Image Courtesy: NUHS Paediatric Residency Program
With more facts,our minds are not only sorting and eliminating but also correlating. The human mind uses several means to correlate. One example is pattern recognition. The German idiom augenblick (“blink of the eye”) illustrates this.
Every examiner brings with him or her a lifetime’s experience. Moreover, observers may have had similar experiences but have incorporated them differently.
To illustrate this, there is the old story of two men walking down the street at the same time a woman is walking on the opposite side. One of the men notices her and says to the other,
“Look at that elderly woman. She seems to be in her early seventies, has gray hair, walks with a mild limp, holds her left arm and wrist slightly flexed, but speaks quite fluently with what seems to be a middle-European accent.”
The second man replies, “Oh, that’s my mother.”
Thus we all look at things in the aggregate or in its parts based on our own personal experience. With less experience, the learner is more likely to use a systematic approach, whereas the more experienced physician may be more likely to use the augenblick approach. However, it is important to realize that no matter how much experience a physician may have, if the augenblick approach does not render a comfortable feeling with the diagnosis, it is necessary to fall back on the systematic approach. Thus it is incumbent on all of us not to forget how to use a systematic approach.
The definition of fever is a core temperature of 38.0°C (100.4°F) or higher. There is a tendency among lay people to call any temperature above 37.0°C (98.6°F) a fever. This often leads to inappropriate treatment with antipyretics and can result in inappropriate diagnostic procedures.
Unlike adults, who become hypotensive early in the course of shock, children are able to preserve their blood pressure until the late stages of shock, partly through peripheral vasoconstriction but primarily by increasing their cardiac output through tachycardia.
Therefore, tachycardia with normal blood pressure is frequently the presentation of shock.
Hypovolemia and hypovolemic shock are usually identifiable in the early stages by tachycardia, but septic shock also can present initially as tachycardia and can, if diagnosed soon enough, be treated with volume.
Orthostatic Changes in Blood Pressure and Heart Rate
Since heart rate and central arterial pressure will vary immediately after changes in position, measurements taken right on position change are almost certain to be abnormal. It is preferable to wait after each position change before the next measurement, as in the following procedure:
- Have the patient lie supine for at least 5 minutes.
- Measure heart rate and blood pressure with the patient still supine.
- Have the patient sit up.
- Wait 2 minutes.
- Hold the patient’s arm so that the cuff is at the level of the heart and measure the sitting heart rate and blood pressure.
- Have the patient stand upright.
- Wait 2 minutes.
- Hold the patient’s arm so that the cuff is at the level of the heart, and measure the standing heart rate and blood pressure.
Orthostatic tachycardia and hypotension may occur in a patient who has been at bed rest for a prolonged time. Thus it is important to have the patient sit up as frequently as possible while in bed.
Other causes of orthostatic tachycardia and hypotension include hypovolemia, autonomic dysfunction, and chronic malnutrition.
Failure to Thrive
Failure to thrive is weight loss or failure to gain weight without obvious cause.
Making correct medical diagnoses is a scientific endeavour. Humankind has employed scientific reasoning since ancient times, although it came more to fruition during the Renaissance.
Over long years, technology has changed, but this only involves the tools we use. Sadly, we often resort to high-technology “tests” before we perform a complete history and physical examination.
Studies have demonstrated that state-of-the art magnetic resonance imaging may yield diagnoses not consistent with those ultimately found at autopsy. Good clinical evaluation is still essential to developing working hypotheses, which then get “tested.”
Tests test hypotheses, not patients. Good working hypotheses serve two purposes: to guide us to which tests to employ and to guide us in their interpretation.
Human minds are capable of thinking on one end of the spectrum, scientifically, based solely on cold facts, or thinking, on the other end of the spectrum, religiously, based solely on faith. Historically, medical reasoning has developed along scientific lines.
However, we all know that medicine is not a perfect science, and although we strive to gather the most appropriate data and to interpret them correctly, physicians and patients are complex entities whose experiences have profound effects on gathering and interpreting data.
Hippocrates knew this when he stated,
“It is more important to know what sort of person has a disease than to know what sort of disease a person has.”
Thus clinicians, although doing their best to apply the scientific method, still find themselves
embedded in that “tug of war” between fact and opinion. We must recognize, humbly, that we can gather imperfect data and that we have to make judgments every day.
Medical Reasoning Within The Diagnostic Framework
The human mind always seeks information,
eliminates what appears to be irrelevant,
correlates the data,
then puts together the remainder into a unifying hypothesis.
It often repeats this sequence, not necessarily consciously. Thus the time-tested diagnostic framework has evolved out of the scientific method (adapted from De Gowin):
Step 1: Take a history. Elicit symptoms.
Step 2: Develop hypotheses. Generate a mental list of pathophysiologic processes and diseases that might produce these symptoms. Then use processes of sorting, eliminating, and correlating to narrow it down.
Step 3: Perform a physical examination. Look for signs of the physiologic processes and diseases suggested by the history, determine what corroborates it, eliminate further what is irrelevant, and perhaps identify new problems to add to the list.
Step 4: Generate a differential diagnosis. List the most probable hypotheses in the order of their possibility.
Step 5: Test the hypotheses. Select laboratory tests, imaging studies, procedures, and consultations with appropriate likelihood ratios to evaluate your hypotheses. Do this mindful of risk, cost, benefit, and logistics.
Step 6: Modify your differential diagnosis. Use the results of the tests to evaluate your hypotheses, perhaps eliminating some and adding others and adjusting the probabilities.
Step 7: Repeat steps 1 to 6. Reiterate your process until you have reached a diagnosis or have decided that a definite diagnosis is neither likely nor necessary.
Step 8: Make the diagnosis or diagnoses. When the tests of your hypothesis are of sufficient certainty that they meet your stopping rule, you have reached a diagnosis.
Step 9: If uncertain, consider a provisional diagnosis or watchful waiting. Decide whether more investigation (return to step 1), consultation, treatment, or watchful observation is the best course based on the severity of the illness, the process, and co-morbidities. If the diagnosis remains obscure, retain a problem list of the unexplained symptoms and signs, as well as the laboratory and imaging findings; assess the urgency for further evaluation; and schedule regular follow-up visits.
Adapted from the Pediatric Diagnostic Examination by
Donald E. Greydanus, MD
Arthur N. Feinberg, MD
Dilip R. Patel, MD
Douglas N. Homnick, MD, MPH