A unified guide to parenteral fluid therapy. I. Maintenance requirements and repair of dehydration

THE JOURNAL OF

PEDIATRICS j u L Y

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1 9 6 9

Volume 75

Number 1

ARTICLE

A unified guide to parenteral fluid therapy. I. Maintenance requirements and repair of dehydration William B. Weil, Jr., M.D. EAST

LANSINGj

]V[IGH.

O U R I N C R E A S I N G knowledge of the fundamental interactions involved in body fluid and electrolyte homeostasis is continuously reducing the empiricism employed in parenteral therapy. Simultaneously, the added complexity could negate the potential advantages for the usual patient by creating new confusion in the minds of physicians. It is the purpose of this r6sum6 to avert this hazard by presenting a practical, unified approach to the management of a variety of problems requiring intravenous hydration. GENERAL

CONSIDERATIONS

Basic to the understanding of this approach is the division of fluid requirements into two categories: those necessary for maintaining normal hydration and those necessary for restoring hydration to normal. In all individuals, water is continuously From the Department of Human Development, Michigan State University.

lost from the body through the skin and lungs; in the presence of functioning kidneys, water is also continuously lost in the formation of urine; intermittently, water is lost from the gastrointestinal tract. In the healthy person these losses are provided for by the intake of food and fluids by mouth. When this oral supply is inadequate to balance the continuous losses, dehydration results; this may be corrected by administration of fluids by other routes. Regardless of the etiology of the dehydration or the age or size of the individual, the same principles apply. The insensible water loss is that volume of fluid which leaves the body as a result of the difference in vapor pressure between the skin and lung surfaces and the surrounding atmosphere. A major determinant of the difference in vapor pressure is the temperature of the skin and lung surfaces. Surface temperature is primarily dependent on the metabolic rate of the individual. Ordinarily approximately 25 per cent of the heat generated Vol. 75, No. 1, pp. 1-12

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within the body is dissipated by the evaporation of water from the body surfaces. As the metabolic rate, or heat production within the body, is increased, heat losses must increase proportionately to avoid a rise in body temperature. Increasing heat loss is accomplished by vasodilation, which increases the surface temperature and results in an increased vapor pressure and thereby an increase in insensible water loss. In general, a rise in body temperature of 1 ~ C. will increase the insensible water loss by approximately 10 per cent. For example, in salicylate intoxication the metabolic rate may be doubled; concomitantly, the rate of insensible water loss will double. Similarly, in untreated hypothyroidism the metabolic rate is decreased and the rate of water loss from the skin and lungs is reduced proportionately. The water component of urine is primarily a vehicle for the excretion of various substances dissolved in the body fluid. For the purpose of discussing urine volume, the various substances dissolved in urine can be collectively considered as solutes. The amount of water loss from the body for the formation of urine depends on the amount of solute requiring excretion and the concentration of these solutes in the urine. The concentration of solutes is expressed in terms of osmolality. Thus a fluid with an osmolality of 300 has the same concentration of solute as does most of the body water. In average urine, this concentration corresponds to a specific gravity of 1.010. The human kidney can concentrate urine to an osmolality of 1,400, corresponding roughly to a specific gravity of 1.035; the maximum dilution that the kidney can produce is an osmolality of 50, corresponding to a specific gravity of approximately 1.001. Thus the volume of urine produced is dependent on the amount of solute to be excreted and on the concentration of that solute produced within the kidney. As an example, if 300 milliosmoles of solute are to be excreted at a concentration of 300 milliosmoles per kilogram ( m O s m . / K g . ) , this will require one liter of urine. Alternatively, if this same solute is excreted at a concentration of 600 niOsm./

The Journal o[ Pediatrics July 1969

Kg., only 500 ml. of urine will be required; at 100 mOsm./Kg., 3 L. of urine would be required. The amount of solute excreted in any period of time is primarily a function of the rate of protein metabolism, since tile catabolic products derived from protein represent the major excretory solutes. These include not only the nitrogenous substances, such as urea and creatinine, but the salts found in both animal and plant cells. Carbohydrates ordinarily are metabolized to carbon dioxide and water, thus no solutes are formed to be excreted by the kidney. Fat similarly is metabolized to carbon dioxide and water, and under usual circumstances requires no renal excretion of solute. Under abnormal situations both glucose and the keto acids derived from lipid metabolism may be solutes requiring excretion. In general, since the rate of protein metabolism is proportional to over-all metabolic rate, the water requirement for urine formation will be proportional to the metabolic rate. A further factor which must be taken into consideration in calculating urine volume is the stimulus to, and ability of, the kidney to produce a concentrated urine. The third source of relatively continuous water loss from the body is the gastrointestinal tract. The amount of water lost via this route is that which remains after the small bowel digestive fluids have passed through the ileocecal valve and have been actively reabsorbed by the large intestine. In health, the reabsorption of water by the large bowel is almost as efficient as the reabsorption of glomerular filtrate by the renal tubules. In the adult over 8 L. of digestive fluids are produced in a 24 hour period but less than 400 ml. of water appear in the 24 hour stool. Any agent which interferes with reabsorption of water by the large bowel results in increased losses in the stool. Stool water losses have been reported to be as high as 12 L. a day in adults with cholera. Although the rate of fluid loss from the body is a function of the metabolic rate of an individual, the symptoms of dehydra~ tion, once it is established, are directly proportional to the percentage diminution of

