Critical Care Medicine
To date, no pharmacologic intervention has been shown to reduce mortality in ARDS. The only therapy that has reduced mortality in ARDS is a careful ventilator strategy aimed at minimizing alveolar overdistension by limiting the patients tidal volume and plateau (or pause) pressure. In a study of groups ventilated with tidal volumes of 6 mL/kg IBW and those ventilated at 12 mL/kg IBW, the 6 mL/kg group (plateau airway pressures maintained > 30 cm H2O) had a 9% absolute reduction in mortality and spent approximately 2 fewer days on the ventilator.1 A corollary to the low tidal volume strategy is that Pco2 may rise due to the decreased minute ventilation. A strategy of permissive hypercapnia, in which the Pco2 is allowed to rise and induce a respiratory acidosis, has been shown to be safe in patients with ARDS.2 Increasing tidal volume and respiratory rate is incorrect because a tidal volume of 600 mL would be overdistending and injurious; the pH does not need to be normalized. Higher PEEP was not associated with an excess of barotraumas in a large randomized trial.3 Because there is no evidence to suggest that an Sao2 of 98% is superior to 89% and since oxygen therapy can induce lung injury, the goals for oxygenation in patients with ARDS are Sao2 of 88% or greater or Pao2 of 55 mm Hg or greater.1 While there is no absolute threshold for oxygen toxicity, most practitioners attempt to reduce the Fio2 below 60% when possible. Tidal volume should be based upon IBW, not actual body weight.
- Decrease the tidal volume to 342 mL (6 mL/kg IBW) and increase the respiratory rate to 34 breaths/min.
1. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network. N Engl J Med 2000;342:
2. Hickling KG, Henderson SJ, Jackson R. Low mortality associated with low volume pressure limited ventilation with permissive hypercapnia in severe adult respiratory distress syndrome. Intensive Care Med 1990;16:372-7.
3. Brower RG, Lanken PN, MacIntyre N, et al. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome. N Engl J Med 2004;
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