Patrick Gleason MS4 University of South Carolina School of Medicine 1

Modes of Ventilation 2

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 3

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 4

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 5

Volume Limited Ventilation – cont. 6

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. 7

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 8

References 9  Hagberg CA. Benumof’s Airway Management: Principles and Practice. 2 nd Edition Mosby Elesevier  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.  Chiumello D, Pelosi P, Calvi E, Bigatello LM, Gattinoni L. Different modes of assisted ventilation in patients with acute respiratory failure. Eur Respir J. 2002;20(4):925.  Bozyk P, Hyzy RC, Parsons P, Wilson, K. Modes of Ventilation. UpToDate  Medscape  Google Images