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SI units
"/ would have everie man write what he knowes and no more."—MONTAIGNE
BRITISH JOURNAL OF ANAESTHESIA VOLUME 41, No. 12
DECEMBER 1969 EDITORIAL SI UNITS
its size. The provision of submultiples and multiples now meets this minor complaint but there is a restriction on the number of these factors. At first sight the newton per square metre sounds a more difficult term to use than centimetres of water. Another name, used in some other countries, the "Pascal", may be more acceptable while "bar", or "millibar", may be easier to say. However, as calculations resulting in composite units should always be in the appropriate basic SI units, it is probably preferable to retain the newton per square metre as the name for the unit of pressure. A further difficulty which anaesthetists may have with the newton per square metre is that we are not accustomed to relating pressure to unit area in the units which we currently use. Use of the new system should encourage clarity of thought about this. In this issue Dr. D. W. Hill gives an account of the application of SI units in anaesthetics. The example, which he gives in his article, about the units for blood pressure serves to illustrate the fact that, once the change to SI units is made, we shall have merely to remember a new scale of numerical values which will, of course, be suitably adjusted to whole numbers. Some of the measurements of circulatory physiology involving blood pressure may become more readily manipulated with the departure of many correction factors which are, at present, essential. In this latter respect the new units are desirable, but otherwise, in terms of blood pressure, medicine is unlikely to benefit. As anaesthetists we owe a great deal to the scientific discipline of physics in our understanding of many aspects of our work. We should therefore examine the decisions of physicists carefully. Previous developments in the terminology of physics have only been accepted somewhat tardily by medicine to the extent that subsequent [continued on p. 1028
Downloaded from http://bja.oxfordjournals.org/ at The Australian National University on March 14, 2015
The British Standards Institute has recommended that this country should adopt SI Units (Systeme Internationale d'Unites). In other fields the BSI has done magnificent work and, notwithstanding the less-than-unanimous support of scientists for this particular recommendation, there seem to be many advantages of universal adoption of the Institute's advice. The initial lack of full and enthusiastic agreement may reflect conservatism but this should not be allowed to obscure the main advantages of a coherent system of units when that system is adopted by everyone. In a coherent system of units the product, or quotient, of two quantities in the system is the unit of the resultant quantity. Many traditional British units are non-coherent; for example, the acre is not coherently linked to the foot, in contrast to the square-foot. Engineers should welcome many of the suggested changes since they stand to lose some of the more cumbersome units, which bear little or no relationship to the fundamental units of physics and thus cause them, and others, confusion. Strangely enough it is from the engineers that some of the main opposition has come. Manufacturers of pressure gauges, will, at last, use only one unit of pressure and thereby a continual source of annoyance will be removed. No longer shall we have to translate from "engineering" units to "physico-medical" units. A particular and practical advantage to anaesthetists in their everyday work is that cylinder manometers will be calibrated using the same units as those of monitoring apparatus and automatic lung ventilators. Similarly, calculation of respiratory work should be easier, firstly in that only metric arithmetic is involved and secondly because the answer will be expressed in coherent units. One unit which does concern anaesthetists is that for pressure—the newton per square metre— which was initially criticized on the grounds of
1028
Telfer, A. B. M., MacDonald, D. J. F., and Dinwoodie, A. J. (1964). Familial sensitivity to suxamethonium due to atypical pseudocholinesterase. Brit. med. J., 1, 153. Wylie, W. D., and Churchill-Davidson, H. C. (1966). A Practice of Anaesthesia, 2nd ed. London: Lloyd-Luke. Zaimis, E. J., Cannard, T. H., and Price, H. L. (1958). Effects of lowered muscle temperature on neuromuscular blockade in man. Science, 128, 34. UN AUTRE FACTEUR CONTRIBUANT A LA SENSIBILITE HEREDITAIRE AU SUXAMETHONIUM SOMMAIRE
On a etudie l'effet de la temperature de reaction sur l'activite de la cholinesterase serique de sujets normaux et de personnes avec des variantes enzymatiques hereditaires. Des graves anomalies ont ete not^es chez les phenotypes les plus sensibles au relachant musculaire suxamethonium. Les auteurs presument que l'inactivation des variantes de cholinesterase a la temperature corporelle pourrait contribuer a la paralysie prolongee, qu'on trouve dans ces cas. In index sur de l'activite de la cholinesterase serique n'est obtenu que lorsque la determination se fait a 37 "C. EIN WEITERER FAKTOR, DER BEI ANGEBORENER SUXAMETHONIUMOBEREMPFINDLICHKEIT VON BEDEUTUNG 1ST ZUSAMMENFASSUNG
Der Effekt der Reaktionstemperatur auf die SerumCholinesterase-Aktivita't von normalen Personen und solchen mit angeborenen Enzym-Varianten wurde untersucht. Bei den am empfindlichsten auf das Muskelrelaxans reagierenden Phanotypen sind erhebliche Anomalien beobachtet worden. Es wird vermutet, dafl die bei normaler Korpertemperatur vorkommende Inaktivierung bei Cholinesterase-Defekten moglicherweise ein Faktor ist, der zu der in solchen Fallen auftretenden prolongierten Paralyse beitragt. Ein korrekter Index der Cholinesterase-Aktivitat ist nur dann zu erzielen, wenn die Bestimmung bei 37 °C durchgefuhrt wird.
