately available source of energy. Therefore, as glycogen reserves fall, amino acids are utilized to provide carbohydrate intermediates. Dale and associates" have shown that after major surgery, plasma amino acids return to preoperative levels by 96 hours, and thus by the seventh postoperative day glycogen depletion is minimal. In this randomly selected population undergoing valve operations, 26 of the 47 patients showed a significant degree of preoperative nutritional depletion, and these patients were identified as the high-risk group in terms of increased deaths, prolonged convalescence, and associated postoperative morbidity as characterized by delayed wound healing, sternal disintegration, and general debility. As the other possible causes of prolonged hospital stay, such as adverse surgical technical factors or postoperative infection, were not present in this series, it is probable that the principal factor delaying full recovery was the patient's poor nutritional state. Difficulties in the determination of all nitrogen losses in human excreta, where collections of all losses from skin, urine, and feces are invariably incomplete, have made conventional nitrogen balance studies difficult to interpret as the errors are unknown. The whole-body counter method for calculating changes in body nitrogen depends ( I) on the assumption that nitrogen and potassium are lost postoperatively in the same ratio as they exist in protoplasm and (2) on the accuracy of the conversion factor of 2.45 mmoles of potassium per I Gm. of nitrogen. We are of the opinion that errors in the whole-body counter technique are less than those encountered in nitrogen balance procedures.
Volume 77 Number 4 April,1979
Manners 13 has quantitated the metabolic response to cardiac operations by determining the daily nitrogen balance by this standard method of measuring daily nitrogen intake and output. He found that the mean negative nitrogen balance over 8 postoperative days was 6.7 Gm. per day, but felt that this may be an underestimate owing to possible incomplete collections. Using the same method, we found the mean daily negative nitrogen balance to be 6.8 Gm. However, when nitrogen balance was calculated from the potassium loss in the postoperative period, as determined by the 4°K method in which no errors of collection are involved, using the factor 2.45 mmoles of potassium per I Gm. of nitrogen, the mean negative balance was 9.8 Gm. of nitrogen per day and the median daily negative nitrogen balance was 11.1 Gm. However, this could be as high as 25.1 Gm. of nitrogen per day without evidence of sepsis yet still be compatible with survival. These results confirm Manners' view that conventional nitrogen balance studies underestimate the severity of the operative procedures. The patients in Manners' series had low oral dietary intake in the postoperative period, including about 4.7 Gm. of nitrogen per day and 12. I kcal. per kilogram of body weight per day, well below the recommended intake of 40 kcal. per kilogram of body weight per day. Similarly, all of our patients were unable to achieve an adequate oral intake in the postoperative period. Abel and colleagues;'! in a retrospective randomized evaluation of early postoperative parenteral nutrition, were unable to demonstrate any improvement in the parenterally fed group. However, it is our opinion that they failed to provide adequate calorie and nitrogen to achieve a positive effect. The over-all intake in our series was shown to be deficient in terms of both nitrogen and calories despite the apparent well-being of the patient. The calorie/nitrogen ratio of 170: I was inappropriate for the immediate postoperative period and did not reach that proposed by Johnston and his co-workers" which was 200: I, providing 14 Gm. of nitrogen with 2,800 calories. Our results were obtained by methods that did not vary from standard postoperative management. Preoperative identification of protein-depleted patients is desirable. If such a patient can be identified then, if at all possible, operation should be delayed until some degree of protein repletion can be accomplished by supplying sufficient calories and protein over a period of time. Poor appetite and debility may interfere with nutritional repletion and operation may have to be undertaken with the patient in a depleted condition. Once the surgical procedure is performed all patients should ideally receive calories and protein in
