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Assessing the risk of in-flight hypoxia: Chronic lung disease of prematurity and children with neuromuscular disorders
Abstract
Most children will experience a small, clinically insignificant drop in oxygen saturation during air travel due to the effects of altitude. Clinically significant hypoxia may occur in individuals with an underlying cardio-respiratory condition, in particular young infants born prematurely or with chronic lung disease of prematurity and in children with neuromuscular disorders. To date there is very little in-flight data available in these clinical populations to allow the development of evidence based guidelines for pre-flight assessment of the risk of hypoxia in-flight. The hypoxia flight simulation test is considered the gold standard for assessing the risk of in-flight hypoxia in adults and existing clinical guidelines for pre-flight assessment are largely based on data extrapolated from adults. The hypoxia challenge test has not been validated in infants and children and there are data to suggest that the test may not be accurate in neonates. We recommend high risk paediatric patients are assessed on a case by case basis by a respiratory paediatrician, with consideration of a hypoxia flight simulation test in certain circumstances.
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Introduction Patients with neuromuscular disorders (NMD) can develop ventilatory impairment due to respiratory muscle weakness but despite disability, many travel by air. The British Thoracic Society (BTS) recommends hypoxic challenge test (HCT) in those who have baseline oxygen saturation (SpO2) at sea level between 92–95%.1 However, this recommendation is based on very limited evidence.
Objectives To determine if baseline pulse oximetry at sea level provides a safe guide to predict hypoxia during flying and preclude a HCT in NMD patients.
Methods HCT performed on 12 NMD patients (11 Motor Neuron Disease and 1 Duchene's Muscular Dystrophy) attending ventilation clinic were retrospectively reviewed. HCT was performed to assess their fitness to fly irrespective of their baseline SpO2. A fall in PaO2<6.6 kPa was considered positive, PaO2 between 6.6 and 7.4 kPa was considered borderline and >7.4 kPa was considered negative.1 Spirometry and sniff nasal inspiratory pressure (SNIP) were also recorded.
Results There were nine male and three female patients, age range 27–72 years (median 63 years). Four patients were positive for HCT and two had borderline results. Only two patients among this group met the criteria for HCT as per BTS recommendation. Six patients were negative for HCT and only one met the criteria for HCT. There was no difference in median FEV1 (1.85 vs 2.04 L/s) and median FVC (2.5 vs 2.41 l) between patient with positive or borderline HCT and patients with negative HCT. SNIP was lower in those who were positive or borderline than those who were negative (median 28.5 vs 43 cmH2O).
Conclusions Patients with NMD and respiratory muscle weakness are prone to develop hypoxia irrespective of their baseline oxygen saturation, FEV1 and FVC. SNIP may be better at predicting the risk of hypoxia during air travel.
This article summarises the key points from the 2011 British Thoracic Society (BTS) recommendations on managing passengers with respiratory disease planning air travel. The guidance aims to provide practical advice for respiratory specialists in secondary care and serves as a valuable reference for other healthcare professionals managing these patients. A greater awareness of the challenges posed by air travel will allow improved clinical assessment and practical advice to encourage patients to fly safely wherever possible.
We read with great interest the paper by Mestry et al 1 which analysed hypoxic challenge flight assessments in patients with restrictive disorders. In their study they dispute the current British Thoracic Society recommendations, demonstrating that, in this subgroup, all patients planning air travel should have a pre-flight evaluation because, even in patients with normal baseline oxygen saturation (Sao2), arterial oxygen tension (Pao2) can fall below 6.6 kPa during hypoxic challenge.
We wanted to establish whether patients with restrictive disorders (with no lung disease) should be ventilated rather than oxygenated when they are hypoxaemic during flights. In fact, as …
We have previously suggested that it is possible to predict oxygen desaturation during flight in children with cystic fibrosis and chronic lung disease by non-invasive measurement of oxygen saturation following inhalation of 15% oxygen--the pre-flight hypoxic challenge. This study reports on the results of measurements over 5 years.
