The chemical society An emotional debate over the decision to remove saccharin from various consumer products because of experimentally produced carcinogenesis was held at the Canadian Medical Association (CMA) General Council in June 1977. Before the debate, a number of resolutions had been presented to General Council on the subject of contamination of food by pesticides, herbicides, antibiotics, heavy metals and other substances potentially hazardous to man.1 In November the Science Council of Canada presented a report entitled "Policies and Poisons. The Containment of Long-term Hazards to Human Health in the Environment and in the Workplace".2 More recently the news media has reported in detail the concerns expressed in New Brunswick and Nova Scotia over the use of aerial spraying to control the spruce budworm. For the past year there has been concern in the Okanagan Valley over contamination of the water supplies by herbicides and pesticides. A recent transformer fire in Toronto released large quantities of polychlorinated biphenyls into the surrounding environment. These are some examples of the chemical environment in which we live today. Each year more than 3000 new chemical substances are brought onto the Canadian market. Chemistry touches our lives constantly; basic necessities such as food, clothing and housing would be considerably different without chemistry. The benefits of chemistry play such a large part in our daily lives that we take them for granted - chemistry produced man-made fibres, detergents, plastics and resins, biologic and pharmaceutical agents, fuels and the associated byproducts of oil refining. The list is long and impressive. But are we producing more hazards than benefits? It has been discovered, in retrospect, that some chemicals, either alone or in combination, that were once believed to be harmless can be dangerous. Some are considered so dangerous that their continued manufacture is questionable.
Chemists and the chemical industry adopted for some constituents has to are striving constantly to produce new be amended considerably. More and substances that can enhance the quality more impurities are being detected of life, but at the same time they must that may be occurring naturally or ensure that the individual and the en- may be chemically manufactured. Some vironment are not harmed. Is this being of these components may produce candone? I believe there is a great amount cer in experimental animals. Scientific of "molecular manipulation" to pro- evidence suggests that there are acceptduce a "new" product. The product is able limits for most naturally occurring then marketed in such a way as to lead contaminants, but opinion is divided the consumer to believe the quality of over the tolerance for synthetically prolife will be enhanced. It may be that duced substances. the "need" has been created by the Do our foods need to contain artimarketing, and that there may be ha- ficial colourings and sweeteners, and zards that completely outweigh the to be packed in synthetic wrappings, benefits. some components of which may be abHow are value judgements made in sorbed by the food? Do the benefits these instances? It seems to me that outweigh the hazards? I do not believe the onus is almost entirely on the con- so. It appears to me that the consumer sumer, who is expected to assess the blindly accepts products simply because risk factor. High pressure advertising he or she is brainwashed into believing techniques minimize the awareness of that the quality of life will suffer in risk so that any probability of danger the absence of those products. is given little consideration. The conOne aspect of our chemical society sequences of misuse and abuse are ever is beginning to receive more attention present and are stressed much more and justifiably so. This is the risk enthan the risks of use. dured by the worker who is closely Thalidomide was regarded as a safe involved with the manufacturing of drug until events showed the relation these chemical products. Recent epidebetween it and limb abnormalities in miologic reports link disease with inthe newborn. Until then the perceived gestion, inhalation or absorption of benefits outweighed the risk; the rela- synthetics, yet the molecular manipulation was then completely reversed. The tion goes on. risk associated with the oral contracepHow then do we approach this probtive in older women now appears to lem? There are two main choices: voloutweigh the benefits, yet the scoffers untary control or legal control. With and doubters are marshalling their voluntary control, the consumer can forces. The tobacco industry consistent- make a value judgement by weighing ly has refused to accept the scientific known risks against known benefits. evidence of