Effect of simulated commercial flight on oxygenation in patients with interstitial lung disease and chronic obstructive pulmonary disease

Prior Ambulatory Mild Coronavirus Disease 2019 Does Not Increase Risk of Acute Mountain Sickness

Small, Elan, Caleb Phillips, William Bunzel, Lakota Cleaver, Nishant Joshi, Laurel Gardner, Rony Maharjan, and James Marvel. Prior ambulatory mild coronavirus disease 2019 does not increase risk of acute mountain sickness. High Alt Med Biol. 24:201-208, 2023. Background: Given its long-term morbidity, understanding how prior coronavirus disease 2019 (COVID-19) may affect acute mountain sickness (AMS) susceptibility is important for preascent risk stratification. The objective of this study was to examine if prior COVID-19 impacts risk of AMS. Materials and Methods: This was a prospective observational study conducted in Lobuje (4,940 m) and Manang (3,519 m), Nepal, from April to May 2022. AMS was defined by the 2018 Lake Louise Questionnaire criteria. COVID-19 severity was defined using the World Health Organization-developed criteria. Results: In the Lobuje cohort of 2,027, 46.2% of surveyed individuals reported history of COVID-19, with 25.7% AMS point-prevalence. There was no significant relationship between prior ambulatory mild COVID-19 and AMS (p = 0.6) or moderate AMS (p = 1.0). In the Manang cohort of 908, 42.8% reported history of COVID-19, with 14.7% AMS point-prevalence. There was no significant relationship between prior ambulatory mild COVID-19 and AMS (p = 0.3) or moderate AMS (p = 0.4). Average months since COVID-19 was 7.4 (interquartile range [IQR] 3-10) for Lobuje, 6.2 (IQR 3-6) for Manang. Both cohorts rarely exhibited moderate COVID-19 history. Conclusions: Prior ambulatory mild COVID-19 was not associated with increased risk of AMS and should not preclude high-altitude travel.

Hypoxia-altitude simulation test to predict altitude-related adverse health effects in COPD patients

Background/aims

Amongst numerous travellers to high altitude (HA) are many with the highly prevalent COPD, who are at particular risk for altitude-related adverse health effects (ARAHE). We then investigated the hypoxia-altitude simulation test (HAST) to predict ARAHE in COPD patients travelling to altitude.

Methods

This prospective diagnostic accuracy study included 75 COPD patients: 40 women, age 58±9 years, forced expiratory volume in 1 s (FEV1) 40-80% pred, oxygen saturation measured by pulse oximetry (S pO2 ) ≥92% and arterial carbon dioxide tension (P aCO2 ) <6 kPa. Patients underwent baseline evaluation and HAST, breathing normobaric hypoxic air (inspiratory oxygen fraction (F IO2 ) of 15%) for 15 min, at low altitude (760 m). Cut-off values for a positive HAST were set according to British Thoracic Society (BTS) guidelines (arterial oxygen tension (P aO2 ) <6.6 kPa and/or S pO2 <85%). The following day, patients travelled to HA (3100 m) for two overnight stays where ARAHE development including acute mountain sickness (AMS), Lake Louise Score ≥4 and/or AMS score ≥0.7, severe hypoxaemia (S pO2 <80% for >30 min or 75% for >15 min) or intercurrent illness was observed.

Results

ARAHE occurred in 50 (66%) patients and 23 out of 75 (31%) were positive on HAST according to S pO2 , and 11 out of 64 (17%) according to P aO2 . For S pO2 /P aO2 we report a sensitivity of 46/25%, specificity of 84/95%, positive predictive value of 85/92% and negative predictive value of 44/37%.

Conclusion

In COPD patients ascending to HA, ARAHE are common. Despite an acceptable positive predictive value of the HAST to predict ARAHE, its clinical use is limited by its insufficient sensitivity and overall accuracy. Counselling COPD patients before altitude travel remains challenging and best focuses on early recognition and treatment of ARAHE with oxygen and descent.

Underlying lung disease and exposure to terrestrial moderate and high altitude: personalised risk assessment

Once reserved for the fittest, worldwide altitude travel has become increasingly accessible for ageing and less fit people. As a result, more and more individuals with varying degrees of respiratory conditions wish to travel to altitude destinations. Exposure to a hypobaric hypoxic environment at altitude challenges the human body and leads to a series of physiological adaptive mechanisms. These changes, as well as general altitude related risks have been well described in healthy individuals. However, limited data are available on the risks faced by patients with pre-existing lung disease. A comprehensive literature search was conducted. First, we aimed in this review to evaluate health risks of moderate and high terrestrial altitude travel by patients with pre-existing lung disease, including chronic obstructive pulmonary disease, sleep apnoea syndrome, asthma, bullous or cystic lung disease, pulmonary hypertension and interstitial lung disease. Second, we seek to summarise for each underlying lung disease, a personalized pre-travel assessment as well as measures to prevent, monitor and mitigate worsening of underlying respiratory disease during travel.

COPD patients’ pre-flight check: A narrative review

 For most of the people with stable and well-controlled chronic obstructive pulmonary disease (COPD), air travel is safe and comfortable, but the flight environment may pose clinical challenges. This narrative review aims to update the requirements for allowance to fly of people with COPD without chronic respiratory failure.  A literature review was performed on platforms: Pubmed, Scopus and Ovid, for citations in English from 2000 to 2021. The following key words were used: COPD AND: air-travel, in-flight hypoxemia, fitness to air travel.  Official regulatory documents and guidelines were also examined. Current air travel statements recommend supplemental oxygen when in flight arterial oxygen tension (PaO2) is expected to fall below 6.6 or 7.3 kPa. Several lung function variables, prediction equations and algorithms have been proposed to estimate in-flight PaO2, the need for in-flight supplemental oxygen, and to select individuals needing more advanced pre-flight testing, such as the hypoxia-altitude simulation test. Exercise induced desaturation and aerobic capacity correlate significantly with in-flight PaO2. COPD patients with late intensification of disease, new changes in medications, recent acute exacerbation/ hospitalization or anticipated emotional and physical stress during the proposed air-travel should be carefully evaluated by the caring family or specialist physician.

