in Annals of Thoracic Surgery and in JAMA. Proper performance of the maneuver does not use compression or squeezing with the arms. It consists of a scientifically developed pressing motion using the rescuer's hands. The method has been studied in the animal laboratory, in the operating room and clinically. It is of interest, for example, that with a patient in the lateral thoracotomy position, gentle pressure in the epigastrium by the surgeon's fist will cause the diaphragm to elevate 6 to 10 cm. A recording respirometer and other instrumentation were used to study adult volunteers and it was found that the maneuver resulted in an average of 940 ml of air being expelled in 0.25 seconds at 31 mm Hg pressure. It was determined that this air came from the expiratory reserve (normal, 1900 ml). It is this flow rate of 205 i/mm that causes either a large or small bolus of food to be expelled. In many of the 160 instances of food-choking "saves.. that have been reported to us the food "popped out of the mouth" or "flew across the room". This has occurred whether the bolus caused total or partial obstruction. While it is true that some of the reports by laymen might be open to question, the 27 reports of lives saved by 14 physicians, 10 nurses and 3 paramedics must be seriously considered. If the victim can cough out the obstructing object, he surely needs no further help and this situation cannot be considered one of potentially fatal food choking. I cannot speak through personal experience of the various methods described by Drs. Brummitt and MacKay except to say that these procedures have been in use for many years, yet nearly 4000 victims died of food choking last year in the United States. Many of the letters we receive tell of unsuccessful attempts at back slapping and reaching into the mouth to remove food, resulting only in deepening cyanosis; the victims were then saved by the maneuver, which immediately expelled the bolus. Three weeks ago a 16-year-old boy in a city 150 miles from my home died choking on a peanut butter sandwich while his parents pounded his back while waiting for medical assistance. We know of an 8-year-old child who has been in a coma for 4 years, supported by gastrostomy feedings and tracheostomy, because it took too long for the rescuer's finger to extract a piece of chicken from her throat. Our findings are available to Drs. Brummitt and MacKay or any other physician with an interest in the subject of "cafe coronary", and they are

welcome to visit our laboratory. They should not delay seeking the facts, for this could be costly in lives lost that might otherwise be saved. It is time to teach the early recognition of the symptoms of food-choking asphyxia in order that the condition can be treated promptly and unnecessary rescue attempts prevented. Through lectures, brochures, posters and a teaching film that will soon be completed we are doing this and making known the proper technique for performing the maneuver as well as the risks involved. HENRY J. HEIMLICH, MD

The Jewish Hospital Cincinnati, Ohio

cH or pH To the editor: I would like to commend the Journal for bringing to the attention of its readers in the editorial "The metric system, the International System of Units (SI) and medicine" (Can Med Assoc J 112: 799, 1975) the advantages of teaching cH, the concentration of hydrogen ions [He] or protons) to medical students rather than the confusing shorthand of pH. Dr. K.A.C. Elliott, the eminent professor of physiological chemistry at McGill University, has stated: "I have struggled for 44 years to help beginning students of science and medicine to grasp the ideas of pH, pK, etc., and the derivation of and calculations by the Henderson-Hasselbalch equation. Many thousands of other instructors and students have endured this struggle. I do not believe it is worth our effort."1 Although our annual class of 250 medical students at the University of Toronto generally do well in their biochemistry course, it later becomes obvious that less than 10% of these students actually understand "pH".2 This confusion has led to great difficulty in teaching the fundamentals involved in drug absorption, aspirin absorption, aspirin poisoning, etc. The concept of pH has also severely clouded the students' understanding of how the kidney eliminates H. and how such excretion is modified by drugs. The confusing pH terminology is spreading to infect other areas of medicine. For example, some people now think it is fashionable to express the concentration of serum Ca2. by using the term pCa. Others are introducing pD for drug concentrations, and so on. To add to the medical student's confusion, the lower-case "p" may also mean partial pressure. The student must then go through a series of mental gymnastics in remembering that as the pCO2 increases, the pH decreases which means that the H. concentration increases.

1384 CMA JOURNAL/JUNE 21, 1975/VOL. 112

Why must we persist in the topsyturvy idea that when the H. concentration increases the pH decreases? It is more meaningful to think directly in terms of the proton or H + concentration. All students are immediately comfortable with the concept of proton concentration expressed as moles of H. per litre, or cH. It is clear and simple to say that the cH of the patient's serum is 40 nmol/l. This terminology is now being used or being considered seriously by teachers at a number of medical schools and universities including Brown University (Rhode Island), Medical College of Ohio, the Massachusetts Memorial Hospital Medical Center,3 University of Virginia school of medicine,4 California College of Medicine at the University of California at Irvine, Marquette University school of medicine,5 The Albany Medical College of Union University (New York) and the school of medicine and dentistry at the University of Rochester. In Canada, in addition to Dr. K.A.C. Elliott at McGill, the editor of the Canadian Journal of Physiology and Pharmacology, as well as the editor of CHEM 13 News (a high school teaching journal out of the University of Waterloo) have expressed interest and support for teaching cH. At the University of Toronto faculty of medicine, the pharmacology department is now producing a pharmacology book wherein only cH is mentioned; the teaching of respiratory physiology, of the renal-electrolyte system and of general pharmacology to our medical students is turning to teaching cH. While it is true that the pH concept is complicated,6'7 the teaching of cH is really very simple. Clear teaching of complicated medical concepts should be one of the goals of our medical schools. PHILIP SEaMAN, MD, PH D Department of pharmacology University of Toronto Toronto, Ont.

References 1. SEaMAN P: Teach cH, not pH. Biochem Educ 1: 44, 1973 2. Idem: The pH concept. Science 177: 835, 1972 3. Hucsc.taaa WE: Henderson vs. Hassiebaich. Clin Res 9: 116, 1961 4. MCGILvERY RW: Biochemistry - A Functional Approach, Philadeiphia, Saunders, 1970 5. LENNON ES, LEMANN S JR: Defense of hydrogen ion concentration in chronic metabolic acidosis. Ann Intern Med 65: 265, 1966 6. Hats AG: pH and the Henderson-Hasselbaich equation. Am S Med 55: 131, 1973 7. D.tvss RP: Logland: A Gibbsian view of acid-base balance. Am I Med 42: 159, 1967

Role of the pharmacist in primary care

To the editor: In the article "The pharmacist as a provider of primary care" (Can Med Assoc J 112: 60, 1975) Bass