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amounts that will minimize losses of protoplasm. These amounts of calories and protein should approximate those required by a healthy individual of the same size and age. A more strenuous effort should be made to achieve nutritional goals for the patient identified as being malnourished preoperatively. The postoperative delivery of large amounts of protein and calories by oral and possibly parenteral routes should be done carefully to avoid fluid overload, and the advantages of maintaining a better state of nutrition would have to be weighed against the risks. One can only speculate on what the optimum level of calorie and protein administration will prove to be. Previous reports of change in hydration associated with cardiopulmonary bypass are confined to those techniques in which blood primes are used. None of our patients had preoperative clinical signs of overhydration, suggesting satisfactory medical therapy. However, the mean overhydration was 13.6 percent for the group although there was no significant difference between observed and predicted total-body water levels. We found no relation between the preoperative nutritional status and the degree of hydration. There was no significant difference for the whole group between total-body water measured preoperatively and that measured on the seventh postoperative day, a finding similar to that of Pacifico, Digemess, and Kirklin!" who found a transient 7 percent increase in extracellular fluid by the fourth postoperative day. From our results we would expect the average patient with a negative nitrogen balance of II. I Gm. per day to lose from muscle alone at least 0.3 kilogram of body weight daily over a 7 day period. A constant body weight in this period can, therefore, only represent fluid retention, while a decrease can only be interpreted in conjunction with the anticipated muscle losses. In general, those patients who ate earliest in the postoperative period lost the least amounts of potassium and nitrogen. In our patients, the duration of perfusion was related only to the type of valve replacement. It was not prolonged either in those patients who were in a nutritionally depleted state before operation or in those with measured overhydration. The determination of preoperative nutritional status using a total-body potassium method is an excellent indicator of high-risk patients. When no other factor was involved, those patients shown to be nutritionally depleted had a significantly greater degree of postoperative morbidity as measured by duration of hospitalization than those who were well nourished before operation. These results agree with the findings of
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Blackburn and associates." who, in a similar series of patients, identified preoperative nutritional depletion by measuring triceps skinfold thickness, arm muscle circumference, and cell-mediated immunity. In our series, there was an excellent correlation between body cell mass measured by total-body potassium and fatfree mass determined by use of Harpenden skinfold calipers. We want to stress that the clinical impression of the patient's nutritional status was frequently erroneous, but we feel that this method is highly sensitive in the selection of patients at higher than normal risk for death and morbidity following cardiac operations. A simple bedside method to identify patients who may have lost body cell mass is by measurement of the fat-free mass using skinfold calipers according to the method of Durnin and Wornersley." In patients who have a normal packed-cell volume and who are clinically free of edema, this is a reasonable approximation of the body cell mass measured from total-body potassium. Multiplication of the kilograms of fat-free mass by 63 for men and 60 for women will give an approximate total-body potassium content. This compared with a prediction of health status derived from the formulas of Goode and Hawkins" will allow quantitation of the approximate loss of body cell mass and will indicate which patients may require further investigation and preoperative nutritional repletion. It is probable that patients with valvular cardiac disease become nutritionally depleted with time as a consequence of their disease. By adopting the routine use of skinfold calipers in institutions in which whole-body counting is not possible, the patient's course may be followed throughout life and operation may be performed electively while he is still in the low-risk group. This does not detract from current routine and specialized clinical markers for the disease processes but adds an extra parameter to a sometimes difficult clinical decision regarding the timing of elective operations. We are most grateful to Professor D. G. Melrose for his advice and help in the preparation of this paper and for the technical advice of Miss R. Arnot of the Department of Medical Physics, Hammersmith Hospital. REFERENCES Pittman JA, Cohen P: The pathogenesis of cardiac cachexia. N Engl J Med 288:695, 1964
Thoracic and Cardiovascular Surgery
