A 68-year-old woman is hospitalized for an acute exacerbation of chronic obstructive pulmonary disease (COPD). She responds well to treatment and is discharged. At her follow-up appointment, she states that she has been compliant with treatment but has had 2 acute exacerbations in the last 9 months. In addition to COPD, her medical history is significant for hypertension, hyperlipidemia, and atrial fibrillation. She takes hydrochlorothiazide, simvastatin, diltiazem, and salmeterol. She also takes inhaled albuterol and ipratropium as needed. She does not smoke, is up to date with the appropriate vaccinations, and is undergoing pulmonary rehabilitation. Her vitals are taken: blood pressure 132/86 mmHg, heart rate 87 beats per minute, respiratory rate 16 breaths per minute, and oxygen saturation 94% on room air.
Which of the following is the most appropriate next step in management?
Add inhaled fluticasone. This patient’s COPD is progressively worsening and she suffered another acute exacerbation, which makes it necessary to step up her treatment to the next level. Treatment of COPD progresses in a stepwise fashion based on symptoms, number of exacerbations, and GOLD staging criteria, which relies on forced expiratory volume in 1 second (FEV1) for staging. For the shelf examination, the most important task is to recognize when a patient requires a step-up in therapy and then to know what the next step in therapy is. The first step in all of these patients is to decrease risk factors: smoking cessation and vaccinations to prevent lung infections (pneumococcal vaccine and annual influenza vaccine). Pulmonary rehabilitation is another supplemental therapy that is useful in patients with at least moderate symptoms. The treatment steps in pharmacologic therapy are summarized in below in a stepwise fashion; when a patient is experiencing worsening of symptoms or acute exacerbations, the next step should be added to the current regimen. Other complicated treatments for advanced disease, such as lung volume reduction surgery, are not typically tested on the shelf examination. This patient’s regimen includes short-acting bronchodilators and a LABA, and therefore the next step in management is an inhaled corticosteroid.
(A) Theophylline blocks phosphodiesterase and increases intracellular cAMP, leading to increased catecholamine release. It is not a first-line therapy, but it may be used in severe COPD for refractory disease. As a sympathomimetic, it can exacerbate tachyarrhythmias and therefore is not a good option in this patient with atrial fibrillation. (C) Oral corticosteroids are used for acute exacerbations but not in chronic disease due to the negative side-effect profile as well as an increase in mortality. (D) This patient does not meet criteria for home oxygen therapy at this time (criteria explained later). (E) The patient has worsening symptoms and the next step in therapy is warranted.
Step-Up Therapy for COPD:
A 33-year-old alcoholic man is hospitalized for fever, chills, and cough productive of currant jelly sputum. Blood and sputum cultures are drawn, and a chest x-ray is consistent with lobar pneumonia. Urine toxicology screen and a serum ethanol level are negative. After being admitted and started on empiric antibiotics, he continues to decompensate and becomes more hypoxemic based on pulse oximetry.
Which of the following choices best represents the pathophysiologic parameters seen in this patient? (Note: A–a gradient is Alveolar– arterial gradient; FiO2 is the fraction of inspired oxygen.)
Low PaO2, normal PaCO2, increased A–a gradient, and no change in response to increased FiO2. This question assumes a background knowledge of the physiology of gas exchange and how to differentiate between hypoxemic and hypercapnic respiratory failure. Most cases of hypoxemia involve an elevation in the Alveolar–arterial (A–a) gradient, which is the product of the partial pressure of alveolar oxygen (PAO2) minus the partial pressure of arterial oxygen (PaO2). The A–a gradient normally increases with aging and is represented by the formula: “age/4 + 4.” (Although there is an equation for calculating the PAO2, the concept is more important than the equation for the shelf examination.) There are many causes of hypoxemia, and it is best to use a systematic approach for this discussion.
