Logical thinking is the method of clinical thinking, the basic method of clinical medicine, the method of reasoning, the tool and the basic skill of doctors. You need systematic training to master it well.

Medical logic, also known as medical logic. In the medical field, the training of logical thinking ability has been emphasized for many years. The book Essentials of Medical Logic was published in 18 19. According to the regulations of the earliest medical university in the west founded by Salero in Italy, "students can't be expected to study medicine unless they have laid a solid foundation in logic." We decided not to study medicine without studying logic three years in advance. " In the past, the term medical logic mainly refers to the description of diagnostic thinking process. For example, chapter 14 1940 "Inference of clinical diagnosis (medical logic)" published in the United States regards medical logic as a synonym for "inference of clinical diagnosis".

Earlier, medical thinking was mainly studied from the traditional formal logic. For example, The Lancet's differential diagnosis is an instrument to help logical thinking and diagnose errors in epistemology and logical characteristics. Since 1960s, people have studied medical thinking from the aspects of mathematical logic and probability logic. For example, "Diagnosing diseases with computers-on the construction of quantitative diagnosis" and "Quantitative Diagnostics". In recent decades, specialized textbooks of medical logic have appeared, such as Medical Logic in the United States and Introduction to Medical Logic in China. There are even books such as Deductive Diagnosis of Congenital Heart Disease. In recent years, there are more and more theories about fuzzy logic and dialectical logic.

Medical logical thinking not only refers to the thinking mode of medical diagnostics, but also includes the analysis and deduction of therapeutics, prognosis, medical psychoanalysis and so on. We simply call it clinical thinking.

Obviously, a clinician can still work without learning logic and medical logic. Of course, this is not because his thinking can be sold without logic and medical logic, but because he has received cultural education since childhood, and his professional education in medical colleges and jobs has already included general logic and medicine; The content of logic. Although it is in an unconscious state where logical terms are not used or rarely used. Because of this, it is easy to make mistakes if the logic is not mastered perfectly. Consciously studying and applying medical logic can reduce mistakes, improve the consciousness, efficiency and correctness of clinical thinking, and make the work better.

The following example is what you may encounter.

Second, the way of thinking that does not conform to medical logic.

1+ 1 = 2, there is no need to beat around the bush.

But you can't think that in medicine. It can't be like this. 1+ 1 = 2. We have to analyze it in combination with other situations.

Many people like this metaphor. According to several symptoms and signs, or according to several examination results, the diagnosis result is straightforward. This is not in line with the logical thinking of medical diagnostics. This is especially true among people who know little about medicine. We can often see that some people are holding a book and a newspaper, describing something and putting it on themselves. Unfortunately, some medical staff are the same, although they are not so "stupid". CT reported a brain tumor, and he was diagnosed, but in the end it was a vascular malformation. If the liver occupies a space and the lung mass is AFP positive, he will diagnose liver cancer with lung metastasis, but in the end it may be testicular cancer with liver and lung metastasis. In a hospital in our city, the patient was dizzy and CT reported cerebral infarction, so it was cerebral infarction. After two months of promoting blood circulation and removing blood stasis, I looked at the CT film again, but it was glioma. Five years after breast cancer surgery, a patient went to the hospital with a cough. According to the chest X-ray, he found a shadow of 2X2 cm in the right lower lung field, which looked like a nipple, so he was diagnosed as nipple shadow. Everyone should know that this is wrong, and finally the lung metastasis of breast cancer.

Analogy without analysis does not conform to the correct medical thinking mode. It is possible to get the correct result, and you will encounter the correct result according to the probability, but there are more opportunities for mistakes and it is easy to lose the possibility of correcting them in time.

Third, the process of medical diagnostic thinking

According to the description in diagnostics and, the correct diagnosis process can be divided into three steps: data collection, comprehensive analysis, preliminary diagnosis and verification in practice.

The book Principles and Practice of Internal Medicine by Johns Hopkins University in China describes the diagnosis process in more detail. The first is to collect facts, including medical history. Physical examination, auxiliary examination and course observation; The second is to analyze the facts, including: ○ 1 critically and objectively evaluate the collected data; (2) Arrange reliable findings according to their importance; (3) Select one (sometimes two or three) central features; (4) List the possible diseases with these central characteristics; (5) Choosing the final clinical diagnosis can be as follows: (a) One disease can best explain all the findings; (b) Several diseases can explain all the findings well; (c) Confirm all positive and negative results with the final clinical diagnosis, and recheck and verify them.

Another aspect of the diagnosis process is to divide the diagnosis target into two parts: classification and measurement. Classification is to classify those that can be classified, such as sickle cell anemia, under the condition of clear natural classification. Measurement is to find out the severity and duration of the disease.

Fourth, suppose.

