First Things First (assess & treat for the following)

• Recognize ALI/ARDS early (acute hypoxemia with bilateral pulmonary infiltrates, which are not primarily due to left atrial hypertension).
• Assess hemodynamic status.
• Decide whether the patient needs intubation or a trial of non-invasive ventilation can be attempted.

History and Physical (assess for the following)

• Identify the risk factors for ARDS/ALI (sepsis, aspiration, pneumonia, alcoholism, transfusion, trauma, drowning, pancreatitis, smoke inhalation, fat emboli).
• Assess vital signs, oxygen saturation, hemodynamic status, work of breathing and end organ perfusion (assess mental status, urine output).
• Trauma survey if indicated
• Intubation and mechanical ventilation when necessary

Diagnostic Tests

• Chest radiograph
• Arterial blood gases
• Central or mixed venous oxygen saturation if available
• Blood lactate
• EKG, echocardiogram
• Serum chemistries and blood counts
• Brain natriuretic peptide
• Microbiological cultures if indicated

General Management Principles

• Early goal-directed resuscitation (within first 6 hours) of patients presenting with severe sepsis/septic shock
• Early and appropriate antibiotic administration for patients with suspected infection
• Administration of sedation and analgesia should be guided by standardized protocols to alleviate patients’ anxiety and discomfort while receiving mechanical ventilation. Care should be taken to avoid excessive administration of sedatives/analgesics, which may prolong the duration of mechanical ventilation and impede bedside neurologic assessments.
• Daily interruption of sedative-drug infusions (daily sedation vacation) decreases the duration of mechanical ventilation and ICU length of stay.
• Patients should be kept in semi-recumbent position (30-45 degrees) to prevent aspiration.
• Stress ulcer prophylaxis in all patients on mechanical ventilation
• Venous thromboembolism prophylaxis should be considered in all patients unless contraindicated (e.g., bleeding).
• Enteral feeding is preferred over parenteral nutrition.
• Be vigilant about central venous catheter infections, and promptly remove the catheters if they appear infected or are no longer required.

Specific Treatment

Protocol for lung protective ventilation (www.ardsnet.org)

(Goals: tidal volume 6 ml/kg, plateau pressure < 30 cmH2O, pH = 7.30-7.45)

• Select volume assist control mode and FiO2 of 100%.
• Set initial tidal volume (VT) at 8 ml/kg using patient’s predicted body weight (PBW).
  • Calculating PBW for males: 50 + [2.3 × (height in inches – 60)]
  • For female patients: 45.5 + [2.3 × (height in inches – 60)]

• Select respiratory rate (RR) to achieve pre-ventilator minute ventilation, but do not exceed 35 breaths/min.
• Add positive end expiratory pressure (PEEP) at 5-8 cmH2O.
• Reduce VT by 1 ml/kg every 2 hours until VT = 6 ml/kg.
• Adjust FiO2 and PEEP to keep PaO2 >55 mm Hg or SaO2 >88%.
• When VT is down to 6 ml/kg, measure plateau pressure (Ppl) and arterial blood PaCO2 and pH.
• If Ppl >30 cmH2O, decrease VT in increments of 1 ml/kg until Ppl is < 30 cmH2O or VT is down to 4 ml/kg.
• If pH is 7.15-7.30, increase RR until pH >7.30 or RR = 35 breaths/min.
• If pH is < 7.15, increase RR to 35 breaths/min. If pH is still < 7.15, increase VT by 1-ml/kg increments until pH is >7.15 or VT = 8 ml/kg.

Allowable combinations of FiO2 and PEEP (cmH2O) for promoting arterial oxygenation in ARDS (www.ardsnet.org)

(Goal: PaO2 55-80 mmHg or SpO2 88-95%)

• FiO2/PEEP combinations: 0.3/5, 0.4/5, 0.4/8, 0.5/8, 0.5/10, 0.6/10, 0.7/10, 0.7/12, 0.7/14, 0.8/14, 0.9/14, 0.9/16, 0.9/18, 1.0/20, 1.0/22, 1.0/24

• Remember the following:
  • Allow partial pressure of arterial carbon dioxide (PaCO2) to increase above normal in order to keep plateau pressure and tidal volumes under the target (permissive hypercapnia).
    • Note: Hypercapnia may worsen intracranial pressure and hence should be avoided in trauma patients with evidence of brain injury.
  • Higher levels of sedation may be needed to offset the respiratory drive induced by permissive hypercapnia and to avoid patient discomfort.
  • Choose optimal PEEP settings to improve lung recruitment and also to avoid cyclic atelectasis at end-expiration.

• Evidence from ARDS network studies
  • Mechanical ventilation with low tidal volumes improves mortality in patients with ALI/ARDS.
  • Routine use of pulmonary artery catheter is not indicated for management of ALI/ARDS.
  • After the initial phase of goal-directed resuscitation, excessive fluid administration should be avoided in the post-resuscitation phase. In patients with established ALI/ARDS, conservative strategy of fluid management (target central venous pressure < 4 mmHg or pulmonary artery occlusion pressure < 8 mmHg) significantly improved lung function and CNS function and shortened the duration of mechanical ventilation and intensive care without increasing nonpulmonary organ failures.
  • Prolonged low-dose corticosteroid therapy does not improve mortality of patients with late ARDS (after 7 days). However, steroid therapy can improve oxygenation, ventilator and shock-free days and pulmonary compliance, at the expense of increased neuromuscular weakness and blood glucose concentrations.

Ongoing Assessment

• Adjust ventilator modes/settings depending on gas-exchange abnormalities, peak airway pressures.
• Assess the need for neuromuscular blockers to improve respiratory mechanics.
• Identify patients who may require tracheostomy.
• Determine need for rescue therapies (e.g., high-frequency oscillatory ventilation, prone positioning, extracorporeal membrane oxygenation, inhaled nitric oxide, etc.).
• Daily assessment of patient’s readiness for a spontaneous breathing trial
• Early rehabilitation

Complications

• Complications of ARDS

• Ventilator-associated pneumonias
• Central venous catheter-related bloodstream infections
• Venous thromboembolism
• Neuromuscular weakness from the steroids, neuromuscular blockers, critical illness myopathy
• Agitated delirium
• Long-term neurocognitive problems
• Multiorgan failure

Author

• Chakradhar Venkata, MBBS