Enric Prats

Predicting nocturnal hypoventilation in hypercapnic chronic obstructive pulmonary disease patients undergoing long-term oxygen therapy.

Background: Chronic obstructive pulmonary disease (COPD) patients are very sensitive to changes in pulmonary mechanics and central ventilation control during sleep and may develop significant gas exchange alterations with increased hypoxemia and hypercapnia. Oxygen therapy improves nocturnal desaturation but can worsen hypoventilation. Objectives: To analyze the prevalence of nocturnal hypoventilation (NHV) in hypercapnic COPD patients and to determine predictive factors for this phenomenon. Methods: This was a prospective multicenter study which enrolled 80 clinically stable COPD patients with hypercapnic respiratory failure who fulfilled the conventional criteria for long-term oxygen therapy (LTOT). All patients had undergone pulmonary function testing, blood gas analysis, and respiratory polygraphy. Arterial blood gas samples were obtained while patients were awake and during sleep. NHV was considered when an increase in PaCO2 >10 mm Hg was observed in any nocturnal arterial blood gas sample as compared to the awake levels. Results: Seventeen patients (21%) developed NHV. NHV was associated with the values of BMI, hemoglobin, hematocrits, DLCO, and PaO2 reached after oxygen administration. In the logistic regression analysis BMI (OR 1.26, 95% CI 1.068–1.481; p = 0.006) and the diurnal increase of PaO2 after O2 (OR 0.89, 95% CI 0.807–0.972; p = 0.010) were the variables that best discriminated with a sensitivity of 82% and a specificity of 78%. Conclusions: NHV is a relatively common finding in stable hypercapnic COPD patients undergoing LTOT and it is related to a higher BMI and lower PaO2 after oxygen administration.

Transcutaneous Carbon Dioxide Monitoring in Subjects With Acute Respiratory Failure and Severe Hypercapnia

BACKGROUND: Transcutaneous carbon dioxide (PtcCO2) monitoring is being used increasingly to assess acute respiratory failure. However, there are conflicting findings concerning its reliability when evaluating patients with high levels of PaCO2. Our study evaluates the accuracy of this method in subjects with respiratory failure according to the severity of hypercapnia. METHODS: We included subjects with respiratory failure, admitted to a respiratory intermediate care unit, who required arterial blood gas analysis. Simultaneously, PtcCO2 was measured using a digital monitor. Relations between PaCO2 and PtcCO2 were assessed by the Pearson correlation coefficient. Bland-Altman analysis was used to test data dispersion, and an analysis of variance test was used to compare the differences between PaCO2 and the corresponding PtcCO2 at different levels (level 1, <50 mm Hg; level 2, 50–60 mm Hg; level 3, >60 mm Hg). RESULTS: Eighty-one subjects were analyzed. The main diagnosis was COPD exacerbation (45%). PtcCO2 correlated well with PaCO2 (r2 = 0.93, P < .001). Bland-Altman analysis showed a mean PaCO2 − PtcCO2 difference of 4.9 ± 4.4 with 95% limits of agreement ranging from −3.6 to 13.4. The difference between variables increased in line with PaCO2 severity: level 1, 1.7 ± 3.2 mm Hg; level 2, 3.7 ± 2.8; level 3, 6.8 ± 4.7 (analysis of variance, P < .001). CONCLUSIONS: Our study showed an acceptable agreement of PtcCO2 monitoring with arterial blood gas analysis. However, we should consider that PtcCO2 underestimates PaCO2 levels, and its accuracy depends on the level of hypercapnia, so this method would not be suitable for acute patients with severe hypercapnia.

Neither questions nor answers, just original data.

To the Editor: We have read with interest the letter by Ewig 1 in relation to our article 2. According to his opinion, our study raises an unproductive debate about the usefulness of bronchoscopic sampling techniques in ventilator-associated pneumonia (VAP). As it is well known, most of the studies dealing with the diagnostic efficacy of bronchoscopic sampling techniques in VAP include a large percentage of patients …