2 Rhoads JE, Fliegelman MT, Panzer LM: The mechanisms of delayed wound healing in the presence of hypoproteinaemia. JAMA 118:21, 1942 3 Lee HA: Intravenous nutrition. Ann R CoIl Surg Engl 56: 59, 1975 4 Moore FD, Olsen KO, McMurray JD, Parker HV, Ball MR, Boyden LM: The Body Cell Mass and Its Supporting Environments, Philadelphia, 1963, W. B. Saunders Company 5 Spinks TI, Bewley DK, Ranicar ASO, Joplin GF: Measurement of total body calcium in bone disease. J Radioanal Chern 37:345, 1977 6 Goode AW, Hawkins T: Use of 4°K counting and its relationship to other estimates of lean body mass, Advances in Parenteral Nutrition. An International Symposium, 1977, IDA Johnston, ed, Lancaster, England, 1978, M.T.P. Press 7 Boddy K, King PC, Hume R, Wyers E: The relation of total body potassium to height, weight and age in normal adults. J Clin Pathol 25:512, 1972 8 Durnin JVGA, Womersley J: Body fat assessed from total body density and its estimation from skinfold thickness. Measurements on 481 men and women aged 16 to 72 years. Br J Nutr 32:77, 1974 9 Hume R, Weyers E: Relationship between total body water and surface area in normal and obese subjects. J Clin Pathol 24:234, 1971 10 Davidson C, Burkinshaw L, McLachlan MSF, Morgan DB: Effect of long term diuretic treatment on body potassium in heart disease. Lancet 2: 1044, 1976 II Goode A, Hawkins T, Feggetter JGW: The effect of furosemide used for post prostatectomy irrigation on total body potassium. Br J Urol 49: 143, 1977 12 Dale G, Young G, Latner AL, Goode A, Tweedle D, Johnson IDA: The effect of surgical operation on venous plasma free amino acids. Surgery 81:295, 1977 13 Manners JM: Nutrition after cardiac surgery. Anaesthesia 29:675, 1974 14 Abel RM, Fischer JE, Buckley MJ, Barnett GO, Austen WG: Malnutrition in cardiac surgical patients. Arch Surg 111:45, 1976 15 Johnston IDA, Marino JD, Stevens JZ: The effects of intravenous feeding on the balance of nitrogen, sodium, and potassium after operation. Br J Surg 53:885, 1966 16 Pacifico AD, Digerness S, Kirklin JW: Alterations of body composition after open intracardiac operations. Circulation 41:331, 1970 17 Blackburn GL, Gibbons GW, Bothe A, Benotti PN, Harken DE, McEnany TM: Nutritional support in cardiac cachexia. J THORAC CARDIOVASC SURG 73:4, 1977
R. K. Walesby, M.B., M.Sc., F.R.C.S.,* A. W. Goode, F.R.C.S., M.D.,** T. J. Spinks, B.Sc., A. Herring, B.Sc., M.Sc., A. S. O. Ranicar, M.I.S.T., and H. H. Bentall, M.B., F.R.C.S., London, England
T
here has been a marked decrease in mortality and morbidity rates associated with cardiac surgery during the past decade. This is due in part to improvements in both cardiopulmonary bypass and surgical techniques, together with better management of complications arising from cardiac surgical procedures. It is well recognized that malnutrition is often associated with chronic congestive cardiac failure, I but to date there has been little direct assessment of either the nutritional depletion of patients requiring cardiac surgery or the nutriFrom the Departments of Cardiothoracic Surgery, Surgery, and Medical Physics and the M.R.C. Cyclotron Unit, Hammersmith Hospital and the Royal Postgraduate Medical School, London, England. Received for publication May 3, 1978.
Accepted for publication Oct. 1I, 1978. No reprints available. *Current address: Thoracic Surgical Unit, The Middlesex Hospital, Mortimer St., W.I, England. **Current address: Academic Surgical Unit, St. Mary's Hospital, London W.2, England.
570
tional consequences of such surgical procedures. It is well documented that nutritional depletion results in increased morbidity after operation, irrespective of the technical excellence of the procedure," and that patients with an acute weight loss (more than 30 percent of desired weight) are unlikely to survive." Moore and associates" have proposed that body cell mass, the energy-utilizing component of the body, is the most accurate index of nutritional status and that this should be determined from the measurement of the total-body potassium. They used a whole-body monitor, thus allowing a noninvasive assessment of both preoperative nutritional depletion and the metabolic response to cardiac surgery, independent of changes in body weight that may be due to changes in hydration.
Patients and methods We studied 47 randomly selected patients undergoing cardiac surgery with cardiopulmonary bypass. There were 29 men and 18 women in the series and they underwent replacement of the mitral or aortic
0022-5223/79/040570+07$00.70/0 © 1979 The C. V. Mosby Co.
Volume 77
Nutrition in cardiac surgery
Number 4 April, 1979
valve or both. The mean age was 45.7 years (range, 22 to 76 years) and the mean body weight was 59.4 kilograms (range, 46 to 76 kilograms). Assessments were made before operation and on the seventh postoperative day by the following criteria: I. Total-body potassium was measured noninvasively by use of a whole-body counter' with an accuracy of ±4 percent. The method relies on measurement of the gamma emission from naturally radioactive potassium (4°K) present in the body as 0.012 percent of the stable isotopes of potassium 9 K and 4IK). As 98 percent of potassium is in the cells of the body cell mass in the nonacidotic patient, this measurement is an index of the lean tissue mass. The acid-base status of each patient was measured prior to each assessment of total-body potassium. The age, sex, height, and desired weight of the patient were recorded and the total-body potassium for good health was predicted from the regression formulas of Goode and Hawkins": Man: