PULMONARYQ
ACUTE RESPIRATORY DISTRESS SYNDROME
New “Berlin” definition ( JAMA 2012;307:2526)
• Acute onset within 1 wk of clinical insult or worsening respiratory status
• Bilateral infiltrates without alternative explanation (eg, effusion, atelectasis, nodules)
• Edema not fully explained by fluid overload or congestive heart failure
• Hypoxemia: PaO2/FiO2 determined with 5 cm H2O of PEEP
PaO2/FiO2 200–300 = mild ARDS (may be on NIPPV), 100–200 = mod, <100 = severe
• Chest CT: heterogeneous lung with densities greater in dependent areas
• Lung bx: diffuse alveolar damage (DAD); Ø req, may give useful dx info (Chest 2004;125:197)
Pathophysiology
• ↑ intrapulmonary shunt → hypoxemia (∴ Rx w/ PEEP to prevent derecruitment)
• ↑ increased dead space fraction (see Appendix), predicts ↑ mort. (NEJM 2002;346:1281)
• ↓ compliance: VT/(Pplat – PEEP) <50 mL/cm H2O
Treatment (primarily supportive) (Lancet 2007;369:1553; NEJM 2007;357:1113)
• Goal is to maintain gas exchange, sustain life, & avoid ventilator-induced lung injury (VILI)
• Fluid balance: target CVP 4–6 cm H2O (if nonoliguric & normotensive) → ↑ vent/ICU-free days, but no Δ mortality (NEJM 2006;354:2564); PA catheter unproven (NEJM 2006;354:2213); using BNP >200 to trigger diuresis (UOP goal 4.5–9 mL/kg/h × 3 h) ↓ time to extubation (AJRCCM 2012;186:1256)
• Steroids: debate continues. Adverse effects include neuromuscular weakness, poor glc control, ? infection. Benefit may vary by time since ARDS onset:
<72 h: older studies w/o benefit (NEJM 1987;317:1565); ? ↓ mortality, ↑ vent/ICU-free days in more recent, controversial study (Chest 2007;131:954)
7–13 d: ? benefit → ↑ vent/ICU-free days, no mortality difference (NEJM 2006;354:1671)
≥14 d: ↑ mortality (NEJM 2006;354:1671)
• Paralysis: if PaO2/FiO2 <150, cisatracurium × 48 h ↓ mortality (NEJM 2010;363:1107)
• Experimental ( JAMA 2010;304:2521)
Inhaled NO or prostacyclins: ↑ PaO2/FiO2, no ↓ mort. or vent-free days (BMJ 2007;334:779)
Prone: ↑ PaO2, but ↑ complications and no ↓ mortality ( JAMA 2009;302:1977); ? ↓ mortality if PaO2/FiO2 <100 (Intens Care Med 2010;36:585)
High-freq oscillatory vent: no benefit and possible harm (NEJM 2013;368:795, 806, & 863)
Lung recruitment: apply CPAP 40–45 cm H2O × 2 min to recruit lung and then ↑ PEEP to maintain; sicker Pts had ↑ recruitable lung (NEJM 2006;354:1775, 1839)
ECMO: may be useful in refractory ARDS, but no good trial data (NEJM 2011;365:1905)
Esoph manometry: adjust PEEP according to esoph pressure (
pleural pressure) to maintain positive transpulm pressure → ↑ PaO2/FiO2, ↑ compliance and possible outcome benefit (NEJM2008;359:2095); helpful in obese Pts or w/ ↑ abdominal pressure
Prognosis
• Mortality ~40% overall in clinical trials; 9–15% resp. causes, 85–91% extrapulm (MODS)
• ↑ BNP & troponin a/w ↑ mortality (Chest 2007;131:964; PLoS One 2012;7:e40515)
• Survivors: PFTs ~normal, ↓ DLCO, muscle wasting, weakness persists (NEJM 2003;348:683), ↓ exercise tolerance, ↓ QoL, ↑ psych morbidity (NEJM 2011;364:1293)