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Committee on Hospital Care

Metrication and SI Units*

Because of the increasing international use of the Weights and Measures at S#{232}vres, , which SI system (International System of Units) in med- acts as an international standards reference labo- icine, the Committee on Hospital Care has written ratory and as the permanent secretariat for the this statement to familiarize pediatricians with this Convention. The General Conference on concept. The current state of the system, its den- Weights and Measures, the diplomatic organization vation, purported advantages, and controversial as- made up of adherents to the Convention (now in- pects are described; and the Committee has made cluding 41 member countries), is the ultimate au- specific recommendations for consideration regard- thority on the definition of units. In 1960 the Gen- ing its future use and development. eral Conference standardized metric units into the simplified and logical system known as SI. Further BACKGROUND refinements have been made by the General Con- ference on four subsequent occasions. ‘ The present The British Imperial System of Weights used in structure of the SI is likely to be the permanent the today derives from a variety of one. ancient cultures. A Roman contribution is the use In parallel with the developments on the gener- of the awkward number 12 as a base. Royal decree alized use of SI units, recommendations for the established the as the distance from the tip of standardized reporting of clinical laboratory data the nose to the end of the thumb of King Henry I. based on SI were proposed by the Commission on The was based on the size of three grains of Clinical Chemistry (CCC) of the International Un- barley “dry and round.” Equally illogically derived ion of Pure and Applied Chemistry (IUPAC) and units evolved to eventually form the irrational Eng- the International Federation of Clinical Chemistry lish “system.” (IFCC).4 The with its “base-lO” or “deci- In recent years, the major industrial nations of mal” system derived its units of mass and volume the world, with the exception of the United States, from its units of length, thus correlating its basic have been using the metric system or converting to units to each other. The need for further refinement its use. The United States has been an “island in of metrics and a single worldwide and interdiscipli- the metric sea.” The British Commonwealth coun- nary system of led to the develop- tries with whom we shared the pounds-quarts- ment of the International System of Units (le Sys- system for so long have all converted to metric. t#{232}meInternational d’Unit#{233}s) with the international has an unofficial goal of being metric by abbreviation “SI.” This is sometimes referred to as 1980. Eventually, the Congress of the United States “the modern metric system” and is said to complete passed the Metric Conversion Act of 1975 stating, the process of metnication.2 “It is therefore declared that the policy of the Seventeen countries, including the United States, United States shall be to coordinate and plan the signed the in 1870. This led to increasing use of the metric system.” Furthermore, the establishment of the International Bureau of the Act states, “. . . the term ‘metric system of mea- surement’ means the International System of

* Abbreviations used in Pediatrics currently follow the Style- Units.”5 This is to be done on a voluntary basis. book/Editorial Manual of the American Medical Association. Industry is becoming increasingly involved in Abbreviations used in this article are slightly different from the metric conversion with the realization that the Stylebook. PEI)IATRICS (ISSN 0031 4005). Copyright © 1980 by the United States cannot be competitive on the inter- American Academy of Pediatrics. national scene without using metrics. Schools in the

