FROM THE AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE
A noninvasive bedside imaging technique can individually calibrate positive end-expiratory pressure settings in patients on extracorporeal membrane oxygenation (ECMO) for severe acute respiratory distress syndrome (ARDS), a study showed.
The step-down PEEP (positive end-expiratory pressure) trial could not identify a single PEEP setting that optimally balanced lung overdistension and lung collapse for all 15 patients. But, electrical impedance tomography (EIT) allowed investigators to individually titrate PEEP settings for each patient, Guillaume Franchineau, MD, wrote ( Am J Respir Crit Care Med. 2017;196:447-57 doi: 10.1164/rccm.201605-1055OC).
“We found that EIT could provide individual, noninvasive, real-time, radiation-free lung imaging with reliable global and regional dynamic analyses of the lungs on ECMO,” wrote Dr. Franchineau of the Pierre and Marie Curie University, Paris. “Using EIT allowed monitoring of the PEEP effect that prevented excessive lung collapse or overdistension … The large variability of EIT-based best compromise PEEP settings … reinforces the notion of an individually tailored approach to mechanical ventilation. Because of the wide diversity of respiratory-system mechanical properties among patients, bedside tools for monitoring mechanical ventilation on ECMO are crucial to achieve this goal.”
The 4-month study involved 15 patients (aged, 18-79 years) who were in acute respiratory distress syndrome for a variety of reasons, including influenza (7 patients), pneumonia (3), leukemia (2), and 1 case each of Pneumocystis, antisynthetase syndrome, and trauma. All patients were receiving ECMO with a constant driving pressure of 14 cm H2O. After verifying that the inspiratory flow was 0 at the end of inspiration, PEEP was increased to 20 cm H2O (PEEP 20) with a peak inspiratory pressure of 34 cm H2O. PEEP 20 was held for 20 minutes and then lowered by 5 cm H2O decrements with the potential of reaching PEEP 0.
The EIT device, consisting of a silicone belt with 16 surface electrodes, was placed around the thorax aligning with the sixth intercostal parasternal space and connected to a monitor. By measuring conductivity and impeditivity in the underlying tissues, the device generates a low-resolution, two-dimensional image. The image was sufficient to show lung distension and collapse as the PEEP settings changed. Investigators looked for the best compromise between overdistension and collapsed zones, which they defined as the lowest pressure able to limit EIT-assessed collapse to no more than 15% with the least overdistension.
There was no one-size-fits-all PEEP setting, the authors found. The setting that minimized both overdistension and collapse was PEEP 15 in seven patients, PEEP 10 in six patients, and PEEP 5 in two patients.
At each patient’s optimal PEEP setting, the median tidal volume was similar: 3.8 mL/kg ideal body weight for PEEP 15, 3.9 mL/kg ideal body weight for PEEP 10, and 4.3 mL/kg ideal body weight for PEEP 5.
Respiratory system compliance was also similar among the groups, at 20 mL/cm H2O, 18 mL/cm H2O, and 21 mL/cm H2O, respectively. However, arterial partial pressure of oxygen decreased as the PEEP setting decreased, dropping from 148 mm Hg to 128 mm Hg to 100 mm Hg, respectively. Conversely, arterial partial pressure of CO2 increased (32-41 mm Hg).
EIT also allowed clinicians to pinpoint areas of distension or collapse. As PEEP decreased, there was steady ventilation loss in the medial-dorsal and dorsal regions, which shifted to the medial-ventral and ventral regions.
“Most end-expiratory lung impedances were located in medial-dorsal and medial-ventral regions, whereas the dorsal region constantly contributed less than 10% of total end-expiratory lung impedance,” the authors noted.
“The broad variability of EIT-based best compromise PEEPs in these patients with severe ARDS reinforces the need to provide ventilation settings individually tailored to the regional ARDS-lesion distribution,” they concluded. “To achieve that goal, EIT seems to be an interesting bedside noninvasive tool to provide real-time monitoring of the PEEP effect and ventilation distribution on ECMO.”
Dr. Franchineau reported receiving speakers fees from Mapquet.
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