the relation between smok- The consumer also may boycott a ing and cardiovascular disease. Lack- product if a high-risk factor is pering intestinal fortitude, the industry ceived and by economic pressure may seeks refuge in platitudinous statements therefore force the discontinuation of and glossy advertising promoting "the manufacture. good life". The second option - legal control Perhaps we should be talking about - tends to evoke an emotional reac"acceptable risk", which implies that a tion. Governments are regarded by certain degree of risk is allowable be- many as collections of faceless bucause the alternative may be unaccept- reaucrats; overlooked in scientific matable. As technology improves, the abil- ters are the expertise and abilities of ity to distinguish components in a sub- government scientists and scientific stance is increased. Now "parts per opinions sought from many sources, million" is replaced by "parts per tril- which provide the data on which decilion": this means that the zero level sions are made. Some members of CMA JOURNAL/MARCH 4, 1978/VOL. 118 475
General Council indicated their lack of confidence in the bases on which governmental regulations are arrived at by presenting resolutions that would require experimental evidence to be evaluated by the nongovernmental medical scientific community, especially members of the CMA with expertise in urology, oncology and metabolism and that the CMA urge the Government of Canada to refrain from banning any drug or chemical until the reasons for this action have been evaluated by the scientific community independent of government influence;1 these resolutions were not approved. Regulations in controls must recognize the abstract. As our knowledge of diseases such as cancer increases, and the degree of uncertainty as to causative factors diminishes, the regulations should be amended. Until then, however, known and potential risk fac-
tors must not be lost from sight in the plethora of glossy advertisements urging everyone to "buy this brand you can't afford to be without it". If the emotional aspects can be eliminated and the probabilities scientifically evaluated, and if the scientific feats are presented honestly and clearly the consumer will be in a better position to make the value judgements necessary and to answer the question, Do the risks outweigh the benefits? Concurrent with this should be a more critical approach by the consumer. Do we need 3000 new chemicals each year when we don't know what they are doing to us and to our environment? Should not manufacturers become more aware of the real need to improve the quality of life rather than embarking on the synthesis of a chemical product for production's sake alone? Currently before the courts in
the United States are felony indictments against the executives of a company manufacturing pesticides. The charges are conspiracy to conceal from the Environmental Protection Agency results of tests that showed that two widely used pesticides may be carcinogenic in humans. The philosophy of medicine has always been primum non nocere. It is a motto that should be adopted by the chemical industry. J.S. BENNETT, MB, FRCS[C], FACOG Director, professional affairs Canadian Medical Association
References I. Proceedings of the 110th Annual Meeting including the Transactions of the General Council, Can Med Assoc, Quebec City, June 20-22, 1977 2. Science Council of Canada: Policies and Poisons. The Containment of Long-term Hazards to Human Health in the Environment and in the Workplace, Don Mills, Thorn Pr, 1977
Mixed venous carbon dioxide tension measured by rebreathing Arterial blood-gas measurements were introduced to routine clinical practice nearly 20 years ago; since then they have become indispensable for the evaluation and management of patients with disturbances of pulmonary gas exchange. However, in recent years they have been criticized for two reasons. First, a 24-hour blood-gas service is very expensive to maintain, particularly in smaller hospitals, and second, arterial blood-gas determinations provide only limited information about the effectiveness of oxygen delivery to and carbon dioxide removal from the tissues. Measurements of blood gases on the venous side are more likely to provide this information because they depend on the balance between mefabolism and blood flow as well as on pulmonary gas exchange. However, in order to measure pulmonary venous blood gases directly, catheterization of the pulmonary artery is required. For some years Campbell1 has argued that indirect measurements of mixed venous carbon dioxide tension (Nco2) are informative as well as being simple and noninvasive. From a rebreathing measurement of Nco2, information is obtained about alveolar ventilation, cardiac output, arterial oxygenation and changes in tissue carbon dioxide, and therefore of tissue pH. With Howell2 he adapted the rebreathing technique of Hackney, Sears and Collier3 to obtain reliable measurements of Pi'co2. Although extensively validated and of clear clinical value, rebreathing methods are not as popular
