Pleural Drainage Enhances Diaphragmatic Pressure Generation in Mechanically Ventilated Patients
CCCF ePoster library. McClelland W. 10/04/17; 198206; 83
Mr. William McClelland
Mr. William McClelland
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Pleural Drainage Enhances Diaphragmatic Pressure Generation in Mechanically Ventilated Patients

William McClelland1; Laurent J. Brochard2,3; Andrea Matte1; Christer Sinderby2,3; Arthur Slutsky2,3; Jennifer Beck2,3; Norm Comtois3; Niall D. Ferguson1,2,4,5; Ewan C. Goligher1,2


Institutional Affiliations

  1. Department of Medicine, Division of Respirology, University Health Network, Toronto, Canada

  2. Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada

  3. Keenan Centre for Biomedical Research, Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Canada

  4. Department of Physiology, University of Toronto, Toronto, Canada

  5. Institute for Health Policy, Management, and Evaluation, University of Toronto, Toronto, Canada

Introduction & Objective
Pleural drainage is sometimes proposed as a means of facilitating weaning from mechanical ventilation, but the mechanism of benefit from this procedure is unclear [1,2]. Experimental data and prior observations in non-mechanically ventilated patients suggest that draining effusions may improve diaphragm mechanics [3,4] but this hypothesis has not been tested in mechanically ventilated patients. We undertook to determine whether pleural drainage enhances diaphragmatic pressure generation in mechanically ventilated patients.
We enrolled mechanically ventilated patients with large pleural effusions on chest radiograph who had been selected by the medical team to undergo pleural drainage. An esophageal catheter was placed to record esophageal (Pes) and transdiaphragmatic pressure (Pdi) and diaphragm electrical activity (Edi). Pressures and Edi were recorded while subjects were placed on a CPAP trial with zero airway pressure (for up to 10 minutes as tolerated) before and after pleural drainage. Changes in Pes were corrected for swings in gastric pressure (Pga) due to expiratory abdominal muscle activity. The primary outcome was neuromuscular coupling (NMC) of the diaphragm, defined as the ratio of Pdi to Edi [5]. We also examined changes in NMC of the respiratory system (Pes/Edi), neuroventilatory coupling (NVC, tidal volume Vt/Edi), dynamic compliance (Cdyn = Vt/PL, transpulmonary pressure), and respiratory timing parameters.
Four patients were enrolled, Three of four subjects could not complete the 10-minute CPAP trial prior to drainage (median 6.6 minutes). All subjects underwent pleural drainage (volume drained 400cc-1510cc). Immediately following pleural drainage, all subjects completed the 10-minute CPAP trial without distress. Venous CO2 tensions were unchanged before and after drainage. Diaphragm NMC increased following drainage (Figure 1A, p<0.001), although the improvement was observed in 3 of 4 patients (NMC increased by 17% to 50%). Respiratory NMC increased in all subjects (Figure 1B, p<0.001, range 19%-87%). Increases in NMC were accompanied by decreases in end-expiratory Pes, though one subject exhibited a paradoxical increase in end-expiratory Pes. Cdyn improved in 2 of 4 subjects (Figure 1C). These combined changes in NMC and Cdyn gave rise to significant improvements in NVC (Figure 1D,  p<0.001, range 13%-77%). One subject exhibited a significant (57%) decrease in respiratory rate after drainage without changes in venous PCO2
We observed significant improvements in diaphragm NMC, respiratory NMC, and CPAP trial tolerance following pleural drainage, consistent with the hypothesis that pleural effusions impede weaning from ventilation by impairing diaphragm mechanics. These findings suggest that pleural drainage may provide the greatest benefit to patients with reduced maximal inspiratory pressure-generating capacity.

Figure 1. Physiological effects of pleural drainage in mechanically ventilated patients. Neuromuscular coupling of the diaphragm (A, top left) and respiratory system (B, top right) improved in 3 out of 4 patients following drainage, while dynamic compliance (C, bottom left) improved in 2 out of 4 patients. These changes gave rise to consistent improvements in neuroventilatory coupling (D, bottom right).

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