Continued...

Management:

High frequency ventilation : It offers an opportunity to use small tidal volumes to prevent ventilation associated lung injury from over distention, and allows higher PEEP with increased recruitment of alveoli. Nearly normal PCO2 can be maintained with high frequency ventilation.

Partial liquid ventilation : Perfluorocarbon is radio-opaque, inert and colorless liquid that carries a large quantity of oxygen and carbon dioxide. It reduces surface tension and maintains patency of surfactant deficient alveoli. It redirects blood flow to improve ventilation - perfusion ratio. Patient can be safely and adequately oxygenated and ventilated with routine mechanical ventilation.

Inverse ratio ventilation :

• When inspiratory time is kept more than expiratory time (more than half of respiratory cycle) I:E > 1:1. It maintains higher mean airway pressure (MAP) which is a major determinant of oxygenation with lower peak inspiratory pressures (PIP).

Disadvantage: Dynamic hyperinflation may occur because of low expiratory time.

Other Supportive Therapies

Inhaled nitric oxide (INO): In ARDS, pulmonary vasoconstriction causes increase in pulmonary arterial pressure which may lead to right ventricular dysfunction. Right ventricular ejection fraction (RVEF) is reduced with reduced cardiac output.

Mechanism of action:

• It reduces regional pulmonary vascular resistance of ventilated areas.
  
  
• Helps in reducing intrapulmonary shunting.
  
  
• Selectively reduces pulmonary artery pressure without systemic vasodilation and hypotension. As off now it is unknown whether iNO reduces mortality rates in ARDS patients.

Surfactant replacement: Surfactant therapy appears to be an attractive treatment modality in view of quantitative and qualitative abnormalities in surfactant in ARDS patients. Currently studies are on regarding different surfactant preparations, dose and modes of administration.

Pharmacological Therapy Corticosteroids: Steroids may be helpful in view of their potent anti-inflammatory effects, but not beneficial in early course of disease. Steroids may be of benefit when given after 7 days of unresolving ARDS (fibroproliferative phase). Before starting steroids, systemic infection should be treated adequately or ruled out.

Ketoconazole: It is an anti fungal agent and is a potent inhibitor of thromboxane A2 which is an important mediator in septic shock and development of ARDS. Few preliminary studies have shown encouraging results in preventing ARDS in patients who are at risk (e.g. sepsis).

Immunonutrition: It is observed that

• Low carbohydrate and high fatty diet reduces ventilatory demand in patients with respiratory failure.
  
  
• Recent studies suggest that this diet when supplemented with Cicosa-pentanoic acid (CPA), - linoleic acid and antioxidants-
  
  
• Reduces pulmonary neutrophil recruitment
  
  
• Improves gas exchange
  
  
• Reduce duration of ventilation and
  
  
• Decrease risk of development of new organ failures
  
  

Weaning from ventilator: Weaning can be done when all of the following criteria are met:

1. FiO2 < 0.40 and PEEP < 8 cm of water
2. Patient is not on neuromuscular blocking agent.
3. Inspiratory efforts are apparent.
4. Systolic blood pressure > 90 mm Hg without vasopressor support.

Prognosis / Outcome :

 Cause of death in ARDS:

• Early (within 72 hours) - attributed to the original presenting illness or injury.
  
  
• Late (after 3 days) - Because of secondary infections, sepsis, persistent respiratory failure and Multi organ dysfunction syndrome (MODS).

In survivors pulmonary functions improve by 3 months and reach maximum levels of correction by 6 months after extubation. 50% of these patients have abnormal lung functions studies such as restrictive impairment or reduced diffusing capacity.

Last updated on 01-07-2005 Vol 2 Issue 7 Art # 34

How to cite this url

Dublish V,Shah I.Acute Respiratory Distress Syndrome (ARDS).Pediatric Oncall [serial online] 2005 [cited 2005 July 1];2. Art # 34. Available from: