**Core Concept**
Optimum oxygenation in mechanically ventilated patients is achieved by adjusting parameters that regulate the balance between ventilation and perfusion, ensuring adequate oxygen delivery to tissues while minimizing lung injury. This involves optimizing the tidal volume, positive end-expiratory pressure (PEEP), and fraction of inspired oxygen (FiO2) to maintain an adequate partial pressure of oxygen in arterial blood (PaO2) while avoiding hyperoxia.

**Why the Correct Answer is Right**
The correct answer involves adjusting PEEP and FiO2 to optimize oxygenation. PEEP helps to maintain lung volume and recruit collapsed alveoli, improving ventilation-perfusion matching and increasing PaO2. FiO2 is adjusted to achieve an adequate PaO2, taking into account the patient's underlying respiratory disease and the presence of any underlying hypoxemia. Tidal volume and respiratory rate are also important parameters, but they are more directly related to ventilation rather than oxygenation.

**Why Each Wrong Option is Incorrect**
**Option A:** Tidal volume is a critical parameter in ventilation, but it is not the primary parameter adjusted to maintain optimum oxygenation. While a large tidal volume can lead to overdistension of alveoli and lung injury, adjusting tidal volume alone may not be sufficient to optimize oxygenation.
**Option C:** Respiratory rate is an important parameter in ventilation, but it is not directly related to oxygenation. A high respiratory rate can lead to respiratory alkalosis, but it does not directly affect PaO2.

**Clinical Pearl / High-Yield Fact**
The ARDS (Acute Respiratory Distress Syndrome) network trial demonstrated that a lower tidal volume (6 mL/kg predicted body weight) and higher PEEP (28-32 cm H2O) resulted in improved survival and fewer ventilator-associated complications in patients with acute lung injury.

**Correct Answer: B. PEEP and FiO2.**