| Abstract: INTRODUCTION: IAH above 15mmHg causes restrictive lung disease due to diminished chest wall (CW) static compliance (Cstat)(1-3). This study will look for a correlation between IAP-Ppleural and IAP-LIP (lower inflection point) by partitioning total respiratory system (TRS) mechanics in lung and CW in pts with(out) IAH.
METHODS: A total of 27 inspiratory and expiratory PV curves (super syringe) were constructed in 5 pts, these curves were partitioned in CW, lung and abdominal curves. M/F ratio: 1/4, age 72.8±5.3, APACHE-II 30.4±4.3, SAPS-II 62.4±7.3.
RESULTS: The values for IAP were 13.7±5.5mmHg vs 12.6±5.2mmHg for Ppl with significant correlation (n=864): Ppl(mmHg)= 0.92xIAP (R2=0.88, p<0.0001). Bland and Altman analysis showed a good agreement: IAP was almost identical to Ppl with a bias of -0.8±1.9 (SD) mmHg (95%CI –1to-0.7); the limits of agreement (LA) were –4.6to3(95% CI –4.8to–4.3 for the LLA and 2.7to3.2 for the ULA). There was a good correlation between IAP (15.4±6.7cmH2O) and LIP (14.5±5.2cmH2O): LIP(cmH2O)= 0.5xIAP + 2.6 (R2=0.93, p<0.0001) and there was an inverse correlation between IAP and Cstat (56.3±17.3ml/cmH2O): Cstat= -1.2x IAP + 74.4 (R2=0.2, p<0.0001). Abdominal compression resulted in an increase in IAP from 7.4±3.2 to 15.6±2 causing flattening of the TRS-PV curve. Partitioning showed that this decrease in Cstat was solely due to the increase in IAP and concomitant increase in Ppl with flattening of the CW-PV curve while the lung-PV curve remained unchanged.
CONCLUSION: IAP-Ppl and IAP-LIP are strongly correlated. This has important implications in daily clinical practise. The mean LIP was around 14.4cmH2O. IAH dimishes TRS Cstat due to a dimished CW-Cstat while lung-Cstat remains unchanged. In ventilated patients with IAH the clinical message from this study is: “best PEEP=IAP”. Since IAP can easily be obtained at the bedside we suggest this simple strategy instead of the more time consuming, not generally accepted and not without risk super syringe method. These results have implications on the American-European consensus definitions on ARDS where it is suggested to limit Pplat<35. We would advise to use Pplat (=Pplat-IAP) instead, otherwise lung protective ventilation in IAH becomes impossible.
|
