Recognizing Zebras in Anesthesiology Clinical Vignettes

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The anesthesiology boards do not attempt to trick you. In other words, they present multiple-choice questions that are fair and clinically relevant. This means that most of the anesthesiology clinical vignettes on the board exams will involve patients who have a commonly occurring form of a disorder. After all, the assessment and treatment of these common cases make up a major part of the clinical practice of a physician. However, the clinician must still be able to identify the rare condition. Hence the question arises, “how do you differentiate whether the question is concerning a ‘horse’ or a ‘zebra?’”

If the question is regarding a “zebra,” the clinical vignette will contain some information about the demographics of the patient that is unusual for the particular disorder, such as the disorder being an unusual occurrence in that patient’s gender, at their age, or perhaps in their ethnic or racial group. For example, if the clinical vignette describes a patient under 20 years of age with hypertension that is difficult to control, the age of the patient should alert you to think about etiologies that are not commonly present in adults, such as pheochromocytoma.

Or perhaps the question is regarding a “zebra” because there is some information included in the clinical vignette that seems to be clearly out of space.

For example: During the preoperative evaluation of a known asthma patient, it is found that he often has symptoms of chest tightness, cough, wheezing, and shortness of breath, particularly while sleeping at night. He reports that he uses “some asthma inhaler” for his symptoms.

This may seem to give the initial impression that his current asthma treatment is not effective. This may certainly be the case. However, another explanation may be that the patient is using a short-acting bronchodilator, not sufficient enough to be able to cover the hours of sleep, thus leading to nocturnal symptoms as the plasma medication levels fall. The fact that the occurrence of nocturnal attacks, along with the use of “some asthma inhaler”, has been mentioned in the vignette may be enough to make you think about something other than your first clinical hypothesis.

Another clue for a “zebra” may be hidden in the nature or setting of a particular disease. For instance, the question may describe that the patient has recently traveled to a tropical country, or the patient has a history of being involved in unusual activity such as spelunking or high-altitude mountain climbing, or the patient’s occupational history may be described. Consider the example of a clinical vignette that describes a plumber who is scheduled to undergo an inguinal hernia repair. The patient has a history of nonproductive cough and dyspnea. Close attention needs to be given to the information regarding the occupation of the patient as well as the associated symptoms, as the presence of interstitial lung disease may affect the management of anesthesia in this patient.

The thing to keep in mind for the board exams is “Nothing has been included in the clinical vignette by accident”. Everything that has been placed in the vignette is there to put you on one diagnostic track or another, or on one treatment track or another. Every piece of information is there to assist you in making diagnostic or treatment distinctions.

Example Exam Question from Anesthesiology

Question: A 22-year-old homeless man with a recent history of incarceration presents to the emergency department with right lower abdominal pain and vomiting. Rebound tenderness is present, and his WBC count is elevated. A diagnosis of acute appendicitis is made, and an emergency appendectomy is planned. The patient reports that he also has a history of low-grade fever and productive, purulent cough for which he has been receiving medications for the last one month. Which of the following statements best describes the management of anesthesia in this patient?

1. Fentanyl may have a longer duration of action in this patient
2. Local anesthetics will be ineffective in this patient
3. Suxamethonium cannot be used in this patient
4. Tracheal intubation should be performed in a negative-pressure environment
5. Cisatracurium is contraindicated for this patient

Tuberculosis is an infection that is caused by Mycobacterium tuberculosis. More than half of all tuberculosis cases in the United States are seen in recent immigrants. Other than immigrants, tuberculosis predominantly affects individuals with specific risks for exposure (e.g., healthcare workers, alcoholics, prisoners, residents of nursing homes and homeless shelters, and chronically debilitated patients). The patient described in this clinical vignette is high-risk for tuberculosis because of his history of homelessness and recent incarceration. The presence of low-grade fever and productive, purulent cough further point towards tuberculosis, and the medications that the patient has been receiving for the last one month are most likely to be anti-tuberculous medications.

An elective surgery should be postponed in a patient with tuberculosis until the patient is no longer considered to be infectious. However, if the surgery cannot be delayed, in order to prevent the spread of infection, the number of involved personnel should be limited and high-risk procedures such as tracheal intubation, suctioning, and bronchoscopy should be performed in a negative-pressure setting if possible. Anti-tuberculous medications may interact with drugs used during anesthesia. For instance, rifampicin is a potent inducer of the CYP450 system, particularly isoenzyme CYP3A4. Fentanyl is extensively metabolized by CYP3A4, and may show a shortened duration of action when used during anesthesia in a patient receiving rifampicin. Local anesthetics exert their action mainly at the injection site and are thus still likely to be effective. The effect of suxamethonium is unaltered unless liver dysfunction has resulted in reduced pseudocholinesterase levels. Similarly, cisatracurium, which has organ-dependent metabolism, is minimally affected by anti-tuberculous therapy.

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