EDITORIAL continued from p. 1015 reversionary changes by physicists have almost coincided with medicine's adoption of the primary change! This must not happen in the present situation, if for no other reason than that we stand to gain a great deal from using a coherent system. Of course, the adoption of this system will not suddenly promote medicine to an exact and precise subject like physics, but the rationalization of the units of measurement will benefit everyone. Furthermore communication is bound to improve between pure scientists and medical scientists; indeed this seems to be one of the main advantages. The speed of change-over will undoubtedly
be slow because there are the obvious problems of transition to be overcome. A cautious rate of change also has the advantage of presenting an opportunity for acclimatization to take place. Initially the process would perhaps be assisted if old and new units were always quoted together but this practice should not be excessively prolonged. Whilst we must beware of hasty action we must also avoid the greater risk of deciding to do nothing. Editorial advice to authors should not only be clear, but also uniform, so that there are excuses neither for sentimental attachment to archaic systems nor for flamboyant esotericism!
Downloaded from http://bja.oxfordjournals.org/ at The Australian National University on March 14, 2015
Hart, S. M., and Mitchell, J. V. (1962). Suxamethonium in the absence of pseudo-cholinesterase. Brit. J. Anaesth., 34, 207. International Union of Biochemistry (1965). Enzyme Nomenclature. Amsterdam: Elsevier. Kalow, W. (1959). The distribution, destruction and elimination of muscle relaxants. Anesthesiology, 20, 505. Genest, K. (1957). A method for the detection of atypical forms of human serum cholinesterase: determination of dibucaine numbers. Canad. J. Biochem., 35, 339. Lindsay, H. A. (1955). A comparison of optical and manometric methods for the assay of human serum cholinesterase. Canad. J. Biochem., 33, 568. Staron, N. (1957). On distribution and inheritance of atypical forms of human serum cholinesterase as indicated by dibucaine numbers. Canad. J. Biochem., 35, 1305. King, J. (1965). Practical Clinical Enzymology. London: Van Nostrand. Lehmann, H., and Liddell, J. (1969). Human cholinesterase (pseudocholinesterase): genetic variants and their recognition. Brit. J. Anaesth., 41, 235. Blackwell, B., O'Connor, D. C , and Daws, A. V. (1963). Two further serum pseudocholinesterase phenotypes as causes of suxamethonium apnoea. Brit. med. J., 1, 116. Patston, V., and Ryan, E. (1958). The inheritance of an idiopathic low plasma cholinesterase level. J. din. Path., 11, 554. Ryan, E. (1956). The familial incidence of low pseudocholinesterase level. Lancet, 2, 124. Simmons, P. H. (1958). Sensitivity to suxamethonium: apnoea in two brothers. Lancet, 2, 981. Liddell, J., Lehmann, H., and Silk, E. (1962). A "silent" pseudocholinesterase gene. Nature, 193, 561. Motulsky, A. G. (1964). Pharmacogenetics; in Progress in Medical Genetics, Vol. I l l (eds. Steinberg, A. G., and Beam, A. G.). New York: Grune and Stratton.