Science has two foundations: hypothesis and experiment. Hypothesis not only exists in medical theory, but also is the basic form of medical diagnostic thinking.

As shown in the following figure

Scientific method

Scientific method of clinical thinking

Russian clinician Botequim has clearly pointed out that the diagnosis of patients is more or less a generous hypothesis, which must be constantly verified. New facts may appear, which may lead to changes in diagnosis or increase the possibility of the original diagnosis. When collecting facts or examining patients, we should have certain guiding ideology. Without this idea, it is easy to fall into mistakes or negligence, so that a lot of time is wasted and a correct conclusion cannot be obtained.

The book "Principles and Practice of Internal Medicine" also wrote: "Clinical problem solving" is the cornerstone of clinical medicine, and its method is parallel to "scientific problem solving".

The scientific methods applied in clinic are equivalent to experiments (inquiry, physical examination, laboratory tests and various special examinations), and the analysis of these examination results is differential diagnosis. Considering various possible diseases, one or more "preliminary diagnoses" or hypotheses are put forward, prompting clinicians to further inquire, continue observation, and then carry out some tests to support, deny or distinguish the differential diagnosis under consideration.

A good hypothesis should meet the following logical conditions ○ 1 compatibility (no contradiction), that is, the hypothesis does not contradict the existing scientific principles and knowledge; (2) completeness, that is, the hypothesis explains not a part of the facts that need to be explained, but all its deductibility, that is, a conclusion that can be confirmed or denied can be deduced from this hypothesis. Obviously. These three points also apply to the diagnostic hypothesis. When considering the diagnosis of patients, we should not violate the established medical knowledge. The proposed preliminary diagnosis should explain as many clinical findings as possible (at least the main clinical manifestations) and should not contradict the existing data. Don't mention a quasi-diagnosis that can neither be diagnosed nor ruled out (denied). Putting forward this diagnostic hypothesis will not help the clinical thinking process of making decisions, but will only give you a headache.

There is a saying that we should wait until all the information is available before making a preliminary diagnosis. In principle, this is wrong, which may lead to indulging in too many examinations and delaying diagnosis. However, due to the pressure of the environment and the prevalence of defensive medicine, we have to complete as many examinations and collect as much information as possible at an early stage to some extent.

Assumption is always some distance from the truth, or it may be far away. One hypothesis may also mask another problem. Whether the hypothesis conforms to the truth and fully reflects the truth needs further verification. Whether a preliminary diagnosis reflects the real situation of patients also needs to be verified. Therefore, the diagnostic hypothesis should be changed in time. The hypothesis of preliminary diagnosis is not the end of diagnosis or clinical thinking, but a new starting point. The initial diagnosis should be adjusted according to new data, such as observation of disease development, new chief complaint and new examination data. Don't be opinionated, and don't be far-fetched and ignore the clinical impression that doesn't match the reality.

V. Logical thinking mode in medical diagnosis

1, clinical analogical reasoning

Simply put, clinical analogical reasoning is what we usually call "a bit like". It is very common, but if it is limited to "image" without detailed analysis, it will often be "wrong".

Attention should be paid to various factors that affect the reliability of analogical reasoning, mainly including: ○ 1. The greater the quantity, the higher the reliability. 2 The essence of homology, the more essential, the higher the reliability of analogy. ○3 The existence of counter indication. If there is a negative reference between the two, no matter how "like", it is not "yes".

There may often be several diseases that are a little "like", so other logical analysis methods are needed to identify them.

2. syllogism

The difference between syllogism and analogy is that all the data should be consistent, but it is almost impossible.

3. Hypothetical reasoning

The most common is hypothetical straightforward reasoning, and this assumption is the result of completely hypothetical reasoning:

Suppose disease D has symptoms S 1, S2, S3,,,,

Now patient P has symptoms of S 1, S2, S3,,,,

Therefore, patient p may suffer from disease D.

Another form is the necessary conditional hypothesis reasoning:

Only those who have symptoms of S 1, S2, S3,,,, are disease D.

Now patient P has symptoms of S 1, S2, S3,,,,

So patient p suffers from disease D.

There are also sufficient conditions to assume the logical negation of the antecedent by denying the antecedent after reasoning:

Suppose disease D has symptoms S 1, S2, S3,,,,

Now patient P has no symptoms S 1, S2, S3,,,,

So patient p can't have disease d.

This kind of reasoning is most commonly used in differential diagnosis and belongs to a kind of exclusion diagnosis.

4. Selective reasoning (outspoken reasoning)

The first premise is selective judgment, and the second premise is the reasoning of outspoken judgment. The most commonly used form is:

The symptoms and signs of patient P are S 1, S2, S3,,,,, which may be found in disease D 1, D2, D3,,,

Now the patient denies the disease D 1, D2,

Therefore, the patient suffers from disease D3.

