Shortness Of Breath Case 1

Shortness Of Breath Case 1


A fire in a local factory brings patients to several hospitals with injuries. A 25-year-old woman is found by firefighters in a smoke-filled enclosed office. She has no apparent burns, but is complaining of shortness of breath and looks quite distressed. She is intubated in the emergency department for hypoxemia and admitted to the intensive care unit, where bronchoscopy reveals carbonaceous material in her large airways.

Q1
Where the bronchoscope camera exits the endotracheal tube, the resident, who has never performed a bronchoscopy before, notes that the rings of the airway are incomplete: the airway has "c-shaped" rings, and the remainder of the airway's circumference appears flat, with no clearly defined cartilaginous rings. Distal to the camera is a bifurcation. What is the significance of these findings?
/ A. The camera is in the trachea
/ B. The camera is in the trachea, but the rings are abnormal
/ C. The camera is in the left mainstem bronchus
/ D. The camera is in the right mainstem bronchus
/ E. There is not sufficient information to determine the location of the camera


Q2
18 hours after ICU admission, a chest x-ray shows bilateral diffuse airspace disease. Despite ventilation with 80% oxygen, her oxygen saturation is 90% and her arterial blood gas reveals a PO2 of 60, a PCO2 of 45, and a pH of 7.36. High airway pressures are required to generate small tidal volumes. What is the pathophysiology underlying this patient's hypoxic respiratory failure?
/ A. Abnormal alveolar capillary permeability
/ B. Acute bronchospasm
/ C. EIevated left atrial pressure
/ D. Rapidly progressive pulmonary fibrosis
/ E. Surfactant deficiency



Q3
Because of her poor pulmonary compliance, the decision is made to ventilate her using small tidal volumes and a high respiratory rate in order to maintain ventilation while avoiding the trauma potentially caused by very high airway pressures.
If her total minute ventilation remains constant, but her tidal volume decreases and respiratory rate increases, which of the following will occur?
/ A. Dead space increases
/ B. Dead space remains constant, but alveolar ventilation decreases
/ C. Dead space ventilation decreases and alveolar ventilation increases
/ D. Shunt decreases
/ E. Shunt remains the same, but alveolar ventilation improves


Q4
A change is made in her ventilator settings. The next arterial blood gas is: P02 60, PCO2 52, pH 7.30. Hemoglobin concentration is constant, as is the patient's temperature. What has happened to the total oxygen content of the blood and the oxygen saturation?
/ A. Arterial blood oxygen content and oxygen saturation has stayed the same
/ B. Arterial blood oxygen content has increased, but oxygen saturation has decreased
/ C. Arterial blood oxygen content has increased, and oxygen saturation has increased
/ D. Arterial blood oxygen content has decreased, and oxygen saturation has decreased
/ E. Arterial blood oxygen content has decreased, but oxygen saturation has increased



Q5
One week after admission, the patient develops fever to 39.4 C (103 F). A new dense infiltrate is seen in her right upper Iobe, and purulent secretions are suctioned from her endotracheal tube. Which of the following organisms is most likely causing a new ventilator-associated pneumonia?

/A.Borrelia burgdorferi

/B.Candida albicans

/C.Chlamydia pneumoniae

/D.Pneumocystis carinii

/E.Staphylococcus aureus

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Shortness Of Breath Case 1 Answers

A1
The correct answer is A. The only complete cartilaginous ring in the trachea is the cricoid cartilage of the larynx. The remainder of the tracheal cartilages are incomplete rings; they are nearly circumferential and maintain the patency of the trachea. The posterior wall of the trachea, directly anterior to the esophagus, is noncartilaginous and appears relatively flat. At the carina, the mainstem bronchi divide: the left mainstem bronchus exits at an angle to divide into left upper and lower lobes, and the right mainstem bronchus continues at a less acute angle off the trachea, where it quickly gives off a branch at an acute angle to the right upper lobe, then continues on to divide into branches to the right middle and lower lobes.
Choice B is incorrect because the tracheal rings are normally incomplete at their posterior aspect.
Choices C and D are incorrect because the cartilaginous rings of the mainstem bronchi are normally complete, thereby excluding the possibility that the camera is in a mainstem bronchus. The posterior membrane also localizes the camera in the trachea.
Choice E is incorrect because the posterior membrane of the trachea is unique to the trachea