as they should be, probably for two reasons. First, the method yields indirect estimates of Nco2 and arterial carbon dioxide tension (Paco2); it is difficult to accept an indirect method when direct measurements of arterial blood gases are available. The physiologic and technical factors that may influence the quality of blood-gas measurements in general are poorly appreciated; it also is not well known that such factors have less influence on the measurement of P.co2. Second, the method as first described appeared complex and required a certain "art" to obtain reliable results. Powles and Campbell state in their article in this issue of the Journal (page 501) that they have overcome the obstacles to a wider use of rebreathing by attending to a number of problems: they have "packaged" the equipment, simplified the procedure to make it easier to use, and developed a teaching program suitable for nurses and technologists without a laboratory background. These steps have resulted in the rebreathing method now routinely being used by these professionals in respiratory and intensive care units in Hamilton. Powles and Campbell outline the applications of the rebreathing method. The method may be used as a screening technique to identify alveolar underventilation (high Paco2 and Nco2) or low cardiac output (high Nco. witb normal or low Paco2). In patients without evidence of cardiac malfunction, the PVco2 may be used instead of the Paco2 to follow alveolar ventilation. The
476 CMA JOURNAL/MARCH 4, 1978/VOL. 118
Pirco2 may be used in conjunction with measurements of Paco2 to estimate cardiac output by the indirect Fick method. Finally, they examine the relation between Nco2 and Paco2 and present the logic that enables a point to be identified at which central venous oxygen saturation has decreased to a level at which tissue hypoxia is likely. From the information given in their article the measurement of P.co2 and Paco2 may be used to make clinical decisions and rigorous calculations of these important variables. Because the rebreathing measurement of P.co2 is noninvasive it may be repeated more frequently than "stab" arterial punctures. .Vhen it is used in conjunction with a modern ear oximeter,4 the same information as obtained from arterial blood-gas determinations is available immediately, leading to more continuous monitoring of patients prone to rapid changes in cardiac and respiratory status. NORMAN L. JONES, MB, B5, MD, FRCP, FRCP[C] McMaster University Medical Centre Hamilton, Ont.
References 1. CAMPBELL F.JM: Simplification of Haldane's
apparatus for measuring COs concentration in respired gases in clinical practice. Br Med I 1: 457, 1960 2. CAMPBELL EJM, HOWELL JBL: Rebreathing method for measurement of mixed venous Pco2. Br Med 1 2: 630, 1962 3. HACKNEY 3D, SEARs CH, COLLIER CR: Estimation of arterial CO2 tension by rebreathing technique. I Appi Physiol 12: 425, 1958 4. SAUNDERS NA, PoWEas ACP, Rasuca AS: Ear oximetry: accuracy and practicability in the assessment of arterial oxygenation. Am Rev Respir Dis 113: 745, 1976
Chemists and the chemical industry adopted for some constituents has to are striving constantly to produce new be amended considerably. More and substances that can enhance the quality more impurities are being detected of life, but at the same time they must that may be occurring naturally or ensure that the individual and the en- may be chemically manufactured. Some vironment are not harmed. Is this being of these components may produce candone? I believe there is a great amount cer in experimental animals. Scientific of "molecular manipulation" to pro- evidence suggests that there are acceptduce a "new" product. The product is able limits for most naturally occurring then marketed in such a way as to lead contaminants, but opinion is divided the consumer to believe the quality of over the tolerance for synthetically prolife will be enhanced. It may be that duced substances. the "need" has been created by the Do our foods need to contain artimarketing, and that there may be ha- ficial colourings and sweeteners, and zards that completely outweigh the to be packed in synthetic wrappings, benefits. some components of which may be abHow are value judgements made in sorbed by the food? Do the benefits these instances? It seems to me that outweigh the hazards? I do not believe the onus is almost entirely on the con- so. It appears to me that the consumer sumer, who is expected to assess the blindly