TABLE 1.

Studies comprising patients with chronic obstructive pulmonary disease (COPD) for prediction of hypoxaemia during air travel

Author [ref.]	Year	Patients	Test/condition used	Results
Gong [ 33 ]	1984	22 moderate COPD	HCT	Sea level PaO2 predicted acute resting altitude PaO2
Dillard [ 51 ]	1989	18 severe COPD	Hypobaric chamber	Ground PaO2 correlated with expected altitude PaO2, combination of FEV1 and ground PaO2 improved prediction of PaO2 at 8000 ft
Schwartz [ 52 ]	1984	13 severe COPD	Inflight ABGs at 1650 m and 2250 m	PaO2 measured <2 h before the flight in room air or a 17.2% oxygen mixture correlated with PaO2 at 1650 m. PaO2 measured several weeks before flight did not correlate with any in-flight measurements
Berg [ 31 ]	1992	18 severe COPD	Hypobaric chamber	Oxygen supplementation via nasal cannula or Venturi mask corrects altitude hypoxaemia
Christensen [ 30 ]	2000	15 severe COPD	HCT	Pre-flight PaO2 >70 mmHg, FEV1 or TLCO values do not predict altitude hypoxaemia. Light exercise may provoke hypoxaemia and there was a correlation between aerobic capacity and altitude PaO2
Robson [ 53 ]	2000	20 COPD (15 severe) and 8 other RD	HCT	Altitude PaO2 could not be predicted from either FEV1 or pre-test SpO2
Seccombe [ 35 ]	2004	10 COPD and 15 ILD	HCT with 50-m walk test	Resting sea level PaO2 is poor for predicting the hypoxaemic response in both COPD and ILD groups. Means of PaO2 of both groups fell below recommended levels at both resting and when walking during HCT
Akero [ 34 ]	2005	18 COPD	In-flight ABG	Significant desaturations were observed during flight, which were worsened with activity. A pre-flight PaO2 >70 mmHg did not predict in-flight hypoxaemia. Aerobic capacity showed the strongest correlation with in-flight PaO2
Chetta [ 54 ]	2007	15 COPD and 15 ILD	HCT and 6MWT	SpO2 in 6MWT can predict oxygen desaturation during HCT
Kelly [ 55 ]	2008	13 severe COPD	In-flight SpO2, post-flight HCT and 6MWT	Significant desaturations were observed during flight, which were worsened with activity. HCT SpO2 was well correlated with in-flight SpO2. Resting PaO2 and the post-flight 6MWT result did not correlate with in-flight SpO2
Akero [ 50 ]	2008	100 COPD	HCT	Pre-flight SpO2 does not help to discriminate patients adequately for in-flight O2 supplementation. 30% of patients with pre-flight SpO2 >95% and 67% of patients with pre-flight SpO2 between 92–95% and without additional risk factors dropped PaO2 below 50 mmHg during HCT
Robson [ 49 ]	2008	74 COPD and 44 other RD	HCT	Desaturation during HCT cannot be predicted reliably from either FEV1 or sea level SpO2. All patients with sea level SpO2 >95% maintained O2 saturation >90% during HCT. One-third of patients with sea level SpO2 between 92–95% and with no risk factor desaturated during HCT
Kelly [ 56 ]	2009	18 severe COPD	Mount Hutt (2086 m altitude)	Ascent from sea level to altitude caused significant hypoxaemia (PaO2 75±9 versus 51±6 mmHg, respectively), and worsened during walk test (41±7 mmHg) which was partially reversed by supplemental oxygen (64±9 mmHg). KCO correlated both with resting altitude SaO2 and exercise PaO2
Edvardsen [ 57 ]	2012	100 severe COPD	HCT and 6MWT	An algorithm was constructed using a combination of resting and 6MWT SpO2. Resting SpO2 >95% combined with 6MWT SpO2 >84% had a sensitivity of 100% and specificity of 80% for fitness to fly
Edvardsen [ 58 ]	2013	82 moderate-to-severe COPD	HCT and pre- and post-flight symptom questionnaire	Post-flight questionnaire results showed that there was no difference in HCT PaO2 between patients with and without symptoms; however, planned use of in-flight supplemental oxygen in patients with HCT PaO2 <50 mmHg resulted in a lower frequency of respiratory symptoms

RD: respiratory disease; ILD: interstitial lung disease; HCT: hypoxic challenge test; ABG: arterial blood gas; 6MWT: 6-min walk test; S_pO2: arterial oxygen saturation measured by pulse oximetry; P_aO2: arterial oxygen tension; FEV₁: forced expiratory volume in 1 s; T_LCO: transfer factor of the lung for carbon monoxide; K_CO: transfer coefficient of the lung for carbon monoxide.