Mechanical power and Power Compliance Index in independent lung ventilation. New insight

Background Unilateral lung disease (ULD) requiring mechanical ventilation is a unique challenge due to individual and interactive lung mechanics. The distribution of volume and pressure may not be even due to inequities in compliance and resistance. Independent lung ventilation (ILV) is a strategy to manage ULD but is not commonly employed. We assessed the mechanical power (MP) between single lung ventilation (SLV) and ILV in a dual lung model with different compliances. Methods A passive lung model with two different compliances (30 ml/cmH2O and 10 ml/cmH2O) and a predicted body weight of 65 kg was used to simulated ULD and ILV. In SLV the ventilator was set with the following: tidal volume (VT) 400 ml, PEEP 7, RR 20, I:E 1:2. In ILV, each lung was given a separate ventilator with equivalent settings to SLV: VT 300 ml, PEEP 7, RR 20, I:E 1:2 in the more compliant lung (MCL) and VT 100 ml, PEEP 7, RR 20, I:E 1:2 in the less compliant lung (LCL). The study was repeated with different PEEP levels and different ventilator modes, volume (VCV) and pressure control (PCV). PEEP was set according to the compliance: VT 300 ml, PEEP 8, RR 20, I:E 1:2 in the MCL and VT 100 ml, PEEP 10, RR 20, I:E 1:2 in the LCL. The MP in each study and compared SLV to the combined results from each lung in ILV. MP was indexed to the compliance in all the studies Results The MP was significantly lower in VCV compared to PCV in all studies. In VCV, the total MP in SLV was 12.61 J/min compared to 11.39 J/min in the combined lungs with the same PEEP levels (8.84 MCL and 2.55 LCL) (p = < 0.001). The total MP in SLV was also higher when comparing to ILV with different PEEP levels 12.57 J/min (9.43 MCL and 3.01LCL) (p= <0.001). In PCV, the total MP was 14.25 J/min which was higher compared to 13.22 in the combined lungs with the same PEEP levels (9.88 MCL and 3.32 LCL) (p =<0.001) however, the MP was lower compared to 14.55 in the combined lungs with different PEEP levels (10.58 MCL and 3.92 LCL) (p=<0.001).The Power Compliance Index (PCI) was significantly lower in ILV with same PEEP level (0.295 MCL and0.255 LCL, compared to 0.315 in the SLV) and similar in the different PEEP levels (0.314 MCL and , 0.314 LCL, compared to 0.315 in the SLV) in VCV. The PCI was significantly lower in the ILV with the same PEEP level (0.329 MCL, 0.332 LCL compared to 0.356 in the SLV). In the different PEEP levels, the MCL was less (0.352), and higher in the LCL (0.392) compared to the SLV (0.356) in PCV. Conclusions ILV can be achieved with lower MP in VCV using the same or higher PEEP levels than SLV, however in PCV the MP was less using the same PEEP but higher using different PEEP levels. Indexing the MP to compliance can be more meaningful in interpreting the results than the MP alone. Further studies are needed to confirm our findings.