Return to High Altitude After Recovery from Coronavirus Disease 2019

Luks, Andrew M. and Colin K. Grissom. Return to high altitude after recovery from coronavirus disease 2019. High Alt Med Biol. 22: 119-127, 2021.-With the increasing availability of coronavirus disease 2019 (COVID-19) vaccines and the eventual decline in the burden of the disease, it is anticipated that all forms of tourism, including travel to high altitude, will rebound in the near future. Given the physiologic challenges posed by hypobaric hypoxia at high altitude, it is useful to consider whether high-altitude travel will pose risks to those previously infected with severe acute respiratory syndrome coronavirus 2, particularly those with persistent symptoms after resolution of their infection. Although no studies have specifically examined this question as of yet, available data on the cardiopulmonary sequelae of COVID-19 provide some sense of the problems people may face at high altitude and who warrants evaluation before such endeavors. On average, most individuals who have recovered from COVID-19 have normal or near normal gas exchange, pulmonary function testing, cardiovascular function, and exercise capacity, although a subset of individuals have persistent functional deficits in some or all of these domains when examined up to 5 months after infection. Evaluation is warranted before planned high-altitude travel in individuals with persistent symptoms at least 2 weeks after a positive test or hospital discharge as well as in those who required care in an intensive care unit or suffered from myocarditis or arterial or venous thromboembolism. Depending on the results of this testing, planned high-altitude travel may need to be modified or even deferred pending resolution of the identified abnormalities. As more people travel to high altitude after the pandemic and further studies are conducted, additional data should become available to provide further guidance on these issues.

Impact of end-expiratory pressure fluctuation on tidal volume in the trilevel positive airway pressure mode

INTRODUCTION

In noninvasive positive-pressure ventilation (NPPV), the changes in the expiratory positive airway pressure (EPAP) directly affect the magnitude of the tidal volume.

OBJECTIVES

This experimental study aims to verify the precise effects of end-expiratory fluctuation on the body tidal volume to better assist NPPV in clinical practice.

METHODS

We selected the TestChest-simulated lung simulation of different populations, including healthy subjects (normal group), patients with chronic obstructive pulmonary disease (COPD) with emphysema as their primary phenotype (COPD1 group), and patients with COPD with bronchitis as their primary phenotype (COPD2 group).

RESULTS

Regarding the tidal volume curves of the three groups under various conditions, sixfold charts revealed that the tidal volume changed with the end-expiratory pressure fluctuations. In addition, regression coefficients for end-expiratory pressure fluctuations, (IPAP-EPAP) and (IPAP-EEPAP) exhibited a significant contribution to the tidal volume. The two coefficients in the normal, COPD1 and COPD2 groups were 52.294 and 10.414, 46.192 and -8.816, and 11.922 and 17.947, respectively. The circuit simulation results showed that the simulation curve fitted the experimental curve better by changing the coefficient of the descending edge of the expiratory phase.

CONCLUSIONS

The study results suggest that the end-expiratory pressure fluctuation affects the body tidal volume. Compared with the bilevel positive airway pressure (PAP), the trilevel PAP provides additional respiratory support to the body during a respiratory difference in initial respiration and descent.

Proof of Concept Study to Assess the Influence of Oxygen Partial Pressure in Capillary Blood on SMBG Measurements

BACKGROUND

Measurement results provided by blood glucose monitoring systems (BGMS) can be affected by various influencing factors. For some BGMS using glucose oxidase (GOx)-based test strips, one of these factors is the oxygen partial pressure (pO₂) of the applied blood sample. Because assessing the potential influence of pO₂ when measuring capillary blood samples is not straight-forward, we performed a proof of concept study.

METHOD

Influence of pO₂ was investigated for two GOx-based BGMS (BGMS A and B). Measurement results of the GOx-based BGMS were compared with measurement results from a pO₂-independent BGMS (BGMS C). A total of 119 samples from 60 subjects were measured, twice with BGMS C, then 6 times each with BGMS A and BGMS B or vice versa, and again twice with BGMS C. Immediately afterward, pO₂ was determined. Linear regression analysis based on relative differences between results from BGMS A or BGMS B and results from BGMS C was performed to estimate the degree of pO₂ influence.

RESULTS

The relative bias between the lowest and highest pO₂ values differed by 14.3% for BGMS A, indicating a pO₂ influence that might be clinically relevant, and by 9.7% for BGMS B, indicating that pO₂ influence may be too small to be reliably detected because of the BGMS' imprecision.

CONCLUSIONS

This proof of concept study showed that with the procedures used, a potentially clinically relevant influence of pO₂ in capillary blood samples on GOx-based BGMS could be detected. Further larger-scale studies are needed to verify this influence.