Volume 75 Number 1

body weight. Thus, an infant who has lost 10 per cent of its body weight as water is in a comparable physiologic state to an adult who has lost 10 per cent of his body weight as water. Because the metabolic rate of the infant is greater on a weight basis than is the metabolic rate of the adult per unit of body weight, the infant will achieve a 10 per cent loss of body water, in the face of limited intake, much more rapidly than the adult. But once a 10 per cent loss occurs, the symptomatology arising from this dehydration will be a function of the proportion. of body weight which has been lost, since the proportion of the body which is water changes only slightly over the life span from early infancy to adulthood and the effects of dehydration are initially hydrodynamic in nature rather than metabolic. In both the infant and the adult, overt symptoms of dehydration become apparent when an individual has had a relatively acute loss of 5 per cent of his body weight as water. When the loss has increased to 10 per cent of body weight, the clinical findings and symptomatology are usually severe. It is at this stage that most physicians would determine that hospitalization is required. An acute loss of 15 per cent of body weight is usually accompanied by peripheral vascular collapse and much more severe evidence of dehydration. An acute loss of 20 per cent of body weight as water is usually fatal. As fluid is lost from the body and dehydration begins, the loss occurs first from the plasma, since it is this volume of body water which is in contact with the external environment. In the nonedematous state the plasma may be considered to be in rapid equilibrium with the extracellular fluid. Then, as soon as fluid is lost from what is functionally the extracellular volume, several different forces come into play and result in a transfer of water from the cells to the extracellular compartment. This transfer of water is accompanied by loss of intracellular ions, primarily potassium and phosphate. Generally, when dehydration occurs over a short period of time, the loss of water from the body will be reasonably equally

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divided between the intra- and extracellular fluid compartments. Thus, in the repair of dehydration, the fluid given should contain ionic elements common to the intracellular space as well as to the extracellular space. SPECIFIC THERAPY-REFERENCE BASE

Consideration of specific therapy requires the determination of a common denominator for individuals of varying size. As has been pointed out under the general considerations, the fluids which are lost continuously from the body are lost in proportion to the metabolic rate. The replacement solutions are described as maintenance fluids. The relationship of metabolic rate to body size is a function of weight to the 2/3 power. This is clearly not a convenient expression to use, but it has been determined that the surface area of an individual appears also to be a function of weight to the 2/3 power. It is thus possible to relate both an individual's caloric requirements (an index of metabolic rate) and his fluid requirements for maintenance of adequate hydration to his surface area. When this is done and the fluid volumes are expressed per square meter of surface area, the maintenance requirements for both infants and adults, as well as individuals of intermediate size, tend to be relatively identical. On the other hand, the symptomatology of dehydration is related to weight directly and thus not to metabolic rate or to surface area, so that the repair of dehydration will be a function of weight and will be comparable on this basis in both the infant and the adult. It is thus not possible to have an ideal denominator which will apply to both the maintenance needs and the repair requirements for states of dehydration. Alternatively, it can be shown that, if maintenance requirements are expressed per kilogram of body weight, one can arbitrarily choose two points, one in infancy and one in young adulthood, which are simply related and between which one can interpolate in a straightforward manner. For this purpose, we have selected the 5- to 6-month-old infant and the 18-

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year-old adult. O n this basis it can be shown that the requirements for maintenance fluids of the adult are exactly half of those required, per kilogram of body weight, for the 6-month-old infant. Therefore, throughout the remainder of this article we will discuss the fluid requirements for maintenance and for repair of dehydration in terms of weight. In the tables, we also present the values for maintenance as a function of surface area. SPECIFIC THERAPY-MAINTENANCE REQUIREMENTS

Table I provides estimates for the maintenance requirements for the typical 5- to 6-month-old infant and the 18-year-old adult on the basis of milliliters per kilogram per day (ml./Kg./d.). The average values are given for each individual; a minimum and maximum range is also indicated. For completeness, the values per square meter are included. The values given as average are not considered basal or standard in any sense. They are reasonably typical for the infant who is active and taking a typical low-solute formula. They are also appropriate for an infant who is ill and requires parenteral alimentation. They do not include any increment for fever or hyperventilation. Thus, an infant with a temperature of 40 ~ C. would require a 30 per cent increase in the fluids necessary for insensible water toss; the average amount would then be 60 ml./Kg./d, rather than 45. Similarly, an infant who is comatose and hypothermic might have a water requirement to meet its insensible loss of only 25 to 30 ml./Kg./d. Comparable considerations apply to older children and adults. Table I I is designed to illustrate the water requirements for urine formation at differing concentrations and differing solute loads; the values are calculated on a square meter basis in order to be applicable to both infants and adults. For example, on an average diet the usual individual produces approximately 750 mOsm. of solute per square meter per day (M.2/d.) when fasting. This is reduced to 500 m O s m . / M Y in starvation. The addition of relatively small a/nounts