The study comprised a pre-flight hypoxic challenge measuring oxygen saturation by finger tip pulse oximetry (SpO(2)) during tidal breathing of 15% oxygen in nitrogen and spirometric testing 1 month before the flight followed by SpO(2) measurements during intercontinental flights to and from holidays abroad with children in wake and sleep states.
Pre-flight tests were completed on 87 children with cystic fibrosis. Desaturation of <90% occurred in 10 children at some stage during the flight, three of whom received supplementary oxygen. Using a cut off SpO(2) of 90%, the pre-flight hypoxic challenge correctly predicted desaturation in only two of these children. The sensitivity and specificity of the pre-flight hypoxic challenge were 20% and 99%, respectively, compared with 70% and 96% for spirometric tests (using a cut off for forced expiratory volume in 1 second (FEV(1)) of <50% predicted). Overall, pre-flight spirometric tests were a better predictor of desaturation during flight with the area under the Receiver Operating Characteristic (ROC) curve of 0.89 compared with 0.73 for the hypoxic challenge test.
In this group of subjects pre-flight spirometric testing was a better predictor of desaturation during flight than the pre-flight hypoxic challenge.
Modern aircraft flying at high altitude are cabin pressurised to an atmospheric partial pressure of up to 8000 feet (2348 metres), equivalent to breathing approximately 15% oxygen. This may expose individuals with cardiorespiratory disease to the risk of developing hypoxia. In 2002 the British Thoracic Society (BTS) issued recommendations for passengers with respiratory diseases who are planning to fly.1 These recommendations included the use of a hypoxic challenge test in children with a history of respiratory disease too young to undergo conventional lung function tests. While pre-flight hypoxic challenge tests have been evaluated in older children2 and adults3 with respiratory disease, there are few data on hypoxic responses in infants and young children with respiratory disease although one study has observed profound desaturation in a small number of healthy infants while asleep.4
In the last 6 years we have tested …
The low oxygen environment during air travel may result in hypoxia in patients with respiratory disease. However, little information exists on the oxygen requirements of infants with respiratory disease planning to fly. A study was undertaken to identify the clinical factors predictive of an in-flight oxygen requirement from a retrospective review of hypoxia challenge tests (inhalation of 14-15% oxygen for 20 minutes) in infants referred for fitness to fly assessment.
Data from 47 infants (median corrected age 1.4 months) with a history of neonatal lung disease but not receiving supplemental oxygen at the time of hypoxia testing are reported. The neonatal and current clinical information of the infants were analysed in terms of their ability to predict the hypoxia test results.
Thirty eight infants (81%) desaturated below 85% and warranted prescription of supplemental in-flight oxygen. Baseline oxygen saturation was >95% in all infants. Age at the time of the hypoxia test, either postmenstrual or corrected, significantly predicted the outcome of the hypoxia test (odds ratio 0.82; 95% confidence intervals 0.62 to 0.95; p = 0.005). Children passing the hypoxia test were significantly older than those requiring in-flight oxygen (median corrected age (10-90th centiles) 12.7 (3.0-43.4) v 0 (-0.9-10.9) months; p < 0.0001).
A high proportion of ex-preterm infants not currently requiring supplemental oxygen referred for fitness-to-fly assessment and less than 12 months corrected age are at a high risk of requiring in-flight oxygen. Referral of this patient group for fitness to fly assessment including a hypoxia test may be indicated.
Up to a third of ex-preterm infants flying near term exhibit pulse oxygen saturation (SpO2) of less than 85% during air travel. A hypoxia challenge test (HCT) is recommended to evaluate the requirement for in-flight supplemental O2. The validity of the HCT in healthy, term infants has not been reported. This study aimed to characterise the in-flight hypoxia response and the accuracy of the HCT to predict this response in healthy, term infants in the first year of life. Infants (n=24: (15 male)) underwent a HCT prior to commercial air travel during which parents monitored SpO2. Thirty-two flights were undertaken with six infants completing multiple flights. The median in-flight SpO2 nadir was 87% and significantly lower than the HCT SpO2 nadir (92%: p<0.001). Infants on seven flights recorded SpO2<85% with one infant recording a HCT with a SpO2 less than 85%. There was marked variability in the in-flight SpO2 in the six infants who undertook multiple flights, and for three of these infants, the SpO2 nadir was both above and below 85%. We report that in healthy term infants an in-flight SpO2 below 85% is common and can vary considerably between flights and that the HCT poorly predicts the risk of in-flight hypoxia (SpO2<85%). As it is common for healthy term infants to have SpO2 less than 85% during air travel further research is needed to clarify whether this is an appropriate cut-off in this age group.
