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Fitness to fly testing in term and ex-preterm babies without bronchopulmonary dysplasia
  1. C J Bossley1,
  2. D Cramer1,
  3. B Mason2,
  4. A Hayward3,
  5. J Smyth4,
  6. A McKee1,
  7. R Biddulph3,
  8. E Ogundipe3,
  9. A Jaffé2,
  10. I M Balfour-Lynn1,4
  1. 1Royal Brompton Hospital, London, UK
  2. 2Department of Paediatric Respiratory Medicine, Sydney Children's Hospital, Sydney, New South Wales, Australia
  3. 3Department of Neonatal Medicine, Royal Hospital for Women, Sydney, New South Wales, Australia
  4. 4Department of Neonatal Medicine, Chelsea & Westminster Hospital, London, UK
  1. Correspondence to Dr I M Balfour-Lynn, Department of Paediatric Respiratory Medicine, Royal Brompton & Harefield NHS Foundation Trust, Sydney Street, London SW3 6NP, UK; i.balfourlynn{at}


Background During air flight, cabin pressurisation produces an effective fraction of inspired oxygen (FiO2) of 0.15. This can cause hypoxia in predisposed individuals, including infants with bronchopulmonary dysplasia (BPD), but the effect on ex-preterm babies without BPD was uncertain. The consequences of feeding a baby during the hypoxia challenge were also unknown.

Methods Ex-preterm (without BPD) and term infants had fitness to fly tests (including a period of feeding) at 3 or 6 months corrected gestational age (CGA) in a body plethysmograph with an FiO2 of 0.15 for 20 min. A ‘failed’ test was defined as oxygen saturation (SpO2) <90% for at least 2 min.

Results 41 term and 30 ex-preterm babies (mean gestational age 39.8 and 33.1 weeks, respectively) exhibited a significant median drop in SpO2 (median −6%, p<0.0001); there was no difference between term versus ex-preterm babies, or 3 versus 6 months. Two term (5%) and two ex-preterm (7%) babies failed the challenge. The SpO2 dropped further during feeding (median −4% in term and −2% in ex-preterm, p<0.0001), with transient desaturation (up to 30 s) <90% seen in 8/36 (22%) term and 9/28 (32%) ex-preterm infants; the ex-preterm babies desaturated more quickly (median 1 vs 3 min, p=0.002).

Conclusions Ex-preterm babies without BPD and who are at least 3 months CGA do not appear to be a particularly at-risk group for air travel, and routine preflight testing is not indicated. Feeding babies in an FiO2 of 0.15 leads to a further fall in SpO2, which is significant but transient.

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During commercial air flight, cabins are pressurised to 1525–2438 m (5000–8000 feet), which is equivalent to breathing 15% oxygen at sea level. This can cause hypoxia in predisposed individuals, which includes infants with bronchopulmonary dysplasia (BPD).1 The British Thoracic Society (BTS) 2004 guidelines recommend that ex-preterm infants with a respiratory infection should probably not fly under the age of 6 months postexpected date of delivery (due to an increased risk of apnoeic episodes).2 They also recommend that children with a history of neonatal respiratory illness should have a preflight fitness to fly test.2

An Australian group3 studied 47 infants with a history of neonatal lung disease that included 32 with a history of BPD, and found that 81% desaturated to below 85% and would therefore need in-flight oxygen. Their baseline saturations were all >95%, so could not be used as a predictor of desaturation, but they found that all babies less than 3 months old desaturated, showing that age was a significant factor. It is less certain whether ex-preterm babies without significant respiratory problems or BPD are susceptible to desaturation when the effective fraction of inspired oxygen (FiO2) is 0.15, and therefore whether routine fitness to fly testing is indicated. The Perth group did find that a proportion of ex-preterm babies with minimal neonatal lung disease required oxygen during interhospital flights, but they were all under 43 weeks corrected gestational age (CGA).4 Finally, it was unknown what effect feeding a baby would have during the hypoxia challenge. This is an important issue as most infants are fed on planes, and one might anticipate that they would be more likely to desaturate during the effort of feeding.

What is already known on this topic

  • Due to cabin pressurisation during air flight, the atmosphere has an equivalent FiO2 of 0.15.

  • This can cause hypoxia in some children, including ex-preterm infants with bronchopulmonary dysplasia (BPD).

  • A preflight hypoxia challenge (fitness to fly test) can indicate which infants might require supplemental oxygen during a flight.

What this study adds

  • Ex-preterm babies without BPD (who are ≥3 months corrected gestational age) are at no greater risk of hypoxia compared with term babies.

  • Routine fitness to fly testing is not mandatory in this group.