Downloaded from www.aappublications.org/newsAMERICAN by guest on ACADEMYSeptember 30, 2021 OF PEDIATRICS 659 United States have begun teaching SI as the pni- factor. Noncoherent units are derived from the base mary system.’ units but contain a factor, eg, the liter (L, recom- In Finland, , and , the use of SI is mended symbol for the liter in the United States) compulsory in medical laboratories. Table 1 lists equals the decimeter cubed (dm’). Table 4 shows the years by which a phased introduction of SI will the prefixes that denote multiples of SI units. be or has been completed in various countries. Although mass concentration (gIL) and sub- stance concentration (mol/L) are both included in SI SYSTEM the SI system,7 there are certain advantages to recording in substance concentration. By reporting SI is a system of “base units” and “derived units” data as we do now, the apparent quantities of and their interrelationships. Seven base units and different materials may be misrepresented. Corn- two supplementary units have been adopted (Table pounds with a high molecular mass might seem to 2). Each unit can be defined in specific terms. For have more molecules present as compared with example, the mole is the amount of substance that those of lower molecular weight. Furthermore, cer- contains as many elementary entities as there are tam biologic relations between blood constituents atoms in 0.012 kg of carbon 12. Base units are may be made clear when measurement is on the multiplied and divided to form derived units (Table basis of their relative number. Such relations may 3). For example, the unit for force, the , is be masked by usage of mass concentration but may derived from three base units according to the be better visualized in molar terms. For example, expression m kg . 2#{149} Coherence is the derivation an unconjugated biirubin concentration might be of a unit from a base unit without the use of a 0.4 mg/dL and the serum albumin, 4.0 g/dL. The concentration of biirubin might seem to be ‘/i,xx of TABLE 1 . Year of Introduction or Anticipated Introduction of SI Units that of albumin. In molar terms, however, there is only a 100-fold difference. The same concentrations Year Country are 6.8 and 620 imol/L, respectively. A serum bili- 1970 rubin concentration of 20 mg/dL, which is a level of 1971 , Finland 1974 clinical importance in neonatology, is 340 imol/L, 1975 or more than half the molar concentration of the 1976 , South Africa, Sweden albumin in this example.” It becomes obvious why 1977 Norway a small change in compounds bound to albumin 1978 Federal Republic of Germany may result in displacement of bilirubin or other 1979 Czechoslovakia, Democratic Republic of Ger- many compounds from their binding sites on the albumin 1980 Hungary, molecule. Another example is the electrolytes, so- 1981 , , Yugoslavia dium, potassium, and chloride, whose interrelations 1982 Ecuador have become more apparent since they have been reported in milliequivalent units. (The new metric system molecular SI unit is numerically the same TABLE 2. SI Base Units as the univalent charged ion when expressed as Quantity Name Symbol milliequivalents.) True ionic balance in serum is Length Meter (metre)* m difficult to understand when constituents are re- Mass kg ported in different terms, eg, the foregoing ions are Time s reported in mEq/L, whereas the divalent ion, cal- Electric current Ampere A Thermodynamic temper- Kelvin K cium and magnesium, are still often expressed as aturet mg/100 ml. SI would impose consistency. Amount of substance Mole mol Luminous intensity Candela cd ADVANTAGES AND DISADVANTAGES Supplementary Units Plane angle Radian Certain stated advantages of metric conversion Solid angle Steradian sr are compelling. Scientists from all fields and of all

* Both spellings acceptable. nationalities might eventually communicate in the t The temperature (formerly called centi- same units of measure. The increase in ease and grade) is used for most medical and commercial purposes. precision of scientific communication and eventual The Kelvin (the unit for thermodynamic temperature) is avoidance of misunderstanding and error by inter- the SI unit for temperature. Although their scale origins national agreement on terminology would be enor- differ, the Celsius equals the Kelvin in magnitude; thus, a rise in body temperature of 1.0 K is equivalent to mous. SI has the advantage of being logical, sys- a rise of 1.0 C. 0 C is defined as 273.15 K, thus 98.6 F = 37 tematic, international, and interdisciplinary.9 It has C = 310.15 K. been suggested that SI would eventually replace

660 PEDIATRICS Vol.Downloaded 65 No. from 3 March www.aappublications.org/news 1980 by guest on September 30, 2021 TABLE 3. Some SI Derived Units

Quantity Name Symbol

Area Square meter Volume Cubic meter rn’ Meter per second rn/s Wave number 1 per meter Density, mass density Kilogram per cubic me- kg/rn’ ter Concentration (amount of Mole per cubic meter rnol/m’ substance) Activity (radioactive) 1 per second s-i Specific volume Cubic meter per kilo- rn’/kg Luminance Candela per square me- cd/rn2 ter Frequency Hertz Hz = Force Newton N = rn.kg.s2

Pressure Pascal Pa = N/rn2 = m ‘. kg . s Energy, quantity of heat, Joule J = N.m = rn2.kg.s2 work Power Watt W = J/S = rn2.kg.s Electric potential, potential Volt V = W/A = rn2.kg.s’.A’ difference, electromotive force

Electric resistance Ohm 2 = V/A = rn2.kg.s’.A2

TABLE 4. SI Prefixes pascal, the SI unit of pressure. Blood pressures are

Factor Prefix Factor Prefix now recorded in millimeters of mercury (or “torr”).

