@article {Scaramuzzorespcare.10242, author = {Gaetano Scaramuzzo and Dan Stieper Karbing and Alberto Fogagnolo and Tommaso Mauri and Elena Spinelli and Matilde Mari and Cecilia Turrini and Federica Montanaro and Carlo Alberto Volta and Stephen Edward Rees and Savino Spadaro}, title = {Heterogeneity of Ventilation/Perfusion Mismatch at Different Levels of PEEP and in Mechanical Phenotypes of COVID-19 ARDS}, elocation-id = {respcare.10242}, year = {2022}, doi = {10.4187/respcare.10242}, publisher = {Respiratory Care}, abstract = {BACKGROUND: COVID-19{\textendash}related ARDS is characterized by severe hypoxemia with initially preserved lung compliance and impaired ventilation/perfusion (V̇/Q̇) matching. PEEP can increase end-expiratory lung volume, but its effect on V̇/Q̇ mismatch in COVID-19{\textendash}related ARDS is not clear.METHODS: We enrolled intubated and mechanically ventilated subjects with COVID-19 ARDS and used the automatic lung parameter estimator (ALPE) to measure V̇/Q̇. Respiratory mechanics measurements, shunt, and V̇/Q̇ mismatch (low V̇/Q̇ and high V̇/Q̇) were collected at 3 PEEP levels (clinical PEEP = intermediate PEEP, low PEEP [clinical - 50\%], and high PEEP [clinical + 50\%]). A mixed-effect model was used to evaluate the impact of PEEP on V̇/Q̇. We also investigated if PEEP might have a different effect on V̇/Q̇ mismatch in 2 different respiratory mechanics phenotypes, that is, high elastance/low compliance (phenotype H) and low elastance/high compliance (phenotype L).RESULTS: Seventeen subjects with COVID-related ARDS age 66 [60{\textendash}71] y with a PaO2/FIO2 of 141 {\textpm} 74 mm Hg were studied at low PEEP = 5.6 {\textpm} 2.2 cm H2O, intermediate PEEP = 10.6 {\textpm} 3.8 cm H2O, and high PEEP = 15 {\textpm} 5 cm H2O. Shunt, low V̇/Q̇, high V̇/Q̇, and alveolar dead space were not significantly influenced, on average, by PEEP. Respiratory system compliance decreased significantly when increasing PEEP without significant variation of PaO2/FIO2 (P = .26). In the 2 phenotypes, PEEP had opposite effects on shunt, with a decrease in the phenotype L and an increase in phenotype H (P = .048).CONCLUSIONS: In subjects with COVID-related ARDS placed on invasive mechanical ventilation for \> 48 h, PEEP had a heterogeneous effect on V̇/Q̇ mismatch and, on average, higher levels were not able to reduce shunt. The subject{\textquoteright}s compliance could influence the effect of PEEP on V̇/Q̇ mismatch since an increased shunt was observed in subjects with lower compliance, whereas the opposite occurred in those with higher compliance.}, issn = {0020-1324}, URL = {https://rc.rcjournal.com/content/early/2022/11/08/respcare.10242}, eprint = {https://rc.rcjournal.com/content/early/2022/11/08/respcare.10242.full.pdf}, journal = {Respiratory Care} }