To assess if the work of breath in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is affected by different extrinsic positive end-expiratory pressure (PEEPe) levels during (neurally adjusted ventilatory assist, NAVA).

From May 2012 to May 2013, 12 AECOPD patients who were admitted to the ICU of Nanjing Zhong-da hospital with an static intrinsic positive end-expiratory pressure (PEEPi_stat more than 5 cmH2O were enrolled in this study.The EFL group was defined as no increase in total-PEEP when we elevated PEEPe from 0 PEEPi_stat to 40% of PEEPi_stat and the Re group defined as the opposite. Being titrated to a level of Ramsay 3 sedation, 12 AECOPD patients were randomized to undergo pressure support ventilation (PSV) or NAVA with four different levels of PEEPe (0, 40%, 80%, 120% of PEEPi_stat). NAVA pressure limit was used to assure the equivalence of supporting pressure between NAVA and PSV. Air flow and airway pressure, esophageal pressure, and EAdi were continuously recorded.PTPes_ins and PTPes_tri at different PEEP levels in each group were calculated offline. We opted for comparison of measured parameters in the ventilation mode and PEEPe using repetitive measure analysis of variance. In NAVA or PSV mode, multiple comparison between different PEEPe level using SNK test.

There were 6 patients in EFL group and 6 in Re group. we found no significant difference in patients age, acute physiology and chronic health evaluation II between these two groups.①The equivalence of NAVA with PSV: no significant difference was found in pressure-time wave, respiratory rate, peak airway pressure and mean airway pressure (t=0.720, 0.817, 0.621, 1.579, P>0.05).② Effects of NAVA on work of breath: at each PEEPe level, PTPes_ins was significantly lower in NAVA patients than in PSV patients (t=3.816, 3.117, 2.758, 2.572, P<0.05). When elevating PEEPe from 0 to 120% of PEEPi_stat in FEL group, PTPes_ins decreased significantly both in NAVA patients and in PSV patients (F=9.78, 10.26, P<0.05) , no significant effect on PTPes_ins was found in RE group (F=8.12, 7.64, P>0.05). ③Effects of PEEPe on work of triggering: at each PEEPe levels, PTPes_tri was significantly lower in NAVA patients than in PSV patients (t=4.624, 4.431, 4.165, 5.082, P<0.05). PTPes_tri was not significantly different among each PEEPe conditions in NAVA patients of both groups (F=5.71, 5.93, P> 0.05). There was a PTPes decrease in EFL patients using PSV when PEEP was elevated, but not in RE patients.

NAVA significantly reduced work of breath and triggering in AECOPD patients compared with PSV. The work of triggering was not impacted by PEEPe in NAVA, while increased PEEPe may decrease triggering work in EFL patients with PSV.