The pascal (kg - m ‘ . 2, or the newton per square Name Symbol Name Symbol meter) is proposed to replace all other pressure 10’exa- E 10 “ atto- a units. Although the pascal is too small for conven- i0’ peta- P 10’ fernto- f tional clinical use, the kilopascal (10’ pascal) has an 1012 tera- T 102 pico- p i0 giga- G 10” nano- n appropriate magnitude. One kPa is equal to 7.5006 io’ mega- M 10 rnicro- mm Hg; therefore, a blood pressure of 130/80 mm i’ kilo- k 1(1’ rnilli- m Hg would be approximately 17/11 kPa. Objections 102 hecto- h 102 centi- c to its use have been summarized.” 101 deca- da 10’ deci- d An especially difficult problem is the measure- ment of enzymatic activity. The previously intro- our present, and often arbitrary, collection of med- duced international unit is defined as the amount ical units. of enzyme that will catalyze the transformation of A potential disadvantage is danger to the patient 1 micromole of substrate per minute under standard by possible error engendered through unfamiliarity. conditions. Acceptance of this unit has been slow, Furthermore, SI is another change thrust on the and many traditional units are still used. To con- physician, who is already overburdened with sci- form with SI, a new base unit for enzymatic activity entific advances and must commit to memory a named the katal ( 1 mole per second) has recently new set of normal values. Also, the logistic consid- been proposed, but it is not an official recommen- erations of recalibration, new report forms, and dation. A wide variety of methods and conditions reeducation are considerable.” are used to measure enzymes, such as pH and temperature. Attempts are being made at the inter- SPECIAL PROBLEMS national level to standardize assay conditions. Ad- ditionally, the mass and purity of proteins are com- Two of the SI-derived units relating to medicine monly unknown. One country suggested that no are unknown to most clinicians.” The existence of change be made in units of tests already being a clear-cut advantage to medicine is debatable. It performed. As new assays are introduced, moles per has been recommended that the joule replace the second (or a submultiple) might be used.’4 calorie in nutrition and dietetics. One calorie equals 4.184 J; therefore, a 1,000-calorie diet equals a 4.18 RECEPTION AND EXPERIENCE IN MEDICINE kilojoule diet. There is dispute about its adoption in the United States, although there is support for Positive reactions from the medical community its use in Great Britain.’2 Equally unfamiliar is the have included the World Health Organization’s rec-

AMERICAN ACADEMY OF PEDIATRICS 661 Downloaded from www.aappublications.org/news by guest on September 30, 2021 ommendation that SI be adopted by medicine sicians? In the Netherlands, 53 senior specialists in worldwide. In 1976 an international symposium internal medicine, who used SI for two to five years, sponsored by the World Association of Societies of were polled. Fifteen said they grasped the units in Pathology, the United States National Bureau of three months, 20 needed from three months to one Standards, and the American Medical Association year, and 18 required longer. More importantly, 47 also endorsed SI.’ The Journal of the American did not think substance concentration enabled them Medical Association has committed itself toward to provide better treatment. Eighteen felt the use progressive usage of SI,’ as has the American of SI units provided them with better insight into Journal of Clinical Pathology.’6 The Annals of chemical processes. In Canada, after six months, Internal Medicine announced a positive editorial 16% of a medical staff no longer converted SI to policy regarding SI, but it intends to maintain a traditional units, and 78% occasionally did It is “balance between innovation and compre- vital to further document advantages and disadvan-