The journal o[ Pediatrics July 1969

of carbohydrate to the intake of an individual who is otherwise Fasting reduces protein metabolism sufficiently so that the solute load is only 300 mOsm./M.2/d. Additions of more carbohydrate do not appear to reduce the solute load any further. The saving in the water requirement to replace urine formation, by the addition of minimal amounts of carbohydrate at any particular concentration, is readily apparent from the table. The last column of Table I I lists the fluid requirement for an ill infant receiving at least 3 Gin. of carbohydrate/Kg./d, and is calculated for the various urinary concentrations. Reference to Table I indicates that a urine concentration of approximately 650 mOsm./Kg., or a specific gravity of 1.020, has been assumed for this average patient with a solute load of approximately 500 m O s m . / M . 2. In this example, the reduction in solute load achieved by the administration of carbohydrate is offset by the increased metabolic rate accompanying the illness which precipitated the need for parenteral alimentation. Thus, in terms of solute excretion, an infant or adult who is ill, but receiving adequate carbohydrate, is comparable to a healthy individual who is fasting. It can be readily determined that: when the solute load is increased, as in a. patient with leukemia under acute treatment, or in one with diabetic acidosis, the volume of water required to match urine output increases comparably and may easily be twice the average value. Furthermore, an inability to concentrate urine, as in chronic nephritis, also doubles the average water requirement for urine formation since the fixed specific gravity (1.010) represents half the osmolar concentration of tile example in the table. It should be noted that the dehydrated adult, even when ill, is normally able to concentrate urine nearly maximally. The small infant, however, when dehydrated and ill, is apt to be less able to concentrate urine as effectively as one who is dehydrated but otherwise healthy. The water requirement for urine volume may be reduced under circumstances when

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Parenteral fluid therapy

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T a b l e I. S u m m a r y of daily fluid r e q u i r e m e n t s

Maintenance requirements [or 24 hr.

In[ant (7 Kg.) (15 lb., 0.36 M. e) (mI./Kg.) Min. I Avg. t Max.

Adult (70 Kg.) (150 lb., 1.73 M. e) (ml./Kg.) Min. I Avg. I Max.

Sur[aee area

(ml./M. e) Min.

I Avg.

I Max.

Insensible

25

45

80

12.5

22.5

40

500

900

1,500

Renal Normal stools

15 0

40 5

120 --

7.5 0

20. 2.5

60 --

300 0

800 100

2,500 --

GI Diarrhea Normal stools Total diarrhea

40 --

35 90 120

70 200 270

17.5 45 60

35 100 135

-800 --

700 1,800 2,400

1,400 4,000 5,400

-20 --

T a b l e I I . U r i n e volume as a function of concentration a n d solute load

Solute load Concentration Urine Specific gravity osmolality 1.005 1.010 1.020 1.030 1.040

150 300 650 1,000 1,400

300mOsm'/M'e ; I Ill in[ant CHO, 100 Gin. ] adult, 1500 mOsm./M3 750 mOsm./M, e 7 Kg., 0.36M. ~, receiving CHO "3 Gm./Kg. in[ant I __ fasting average diet Volume o[ urine (ml./M.2/day) Vol. ml./K~./d. 2,000 1,000 450 300 20'0

3,200 1,60'0 750 500 350

5,000 2,500 1,150 750 500

160 80 40 25 18

Urine volume: Absolute minimum with maxiin~lm concentration, without azotemia, is about 200 ml./M.2/d. Absolute maximum may be up to 10,000 ml./M.2/d., as in diabetes insipidus. In m l . / K g . / d . : infant minimum, 10; adult minimum, 5; infant maximum, 500; adult maximum, 250.

m a x i m u m concentrating ability is a p p r o p r i ate a n d possible a n d when the solute load is minimal. Obviously, during complete a n u r i a the w a t e r r e q u i r e m e n t to replace urine form a t i o n is zero. T h e w a t e r losses t h a t a c c o m p a n y o r d i n a r y bowel function are extremely small a n d are estimated at a p p r o x i m a t e l y 5 m l . / K g . / d . for the i n f a n t a n d half this for the typical adult. I n the usual d i a r r h e a for which p a r enteral fluid therapy is required, the gastrointestinal loss of w a t e r in the i n f a n t will a p p r o x i m a t e 35 m l . / K g . / d . ; in extreme situations, however, the stool volumes of infants m a y a p p r o a c h 70 m l . / K g . / d . I t should also be r e m e m b e r e d that, when the infant is given n o t h i n g by m o u t h a n d p a r e n t e r a l alim e n t a t i o n is begun, stool volume m a y begin to a p p r o a c h zero. Gastrointestinal suction losses should not be estimated b u t m u s t

be measured as they occur. Such losses, as well as those from fistula drainage a n d the like, must be included in those r e q u i r i n g replacement. S U M M A R Y OF M A I N T E N A N C E REQUIREMENTS