This kind of reasoning is also often used in differential diagnosis, which belongs to a link of exclusion diagnosis. However, because it is difficult to enumerate D in clinical work, the result of reasoning here can only be a possible judgment, not absolutely correct. Only by establishing this concept can we avoid blocking the thinking of considering other diseases, thus avoiding the mistakes caused by it.

5. Combination of analogical reasoning, selective reasoning and hypothetical reasoning.

The combination of analogical reasoning, selective reasoning and hypothetical reasoning is the most commonly used method in clinical diagnostic reasoning. Analogical reasoning is used to put forward the possible diseases of medical patients, thus forming the premise of selective reasoning, negative reasoning of hypothetical reasoning is used to exclude some possibilities, and positive reasoning of hypothetical reasoning is used to get possible diagnosis or definite diagnosis.

Here is a simple example to illustrate.

Patient p, an adult male, has the following symptoms and signs: severe illness, pain in the upper abdomen for one day, frequent and severe vomiting, obvious increase in muscle tension in the upper abdomen, and 22,200 white blood cells per cubic millimeter.

① According to analogical reasoning, it is preliminarily considered that the patients may be perforation of gastric ulcer soup, cholecystitis, acute gastritis, acute appendicitis, intestinal obstruction and acute pancreatitis, because some symptoms and signs are similar to these diseases.

② First, select a disease for exclusion diagnosis. Stomach ulcer soup perforation. We need to do some more tests to get more information, such as abdominal fluoroscopy, and find that there is no free gas under the diaphragm.

Negative form of hypothetical reasoning

If it is a perforated gastric ulcer, there is often a history of gastric ulcer, and gas can be seen under the diaphragm. There should be no repeated violent vomiting.

Now the patient vomits repeatedly and violently, and there is no free gas under the diaphragm.

Therefore, patient P did not suffer from perforation of gastric ulcer.

3 Repeat the above process to exclude cholecystitis, acute gastritis, acute appendicitis and intestinal obstruction.

○4 According to selective reasoning, diseases such as cholecystitis, acute gastritis, acute appendicitis and intestinal obstruction are excluded, and the diagnosis points to acute pancreatitis.

○5 Further verification according to other test results and the progress of the disease.

Step 6 split

This is a method of classification and selection.

According to some characteristic symptoms, signs and examination results of patients, diseases are classified, and then they are classified continuously, so as to get the final possible diagnosis or definite diagnosis.

Such as pancreatitis mentioned above. According to the classification of abdominal pain, there are many diseases of this kind. According to the classification of severe vomiting, diseases without severe vomiting were excluded. According to the classification of amylase, only pancreatitis is left.

This is a continuous dichotomy. Obviously, this is a very effective method with high accuracy. At present, some monographs on differential diagnosis mostly adopt dichotomy or similar classification and classification methods.

7, mathematical diagnosis method

The thinking of clinical diagnosis, to a great extent, is the understanding and judgment of possibility. Clinical data usually have statistical characteristics. Strict and specific symptoms, signs and examination results are very rare. Even pathological data can hardly be said to be completely specific, and it also has statistical characteristics.

It is often a variety of different substances that appear in different diseases at different frequencies, or a combination of many different substances that appear in different diseases at different frequencies. In this way, the disease can be judged or diagnosed according to the probability. Or according to the size of the probability, list all kinds of diseases and sort them.

We often describe it this way: the possibility is high, small, common and so on. This is actually a fuzzy probability. There are also relatively accurate, such as the reliability of ultrasound diagnosis of liver cancer is 90%, and the error of diagnosis of bile duct stones is 10%.

In foreign countries, even ordinary people are now very concerned about the probability of certain situations, especially when patients need to take risks and make choices. They often ask, "What is the probability of this happening?" "How reliable is it?" . In fact, we have encountered this situation for a long time, but we just didn't care.

At present, the evaluation of various diagnostic criteria is mostly based on probability.

Combined with dichotomy, there are many mathematical diagnosis models. With the development of computer technology and software technology, mathematical diagnosis may be further developed.

Six Differential Diagnoses —— "Exclusion Diagnosis"

We also call clinical logical thinking method "exclusion diagnosis method". "Exclusion diagnosis" is one of the most basic diagnostic methods. Whether a diagnosis process and diagnostic thinking are correct often depends on whether the exclusion diagnosis is consciously carried out.

As mentioned above, we can list some similar diseases according to some characteristic data, such as fever, cough, phlegm and so on. Naturally, it is best to list all diseases that meet these "characteristic data", but this is limited by our memory ability and experience. According to other characteristic data, some diseases are excluded, and the rest is the diagnosis we need. In the process of enumeration and exclusion, we need to use some logical methods introduced above. I won't explain it in detail here.