‘7 tages actually experienced in those countries using A study committee of the Massachusetts Medical SI. Society, charged to consider the principle that “changes in well established units be made only when definite advantages to the physician or the MEDICAL LITERATURE patient have been clearly demonstrated,” suggested that there be “no abrupt change in the current use Contemporary medical literature in the United of mass concentration.” ‘ More recently, the Coun- States has fallen “out of step” with many of the cil on Scientific Affairs of the American Medical prominent European medical journals, which now Association “advises that the AMA proceed to de- report in SI units. Many readers in the United velop a wide concensus on how broadly SI units States are unprepared to interpret data recorded in should be adopted by medical groups as well as unfamiliar terms. Likewise, non-Americans are now medically oriented groups: nurses, biomedical sci- beginning to lose familiarity with conventional entists, laboratory technicians, other paramedical units. This situation is intolerable and detrimental groups, and manufacturers of medical and labora- to progress in medicine, and it eventually will ad- tory equipment. It suggests a broad educational versely affect patient care. But it is avoidable. effort, once new units have been generally decided Medical journals both here and abroad should upon, to disseminate the information widely before publish data in recommended SI and traditional a prearranged transition date. For a year or more units.2’ Appropriate conversion data could be in- prior to the transition date, new units would be cluded. The educational benefit, as well as clarity used parenthetically with the comparable old units of communication, would be great. Medical person- in all AMA and other cooperating publications. For nel in this country could begin thinking in new at least a year after the transition date, the old units terminology as well as begin testing the advantages will be used parenthetically with the new. of SI. Hopefully, a dual reporting system would avoid confusion and inaccuracy, as well as the in- Until the above arrangements can be brought to frui- ability to interpret data, while promoting interna- tion, the Council makes the following recommendations tional medical communication. Most importantly, regarding the use of SI units in clinical chemistry: by familiarizing ourselves with SI, the members of 1. That the use of mass concentration units (wgt/vol) be retained by medical laboratories until it is shown that the United States’ medical community might then a change to mole concentrations will improve patient care participate more fully in the further refinement of (diagnosis, treatment, or follow-up), or prove a significant the system. We could assist in perfecting and ex- advantage with respect to laboratory measurement tech- tending the system in a manner acceptable to Amer- nique. ican medical scientists rather than having a system 2. That no abrupt changes in the current use of mass that is completed elsewhere thrust on us. concentrations, or in mihiequivalent units for certain The disadvantage to dual reporting would be the electrolytes, be undertaken until an overall plan and extra time demanded of authors to supply data in schedule has been agreed upon by representative medi- two forms. However, this is not an unreasonable cally oriented groups and appropriate councils of the demand of careful investigators. Dual reporting American Medical would imply no firm commitment to SI in its en- SI would likely be much more readily accepted tirety, but rather a willingness to familiarize and by physicians if they could better monitor patients, participate in the process of international agree- diagnose diseases, or treat patients. The proponents ment. Only through such familiarity will physicians of the system have described theoretical advantages be able to test the declared logic and beneficial without demonstrating actual benefits. What has qualities of the system. Several helpful references the reported experience with SI been among phy- for authors and readers are available.’9 14,22