Total-body potassium (mmoles) = (30.84 x W) + (17.85 x H) - (8.14 x A) - 1,402, Woman: Total-body potassium (mmoles) = (23.80 x W) + (18.39 x H) - (1.72 x A) - 1.887, where W = weight in kilograms, H = height in centimeters, and A = age in years. The coefficient of variation for men is 6.9 percent and for women is 8.9 percent. The predicted values were compared with those obtained from the two prediction formulas of Boddy and colleagues," with weight included in the first calculation and excluded in the second. No significant difference in the predicted values of total-body potassium was calculated using the three methods (p > 0.4). The degree of preoperative depletion was calculated from the difference between the predicted and measured preoperative values, and the metabolic response to operation was calculated from the difference between the measured preoperative and postoperative total-body potassium levels. 2. Total-body fat was measured by use of Harpenden skinfold calipers according to the method of Durnin and Womersley. 8 The fat-free mass was calculated by subtraction of the total-body fat from body weight. 3. Total-body water was measured before operation and on the seventh postoperative day in the first 20 patients in our series. Nine of these patients required mitral valve operations, seven needed aortic valve replacement, and four underwent double-valve operations. An oral dose of 250 /LCi of tritiated water (3H 20 ) was administered before operation and 1,250 /LCi was administered after operation. Blood samples were taken within 3 to 6 hours of administration of the first dose
e
57 I
and an intermediate sample was taken prior to administration of the second dose, in order to measure the residual activity. Duplicate plasma samples were counted by liquid scintillation and these values were compared with a standard of known dilution. Counting efficiency corrections were carried out by internal standardization. Agreement in corrected counts between duplicate samples was better than 4 percent. Predicted total-body water was calculated from the formulas of Hume and Weyers." Before the preoperative and seventh day postoperative measurements, body weight was recorded, the patient was examined to exclude edema, the packed-cell volume was determined, and the acid-base status was checked. Over the seven postoperative days, all urine and drainage losses were collected to determine urea nitrogen levels, and from these nitrogen balance. Fecal and skin losses were ignored. The oral calorie and nitrogen intakes were determined. Bypass technique All patients underwent valve replacements using cardiopulmonary bypass, in which either a RyggKyvsgaard or a Harvey bubble oxygenator was used. A Harvey oxygenator was chosen only for use in operations in which the anticipated bypass time would exceed 90 minutes. The pump prime was entirely bloodless, comprising 1,800 C.c. of Hartmann's solution with 20 mmoles of sodium bicarbonate. The patients were perfused at 2.4 L. per square meter per minute, with cooling to 30° C. during perfusion. The mean bypass time was 102 minutes (range, 50 to 180 minutes). The perfusate was supplemented with Hartmann's solution at a volume of approximately 500 c.c. per lf2 hour of bypass time in order to maintain a constant perfusion volume.
Results The distribution of results of the total-body potassium measurements is shown in Fig. I as percentage ratios of predicted values. No patient showed a decreased potassium concentration in the fat-free mass, derived anthropometrically, outside the range of 63.1 ± 3.67 mmoles per I Kg. of fat-free mass for men and 60. I ± 4.9 mmoles per I Kg. of fat-free mass for women, as documented by Goode and Hawkins." Cellular potassium concentration was normal; therefore, the observed depletion was interpreted as a loss of lean tissue and not depletion of cellular potassium concentration. Twenty-one patients had measured values of total-body potassium in excess of the ninety-fifth percentile of that predicted from the formula of Goode
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572 Walesby et al.
W
10
Thoracic and Cardiovascular Surgery
n = 47
DEATHS
Boddy ( HI. Age. )
8
6 4 2 0 >-
n = 47
~IO
.... ::::l 0 ....
""u..
I-
z ....
I-
( HI. WI. Age)
Boddy
8
6 4 2 0 n • 47
10
Goode (HI. WI. Age)
8
6 4 2
o
'--.L<.LU-....JULL
-40 -35 -30 -25 -20 -15 -10 -5 +5 +10 +15 +20 +25 +30 PERCENTAGE RATIO OF MEASURED I PREDICTED TOTAL BODY POTASSIUM
Fig. 1. The relationship between fat-free mass calculated from anthropometric measurements and bodycell masscalculated from total-body potassium (r = 0.85; P < 0.01). The 95 percent confidence limits are shown for the line.
• •
70 60
""'"
50
40
:E
.....
..... ....
30
>c
20
n • 47
10
P <0.01
u 0
r • 0.85
."
0 10
20
30
40
50
60
70
80
FAT FREE MASS (Kg)
Fig. 2. The distribution of total-body potassium measurements as a percentage of thosepredicted by the regression equations of Boddy and his associates (height, age, sex, or height, weight, age, sex) and Goode and Hawkins (height, weight, age, sex).