The causes of respiratory failure can be broken up by whether there is hypoxemia with a low/normal PaCO2 (hypoxemic respiratory failure) or there is hypoxemia and an elevated PaCO2 (hypercapnic respiratory failure). Major causes of hypoxemic respiratory failure include ventilation/perfusion (V/Q) mismatch, right-to-left shunts, and diffusion impairment. V/Q mismatch is a disease process that causes an imbalance between blood flow and gas exchange, which decreases the efficiency of gas exchange and causes hypoxemia. This is really a gray zone in between two states: if taken to one end of the spectrum with a pure loss of perfusion (e.g., pulmonary embolism), this causes “dead space ventilation” (normal air flow but no blood flow). If taken to the other end of the spectrum with a pure loss of ventilation (e.g., atelectasis or pneumonia with consolidation), then this becomes a shunt. Shunts are simply the result of blood bypassing any area of gas exchange, carrying hypoxemic blood back into the circulation. Shunts can also be extrapulmonary (e.g., intracardiac shunts like an atrial septal defect). An example of diffusion impairment is interstitial lung disease with fibrosis that increases the distance that oxygen must traverse to get from the alveoli to the blood stream; processes that increase the rate of blood flow (exercise) or decrease the oxygen-carrying capacity (anemia) can exacerbate hypoxemia caused by diffusion impairment. Other causes besides the above three mechanisms include poisoning (carbon monoxide, methemoglobinemia, and cyanide) and high altitudes (same fraction of inspired oxygen but lower atmospheric pressure). Hypercapnic respiratory failure is caused by inadequate ventilation (respiratory rate × tidal volume), and results from processes such as neuromuscular disease, oversedation, COPD, and obesity hypoventilation syndrome. In hypoxemic respiratory failure, the patient attempts to compensate for the hypoxemia by increasing ventilation, which results in a normal or low PaCO2.
This patient has hypoxemic respiratory failure from pneumonia, and there are no reasons for hypoventilation (no sedation and a negative drug screen). In a process like a lobar pneumonia, where alveoli are completely filled with pus, shunting will predominate over V/Q mismatch and therefore the hypoxemia will not be corrected with increased oxygen administration. Positive end-expiratory pressure (PEEP) might help to open some of the alveoli in areas of consolidation, converting a shunt to a V/Q mismatch, but this question asks about the response to FiO2 alone.
A 62-year-old woman presents to the hospital with shortness of breath. She has a history of HIV infection and was recently hospitalized for PCP pneumonia and was discharged 3 days ago in stable condition on oral antibiotics. After discharge, she started to experience a headache and subsequently developed worsening shortness of breath. The rest of her medical history is significant for hypertension, diabetes, peripheral arterial disease, hypothyroidism, and gastroesophageal reflux disease (GERD). Her regular medications include aspirin, amlodipine, hydrochlorothiazide, metformin, levothyroxine, and pantoprazole. She has not been compliant with her antiretrovirals. Her allergies include trimethoprim–sulfamethoxazole and penicillin. She drinks alcohol moderately and has a 30 pack-year smoking history. On examination, she has a temperature of 37.6°C, blood pressure of 158/96 mmHg, heart rate of 86 beats per minute, and respiratory rate of 26 breaths per minute. There are no murmurs or jugular venous distention, and there are no wheezes or rales on pulmonary examination. There is blue discoloration of her digits and lips. An arterial blood gas shows a normal PaO2, although the blood has a brownish discoloration.
Which of the following is the most likely diagnosis?
Methemoglobinemia. The differential of dyspnea is broad, but it can be narrowed based on the history and physical examination (even in a complicated patient like this one!). The two broad categories that can be considered first are pulmonary and cardiovascular disease. Pulmonary disease may be broken down into airway disease (e.g., bronchitis, asthma, bronchiectasis, tumor), parenchymal disease (e.g., interstitial lung disease, pulmonary edema), or pleural disease (e.g., pleural effusion). Important cardiovascular diseases that cause dyspnea include left heart failure, pulmonary hypertension, pulmonary embolism, and vasculitides affecting the pulmonary vasculature.
In addition to these two categories, there are neuromuscular causes (e.g., myasthenic crisis), metabolic causes (e.g., metabolic acidosis), psychological causes (e.g., panic disorder), and causes relating to the oxygen-carrying capacity of the blood. The diagnosis in this case relates to this last category. Methemoglobinemia may be congenital or acquired, and certain medications such as dapsone and nitric oxide can cause methemoglobinemia. The pathophysiology involves oxidation of iron to the ferric state (Fe3+ ), which cannot bind oxygen but causes the other heme groups in hemoglobin to bind oxygen more tightly, shifting the hemoglobin dissociation curve to the left. The result is an inability of the circulating hemoglobin to provide oxygen to tissues. PaO2 will be normal and the pulse oximetry will typically be in the 85% to 89% range. The blood is sometimes described as “chocolate blood” due to its dark red or brown appearance. Treatment is with methylene blue, an agent that reduces Fe3+ back to Fe2+ . This patient likely has methemoglobinemia secondary to dapsone, since dapsone is an alternative to trimethoprim–sulfamethoxazole for the treatment of PCP pneumonia.