662 PEDIATRICS Vol. 65 No. 3 March 1980 Downloaded from www.aappublications.org/news by guest on September 30, 2021 RECOMMENDATIONS FOR THE PRESENT COMMITTEE ON HOSPITAL CARE, 1978-79 Arno R. Hohn, MD, Chairman Suggestions have been made in hospitals for con- version to the metric system.24 The Committee on Alfred B. Amler, MD Paul S. Bergeson, MD Hospital Care joins in supporting hospital adoption Harvey R. Gold, MD of the metric system in the following hospital areas: Stewart L. Griggs, MD ( 1 ) the recording of all patient measurements, in- Gerald B. Shattuck, MD cluding temperature (in Celsius scale), body mass (in ), and linear dimensions (in meters or Stanford A. Singer, MD subunits); (2) internal ordering and administering Edwin Ide Smith, MD Willis A. Wingert, MD of all drugs and medication (in mass concentration for the present); (3) food service and dietary for- mulas (the calorie should be retained for the pres- REFERENCES ent); (4) all reports and records; and (5) external ordering and purchasing. 1. Brief Systems with a Chart of the Modernized Metric System. National Bureau of Standards, Also encouraged (although not an SI term) is the Special Publication 304A, revised August 1976 keeping of time records on the 24-hour clock to 2. Baron DN: SI units. Br Med J 4:509, 1974 3. Lehmann HP: Metrication of clinical laboratory data in SI avoid confusion between AM and PM notations. Ad- units. Am J Clin Pathol 65:2, 1976 vantages to hospitals have been listed and proce- 4. International Union of Pure and Applied Chemistry Com- dures for hospital implementation suggested, in- mission on Quantities and Units, Clinical Chemistry and cluding involvement of boards of directors, use of International Federation of Clinical Chemistry: Expert panel on quantities and units. List of quantities in clinical chem- target dates, and training programs.2’ Successful istry recommendation 1973. Pure Appi Chem 37:519, 549, hospital experiences have been documented.2’27 1974 5. Metric Conversion Act of1975, Public Law 94-168. 89 Stat. 1007 6. McGehan FP: America joins a metric world. Dimensions (National Bureau of Standards) 60:6, February 1976 RECOMMENDATIONS FOR THE FUTURE 7. Copeland BE: SI units: A clarification. Am J (‘tin Pathol 65:20, 1976 The Committee on Hospital Care recommends 8. Young DS: Standardized reporting of laboratory data: The that the American Academy of Pediatrics join with desirability of using SI units. N Engi .1 Med 29():368, 1974 the American Medical Association and other inter- 9. Lippert H, Lehmann HP: SI Units in Medicine: An Intro- duction to the International System of Units with (‘onver- ested organizations such as the American National sion Tables and Normal Ranges. Baltimore, Urban and Metric Council to further clarify biomedical issues Schwarzenberg, 1978 concerning SI. Among the specific issues which 10. Shepard I)A: The metric system, the international system of units (SI) and medicine. Can Med Assoc J 112:799, 1975 should be examined are the following: (1) dual 11. Huth El: Metricating medicine: How fast, how far? N Engi reporting by American medical journals; (2) reten- J Med 290:398, 1974 tion of the term pH, with simultaneous reporting of 12. The Royal Society: Metric units, conversion factors and nomenclature in nutritional and food sciences: Report of the hydrogen ion concentration in nanomoles per liter; subcommittee on metrication of the British National Corn- (3) use of substance versus mass concentration or mittee for Nutritional Sciences. Proc Nutr Soc 31 :239, Sep- a combination of the two; (4) use of millimoles per tember 1972 13. Rose JC: Pressures on the millimeter of mercury. N EngI J liter for hemoglobin concentration versus per Med298:1361, 1978 deciliter; (5) use of freezing point depression versus 14. Pannall PR: The introduction of SI units and the standard- retention of reporting of osmolality in traditional ization of laboratory reports: Recommendations of the South African As.sociation of Clinical Biochemists. S Afr Med J terms; (6) use of the pascal versus millimeter of 50:1539, 1976 mercury; (7) use of the joule versus calorie; (8) 15. Barclay WR: Standardizing units to measurements. JAMA 236:1981, 1976 encouragement of academic centers to use and 16. Beeler MS: Metrication from crawl to walk. Am J Clin teach SI; and (9) use of the katal if it is officially Pathol 65:19, 1976 recommended for the unit of enzyme activity. 17. Huth EJ: SI for metric medicine? Ann Intern Med 76:322, 1972 Once agreement has been reached on desirable 18. Copeland BE, Beautyman W. Bradley R. et al: Study corn- SI uses, programs of orderly adoption should be mittee to evaluate changes in units of clinical chemistry implemented. tests. N Engi J Med 293:43. 1975 19. Report E of the Council on Scientific Affairs of the American Medical Association (A-78): Adoption of International Sys- tern of (SI) Units for clinical chemistry. American Medical ACKNOWLEDGMENTS Association House of I)elegates Proceedings, St Louis, June 18-22, 1978, p 291 The Committee is grateful for invaluable input by the 20. Karnauchow PN, Suvanto L: Experience with SI units in following individuals in the preparation of the manu- biochemistry. Can Med Assoc J 114:533, 1976 script: H. Peter Lehmann, PhD, Bradley E. Copeland, 21. Young 1)5: SI units for clinical laboratory data. .JAMA MD, and Alan K. Done, MD. 240:1618, 1978