and Hawkins." Twenty-six patients had total-body potassium measurements below the ninety-fifth percentile and we regarded these patients as being relatively potassium deficient and hence nutritionally depleted. The equivalence of the three predictive formulas was tested by assessing the differences between the various patient groups using each formula to see if conclusions were the same. This was the case. Each equation indicated that the mean values of measured/total-body potassium before operation were not significantly different between the groups (0.6 < p < 0.8). The metabolic response to cardiac surgery was measured as the difference between potassium levels preoperatively and on the seventh postoperative day. The loss of body cell mass in kilograms was calculated by the method of Goode and Hawkins," where 82 mmoles of potassium represent I Kg. of muscle tissue and I Gm. of nitrogen is equivalent to 6.25 Gm. of protein or 30 Gm. of muscle tissue. The loss of nitrogen in the patients was nonparametrically distributed, with a positive skew distribution. The median loss of body cell mass, as calculated from the total-body potassium loss and expressed in conventional terms of grams of nitrogen per day, resulted in a negative nitrogen balance of 11.1 Gm. of nitrogen per day (range, 1.34 to 25.1 Gm. per day). This result may also be obtained from the conversion factor of 2.45 mmoles of potassium per I Gm. of nitrogen, as derived in 115 normal subjects at our laboratories. The postoperative nitrogen balance was also calculated using the conventional methods of determining daily nitrogen intake and loss with an allowance of 1.5 Gm. of nitrogen per day for insensible loss in the feces and skin. The mean negative nitrogen balance was 6.8 Gm. of nitrogen each day (range, 2.1 to 7.4 Gm. per day). In the postoperative period, the nutritional requirements of the patients were met almost entirely by oral feeding according to standard clinical practice . Weighed amounts were analyzed for nitrogen and calorie content, and from this, the mean daily intake over the first 7 postoperative days was 3.97 ± 1.76 Gm. of nitrogen per day (range, 1.2 to 6.7 Gm.). The mean daily calorie intake over 7 days was 662 ± 297 (range, 226 to 1,178) kcal. per day. The loss of body cell mass was only partially reflected in the postoperative weight loss. The mean loss of weight was 1.86 ± 3.6 kilograms by the postoperative day 7, whereas the average loss of body cell mass was 2.058 Kg. (9.8 Gm. of nitrogen per day x30 Gm. of protoplasm per 1 Gm. of nitrogen x 7 days = 2.058 Kg. of protoplasm per week). The mean weight loss of the nutritionally normal patients was
Volume 77
Nutrition in cardiac surgery
Number 4
573
April. 1979
Table I. Measured preoperative and postoperative total-body water levels and predicted preoperative normal total-body water Patient No.
Predicted preop. TRW (L.)
Measured preop. TRW (L.)
Measured/predicted TRW (%)
I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18
29.1 32.6 32.1 37.6 39.5 25.8 28.6 41.8 39.8 37.8 26.0 44.0 35.3 34.8 41.2 28.6 35.1 28.9
29.1 39.7 36.8 35.2 51.2 28.9 33.5 47.0 41.4 45.7 30.3
100 121 116 96 130 112 114 112 104 121 117
40.6 39.3 50.3 39.0 35.1 29.5
115 113 122 135 100 102
19 20
35.1 40.1
39.6
113
*
*
Postop. change in TRW (L.)
28.7 35.3
*
-0.4 -4.4
49.7 47.0 21.5 31.6 53.8 43.5 51.1 27.0 44.4 37.9 38.1 47.8 38.5 34.0 33.4
+14.5 -4.2 -7.4 -1.9 +6.8 +2.1 +5.4 -3.3
28.7 45.7
-10.9
-2.7 -1.2 -2.5 -0.5 -1.1 +3.9
Operations performed AVR + MVR AVR + MVR MVR Open mitral valvotomy AVR MVR MVR AVR AVR + MVR AVR AVR AVR MVR MVR MV repair MV repair MV repair Aortic and mitral valvotomies AVR AVR
Legend: TBW. Total-body water. AYR. Aortic valve replacement. MVR, Mitral valve replacement. MV, Mitral valve.
'Technical error.
