1. Which of the following treatments for ARDS is generally thought to lack significant evidence of clinical benefit (including adult and pediatric literature)?
a) Prone positioning
b) Early neuromuscular blockade
d) Low tidal volume strategy
2. Your patient has ARDS and is being mechanically ventilated with PC/AC 30/12 X14 60% FiO2 with most recent ABG 7.25/60/60. You are considering steroid therapy to potentially improve his lung inflammation and resolution of ARDS. Which of the following time periods would steroids be LEAST indicated?
a) Day 2 of illness
b) Day 7 of illness
c) Day 12 of illness
d) Day 15 of illness
3. You have a patient who is being mechanically ventilated for ARDS due to aspiration pneumonia. His current ventilator settings include Vt 6 cc/kg, PIP 35, P plateau 28, 100% FiO2 with oxygen saturation of 86%. You decide to trial HFOV. What would be the most likely benefit of transitioning to HFOV in this patient?
a) Reduced volutrauma
b) Reduced biotrauma
c) Reduced barotrauma
d) Improved survival
4. Which of the following is NOT part of the criteria for ARDS?
a) acute onset
b) P/F ratio less than 200
c) bilateral infiltrates on CXR
d) PCWP <10 mmHg
ANSWERS & EXPLANATIONS
1. C- Prone positioning (PROSEVA), early neuromuscular blockade (ACURASYS), and low tidal volume strategy (ARDSnet NEJM 2000) have all been demonstrated (at least in some large clinical trials) to demonstrate clinical benefit in ARDS. iNO, while improving oxygenation, has not been shown to have significant clinical benefit although it is routinely used in an effort to improve oxygenation with severe ARDS and refractory hypoxemia
2. D- While controversial in the treatment of ARDS, Meduri and others have suggested some benefit to steroids in ARDS. However, further studies (Steinberg NEJM 2006) have demonstrated no benefit and potential harm in the group of patients given steroids later (>14 days). Hence, if steroids are to be used, they should probably be used early. Thus, answer choice D, 15 days, is the least appropriate choice of when to give steroids to this patient for ARDS.
3. C- HFOV maintains a constant mean airway pressure and ventilates at very small tidal volumes (2-3 cc/kg estimated). ARDS is a heterogenous disease, meaning that different lung units are affected differently. For example, the dependent lung regions are often completely collapsed due to compression from the weight of an edematous lung, meaning they have very little ventilation (V/Q ratio close to zero) whereas the most apical regions of the lung may be more open. Hence, when you ventilate at a tidal volume of 6 cc/kg, although limited, this 6 cc/kg distributes primarily to more compliant/open areas of lung, leading to overdistension of this smaller effective lung volume and thus, volutrauma. By maintaining a constant mean airway pressure, one eventually recruits more of this lung, thus mitigating the volutrauma effects. HFOV has not been shown to improve survival (see OSCAR and OSCILLATE studies in adults) in ARDS, still uses relatively high airway pressures (and this patient's plateau pressure-the pressure the alveolus sees- is 28 cm H20, below the typical upper target of 30 cm H20), and still leads to inflammation (biotrauma)
4. D- the pulmonary capillary wedge pressure is an estimate of left atrial pressure. If this value were elevated, it would suggest that cardiac dysfunction with subsequent pulmonary venous congestion could be leading to pulmonary edema and hypoxemia. While not routinely obtained in pediatric patients (typically if there is no clinical suspicion of cardiac disease, this is sufficient), if obtained, a PCWP <18 mmHg, not 10 mmHg is used for diagnosis of ARDS.