Hypoxic Challenge Testing Research Articles

165 Hypoxic challenge testing and air travel: the Welsh experience

165 Hypoxic challenge testing and air travel: the Welsh experience

P2 In-flight hypoxaemia in patients with pulmonary arterial hypertension (PAH)

Background and AimAircraft travel can worsen hypoxaemia in patients with PAH since pressurised cabins reduce inspired oxygen (FiO2) to the equivalent of breathing 15.1% at sea level. The British Thoracic...

Short-term exposure to hypoxia for work and leisure activities in health and disease: which level of hypoxia is safe?

Exposures to natural and simulated altitudes entail reduced oxygen availability and thus hypoxia. Depending on the level of hypoxia, the duration of exposure, the individual susceptibility, and preexisting diseases, health problems of variable severity may arise. Although millions of people are regularly or occasionally performing mountain sport activities, are transported by airplanes, and are more and more frequently exposed to short-term hypoxia in athletic training facilities or at their workplace, e.g., with fire control systems, there is no clear consensus on the level of hypoxia which is generally well tolerated by human beings when acutely exposed for short durations (hours to several days). Available data from peer-reviewed literature report adaptive responses even to altitudes below 2,000m or corresponding normobaric hypoxia (F(i)O(2) > 16.4%), but they also suggest that most of exposed subjects without severe preexisting diseases can tolerate altitudes up to 3,000m (F(i)O(2) > 14.5%) well. However, physical activity and unusual environmental conditions may increase the risk to get sick. Large interindividual variations of responses to hypoxia have to be expected, especially in persons with preexisting diseases. Thus, the assessment of those responses by hypoxic challenge testing may be helpful whenever possible.

Hypoxic challenge assessment in individuals with obstructive sleep apnea

Background The degree of arterial hypoxemia during air travel in individuals with obstructive sleep apnea (OSA) is not known. The Aerospace Medical Association considers a ground level arterial oxygen tension (PaO 2) above 9.3 kPa as safe before air travel. Methods Fifteen subjects with untreated OSA (mean apnea–hypopnea index [AHI] 43/h) and 14 with treated OSA (mean AHI on CPAP 1.9/h) completed an assessment including hypoxic challenge test (HCT). The groups had similar mean age, mean BMI and pre-treatment OSA severity. Results Four subjects, all in the untreated group and with resting PaO 2 >9.3 kPa and oxygen saturation (SpO 2) >95%, had a positive HCT (PaO 2 <6.6 kPa and/or SpO 2 <85%). The PaO 2 at the end of the HCT was significantly correlated with the minimum overnight SpO 2 ( r = .754, p = .002) but not with the daytime PaO 2 and SpO 2. Using a cut off value of 65%, the minimum overnight SpO 2 had positive and negative predictive values of 57% and 100% respectively. Conclusions OSA can be an additional risk factor for developing significant arterial hypoxemia during HCT. Baseline PaO 2 and SpO 2 did not predict arterial hypoxemia during the HCT. Minimum overnight SpO 2 <65% may be used as a cut off to advise further assessment. Effective treatment of OSA seems to be the best option before air travel.

Fit for high altitude: are hypoxic challenge tests useful?

Altitude travel results in acute variations of barometric pressure, which induce different degrees of hypoxia, changing the gas contents in body tissues and cavities. Non ventilated air containing cavities may induce barotraumas of the lung (pneumothorax), sinuses and middle ear, with pain, vertigo and hearing loss. Commercial air planes keep their cabin pressure at an equivalent altitude of about 2,500 m. This leads to an increased respiratory drive which may also result in symptoms of emotional hyperventilation. In patients with preexisting respiratory pathology due to lung, cardiovascular, pleural, thoracic neuromuscular or obesity-related diseases (i.e. obstructive sleep apnea) an additional hypoxic stress may induce respiratory pump and/or heart failure. Clinical pre-altitude assessment must be disease-specific and it includes spirometry, pulsoximetry, ECG, pulmonary and systemic hypertension assessment. In patients with abnormal values we need, in addition, measurements of hemoglobin, pH, base excess, PaO2, and PaCO2 to evaluate whether O2- and CO2-transport is sufficient.Instead of the hypoxia altitude simulation test (HAST), which is not without danger for patients with respiratory insufficiency, we prefer primarily a hyperoxic challenge. The supplementation of normobaric O2 gives us information on the acute reversibility of the arterial hypoxemia and the reduction of ventilation and pulmonary hypertension, as well as about the efficiency of the additional O2-flow needed during altitude exposure. For difficult judgements the performance of the test in a hypobaric chamber with and without supplemental O2-breathing remains the gold standard. The increasing numbers of drugs to treat acute pulmonary hypertension due to altitude exposure (acetazolamide, dexamethasone, nifedipine, sildenafil) or to other etiologies (anticoagulants, prostanoids, phosphodiesterase-5-inhibitors, endothelin receptor antagonists) including mechanical aids to reduce periodical or insufficient ventilation during altitude exposure (added dead space, continuous or bilevel positive airway pressure, non-invasive ventilation) call for further randomized controlled trials of combined applications.

