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Patrick Gleason MS4 University of South Carolina School of Medicine. Pressure vs. Volume Limited Ventilation- Is one safer or more effective than the other?. Modes of Ventilation. Ventilator Induced Lung Injury (VILI). 2 main types of injury: 1. Overdistention
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Patrick Gleason MS4 University of South Carolina School of Medicine Pressure vs. Volume Limited Ventilation- Is one safer or more effective than the other?
Ventilator Induced Lung Injury (VILI) • 2 main types of injury: 1. Overdistention 2. Collapse and reexpansion • VILI is histologically indistinguishable from ARDS • Obesity may be protective at high pressures
Pressure Limited Ventilation • Set Peak Inspiratory Pressure (PIP) level, I:E ratio, respiratory rate, applied PEEP, and FiO2 • Tidal volume is variable from breath to breath • No consensus on ideal pressures • Peak airway pressure is constant during pressure limited ventilation
Volume Limited Ventilation • Set peak flow rate, flow pattern, tidal volume, respiratory rate, PEEP, and FiO2. • PIP is variable from breath to breath • Important distinction in the flow patterns: • Square wave vs. ramp wave
Pressure vs. Volume • There were no statistically significant differences in mortality, oxygenation, or work of breathing • Pressure-limited ventilation was associated with lower peak airway pressures, a more homogeneous gas distribution, improved patient-ventilator synchrony, and earlier liberation from mechanical ventilation than volume-limited ventilation. • Studies comparing pressure-limited and volume-limited ventilation used a square wave pattern for both modes. When volume-limited mechanical ventilation with a ramp wave pattern was compared to pressure-limited ventilation, lower peak airway pressures were no longer an advantage of pressure-limited ventilation.
Recommendations • Use PEEP in both pressure and volume limited ventilation – the higher the PIP, the higher the PEEP. • Tidal volumes should be between 5-10 mL/kg of IBW • Preferable to use either pressure limited or volume limited with ramp wave flow • Previous pulmonary injury increases risk for subsequent VILI
References • Hagberg CA. Benumof’s Airway Management: Principles and Practice. 2nd Edition Mosby Elesevier. 1996 • Rappaport SH, Shpiner R, Yoshihara G, Wright J, Chang P, Abraham E. Randomized, prospective trial of pressure-limited versus volume-controlled ventilation in severe respiratory failure. Crit Care Med. 1994;22(1):22. • Prella M, Feihl, Domenighetti G. Effects of short-term pressure-controlled ventilation on gas exchange, airway pressures, and gas distribution in patients with acute lung injury/ARDS: comparison with volume-controlled ventilation. Chest. 2002;122(4):1382. • ChiumelloD, Pelosi P, Calvi E, Bigatello LM, GattinoniL. Different modes of assisted ventilation in patients with acute respiratory failure. EurRespir J. 2002;20(4):925. • Bozyk P, Hyzy RC, Parsons P, Wilson, K. Modes of Ventilation. UpToDate 2010. • Medscape • Google Images