T h e o r d i n a r y fluid requirements for m a i n t e n a n c e of an infant 5 to 6 m o n t h s of age are a p p r o x i m a t e l y 90 m l . / K g . / d . , a n d for an a d u l t of 18 years or older a p p r o x i mately 45 m l . / K g . / d . F o r i n t e r m e d i a t e ages, a direct interpolation on the basis of age can be calculated. Thus, a 9-year-old child requires a p p r o x i m a t e l y 60 m l . / K g . / d , for m a i n t e n a n c e requirements, a n d a 6-year-old child a p p r o x i m a t e l y 75 m l . / K g . / d . I n the presence of m o d e r a t e l y severe d i a r r h e a the m a i n t e n a n c e r e q u i r e m e n t for the i n f a n t increases to an average of 125 m l . / K g . / d . ,

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The Journal of Pediatrics July 1969

but it can range as high as 270 m l . / K g . / d . In the absence of diarrhea, and in the absence of renal function, the maintenance fluids would be limited to those required to replace the insensible water loss. When the maintenance requirements for fluids are low, the addition of water to the body fluids from the metabolism of tissues must be taken into consideration. This additional water can be calculated as 0.1 ml. per calorie metabolized. An infant who weighs 7 kilograms utilizes about 100 cal./ Kg. or about 700 cal. per day. This would yield 70 ml. of water per day, or 10 ml./Kg. Water derived from this source is available for the body's fluid needs. If the insensible water loss for such an infant were calculated at 40 ml./Kg., only 30 ml./Kg, would have to be administered parenterally under these circumstances. REPAIR

OF DEHYDRATION

The fluids that are provided as maintenance and are used to compensate for the ongoing losses through the skin, lungs, kidney, and gastrointestinal tract must, of necessity, be calculated and given on a daily basis. On the other hand, those fluids that are used for the repair of dehydration are needed only once. If the amount of fluid required to repair the dehydration is calculated correctly, and if no discrepancy occurs between the provision of maintenance fluids and the need for these fluids, there should be only one occasion for the administration of fluids to repair dehydration. The time taken to effect this repair may vary from 12 to 72 hours. In general, one administers repair fluids over a period of 36 to 48 hours. The volume of fluid necessary to repair abnormal hydration is determined by assessment of the clinical state of the patient. If dehydration is mild and just detectable, the amount of fluid required would be approximately 50 ml./Kg., corresponding to a loss of 5 per cent of body weight as water. Similarly, if the loss is severe and the symptoms and signs of dehydration are marked, one would calculate approximately 100 ml./Kg. for the repair of the dehydrated state.-. If not

only are the signs and symptoms severe but also the patient is in shock or potentially in shock, one can reasonably assume that he will require approximately 150 ml./Kg, of body weight to effect the repair of dehydration. Clearly, during the period in which repair fluids are being administered, maintenance fluids must also be administered; thus, the actual volume of solution given will be the sum of that calculated for maintenance plus that calculated for repair until such repair is accomplished. FLUID

COMPOSITION

Composition of the fluids which are administered to a dehydrated individual is based on a variety of considerations. To minimize protein metabolism, the infant needs at least 3 Gm./Kg. of carbohydrate per day. If the total fluids to be administered are at least 125 ml./Kg./d., this amount of carbohydrate may be obtained from a solution which has a 2.5 per cent glucose content. No harm is done if the solution contains 5 per cent glucose, but only when the volume of fluids must be severely restricted because of, for example, absent renal function, should one need 10 per cent or greater concentrations of glucose. The electrolyte content of maintenance solutions is usually low. The water lost by evaporation from the skin and lungs has a minimal salt content. The water excreted as urine contains salt,* but it does so primarily because of the excess of salts which need excretion from the body. The renal tubules can achieve a minimum concentration of salts but this is extremely low and for most purposes can be considered negligible. On the other hand, all gastrointestinal losses contain a moderate to large amount of salt. In general, small bowel fluid is isotonic with extracellular fluid as far as the salt content is concerned. However, after passage of this fluid through the ileocecal valve, the large bowel not only reabsorbs water but preferentially reabsorbs salt, especially sodium and "X'Salt in this context refers to the metallic cations (Na +, K +, Mg++ Ca++) and their appropriate anions.

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chloride, while at the same time exchanging some of these ions for potassium and bicarbonate. In an over-all view of the salt content of gastrointestinal losses, one can assume that these will vary from approximately 89 isotonic to fully isotonic in relation to the major body fluids. In addition, the gastrointestinal fluids generally contain a moderate amount of potassium and bicarbonate as well as sodium and chloride. Thus, the fluids required for meeting the maintenance needs of the patient are relatively dilute and certainly less than isotonic with regard to salt content. Isotonicity is achieved by the addition of either 2.5 or 5 per cent glucose. Until the serum potassium concentration is known and it is certain that the p a t i e n t will have a reasonable urinary output, the fluid for maintenance should not contain potassium. When there is reasonable urine output and renal function appears to be good, the maintenance solution may contain approximately equal quantities of sodium and potassium. When the period of parenteral fluid therapy is brief, little difficulty is usually created by the divalent cations M g F+ and Ca ++. However, if parenteral fluids are to be administered over a period of more than a few days, magnesium deficiency may occur. Therefore, maintenance fluids should contain magnesium at a concentration of 1 to 4 mEq./L, under these circumstances. The fluid required for the repair of dehydration normally should contain the same salt composition as do body fluids in general. The fluid loss which has occurred when dehydration is present has been derived almost equally from the extracellular and intracellular fluid volumes. The primary ionic constituents of the extracellular fluid are sodium, chloride, and bicarbonate, whereas those from the intracellular fluid are primarily potassium and phosphate. In theory, an ideal replacement solution would contain sodium and potassium in more or less equal amounts as well as chloride, bicarbonate, and phosphate. However, since the fluid to be administered will go directly into the extracellular fluid and since the transfer of

Parenteral fluid therapy 7

this fluid into the intracellular volume must occur through active transport, modification of this theoretical solution must be made. Transport of potassium into cells occurs at a relatively slow rate which has been shown to approximate 3 m E q . / K g . / d . Under unusual circumstances this rate has been shown to be at least twice this value. Anion transport into cells is even more restricted; as a result, little phosphate is ordinarily added to parenteral solutions. The limitation on potassium transport suggests that the m a x i m u m amount of potassium to be administered to a patient in a 24 hour period is generally not greater than 3 mEq./Kg./d., but, under unusual circumstances of severe depletion of cellular potassium or when excessive losses of potassium are taking place through the kidney or gastrointestinal tract, quantities up to 3 times this amount, or 9 m E q . / K g . / d . , can be administered. However, extreme precaution should be exercised when potassium is given at a rate exceeding 3 m E q . / K g . / d . Furthermore, because of the possibility of transient hyperkalemia producing cardiac arrhythmia or arrest, no solution for intravenous administration should contain more than 30 to 40 mEq. of potassium per liter of solution. Thus, the fluid administered for repair of dehydration should be an isotonic salt solution containing primarily sodium and chloride, but with a potassium concentration of 30 to 40 mEq./L, and bicarbonate concentration of 25 to 50 m E q . / L . The lactate ion has been used in the past as a substitute for the bicarbonate ion but the only advantage today may be availability. Furthermore, if the lactate ion cannot be metabolized rapidly (most commonly found in anoxic states) the use of lactate is probably contraindicated. ILLUSTRATIVE

CASE

An example of the previously described program may be illustrated by the case of a 1-yearold infant who weighed 10 kilograms and who had had diarrhea with some vomiting for 3 days. When seen by his physician at the end of that period, he appeared quite dehydrated and was not tearing; his mucous membranes were dry. He was conscious but listless; his pulse was

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strong. His body temperature was 39.5~ C. and he had moderate hyperventilation. The remainder of his physical examination was unremarkable. To calculate his fluid requirements, we can estimate the required amount as follows: for insensible water loss, a 7 kilogram infant would have, on the average, a loss of 45 ml./Kg./hr. This infant is somewhat larger and older and therefore his toss per kilogram would be slightly smaller, perhaps 42 ml./Kg./hr. On the other hand, he is hyperventilating and his body temperature is elevated 2~ C., which would suggest a 20 per cent increase in metabolic rate and therefore a 20 per cent increase in insensible water loss, or an additional 8 ml./Kg./d. The total fluid required to provide for insensible water loss therefore would be 50 ml./Kg./d. His urinary water requirement can be computed from the 7 kilogram infant whose requirement would be 40 ml./Kg./d. This child, being slightly larger, would have a somewhat smaller water requirement per kilogram--35 to 40 ml./Kg./d. Without evidence to the contrary we can assume his concentrating ability to be adequate and we have no evidence for any increased solute load. Therefore, we would select a value of 38 ml./Kg./d. For gastrointestinal losses, this child has had a large stool volume and we can take the average value of 35 ml./Kg./d. Thus, the total maintenance requirement for this child would be 50 + 38 + 35 ml., or 123 ml./Kg./d. In addition, we must repair the dehydration which is present. We can estimate from the description that the water loss which had already occurred was equivalent to approximately 10 per cent of body weight, or 100 ml./Kg. We can choose to repair this dehydration over a 2 day period. However, we may wish to give the majority of this repair, perhaps 70 ml./Kg., in the first day and 30 ml./Kg, in the second. Then if we add the 70 ml. of repair to the 123 ml. of maintenance, we arrive at 193 m l . / Kg. for the total requirement in the first 24 hours; this can be rounded out to 200 ml./Kg. Translating this to the 10 kilogram child would produce a value of 1,930 ml. per 24 hours (rounded out value = 2,000 ml.). In addition, we may wish to give fluids to this child somewhat more rapidly during the first 8 hours of this 24 hour period than in the remaining 16 hours. We could achieve this by giving 880 ml. in the first 8