2.1 ± 2.9 kilograms by the seventh postoperative day and that of the depleted patients 1.4 ± 1.7 kilograms by the seventh day. This difference is not statistically significant but it is in keeping with the concept that previously depleted patients lose less protoplasm than previously unstressed subjects when subjected to the stress of surgery. 4 The results of the total-body water measurements are shown in Table I. Taken as a group they show a mean preoperative overhydration of 13.6 percent (range, 0 to 35 percent). A chi-square test showed that with regard to total-body water before operation, the predicted distribution did not differ significantly from the observed one. Both a paired t test and a Wilcoxon rank sum test indicate no significant difference between preoperative total-body water and that measured on the seventh postoperati ve day. In three patients there was a technical error in the analysis. These patients were excluded from the statistical analysis. No patient was clinically edematous either before or after operation. The packed-cell volume was within the normal range for each patient. Fig. 2 shows a comparison of the preoperative values, for each patient, of lean body mass derived from total-body potassium measurement and fat-free mass derived anthropometrically using Harpenden skinfold calipers. The agreement between the two
methods of determining body cell mass was highly significant (p < 0.01, r = 0.85). The perfusion data were analyzed according to Student's t test in order to calculate the probability that values for the depleted patients were the same as those of patients requiring loss perfusions. No such postulate was substantiated (p > 0.5). Fourteen patients underwent aortic valve replacement alone, and in this group there were two deaths during the postoperative hospital stay. Twenty-five patients underwent mitral valve operations, of whom seven had mitral valve repairs and two died in the postoperative period. Eighteen patients underwent prosthetic mitral valve replacement; two died in the postoperative hospitalization period. In addition three patients with mitral valve replacements, although they came off bypass, died in the operating room and were shown to have had severe coronary artery disease at postmortem examination. Eight patients had doublevalve operations; five with double-valve replacements, two with aortic valve replacements with an open mitral valvotomy, and one with open aortic and open mitral valvotomies. There were no deaths in this group. Of the six patients who died in low-output cardiac failure in the postoperative period (5 to 30 days), two had had aortic valve replacements, two mitral valve replacements, and two mitral valve repairs. All
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deaths occurred in the nutritionally depleted group of patients, and this striking difference in mortality rate, zero in nondepleted patients and nine out of 23 in depleted patients, is significant (Fisher's exact p = 0.009). Thirty-eight (81 percent) of our patients who had valve replacement left the hospital, and we used the duration of the postoperative hospital stay as an index of morbidity. Since this index is nonparametrically distributed, the data were analyzed according to a Wilcoxon ranked sum test. The mean stay of the 21 nutritionally normal patients was 17 days (range, II to 25) while that of the nutritionally depleted patients was 27 (range, 12 to 60). The difference is significant (p < 0.01). We have recently learned that since the study (June, 1976, to December, 1977) there have been two further late deaths, both in severely depleted patients (88 and 79 percent), at 4 and IO months, respectively. Details of the causes of death are currently unavailable. Discussion Clinically, malnutrition is a common feature in patients requiring cardiac surgery. Although cardiac cachexia is generally associated with end-stage mitral valve disease, in our group of 26 malnourished patients there were 18 with mitral valve disease for whom the operative mortality rate was approximately 39 percent; there were eight patients in the depleted group with aortic valve disease, two of whom died; and there were four who required double-valve replacement, all of whom survived. The overall unit mortality rate for valve replacement was 8 percent during the period of the study, so it is difficult to account for an 18 percent rate in the study group and a 50 percent incidence of quantifiable malnutrition. We feel that the subselection may be biased due to II patients, nine of whom were depleted, who were referred from a distant source in the United Kingdom, who had been given late medical treatment for rheumatic valve disease, and who were prematurely admitted to the hospital for preoperative catheter studies. Twelve patients were non-British Europeans who also had a longer-than-normal preoperative hospitalization period. They were more accessible for a study for a longer period before operation, allowing whole-body counts, so the series represented an atypical sample. The degree of malnutrition associated with cardiac valve disease has been difficult to quantitate, as the normal criteria of change in body weight or measurement of skinfold thickness may be unreliable because of an unknown degree of fluid retention. Moore and
Thoracic and Cardiovascular Surgery
colleagues" have documented that loss of body cell mass, clinically seen as muscle wasting, is associated with a decreased ability to utilize energy and support vital body functions. Total-body potassium measured noninvasively with a whole-body monitor has been used as an absolute index of the body cell mass. Some of the patients had been treated with diuretics preoperatively, but a recent study by Davidson and his co-workers 10 has shown that long-term diuretic therapy is not associated with a depletion of potassium concentration in the body cell mass. Similarly, Goode, Hawkins, and Feggetter" have shown that in the immediate postoperative period furosemide therapy is also unassociated with a reduction of total-body potassium in the body cell mass. A reduction in the amount of potassium in the body cell mass without a proportional loss of nitrogen could be accounted for by the loss of muscle and liver glycogen, by oxidative deamination of amino acids, which is inversely related to liver glycogen content and is an immediately available source of energy. Therefore, as glycogen reserves fall, amino acids are utilized to provide carbohydrate intermediates. Dale and associates" have shown that after major surgery, plasma amino acids return to preoperative levels by 96 hours, and thus by the seventh postoperative day glycogen depletion is minimal. In this randomly selected population undergoing valve operations, 26 of the 47 patients showed a significant degree of preoperative nutritional depletion, and these patients were identified as the high-risk group in terms of increased deaths, prolonged convalescence, and associated postoperative morbidity as characterized by delayed wound healing, sternal disintegration, and general debility. As the other possible causes of prolonged hospital stay, such as adverse surgical technical factors or postoperative infection, were not present in this series, it is probable that the principal factor delaying full recovery was the patient's poor nutritional state. Difficulties in the determination of all nitrogen losses in human excreta, where collections of all losses from skin, urine, and feces are invariably incomplete, have made conventional nitrogen balance studies difficult to interpret as the errors are unknown. The whole-body counter method for calculating changes in body nitrogen depends ( I) on the assumption that nitrogen and potassium are lost postoperatively in the same ratio as they exist in protoplasm and (2) on the accuracy of the conversion factor of 2.45 mmoles of potassium per I Gm. of nitrogen. We are of the opinion that errors in the whole-body counter technique are less than those encountered in nitrogen balance procedures.
