In a patient with suspected neuromuscular disease causing ventilatory failure, which parameter is most useful to monitor for impending ventilatory failure?

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Assessing ventilation and acid-base status with an arterial blood gas is the most useful parameter because it directly reflects how effectively the patient is ventilating. In neuromuscular disease, weakness of the respiratory muscles leads to hypoventilation, causing CO2 to accumulate. An ABG will reveal rising PaCO2 and a dropping pH, often signaling impending ventilatory failure before oxygenation markers or obvious breathing pattern changes become evident.

Oxygen saturation measured by pulse oximetry can remain reassuringly normal, especially if supplemental oxygen is used, so it may not detect hypoventilation. Respiratory rate can be variable and may not accurately represent the level of ventilation, particularly in fatigued patients who cannot sustain an increased rate. Blood pressure, while important clinically, does not directly indicate ventilatory status or CO2 retention.