Acute Respiratory Distress Syndrome (ARDS)
RDS is a life-threatening form of respiratory failure characterized by inflammatory pulmonary edema
resulting in severe hypoxemia . ARDS is common, associated with substantial morbidity and frequently fatal. According to Berlin definition, ARDS is defined as an acute form of diffuse lung injury occurring in patients with a predisposing risk factor. Common risk factors of developing ARDS are pneumonia, sepsis, gastric content aspiration, trauma, pancreatitis, inhalation injury, burns, non-cardiogenic shock, drug overdose, transfusion-related acute lung injury (TRALI), and drowning.
Characteristics and clinical presentations of ARDS
Timing: Onset within 1 week after the trigger insult
Imaging: Bilateral opacities on chest X-ray, not fully explained by effusion,
lobar/lung collapse, or nodules
Non-cardiogenic origin
Respiratory failure not fully explained by cardiac failure or fluid overload
Classification
Presence of hypoxemia base on PaO2/FiO2 ratio measured with PEEP ≥5 cm H2O:
Mild (PaO2/FiO2 201- 300 mm Hg)
Moderate (PaO2/FiO2 101-200 mm Hg)
Severe (PaO2/FiO2 ≤ 100 mm Hg
Management of ARDS
The primary target in ARDS treatment is to ensure adequate gas exchange while minimizing the risk of ventilator induced lung injury. To date, the mainstay treatment is supportive. Lung protective ventilatory strategy is recommended to ensure adequate oxygenation and CO2 clearance, and minimizing the extent of damage due to mechanical ventilation when required.
Management of ARDS
Non-pharmacological intervention
Mechanical ventilation
Lung recruitment and PEEP selection
Tidal volume setting
Oxygen and carbon dioxide target
Pharmacological intervention
Neuromuscular blocking agent – cisatracurium within 48 hours in severe ARDS patient has showed to
improve survival, increased the ventilator free days without increasing muscle weakness. A 48-hour
continuous infusion of cisatracurium in critically ill patients reduced the risk of death, reduced the risk of
barotrauma, and did not affect the duration of mechanical ventilation or the risk of ICU-acquired weakness.
Corticosteroids – American College of Critical Care Medicine consensus recommends that glucocorticoid should be initiated early (<14 days of ARDS). Methylprednisolone of 1 mg/kg/ day for ≥14 days is recommended in patients with severe early ARDS. Glucocorticoids should be weaned and not stopped abruptly. Meduri et al. in its meta-analysis found that methylprednisolone at dose 1-2mg/kg/day for ≥7 days reduced ICU mortality rates.
Inhaled nitric oxide – Seemed promising in early trials, but in larger controlled trials, did not change mortality rates in adults with ARDS. Inhaled nitric oxide did not reduce mortality and may results in only a transient improvement in oxygenation.
Acute Exacerbation of Asthma
Exacerbations of asthma is characterized by a progressive increase in symptoms of shortness of breath, cough, wheezing or chest tightness, and a progressive decrease in lung function. Acute exacerbation of asthma carries a high mortality. Patients who are at high risk of asthma-related death should be assessed carefully and should be managed in a high care setting. Risk of asthma-related death:
History of near-fatal asthma requiring intubation and mechanical ventilation
Hospitalization or emergency care visit for asthma in the past year
Currently using or having recently stopped using oral corticosteroids (a marker of event severity)
Over-use of SABAs, especially the use of more than one canister of salbutamol (or equivalent) monthly
A history of psychiatric disease or psychosocial problems
Poor adherence with asthma medications and/or poor adherence with (or lack of) a written asthma action plan
Food allergy in a patient with asthma