The Journal o[ Pediatrics July 1969

hours, or providing the fluids at approximately 110 mh per hour for 8 hours and then giving the remaining 1,120 ml. at 70 ml. per hour for the remaining 16 hours. The composition of this fluid would be based on the assumption that the 50 ml. for the insensible water requirement and the 38 ml. for the renal water loss can be provided as a salt-free solution and that the 35 ml. for the gastrointestinal loss plus the 70 ml. for repair can be given as an isotonic salt-containing solution. These represent approximately equivalent amounts of salt-containing solution and non-saltcontaining solution, so that we can provide the total quantity as a solution which is essentially isotonic in terms of the salt concentration in body water. In the first few hours of therapy, we will not be sufficiently aware of the renal function of this child to be certain that administration of potassium is safe. Therefore, we will give a solution of approximately 75 mEq./L, of sodium, 50 mEq./L, of chloride, and 25 mEq./L, of bicarbonate (or lactate) with 2.5 or 5 per cent glucose for the first 8 hours. A commonly available commercial solution which approximates this concentration is Y2 lactated Ringer's solution in glucose. After the first 8 hours, when it is certain that the child has voided and that the serum potassium is normal, administration of potassium may be instituted. For the next 16 hours, we could administer a solution containing 40 to 50 mEq./L, of sodium with 30 to 40 mEq./L, of potassium and the same chloride and bicarbonate concentrations as in the first 8 hours. A solution comparable to this is prepared by various manufacturers under such titles as Solution 75 and Isolyte M. Parenthetically, re-evaluation of the patient should be as frequent as his condition warrants; it may be quite appropriate to modify the treatment plan more often than is outlined here. During the second 24 hour period, the body temperature might well have returned to normal and hyperventilation ceased, so that we could then provide for the insensible water loss (IWL) at a rate of 40 to 45 ml./Kg./d. The renal water requirement would probably remain at 35 to 40 ml./Kg./d.; the gastrointestinal losses would have been markedly reduced and we could reduce the fluids for this to 15 ml./Kg. Thus, the total maintenance requirement for the second day would be approximately 95 ml./Kg. The repair fluids not administered during the first day would be approximately 30 ml./Kg.,

Volume 75 Number 1

making a total of 125 ml./Kg, for the second 24 hours. For this infant of 10 kilograms, this total would be 1,250 ml. This fluid would contain a nonsalt solution of approximately 80 ml./ Kg. (40 for IWL and 40 for renal) and a salt containing solution of 45 ml./Kg. (15 for GI and 30 for repair). This solution is essentially ~ isotonic for salt and could be administered as any one of a number of commercial fluids (e.g., Isolyte P, Electrolyte 48). Each of these solutions contains adequate glucose, in the volume being administered, to provide sufficient carbohydrate to achieve a maximum protein-sparing effect. By the third day of this infant's care, he should be ready to take fluids orally; presumably one would begin by administering either glucose water or dilute boiled skimmed milk by month. RECAPITULATION

This approach to fluid management can be applied to any patient requiring parenteral alimentation. Each component of the maintenance needs is analyzed separately for its age-specific average value from the data in Table I; then the modification in this value is determined by assessment of the clinical state of the patient (fever, activity, urinary excretion, and so on). T h e individual maintenance needs are added to determine the total maintenance requirement. This total requirement will tend to average 1,800 to 1,900 m l . / M ? / d , in the absence of increased gastrointestinal losses, and will increase toward 2,600 ml./MY/d, in the presence of such losses, depending on their rate. Another method of arriving at an average value for total maintenance needs is to recognize that this value will be comparable to the total caloric needs. SimiIarly, the average value per kilogram can be derived from the equation: Total daily maintenance fluids per kilogram = 95 - 3 times the age in years. Thus, the value for a 7-year-old child = 95 - 3(7) = 74 ml./Kg./d. However, it must always be borne in mind that these average values do not take into account abnormal rates of loss from skin, lungs, kidneys, or gastrointestinal tract; when any of these are present, each component of the