In infants and children with chronic respiratory disease, hypoxia is a potential risk of aircraft travel. Although guidelines have been published to assist clinicians in assessing an individual's fitness to fly, they are not wholly evidence based. In addition, most evidence relates to adults with chronic obstructive pulmonary disease and thus cannot be extrapolated to children and infants. This review summarises the current literature as it applies to infants and children potentially at risk during air travel. Current evidence suggests that the gold standard for assessing fitness to fly, the hypoxia flight simulation test, may not be accurate in predicting in flight hypoxia in infants and children with respiratory disease. Further research is needed to determine the best methods of assessing safety of flight in infants and children.
During air flight, cabin pressurisation produces an effective fraction of inspired oxygen (FiO(2)) 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.
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 FiO(2) of 0.15 for 20 min. A 'failed' test was defined as oxygen saturation (SpO(2)) <90% for at least 2 min.
41 term and 30 ex-preterm babies (mean gestational age 39.8 and 33.1 weeks, respectively) exhibited a significant median drop in SpO(2) (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 SpO(2) 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).
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 FiO(2) of 0.15 leads to a further fall in SpO(2), which is significant but transient.
The British Thoracic Society (BTS) recommendations for patients with respiratory disease planning air travel suggest that an oxygen saturation (SaO(2)) >95% precludes the need for any further assessment of the need for supplemental oxygen during flight. A hypoxic challenge test (HCT) is recommended for patients with a resting SaO(2) between 92% and 95% with an additional risk factor, including kyphoscoliosis (KS) or neuromuscular disease (NMD). However, this recommendation was based on very few data. Patients and
HCTs were performed on 19 adult patients with KS and/or NMD (age 22-73 years, forced expiratory volume in 1 s (FEV(1)) 0.76, forced vital capacity (FVC) 0.92, SaO(2) 95%, partial pressure of arterial CO(2) (PaCO(2)) 5.7 kPa) who were at risk for nocturnal hypoventilation. 15 were home ventilator users. Arterial blood gas measurements were made before and at the end of the hypoxic challenge.
The results of HCTs show that the majority (15 of 19) of this cohort of patients met the criteria suggested by the BTS Standards of Care Committee for in-flight oxygen regardless of baseline SaO(2).
This finding suggests that all patients with severe extrapulmonary restrictive lung disease should undergo assessment with HCT prior to air travel. The study confirms that even patients with a resting saturation of >95% can desaturate significantly during hypoxic challenge. This study does not address the question of whether desaturation at altitude has any adverse consequences for patients. A decision as to whether it is safe for a patient to fly should be made by an experienced clinician and based on a number of factors, which should include previous travel experience, the patient's overall condition and the results of an HCT.