accepts products simply because risk factor. High pressure advertising he or she is brainwashed into believing techniques minimize the awareness of that the quality of life will suffer in risk so that any probability of danger the absence of those products. is given little consideration. The conOne aspect of our chemical society sequences of misuse and abuse are ever is beginning to receive more attention present and are stressed much more and justifiably so. This is the risk enthan the risks of use. dured by the worker who is closely Thalidomide was regarded as a safe involved with the manufacturing of drug until events showed the relation these chemical products. Recent epidebetween it and limb abnormalities in miologic reports link disease with inthe newborn. Until then the perceived gestion, inhalation or absorption of benefits outweighed the risk; the rela- synthetics, yet the molecular manipulation was then completely reversed. The tion goes on. risk associated with the oral contracepHow then do we approach this probtive in older women now appears to lem? There are two main choices: voloutweigh the benefits, yet the scoffers untary control or legal control. With and doubters are marshalling their voluntary control, the consumer can forces. The tobacco industry consistent- make a value judgement by weighing ly has refused to accept the scientific known risks against known benefits. evidence of the relation between smok- The consumer also may boycott a ing and cardiovascular disease. Lack- product if a high-risk factor is pering intestinal fortitude, the industry ceived and by economic pressure may seeks refuge in platitudinous statements therefore force the discontinuation of and glossy advertising promoting "the manufacture. good life". The second option - legal control Perhaps we should be talking about - tends to evoke an emotional reac"acceptable risk", which implies that a tion. Governments are regarded by certain degree of risk is allowable be- many as collections of faceless bucause the alternative may be unaccept- reaucrats; overlooked in scientific matable. As technology improves, the abil- ters are the expertise and abilities of ity to distinguish components in a sub- government scientists and scientific stance is increased. Now "parts per opinions sought from many sources, million" is replaced by "parts per tril- which provide the data on which decilion": this means that the zero level sions are made. Some members of CMA JOURNAL/MARCH 4, 1978/VOL. 118 475
General Council indicated their lack of confidence in the bases on which governmental regulations are arrived at by presenting resolutions that would require experimental evidence to be evaluated by the nongovernmental medical scientific community, especially members of the CMA with expertise in urology, oncology and metabolism and that the CMA urge the Government of Canada to refrain from banning any drug or chemical until the reasons for this action have been evaluated by the scientific community independent of government influence;1 these resolutions were not approved. Regulations in controls must recognize the abstract. As our knowledge of diseases such as cancer increases, and the degree of uncertainty as to causative factors diminishes, the regulations should be amended. Until then, however, known and potential risk fac-
tors must not be lost from sight in the plethora of glossy advertisements urging everyone to "buy this brand you can't afford to be without it". If the emotional aspects can be eliminated and the probabilities scientifically evaluated, and if the scientific feats are presented honestly and clearly the consumer will be in a better position to make the value judgements necessary and to answer the question, Do the risks outweigh the benefits? Concurrent with this should be a more critical approach by the consumer. Do we need 3000 new chemicals each year when we don't know what they are doing to us and to our environment? Should not manufacturers become more aware of the real need to improve the quality of life rather than embarking on the synthesis of a chemical product for production's sake alone? Currently before the courts in
the United States are felony indictments against the executives of a company manufacturing pesticides. The charges are conspiracy to conceal from the Environmental Protection Agency results of tests that showed that two widely used pesticides may be carcinogenic in humans. The philosophy of medicine has always been primum non nocere. It is a motto that should be adopted by the chemical industry. J.S. BENNETT, MB, FRCS[C], FACOG Director, professional affairs Canadian Medical Association