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maintenance needs must be estimated separately. Once the ongoing requirements are determined, the degree of dehydration or overhydration that is present must be assessed. This is a judgment which is based both on physical appraisal and on changes in weight. The state of hydration cannot be judged by the concentration of substances in body fluids, because these substances may have been lost from the body at a rate equal to, or slower than, or faster than the rate of water loss. Thus, concentrations of sodium, chloride, urea, hemoglobin, and the like may be normal, increased, or decreased in the presence of dehydration or of overhydration. When the dehydration or overhydration has been evaluated and an estimate of the water deficit or excess has been made, the amount to be corrected in each 24 hour period is arbitrarily decided. The major portion of any correction is generally made in the first 24 hour period, the remainder (30 to 40 per cent) in the second day. However, in. patients with manifest or borderline cardiac failure, such corrections may be spread over 3 to 5 days. In the presence of impending or manifest shock, up to 10 per cent of the intravenous fluids may be given very rapidly (30 to 60 minutes) by syringe injection. For each day, the volume of maintenance fluids is added to the volume of repair fluids to determine the total amount of fluids to be administered during the 24 hour period. This 24 hour volume rarely should exceed 200 m l . / K g . / d , in an infant or 100 m l . / Kg./d. in an adult (4,000 m l . / M Y / d . ) . The salt content of this total solution will vary. It may be none when one is providing fluid for insensible water loss alone for an adequately hydrated individual who is in renal shutdown and has no abnormal gastrointestinal loss. The salt content may be half isotonic solution (75 mEq./L, of cation - - N a + + K § as in the previously described case. On occasion a greater concentration of salt is required; an example is included below. From analysis of each of the following

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The Journal o[ Pediatrics July 1969

e x a m p l e s it should be clear t h a t this simplified a p p r o a c h to fluid t h e r a p y is a p p l i c a b l e to all types of w a t e r a n d electrolyte p r o b lems. FURTHER

ILLUSTRATIVE

CASES

Case A. A 6-year-old child had bowel obstruction and vomiting for 2 days; scant urine with a specific gravity of 1.032; Na +, 137 m E q . / L . ; CO2, 20 m E q . / L . ; blood urea nitrogen ( B U N ) , 26 mg./100 ml.; weight, 20 kilograms; temperature, 37 ~ C. The nonsalt solution = 760 + 660 = 1,420. The isotonic salt solution = 480 + 700 = 1,180. Optimal cation concentration = (1,180/2,600) x 150 = 68 m E q . / L . (1,180 = amt. of isotonic salt solution; 2,600 = total volume of fluid; 150 = assumed cation concentration of body fluids). Commercial solution, !,{ lactated Ringer's (cation concentration = 65 m E q . / L . ) . After 6 hours, if serum K + is not elevated and urine volume is adequate, give fluids as Isolyte M, Solution 75, or comparable mixture with Na + appproximately 45 m E q . / L , and K + 30 mEq./L. On the second day, recalculate maintenance and add 300 ml. of remaining replacement fluid. All patients should be weighed every 12 hours during the first two days to determine if weight gain is what is expected on basis of fluid administration. If weight gain is not as expected, the entire fluid problem should be analyzed on the basis of additional data so that errors in estimation can be corrected or refined. Case B. A 12-year-old boy had diabetic ketoacidosis of 18 hours' duration associated with occasional vomiting, polyuria, and weight loss. The blood sugar was 720 mg./100 ml.; Na +, 120 m E q . / L . (see note 1 below); COx, 8 m E q . / L . ; pH, 7.10; weight, 40 kilograms (see note 2 below). Note 1. Serum sodium does not reflect hypotonicity of body fluids as glucose concentration ---40 m O s m . / L . , which will be equivalent to 20 m E q . / L , of cation (and anion). Note 2. Administration of insulin is not considered in this analysis. Note 3. Solute diuresis in such circumstances may double expected urine volume and force excretion of salt so that half of urine volume may be calculated as isotonic salt loss.

The nonsalt solution --- 1,400 + 1,000 ~ 2,400 ml. The isotonic salt solution = 1,000 + 120 + 1,000 = 2,!20 ml. Optimal cation cone. = (2,120/4,520) x 150 --- 70 m E q . / L . Commercial solution, ~ lactated Ringer's. After 4 to 6 hours, if serum K § is not elevated and urine volume is adequate, give fluids as Isolyte M, Solution 75, or comparable mixture. After 10 to 14 hours, when blood sugar approaches normal levels, additional glucose may need to be added to intravenous fluids. Case C. A 5-month-old infant has vomiting and severe diarrhea of 3 days' duration. The child was hyperventilating but extremely lethargic; the pulse was rapid and weak; the weight was 3.00 kilograms; the temperature, 38 ~ C.; Na +, 120 m E q . / L . ; COz, 10 m E q . / L . ; K +, 3.5