Should I stay or should I go? COPD and air travel

Chronic obstructive pulmonary disease (COPD) is a challenging respiratory problem throughout the world. Although survival is prolonged with new therapies and better management, the magnitude of the burden resulting from moderate-to-severe disease is increasing. One of the major aims of the disease management is to try to break the vicious cycle of patients being homebound and to promote an active lifestyle. A fundamental component of active daily life is, of course, travelling. Today, the world is getting smaller with the option of travelling by air. Air travel is usually the most preferred choice as it is easy, time saving, and relatively inexpensive. Although it is a safe choice for many passengers, the environment inside the aeroplane may sometimes have adverse effects on health. Hypobaric hypoxaemia due to cabin altitude may cause health risks in COPD patients who have limited cardiopulmonary reserve. Addressing the potential risks of air travel, promoting proactive strategies including pre-flight assessment, and education of COPD patients about the "fitness to fly" concept are essential. Thus, in this narrative review, we evaluated the current evidence for potential risks of air travel in COPD and tried to give a perspective for how to plan safe air travel for COPD patients.

Physiological predictors of Hypoxic Challenge Testing (HCT) outcomes in Interstitial Lung Disease (ILD)

BACKGROUND

Pre-flight risk assessments are currently recommended for all Interstitial Lung Disease (ILD) patients. Hypoxic challenge testing (HCT) can inform regarding the need for supplemental in-flight oxygen but variables which might predict the outcome of HCT and thus guide referral for assessment, are unknown.

METHODS

A retrospective analysis of ILD patients attending for HCT at three tertiary care ILD referral centres was undertaken to investigate the concordance between HCT and existing predictive equations for prediction of in-flight hypoxia. Physiological variables that might predict a hypoxaemic response to HCT were also explored with the aim of developing a practical pre-flight assessment algorithm for ILD patients.

RESULTS

A total of 106 ILD patients (69 of whom (65%) had Idiopathic Pulmonary Fibrosis (IPF)) underwent HCT. Of these, 54 (51%) patients (of whom 37 (69%) had IPF) failed HCT and were recommended supplemental in-flight oxygen. Existing predictive equations were unable to accurately predict the outcome of HCT. ILD patients who failed HCT had significantly lower resting SpO₂, baseline PaO_2, reduced walking distance, FEV1, FVC and TLCO, but higher GAP index than those who passed HCT.

CONCLUSIONS

TLCO >50% predicted and PaO₂ >9.42 kPa were independent predictors for passing HCT. Using these discriminators, a novel, practical pre-flight algorithm for evaluation of ILD patients is proposed.

Pre-flight evaluation of adult patients with cystic fibrosis: a cross-sectional study

BACKGROUND

Air travel may imply a health hazard for patients with cystic fibrosis (CF) due to hypobaric environment in the aircraft cabin. The objective was to identify pre-flight variables, which might predict severe hypoxaemia in adult CF patients during air travel.

METHODS

Thirty adult CF-patients underwent pre-flight evaluation with spirometry, arterial oxygen tension (PaO₂), pulse oximetry (SpO₂) and cardiopulmonary exercise testing (CPET) at sea level (SL). The results were related to the PaO₂ obtained during a hypoxia-altitude simulation test (HAST) in which a cabin altitude of 2438 m (8000 ft) was simulated by breathing 15.1% oxygen.

RESULTS

Four patients fulfilled the criteria for supplemental oxygen during air travel (PaO_{2 HAST} < 6.6 kPa). While walking slowly during HAST, another eleven patients dropped below PaO_{2 HAST} 6.6 kPa. Variables obtained during CPET (PaO_{2 CPET}, SpO_{2 CPET}, minute ventilation/carbon dioxide output, maximal oxygen uptake) showed the strongest correlation to PaO_{2 HAST}.

CONCLUSIONS

Exercise testing might be of value for predicting in-flight hypoxaemia and thus the need for supplemental oxygen during air travel in CF patients. Trial registration The study is retrospectively listed in the ClinicalTrials.gov Protocol Registration System: NCT01569880 (date; 30/3/2012).

Physiology in Medicine: Acute altitude exposure in patients with pulmonary and cardiovascular disease

Travel is more affordable and improved high-altitude airports, railways, and roads allow rapid access to altitude destinations without acclimatization. The physiology of exposure to altitude has been extensively described in healthy individuals; however, there is a paucity of data pertaining to those who have reduced reserve. This Physiology in Medicine article discusses the physiological considerations relevant to the safe travel to altitude and by commercial aircraft in patients with pulmonary and/or cardiac disease.

Hypoxic challenge test applied to healthy children: influence of body positions and exertion on pulse oximetric saturation

BACKGROUND

Commercial aircraft are pressurised to ~2438 m (8000 ft) above sea level that equates breathing 15% oxygen at sea level. A preflight hypoxic challenge test (HCT) is therefore recommended for children with cystic fibrosis or other chronic lung diseases and inflight oxygen is advised if pulse oximetric saturation (SpO2) decreases <90%.

OBJECTIVE

Study responses to a modified HCT, encompassing various body positions and light physical activity, reflecting relevant activities of children during flight, with a view to challenge the evidence of the current cut-off.

METHODS

Oxygenation, heart rate and ventilation were observed in 34 healthy schoolchildren (17 boys) undergoing a modified HCT, alternating between breathing room air and 15% oxygen in nitrogen while seated, supine, standing and walking at 3 km/h and 5 km/h.

RESULTS

Nadir SpO2 <90%, median (range), occurred in 9 subjects sitting, 89% (78-89%); 6 supine, 88.5% (87-89%); 9 standing, 89% (85-89%); 23 walking 3 km/h, 87% (74-89%); and 21 walking 5 km/h, 86% (74-89%). Total time <90% for these subjects in seconds was 20 (10-80) sitting, 30 (10-190) supine, 50 (10-150) standing, 80 (10-260) walking 3 km/h and 125 (10-300) walking 5 km/h. Light exercise in general led to lower SpO2: 91% (77-96%), p<0.0001.