References I. Proceedings of the 110th Annual Meeting including the Transactions of the General Council, Can Med Assoc, Quebec City, June 20-22, 1977 2. Science Council of Canada: Policies and Poisons. The Containment of Long-term Hazards to Human Health in the Environment and in the Workplace, Don Mills, Thorn Pr, 1977
Mixed venous carbon dioxide tension measured by rebreathing Arterial blood-gas measurements were introduced to routine clinical practice nearly 20 years ago; since then they have become indispensable for the evaluation and management of patients with disturbances of pulmonary gas exchange. However, in recent years they have been criticized for two reasons. First, a 24-hour blood-gas service is very expensive to maintain, particularly in smaller hospitals, and second, arterial blood-gas determinations provide only limited information about the effectiveness of oxygen delivery to and carbon dioxide removal from the tissues. Measurements of blood gases on the venous side are more likely to provide this information because they depend on the balance between mefabolism and blood flow as well as on pulmonary gas exchange. However, in order to measure pulmonary venous blood gases directly, catheterization of the pulmonary artery is required. For some years Campbell1 has argued that indirect measurements of mixed venous carbon dioxide tension (Nco2) are informative as well as being simple and noninvasive. From a rebreathing measurement of Nco2, information is obtained about alveolar ventilation, cardiac output, arterial oxygenation and changes in tissue carbon dioxide, and therefore of tissue pH. With Howell2 he adapted the rebreathing technique of Hackney, Sears and Collier3 to obtain reliable measurements of Pi'co2. Although extensively validated and of clear clinical value, rebreathing methods are not as popular
as they should be, probably for two reasons. First, the method yields indirect estimates of Nco2 and arterial carbon dioxide tension (Paco2); it is difficult to accept an indirect method when direct measurements of arterial blood gases are available. The physiologic and technical factors that may influence the quality of blood-gas measurements in general are poorly appreciated; it also is not well known that such factors have less influence on the measurement of P.co2. Second, the method as first described appeared complex and required a certain "art" to obtain reliable results. Powles and Campbell state in their article in this issue of the Journal (page 501) that they have overcome the obstacles to a wider use of rebreathing by attending to a number of problems: they have "packaged" the equipment, simplified the procedure to make it easier to use, and developed a teaching program suitable for nurses and technologists without a laboratory background. These steps have resulted in the rebreathing method now routinely being used by these professionals in respiratory and intensive care units in Hamilton. Powles and Campbell outline the applications of the rebreathing method. The method may be used as a screening technique to identify alveolar underventilation (high Paco2 and Nco2) or low cardiac output (high Nco. witb normal or low Paco2). In patients without evidence of cardiac malfunction, the PVco2 may be used instead of the Paco2 to follow alveolar ventilation. The
476 CMA JOURNAL/MARCH 4, 1978/VOL. 118
Pirco2 may be used in conjunction with measurements of Paco2 to estimate cardiac output by the indirect Fick method. Finally, they examine the relation between Nco2 and Paco2 and present the logic that enables a point to be identified at which central venous oxygen saturation has decreased to a level at which tissue hypoxia is likely. From the information given in their article the measurement of P.co2 and Paco2 may be used to make clinical decisions and rigorous calculations of these important variables. Because the rebreathing measurement of P.co2 is noninvasive it may be repeated more frequently than "stab" arterial punctures. .Vhen it is used in conjunction with a modern ear oximeter,4 the same information as obtained from arterial blood-gas determinations is available immediately, leading to more continuous monitoring of patients prone to rapid changes in cardiac and respiratory status. NORMAN L. JONES, MB, B5, MD, FRCP, FRCP[C] McMaster University Medical Centre Hamilton, Ont.
References 1. CAMPBELL F.JM: Simplification of Haldane's
apparatus for measuring COs concentration in respired gases in clinical practice. Br Med I 1: 457, 1960 2. CAMPBELL EJM, HOWELL JBL: Rebreathing method for measurement of mixed venous Pco2. Br Med 1 2: 630, 1962 3. HACKNEY 3D, SEARs CH, COLLIER CR: Estimation of arterial CO2 tension by rebreathing technique. I Appi Physiol 12: 425, 1958 4. SAUNDERS NA, PoWEas ACP, Rasuca AS: Ear oximetry: accuracy and practicability in the assessment of arterial oxygenation. Am Rev Respir Dis 113: 745, 1976
