In the case of an unrestrained 2-year-old with a severe closed head injury on mechanical ventilation, what should be increased to improve oxygen levels?

In this scenario, increasing the fraction of inspired oxygen (FiO2) is the most appropriate intervention to improve oxygen levels in a mechanically ventilated patient, especially in the context of a severe closed head injury. This situation often results in compromised oxygenation due to potential neurogenic pulmonary edema or other physiological changes. By increasing FiO2, the concentration of oxygen being delivered to the patient increases, directly enhancing the amount of oxygen available for gas exchange in the lungs.

Increasing FiO2 is a standard approach in managing hypoxemia, particularly when there are signs of inadequate oxygenation. It can be a rapid intervention providing immediate benefits while other adjustments, such as ventilatory settings or recruitment maneuvers, are made.

Other interventions, such as increasing tidal volume or the mandatory rate, can also affect ventilation parameters, but they primarily focus on carbon dioxide removal rather than directly improving oxygen levels. Adjustments to PEEP can help recruit collapsed alveoli and improve oxygenation in some cases, but it may also compromise hemodynamics in an injured pediatric patient. Therefore, focusing on increasing FiO2 is the most effective and immediate strategy to enhance oxygenation under these circumstances.