CONCLUSIONS

A modified HCT led to moments of desaturation below 90% in various body positions at rest and during light physical activity in healthy schoolchildren. It is questionable whether the international recommended cut-off of 90% for children with chronic lung disease reflects clinical oxygen dependence during flights.

Effects of commercial air travel on patients with pulmonary hypertension air travel and pulmonary hypertension

BACKGROUND

Limited data are available on the effects of air travel in patients with pulmonary hypertension (PH), despite their risk of physiologic compromise. We sought to quantify the incidence and severity of hypoxemia experienced by people with PH during commercial air travel.

METHODS

We recruited 34 participants for a prospective observational study during which cabin pressure, oxygen saturation (Sp O 2 ), heart rate, and symptoms were documented serially at multiple predefined time points throughout commercial flights. Oxygen desaturation was defined as SpO2, <85%.

RESULTS

Median flight duration was 3.6 h (range, 1.0-7.3 h). Mean ± SD cabin pressure at cruising altitude was equivalent to the pressure 1,968 ± 371 m (6,456 ± 1,218 ft) above sea level (ASL)(maximum altitude 5 2,621 m [8,600 ft] ASL). Median change in Sp O 2 from sea level to cruising altitude was 2 4.9% (range, 2.0% to 2 15.8%). Nine subjects (26% [95% CI, 12%-38%]) experienced oxygen desaturation during flight (minimum Sp O 2 5 74%). Thirteen subjects (38%) reported symptoms during flight, of whom five also experienced desaturations. Oxygen desaturation was associated with cabin pressures equivalent to . 1,829 m (6,000 ft) ASL, ambulation, and flight duration(all P values , .05).

CONCLUSIONS

Hypoxemia is common among people with PH traveling by air, occurring in one in four people studied. Hypoxemia was associated with lower cabin pressures, ambulation during flight, and longer flight duration. Patients with PH who will be traveling on flights of longer duration or who have a history of oxygen use, including nocturnal use only, should be evaluated for supplemental in-flight oxygen.

Hypoxaemia in patients with pulmonary arterial hypertension during simulated air travel

BACKGROUND

Recent air travel recommendations suggest patients with precapillary pulmonary hypertension (PCPH) in New York Heart Association (NYHA) functional class 3 and 4 should have in-flight oxygen without the need for pre-flight testing. However it remains unclear as to how best to determine patients fitness to fly.

METHODS

This study (i) investigates the effect of hypoxic challenge testing (HCT) on the arterial oxygen levels in a cohort of 36 patients with PCPH and (ii) compares the relative frequency with which FC and HCT predict the requirement for in-flight oxygen.

RESULTS

The degree of arterial hypoxaemia induced by HCT (fall in partial pressure of oxygen in arterial blood (PaO(2)) 2.36 kPa, 95% CI 2.06-2.66 kPa) was similar to the drop observed in other published studies of chronic respiratory diseases. Following current air travel recommendations based on FC, 25 patients of the cohort would require in-flight oxygen whilst 10 subjects failed the HCT. Fourteen subjects had flown post-diagnosis. Of these, nine subjects should have had in-flight oxygen based on FC but were asymptomatic without. Also one who passed the HCT had developed symptoms during the flight whilst three who failed the HCT were asymptomatic flying without in-flight oxygen.

CONCLUSIONS

Hypoxaemia induced by simulated air travel in patients with PCPH is similar to that seen in published studies of patients with other chronic respiratory diseases. HCT failed to predict correctly who had developed symptoms during an aircraft flight in a significant minority of the study subjects. Similarly guidelines based on functional class result in a major increase in the proportion of patients being advised to use oxygen, many of whom had been asymptomatic on previous flights without it. More work is required to improve prediction of need for in-flight oxygen in patients with PCPH.

Air travel and the risks of hypoxia in children

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.

Lung disease at high altitude

Large numbers of people travel to high altitudes, entering an environment of hypobaric hypoxia. Exposure to low oxygen tension leads to a series of important physiologic responses that allow individuals to tolerate these hypoxic conditions. However, in some cases hypoxia triggers maladaptive responses that lead to various forms of acute and chronic high altitude illness, such as high-altitude pulmonary edema or chronic mountain sickness. Because the respiratory system plays a critical role in these adaptive and maladaptive responses, patients with underlying lung disease may be at increased risk for complications in this environment and warrant careful evaluation before any planned sojourn to higher altitudes. In this review, we describe respiratory disorders that occur with both acute and chronic exposures to high altitudes. These disorders may occur in any individual who ascends to high altitude, regardless of his/her baseline pulmonary status. We then consider the safety of high-altitude travel in patients with various forms of underlying lung disease. The available data regarding how these patients fare in hypoxic conditions are reviewed, and recommendations are provided for management prior to and during the planned sojourn.

[Recommendations for management of patients with lung disease planning a flight or high altitude travel]

Every year a large number of children travel by plane and/or to places with high altitudes. Most of these journeys occur without incident. Immigration and recent socioeconomic changes have also increased the number of patients with cardiopulmonary disease who travel. Environmental changes in these places, especially lower oxygen, can lead to a risk of significant adverse events. The paediatrician must be aware of the diseases that are susceptible to complications, as well as the necessary preliminary studies and recommendations for treatment in these circumstances. The Techniques Group of the Spanish Society of Paediatric Chest Diseases undertook to design a document reviewing the literature on the subject, providing some useful recommendations in the management of these patients.

