The patient was treated with dexamethasone, 4 mg IV q6h, and IV Ig, but over the subsequent week he experienced increasing weakness, dyspnea, and confusion. Serum viscosity, relative to saline solution, was normal at 1.7. Arterial blood gas levels measured while breathing room air revealed respiratory alkalosis (pH, 7.44; Paco2, 23 mm Hg; Pao2, 84 mm Hg) with a respiratory rate of 26 breaths/min; his negative inspiratory force was measured at −17 cm H2O. Fourteen days into his hospitalization, the patient was admitted to the ICU with a respiratory rate of 32 breaths/min, increasing somnolence, and the following arterial blood gas levels while breathing 50% O2 by nonrebreather face mask: pH, 7.10; Paco2, 53 mm Hg; Pao2, 102 mm Hg. His acid-base disorder was complex, with a respiratory acidosis superimposed on a myeloma-induced distal (type I) renal tubular acidosis. He was intubated for ventilatory failure and began receiving mechanical ventilation (model 7200ae; Respironics; Murrysville, PA) in a volume-cycled assist-control mode with the following settings: rate, 14 breaths/min; tidal volume, 450 mL; positive end-expiratory pressure (PEEP), 5 cm H2O; and fraction of inspired oxygen, 50%. Other ventilator settings included a pressure-triggered inspiratory sensitivity of −2 cm H2O, a set flow rate of 60 L/min, and a square waveform. He required no sedation after his induction for intubation and remained passive on the ventilator, with rare spontaneously triggered breaths above his set rate. On these settings, arterial blood gas levels were as follows: pH, 7.27; Paco2, 36 mm Hg; Pao2, 120 mm Hg. Peak inspiratory pressure was measured at 26 cm H2O, and plateau pressure was measured at 8 cm H2O, which prompted the initiation of nebulized albuterol and ipratropium treatments every 6 h. The patient was a pipe smoker.