Volume 77 Number 4 April,1979
Manners 13 has quantitated the metabolic response to cardiac operations by determining the daily nitrogen balance by this standard method of measuring daily nitrogen intake and output. He found that the mean negative nitrogen balance over 8 postoperative days was 6.7 Gm. per day, but felt that this may be an underestimate owing to possible incomplete collections. Using the same method, we found the mean daily negative nitrogen balance to be 6.8 Gm. However, when nitrogen balance was calculated from the potassium loss in the postoperative period, as determined by the 4°K method in which no errors of collection are involved, using the factor 2.45 mmoles of potassium per I Gm. of nitrogen, the mean negative balance was 9.8 Gm. of nitrogen per day and the median daily negative nitrogen balance was 11.1 Gm. However, this could be as high as 25.1 Gm. of nitrogen per day without evidence of sepsis yet still be compatible with survival. These results confirm Manners' view that conventional nitrogen balance studies underestimate the severity of the operative procedures. The patients in Manners' series had low oral dietary intake in the postoperative period, including about 4.7 Gm. of nitrogen per day and 12. I kcal. per kilogram of body weight per day, well below the recommended intake of 40 kcal. per kilogram of body weight per day. Similarly, all of our patients were unable to achieve an adequate oral intake in the postoperative period. Abel and colleagues;'! in a retrospective randomized evaluation of early postoperative parenteral nutrition, were unable to demonstrate any improvement in the parenterally fed group. However, it is our opinion that they failed to provide adequate calorie and nitrogen to achieve a positive effect. The over-all intake in our series was shown to be deficient in terms of both nitrogen and calories despite the apparent well-being of the patient. The calorie/nitrogen ratio of 170: I was inappropriate for the immediate postoperative period and did not reach that proposed by Johnston and his co-workers" which was 200: I, providing 14 Gm. of nitrogen with 2,800 calories. Our results were obtained by methods that did not vary from standard postoperative management. Preoperative identification of protein-depleted patients is desirable. If such a patient can be identified then, if at all possible, operation should be delayed until some degree of protein repletion can be accomplished by supplying sufficient calories and protein over a period of time. Poor appetite and debility may interfere with nutritional repletion and operation may have to be undertaken with the patient in a depleted condition. Once the surgical procedure is performed all patients should ideally receive calories and protein in
Nutrition in cardiac surgery
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amounts that will minimize losses of protoplasm. These amounts of calories and protein should approximate those required by a healthy individual of the same size and age. A more strenuous effort should be made to achieve nutritional goals for the patient identified as being malnourished preoperatively. The postoperative delivery of large amounts of protein and calories by oral and possibly parenteral routes should be done carefully to avoid fluid overload, and the advantages of maintaining a better state of nutrition would have to be weighed against the risks. One can only speculate on what the optimum level of calorie and protein administration will prove to be. Previous reports of change in hydration associated with cardiopulmonary bypass are confined to those techniques in which blood primes are used. None of our patients had preoperative clinical signs of overhydration, suggesting satisfactory medical therapy. However, the mean overhydration was 13.6 percent for the group although there was no significant difference between observed and predicted total-body water levels. We found no relation between the preoperative nutritional status and the degree of hydration. There was no significant difference for the whole group between total-body water measured preoperatively and that measured on the seventh postoperative day, a finding similar to that of Pacifico, Digemess, and Kirklin!" who found a transient 7 percent increase in extracellular fluid by the fourth postoperative day. From our results we would expect the average patient with a negative nitrogen balance of II. I Gm. per day to lose from muscle alone at least 0.3 kilogram of body weight daily over a 7 day period. A constant body weight in this period can, therefore, only represent fluid retention, while a decrease can only be interpreted in conjunction with the anticipated muscle losses. In general, those patients who ate earliest in the postoperative period lost the least amounts of potassium and nitrogen. In our patients, the duration of perfusion was related only to the type of valve replacement. It was not prolonged either in those patients who were in a nutritionally depleted state before operation or in those with measured overhydration. The determination of preoperative nutritional status using a total-body potassium method is an excellent indicator of high-risk patients. When no other factor was involved, those patients shown to be nutritionally depleted had a significantly greater degree of postoperative morbidity as measured by duration of hospitalization than those who were well nourished before operation. These results agree with the findings of
