Annals of
Intensive Care volume 14, Article number: 149, Published: 23
September 2024
Background
Efficacy of inhaled therapy such as Nitric Oxide (iNO)
during mechanical ventilation may depend on airway patency. We hypothesized
that airway closure and lung collapse, countered by positive end-expiratory
pressure (PEEP), influence iNO efficacy. This could support the role of an
adequate PEEP titration for inhalation therapy. The main aim of this study was
to assess the effect of iNO with PEEP set above or below the airway opening
pressure (AOP) generated by airway closure, on hemodynamics and gas exchange in
swine models of acute respiratory distress syndrome. Fourteen pigs randomly
underwent either bilateral or asymmetrical two-hit model of lung injury. Airway
closure and lung collapse were measured with electrical impedance tomography as
well as ventilation/perfusion ratio (V/Q). After AOP detection, the effect of
iNO (10ppm) was studied with PEEP set randomly above or below regional AOP.
Respiratory mechanics, hemodynamics, and gas-exchange were recorded.
Results
All pigs presented airway closure (AOP > 0.5cmH2O) after injury. In bilateral
injury, iNO was associated with an improved mean pulmonary pressure from 49 ± 8 to 42 ± 7mmHg; (p = 0.003),
and ventilation/perfusion matching, caused by a reduction in pixels with low
V/Q and shunt from 16%[IQR:13–19] to 9%[IQR:4–12] (p = 0.03) only at PEEP set above
AOP. iNO had no effect on hemodynamics or gas exchange for PEEP below AOP (low
V/Q 25%[IQR:16–30] to 23%[IQR:14–27]; p = 0.68).
In asymmetrical injury, iNO improved pulmonary hemodynamics and
ventilation/perfusion matching independently from the PEEP set. iNO was
associated with improved oxygenation in all cases.
Conclusions
In an animal model of bilateral lung injury, PEEP level
relative to AOP markedly influences iNO efficacy on pulmonary hemodynamics and
ventilation/perfusion match, independently of oxygenation.
