The following is a summary of the “Heterogeneity of Ventilation/Perfusion Mismatch at Different Levels of PEEP and in Respiratory Mechanics Phenotypes of COVID-19 ARDS,” published in the February 2023 issue of Respiratory Care by Scaramuzzo, et al.

Severe hypoxemia, early preserved lung compliance, and impaired ventilation/perfusion (VV̇/Q̇) matching are hallmarks of ARDS caused by COVID-19. The effect of PEEP on V̇/Q̇ mismatch in COVID-19-related ARDS is unclear, but PEEP can increase end-expiratory lung volume. Therefore, subjects with COVID-19 ARDS were enrolled, and V̇/Q̇ was measured using the automatic lung parameter estimator (ALPE) while they were intubated and receiving mechanical ventilation. At three PEEP levels (clinical PEEP = intermediate PEEP, low PEEP [clinical 50%], and high PEEP [clinical + 50%]), data on respiratory mechanics, shunt, and V̇/Q̇ mismatch (low V̇/Q̇ and high V̇/Q̇) were collected. 

The effect of PEEP on V̇/Q̇ was calculated using a mixed-effects model. In addition, the effect of PEEP on V̇/Q̇ mismatch was also studied to see if it varied between the high elastance/low compliance (phenotype H) and low elastance/high compliance (phenotype L) respiratory mechanics phenotypes (phenotype L). In this study, they compared the effects of low PEEP = 5.6 2.2 cm H₂O, intermediate PEEP = 10.6 3.8 cm H₂O, and high PEEP = 15 5 cm H2O on 17 patients with COVID-related ARDS aged 66 [60-71] years, with a P_ao2/F_IO2 of 141 74 mm Hg. On average, PEEP had no discernible effect on the shunt, low V̇/Q̇, high V̇/Q̇, or alveolar dead space.

Despite no discernible shift in P_ao2/F_IO2, increasing PEEP significantly decreased respiratory system compliance (P =.26). The shunt was reduced in phenotype L but increased in phenotype H due to PEEP, with a corresponding P =.048 difference. PEEP had a variable effect on V̇/Q̇ mismatch. On average, higher levels could not reduce shunt in patients with COVID-related ARDS ventilated with invasive mechanical support for more than 48 hours. PEEP’s effect on V̇/Q̇ mismatch may be subject-dependent; subjects with lower compliance showed a greater shunt in response to PEEP than those with higher compliance.

Source: rc.rcjournal.com/content/68/2/188