The effect of hypoxia on cognitive performance in patients with chronic obstructive pulmonary disease

Air travel may cause significant hypoxia in passengers with chronic obstructive pulmonary disease (COPD). It is not known whether this level of hypoxia will cause impairment in cognitive function. The aim of this study was to determine the effect of hypoxia on cognitive performance in patients with COPD when Pa(O2) was decreased <6.6 kPa. In ten patients with moderate to severe COPD trail making tasks and complex figure tasks were used to assess cognitive performance when the patients breathed 21% O(2), and when Pa(O2) was decreased to <6.6 kPa. During administration of 21% O(2), Pa(O2) was 9.5 (8.9-10.2) kPa. When Sp(O2) was decreased to 85% via manipulation of the FI(O2) (inspired fraction of oxygen) Pa(O2), decreased to 6.1 (5.9-6.2) kPa. No short term deterioration in visual search, mental flexibility or visuospatial constructional ability was detected when Pa(O2) was decreased to <6.6 kPa. The results show that short term exposure to hypoxia had no adverse effect on cognitive function.

Travelling with cystic fibrosis: recommendations for patients and care team members

There are no European Guidelines on issues specifically related to travel for people with cystic fibrosis (CF). The contributors to these recommendations included 30 members of the ECORN-CF project. The document is endorsed by the European Cystic Fibrosis Society and sponsored by the Executive Agency of Health and Consumers of the European Union and the Christiane Herzog Foundation. The main goal of this paper is to provide patient-oriented advice that complements medical aspects by offering practical suggestions for all aspects involved in planning and taking a trip. The report consists of three main sections, preparation for travel, important considerations during travel and at the destination, and issues specific to immunocompromised travellers. People with CF should be encouraged to consult with their CF centre prior to travel to another country. The CF centre can advise on the necessary preparation for travel, the need for vaccinations, essential medications that should be brought on the trip and also provide information relating to CF care in the region and plan of action in case of an emergency.

Evaluating the safety of high-altitude travel in patients with adult congenital heart disease

As medical management and surgical techniques continue to improve, patients with congenital heart disease are surviving further into adulthood and seeking to participate in multiple activities. Given the increasing popularity of adventure recreation, it is likely that many of these individuals will express interest in travel to and activities at high altitude. At first glance, the hypoxia associated with acute altitude exposure would appear to pose high risks for patients with underlying cardiopulmonary disease, but few studies have systematically addressed these concerns in the adult congenital heart disease population. In this review, we consider the safety of high-altitude travel in these patients. After reviewing the primary cardiopulmonary responses to acute hypoxia and the risks of high altitude in all individuals regardless of their underlying health status, we consider the risks in adult congenital heart disease patients, in particular. We focus on broad concerns that should be considered in all patients such as whether they have underlying pulmonary hypertension, the adequacy of their ventilatory responses, and their ability to compensate for hypoxemia and right-to-left shunting. We then conclude by providing basic recommendations for pretravel assessment in patients with congenital heart disease of moderate or great complexity.

Predicting the need for supplemental oxygen during airline flight in patients with chronic pulmonary disease: a comparison of predictive equations and altitude simulation

BACKGROUND

Patients with chronic pulmonary diseases are at increased risk of hypoxemia when travelling by air. Screening guidelines, predictive equations based on ground level measurements and altitude simulation laboratory procedures have been recommended for determining risk but have not been rigorously evaluated and compared.

OBJECTIVES

To determine the adequacy of screening recommendations that identify patients at risk of hypoxemia at altitude, to evaluate the specificity and sensitivity of published predictive equations, and to analyze other possible predictors of the need for in-flight oxygen.

METHODS

The charts of 27 consecutive eligible patients referred for hypoxia altitude simulation testing before flight were reviewed. Patients breathed a fraction of inspired oxygen of 0.15 for 20 min. This patient population was compared with the screening recommendations made by six official bodies and compared the partial pressure of arterial oxygen (PaO(2)) obtained during altitude simulation with the PaO(2) predicted by 16 published predictive equations.

RESULTS

Of the 27 subjects, 25% to 33% who were predicted to maintain adequate oxygenation in flight by the British Thoracic Society, Aerospace Medical Association or American Thoracic Society guidelines became hypoxemic during altitude simulation. The 16 predictive equations were markedly inaccurate in predicting the PaO(2) measured during altitude simulation; only one had a positive predictive value of greater than 30%. Regression analysis identified PaO(2) at ground level (r=0.50; P=0.009), diffusion capacity (r=0.56; P=0.05) and per cent forced expiratory volume in 1 s (r=0.57; P=0.009) as having predictive value for hypoxia at altitude.

CONCLUSIONS

Current screening recommendations for determining which patients require formal assessment of oxygen during flight are inadequate. Predictive equations based on sea level variables provide poor estimates of PaO(2) measured during altitude simulation.

Do lung disease patients need supplemental oxygen at high altitude?

As medical care and the quality of life for patients with lung disease improve, many of these individuals may engage in various forms of travel, including, possibly, travel to high altitude. Because the hypobaric hypoxia at high altitude may cause severe hypoxemia or impaired exercise tolerance in these patients, clinicians may be asked to assess whether they should use supplemental oxygen during their planned sojourn. This review considers this question in greater detail. After considering how the issue is approached in commercial airplane flight, we consider changes in oxygenation in lung disease patients in ambient hypoxia, the complications associated with such changes, tools for predicting the degree of hypoxemia at high altitude and important logistical issues associated with traveling with supplemental oxygen. The review concludes by providing tentative recommendations for assessing which patients should travel with supplemental oxygen. Patients already on supplemental oxygen at baseline should increase their flow rates at high altitude; patients with sufficiently severe disease who are not on such therapy should undergo pretravel assessment to determine the likely degree of hypoxemia at high altitude, with hypoxia altitude simulation testing being the preferred modality for this assessment. Those patients who develop symptomatic hypoxemia during such testing should travel with supplemental oxygen; those who remain asymptomatic or maintain adequate oxygenation may travel without oxygen, but they should have plans to monitor symptoms and oxygen saturation following arrival and arrange for oxygen therapy if necessary.