AMERICAN ACADEMY OF PEDIATRICS 663 Downloaded from www.aappublications.org/news by guest on September 30, 2021 22. Young 1)5: Normal laboratory values” (case records of the Canadian teaching hospital. Can Med Assoc J 1 14:536, 1976 Massachusetts General Hospital) in SI units. N EngI J Med 25. Rennie G: Yes! to metric system conversion. Hosp Prog 292:795, 1975 58:36, 1977 23. Frost I)V, Helgren FJ, Sokol LF: Metric Handbook for 26. Timmerman MR, Lobel J: Beating the deadline: Converting Hospitals, ed 2. Boulder, Colorado, US Metric Association, to metric system now. Hosp Prog 58:72, 1977 Inc. 1975 27. Weissman ME: No more , no more pounds. Hospitals 24. Itiaba K, Crawhall JC: Metrication on the move in a large 51:103, 1977

DR WILLIAM A. ALCOTT ON MATERNAL DOSING AND DRUGGING AS THE MAJOR CAUSE OF INFANT MORTALITY IN 1854

Among the most outspoken of American health reformers of the mid-nine- teenth century was Dr William A. Alcott of Boston. The health reformers offered an alternative to a public dissatisfied with the heroic practice of most physicians of this period by emphasizing that the individual had it in his or her own power to keep all members of the family in good health by forgoing most of the drugs prescribed by allopathic physicians. Alcott’ was particularly concerned with the huge extent of infant mortality caused by “maternal dosing and drugging.” He wrote: But whether ignorant or somewhat enlightened, the vast majority of our mothers doctor, more or less, their own children. At least, if they refuse to call it doctoring, they give them a vast amount of small elixirs, cordials, etc. The closets of not a few house- keepers are a complete apothecary’s shop. They may, it is true, have smaller parcels then the regular apothecary; but they have almost as great an assortment. And they not only keep it; they administer it. They may not intend it; they do not mean to give much; sometimes they really think they do not give much. But it comes to pass, in the course of the year, that much is given by somebody; and I greatly fear that the mother must be

held responsible for it. ... But now for the consequences of this maternal dosing; for this it is with which medical men have chiefly to do. Next to bad food and wretched cookery, as I have before intimated, this error is productive of more sickness and premature death than any other.

No physician knows what to do with a sick child, who has been thus tampered with. ... He may indeed guess a little better than others; but even he will often guess wrong. Their first passages are irritated, and perhaps inflamed; and if it were possible to make the right appliances either internally or externally, it would stifi puzzle the wisest head to know how to apportion the quantity so as to be more likely to do good than harm. Diseases, in these circumstances, as you know, are more apt to be severe and complicated, and the termination more likely to be fatal, especially if much medicine is used. The worst remains to be told. As it is not always easy to trace the cause of severe, protracted or fatal infantile disease to maternal error, we not only contrive to kill, from generation to generation, by thousands and tens of thousands; but we partly kill by

millions. ... We bring on, gradually, some disease or other; or we render an inherited disease, which might have been mild, very severe, or early fatal; or we aggravate, by over dosing, the symptoms of acquired diseases from other causes. Noted by T.E.C., Jr, MD

REFERENCE

1. Alcott WA: Mortality among children. Boston Med Sung J 51:260, 1854

664 PEDIATRICS Vol. 65 No. 3 March 1980 Downloaded from www.aappublications.org/news by guest on September 30, 2021 Metrication and SI Units Arno R. Hohn, Alfred B. Amler, Paul S. Bergeson, Harvey R. Gold, Stewart L. Griggs, Gerald B. Shattuck, Stanford A. Singer, Edwin Ide Smith and Willis A. Wingert Pediatrics 1980;65;659

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Downloaded from www.aappublications.org/news by guest on September 30, 2021 Metrication and SI Units Arno R. Hohn, Alfred B. Amler, Paul S. Bergeson, Harvey R. Gold, Stewart L. Griggs, Gerald B. Shattuck, Stanford A. Singer, Edwin Ide Smith and Willis A. Wingert Pediatrics 1980;65;659

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Pediatrics is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1948. Pediatrics is owned, published, and trademarked by the American Academy of Pediatrics, 345 Park Avenue, Itasca, Illinois, 60143. Copyright © 1980 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 1073-0397.

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