Acute Respiratory Distress Syndrome

Question 1

What is acute respiratory distress syndrome?

Answer 1

• A form of lung insult or injury that happens acutely.
• There are a variety of etiologies with all of them causing a diffuse inflammatory response
• The condition has a high mortality without prompt recognition and treatment.

Question 2

How do you determine the severity of ARDS?

Answer 2

The severity of ARDS can be stratified upon this ratio using PEEP as a constant as an increase in PEEP can alter the value.

1. Mild: > 200 - < 300 on PEEP > 5 cmH2O
2. Moderate > 100 - < 200 on PEEP > 5cmH2O
3. Severe < 100 on PEEP > 5cmH2O

Question 3

What are the clinical features associated with ARDS?

Answer 3

Patients present with both symptoms of ARDS and the underlying inciting event. The ARDS Definition Task Force redefined ARDS as:

1. Onset within 1 week of a known clinical insult or new or worsening respiratory symptoms
2. Bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules
3. Respiratory failure that is not explained by cardiac failure or volume overload
4. Impaired oxygenation with a low PaO2 to fraction of inspired oxygen (FIO2) < 300 mmHg. The ratio is calculated as PaO2/FIO2. For example, if a patient has a PaO2 on their blood gas of 65 and on 85% oxygen, has a ratio of 112.

Question 4

What diagnostic tests are used to diagnose ARDS?

Answer 4

• CXR – abnormal findings are essential to support the diagnosis and help determine the underlying cause. Are there lobar consolidations, infiltrates or bronchograms consistent with PNA? Do you see Kerley B lines and/or cardiomegaly to suggest CHF?
• Chest CT – is not essential unless the CXR findings are not clear or if you are looking for cavitation due to TB. If pancreatitis is the suspected cause, an abdominal CT is done
• EKG – look for cardiac dysfunction including MI, arrhythmias
• BNP – will not diagnose ARDS but helps distinguish the presence of edema
• Echocardiogram – either TTE or TEE depending on the suspicion of valvular heart disease
• Cultures – Bacterial, fungal, viral cultures if an infectious process is suspected

Question 5

What are the most common causes of ARDS?

Answer 5

• Sepsis
• Infectious or aspiration pneumonia
• Trauma and burns
• Pancreatitis
• Smoke inhalation
• Shock
• Transfusion related lung injury
• Complications of cardiothoracic surgery
• Complications of hematopoietic stem cell transplant
• Drug toxicity

Question 6

How do you treat patients with ARDS?

Answer 6

• Ventilatory support – with _low tidal volumes 6 ml/kg of ideal body weigh_t. Adjust PEEP to maintain saturations
• Oxygenation – maintain oxygen saturations > 88%
• Treatment of underlying cause
• Nutrition- monitor serum protein, albumin and pre albumin levels. Initiate feedings if no contraindication
• Fluid management – After resolution of shock, effort should be made to attempt diuresis CVP used as guide, goal <4
  
  • Shortens time on vent and ICU length of stay (13 days vs 11 days)

Question 7

What indicator is the most predictive of lung injury in ARDS?

Answer 7

Plateau pressure

Question 8

What is the goal plateau pressure in ARDS?

Answer 8

• Goal plateau pressure < 30, the lower the better
  
  • Decreases alveolar over-distention and reduces risk of lung strain
• Adjust tidal volume to ensure plateau pressure at goal
• It may be permissible to have plateau pressure > 30 in some cases
  
  • Obesity
  • Pregnancy
  • Ascites