Correspondence  |   March 2018
Impact of Weaning from Mechanical Ventilation: The Importance of Pleural Effusions and Their Effect on Pulmonary Vascular Resistance
Author Notes
  • University of Manitoba, Winnipeg, Manitoba (E.J.). ejacobsohn@hsc.mb.ca
  • (Accepted for publication November 21, 2017.)
    (Accepted for publication November 21, 2017.)×
Article Information
Correspondence
Correspondence   |   March 2018
Impact of Weaning from Mechanical Ventilation: The Importance of Pleural Effusions and Their Effect on Pulmonary Vascular Resistance
Anesthesiology 3 2018, Vol.128, 677-678. doi:10.1097/ALN.0000000000002040
Anesthesiology 3 2018, Vol.128, 677-678. doi:10.1097/ALN.0000000000002040
The recent multicenter prospective observational study by Dres et al.1  examining the impact of pleural effusions on liberation from mechanical ventilation showed that 13% of their patients had a pleural effusion at the time of ventilator weaning, but that there was no relationship to the successful discontinuation of ventilation. Indeed, in their discussion on the potential reasons why pleural effusions might influence ventilator weaning failure, they identified three principal mechanisms. The first of these was the impact on respiratory mechanics, suggesting that large pleural effusions could reduce the end-expiratory lung volumes. The second mechanism was linked with the potential for pleural effusions to have an impact on the impairment of gas exchange, stating that associated lung collapse caused by the effusion could increase hypoxemia due to ventilation perfusion mismatch or intrapulmonary shunting. The third mechanism that they outlined related to the potential impact on cardiac filling pressures, with pleural effusions potentially increasing these filling pressures, and as a result, weaning-induced pulmonary edema. We contend that this last mechanism seems far less likely given that it would have to be the result of a significant leftward shift of the interventricular septum or some another cause of left-sided systolic or diastolic dysfunction. What is far more common is that pleural effusions often are the consequence of high left atrial pressure (i.e., forming due to hydrostatic forces), and therefore represent the same underlying pathophysiologic state, that is heart failure or fluid overload. The elevated left atrial pressure, when coupled with increased venous return that occurs with reduced intrathoracic pressures during weaning, may result in pulmonary edema.
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