- Acute onset and progression within hours
- Respiratory: Not cardiogenic clinically or by echo. PA occlusion pressure (wedge) <18 cm H2O
- Distress: Decreased oxygenation:
- PaO2/FiO2 <200 mm Hg
- <300 for ALI regardless of PEEP
- Mortality with current management still 25–50%
- Survivors suffer from significant morbidity and reduced quality of life because of respiratory sequelae such as chronic infections and tracheostomy
- Pulmonary HTN and RV failure may be present:
- Acute RV failure on echo: RV dilation and paradoxical septum motion
- Sepsis (30%)
- Aspiration (36%)
- Trauma (11%)
- TRALI and others (burns and toxic fumes, drug overdose, drowning, acute pancreatitis)
- Treat underlying cause if possible (especially sepsis)
- Sedate as little as possible
- Respiratory management:
- First goal: Avoid secondary lung injury with hyperinflation:
- Low tidal volume ventilation (6 mL/kg IBW):
- VC and PCV same efficacy. Watch TV and maintain plateau pressure (Ppl) <30 cm H2O (add 0.2 second inspiratory pause to measure Ppl)
- Absolute mortality risk reduction from 40% to 31% with NNT = 11
- Second goal: Optimize oxygenation and V/Q matching:
- Place arterial line and titrate to PaO2 >60 with incremental PEEP up to 12 first and then increasing FiO2
- Third goal: Permissive hypercapnia (accept PacO2 up to 60 mm Hg):
- RR up to 30 if needed, but watch auto-PEEP with risk of breath stacking
- No indication to NaHCO3 with respiratory acidosis
- Troubleshooting: when the goals are difficult to achieve:
- Recruitment maneuver to reopen atelectatic areas of lungs:
- Set APL valve to 40, squeeze bag to achieve peak airway pressures of 40 cm H2O, hold for 30 seconds (8–12 seconds probably sufficient), and repeat a few times
- May transiently improve oxygenation by opening collapsed alveoli (but also by reducing pulmonary shunt by decreasing cardiac output)
- Watch for hypotension (usually brief, due to decrease in venous return) and pneumothorax
- Contraindicated if elevated ICP
- Conservative fluid strategy (ARDSNet trial in ICU setting):
- Guided strictly by CVP, PAOP, urine output, MAP, cardiac output, and capillary refill
- Elaborate treatment algorithm using fluid boluses, KVO fluid, dopamine, or furosemide
- Conservative strategy improved lung function and shortened mechanical ventilation without increasing nonpulmonary organ failures
- No proven mortality benefit but can be considered:
- Prone position: Improves oxygenation, but does not reduce mortality
- Steroids: May shorten course and decrease fibrosis if given <7 days (methylprednisolone 2 mg/kg per day), but may worsen mortality if given >2 weeks into ARDS. Avoid combining with NMB (risk of critical illness myo/neuropathy)
- Inhaled nitric oxide: Improves oxygenation but not survival. May be useful with refractory hypoxemia, severe pulmonary hypertension, or RV failure
- Inhaled surfactant/prostaglandins, ECMO for intractable hypoxemia
- Nutritional support: Avoid hypophosphatemia; reduce CO2 with increased lipid proportion in diet
- PA catheter not useful
- Use pressure-controlled-volume-guaranteed (PCVG) mode if available to optimize Vt to 6–8 mL/kg IBW while limiting Paw to 40 cm Hg and Pplateau to 30 cm Hg with paralysis. Otherwise, use PCV mode. Consider using ICU ventilator + TIVA
- Start with PEEP of 10 cm ...
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