A right answer to a wrong question

“Judge a man by his questions rather than by his answers.” ―Voltaire

“The scientist is not a person who gives the right answers; he's one who asks the right questions.” ―Claude Levi-Strauss.

When I was a medical student, we started studying internal medicine in the fourth college year. This changed later and students started to learn their internal medicine in the third year. A meeting of medical teachers of the various Iraqi medical colleges was arranged one day in Baghdadto discuss which of the two ways is better and whether we should go back to starting in the fourth year. The discussion concentrated on the training of fourth year students and whether having studied medicine in their third year has benefited them. In other words the assembling teachers were trying to answer the question: Are fourth year students better in internal medicine if they have started studying the subject in their third year? The meeting was convened early during the academic year. All attendants agreed that the level of fourth year students is better when they have studied medicine in their third year; an obvious finding that should go without saying! Students who had some training in the previous year should be better than those who are starting afresh. The teachers went on from this to conclude that it is better to start training of internal medicine in the third year. Nobody tried to answer the right question: Are students who start their training in the third year better than those who start in the fourth when they graduate or at least at the end of the fourth year? It is quite possible that during the fourth year (or the years after) students starting in the fourth can catch up with (or even pass) those starting in the third year especially if they have more hours during the fourth year as is usually the case if training starts in the fourth. I pointed out that the meeting was addressing the wrong question but no body seemed to care or to see the difference!

I am not claiming that starting in the fourth year is better than starting in the third or vice versa. The answer to this is to be left to specialists in medical education and should be built on properly designed studies. I only wanted to say that asking the right questionis more important than knowing the right answer of a wrong question.

BASICS OF ACID BASE BALANCE 1

(To our junior colleagues and students)

كاتب عدل مرة أخرى

أذا كنت عزيزي القارئ قد قرأت المقالة السابقة المعنونة "وكالة" فسوف تفهم ما أقول بصورة أوضح وأعمق. أحتجت الى كاتب عدل مرة اخرى ولكني كنت هذه المرة في مدينة اخرى في بلد اخر. دخلت على الانترنت من حاسوبي المحمول في غرفتي وطلبت اسماء كتاب عدول في منطقتي. أجابت الانترنت بعدد من الاسماء مع ارقام هواتفهم وعناوينهم وخارطة اماكنهم. أخترت احد القريبين من سكني وادخلت عنوانه على موقع الانترنت لأحدى وسائط النقل العام فشرح لي الموقع كيفية الوصول اليه: رقم الحافلة ومن اين استقلها واوقات وصولها والفترة التي تستغرقها.. ألخ. ذهبت الى مكتب الكاتب العدل فأستقبلني السكرتير وكنت محظوظا حيث لم يكن لدى الكاتب العدل أحد في ذلك الوقت فدخلت عليه. ألقيت التحية وجلست فرحب بي وسألني بعض الاسئلة عن بلدي من باب المجاملة ثم سأل عن سبب مجيئي فأخبرته أن عندي تعهدا ينبغي أن أوقع عليه أمام كاتب عدل ويصادق عليه. سلمته التعهد فقرأه ثم طلب مني بعد ان تأكد من هويتي أن أوقع في المكان المحدد لي وأخذه وكتب اسمه في المكان المحدد له ووقع وختمه بالختمين الخاصين به وسلمه الي. سلمته المبلغ المطلوب (ولكي أكون عادلا ومتوازنا فان المبلغ اكثر بكثير من المبلغ الرمزي الذي ندفعه في دوائر الكتاب العدول في بلدي). شكرني وشكرته وانصرفت عائدا الى بيتي. لم أجد في الطريق بائع رقي ولم أكن في حاجة اليه!! ولكنني تذكرت معاناة الوكالة التي عملتها عند كاتب عدل في بلدي فابتسمت وقلت لا حول ولا قوة الا بالله.

Measuring blood pressure

(To our junior colleagues and students) 

1. Patient should be comfortable, lying or sitting with the arm supported. Actively holding the arm up by the patient raises blood pressure. The patient should avoid smoking or drinking coffee or tea shortly before measurement as this may raise blood pressure.

2. Mercury sphygmomanometer is reliable. Aneroid sphygmomanometer is reliable if calibrated against a mercury one.

3.   Apply the cuff neatly around the upper arm well above the cubital fossa (to leave a place for the stethoscope). Any of the two arms may be used. However if the pressure is measured for the first time, especially in an elderly patient, it is advisable to measure it in both arms and consider the higher one as the true representation of the patient’s blood pressure. It is not uncommon, especially in elderly people, to get a lower reading in one arm as a result of atherosclerosis in the arteries supplying that arm. Subsequent measurements in such a patient should use the arm with the higher pressure.

4. The arm should be at the same level as the heart. The pressure inside the brachial artery decreases when the arm is raised and increases when it is lowered. The position of the sphygmomanometer is not important because the cuff and the tubing are filled with air and the pressure in a container filled with gas (unlike liquid) is the same at any point regardless of its position.

5. If you find (more often in women) that rolling up the arm clothing will constrict the upper arm and it is not practical to ask the patient to undress, then it is better to apply the cuff over the clothing provided it is not thick. Thin clothing does not significantly impair transmission of pressure from the cuff to the arm or transmission of sound from the arm to the stethoscope.⁽¹⁾

6.  It is advisable to develop the habit of measuring blood pressure by palpation first. It has the following advantages:

a)      It gives an idea about the systolic pressure so that when you take it by auscultation you only raise the pressure to a little above the systolic before starting to deflate. In this way you avoid raising it too high which is painful and may result in a reflex rise of blood pressure.

b)      It avoids the possibility of raising the pressure in the cuff to a point in the silent gap (in patients who have a silent gap) and starting deflation. You will then wrongly consider the reappearance of sounds (phase three Korotkoff sound) as the systolic pressure.

c)       It makes you check the pressure twice which is advisable. The second measurement has been found to be generally lower than the first and more representative of the real.

