Overview Therapeutic indications for mechanical ventilation include Inadequate alveolar ventilation (clearance of CO2) Inadequate Oxygenation Excessive work of breathing Circulatory shock Septic, hemorrhagic, etc congestive heart failure decrease oxygen consumption of respiratory system Positive end-expiratory pressure (PEEP) reduces afterload on the left ventricle and may improve cardiac output in failing heart There are several main modes Assist-Control (Volume-cycled or Pressure-targeted) Volume Cycled Settings: tidal volume, flow rate, flow waveform, FiO2, PEEP, frequency Airway pressures and auto-PEEP are dependent on respiratory system Pressure-targeted Settings: pressure target, inspiratory time, inspiratory rise rate, FiO2, PEEP, frequency Tidal volume and auto-PEEP are dependent upon respiratory system Pressure-Support Ventilation Usually with set CPAP (PEEP) Spontaneous mode where support can be adjusted; cannot set frequency or tidal volume, these are dependent upon patient effort, strength and compliance of respiratory system Tolerated well because flow, depth and length are all patient controlled Synchronized intermittent mechanical ventilation (SIMV) combination of spontaneous breathing and set number of ventilator breaths that are fully supported but coincide with spontaneous efforts Complications Cardiovascular impairment positive intrathoracic pressure can decrease venous return, decreasing cardiac output most problematic in patients who are intravascularly volume deplete Barotrauma Subcutaneous emphysema, pneumomediastinum, pneumothorax, pneumoperitoneum and interstitial emphysema Associated with high mean alveolar pressure high peak airway pressures necrotizing lung pathology high minute ventilation longer duration of mechanical ventilation Ventilator-induced lung injury (including volutrauma) Low tidal volume strategy (6 mL/kg ideal body weight) reduces mortality in ARDS lower driving pressure needed to achieve lower goal tidal volumes in damaged lungs Tissues stress can be decreased by increased levels of PEEP when plateau pressures are elevated (goal plateau pressure < 30 cmH2O) Use PEEP to prevent widespread alveolar unit closure at end-expiration to decrease tissue stress, which leads to shearing and inflammatory signaling Infections Ventilator-associated Pneumonia Sinusitis