Physiologic Determinants of Prolonged Mechanical Ventilation and Unweanable Patients



Fig. 1.1
Balance between load (↑motor drive, ↑resistive, ↑elastic, cardiovascular impairment) and capacity (↓motor drive, ↓neurotransmission, inspiratory muscle weakness) determines the ability to sustain spontaneous ventilation




Key Points





  • In PMV and unweanable patients, the imbalance between inspiratory muscle work load and inspiratory muscle capacity is of paramount importance.


  • The rapid shallow breathing pattern is the hallmark of weaning failure.


  • In PMV patients, the major determinant of prolonged weaning is inspiratory muscle weakness or dysfunction, as expressed by TTIdi that is above the fatigue threshold.


  • During the course of a weaning trial, most WF patients significantly increase respiratory load as a result of severe worsening of respiratory mechanics (e.g., resistance, elastance, or PEEPi).


  • In PMV patients, the recovery of inadequate inspiratory muscle force seems to be the major determinant of WS allowing them to breathe below the diaphragmatic fatigue threshold.


  • A less common cause of WF is impairment of cardiovascular performance.



References



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Schulman RC, Mechanick JI. Metabolic and nutrition support in the chronic critical illness. Respir Care. 2012;57(6):958–78.PubMedCrossRef


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Nevins ML, Epstein SK. Weaning from prolonged mechanical ventilation. Clin Chest Med. 2001;22:13.PubMedCrossRef


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Tobin MJ, Jubran A. Weaning from mechanical ventilation. In: Todin MJ, editor. Principles and practice of mechanical ventilation. 3rd ed. New York: McGrawHill; 2013.


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Jubran A, Tobin MJ. Pathophysiologic basis of acute respiratory distress in patients who fail a trial of weaning from mechanical ventilation. Am J Respir Crit Care Med. 1997;155:906–15.PubMedCrossRef


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Tobin MJ, Laghi F, Brochard L. Role of the respiratory muscles in acute respiratory failure of COPD: lessons from weaning failure. J Appl Physiol. 2009;107:962–70.PubMedCrossRef


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Vassilakopoulos T, Zakynthinos S, Roussos C. The tension-time index and the frequency/tidal volume ratio are the major pathophysiologic determinants of weaning failure and success. Am J Respir Crit Care Med. 1998;158:378–85.PubMedCrossRef


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Tobin MJ, Langhi F, Jubran A. Ventilatory failure ventilator support, and ventilator weaning. Compr Physiol. 2012;2:2871–921.PubMed

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Oct 12, 2016 | Posted by in CRITICAL CARE | Comments Off on Physiologic Determinants of Prolonged Mechanical Ventilation and Unweanable Patients

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