New Study Highlights Key Correlations Between Lung Tissue and Respiratory Compliance in COVID-19 Patients

Normally aerated lung tissue on CT is correlated with static respiratory system compliance at zero end-expiratory pressure. However, in clinical practice, patients with acute respiratory failure are often managed using elevated levels of positive end-expiratory pressure (PEEP).

Up until recently, no single study had validated the relationship between lung volume and tissue and static respiratory system compliance at the applied PEEP.

That was the catalyst of a new study published in the June 2024 issue of Scientific Reports in Nature, which examined the correlation between normally aerated lung and respiratory system compliance at clinically high positive end-expiratory pressure in COVID-19 patients. As a secondary outcome, the study also looked to evaluate the relationship between CT characteristics and static respiratory system compliance, when factoring in the R/I ratio.

The study was conducted by Keishi Ogura and Ryuichi Nakayama, both in the division of radiology and nuclear medicine at the Sapporo Medical University Hospital in Sapporo, Japan.

In their study, static respiratory system compliance at the applied PEEP was significantly correlated with normally aerated lung volume and tissue on CT. Additionally, recruitability, as indicated by the R/I ratio, and static respiratory system compliance were significantly associated with the normally aerated lung volume.

Therefore, the authors highlighted that the research underscores the significance of static respiratory system compliance at the applied PEEP as a bedside-measurable parameter and sheds new light on the link between recruitability and normally aerated lung.

To do so, the researchers analyzed the CT and respiratory mechanics data of 30 patients with COVID-19 who were mechanically ventilated, with all CT images collected during mechanical ventilation at PEEP level of 15 cmH2O. From there, the images were analyzed using Synapse Vincent system version 6.4.

The data was put into two groups— high and low recruitability. Of the cohort, 30 patients were included in the analysis with the median R/I ratio of 0.71.

Ogura and Nakayama hypothesized that static respiratory system compliance could be correlated with aerated lung volume and tissue on CT at the applied PEEP but that the situation would vary depending on recruitability.

A key finding of their analysis was that static respiratory system compliance at the applied PEEP was significantly correlated with normally aerated lung volume and tissue on CT.

The researchers also concluded that recruitability was statistically significantly associated with the normally aerated lung air volume.

“Owing to the substantial resources required and risks associated with transporting patients on mechanical ventilation, CT evaluation is not a feasible procedure that can be performed routinely for patients with ARDS15,” the authors wrote. “Therefore, this study not only reaffirms the importance of static respiratory system compliance at the applied PEEP as a parameter that can be determined at the bedside but also newly elucidates the relationship between recruitability and normally aerated lung.”

What’s more, the authors presented clinical validity to the relationship between static respiratory system compliance and the “baby lung” at PEEP settings based on the best compliance method.