Seven, diagnostic principles

Professor Zhang Xiaoqiao, a famous physician, said, "What is worth mentioning here are several principles commonly used in clinic, such as giving priority to common diseases and frequently-occurring diseases and giving less consideration to rare diseases; Try to choose a single diagnosis instead of multiple diagnoses to explain different symptoms; Before the diagnosis of functional diseases, organic diseases must be clearly excluded, and there must be direct manifestations of functional diseases themselves; Exclusive diagnosis is usually unreliable; Experimental treatment is generally not a good method, and so on. These are all from experience. Although there are exceptions, it is generally in line with the guidelines of clinical thinking. "

1, the principle of relativity

We should not only attach importance to the guiding role of diagnosis in treatment, but also make it clear that the purpose of diagnosis is to treat, and if necessary, treat without a clear diagnosis, especially rescue treatment.

For those "cases to be diagnosed" that do not belong to the emergency department but have not been diagnosed for a long time, they are not ignorant, but they cannot be diagnosed, but they want to deal with them without basis; Without treatment, it is not conducive to the treatment process, and it is in a dilemma. There is a bias of "more examinations and less treatment". At this time, it should be considered that the measures taken should not hinder the diagnosis, and the examination and diagnosis plan adopted should not delay the start of necessary treatment. According to the current requirements, patients and their families should be informed truthfully when encountering such difficulties to avoid unnecessary disputes.

The diagnosis of diseases is not limited to the definite taxonomic diagnosis or definite diagnosis, but also to the definite diagnosis as far as possible in order to improve its guiding role in treatment. How to choose should meet the requirements of modern medical model for clinical diagnosis.

It is necessary to explain all symptoms with one disease as much as possible, but also to realize that there may be many diseases.

We should not only consider common diseases and frequently-occurring diseases, but also consider rare diseases properly, not biased, and based on the analysis of clinical data.

When it is difficult to determine the real diagnosis, to establish an extreme "safety principle", we must first choose a possible diagnosis that is most beneficial to the patient in order to win the opportunity of treatment. At this time, we should actively inform patients and strive for understanding and cooperation. Take the lesser of the two evils and the heavier of the two benefits.

The possibility of higher risk takes precedence over the possibility of lower risk.

Compared with functional diseases, organic diseases should be given priority, and neurosis cannot be easily diagnosed.

Give priority to treatable diseases, not incurable diseases.

Compared with diseases that do not need emergency surgery, diseases that need emergency surgery are given priority, and differential diagnosis of diseases that need emergency surgery is given priority.

Compared with diseases with slow progress, diseases with rapid course change are given priority, which are prone to rapid change or even sudden death.

Compared with non-communicable diseases, infectious diseases have priority. In order to avoid infection caused by missed diagnosis of infectious diseases.

We should be very careful in choosing between being sick and not being sick, not only to avoid misdiagnosis, but also to prevent iatrogenic diseases caused by patients' mental burden.

We should not only acknowledge the validity of clinical thinking mode and the correctness of diagnosis in most cases, but also acknowledge the possibility of diagnosis in most cases. We have to admit that in most cases, we can only get different degrees of judgment, so we should correct our diagnosis in time and dare to deny it.

It is not only necessary to admit that the change of the disease is often the development of the primary disease, the emergence of complications, or the response to treatment, but also to consider the possibility of new diseases.

Admittedly, in most cases, clinical diagnosis is only to judge the clinical symptoms and signs that have been shown. At the same time, we should also know that in some cases, it is necessary to predict the potential dangers that patients have not shown, such as delayed splenic rupture, abdominal hemorrhage and intracranial hemorrhage.

We should actively take further inspection measures to make a clear diagnosis, and we should also know that sloppy inspection should not be done. It is particularly important to note that the risk of inspection measures is less than the risk of the disease itself.

We should not only consider the diseases of our own specialty, but also consider the diseases of other specialties, and even give priority to whether it may be an important disease belonging to other departments to avoid misdiagnosis, because in general, the diseases of a specialty elbow surgery specialty are often unfamiliar and easily overlooked.

2, the highest principle of diagnosis

All the above principles are relative. The law of logic is just a tool. What is the highest principle? There is only one: the specific situation of the patient!

Professor Zhang pointed out in the report "Talking about Clinical Thinking": "In medical work, whether it is collecting clinical data or making diagnosis and treatment, we must go deep into the clinic, accurately understand the condition, and use correct clinical thinking and working methods. In short, specific analysis of specific problems can complete clinical tasks well and will not be subjective and arbitrary. "

3. The irrationality of diagnosis

Clinical thinking sometimes has an intuitive and artistic side.

Clinical thinking is also influenced by other factors. Such as the feedback influence of patients, social factors, ethical factors, legal factors, emotional factors and so on.

The influence of these factors is very significant. Reflected in the huge difference between computer diagnosis and human brain diagnosis. This is an objective reality.