A2
The correct answer is A. This patient has the adult respiratory distress syndrome (ARDS), caused principally by alterations in capillary permeability. The normal blood-gas interface permits the transudation of water into the alveolus when the difference in hydrostatic pressure between the airspace and the capillary exceeds the plasma oncotic pressure. This interface, however, is not normally permeable to protein. With injury, whether direct toxic injury (as in this case) or due to inflammatory mediators and oxidative injury (in the case of sepsis), plasma proteins leak into the interstitial space and the airspace. This leaves the hydrostatic gradient unopposed and pulmonary edema ensues, despite normal hydrostatic pressures (i.e., in the absence of elevation of left atrial pressure).
Acute bronchospasm (choice B) can result from smoke inhalation. However, on chest x-ray films, this would appear as hyperinflated, abnormally radiolucent lungs. In addition, bronchospasm alone seldom results in this degree of hypoxemia.
Elevated left atrial pressure (choice C) causes cardiogenic pulmonary edema as the result of left heart failure, which is unlikely in this otherwise healthy 25-year-old who has sustained airspace injury as the result of inhalation of a toxic gas.
Pulmonary fibrosis (choice D) is a chronic disorder that can produce bilateral abnormalities on chest x-ray films, hypoxemia, and decreased pulmonary compliance. However, fibrosis as a pathologic process does not develop over hours and is not compatible with such an acute onset.
Surfactant deficiency (choice E) causes the neonatal respiratory distress syndrome, which is characterized by a similar clinical picture of decreased compliance, hypoxemia, and bilateral diffuse airspace disease. Surfactant has never been shown to be deficient in or beneficial in the treatment of ARDS.


A3
The correct answer is B. Dead space (volume that is ventilated, but does not participate in gas exchange) remains constant, but with an increase in respiratory rate and a decrease in tidal volume, alveolar ventilation declines. That is, the amount of the minute ventilation that goes to the dead space increases:
Alveolar ventilation/min = (Tidal volume - Dead space volume) x Respiratory rate
As an example: a patient is breathing a tidal volume of 600 cc, 150 cc of which is dead space, at 12 x/minute. This translates into a total minute ventilation of 7.2 liters/min: alveolar ventilation/min is (600 cc-150 cc) x 12, or 5.4 liters/min. If her tidal volume decreases to 400 cc per breath, and she breathes at 18 breaths/min, minute ventilation is still 7.2 liters/min, but alveolar ventilation/min = (400 cc-150 cc) x 18 = 4.5 liters/min.
Choice A is incorrect because the dead space is not significantly altered by a drop in tidal volume.
Choice C is incorrect because dead space ventilation would increase. Before her ventilator was adjusted, dead space ventilation would be 1.8 L/min (150 cc x 12/min) and after the adjustment, it would be 2.7 L/min (150 cc x 18/min). And as shown above, alveolar ventilation would decrease.
Choice D is incorrect because with a drop in tidal volume, the shunt can remain the same or can actually increase, if the lower tidal volume results in closure of previously ventilated alveoli. (A shunt can be thought of as the opposite of dead space in the lung: an area that is perfused, but not ventilated.)
Choice E is incorrect because alveolar ventilation decreases (see above)


A4
The correct answer is D. Arterial blood oxygen content has declined because of the rightward shift of the oxyhemoglobin dissociation curve. Arterial blood oxygen content is a function of hemoglobin concentration, of partial pressure of oxygen in the blood, and of the affinity of hemoglobin for oxygen. In this example, partial pressure of oxygen and hemoglobin concentrations are constant. Because of the lower pH and the higher CO2, however, the oxyhemoglobin dissociation curve has shifted to the right. That is, for a given partial pressure of oxygen, the hemoglobin saturation is lower. At higher concentrations of H+ ions, PCO2, temperatures, and concentrations of 2,3-DPG, hemoglobin has less affinity for oxygen. "A simple way to remember these shifts is that exercising muscle is acid, hypercarbic, and hot, and it benefits from increased unloading of O2 from its capillaries." (West, Respiratory Physiology, Chapter 6.)
Choices B and E are incorrect because oxygen saturation is the principal determinant of oxygen content. That is, the majority of the oxygen in the blood is carried bound to hemoglobin. As saturation declines, content declines.


A5
The correct answer is E. Staphylococcus aureus is a gram-positive coccus that is a common cause of ventilator-associated pneumonia. It is a colonist of the skin and the nasopharynx, and is a common cause, not only of pneumonia (particularly ventilator-associated and post-influenza), but of endocarditis, superficial skin infections, surgical wound infections, and bacteremia (especially associated with indwelling catheters).
Borrelia burgdorferi(choice A) is a tick-transmitted spirochete that is responsible for Lyme disease. This disorder is characterized by erythema migrans in its early stage, followed by a variable presentation that can include malaise and fatigue accompanied by arthralgias, carditis, migratory musculoskeletal pain, meningitis, neuritis, chronic oligoarticular arthritis, and skin and neurological abnormalities.
Candida albicans(choice B) is a common yeast, which occasionally colonizes the upper airways of debilitated patients, but rarely is a cause of pneumonia. It is a common cause of vaginitis and can cause thrush, stomatitis, and esophagitis in immunosuppressed patients, and can cause bloodstream infections in patients with indwelling vascular appliances.
Chlamydia pneumoniae(choice C) is a common cause of community-acquired pneumonia as well as upper respiratory tract infection. Like all Chlamydia, it is an obligate intracellular parasitic bacterium.
Pneumocystis carinii(choice D) is an opportunistic pathogen (closely related to fungi and to protozoa), which causes pneumonia in hosts with compromised cellular immunity due to AIDS, corticosteroids, cancer chemotherapeutic agents, or primary defects of cellular immunity.