Question 1

Which of the following indirect insults can cause ARDS?

Accepted Answer

ARDS can be caused by numerous insults (risk factors) that both directly and indirectly affect the lung via the generation of inflammatory mediators. Direct pulmonary insults include pneumonia, aspiration, chest trauma, and smoke inhalation. Indirect lung injury may be the result of generalized systemic conditions, such as sepsis, closed head injury, multiple trauma, transfusion reactions, and hemorrhagic shock.

Question 2

What acid-base abnormality does a patient generally display when experiencing stage 2 of ARDS?

Accepted Answer

The second stage, or latent period, lasts a variable period after the onset of acute injury. During this time the patient may appear clinically stable but begins to develop early signs of pulmonary injury or insufficiency manifested by hyperventilation with hypocarbia and respiratory alkalosis.

Question 3

Which of the following clinical signs characterizes the onset of the third stage of ARDS?

Accepted Answer

The third stage, acute respiratory failure, is heralded by the rapid onset of respiratory failure with hypoxemia refractory to supplemental oxygen. Diffuse pulmonary edema and worsening compliance cause significant atelectasis and intrapulmonary shunting.

Question 4

On the basis of the Berlin definition of Acute Respiratory Distress Syndrome (ARDS), the definition of moderate acute respiratory distress syndrome comprises which of the following components? I. PaO₂/FiO₂ $\le$ 300 mm Hg II. Onset of respiratory symptoms within 1 week of clinical insult III. Pulmonary capillary wedge pressure greater than 18 mm Hg IV. Chest imaging findings of new infiltrate consistent with acute pulmonary parenchymal disease

Accepted Answer

Within 1 week of known clinical insult or new/worsening respiratory symptoms; bilateral opacities that are not fully explained by effusions, lobar/lung collapse, or nodules. Can be either on CXR or CT scan; with PEEP $\ge$5, mild ARDS: PaO₂/FiO₂ 201 to 300, moderate ARDS: PaO₂/FiO₂ $\le$ 200, severe ARDS: PaO₂/FiO₂ $\le$ 100; risk factors for ARDS must be present. Respiratory failure that is not fully explained by cardiac failure or fluid overload. If no risk factors are present, objective assessment (e.g., echocardiography) is required to exclude hydrostatic edema.

Question 5

How should the therapist use the point on the pressure-volume loop where the shape changes from concave to exponential?

Accepted Answer

The point on the pressure-volume loop where the shape changes from concave to exponential is known as the lower inflection point. It reflects the pressure point at which alveoli begin to open and is located above functional residual capacity (see Figure 29-2 in the textbook). This suggests that many gas exchange units will collapse at normal transpulmonary pressures in acutely injured lungs and may need significant PEEP to maintain patency during expiration.

Question 6

Which of the following regions of the lungs is most likely to be unaffected by pathophysiology associated with ARDS?

Accepted Answer

Lung injury and areas of involvement in ARDS are heterogeneous and not uniform through all lung units. Some areas of the lung, typically in the dependent regions, are grossly affected. Other regions of the lung, typically in the nondependent regions, may be relatively unaffected. This creates varying areas of compliance within the lung itself. Dependent regions are generally fluid filled, atelectatic, and noncompliant. Nondependent areas are relatively normal and, thus, at risk for overdistention (i.e., volutrauma) and/or barotrauma during mechanical ventilation.

Question 7

What level of FiO₂ should the therapist avoid using long term in patients with ARDS?

Accepted Answer

Every patient with ARDS is hypoxemic by definition. Prolonged administration of high concentrations of oxygen can damage the lungs, owing to the formation of highly reactive oxygen free radicals. Human and animal studies suggest that a prolonged FiO₂ greater than 0.60 should be avoided to prevent oxygen-induced pulmonary damage.

Question 8

Which of the following pathophysiologic changes seen in ARDS is responsible for the decrease in available surface area for gas exchange?

Accepted Answer

Vascular changes occur throughout the later stages of ARDS with obliteration of small precapillary vessels and an increase in the medial thickness of intra-acinar pulmonary arteries. Overall, these changes markedly decrease the available surface area for gas exchange and result in intractable respiratory failure or chronic lung disease, potentially requiring prolonged ventilator support.

Question 9

During the implementation of permissive hypercapnia, which of the following concepts is the most critical to prevent complications of this strategy?

Accepted Answer

A logical consequence of low tidal volume ventilation is hypercapnia. Limiting the peak inspiratory pressure by reducing the tidal volume may decrease minute ventilation and result in hypercapnia. The exact degree of respiratory acidosis that can be safely tolerated remains controversial. However, most undesirable effects are reversible and minor with respiratory acidosis when pH is greater than approximately 7.20.

