High altitudes and partial pressure of arterial oxygen in patients with chronic obstructive pulmonary disease - A systematic review and meta-analysis.

Importance: Prior study in healthy subjects has shown a reduction of partial pressure of arterial oxygen (PaO₂) by -1.60 kPa/kilometre of altitude gain. However, the association of altitude-related change in PaO₂ and altitude-related adverse health effects (ARAHE) in patients with chronic obstructive pulmonary disease (COPD) remain unknown.

Objective: To provide an effect size estimate for the decline in PaO₂ with each kilometre of altitude gain and to identify ARAHE in relation to altitude in patients with COPD. www.crd.york.ac.uk/prospero: CRD42020217938.

Data sources: A systematic search of PubMed and Embase was performed from inception to May 30, 2023.

Study selection: Peer-reviewed and prospective studies in patients with COPD staying at altitudes >1500 m providing arterial blood gases within the first 3 days at the target altitude.

Data extraction and synthesis: Aggregate data (AD) on study characteristics were extracted, and individual patient data (IPD) were requested. Estimates were pooled using random-effects meta-analysis.

Main outcome and measures: Relative risk estimates and 95 % confidence intervals for the association between PaO₂ and altitude in patients with COPD.

Results: Thirteen studies were included in the AD analysis, of which 6 studies (222 patients, 45.2 % female) provided IPD, thus were included in the quantitative analysis. The estimated effect size of PaO₂ was -0.84 kPa [95 %CI, -0.92 to -0.76] per 1000 m of altitude gain (I²=65.0 %, P < 0.001). In multivariable regression analysis, COPD severity, baseline PaO₂, age and time spent at altitude were predictors for PaO₂ at altitude. Overall, 37.8 % of COPD patients experienced an ARAHE, whereas older age, female sex, COPD severity, baseline PaO_2, and target altitude were predictors for the occurrence of ARAHE (area under ROC curve: 0.9275, P < 0.001).

Conclusions and relevance: This meta-analysis, providing altitude-related decrease in PaO₂ and risk of ARAHE in patients with COPD ascending to altitudes >1500 m, revealed a lower altitude-related decrease in PaO₂ in COPD patients compared with healthy. However, these findings might improve patient care and facilitate decisions about initiating preventive measures against hypoxaemia and ARAHE in patients with COPD planning an altitude sojourn or intercontinental flight, i.e. supplemental oxygen or acetazolamide.