Capillary PO2 does not adequately reflect arterial PO2 in hypoxemic COPD patients

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Abstract

Purpose

To compare arterial (P _aO ₂) with capillary (P _cO ₂) partial pressure of oxygen in hypoxemic COPD patients because capillary blood gas analysis (CBG) is increasingly being used as an alternative to arterial blood gas analysis (ABG) in a non-intensive care unit setting, although the agreement between P _cO ₂ and P _aO ₂ has not been evaluated in hypoxemic COPD patients.

Patients and methods

Bland–Altman comparison of P _aO ₂ and P _cO ₂ served as the primary outcome parameter if P _cO ₂ values were ≤60 mmHg and the secondary outcome parameter if P _cO ₂ values were ≤55 mmHg. Pain associated with the measurements was assessed using a 100-mm visual analog scale.

Results

One hundred and two P _aO ₂/P _cO ₂ measurement pairs were obtained. For P _cO ₂ values ≤60 mmHg, the mean difference between P _aO ₂ and P _cO ₂ was 5.99±6.05 mmHg (limits of agreement: −5.88 to 17.85 mmHg). For P _cO ₂ values ≤55 mmHg (n=73), the mean difference was 5.33±5.52 mmHg (limits of agreement: −5.48 to 16.15 mmHg). If P _aO ₂ ≤55 (≤60) mmHg was set as the cut-off value, in 20.6% (30.4%) of all patients, long-term oxygen therapy have been unnecessarily prescribed if only P _cO ₂ would have been assessed. ABG was rated as more painful compared with CBG.

Conclusions

P _cO ₂ does not adequately reflect P _aO ₂ in hypoxemic COPD patients, which can lead to a relevant number of unnecessary long-term oxygen therapy prescriptions.

Related collections

Most cited references 22

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In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analysed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.

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WA Conway, EO Coates, PA Kvale (1980)

At six centers, 203 patients with hypoxemic chronic obstructive lung disease were randomly allocated to either continuous oxygen (O2) therapy or 12-hour nocturnal O2 therapy and followed for at least 12 months (mean, 19.3 months). The two groups were initially well matched in terms of physiological and neuropsychological function. Compliance with each oxygen regimen was good. Overall mortality in the nocturnal O2 therapy group was 1.94 times that in the continuous O2 therapy group (P = 0.01). This trend was striking in patients with carbon dioxide retention and also present in patients with relatively poor lung function, low mean nocturnal oxygen saturation, more severe brain dysfunction, and prominent mood disturbances. Continuous O2 therapy also appeared to benefit patients with low mean pulmonary artery pressure and pulmonary vascular resistance and those with relatively well-preserved exercise capacity. We conclude that in hypoxemic chronic obstructive lung disease, continuous O2 therapy is associated with a lower mortality than is nocturnal O2 therapy. The reason for this difference is not clear.

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A controlled trial of long term domiciliary oxygen therapy has been carried out in three centres in the U.K. The 87 patients, all under 70 years of age, who took part had chronic bronchitis or emphysema with irreversible airways obstruction, severe arterial hypoxaemia, carbon dioxide retention, and a history of congestive heart failure. The patients were randomised to oxygen therapy (treated) or no oxygen (controls). Oxygen was given by nasal prongs for at least 15 h daily, usually at 2 1/min. The two groups were well matched, both clinically and in terms of lung function and other laboratory findings. 19 of the 42 oxygen treated patients died in the five years of survival follow-up compared with 30 out of 45 controls: in the 66 men in this trial the survival advantage of oxygen did not emerge until 500 days had elapsed. Survival for the 12 female controls was surprisingly poor, 8 of them being dead at 3 years. Mortality was not easy to predict, though a summation of arterial carbon dioxide tension and red cell mass was helpful. Neither time spent in hospital because of exacerbations of respiratory failure nor work attendance were affected by oxygen therapy, but these patients were very ill at the start of the trial and many had already retired on grounds of age or ill-health. Physiological measurements suggested that oxygen did not slow the progress of respiratory failure in those who died early. However, in longer term survivors on oxygen, arterial oxygenation did seem to stop deterioration.

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Author and article information

Journal

Journal ID (nlm-ta): Int J Chron Obstruct Pulmon Dis

Journal ID (iso-abbrev): Int J Chron Obstruct Pulmon Dis

Journal ID (publisher-id): International Journal of COPD

Title: International Journal of Chronic Obstructive Pulmonary Disease

Publisher: Dove Medical Press

ISSN (Print): 1176-9106

ISSN (Electronic): 1178-2005

Publication date Collection: 2017

Publication date (Electronic): 06 September 2017

Volume: 12

Pages: 2647-2653

Affiliations

[1 ]Department of Pneumology, Cologne Merheim Hospital, Kliniken der Stadt Köln gGmbH Witten/Herdecke University, Faculty of Health/School of Medicine, Cologne, Germany

[2 ]Clinical Trials Unit, Medical Center – University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany

[3 ]Department of Intensive Care, Sleep Medicine and Mechanical Ventilation, Asklepios Fachkliniken Munich-Gauting, Gauting, Germany

[4 ]Department of Pneumology, University Medical Hospital, Freiburg, Germany

Author notes

Correspondence: Jan Hendrik Storre, Department of Intensive Care, Sleep Medicine and Mechanical Ventilation, Asklepios Fachkliniken Munich-Gauting, Robert-Koch-Allee 2, D-82131 Gauting, Germany, Tel +49 89 85 7910, Fax +49 89 85 791 4306, Email j.storre@ 123456asklepios.com

Article

Publisher ID: copd-12-2647

DOI: 10.2147/COPD.S140843

PMC ID: 5593412

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