Telemedical assistance for in-flight emergencies on intercontinental commercial aircraft

We have conducted a three-year prospective study of medical incidents on a commercial airline. A telemedicine service was available via an on-board satellite phone. During the study period there were 3364 medical incidents. The most common incident was collapse ( n = 2310, 57%). Telemedicine was used in 323 of the cases (9%). Neurological patients, mostly stroke and seizures, excluding psychiatric diseases, were seen in 27% of the telemedicine cases ( n = 83). Most of the cases involved middle-aged people, not the elderly. The group of patients that needed diversion ( n = 27) was compared to the cases staying on board ( n = 275). None of the patients in the non-diversion group deteriorated. All unstable patients forced a diversion. Doctors on board used the service in more severe cases, whereas laymen used the service in less severe cases. The results of the present study demonstrate the advantage of using simple teleconsultation in cases of medical emergency on board an aircraft.

Advanced lung disease: quality of life and role of palliative care

Advanced restrictive lung diseases remain a challenge for both the clinician and patient alike. Because there are few available treatment options that prolong survival for patients with diseases such as idiopathic pulmonary fibrosis, improvement in quality of life and palliation of significant symptoms become realistic treatment goals. Several validated instruments that assess quality of life and health-related quality of life have demonstrated the dramatic impact that lung disease has on patients. Quality-of-life assessments of patients with interstitial lung disease have commonly cited respiratory complaints as problematic, but other distressing symptoms often not addressed include fear, social isolation, anxiety, and depression. Not only do respiratory symptoms limit this patient population, but the awareness of decreased independence and ability for social participation also has an impact on the quality of life. Some patients describe a deepened spiritual well-being during their disease process; however, many patients' mental health suffers with experiences of fear, worry, anxiety, and panic. Many patients express desire for more attention to end-of-life issues from their physicians. Fears of worsening symptoms and suffocation exist with an expressed desire by most to die peacefully with symptom control. Interventions to improve quality of life are largely directed at symptom control. Pharmacologic and nonpharmacologic interventions have been helpful in relieving dyspnea. Studies have demonstrated that the use of supplemental oxygen in the face of advancing hypoxemia can have both positive and negative effects on quality of life. Patients using nasal prongs describe feelings of self-consciousness, embarrassment, and social withdrawal. Pulmonary rehabilitation is recommended, with some studies noting increased quality-of-life scores and decreased sensations of dyspnea. Sleep deprivation and poor sleep quality also have a negative impact on quality of life. Recognition and correction of nocturnal hypoxemia and other sleep disturbances should enhance quality of life in patients with restrictive lung disease; however, there is currently no evidence to support this claim. End-of-life care needs more attention by clinicians in the decision-making and preparatory phase. Physicians need to maintain their focus on quality-of-life issues as medical management shifts from curative therapies to comfort management therapies. Palliative care and hospice appear to be underused in patients with advanced diseases other than cancer. Because the only curative option for some end-stage restrictive lung diseases is lung transplantation, if transplantation is not an option, palliation of symptoms and hospice care may offer patients and families the opportunity to die with dignity and comfort.

The effect of a hypobaric, hypoxic environment on acute skeletal muscle edema after ischemia-reperfusion injury in rats

BACKGROUND

Clinicians have postulated that decreased atmospheric pressure during air evacuation exacerbates muscle edema and necrosis in injured limbs. The present study investigated whether the mild hypobaric, hypoxic conditions of simulated flight during muscle reperfusion worsened muscle edema and muscle injury in an established animal model.

METHODS

Twenty male Sprague-Dawley rats underwent tourniquet-induced hind limb ischemia for 2h. After removal of the tourniquet, rats were divided into two groups (n=10/group), and exposed to either (1) hypobaric, hypoxic conditions (HB) of 522 mm Hg (simulating 10,000 feet, the upper limit of normal aircraft cabin pressure), or (2) normobaric, normoxic conditions (NB) of 760 mm Hg (sea level), for 6h. Muscle wet weight, muscle dry:wet weight ratios, viability, and routine histology were measured on the gastrocnemius and tibialis anterior muscles. Blood samples were analyzed for percentage hematocrit, leukocyte count, and coagulation status.

RESULTS

Ischemia resulted in significant edema in both groups (P<0.05). Normobaric normoxia caused greater edema in the gastrocnemius compared with hypobaric hypoxia; the tibialis anterior was not significantly different between groups. The decrease in body weight for NB and HB was 3.4+/-1.4 and 10.7+/-1.2g, respectively (P<0.05). Hematocrit was 44.7+/-0.5 and 42.6+/-0.6 (P<0.05).

CONCLUSIONS

The hypobaric, hypoxic conditions of simulated medical air evacuation were not associated with increased muscle edema following 2h of ischemic injury. This suggests that other factors, such as resuscitation, may be the cause of muscle edema in flight-evacuated patients.

Predicting the response to air travel in passengers with non-obstructive lung disease: are the current guidelines appropriate?

BACKGROUND AND OBJECTIVE

Air travel guidelines recommend using baseline arterial oxygen levels and the hypoxic challenge test (HCT) to predict in-flight hypoxaemia and the requirement for in-flight oxygen in patients with lung disease. The purpose of the present study was to (i) quantify the hypoxaemic response to air travel and (ii) identify baseline correlate(s) to predict this response in passengers with non-obstructed lung disease.

