A 58-year-old male with COPD is admitted to the ICU with acute exacerbation and hypercapnic respiratory failure (pH 7.28, PaCO₂ 72 mmHg, PaO₂ 55 mmHg on room air). He is intubated and placed on mechanical ventilation. The respiratory therapist notes that the patient is triggering the ventilator 24 times per minute, with a set rate of 12/min. The patient appears anxious and is fighting the ventilator. Which ventilation mode would be most appropriate to reduce patient work of breathing while allowing spontaneous breathing effort?