BRITISH JOURNAL OF ANAESTHESIA
BRITISH JOURNAL OF ANAESTHESIA VOLUME 41, No. 12
DECEMBER 1969 EDITORIAL SI UNITS
its size. The provision of submultiples and multiples now meets this minor complaint but there is a restriction on the number of these factors. At first sight the newton per square metre sounds a more difficult term to use than centimetres of water. Another name, used in some other countries, the "Pascal", may be more acceptable while "bar", or "millibar", may be easier to say. However, as calculations resulting in composite units should always be in the appropriate basic SI units, it is probably preferable to retain the newton per square metre as the name for the unit of pressure. A further difficulty which anaesthetists may have with the newton per square metre is that we are not accustomed to relating pressure to unit area in the units which we currently use. Use of the new system should encourage clarity of thought about this. In this issue Dr. D. W. Hill gives an account of the application of SI units in anaesthetics. The example, which he gives in his article, about the units for blood pressure serves to illustrate the fact that, once the change to SI units is made, we shall have merely to remember a new scale of numerical values which will, of course, be suitably adjusted to whole numbers. Some of the measurements of circulatory physiology involving blood pressure may become more readily manipulated with the departure of many correction factors which are, at present, essential. In this latter respect the new units are desirable, but otherwise, in terms of blood pressure, medicine is unlikely to benefit. As anaesthetists we owe a great deal to the scientific discipline of physics in our understanding of many aspects of our work. We should therefore examine the decisions of physicists carefully. Previous developments in the terminology of physics have only been accepted somewhat tardily by medicine to the extent that subsequent [continued on p. 1028
Downloaded from http://bja.oxfordjournals.org/ at The Australian National University on March 14, 2015
The British Standards Institute has recommended that this country should adopt SI Units (Systeme Internationale d'Unites). In other fields the BSI has done magnificent work and, notwithstanding the less-than-unanimous support of scientists for this particular recommendation, there seem to be many advantages of universal adoption of the Institute's advice. The initial lack of full and enthusiastic agreement may reflect conservatism but this should not be allowed to obscure the main advantages of a coherent system of units when that system is adopted by everyone. In a coherent system of units the product, or quotient, of two quantities in the system is the unit of the resultant quantity. Many traditional British units are non-coherent; for example, the acre is not coherently linked to the foot, in contrast to the square-foot. Engineers should welcome many of the suggested changes since they stand to lose some of the more cumbersome units, which bear little or no relationship to the fundamental units of physics and thus cause them, and others, confusion. Strangely enough it is from the engineers that some of the main opposition has come. Manufacturers of pressure gauges, will, at last, use only one unit of pressure and thereby a continual source of annoyance will be removed. No longer shall we have to translate from "engineering" units to "physico-medical" units. A particular and practical advantage to anaesthetists in their everyday work is that cylinder manometers will be calibrated using the same units as those of monitoring apparatus and automatic lung ventilators. Similarly, calculation of respiratory work should be easier, firstly in that only metric arithmetic is involved and secondly because the answer will be expressed in coherent units. One unit which does concern anaesthetists is that for pressure—the newton per square metre— which was initially criticized on the grounds of
1028
Telfer, A. B. M., MacDonald, D. J. F., and Dinwoodie, A. J. (1964). Familial sensitivity to suxamethonium due to atypical pseudocholinesterase. Brit. med. J., 1, 153. Wylie, W. D., and Churchill-Davidson, H. C. (1966). A Practice of Anaesthesia, 2nd ed. London: Lloyd-Luke. Zaimis, E. J., Cannard, T. H., and Price, H. L. (1958). Effects of lowered muscle temperature on neuromuscular blockade in man. Science, 128, 34. UN AUTRE FACTEUR CONTRIBUANT A LA SENSIBILITE HEREDITAIRE AU SUXAMETHONIUM SOMMAIRE
On a etudie l'effet de la temperature de reaction sur l'activite de la cholinesterase serique de sujets normaux et de personnes avec des variantes enzymatiques hereditaires. Des graves anomalies ont ete not^es chez les phenotypes les plus sensibles au relachant musculaire suxamethonium. Les auteurs presument que l'inactivation des variantes de cholinesterase a la temperature corporelle pourrait contribuer a la paralysie prolongee, qu'on trouve dans ces cas. In index sur de l'activite de la cholinesterase serique n'est obtenu que lorsque la determination se fait a 37 "C. EIN WEITERER FAKTOR, DER BEI ANGEBORENER SUXAMETHONIUMOBEREMPFINDLICHKEIT VON BEDEUTUNG 1ST ZUSAMMENFASSUNG
Der Effekt der Reaktionstemperatur auf die SerumCholinesterase-Aktivita't von normalen Personen und solchen mit angeborenen Enzym-Varianten wurde untersucht. Bei den am empfindlichsten auf das Muskelrelaxans reagierenden Phanotypen sind erhebliche Anomalien beobachtet worden. Es wird vermutet, dafl die bei normaler Korpertemperatur vorkommende Inaktivierung bei Cholinesterase-Defekten moglicherweise ein Faktor ist, der zu der in solchen Fallen auftretenden prolongierten Paralyse beitragt. Ein korrekter Index der Cholinesterase-Aktivitat ist nur dann zu erzielen, wenn die Bestimmung bei 37 °C durchgefuhrt wird.
