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# Effect of Positive Pressure Ventilation and O₂ Delivery **Figure 2-1:** Comparison of Mean Airway Pressure between CPAP and PEEP. The mean airway pressure is higher in PEEP (10 cm H₂O) because it is used in addition to positive pressure ventilation. **Blood Pressure Changes** During spontaneou...

# Effect of Positive Pressure Ventilation and O₂ Delivery **Figure 2-1:** Comparison of Mean Airway Pressure between CPAP and PEEP. The mean airway pressure is higher in PEEP (10 cm H₂O) because it is used in addition to positive pressure ventilation. **Blood Pressure Changes** During spontaneous inspiration, there's a temporary decrease in arterial blood pressure. In conditions like cardiac tamponade or acute asthma exacerbation, this decrease is exaggerated (>10 mm Hg). This is known as pulsus paradoxus. During positive pressure ventilation, the reverse pulsus paradoxus occurs; arterial blood pressure is slightly higher than during spontaneous breathing. Measures in the aorta, left atrium, pulmonary artery, and right atrium will be slightly higher with positive pressure ventilation. Positive pressure ventilation also displaces the ventricle walls. This enhances ventricular emptying, leading to a slight rise in systolic pressure. The reverse pulsus paradoxus mechanism involves reduction in left ventricular afterload. A significant reverse pulsus paradoxus (increase of systolic pressure >15 mm Hg) during positive pressure ventilation signifies hypovolemia. For patients with compromised cardiovascular reserve, positive pressure ventilation and PEEP may further reduce venous return, compromising cardiovascular function. **Use of Positive Pressure Ventilation** In positive pressure ventilation, the body's oxygen supply can be reduced due to increased intrathoracic pressure. This pressure is transmitted to airways, alveoli, and mediastinum, along with blood vessels. Compression of vessels leads to reduced venous return to the heart. A decreased venous return to the ventricles decreases stroke volume and cardiac output. Oxygen delivery is the product of oxygen content and cardiac output, so reduced stroke volume and cardiac output reduces oxygen delivery. The equation for this is: O₂ Content $\times$ Cardiac Output = O₂ Delivery **Figures (A) and (B)** * **Figure A**: CPAP (Continuous Positive Airway Pressure) * **Figure B**: PPV + PEF (Positive Pressure Ventilation + Positive End-Expiratory Pressure) **Other Information from the Image:** * **Treatment**: PEEP (Positive End-Expiratory Pressure) and FIO₂ (Fraction of Inspired Oxygen), plus position. * **Patient**: Patient with low lobe pneumonia, and end-up hypoxemia. * **Preliminary/After**: Various treatments, positions, etc.