7.     Apply the stethoscope over the brachial artery in the cubital fossa and avoid inserting it between the cuff and the arm. The hard structure of the stethoscope may interfere with the even distribution of pressure on various points of the arm circumference.

8.  Deflation of the cuff should be slow to give time for the mercury column or the dial pointer to change position as the pressure drops. Too rapid deflation gives a higher reading as a result of inertia of the mercury or the pointer causing it to lag behind the decreasing pressure inside the cuff.

9. Diastolic blood pressure (as measured intra arterially) falls between phase four (sudden muffling) and phase five (complete disappearance) of Korotkoff sounds but nearer the latter. So it is better to take disappearance of sounds as the diastolic pressure except in the occasional case when the sounds persist down to a very low level or zero.

(1) Hovsrpian R.,  Al-Haddad M.,  Abdulla K., Comparison of blood pressure measurements in bare arm, clothed arm and forearm,  J. Fac. Med. Baghdad, 1996, 38, 221-224.

Confidence Interval

(To our junior colleagues and students)

Confidence interval is a statistical term frequently encountered in papers describing various kinds of medical research. It is one of the terms that postgraduate medical students need to know.

The following examples serve to explain it.

If you want to find the mean weight of a group of 30 men, you measure the weight of each one, add the figures and divide by 30. The result is the mean weight of the group.

If you want to find the mean body weight of men residents of a big city, it is not practical to do the same because of the large number involved. Statisticians get around this by taking a random sample of the men in question. They calculate the mean weight of the men in the sample and consider it a satisfactory representation of the required mean of the total. They may take e.g. a thousand men, chosen randomly from various districts of the city, measure the weight of each and then add and divide to find the mean. They consider this representative of the mean body weight of the men of that city. Now imagine yourself to be the person who requested that mean because you wanted to assess the nutrition status of the people in the city and you asked a statistician to do it for you. Imagine also that the mean weight of the thousand men was 60 kg. You may then have the following dialogue with the statistician:

·         Are you sure the figure you gave me is exactly the same as the figure you would have obtained had you taken all the men in the city?

·         No, most probably it is not, but it is very near that figure and is sufficient for your purpose.

·         How near is it? How much is the difference?

·       I cannot tell you the exact difference because I do not know the true figure of all the men in the city. We statisticians usually deal with probabilities. I can tell you the probability of the difference being of a certain magnitude. I can work out from the data of the thousand men a figure we call the Standard Error (SE). In fact I have already done that and found the standard error of the mean of the sample to be 2. We know from statistics laws and rules that the probability of the difference being not more than one standard error (1SE) is approximately 67% and being not more than 2SE approximately 95%. In other words I can tell you that I am practically 95% confident that the true figure of the mean weight of all men in the city is within 2SE above and below the figure of 60 i.e. between 56 and 64 kg. That is what I mean when I say the mean body weight of the sample of men is 60 kg. and its 95% Confidence Interval (CI) is 56 - 64.

The 95% probability (or confidence) becomes approximately 67% if you choose 1SE above and below the mean as the limits of your confidence interval and approximately 99% if you choose 2.5 SE. The 95% (i.e. mean ± 2SE) is commonly used and if the percentage is not written it usually means 95%.

I used the mean as an example to explain the confidence interval. The same applies to other parameters like proportions when samples are used instead of the total.

Evidence based medicine

When I came across the phrase “evidence based medicine” for the first time many years ago, I was somewhat bewildered. Was medicine we had learned in the college and practiced since not based on evidence?! Are there two types of medicine, one evidence based and one not?! Shouldn’t all medicine be evidence based?!

The key to the answer to these questions lies in the word “evidence”. Like almost any word in the language (any language), evidence can mean different things to different people or in different contexts. In the field of medicine, evidence can come through reasoning from known (thought to be known) pathophysiological facts. For example, in heart failure the heart does not pump blood to the tissues efficiently. Digitalis increases the force of myocardial contraction. So digitalis should be useful to patients with heart failure. Evidence can be the result of opinions of experienced doctors who obtained it from their practice. It may come from opinions of patients who expressed their satisfaction or dissatisfaction of a certain medical intervention. Evidence can also come from planned scientific experimentation.

During the last century and especially in the latter half of it, a trend towards examining medical interventions (drugs, surgical operations, diagnostic tests, life style changes etc) in a planned scientific way following the steps of the scientific method appeared and evolved. It aimed at properly evaluating the benefits and harms of various medical interventions. The trend became more powerful with the evolution and increasing use of clinical trials (including controlled clinical trials). Doctors, and increasingly the public, are not any more satisfied with the results of mere reasoning or opinions of experts. Reasoning that an intervention should be useful because it sounds logical according to our knowledge of medical facts is not enough. Our knowledge is not necessarily complete or perfect and usually, if not always, it is not. Opinions of experts and patients can be, and usually are, biased. The intervention should be tried on people under strictly controlled conditions and the results interpreted in a proper scientific way to find out if the intervention is really useful. And even if it is, we should make sure that it has no adverse effects that outweigh its benefits.

Medicine based on this kind of evidence is what is called evidence based medicine. This should not mean that the rest of medicine is not based on evidence but it means that the evidence for it is not satisfactory. The phrase does not express this in a clear unambiguous way. But that is language, however meticulous and careful one tries to be, language remains liable to be interpreted in various ways!

Should we conclude that evidence obtained from properly controlled clinical trials is infallible? Certainly not. We regularly hear of drugs withdrawn from the market and processes abandoned after being properly and scientifically evaluated and after years of use. Nothing in life is infallible.