Acute respiratory distress syndrome: A clinical review

Abstract

The acute respiratory distress syndrome (ARDS) is a complex disorder of heterogeneous etiologies characterized by a consistent, recognizable pattern of lung injury. Extensive epidemiologic studies and clinical intervention trials have been conducted to address the high mortality of this disorder and have provided significant insight into the complexity of studying new therapies for this condition. The existing clinical investigations in ARDS will be highlighted in this review. The limitations to current definitions, patient selection, and outcome assessment will be considered. While significant attention has been focused on the parenchymal injury that characterizes this disorder and the clinical support of gas exchange function, relatively limited focus has been directed to hemodynamic and pulmonary vascular dysfunction equally prominent in the disease. The limited available clinical information in this area will also be reviewed. The current standards for cardiopulmonary management of the condition will be outlined. Current gaps in our understanding of the clinical condition will be highlighted with the expectation that continued progress will contribute to a decline in disease mortality.

Keywords: ARDS; acute cor pulmonale; acute lung injury; adult respiratory distress syndrome; clinical trial; gas exchange; hypoxia; hypoxic pulmonary vasoconstriction; positive end expiratory pressure.

Figure 1

Reclassification of patients meeting AECC ARDS criteria into acute respiratory distress syndrome (ARDS), acute lung injury (ALI), or acute respiratory failure (ARF) categories based upon response to four standard ventilator settings on Day 1. Mortality rate for individual groups is shown based upon the reclassification. P values refer to the differences in mortality rates. Reference 19 with permission.

Figure 2

The stress index is the coefficient b of a power equation (airway pressure = a · inspiratory time b+c), fitted on the airway opening pressure (Pao) segment (bold lines) corresponding to the period of constant-flow inflation (dotted lines), during constant-flow, volume-cycled mechanical ventilation. For stress index values of less than 1, the Pao curve presents a downward concavity, suggesting a continuous decrease in elastance during constant-flow inflation. For stress index values higher than 1, the curve presents an upward concavity suggesting a continuous increase in elastance. Finally, for a stress index value equal to 1, the curve is straight, suggesting the absence of tidal variations in elastance. Reference 78, with permission.

Figure 3

Cumulative fluid balance over first 7 days post randomization in FACTT patients in the liberal fluid management (FACTT-liberal) and conservative fluid management (FACTT-conservative) strategies of the Fluids and Catheter Therapy Trial. The two study groups are compared to fluid balance data available from two additional ARDSNet ventilator trials (ARMA and ALVEOLI). In comparison to all three other trials, the FACTTconservative arm ended up with an overall even fluid balance over the 7-day interval. Reference 8 with permission.

Figure 4

Ratio of PaO²/FIO² during positive end-expiratory pressure (PEEP) titration in patients who had acute respiratory distress syndrome with echo findings of moderate-to-large shunting (shaded squares) or without shunting (white squares) across a patent foramen ovale. Reference 51 with permission.