A 58-year-old male with COPD is admitted to the ICU with acute exacerbation and hypercapnic respiratory failure (pH 7.28, PaCO₂ 68 mmHg, PaO₂ 55 mmHg on 40% O₂). He is intubated and placed on mechanical ventilation. The respiratory therapist sets the ventilator to deliver a fixed tidal volume of 8 mL/kg of predicted body weight with a set respiratory rate of 14 breaths/min. The patient is triggering additional breaths above the set rate due to anxiety and air hunger. Which ventilation mode would be most appropriate to allow the patient to breathe spontaneously while ensuring a guaranteed minute ventilation and preventing hypoventilation?