Transcutaneous blood gas analysis during sleep and exercise in cystic fibrosis

Forty patients with cystic fibrosis (CF) (mean age, 13 +/- 2.5 years) were studied with transcutaneous (tc) blood gas monitoring (TCM) during sleep and exercise. By comparing arterial blood samples and TCM in 24 of them (27 samples), a mean bias of tcO2 -15.91 mmHg with a precision of 8.4 mmHg was found. The mean bias of tcCo2 was 7.21 mmHg with a precision of 3.9 mmHg. A standardized submaximal exercise test (1.7 W/kg) was performed in all 40 CF patients and in 14 healthy control subjects (mean age, 13 +/- 0.5 years). The typical tc trend during exercise for CF and healthy subjects was a slight increase of tcO2 levels and tcCO2 stability. A minor decrease of tcO2 values occurred in four CF patients (no greater than 7 mmHg). In 28 patients (mean age, 13 +/- 3 years), tcO2 and tcCO2 were recorded during sleep. In 13 of them, apparent hypoxemic episodes were noted, without relation to the degree of airway obstruction. There were simultaneous episodes of hypercapnia in ten patients. Some difficulties were encountered in analyzing long-term recordings. TcO2 drifts upward and tcCO2 decreases during the recordings over several hours. The change in electrode position after 4 h of sleep modified tcO2 and tcCO2 values. Such difficulties limit the usefulness of long-term but not short-term recordings.