Increasing hypoxia with altitude ascent is a potentially serious problem for patients with hypoxemic chronic airway obstruction (CAO) at sea level. We developed a hypoxia-altitude simulation test (HAST) to assess acute cardiopulmonary responses to the inhalation of hypoxic gas mixtures (equivalent to the inspired oxygen tension (PO2) present at 5,000, 8,000, and 10,000 feet above sea level) alone and in combination with supplemental oxygen (O2). Twenty-two subjects with stable normocapnic CAO were studied at sea level with a computer-based system that measured on-line, breath-by-breath resting ventilatory and gas exchange variables. Subjects breathed 20.9% (baseline), 17.1, 15.1, 13.9, and 20.9% (recovery) O2, and measurements were obtained once a "steady state" was reached at each level. Steady-state arterial PO2 (PaO2) and O2 saturation, alveolar PO2, and alveolar-to-arterial PO2 gradient decreased markedly during successive hypoxic levels, whereas arterial carbon dioxide tensions decreased only modestly. Minute ventilation and heart rate during 13.9% O2 increased only 12 and 10% above baseline. Ten subjects had asymptomatic cardiac arrhythmias during the HAST. Supplemental O2 significantly improved nearly all physiologic indexes. Sea level PaO2 best predicted acute, resting altitude PaO2. Sea level PaO2 values of 68 and 72 mmHg successfully classified more than 90% of the subjects with a PaO2 greater than 55 mmHg at 5,000 feet and a PaO2 greater than 55 mmHg at 8,000 feet, respectively. A regression equation and nomogram were derived to estimate PaO2 at altitudes between 5,000 to 10,000 feet in patients with normocapnic CAO.(ABSTRACT TRUNCATED AT 250 WORDS)
Editor,—Probably like most doctors looking after children, we feel uneasy when asked whether it would “be alright” to take small children and infants on plane journeys for holidays. Controversy continues as to whether flying might be harmful for infants,1-4 and it is questionable whether infants benefit from weekend breaks or long distance holidays in search of better weather. However, we suspect that the air travelling population will get increasingly younger and we will be asked more frequently. As long as solid data about the safety of …
The hypoxia test can be performed to identify potential hypoxia that might occur in an at-risk individual during air travel. In 2004, the British Thoracic Society increased the hypoxia test cutoff guideline from 85 to 90% in young children. The aim of this study was to investigate how well the cutoff values of 85% and 90% discriminated between healthy children and those with neonatal chronic lung disease (nCLD).
We performed a prospective, interventional study in young children with nCLD who no longer required supplemental oxygen and healthy control subjects. A hypoxia test (involving the administration of 14% oxygen for 20 min) was performed in all children, and the nadir in pulse oximetric saturation (Spo(2)) recorded.
Hypoxia test results were obtained in 34 healthy children and 35 children with a history of nCLD. Baseline Spo(2) in room air was unable to predict which children would "fail" the hypoxia test. In those children < 2 years of age, applying a cutoff value of 90% resulted in 12 of 24 healthy children and 14 of 23 nCLD children failing the hypoxia test (p = 0.56), whereas a cutoff value of 85% was more discriminating, with only 1 of 24 healthy children and 6 of 23 nCLD children failing the hypoxia test (p = 0.048).
In the present study, using a hypoxia test limit of 90% did not discriminate between healthy children and those with nCLD. A cutoff value of 85% may be more appropriate in this patient group. The clinical relevance of fitness to fly testing in young children remains to be determined.
Air travel may pose risks to ex-preterm neonates due to the low oxygen environment encountered during flights. We aimed to study the utility of the preflight hypoxia challenge test (HCT) to detect in-flight hypoxia in such infants.
Ex-preterm (gestation < or = 35 completed weeks) infants ready for air transfer from the intensive/special care nursery to regional hospitals were studied. A pretransfer HCT was performed by exposing infants to 14% oxygen for 20 min. Failure was defined as a sustained fall in pulse oxygen saturation (Spo(2)) < or = 85%. A nurse blinded to the test result monitored the in-flight oxygen saturations in each infant. If Spo(2) fell to < or = 85%, oxygen was administered.
Forty-six infants with median gestation of 32.2 weeks (range, 24 to 35.6 weeks) and birth weight of 1,667 g (range, 655 to 2,815 g) were recruited. No infants were receiving supplemental oxygen at the time of transfer. The HCT was performed at a median corrected age of 35.8 weeks (range, 33.1 to 43 weeks). Thirty-five infants (76%) passed the test, and the remainder failed. During the flight, 16 infants met the criteria for in-flight oxygen, but 12 of these infants (75%) had passed the preflight HCT. Of the 11 infants who failed the HCT, only 4 infants (36%) required in-flight oxygen. The HCT incorrectly predicted in-flight responses in 42% (19 of 46 infants).
A significant percentage of ex-preterm neonates require in-flight oxygen supplementation. The HCT is not accurate for identifying which infants are at risk for in-flight hypoxia.