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Central Respiratory Drive in Patients With Neuromuscular Diseases

BACKGROUND: The contribution of the central respiratory drive in the hypercapnic respiratory failure of neuromuscular diseases (NMD) is controversial. OBJECTIVE: To compare the CO2 response and the duration of weaning of mechanical ventilation between a group of NMD patients and a group of quadriplegic patients due to ICU-acquired weakness (ICU-AW). METHODS: We prospectively studied 16 subjects with NMD and 26 subjects with ICU-AW ready for weaning, using the method of the re-inhalation of expired air. We measured the hypercapnic drive response, defined as the ratio of change in airway occlusion pressure 0.1 second after the start of inspiration (ΔP0.1) to the change in Paco2 (ΔPaco2), and the hypercapnic ventilatory response, defined as the ratio of the change in minute ventilation (ΔV̇e) to ΔPaco2. We considered a value of ≤ 0.19 cm H2O/mm Hg as reduced hypercapnic drive response. RESULTS: Hypercapnic drive response (ΔP0.1/ΔPaco2 = 0.14 ± 0.08 cm H2O/mm Hg vs 0.37 ± 0.27 cm H2O/mm Hg, P = .002) and hypercapnic ventilatory response (ΔV̇e/ΔPaco2 = 0.21 ± 0.19 L/min/mm Hg vs 0.44 ± 0.40 L/min/mm Hg, P = .02) were lower in the NMD than in the ICU-AW subjects. Duration of weaning values, according to the Kaplan-Meier curves, were similar in both groups (Log-rank = 0.03, P = .96). Eleven NMD (69%) and 9 ICU-AW (35%) subjects had hypercapnic drive response ≤ 0.19 cm H2O/mm Hg. The duration of weaning was longer in subjects with hypercapnic drive response ≤ 0.19 cm H2O/mm Hg (log-rank = 15.4, P < .001). CONCLUSIONS: Subjects with acute hypercapnic respiratory failure due to NMD had reduced hypercapnic drive response, compared to ICU-AW subjects. The duration of weaning was longer in subjects with reduced hypercapnic drive response.