Effects of PEEP on regional ventilation-perfusion mismatch in the acute respiratory distress syndrome

Abstract

Abstract Purpose In the acute respiratory distress syndrome (ARDS), decreasing Ventilation-Perfusion $$\left( {{{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}} \right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> </mml:math> mismatch might enhance lung protection. We investigated the regional effects of higher Positive End Expiratory Pressure (PEEP) on $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> mismatch and their correlation with recruitability. We aimed to verify whether PEEP improves regional $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> mismatch, and to study the underlying mechanisms. Methods In fifteen patients with moderate and severe ARDS, two PEEP levels (5 and 15 cmH 2 O) were applied in random order. $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> mismatch was assessed by Electrical Impedance Tomography at each PEEP. Percentage of ventilation and perfusion reaching different ranges of $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> ratios were analyzed in 3 gravitational lung regions, leading to precise assessment of their distribution throughout different $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> mismatch compartments. Recruitability between the two PEEP levels was measured by the recruitment-to-inflation ratio method. Results In the non-dependent region, at higher PEEP, ventilation reaching the normal $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> compartment ( p = 0.018) increased, while it decreased in the high $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> one ( p = 0.023). In the middle region, at PEEP 15 cmH 2 O, ventilation and perfusion to the low $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> compartment decreased ( p = 0.006 and p = 0.011) and perfusion to normal $${{\dot{V}} \mathord{\left/ {\vphantom {{\dot{V}} {\dot{Q}}}} \right. \kern-\nulldelimiterspace} {\dot{Q}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mover> <mml:mi>Q</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> </mml:math> increased ( p = 0.003). In the dependent lung, the percentage of blood flowing through the non-ventilated compartment decreased ( p = 0.041). Regional $${{\d

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