Continuous Abdominal Negative Pressure - Augments PEEP, Reduces Lung Injury
CCCF ePoster library. Yoshida T. Oct 31, 2016; 150886; 8
Dr. Takeshi Yoshida
Dr. Takeshi Yoshida
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Topic: Basic or Translational Science

Continuous Abdominal Negative Pressure – Augments PEEP, Reduces Lung Injury

Takeshi Yoshida1,2,3, Doreen Engelberts1, Gail Otulakowski1, Bhushan Katira1,2,3, Martin Post1, Niall D. Ferguson3,4, Laurent Brochard3,5, Marcelo B.P. Amato6, Brian P. Kavanagh1,2,3

1 Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Canada

2 Departments of Critical Care Medicine and Anesthesia, Hospital for Sick Children, University of Toronto, Toronto, Canada

3 Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada

4 Division of Respirology, Department of Medicine, University Health Network and Mount Sinai Hospital, Toronto, ON, Canada

5 Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada

6 Laboratório de Pneumologia LIM–09, Disciplina de Pneumologia, Heart Institute (Incor) Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, Brazil

Grant acknowledgements:
T Yoshida is funded by a RESTRACOMP training award from the Research Institute of the Hospital for Sick Children, Toronto, Canada. BP Kavanagh is funded by the Canadian Institutes of Health Research, and holds the Dr Geoffrey Barker Chair in Critical Care Research.


In supine patients with ARDS, the lung usually partitions into extensive dorsal atelectatic and small ventral aerated (‘baby lung’) regions. Conventional positive-pressure ventilation directs tidal volume (VT) preferentially to ventral aerated areas. Recruiting atelectasis with increasing positive airway pressure usually overinflates ventral (already aerated) regions; this may have contributed to the unsuccessful clinical trials. This occurs due to a large vertical gradient of pleural pressure (Ppl) in ARDS. Prone positioning is the only effective means to lessen this Ppl gradient.
To test 2 hypotheses - That Continuous Negative Abdominal Pressure (CNAP), by selectively recruiting basal atelectasis, would:
(1) improve lung function in a stable lung injury model;
(2) attenuate ventilator-induced lung injury in a model of progressive lung injury.
An established model of ventilator-induced lung injury (VILI) was used (anesthetized pig, surfactant depletion) and all animals were monitored using esophageal manometry (Pes, pleural pressure), Electrical Impedance Tomography (EIT, regional ventilation) and pulmonary artery catheter (hemodynamics). 2 series of experiments were performed.
Series 1 – Stable Lung Injury. 7 pigs were subject to maximal lung recruitment using PEEP (20 cmH2O) followed with progressive derecruitment by lowering PEEP in serial increments of 2 cmH2O; full physiologic assessment was performed at each decrement of PEEP. This series of assessments was performed twice in each animal: once with CNAP (-5 cmH2O) and once with no CNAP (the order was randomized).  
Series 2 – Progressive Lung Injury. Animals were randomized to ‘CNAP’ or ‘no CNAP’ (5 per group) and both groups were exposed to standardized injurious ventilation: VT 20 mL/kg, low PEEP, and the same expiratory transpulmonary pressure (PL, -3 cmH2O) for 4 h.
Series 1 – Stable Lung Injury. The application of CNAP significantly decreased Ppl in dependent lung regions at all levels of PEEP, but did not alter Ppl in non-dependent lung; thus, CNAP resulted in a narrower vertical gradient of Ppl at all levels of PEEP: at PEEP=4: 11.3±3.5 vs. 6.6±2.5 cmH2O, PEEP vs. PEEP+CNAP (P<0.01). Application of CNAP consistently resulted in better oxygenation, respiratory system compliance, and more homogeneous ventilation at descending PEEP values from 12 to 4 cmH2O. At PEEP=4, the P/F ratio (mmHg) was 67±5 (no CNAP) vs. 263±36 (with CNAP, P<0.01). At most levels of PEEP, oxygenation with added CNAP was greater despite a lower global PL (Fig. 1). CT demonstrated that addition of CNAP (-5 cmH2O) to a PEEP level of 10 cmH2O yielded the same amount of aeration as a PEEP of 18 cmH2O. 
Series 2 – Progressive Lung Injury. Ventilation with no CNAP resulted in progressive lung injury; use of CNAP reduced the progression of lung injury resulting in greater oxygenation, respiratory system compliance, and homogeneity of ventilation (Figs. 2, 3). The level of IL-6 in bronchoalveolar lavage fluid and lung tissue was significantly lower in CNAP group (P<0.01).
CNAP is the only approach to mechanical ventilation that selectively recruits atelectatic lung; it achieves this by reducing the vertical gradient of Ppl thereby realigning the displaced diaphragm and changing the shape of the lung. The impact of these effects is reduced lung injury and improved oxygenation.


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