Final answer:
Optimal PEEP in mechanical ventilation is achieved not just by keeping the pressure under a specific threshold, but by ensuring that PaO₂ remains at or above 60 torr and that oxygen delivery to the tissues is maximized.
Step-by-step explanation:
Setting the Positive End-Expiratory Pressure (PEEP) optimally is crucial in mechanically ventilated patients to ensure efficient oxygenation and ventilation. Optimal PEEP does not solely depend on maintaining the PEEP levels below a certain value, such as 18 cm H₂O. Instead, it is determined by several clinical endpoints. One critical endpoint is ensuring a patient's arterial oxygen partial pressure (PaO₂) is maintained at 60 torr or greater, which suggests adequate oxygenation. Additionally, optimal PEEP is considered as the level at which oxygen delivery to the tissues is maximized. This means enhancing the oxygenation of the blood without causing harm such as lung injury or decreased cardiac output. The mixed venous-arterial oxygen content difference (C(a-v)O₂) is a complex parameter that reflects the balance between oxygen delivery and consumption. A decreasing C(a-v)O₂ suggests improved tissue oxygenation but is not solely used to set PEEP levels.