Individualized Positive End-expiratory Pressure and Regional Gas Exchange in Porcine Lung Injury

• Background: In acute respiratory failure elevated intraabdominal pressure aggravates lung collapse, tidal recruitment, and ventilation inhomogeneity. Low positive end-expiratory pressure (PEEP) may promote lung collapse and intrapulmonary shunting, whereas high PEEP may increase dead space by inspiratory overdistension. The authors hypothesized that an electrical impedance tomography-guided PEEP approach minimizing tidal recruitment improves regional ventilation and perfusion matching when compared to a table-based low PEEP/no recruitment and an oxygenation-guided high PEEP/full recruitment strategy in a hybrid model of lung injury and elevated intraabdominal pressure. Methods: In 15 pigs with oleic acid-induced lung injury intraabdominal pressure was increased by intraabdominal saline infusion. PEEP was set in randomized order: (1) guided by a PEEP/inspired oxygen fraction table, without recruitment maneuver; (2) minimizing tidal recruitment guided by electrical impedance tomography after a recruitment maneuver; and (3) maximizing oxygenation after a recruitment maneuver. Single photon emission computed tomography was used to analyze regional ventilation, perfusion, and aeration. Primary outcome measures were differences in PEEP levels and regional ventilation/perfusion matching. Results: Resulting PEEP levels were different (mean +/- SD) with (1) table PEEP: 11 +/- 3 cm H2O; (2) minimal tidal recruitment PEEP: 22 +/- 3 cm H2O; and (3) maximal oxygenation PEEP: 25 +/- 4 cm H2O; P < 0.001. Table PEEP without recruitment maneuver caused highest lung collapse (28 +/- 11% vs. 5 +/- 5% vs. 4 +/- 4%; P < 0.001), shunt perfusion (3.2 +/- 0.8 l/min vs. 1.0 +/- 0.8 l/min vs. 0.7 +/- 0.6 l/min; P < 0.001) and dead space ventilation (2.9 +/- 1.0 l/min vs. 1.5 +/- 0.7 l/min vs. 1.7 +/- 0.8 l/min; P < 0.001). Although resulting in different PEEP levels, minimal tidal recruitment and maximal oxygenation PEEP, both following a recruitment maneuver, had similar effects on regional ventilation/perfusion matching. Conclusions: When compared to table PEEP without a recruitment maneuver, both minimal tidal recruitment PEEP and maximal oxygenation PEEP following a recruitment maneuver decreased shunting and dead space ventilation, and the effects of minimal tidal recruitment PEEP and maximal oxygenation PEEP were comparable.

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MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Anestesi och intensivvård (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Anesthesiology and Intensive Care (hsv//eng)

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