EDITORIAL continued from p. 1015 reversionary changes by physicists have almost coincided with medicine's adoption of the primary change! This must not happen in the present situation, if for no other reason than that we stand to gain a great deal from using a coherent system. Of course, the adoption of this system will not suddenly promote medicine to an exact and precise subject like physics, but the rationalization of the units of measurement will benefit everyone. Furthermore communication is bound to improve between pure scientists and medical scientists; indeed this seems to be one of the main advantages. The speed of change-over will undoubtedly
be slow because there are the obvious problems of transition to be overcome. A cautious rate of change also has the advantage of presenting an opportunity for acclimatization to take place. Initially the process would perhaps be assisted if old and new units were always quoted together but this practice should not be excessively prolonged. Whilst we must beware of hasty action we must also avoid the greater risk of deciding to do nothing. Editorial advice to authors should not only be clear, but also uniform, so that there are excuses neither for sentimental attachment to archaic systems nor for flamboyant esotericism!
Downloaded from http://bja.oxfordjournals.org/ at The Australian National University on March 14, 2015
Hart, S. M., and Mitchell, J. V. (1962). Suxamethonium in the absence of pseudo-cholinesterase. Brit. J. Anaesth., 34, 207. International Union of Biochemistry (1965). Enzyme Nomenclature. Amsterdam: Elsevier. Kalow, W. (1959). The distribution, destruction and elimination of muscle relaxants. Anesthesiology, 20, 505. Genest, K. (1957). A method for the detection of atypical forms of human serum cholinesterase: determination of dibucaine numbers. Canad. J. Biochem., 35, 339. Lindsay, H. A. (1955). A comparison of optical and manometric methods for the assay of human serum cholinesterase. Canad. J. Biochem., 33, 568. Staron, N. (1957). On distribution and inheritance of atypical forms of human serum cholinesterase as indicated by dibucaine numbers. Canad. J. Biochem., 35, 1305. King, J. (1965). Practical Clinical Enzymology. London: Van Nostrand. Lehmann, H., and Liddell, J. (1969). Human cholinesterase (pseudocholinesterase): genetic variants and their recognition. Brit. J. Anaesth., 41, 235. Blackwell, B., O'Connor, D. C , and Daws, A. V. (1963). Two further serum pseudocholinesterase phenotypes as causes of suxamethonium apnoea. Brit. med. J., 1, 116. Patston, V., and Ryan, E. (1958). The inheritance of an idiopathic low plasma cholinesterase level. J. din. Path., 11, 554. Ryan, E. (1956). The familial incidence of low pseudocholinesterase level. Lancet, 2, 124. Simmons, P. H. (1958). Sensitivity to suxamethonium: apnoea in two brothers. Lancet, 2, 981. Liddell, J., Lehmann, H., and Silk, E. (1962). A "silent" pseudocholinesterase gene. Nature, 193, 561. Motulsky, A. G. (1964). Pharmacogenetics; in Progress in Medical Genetics, Vol. I l l (eds. Steinberg, A. G., and Beam, A. G.). New York: Grune and Stratton.
BRITISH JOURNAL OF ANAESTHESIA