METHODS

Fourteen passengers (seven women) with chronic non-obstructed lung disease volunteered for this study. The study involved three phases: (i) respiratory function testing; (ii) in-flight measures (SpO(2), cabin pressure and dyspnoea); and (iii) a HCT. The in-flight hypoxaemic response was compared with the baseline arterial oxygen level, respiratory function and the HCT.

RESULTS

All subjects flew without oxygen and no adverse events were recorded in-flight. Mean cabin pressure was 593 +/- 16 mm Hg. Pre-flight SpO(2) was 95 +/- 3% and significantly decreased to 85 +/- 9% in-flight, with further significant falls in subjects who walked during the flight (nadir SpO(2) 78 +/- 11%). The pre-flight SpO(2) showed the strongest correlation with in-flight SpO(2) (r = 0.91, P < 0.001). The HCT SpO(2) was moderately correlated to the in-flight SpO(2) (r = 0.58, P < 0.05). Spirometry, D(L,CO) and TLC measurements did not correlate with in-flight SpO(2).

CONCLUSION

Significant in-flight desaturation can be expected in passengers with non-obstructive lung disease. Respiratory function did not predict in-flight desaturation. We found a good relationship between pre-flight SpO(2) and in-flight SpO(2) which supports the role of pre-flight oximetry for predicting in-flight hypoxaemia in passengers with non-obstructed lung disease.

Using laboratory measurements to predict in-flight desaturation in respiratory patients: are current guidelines appropriate?

In an attempt to guide physicians asked by respiratory patients for advice on flight fitness, the British Thoracic Society (BTS) have published guidelines on fitness to fly. The main potential hazard is hypobaric hypoxia, and efforts have focused on the prediction of hypoxia in individuals. The present study examines 10 years' experience of hypoxic challenge (HC) of respiratory patients to evaluate if the guidelines recommended by the BTS are appropriate. One hundred and eighteen patients (67 female, mean age 65.6+/-11.4 (SD) years) were referred for assessment. Patients underwent HC using a 40% Venturi mask supplied with 100% N(2) which lowered the F(i)O(2) to 15.1%. A further 13 patients on long-term oxygen therapy also underwent HC whilst receiving supplemental oxygen. In agreement with the BTS guidelines, all patients with a sea level SpO(2) of over 95% maintained their SpO(2) > or = 90% during HC. One third of patients with sea level SpO(2) of 92-95%, but no other risk factor (as defined by the guidelines) also desaturated below 90% during HC. Thirty-two patients were assessed as fit to fly with supplemental oxygen. Our results support the BTS guidelines for patients with a sea level SpO(2) > 95% but suggest that some revision is required for patients with a sea level SpO(2) of 92-95%. It was not possible to predict from either initial SpO(2) or spirometry which individuals were at risk of desaturation below 90% during hypoxic challenge.

A patient with vanishing lung syndrome and remarkable tolerance to high altitude

Very little information is known about patients with chronic obstructive pulmonary disease who travel to high altitude for work or pleasure. Even less is known about the outcomes at high altitude for patients with severe bullous lung disease. We present the case of a 54-yr-old man with vanishing lung syndrome, an idiopathic form of severe bullous emphysema, who has made repeated trips to altitudes as high as 3400 m, where he has engaged in physical activity, such as downhill skiing. We consider the issues of adequacy of oxygenation and the risks of barotrauma in patients with obstructive lung disease traveling to high altitude, and we also consider factors, such as improved air-flow limitation, maintenance of adequate ventilation-perfusion matching, and underlying physical fitness, which may affect our patient's ability to tolerate physical activity in this environment. The case demonstrates that the presence of severe lung disease does not necessarily preclude travel to and moderate activity at high altitude. Such travel may, in fact, be safe as long as the patient has undergone appropriate pretravel evaluation, and we provide recommendations regarding such evaluation in patients with chronic obstructive pulmonary disease.

Air travel hypoxemia vs. the hypoxia inhalation test in passengers with COPD

BACKGROUND

Limited data are available comparing air travel with the hypoxia inhalation test (HIT) in passengers with COPD. The aim of this study was to assess the predictive capability of the HIT to in-flight hypoxemia in passengers with COPD.

METHODS

Thirteen passengers (seven female passengers) with COPD (mean [+/- SD], FEV(1)/FVC ratio, 44 +/- 17%) volunteered for this study. Respiratory function tests were performed preflight. Pulse oximetry, cabin pressure, and dyspnea were recorded in flight. The HIT and a 6-min walk test were performed postflight. The in-flight oxygenation response was compared to the HIT results and respiratory function parameters.

RESULTS

All subjects flew without the use of oxygen, and no adverse events were recorded in-flight (mean cabin altitude, 2,165 m; altitude range, 1,892 to 2,365 m). Air travel caused significant desaturation (mean preflight oxygen saturation, 95 +/- 1%; mean in-flight oxygen saturation, 86 +/- 4%), which was worsened by activity (nadir pulse oximetric saturation [Spo(2)], 78 +/- 6%). The HIT caused mean desaturation that was comparable to that of air travel (84 +/- 4%). The mean in-flight partial pressure of inspired oxygen (Pio(2)) was higher than the HIT Pio(2) (113 +/- 3 mm Hg vs 107 +/- 1 mm Hg, respectively; p < 0.001). The HIT Spo(2) showed the strongest correlation with in-flight Spo(2) (r = 0.84; p < 0.001).

CONCLUSION

Significant in-flight desaturation can be expected in passengers with COPD. The HIT results compared favorably with the air travel data, with differences explainable by Pio(2) and physical activity. The HIT is the best widely available laboratory test to predict in-flight hypoxemia.

