['To compare the effects of conventional mechanical ventilation with low-volume, pressure-limited ventilation (LVPLV) and permissive hypercapnia on ventilation-perfusion (V/Q) distributions in patients with acute respiratory distress syndrome. We hypothesized that the advantageous cardiopulmonary effects of LVPLV would be greater in patients with sepsis than in those without sepsis.', 'Twenty-two patients with acute respiratory distress syndrome were studied (group 1: 12 patients with hyperdynamic sepsis; group 2: 10 nonseptic patients). Intrapulmonary shunt (Qsp/Qt) (percentage of cardiac output), perfusion of "low" V/Q areas (percentage of cardiac output), ventilation of "high" V/Q areas (percentage of total ventilation [VE]), and deadspace ventilation (percentage of VE) were calculated from the retention/excretion data of six inert gases. Data were obtained during conventional mechanical ventilation and during LVPLV.', 'In group 1, LVPLV increased PaCO(0)rom 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 61 +/- 12 torr (8.1 +/- 1.6 kPa). Qsp/Qt increased from 28 +/- 16% to 36 +/- 17%, whereas Pao2 (84 +/- 15 torr [11.1 +/- 2.0 kPa] vs. 86 +/- 21 torr [11.5 +/- 2.8 kPa]) and Qt (10.6 +/- 2.3 vs. 11.5 +/- 2.5 L x -1) remained unchanged and PVO(2) (40 +/- 4 [5.3 +/- 0.5 kPa] vs. 49 +/- 6 torr [6.5 +/- 0.3]) increased. In group 2, LVPLV increased PaCO(2) from 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 63 +/- 11 torr (8.4 +/- 1.5 kPa). For Qsp/Qt (24 +/- 9% to 34 +/- 16%), the increase was not significant, whereas Qt (7.4 +/- 1.8 vs. 10.2 +/- 2.2 L x -1), PVO(2)(38 +/- 4 torr [5.1 +/- 0.5 kPa] vs. 50 +/- 6 mm Hg [6.7 +/- 0.8 kPa]), and PaO(2) (89 +/- 16 torr [11.9 +/- 2.1 kPa] vs. 98 +/- 19 torr [13.1 +/- 2.5 kPa]) increased. In both groups, the scatter of perfusion distribution (log SDQ) was greater than expected for normal subjects but was not different between the groups or altered by the treatments.'] Does mechanical ventilation with permissive hypercapnia increase intrapulmonary shunt in septic and nonseptic patients with acute respiratory distress syndrome?