Fast versus slow PEEP trial guided by electrical impedance tomography in hypoxemic patients following cardiac surgery: randomized controlled trial

Author(s)

Maria Aparecida Miyuki Nakamura

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2018-04-04

Examining board members

Marcelo Britto Passos Amato; Eduardo Leite Vieira Costa; Marcelo Park; Mauro Roberto Tucci

• Advisor: Marcelo Britto Passos Amato

Abstract

OBJECTIVE: to assess the agreement of \"optimum-PEEP\" values selected by two decremental PEEP trials guided by electrical impedance tomography (EIT): a Fast one lasting less than 7 minutes, and a Slow one lasting 40 minutes, and to compare the hemodynamic effects caused by these two trials; as secondary objectives, we aimed at comparing the physiological effects of the optimum-PEEP chosen by EIT (Fast or Slow) with those chosen by ARDSNet PEEP-FiO2 table during the subsequent 4 hours of mechanical ventilation. METHODS: in this single center, randomized controlled trial, hypoxemic patients immediately after cardiac surgery were randomized into three groups: Fast Titration (FAST-EIT), Slow Titration (SLOW-EIT) and Control (ARDSNet PEEP-FiO2 table). After recruiting maneuvers, and starting from a PEEP of 23 cmH2O, the FAST-EIT and SLOW-EIT groups were submitted to decremental PEEP trials, in steps of 2 cmH2O, until reaching 5 cmH2O, with two different durations: 40 seconds (the entire maneuver lasted < 7 minutes) or 4 minutes (entire maneuver lasted 40 minutes). The optimum-PEEP (PEEPTIT) was defined as the lowest PEEP with less than 5% of collapse estimated by EIT. In the control group, PEEP was adjusted according to oxygenation based on ARDSNet protocol. All patients were ventilated for 4 hours with PEEP according to their randomized groups, and all were monitored with EIT during the study. The comparison between Fast and Slow PEEP trials included: recruitable collapse and hyperdistension estimated by EIT, level of optimum PEEP, lowest mean arterial pressure and norepinephrine doses during the trials. The comparison with the control group included: level of PEEP, compliance and driving pressure, collapse (aeration) and hyperdistension estimated with EIT, and oxygenation (PaO2/FiO2) during 4 hours of mechanical ventilation. RESULTS: There was no difference between recruitable collapse and hyperdistension estimated by EIT between Fast and Slow maneuvers, as well as for the PEEPTIT (13 ± 4 vs 14 ± 4 cmH2O, P=0.13). Mean arterial pressure was higher during the Fast maneuver in comparison to the Slow maneuver (92mmHg [IQ25-75%: 81-111] vs 83mmHg [71-93], P=0.035), without differences in norepinephrine. FAST-EIT and SLOW-EIT groups presented similar changes during the time: after set PEEPTIT there was an immediate and significant improvement in respiratory-system compliance, which remained above baseline condition during the 4 hours of mechanical ventilation (SLOW-EIT: from 0.73 ± 0.2 to 0.89 ± 0.1 mL/cmH2O/Kg of PBW, P < 0.001; FAST-EIT: from 0.7 ± 0.1 to 0.85 ± 0.2 mL/cmH2O/Kg of PBW, P < 0.001); as respiratory compliance improved, driving pressure significantly reduced and remained lower than the baseline condition after 4 hours. In the control group, respiratory compliance did not change between baseline and 4 hours (from 0.63 ± 0.1 to 0.58 ± 0.1 mL/cmH2O/Kg of PBW, P=0.34) but driving pressure significantly increased as PEEP decreased. Oxygenation improved in all groups, but it was higher in the EIT groups. After setting PEEPTIT in both EIT groups (Fast or Slow), there was an increase in aeration in both, nondependent and dependent regions. In contrast, regional compliance increased in the dependent region and didn\'t change in nondependent region, suggesting that the strategy caused long-lasting recruitment of dependent regions and did not produced hyperdistension of non-dependent lung. In the control group, the required PEEP, adjusted by ARDSNet PEEP-FiO2 table, decreased along the time, causing evident collapse in EIT derived signals. CONCLUSION: There was no difference between recruitable collapse and hyperdistension estimated by EIT and PEEPTIT between Fast and Slow maneuvers; Fast PEEP trial guided by EIT could be performed in less than 7 minutes, with less hemodynamic consequences than the traditional Slow maneuver. Individualized PEEP guided by EIT improved respiratory compliance, reduced driving pressure and improved oxygenation without causing hyperdistension - when compared to a PEEP set according the ARDSNet protocol (AU)

• FAPESP's process: 13/22910-9 - Pulmonary function stability monitored by electrical impedance tomography (EIT) with ideal PEEP chosen by rapid versus slow PEEP titration maneuver
• Grantee: Maria Aparecida Miyuki Nakamura
• Support type: Scholarships in Brazil - Doctorate