Weaning: The Respiratory Muscles

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Weaning: The Respiratory Muscles Ewan C. Goligher MD FRCPC Critical Care Medicine, University Health Network, Toronto Dept. of Physiology, University of Toronto Disclosures Sources of Funding CIHR Ministry of Health, Ontario PSI Foundation UHN AFP Innovation Fund OSCILLATE Subgrant (CIHR) Conflicts of Interest None to report Respiratory Muscle Dysfunction and Mechanical Ventilation Key Messages 1. Respiratory muscle dysfunction is an important barrier to liberation from mechanical ventilation 2. Respiratory muscle dysfunction is prevalent among critically ill patients 3. Mechanical ventilation may contribute to the development of respiratory muscle dysfunction Key Messages 1. Respiratory muscle dysfunction is an important barrier to liberation from mechanical ventilation 2. Respiratory muscle dysfunction is prevalent among critically ill patients 3. Mechanical ventilation may contribute to the development of respiratory muscle dysfunction Weaning: Supply and Demand MacIntyre Respir Care 2005 Tension-Time Index Time to task failure determined by the energetic load on the diaphragm Magnitude of load Duration of load TTI = P i P i,max T i T tot Bellemare and Grassino JAP 1982 Pathophysiological Determinants of Weaning Success 160% 140% 120% 100% 80% 60% SBT Failure SBT Success 40% 20% 0% Resistance Compliance PEEPi Pi,max TTI Vassilakopoulos et al AJRCCM 1998 Tension-Time Index and Liberation Independent predictors of passing SBT Tension-time index OR 10.3 (95% CI ) RSBI OR 3.2 (95% CI ) Vassilakopoulos et al AJRCCM 1998 Time (hours) Time (days) Diaphragm Dysfunction Predicts Difficult Weaning from Ventilation Time on ventilator Time on weaning 0 ICU LOS Hospital LOS Figures from Sarwal et al Musc Nerve 2013 Kim et al Crit Care Med 2011 Key Messages 1. Respiratory muscle dysfunction is an important barrier to liberation from mechanical ventilation 2. Respiratory muscle dysfunction is prevalent among critically ill patients 3. Mechanical ventilation may contribute to the development of diaphragm dysfunction Measuring Diaphragm Function Twitch transdiaphragmatic pressure Figures from Man et al ERJ 2004 & Tobin et al Annals Int Med 2010 Early Respiratory Muscle Dysfunction Diaphragm dysfunction was common on MV day 1 (37%) Key predictors Sepsis SAPS II Associated with mortality Not associated with duration of MV or LOS Demoule et al AJRCCM 2013 Twitch Transdiaphragmatic Pressure (cm H2O) Late Respiratory Muscle Dysfunction Key Messages 1. Respiratory muscle dysfunction is an important barrier to liberation from mechanical ventilation 2. Respiratory muscle dysfunction is prevalent among critically ill patients 3. Mechanical ventilation may contribute to the development of diaphragm dysfunction Etiologies of Diaphragm Dysfunction Shock Medications Critical illness myopathy Myotrauma Mechanical Ventilation Sepsis/SIRS Electrolyte imbalances Diaphragm Injury Diaphragm Dysfunction Fatigue Pectoralis Pectoralis Major Muscle Fiber CSA (µm 2 ) Evidence for Myotrauma Diaphragm Pectoralis major Levine et al Online Supplement 21 C. FIGURES 8000 Control (n=6) Case (n=6) 6000 P=NS P=NS Slow 2.25 Fast 4.5 Fiber Types Figure S1 Levine et al N Engl J Med 2008 Evidence for Myotrauma Jaber et al AJRCCM 2011 Mechanism 1. Disuse Atrophy Spontaneous Breathing Controlled Ventilation Powers et al J Appl Phys 2002 Mechanism 1. Disuse Atrophy Pressure Support Ventilation Hudson et al Crit Care Med 2012 Mechanism 2. Eccentric Contractions Short-term Effect Ineffective Efforts Mid-term Effect Fig. 1 Flow and airway pressure tracings showing ineffective triggering, i.e., a wasted effort, defined as Gea anet airway Thille al Arch pressure et Bronchopneumol al Int drop Care simultaneous to a flow decrease during the expiratory period and Med not chrony tha triggering w abrupt airw to a flow d by an assis In PSV on during the (Fig. 2). Do arated by a one-half of patient-trig acycle del pressure de abreath tha was define Summary 1. Respiratory muscle dysfunction is an important barrier to liberation from mechanical ventilation 2. Respiratory muscle dysfunction is prevalent among critically ill patients 3. Mechanical ventilation may contribute to the development of diaphragm dysfunction Future Directions Feasible monitoring techniques Characterize myotrauma in the clinical setting Respiratory muscle rehabilitation Muscle-protective mechanical ventilation