  • Feeding babies in an FiO2 of 0.15 leads to a further fall in oxygen saturation, which is significant but transient.

The aim of the study was to perform fitness to fly tests using a body plethysmograph in ex-preterm babies without BPD, and compare them with normal term babies. Testing would be carried out at either 3 or 6 months CGA, and babies would also be tested while feeding. This would help determine whether routine preflight testing should be recommended in ex-preterm babies without BPD.



Preterm babies were recruited from the neonatal units, and term babies from the postnatal wards at Chelsea & Westminster Hospital, London; Royal Hospital for Women, Sydney; and Sydney Children's Hospital, Randwick. Preterm babies were defined as those born <37 weeks gestational age. Exclusion criteria included preterm infants with a history of BPD (defined as receiving continuous oxygen at 36 weeks gestational age or if born >32 weeks gestational age in oxygen at 28 days); respiratory infection at the time of testing; current oxygen requirement; and other underlying cardiorespiratory disorder. Birth history and neonatal complications including any oxygen or ventilatory requirements were recorded. Written informed consent was taken from the parents. Ethical approval was granted by the Brompton, Harefield & National Heart Lung Institute Research Ethics Committee (07/Q0404/40) and South Eastern Sydney and Illawarrah Human Research Ethics Committee – Northern Hospital Network Sector (07/254).

Fitness to fly test

All testing was performed using an identical protocol at Royal Brompton Hospital, London, or Sydney Children's Hospital, Randwick, during 2007–2009. Infants were assigned to testing at 3 or 6 months CGA (by parental choice for pragmatic reasons as some were planning flights). The infant and an adult (usually the parent) sat inside a sealed body plethysmograph. The infant's SpO2 (arterial oxygen saturation measured by pulse oximetry) and pulse rate were measured continuously with N-200 Nellcor (Tyco Healthcare, Hampshire, UK) and Nonin 4000 (Nonin Medical, Plymouth, Minnesota, USA) bluetooth pulse oximeters at the Royal Brompton and Sydney Children's Hospitals, respectively, and were attached to the infant's foot or hand. The monitor and baby were continually observed, and SpO2 recorded when there was a stable reproducible trace (excluding artefact), and the child was not moving too much. Once settled, baseline readings were made in room air, and then the oxygen level inside the box was reduced to an FiO2 of 0.15 over 5 min, by adding nitrogen into the chamber. Timings were recorded from when the FiO2 reached 0.15. If desaturation occurred to 85%, oxygen was administered immediately to the child and titrated to reach the baseline SpO2 (nasal cannulae were already in place). The minimum amount of oxygen required to normalise saturation was documented. It was noted whether the baby was awake (calm, restless or crying) or asleep. If the baby did not require supplemental oxygen by 10 min and there were no concerns, the baby was offered a feed (bottle or breast milk) and the test continued to see if feeding caused oxygen desaturation. A failed test was defined as SpO2 < 90% for a minimum of 2 min, and then supplemental oxygen was recommended for flying (as per the BTS 2004 guideline, which was current when conducting the study2). The parents were informed of the results immediately, and it was planned to repeat the test 6 months later for any baby who failed.

Statistical analysis

Mann–Whitney U tests were used for unpaired and Wilcoxon tests for paired non-parametric continuous data, and χ2 tests for ordinal data. SPSS (Statistical Package for the Social Sciences) software (version 17.0; SPSS, Chicago, Illinois, USA) was used for all statistical analysis. Differences were considered statistically significant if p<0.05. Power studies using our previous data5 on ex-preterm infants with BPD (mean fall in SpO2 10.6%, SD 4.3%) showed 50 patients in each group were required to have an 85% chance of detecting a difference in the SpO2 fall of 2.5%, and 20 patients per group for a 4% difference. We anticipated that fewer numbers would be required in this study as it was likely that healthier infants would have a lower mean fall in SpO2.



There were 41 term and 30 ex-preterm infants tested (44 from London and 27 from Sydney); tests were carried out on 48 babies at 3 months and on 23 babies at 6 months CGA (table 1). None of the term babies had required mechanical ventilation, continuous positive airways pressure (CPAP) or supplemental oxygen. Eight preterm babies had required mechanical ventilation (six with supplemental oxygen), seven of them subsequently went on to CPAP. Median ventilation time was 24 (range 6–120) h; mean peak inspiratory pressure was 20 (range 16–26) cm H2O. Nine babies required CPAP without ventilation (two with supplemental oxygen), for a median 28 h (range 7 h to 43 days); mean maximum pressure was 6 (range 5–7) cm H2O. Two babies required supplemental oxygen alone. For the total of 10 babies who had supplemental oxygen, median time was 4 (range 1–43) days. Neonatal complications in term babies were physiological jaundice (n=8), gastro-oesophageal reflux (n=2) and cow's milk intolerance (n=1). Complications in the preterm babies were infection (n=4, including 1 with congenital pneumonia), physiological jaundice (n=3), gastro-oesophageal reflux (n=2), cow's milk intolerance (n=1) and a patent ductus arteriosus that had resolved (n=1).

