Introduction: Residual hypercapnia can be present in daytime or during sleep in patients with chronic hypoventilation treated with NIV; thus CO 2 should be monitored both during daytime and sleep. Aims: 1) to compare arterial CO 2 (PaCO 2 ) measured by radial puncture with TcCO 2, 2) to measure overnight drift of the TcCO 2 sensor and 3) to evaluate the contribution of overnight TcCO 2 vs. solely using pulse oximetry (SpO 2 ) for detecting nocturnal hypoventilation (NH). Methods: 42 patients with: neuromuscular diseases (23), central hypoventilation syndrome (3), obesity hypoventilation syndrome (12) and restrictive thoracic disorders (4) were studied. PaCO 2 (room air) was compared with simultaneously measured TcCO 2 values. Overnight drift was estimated by measuring a defined gas concentration in the evening, after calibration of the sensor, and repeating this measurement in the morning. Overnight TcCO 2 and SpO 2 were measured during NIV. Definition of: NH: TcCO 2 7,3 kpa or ≥1,33 kpa increase to above 6,7 kpa ≥10 minutes. Normal SpO 2 : SpO2 90% in 10% of the recording time. Results: TcCO 2 correlated significantly with PaCO 2 (r = 0.966 p0.0001). The Bland-Altman plot showed a mean bias of 0.25 kpa (Limits of agreement; -0.26 – 0.76). Mean technical drift was 0.01 kpa/hr(± 0.08). NH was found in 15 patients, 8(53%) had normal and 7(47%) had an abnormal overnight SpO2. Conclusions: TcCO 2 accurately reflects PaCO 2 in patients with chronic hypoventilation and can be used to monitor CO 2 overnight during NIV without any clinically significant drift. TcCO 2 can detect NH in patients with normal nocturnal SpO 2 , and can differentiate NH from other causes of nocturnal hypoxemia.
Aarrestad et al. (Mon,) studied this question.
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