Directly measured cabin pressure conditions during Boeing 747-400 commercial aircraft flights

BACKGROUND AND OBJECTIVES

In the low pressure environment of commercial aircraft, hypoxaemia may be common and accentuated in patients with lung or heart disease. Regulations specify a cabin pressure not lower than 750 hPa but it is not known whether this standard is met. This knowledge is important in determining the hazards of commercial flight for patients and the validity of current flight simulation tests.

METHODS

Using a wrist-watch recording altimeter, cabin pressure was recorded at 60 s intervals on 45 flights in Boeing 747-400 aircraft with three airlines. A log was kept of aircraft altitude using the in-flight display. Change in cabin pressure during flight, relationship between aircraft altitude and cabin pressure and proportion of flight time with cabin pressure approaching the minimum specified by regulation were determined.

RESULTS

Flight duration averaged 10 h. Average cabin pressure during flight was 846 hPa. There was a linear fall in cabin pressure as the aircraft cruising altitude increased. At 10,300 m (34,000 ft) cabin pressure was 843 hPa and changed 8 hPa for every 300 m (1000 ft) change in aircraft altitude (r(2) = 0.993; P < 0.001). Lowest cabin pressure was 792 hPa at 12 200 m (40,000 ft) but during only 2% of flight time was cabin pressure less than 800 hPa.

CONCLUSIONS

Cabin pressure is determined only by the engineering of the aircraft and its altitude and in the present study was always higher than required by regulation. Current fitness-to-fly evaluations simulate cabin conditions that passengers will not experience on these aircraft. There may be increased risks to patients should new or older aircraft operate nearer to the present minimum standard.

A chronic pneumothorax and fitness to fly

According to Boyle's law, as the pressure falls, the volume of gas rises in an inversely proportional manner. This means that during an aircraft flight, the volume of trapped air in gas filled body chambers will increase. As a consequence, it is fairly well established that individuals with an untreated pneumothorax should not participate in commercial flying due to the risk of it enlarging and the possible development of tension. However, whether this also applies to individuals who have a long-standing, clinically stable pneumothorax is uncertain. The following article describes two adult patients each with a chronic pneumothorax who asked whether they would be fit to fly in an aircraft. We outline their histories and subsequent evaluation which consisted of clinical assessment, computed tomographic imaging, a hypoxic challenge test and exposure to a hypoxic hypobaric environment in a decompression chamber.

Air travel in women with lymphangioleiomyomatosis

BACKGROUND AND OBJECTIVE

The safety of air travel in patients with pneumothorax-prone pulmonary diseases, such as lymphangioleiomyomatosis (LAM), has not been studied to any great extent. A questionnaire-based evaluation of air travel in patients with LAM was conducted to determine experiences aboard commercial aircraft.

METHODS

A survey was sent to women listed in the US LAM Foundation registry (n = 389) and the UK LAM Action registry (n = 59) to assess air travel, including problems occurring during flight. Women reporting a pneumothorax in flight were followed up to ascertain further details about the incident.

RESULTS

327 (73%) women completed the survey. 308 women answered the travel section, of whom 276 (90%) had "ever" travelled by aeroplane for a total of 454 flights. 95 (35%) women had been advised by their doctor to avoid air travel. Adverse events reported included shortness of breath (14%), pneumothorax (2%, 8/10 confirmed by chest radiograph), nausea or dizziness (8%), chest pain (12%), unusual fatigue (11%), oxygen desaturation (8%), headache (9%), blue hands (2%), haemoptysis (0.4%) and anxiety (22%). 5 of 10 patients with pneumothorax had symptoms that began before the flight: 2 occurred during cruising altitude, 2 soon after landing and 1 not known. The main symptoms were severe chest pain and shortness of breath.

DISCUSSION AND CONCLUSION

Adverse effects occurred during air travel in patients with LAM, particularly dyspnoea and chest pain. Hypoxaemia and pneumothorax were reported. The decision to travel should be individualised; patients with unexplained shortness of breath or chest pain before scheduled flights should not board. Patients with borderline oxygen saturations on the ground should be evaluated for supplemental oxygen therapy during flight. Although many women had been advised not to travel by air, most travelled without the occurrence of serious adverse effects.

Oxygen supplementation for chronic obstructive pulmonary disease patients during air travel

PURPOSE OF REVIEW

By 2008 it is projected that over two billion people will be travelling by commercial aircraft each year. With an ageing population and treatment improvements, many of these travellers will have lung disease, particularly chronic obstructive pulmonary disease. Current guidelines as to whether a patient requires supplemental oxygen during the flight are based on limited research evidence. Awareness of the increased risk has resulted in recent scientific interest in this area.

RECENT FINDINGS

Studies have demonstrated a lack of consistency in international guideline recommendations when performing assessments within the respiratory laboratory. This has led to more specific analysis of patients, including in-flight assessments, the inclusion of exercise stress and more interest in actual cabin pressure conditions.

SUMMARY

Commercial air travel is generally safe for patients with chronic obstructive pulmonary disease when their disease is stable. All current guidelines reflect the considerable uncertainty in relation to the clinical circumstances when oxygen prescription during flight is essential. Currently planned flight outcome studies will provide more precise risk quantification.

Pulmonary function testing and extreme environments

Millions of people worldwide engage in leisure or occupational activities in extreme environments. These environments entail health risks even for normal subjects. The presence of lung disease, or other conditions, further predisposes to illness or injury. Patients who have lung conditions should, but often do not, consult with their pulmonary clinicians before traveling. Normal subjects, including elderly or deconditioned adults, may be referred to pulmonologists for evaluation of risk prior to exposure. Other patients may present for consultations after complications occur. Pulmonary function testing before or after exposure can assist physicians counseling patients about the likelihood of complications.