mEq./L. The cation concentration deficit = i40 - 120 m E q . / L . = 20. The cation deficit = concentration deficit x body water volume; which = 20 x % body weight (Kg.); which = 20 x 2, or 40 mEq. The half of the deficit to be replaced in first day = 20 mEq. The nonsalt solution = 150 + 120 = 270. The salt solution = 120 + 300 ---- 420. However, an additional 20 mEq. of salt is necessary to replace half of the body water deficit, and 20 mEq. of salt are contained in 130 mh of isotonic salt solution. Therefore, instead of 270 ml. of nonsalt solution, this figure becomes 270 - 130 = 140 mh, and the value for salt solution becomes 420 + 130 = 550. The optimal cation concentration = (550/ 690) x 150 = 120 m E q . / L . This can be prepared by using 890 ml. of lactated Ringer's and 110 ml. of 5 per cent glucose in water to prepare 1 L., or 615 ml. of lactated Ringer's plus 75 ml. of 5 per cent glucose in water to prepare 690 ml. On the second day, diarrhea and vomiting stopped. The Na + was 130 m E q . / L . ; CO2, 18 m E q . / L . ; weight 3.30 kilograms. The nonsalt solution = 150 + 130 = 280. The salt solution = 15 + 150 = 165. The remaining salt deficit = 20 mEq. = 130 ml. of isotonic salt solution. Therefore, the non-

~l{alf of urine volume is replaced with salt solution.

Volume 75 Number 1

Parenteral fluid therapy

Case A

Type of loss

I Interpolated value for age (ml./Kg./d.)

IWL Renal GI

38 33 4

Clinical modification

Fluid estimate M1./Kg./d. ] Total ml./d.

None None Measured suction 1 hour=20ml.

38 33

760 660 480

Total maintenance

1,900

Minimal dehydration (5 per cent) (50 ml./Kg. = 1,000 ml.) first day replace 70 per cent

700

Total first 24 hr.

2,600

Case B

Type of loss

Interpolated value for age (ml./Kg./d.)

IWL Renal

30 27

GI

3

Total maintenance

Clinical modification

Fluid estimate Ml./Kg./d. J Total ml./d.

Hyperventilation Solute diuresis (see note 3 below) None

60

35 50

1,400 2,000

3

120

88

3,520

Detectable dehydration (5 per cent) (50 ml./Kg. -= 2,000 ml.) first day replace 50 per cent -~

1,000

Total first 24 hr.

4,520

C a s e C . F i r s t 24 h o u r s

Type ,o[ loss

Interpolated value /or age (ml./Kg'./d.)

Clinical modification

45 40 5

Hyperventilation None Severe diarrhea

IWL Renal GI Total maintenance

Fluid estimate M1./Kg./d. J Total ml./d. 50 40 40

150 120 120

130

390

Dehydration + shock 300

(15 per cent) (150 ml./Kg. = 450 ml.) first day replace ~ = Total first 24 hr.

690

C a s e C. S e c o n d 24 h o u r s

Type of loss IWL Renal GI

Interpolated value /or age (mL/Kg./d.)

Clinical modification

45 40 5

None None None

Total maintenance

Fluid estimate Ml./Kg./d. J Total ml./d. 45 4O 5

150 130 15

90

295

Remainder of volume deficit to repair

150

Total second 24 hr.

445

11

12

Well

salt solution = 280 - 130 = 150; the salt solution = 165 + 130 = 295; the optimal cation concentration = (295/445) x 140 = 100 m E q . / L. This can be prepared either by using ~2 lactated Ringer's and adding 35 mEq. of a concentrated solution of KC1 to 1 L. of ~2 lactated Ringer's (final cation concentration = 102 m E q . / L . ) or using a commercial solution with a cation concentration of 90 m E q . / L . REFERENCES !. Ad I-Ioc Committee on Acid-Base Terminology, Conference on current concepts of acid-base measurement, Ann. New York Acad. Sc. 133: 251, 1966. 2. Barness, L. A., editor: Symposium on fluid and electrolyte problems, Pediat. Clin. North America 11: 789, 1964. 3. Bernstein, L. M., Allender, J. S., Elstein, A. S., and Epstein, R. B.: Renal function and renal failure, Baltimore, 1965, The Williams & Wilkins Company.

The Journal of Pediatrics July 1969

4. Christensen, H. N.: Body fluids and the acidbase balance, Philadelphia, 1964, W. B. Saunders Company. 5. Darrow, D. C.: A guide to learning fluid therapy, Springfield, Ill., 1964, Charles C Thomas, Publisher. 6. Fox, C. L., Jr.: An approach to the treatment of burns in your hospital, Hosp. Prac. 2: 61, 1967. 7. Gamble, G. L.: Chemical anatomy, physiology and pathology of extracellular fluid, Cambridge, Mass., 1953, Harvard University Press. 8. tIolliday, M. A., Kalayci, M. N., and Harrah, J.: Factors that limit brain volume changes in response to acute and sustained hyper- and hyponatremia, J. Clin. Invest. 47: 1916, 1968. 9. Holliday, M. A., and Segar, W. E.: The maintenance need for water in parenteral fluid therapy, Pediatrics 19: 823, 1957. 10. Pitts, R. F.: Physiology of the kidney and body fluids, ed. 2, Chicago, 1963, Year Book Medical Publishers, Inc. 11. Winters, R. W., Engel, K., and Dell, R. B.: Acid base physiology in medicine, Cleveland, 1967, The London Company.