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. 2023 Jan 30;68(2):188-198.
doi: 10.4187/respcare.10242.

Heterogeneity of Ventilation/Perfusion Mismatch at Different Levels of PEEP and in Respiratory Mechanics Phenotypes of COVID-19 ARDS

Gaetano Scaramuzzo  1 , Dan Stieper Karbing  2 , Alberto Fogagnolo  3 , Tommaso Mauri  4 , Elena Spinelli  5 , Matilde Mari  6 , Cecilia Turrini  3 , Federica Montanaro  3 , Carlo Alberto Volta  1 , Stephen Edward Rees  2 , Savino Spadaro  7
Affiliations

Heterogeneity of Ventilation/Perfusion Mismatch at Different Levels of PEEP and in Respiratory Mechanics Phenotypes of COVID-19 ARDS

Gaetano Scaramuzzo et al. Respir Care. .

Abstract

Background: COVID-19-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-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 [60-71] y with a PaO2 /FIO2 of 141 ± 74 mm Hg were studied at low PEEP = 5.6 ± 2.2 cm H2O, intermediate PEEP = 10.6 ± 3.8 cm H2O, and high PEEP = 15 ± 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'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.

Keywords: ARDS; COVID-19; PEEP; V̇/Q̇ mismatch; phenotypes; shunt.

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Conflict of interest statement

Drs Karbing and Rees disclose relationships with Mermaid Care. The remaining authors have disclosed no conflicts of interest.

Figures

Fig. 1.
Fig. 1.
Effect of PEEP on ventilation/perfusion mismatch in the overall population. Data are expressed as mean and standard error of the mean. P value for PEEP effect (mixed-effect analysis). V̇/Q̇ = ventilation/perfusion ratio; VDalv = alveolar dead space.
Fig. 2.
Fig. 2.
Shunt and respiratory system compliance in the 2 mechanical phenotypes: phenotype L (A) and phenotype H (B). Data are shown as mean ± standard error of the mean. CRS = respiratory system compliance.
Fig. 3.
Fig. 3.
Difference in Shunt (ΔShunt) between high PEEP and low PEEP (ΔShunt = Shunt high PEEP − shunt low PEEP) in the 2 phenotypes. Mean ± SD.
See this image and copyright information in PMC

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