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A slide-rule calculator for intravenous fluid requirements
A Slide-Rule
Calculator for Intravenous
Fluid Requirements By BERTRAMD. COHK ETERMINATION of fluid replacement values for intravenous therapy involves a basic preliminary estimate with subsequent revisions determined by the feedback of clinical response, urinary output, continued abnormal losses, and laboratory data. This basic preliminary estimate is a starting point, and provides the framework upon which subsequent modifications may be structured. The initial estimate may be calculated in a variety of ways. All methods have inherent drawbacks and intrinsic errors; they represent nothing more than approximations. Generally, a curvilinear relationship exists between baseline maintenance fluid needs and weight. is5 Such fluid needs are in direct proportion to the body surface area (BSA) and total metabolism (caloric expenditure). Within reasonable limits, BSA and caloric expenditure parallel each other.2 Estimation of body surface area using a calculation based on height and weight involves an error of about 10 per cent, For this purpose, Talbot’s nomogram embodies the formula of DuBois3v5:
D
Wt..4’” x Ht..725 x 71.84 = BSA( cm.2) Of equal accuracy is West’s nomogram6 based on weight alone which recognizes that BSA is related to Wt. raised to the 0.7 power.4p6 Darrow, a proponent of fluid therapy based on caloric expenditure, states that caloric estimates may have an intrinsic error of 25 per cent. 2 For these reasons, the West nomogram, based on weight alone, is sufficiently accurate, with a 10 per cent adjustment in cases of extreme thinness or obesity. Of some practical importance is the fact that weight can be quickly and accurately determined in any individual patient. A slide-rule calculator has been designed to provide fluid requirements over a wide range of values, based on the body weight-body surface area relationship, with fluid volumes expressed in terms of volume per square meter (BSA). (See Fig. 1.) At the extremes of the weight scale values may have to be modilied, particularly for the newborn and the large adult. Otherwise, basic maintenance is assumed to be 1.5-2.0 L./M.a/ 24 hours. Replacement for dehydration is estimated at 2.5-3.0 L./M.2/ 24 hours. When indicated in cases of severe dehydration, initial rapid rehydration is calculated at the rate of 12 L./M.2/ 24 From the Departments of Surgery, Maimonides Medical Center, Kings County Medical Center, and State University of New York, Downstate Medical Center, Brooklyn, New York. BERTFLAMD. COHN; M.D.: Associate Attending in charge of Pediatric Surgery, Maimonides Medical Center; Lecturer, Department of Surgery, Downstate Medical Center’, State lJniuersity of New York; Associate Visiting Surgeon, Pediatric Surgery Service, Rings County Medical Center. 414
JOURNAL OF PEDIATRICSURGERY,VOL. 3, No. 3 (JUNE ), 1968
413
SLIDE-RULE CALCULATOR
Fig. I.-The slide-rule calculator is shown as set for a patient of average build who weighs 24 pounds. The body surface area is 0.5 M2 and average 24 hour fluid requirement is 750-1000 cc. The 24-hour requirement for moderate to severe dehvdration is 1250-1500 cc. A volume for initial rapid rehydration over a 45-60 minute period is indicated as 185-250 cc. The surface area and fluid figures would apply as well to an unusuallv thin patient of 21 pounds or an unusually obese patient of 27 pounds.
hours or 05 L./M.“/ 1 hour. A proportiona Such
amounts
given
initially
are subtracted
amount from
is indicated the
24-hour
for “i hour. total.’
