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# Principles of Mechanical Ventilation ## Effects on Ventilation and Oxygenation Airway resistance is inversely related to minute ventilation. Patients with chronic airway obstruction may have highly compliant lung parenchyma, leading to deeper but slower breathing. Conversely, patients with res...

# Principles of Mechanical Ventilation ## Effects on Ventilation and Oxygenation Airway resistance is inversely related to minute ventilation. Patients with chronic airway obstruction may have highly compliant lung parenchyma, leading to deeper but slower breathing. Conversely, patients with restrictive lung disease (low compliance) breathe more shallowly but faster. Excessive airway resistance, when sustained, can fatigue respiratory muscles and lead to ventilation and oxygenation failure. Ventilatory failure occurs when minute ventilation cannot keep up with CO2 production; often followed by oxygenation failure when the cardiopulmonary system cannot provide adequate oxygen. ## Airflow Resistance Airflow resistance of a patient-ventilator system can be monitored using a pressure-volume (P-V) loop display. Increased bowing of the P-V loop suggests overall increased airflow resistance, which can be caused by excessive inspiratory flow or increased expiratory resistance. This is shown graphically in Figure 1-1. **Figure 1-1:** A graph displays pressure (cm H2O) on the y-axis and volume (mL) on the x-axis. The dashed lines demonstrate the original P-V loop. The solid lines show an increase in airflow resistance, bowing from the dotted line. Bowing of the inspiratory limb (A1 to A2) may signify excessive inspiratory flow. Bowing of the expiratory limb (B1 to B2) may suggest an increase in expiratory resistance. **Patient Notes:** * Patient with low lobe pneumonia * Patient with end-up hypoxemia * Patient with upper lung problems