title: Mechanisms of pulmonary gas exchange improvement during a protective ventilatory strategy in acute respiratory distress syndrome.
abstract: To investigate the mechanisms underlying improvement of arterial oxygenation during a protective ventilatory strategy (PVS) in early acute respiratory distress syndrome (ARDS), we studied eight patients during volume-controlled mechanical ventilation, keeping respiratory rate and fraction of inspired oxygen (FI(O(2))) (0.82 +/- 0.20) unchanged: (1) at baseline (tidal volume [VT] 10 to 12 ml x kg(-1); positive end-expiratory pressure [PEEP] 8 to 10 cm H(2)O); (2) during PVS (PEEP 2 cm H(2)O above the low inflexion point (P(FLEX)) and VT of 5 to 7 ml x kg(-1)); and (3) post-PVS, back to baseline conditions. Inert gas measurements were done after 30 min in each ventilatory modality. During PVS, Pa(O(2)) increased significantly from 93 +/- 27 to 166 +/- 77 mm Hg (p < 0.008) and Pa(CO(2)) rose from 39 +/- 7 to 57 +/- 11 mm Hg (p < 0.0002) because of the decrease in minute ventilation (V E) (-3.6 L x min(-1)) (p < 0.005). Both heart rate (HR, +13 min(-1)) (p < 0.002) and cardiac output (Q, +1.2 L x min(-1)) (p < 0.05) increased. Static respiratory system linear compliance increased from 36 +/- 14 to 44 +/- 16 ml. cm H(2)O(-1) (p < 0.0002). PVS provoked recruitment of previously collapsed alveoli and redistribution of pulmonary blood flow from nonventilated alveoli to normal lung. Despite the increase in Q, intrapulmonary shunt fell from 39 +/- 15% to 31 +/- 11% (p < 0.04). We conclude that the decrease in intrapulmonary shunt owing to alveolar recruitment remains the pivotal mechanism to explain improvement of arterial oxygenation during this PVS.
authors.affiliation: Servei de Pneumologia (ICPCT), Unitat de Cures Intensives Quirúrgiques, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Hospital de la Santa Creu i Sant Pau, Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Mancini
authors.forename: E
authors.initials: E
authors.lastname: Zavala
authors.forename: J
authors.initials: J
authors.lastname: Mancebo
authors.forename: C
authors.initials: C
authors.lastname: Fernandez
authors.forename: J A
authors.initials: JA
authors.lastname: Barberà
authors.forename: A
authors.initials: A
authors.lastname: Rossi
authors.forename: J
authors.initials: J
authors.lastname: Roca
authors.forename: R
authors.initials: R
authors.lastname: Rodriguez-Roisin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011659:Pulmonary Gas Exchange; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D013990:Tidal Volume