Table 1

Demographics and results of standard fitness to fly testing and feeding in FiO2 0.15, comparing term with ex-preterm babies without bronchopulmonary dysplasia, measured at 3 and 6 months corrected gestational age

Term versus ex-preterm babies

There was a significant drop in SpO2 during the test with a median change of −6% (p<0.0001), and a range from −12% to −1% in the term and −13% to −3% in the ex-preterm babies (table 1 and figure 1). There were no differences between the term and ex-preterm babies, apart from a significantly (although clinically insignificant) higher baseline pulse rate in the ex-preterm babies. Time taken to reach lowest SpO2 ranged from 4 to 18 min in the term and 4 to 12 min in the ex-preterm babies. Two term babies failed the test with a drop in SpO2 to 86% and 88%; they were tested at 3 and 6 months and required 1 and 0.2 l/min of oxygen, respectively, in order to restore the saturations to baseline levels. Neither had any birth or subsequent medical problems; neither parents wished retesting. There were no obvious differences comparing them with the 39 term babies who passed. Fifty-seven babies were awake and calm, two awake and restless, eight awake and crying, while four were asleep. Two ex-preterm babies tested at three months failed the test with a drop in SpO2 to 87% and 88%; both required 0.2 l/min oxygen to restore their SpO2 to baseline. The former was born at 36 weeks gestation weighing 2.52 kg and required no ventilation/CPAP; the other was born at 34 weeks gestation weighing 2.04 kg and required nasal CPAP for 24 h. There were no differences when comparing them with the 28 ex-preterm babies who passed. When retested 6 months later, both babies passed.

Figure 1

Oxygen saturation (SpO2) in 41 term and 30 ex-preterm babies, measured at baseline in room air (Base); during the fitness to fly test at FiO2 0.15 (Test); and subsequently when feeding (Feed). Measurements were made in (A) 24 term babies at 3 months chronological age, (B) 24 ex-preterm babies at 3 months corrected gestational age, (C) 17 term babies at 6 months and (D) 6 ex-preterm babies at 6 months corrected gestational age. Line at 90% represents a failed test (in accordance to the BTS guidelines at the time of the study2) and that at 85% represents the level at which supplemental oxygen was administered (the revised draft BTS 2011 guidelines now recommend this level for a failed test). FiO2, fraction of inspired oxygen.

Three versus six months testing

Median chronological age for term babies was 13.5 weeks at 3-month tests and 26 weeks at 6-month test; median CGA for ex-preterm babies was 12.5 and 25 weeks, respectively. Comparison of testing at 3 versus 6 months revealed no differences in baseline or test results.

Feeding at effective FiO2 0.15

When starting to feed, there was a significant drop in SpO2 with a median change of −4% in the term babies and −2% in ex-preterm babies (p<0.0001); the difference between term and ex-preterm was not significant (table 1 and figure 1). Ex-preterm babies – The two ex-preterm babies who failed the tests were not offered a feed and none of the others refused to feed. This left 28 who were fed and 9 babies (32%) desaturated to <90%. The change was seen quickly with a median time to lowest SpO2 of 1 min (range 0–13 min). Term babies – The two term babies who failed the tests were fed, and desaturated further, one from 89% to 88%, and the other from 86% to 81%. Five term babies refused to feed, leaving 36 babies who were fed, and 8 babies (22%) desaturated to <90%. The median time to lowest SpO2 was 3 min (range 0–16 min).

The only significant difference noted when comparing term versus ex-preterm babies was that the ex-preterm desaturated significantly quicker (median 1 vs 3 min, p=0.002). However, all feed-related desaturations resolved spontaneously within 1 min (mostly by 30 s). There were no differences comparing testing at 3 versus 6 months.