Fluids
during anesthesia may be given at the rate of 3.0 L./M.2/ 24 hours. A single continuous fluid volume scale avoids the danger of a dropped or misplaced decimal point. The direct read-out eliminates the need for pencil and paper calculations. The reverse side of the device shows drop rates for droppers of varying calibrations. During a period of use on a teaching pediatric surgical service, the slide-rule calculator provided quick accurate data for the physicians. The nursing staff found it of use in calculation of drop rates for varying fluid intakes. As a teaching tool, it served to emphasize the relationship of weight, body surface area, and fluid requirements. SUMMARY
A slide-rule calculator for intravenous fluid requirements is described. Starting with weight or body surface area, requirements are stated in terms of volume per square meter of body surface area. Average basic maintenance, replacement for dehydration, and initial rapid rehydration are indicated. are possible, with elimination of decimai Rapid and accurate calculations
416
COHN
error. As a teaching tool, relationships requirements are demonstrated. SUMMARIO
of weight,
surface
area,
and fluid
IN INTERLINGUA
Es describite un calculator pro determinar le requirimentos de liquid0 intravenose. Le dispositivo ha le forma de un “regula a calcular.” Le dato initial pote esser le peso de1 patiente o le superficie de su corpore. Le information obtenite se presenta in le forma de volumine per metro quadrato de area de superficie corporee. Le information include le requirimento medie de mantenentia basic, le requirimento pro le reimplaciamento post dishydration, e le requirimento pro le rapide rehydration initial. Rapide e accurate calculationes es possible, e le elimination de errores decimal es facile. Usate coma auxilio de instruction, le dispositivo demonstra le relationes inter peso, area de superficie corporee, e requirimentos de liquido. Varie methodos pro le calculation de1 superficie corporee es comparate brevemente e evalutate relative a lor accuratia. REFERENCES 1. Crawford, J. D., Terry, M. E., and Rourke, G. M.: Simplification of drug dosage calculation by application of the surface area principle. Pediatrics 5:783, 1950. 2. Darrow, D. C.: The physiologic basis for estimating requirements for parenteral fluids. Pediat. Clin. N. Amer. 11:819, 1964. 3. DuBois, E. F.: Heat loss from the human body. Harvey Lecture. Bull. NY Acad. Med. 15:143,1939. 4. Oliver, W. J., Graham, B. D., and Wilson, J. L.: The lack of scientific validity of
surface area as basis for parenteral fluid dosage. J.A.M.A. 167:1211, 1958. 5. Talbot, N. B., Crawford, J. D., and Butler, A. M.: Homeostatic limits to safe parenteral fluid therapy. New Eng. J. Med. 2481100, 1953. 6. Shirkey, H. C.: Pediatric Therapy. St. Louis, Mosby, 1966. 7. Snively, W. D., Jr.: Body surface area as a dosage criterion in fluid therapy: theory and application. Metabolism 6:70, 1957.
Calculator for Intravenous
Fluid Requirements By BERTRAMD. COHK ETERMINATION of fluid replacement values for intravenous therapy involves a basic preliminary estimate with subsequent revisions determined by the feedback of clinical response, urinary output, continued abnormal losses, and laboratory data. This basic preliminary estimate is a starting point, and provides the framework upon which subsequent modifications may be structured. The initial estimate may be calculated in a variety of ways. All methods have inherent drawbacks and intrinsic errors; they represent nothing more than approximations. Generally, a curvilinear relationship exists between baseline maintenance fluid needs and weight. is5 Such fluid needs are in direct proportion to the body surface area (BSA) and total metabolism (caloric expenditure). Within reasonable limits, BSA and caloric expenditure parallel each other.2 Estimation of body surface area using a calculation based on height and weight involves an error of about 10 per cent, For this purpose, Talbot’s nomogram embodies the formula of DuBois3v5:
D
Wt..4’” x Ht..725 x 71.84 = BSA( cm.2) Of equal accuracy is West’s nomogram6 based on weight alone which recognizes that BSA is related to Wt. raised to the 0.7 power.4p6 Darrow, a proponent of fluid therapy based on caloric expenditure, states that caloric estimates may have an intrinsic error of 25 per cent. 2 For these reasons, the West nomogram, based on weight alone, is sufficiently accurate, with a 10 per cent adjustment in cases of extreme thinness or obesity. Of some practical importance is the fact that weight can be quickly and accurately determined in any individual patient. A slide-rule calculator has been designed to provide fluid requirements over a wide range of values, based on the body weight-body surface area relationship, with fluid volumes expressed in terms of volume per square meter (BSA). (See Fig. 1.) At the extremes of the weight scale values may have to be modilied, particularly for the newborn and the large adult. Otherwise, basic maintenance is assumed to be 1.5-2.0 L./M.a/ 24 hours. Replacement for dehydration is estimated at 2.5-3.0 L./M.2/ 24 hours. When indicated in cases of severe dehydration, initial rapid rehydration is calculated at the rate of 12 L./M.2/ 24 From the Departments of Surgery, Maimonides Medical Center, Kings County Medical Center, and State University of New York, Downstate Medical Center, Brooklyn, New York. BERTFLAMD. COHN; M.D.: Associate Attending in charge of Pediatric Surgery, Maimonides Medical Center; Lecturer, Department of Surgery, Downstate Medical Center’, State lJniuersity of New York; Associate Visiting Surgeon, Pediatric Surgery Service, Rings County Medical Center. 414
JOURNAL OF PEDIATRICSURGERY,VOL. 3, No. 3 (JUNE ), 1968
413
SLIDE-RULE CALCULATOR
Fig. I.-The slide-rule calculator is shown as set for a patient of average build who weighs 24 pounds. The body surface area is 0.5 M2 and average 24 hour fluid requirement is 750-1000 cc. The 24-hour requirement for moderate to severe dehvdration is 1250-1500 cc. A volume for initial rapid rehydration over a 45-60 minute period is indicated as 185-250 cc. The surface area and fluid figures would apply as well to an unusuallv thin patient of 21 pounds or an unusually obese patient of 27 pounds.