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Blackburn and associates." who, in a similar series of patients, identified preoperative nutritional depletion by measuring triceps skinfold thickness, arm muscle circumference, and cell-mediated immunity. In our series, there was an excellent correlation between body cell mass measured by total-body potassium and fatfree mass determined by use of Harpenden skinfold calipers. We want to stress that the clinical impression of the patient's nutritional status was frequently erroneous, but we feel that this method is highly sensitive in the selection of patients at higher than normal risk for death and morbidity following cardiac operations. A simple bedside method to identify patients who may have lost body cell mass is by measurement of the fat-free mass using skinfold calipers according to the method of Durnin and Wornersley." In patients who have a normal packed-cell volume and who are clinically free of edema, this is a reasonable approximation of the body cell mass measured from total-body potassium. Multiplication of the kilograms of fat-free mass by 63 for men and 60 for women will give an approximate total-body potassium content. This compared with a prediction of health status derived from the formulas of Goode and Hawkins" will allow quantitation of the approximate loss of body cell mass and will indicate which patients may require further investigation and preoperative nutritional repletion. It is probable that patients with valvular cardiac disease become nutritionally depleted with time as a consequence of their disease. By adopting the routine use of skinfold calipers in institutions in which whole-body counting is not possible, the patient's course may be followed throughout life and operation may be performed electively while he is still in the low-risk group. This does not detract from current routine and specialized clinical markers for the disease processes but adds an extra parameter to a sometimes difficult clinical decision regarding the timing of elective operations. We are most grateful to Professor D. G. Melrose for his advice and help in the preparation of this paper and for the technical advice of Miss R. Arnot of the Department of Medical Physics, Hammersmith Hospital. REFERENCES Pittman JA, Cohen P: The pathogenesis of cardiac cachexia. N Engl J Med 288:695, 1964
Thoracic and Cardiovascular Surgery
2 Rhoads JE, Fliegelman MT, Panzer LM: The mechanisms of delayed wound healing in the presence of hypoproteinaemia. JAMA 118:21, 1942 3 Lee HA: Intravenous nutrition. Ann R CoIl Surg Engl 56: 59, 1975 4 Moore FD, Olsen KO, McMurray JD, Parker HV, Ball MR, Boyden LM: The Body Cell Mass and Its Supporting Environments, Philadelphia, 1963, W. B. Saunders Company 5 Spinks TI, Bewley DK, Ranicar ASO, Joplin GF: Measurement of total body calcium in bone disease. J Radioanal Chern 37:345, 1977 6 Goode AW, Hawkins T: Use of 4°K counting and its relationship to other estimates of lean body mass, Advances in Parenteral Nutrition. An International Symposium, 1977, IDA Johnston, ed, Lancaster, England, 1978, M.T.P. Press 7 Boddy K, King PC, Hume R, Wyers E: The relation of total body potassium to height, weight and age in normal adults. J Clin Pathol 25:512, 1972 8 Durnin JVGA, Womersley J: Body fat assessed from total body density and its estimation from skinfold thickness. Measurements on 481 men and women aged 16 to 72 years. Br J Nutr 32:77, 1974 9 Hume R, Weyers E: Relationship between total body water and surface area in normal and obese subjects. J Clin Pathol 24:234, 1971 10 Davidson C, Burkinshaw L, McLachlan MSF, Morgan DB: Effect of long term diuretic treatment on body potassium in heart disease. Lancet 2: 1044, 1976 II Goode A, Hawkins T, Feggetter JGW: The effect of furosemide used for post prostatectomy irrigation on total body potassium. Br J Urol 49: 143, 1977 12 Dale G, Young G, Latner AL, Goode A, Tweedle D, Johnson IDA: The effect of surgical operation on venous plasma free amino acids. Surgery 81:295, 1977 13 Manners JM: Nutrition after cardiac surgery. Anaesthesia 29:675, 1974 14 Abel RM, Fischer JE, Buckley MJ, Barnett GO, Austen WG: Malnutrition in cardiac surgical patients. Arch Surg 111:45, 1976 15 Johnston IDA, Marino JD, Stevens JZ: The effects of intravenous feeding on the balance of nitrogen, sodium, and potassium after operation. Br J Surg 53:885, 1966 16 Pacifico AD, Digerness S, Kirklin JW: Alterations of body composition after open intracardiac operations. Circulation 41:331, 1970 17 Blackburn GL, Gibbons GW, Bothe A, Benotti PN, Harken DE, McEnany TM: Nutritional support in cardiac cachexia. J THORAC CARDIOVASC SURG 73:4, 1977