Article Figures & Data
Figures
- Fig. 1.
Mortality versus quartile of day-1 plateau pressure (Pplat) at tidal volume (VT) of 6 mL/kg ideal body weight (IBW) or 12 mL/kg IBW. The bars show the VT, the Pplat range, and the number of patients in each category. ARR = absolute risk reduction. (Data from Reference 76. Adapted from Reference 16, with permission.)
- Fig. 2.
Estimation of transpulmonary pressure during spontaneous breathing on pressure-targeted ventilation. Note that the pressure across the alveolus is determined not only by the pressure applied to the airway, but also by the change in pleural pressure. Paw = proximal airway pressure. PS = pressure support. PR = pressure drop due to airways resistance. PA = alveolar pressure. ΔPA = transalveolar pressure. Patm = atmospheric pressure. Ppl = pleural pressure. (Adapted from Reference 34, with permission.)
- Fig. 3.
Potential effects of an increase in PEEP. If the potential for recruitment is low, an increase in PEEP results in a large increase in plateau pressure (Pplat) (increased driving pressure), to an unsafe level. In this case, the potential harm from over-distention probably outweighs any benefit resulting from increased alveolar recruitment. If the potential for recruitment is high, an increase in PEEP results in little increase in Pplat. In this case, the potential benefit of increased PEEP probably outweighs the harm due to the small increase in Pplat.
- Fig. 4.
The pressure-volume curve of a normal subject (dashed curve) and a patient with acute respiratory distress syndrome (ARDS) (solid curve). The pressure-volume curve is shifted downwards on the volume axis and has a reduced total lung capacity (TLC). The sigmoid shape of the curve is much more evident in ARDS. Note the small amount of pressure at the start of the ARDS pressure-volume curve, indicating a small amount of intrinsic PEEP (PEEPI) at end-expiratory lung volume (EELV). Some investigators divide the curve into linear segments: Cstart, Cinf or Clin, and Cend (thin lines, explained below). Using these segments, the upper and lower Pflex (the pressure at the intersection of 2 lines: a low-compliance region at low lung volumes [Cstart] and a higher-compliance region at higher lung volumes [Cinf]) were defined by the intersection of these lines. The lower inflection point (LIP) and upper inflection point (UIP) are defined by where the curve first begins to deviate from the line Clin. Mathematically these are not inflection points; the true inflection point (where concavity changes direction) is marked by the solid dot. (Adapted from Reference 94.)
- Fig. 5.
Top: Stress index in a patient early in the course of acute respiratory distress syndrome (ARDS) secondary to H1N1 infection. In this case the stress index improved as PEEP was increased. Bottom: Stress index (SI) in a patient late in the course of ARDS. In this case the stress index improved as PEEP was decreased.
- Fig. 6.
Effect of a stiff chest wall on transpulmonary pressure. In this example, although the plateau pressure (Pplat) is 35 cm H2O, the distending pressure across the alveolus is only 10 cm H2O because the pleural pressure is 25 cm H2O. PR = pressure drop due to airways resistance. PA = alveolar pressure. ΔPA = transalveolar pressure. Patm = atmospheric pressure. Ppl = pleural pressure.
- Fig. 7.
Example of PEEP titration in a patient with morbid obesity. Top: Esophageal pressure (Pes), as a surrogate for pleural pressure, is greater than the setting on PEEP. Bottom: PEEP setting is increased so that the collapsing effect of the intrapleural pressure is counterbalanced. Note that, despite the plateau pressure of 40 cm H2O, the alveolar distending pressure is only 14 cm H2O.
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