(A, B, C, D) The rest of these conditions, except for carbon monoxide poisoning, would have a depressed PaO2. (D) Carbon monoxide poisoning may present with headache and cyanosis due to carbon monoxide displacing oxygen from heme and reducing the oxygen carrying capacity of the blood. Pulse oximetry and PaO2 will be normal in this condition.
A 19-year-old boy complains of difficulty breathing during exercise. He reports being in good physical shape, but occasionally experiences coughing and have to stop and catch his breath. This seems to occur more often in cold weather. The patient has no significant medical history other than seasonal allergies, and he takes no medication. He has some patchy dry skin over the elbows with some erythema and excoriations; otherwise the physical examination is normal. He is referred for spirometry, which is normal.
Methacholine challenge. Although the diagnosis of asthma is tested more often on the Pediatrics shelf examination, it may show up on the Medicine shelf examination and therefore a brief overview may be useful. Asthma is an intermittent obstructive lung disease that is classically described as airway hyper-responsiveness with variable airflow obstruction. It is a common condition, especially in those with other features of the atopic triad (seasonal allergies, eczema, and asthma). Symptoms are usually caused by common triggers such as infections, environmental exposures (smoke, allergens, etc.), medications (β-blockers, aspirin, NSAIDs), cold air, and exercise. Because symptoms of asthma may be intermittent, the physical examination is often normal. If spirometry is consistent with an obstructive pattern, then asthma can be differentiated from COPD by assessing the improvement in FEV1 after bronchodilator administration (e.g., albuterol); if FEV1 improves by at least 12%, then the diagnosis is more consistent with asthma. If spirometry is normal, as in this patient, a provocative test such as the methacholine challenge can be performed. Methacholine is a muscarinic agonist that will cause bronchoconstriction; asthmatics will be much more sensitive to lower doses of methacholine than the regular population and will develop an obstructive pattern on spirometry with a prolonged FEV1.
(A) This patient has normal findings on spirometry and therefore the administration of albuterol will not change the findings. (C) A chest x-ray would likely be normal in this patient. During an acute exacerbation, there may be hyperinflation of the lungs. (D) Allergen skin testing is not a bad idea, especially since the patient has a history of seasonal allergies and eczema, but it is not the best next step in management. (E) If the initial workup is negative, then the patient might be encouraged to measure peak expiratory flow or try a bronchodilator while symptomatic. Since he is undergoing spirometry already, a methacholine challenge should be attempted first to make the diagnosis.
A 38-year-old woman presents to the hospital with fever, cough, and shortness of breath. On imaging, a lobar pneumonia is confirmed, but a lung mass is also noted. She is treated with antibiotics and at a later time the mass is biopsied via bronchoscopy. Eventually the patient is discharged to follow up as an outpatient. The biopsy report suggests a benign lesion, and the patient agrees to have the lesion followed with imaging. Several months later, the patient presents with difficulty breathing for a few weeks. Her vitals are normal, but inspiratory and expiratory stridor is heard along with rhonchi on lung auscultation. There are no wheezes or rales. Examination of the oropharynx is unremarkable. Spirometry with flow-volume loops shows a plateau during inspiration and expiration, with decreased peak inspiratory and expiratory flow.
What is the most likely diagnosis?
Subglottic stenosis. Auscultation of lung sounds helps to define the site of pathology within the airway anatomy. Rhonchi are lowpitched, sonorous sounds that typically indicate secretions in the upper airway. High-pitched sounds as a result of upper airway obstruction are termed stridor. Wheezes are high-pitched musical sounds caused by narrowing of bronchioles. Rales, also known as crackles, come in two types (wet and dry), and the pathology in both types involve the distal airway. Wet rales are caused by fluid accumulation within alveoli, which overwhelms the mechanism of surfactant to decrease surface tension and causes the alveoli to collapse and open back up during the end of inspiration; dry rales (velcro sound) typically involve the smaller airways leading into the alveoli and are usually due to interstitial processes such as pulmonary fibrosis.
This patient has stridor, which suggests that the problem involves the upper airway. In addition, the reduction in peak inspiratory and expiratory flow with plateaus seen on the flow-volume loops are indicative of a fixed obstruction. The only answer choice that fits with a fixed obstruction of the upper airway is subglottic stenosis, which can be congenital or acquired from trauma during procedures such as bronchoscopy. The rhonchi are likely a result of excess secretion build up below the obstruction. It is likely that the tumor is indeed benign and is not responsible for this patient’s symptoms. (B, C) A carcinoid tumor and viral bronchiolitis would both produce wheezing, which is not heard in this patient. (D) Postobstructive pneumonia could occur in this patient given that she has a lung mass near the airway, however this would produce rales and not stridor.
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