Question 10

Radiographically, what features are typically seen in ARDS?

Accepted Answer

Subsequently, hypoxemia and widespread infiltrates on chest radiograph can occur. This sequence of events may be triggered by both pulmonary and nonpulmonary insults.

Question 11

The therapist is auscultating a 2-year-old patient with ARDS. Which of the following is a common auscultatory finding in ARDS?

Accepted Answer

Lung examination usually reveals diffuse crackles on auscultation.

Question 12

Which of the following ventilatory strategies is appropriate when mechanically ventilating a patient with ARDS?

Accepted Answer

The ARDS Network investigated the optimal PEEP-FiO₂ strategy for adults with ARDS. The results of this prospective, randomized, multicenter study indicate that in adult ARDS patients who are ventilated with 6 mL/kg tidal volumes and an end-inspiratory plateau pressure of less than 30 cm H₂O, a "moderately high" or "very high" PEEP strategy produced similar survival rates. It must be noted that this study investigated two relatively aggressive PEEP strategies. Subsequent studies performed outside the United States also showed similar results. In a study involving 30 ICUs and 983 adult patients with ARDS, there was no difference in hospital mortality despite the reduction in the need of rescue therapies in the "high" PEEP group. A recent systematic review on the effect of PEEP in ARDS showed that the subgroup of ARDS patients who may stand to benefit most from a "high" PEEP strategy are those with the worst degree of hypoxemia.

Question 13

The therapist was titrating PEEP levels to maintain an SaO₂ of 85% and found that 13 cm H₂O were required to achieve this goal. What should be the most important concern with this level of PEEP?

Accepted Answer

PEEP is typically increased to a level that allows adequate oxygenation as defined by an arterial oxygen saturation (SaO₂) of 85% or greater at an acceptable FiO₂ of 0.60 or less. It should be noted that the minimal acceptable arterial oxygen saturation remains very controversial. A PEEP level of 10 to 15 cm H₂O, or even higher, may be required to achieve adequate oxygenation. However, as PEEP levels exceed from 12 to 15 cm H₂O, the increase in intrathoracic pressure may adversely affect cardiac output, primarily by decreasing systemic venous return. As PEEP is increased, the ARDS patient should be monitored for a decrease in cardiac output with a decrease in peripheral perfusion.

Question 14

A therapist is evaluating the progress of a patient with ARDS. The arterial blood gas reveals a PaO₂ of 55 mm Hg and a PaCO₂ of 65 mm Hg. The PEEP is set at 12 cm H₂O, and the mean airway pressure is 18 on an FiO₂ of 0.60. What is the OI in this patient?

Accepted Answer

OI = ( 11eb6937_bd1c_7a8d_bb3a_937b25b97fce_TB8261_11 *FiO₂)/PaO₂ *

Question 15

What pathophysiologic change accounts for the alteration of the hysteresis curve during ARDS?

Accepted Answer

During ARDS, marked hysteresis of the pressure-volume loop occurs, making significantly higher transpulmonary pressures during inspiration than during expiration necessary to achieve a given lung volume.

Question 16

What are some of the physical signs of respiratory failure among children?
I. Head bobbing
II. Nasal flaring
III. Crying
IV. Grunting

Accepted Answer

The physical signs of respiratory failure will vary with age and include subcostal and supraclavicular retractions, grunting (i.e., an attempt to generate increased intrinsic positive end-expiratory pressure, PEEP), nasal flaring, and head bobbing.

Question 17

Which of the following interventions should the therapist implement to decrease mortality in patients with ARDS?

Accepted Answer

Except for low tidal volume ventilation, no single intervention for adult ARDS has been clearly shown to decrease mortality. This highlights the pressing need for the development of effective management strategies for ARDS.

Question 18

What level of Pplateau should the therapist target to improve outcomes in patients with ARDS?

Accepted Answer

Thus the data support the conclusion that for adult patients with ARDS, the plateau should be limited to less than approximately 32 cm H₂O to improve outcome. The applicability of this conclusion to pediatric ARDS patients requires investigation. It is very possible that the "critical" limit on plateau pressure for infants and children will be less than 32 cm H₂O and may vary with patient age and size.

Question 19

Which of the following pathophysiologic conditions contribute to the decreased pulmonary compliance associated with ARDS?

Accepted Answer

Pulmonary compliance is significantly worsened by the presence of edema and can result in widespread atelectasis. Pulmonary compliance is further impacted by the inactivation of surfactant that results from the presence of plasma protein, such as fibrin, and inflammatory mediators, such as proteinases, in the alveolar space.

Quiz 29: Acute Respiratory Distress Syndrome