Estimating the intratidal compliance profile with the new gliding-SLICE method

Introduction

At the bedside, but even in most research work, the analysis of respiratory system mechanics is limited to quasi-static conditions excluding any insight into what happens during the breath. The new gliding-SLICE method helps looking into the breath. It is a further development of the SLICE method for calculating compliance and resistance of subsequent intratidal volume ranges (slices) of the pressure-volume (PV) loop by multiple linear regression analysis in a continuous way. This allows for detecting intratidal compliance and resistance nonlinearity during ongoing ventilation. Our objective was to determine whether the nonlinear intratidal compliance profile hints at what level to set PEEP and tidal volume (VT) to make lung ventilation protective.

Methods

In 12 piglets, atelectasis was induced by application of negative pressure. The PV relationship and the ECG signal were recorded during mechanical ventilation at different levels of end-expiratory pressure (PEEP: 0, 5, 10 and 15 cmH₂O) and a VT of 12 ml/kg BW. Using the gliding-SLICE method [1], intratidal compliance profiles were calculated and compared with the conventional quasi-static compliance.

Results

In contrast to quasi-static compliance, the gliding-SLICE method revealed pronounced intratidal nonlinearity of the compliance profile under ongoing ventilation (Figure 1). At low levels of PEEP, intratidal compliance increased in the low volume range, remained at a high level while further volume was delivered, and finally decreased with volume >6 ml/kg BW. With higher levels of PEEP, intratidal compliance decreased from the onset of inspiration.

Figure 1

Conclusions

The gliding-SLICE method gives detailed insights into the intratidal course of compliance during uninterrupted ventilation. From the profile of the intratidal compliance, the occurrence of intratidal recruitment and/or overdistension can be identified.