hours or 05 L./M.“/ 1 hour. A proportiona Such
amounts
given
initially
are subtracted
amount from
is indicated the
24-hour
for “i hour. total.’
Fluids
during anesthesia may be given at the rate of 3.0 L./M.2/ 24 hours. A single continuous fluid volume scale avoids the danger of a dropped or misplaced decimal point. The direct read-out eliminates the need for pencil and paper calculations. The reverse side of the device shows drop rates for droppers of varying calibrations. During a period of use on a teaching pediatric surgical service, the slide-rule calculator provided quick accurate data for the physicians. The nursing staff found it of use in calculation of drop rates for varying fluid intakes. As a teaching tool, it served to emphasize the relationship of weight, body surface area, and fluid requirements. SUMMARY
A slide-rule calculator for intravenous fluid requirements is described. Starting with weight or body surface area, requirements are stated in terms of volume per square meter of body surface area. Average basic maintenance, replacement for dehydration, and initial rapid rehydration are indicated. are possible, with elimination of decimai Rapid and accurate calculations
416
COHN
error. As a teaching tool, relationships requirements are demonstrated. SUMMARIO
of weight,
surface
area,
and fluid
IN INTERLINGUA
Es describite un calculator pro determinar le requirimentos de liquid0 intravenose. Le dispositivo ha le forma de un “regula a calcular.” Le dato initial pote esser le peso de1 patiente o le superficie de su corpore. Le information obtenite se presenta in le forma de volumine per metro quadrato de area de superficie corporee. Le information include le requirimento medie de mantenentia basic, le requirimento pro le reimplaciamento post dishydration, e le requirimento pro le rapide rehydration initial. Rapide e accurate calculationes es possible, e le elimination de errores decimal es facile. Usate coma auxilio de instruction, le dispositivo demonstra le relationes inter peso, area de superficie corporee, e requirimentos de liquido. Varie methodos pro le calculation de1 superficie corporee es comparate brevemente e evalutate relative a lor accuratia. REFERENCES 1. Crawford, J. D., Terry, M. E., and Rourke, G. M.: Simplification of drug dosage calculation by application of the surface area principle. Pediatrics 5:783, 1950. 2. Darrow, D. C.: The physiologic basis for estimating requirements for parenteral fluids. Pediat. Clin. N. Amer. 11:819, 1964. 3. DuBois, E. F.: Heat loss from the human body. Harvey Lecture. Bull. NY Acad. Med. 15:143,1939. 4. Oliver, W. J., Graham, B. D., and Wilson, J. L.: The lack of scientific validity of
surface area as basis for parenteral fluid dosage. J.A.M.A. 167:1211, 1958. 5. Talbot, N. B., Crawford, J. D., and Butler, A. M.: Homeostatic limits to safe parenteral fluid therapy. New Eng. J. Med. 2481100, 1953. 6. Shirkey, H. C.: Pediatric Therapy. St. Louis, Mosby, 1966. 7. Snively, W. D., Jr.: Body surface area as a dosage criterion in fluid therapy: theory and application. Metabolism 6:70, 1957.