Acute Respiratory Distress Syndrome

Question 1

Definition of ARDS: clinical syndrome of

Answer 1

1. Severe dyspnea of rapid onset
2. Hypoxemia
3. Diffuse pulmonary infiltrates leading to respiratory failure

Question 2

Medical illness associated with development of ARDS

Answer 2

MC: penumonia (80%)
2nd: sepsis (40-60%)

Question 3

Surgical conditions associated with ARDS

Answer 3

Pulmonary contusion
Multiple bone fractures
Chest wall trauma/flail chest

Question 4

Clinical variables associated with development of ARDS

Answer 4

Older age
Chronic alcohol abuse
Pancreatitis
Pneumonia
Sepsis (40-60%)
Severity of critical illness

Question 5

Three phases of ARDS

Answer 5

Exudative phase
Proliferative phase
Fibrotic phase

Question 6

Exudative phase

Answer 6

Injured cells: alveolar capillary endothelial cells & Type I pneumocytes (alveolar epithelial cells)

Edema fluid rich in protein
(+) Inflam cytokines (IL1,IL8, TNF) and leukotriene B4

Plasma protein+dysfunctional pulmonary surfactant=hyaline membrane whorl

Alveolar edema: in dependent portion (diminished aeration)->collapse of dependent lung-> decreased lung compliance ->intrapulmonary shunting and hypoxemia ->dyspnea

Microvascular occlusion-> dec pulmonary arterial blood flow ->inc dead space ->pulmonary hypertension

Question 7

Prominent findings in early ARDS (Exudative phase)

Answer 7

Severe hypoxemia
Hypercapnia

**Secondary to increase in pulmonary dead space

Question 8

Differential diagnosis of ARDS

Answer 8

Cardiogenic pulmonary edema
Bilateral pneumonia
Alveolar hemorrhage

Question 9

Proliferative phase

Answer 9

Occur in day 7 to 21
Patients liberated from MV

Fate of patients
1. Develop progressive lung injury
2. Resolution of symptoms

Question 10

First signs of Resolution in ARDS (Seen in proliferative phase)

Answer 10

Initiation of lung repair
Organization of alveolar exudates
Shift from neutophil to lymphocyte-predominant pulmonary infiltrates (type II pneumocytes)

Question 11

Fibrotic phase

Answer 11

After 3-4 weeks

Alveolar edema and inflammatory exudates convert to alveolar duct and interstitial fibrosis

Hallmarks: disruption of acinar architecture ->emphysema like changes with large bullae

Question 12

Marker associated with increased mortality risk

Answer 12

Lung biopsy evidence for pulmonary fibrosis in ANY phase of ARDS

Question 13

General principles in the treatment of ARDS

Answer 13

1. recognition and treatment of underlying medical disorders (pneumonia, sepsis, aspiration, trauma)
2. Minimization of uneccesary procedures
3. Bundled care for ICU patients (prophy for DVT, GI bleeding, aspiration, excerssive sedation, prolonged MV, central venous catheter infections)
4. Prompt recognition of nosocomial infections
5. Adequate nutrition vua enteral route

Question 14

2 Principal mechanisms for lung injury

Answer 14

1. Volutrauma (overdistention from excess tital volume) and barotrauma (increased alveolar pressures)
2. Atelectrauma (from recurrent alevolar collapse)

Question 15

Chest CT findings of ARDS

Answer 15

Principally involving dependent portions of the lung with relative sparing of other regions

**Compliance differs in affected vs normal areas->attempts to fully inflate consolidated lungs–>overdistention and injury to the more normal areas

Question 16

Ventilator induced injury: seen particularly with high tidal volume ventilation

Answer 16

High tidal volume ventilation

Question 17

Strategies to prevent ARDS during ventilation

Answer 17

low VT ventilation (6 ml/kg of PBW)
Plateau pressue at <=30 cm H20
PEEP adjusted to minimize FIo2

Mortality rate is lower by 31%

Question 18

Causes for reduced lung compliance

Answer 18

1.Presence of alveolar and interstitial fluid
2. Loss of surfactant

Question 19

Best PEEP

Answer 19

1. Able to promote alveolar recruitment
2. Minimize alveolar overdistentionand hemodynamic instability
3. Provide adequate PaO2 while minimizing Fio2

Question 20

Prone positioning

Answer 20

Reduction in 28 day mortality for patients with severe ARDS PAO2/Fio2 <150 mmg HG

Question 21

Recruitment maneuvers

Answer 21

1. Increase PEEP to high levels to recruit atelectatic lung
2. Alternate modes of MV (airway pressure release ventilation and high frequency oscillatory ventilation)
3. Lung-replacement therapy with extracorporeal membrane oxygenation (ECMO)

Question 22

Fluid management

Increased pulmonary vascular permeability ->leading to intersitial and alveolar edema fluid rich in protein

***CENTRAL FEATURE IN ARDS

Answer 22

Agressive attempts to reduce left atrial filing pressures with fluid restriction and diuresis

this is limited by hypotension and hypoperfusion

Question 23

True or false

current evidence does not support the routine use of glucocorticoids in the care of ARDS patients

Answer 23

True

Question 24

Mortality in ARDS is attributable to

Answer 24

Non pulmonary causes

Sepsis and nonpulmonary organ failure >80% of deaths

Question 25

Major risk factors for ARDS mortality: nonpulmonary

Answer 25

1.Advanced age >75 2.Preexisting organ dysfunction: chronic liver disease, chronic alcohol abuse, chronic immunosuppression **Direct lung injury (pneumonia, pulmonary contusion, aspiration) have higher mortality rates as compared to indirect causes Surical and trauma patients with ARDS have higher survival rate than other ARDS patients

Question 26

Increasing severity of ARDs: predicts mortality

Answer 26

Predicting ARDS mortality from other parameters of lung injury includes 1. PEEP >=10 cm H20 2. Respiratory system compliance <= 40 ml/cm H20 3.Extent of alveolar infiltrates on chest radiography 4. Corrected expired volume per minute >=10L/min (surrogate measure of dead space)

Question 27

Recovery of maximal lung function: within 6 months

Answer 27

Recovery of lung function is strongly associated with 1. Extent of lung injury in early ARDS Factors associated with less recovery of pulmonary function 1. Low static respiratory compliance 2. High levels of required PEEP 3. longer duration of MV 4. jigh lung injury scores

Question 28

Severity of ARDS: oxygenation

Answer 28

Mild: 200 mmHg