The following is the summary of “Correlation between the hysteresis of the pressure–volume curve and the recruitment-to-inflation ratio in patients with coronavirus disease 2019” published in the November 2022 issue of Intensive Care by Nayakama, et al.

Lung recruit ability should be evaluated before recruitment techniques are performed on a patient undergoing mechanical ventilation since the response to recruitment varies widely among patients. At the bedside, lung recruit ability can be assessed, and positive end-expiratory pressure (PEEP) can be customized using the pressure-volume (PV) curve and the recruitment-to-inflation (R/I) ratio (PEEP). The normalized maximal distance (NMD) of a quasi-static power versus work (PV) curve has been found to correspond with lung tissue recruitment on computed tomography. The NMD measures the greatest possible difference between the PV curve’s inspiratory and expiratory limbs. Nonetheless, the connection between the various hysteresis parameters of a quasi-static PV curve and the R/I ratio for enlistability is unclear.

About 33 patients with severe 2019 coronavirus illness (COVID-19) were studied; all of them required invasive mechanical breathing. Ventilator respiratory waveform data were acquired using custom-built acquisition software. Researchers looked at how factors such as the R/I ratio, quasi-static PV curve elements like NMD, and respiratory system compliance are all interconnected (Crs). The median R/I was 0.90 (IQR: 0.70-1.15), and the median NMD was 41.0 (IQR: 37-44.1). Significantly linked with the R/I ratio was the NMD (rho=0.74, P<0.001). Sub-analysis demonstrated that at lower PEEP, there was no correlation between NMD and Crs (0.057, P=0.75; and rho=0.15, P=0.41). 

Alternatively, the NMD and R/I ratio were modestly linked with the Crs ratio (higher/lower) (rho=0.64, P<0.001; and rho =0.67, P<0.001, respectively).  There is a robust correlation between the R/I ratio used to evaluate recruit ability and NMD of the quasi-static PV curve. Increased or decreased Crs ratio was also linked with NMD and the R/I ratio. So, NMD and the R/I ratio may be useful at-the-bedside measures of recruitability.