As expected, all babies experienced significant desaturation when breathing FiO2 0.15, with a marked median drop of 6%. However, we did not see a difference between the healthy term babies, and the ex-preterm babies without BPD, who were measured at either 3 or 6 months CGA. This would suggest that routine preflight testing is not indicated in ex-preterm babies without chronic lung disease. We also did not see a difference in results comparing those tested at 3 versus 6 months corrected age, although a firm conclusion cannot be made since randomisation was not used to allocate age of testing. This was useful to know as previous work has suggested that all babies tested under 3 months failed the test, using the facemask method.3

Although more than one in four babies desaturated further when fed at FiO2 0.15, by a median of 2% (ex-preterm) or 4% (term), the fall in SpO2 was transient. This is important since a recommendation not to feed babies would be impractical, and would preclude them flying for more than a few hours. It is already known that at term, normal feeding produces a greater oxygen desaturation in infants with BPD who require supplemental oxygen than those with BPD but no oxygen requirement; and they, in turn, desaturate more than ex-preterm babies without BPD.6 This difference is maintained at 2–6 months corrected age, with infants with severe BPD having lower SpO2 than those with mild BPD and term babies during feeding, although no differences were seen in their SpO2 at baseline.7 This effect is likely to be exaggerated during air flight.

Most of the babies (80%) were tested in a calm awake state, with only four babies asleep, but during air flight, SpO2 could be affected by sleeping, particularly during long haul flights. SpO2 have been shown to fall in sleeping babies,8 and ‘active sleep’ was associated with more desaturations.9 It was not the intention of this study to test babies while asleep as we also wished to see the effect of feeding, but that would be a useful further study. However, if the test was borderline during the awake state, one might assume that the baby is likely to have a lower SpO2 if it sleeps during a flight, and this should be taken into account when interpreting the result of the test.

Fitness to fly testing with a body plethysmograph has been in use for many years,10 and is the method recommended in the BTS 2004 guidelines.2 Although it is the BTS recommended method of preflight assessment, it is true that results using this method have not been compared with actual in-flight measurements. The technique has been used in older children,11 12 with its successful use reported in 20 children aged 2–54 months with a history of a variety of chronic pulmonary conditions in early infancy.13 This series included nine ex-preterm infants (23–34 weeks gestation, median 27 weeks), who were tested aged 3–19 months (median 6 months). Finally, we have reported our previous experience in 16 ex-preterm infants (24–35 weeks gestation, median 28 weeks) who were tested at a CGA of 3–9 months (median 5 months).5 Since not all centres have access to a body plethysmograph, an alternative method using a non-rebreathing facemask incorporating a one-way valve assembly has been devised, with much of the paediatric work coming from one centre in Perth, Australia.3 4 14 15 From one of their early studies, they suggested that all children with a history of neonatal lung disease and a corrected age under 3 months would require in-flight oxygen, and that testing was indicated in all infants less than 1 year corrected age.3 However, this was followed by a study in which they performed their hypoxia challenge in 46 preterm babies being transferred back to local hospitals on commercial flights at a CGA of 33–43 weeks (median 36).4 None were requiring supplemental oxygen and 76% passed the test (with an 85% cut-off level for SpO2). However, 12/35 (34%) who had passed, required oxygen on the flight and 7/11 (64%) who had failed the test did not require oxygen. The authors concluded that their hypoxia challenge with a facemask was not accurate at identifying who would require oxygen during air flight, at least in young ex-preterm babies. It is true that the patients in our own study were not followed up with actual in-flight SpO2 recordings to check the validity of our method of testing in a body plethysmograph. Nevertheless, we believe that sitting in a chamber inhaling 15% oxygen is a closer approximation to air flight than breathing through a facemask, as it is probably more physiological. This is further supported by the fact that in one of the facemask studies, 12/24 healthy children aged <2 years desaturated to below 90%,15 and it would be surprising that such a high proportion of normal children desaturate to that degree during air flight.

It is still unclear whether a short period with an SpO2 of 85–90% has any detrimental effect on infants.1 It will partly depend on any underlying respiratory disease, how well the child is at the time, and possibly the length of the flight. Nevertheless, the suggestion of 90% as a cut-off for a failed test, and a recommendation for supplemental oxygen, has been revised so the BTS 2011 draft guidelines are now recommending the lower cut-off of 85% (draft previously available on BTS website). Using that limit, none of the babies tested in this study would be deemed to have failed. In conclusion, we recommend that routine preflight testing is not indicated in ex-preterm babies without chronic lung disease, who are at least 3 months beyond their expected date of delivery. Caution is still warranted though if they have a current respiratory infection at the time of flying, while they are still younger than 6 months of age.


Thanks to the parents for agreeing to have their babies tested. Thanks also to the lung function technicians who carried out the fitness to fly tests. Finally, thanks are due to Dr Shu-Ling Chuang who suggested feeding the babies during the study.



  • Correction notice This article has been corrected since it was published Online First. The authors have requested that AH be added as the fourth author to this paper.

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval This study was conducted with the approval of the Brompton, Harefield & National Heart Lung Institute Research Ethics Committee South Eastern Sydney and Illawarrah Human Research Ethics Committee – Northern Hospital Network Sector.

  • Provenance and peer review Not commissioned; externally peer reviewed.