P131 Fitness to fly assessment in patients with neuromuscular disease

IntroductionPatients 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...

Is there an alternative to pre-flight hypoxic challenge testing in scoliotic patients?

Hypoxic challenge testing (HCT) is not readily available in all hospitals. It has recently been shown that resting oximetry does not reliably predict the results of HCT in patients with extrapulmonary restrictive lung disease. We assessed other clinical tests to see if they might be used as an alternative screen for HCT. People with primary thoracic scoliosis were recruited. Resting SpO(2), arterial blood gases (ABG's), lung function and shuttle walking test (SWT) were measured. All subjects underwent HCT breathing an inhaled oxygen fraction of 15% for 20 min, or until SpO(2) fell below 85%, when ABG's were taken. Fourteen people (5 male) with thoracic scoliosis, Cobb angle 93 (31) degrees , aged 65 (8.5) years, FEV(1) 0.86 (0.4) L, FVC 1.2 (0.4)L were studied. The resting SpO(2) was 96 (2) %, PaO(2) 9.2 (1) kPa and PaCO(2) 6.1 (0.4) kPa. HCT was positive in 11 subjects (PaO(2) <6.6 kPa). Eight of 11 HCT positive subjects had a resting SpO(2) > 95%. Positive correlation was found between SpO(2) at SWT termination and PaO(2) following HCT (r = 0.56, p = 0.02). Those with saturations of 92% or under at SWT termination had positive HCT. Despite normal resting SpO(2) subjects with thoracic scoliosis may have positive HCT. Current recommendations for air travel do not accurately identify these people. Desaturation following a SWT may provide a useful screening tool, however a low threshold for performing HCT on people with thoracic scoliosis prior to air travel is warranted.

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

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. 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. 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). 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.

Hypoxic challenge flight assessments in patients with severe chest wall deformity or neuromuscular disease at risk for nocturnal hypoventilation

Background:The British Thoracic Society (BTS) recommendations for patients with respiratory disease planning air travel suggest that an oxygen saturation (SaO2) >95% precludes the need for any further assessment of the...

Is air travel safe for those with lung disease?

Airlines commonly report respiratory in-flight emergencies; flight outcomes have not been examined prospectively in large numbers of respiratory patients. The current authors conducted a prospective, observational study of flight outcomes in this group. UK respiratory specialists were invited to recruit patients planning air travel. Centres undertook their usual pre-flight assessment. Within 2 weeks of returning, patients completed a questionnaire documenting symptoms, in-flight oxygen use and unscheduled healthcare use. In total, 616 patients were recruited. Of these, 500 (81%) returned questionnaires. The most common diagnoses were airway (54%) and diffuse parenchymal lung disease (23%). In total, 12 patients died, seven before flying and five within 1 month. Pre-flight assessment included oximetry (96%), spirometry (95%), hypoxic challenge (45%) and walk test (10%). Of the patients, 11% did not fly. In those who flew, unscheduled respiratory healthcare use increased from 9% in the 4 weeks prior to travel to 19% in the 4 weeks after travel. However, when compared with self-reported data during the preceding year, medical consultations increased by just 2%. In patients flying after careful respiratory specialist assessment, commercial air travel appears generally safe.

The Hypoxia Challenge Test Does Not Accurately Predict Hypoxia in Flight in Ex-Preterm Neonates

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.

Is air travel safe for those with lung disease?

Airlines commonly report respiratory in-flight emergencies; flight outcomes have not been examined prospectively in large numbers of respiratory patients. The current authors conducted a prospective, observational study of flight outcomes in this group. UK respiratory specialists were invited to recruit patients planning air travel. Centres undertook their usual pre-flight assessment. Within 2 weeks of returning, patients completed a questionnaire documenting symptoms, in-flight oxygen use and unscheduled healthcare use. In total, 616 patients were recruited. Of these, 500 (81%) returned questionnaires. The most common diagnoses were airway (54%) and diffuse parenchymal lung disease (23%). In total, 12 patients died, seven before flying and five within 1 month. Pre-flight assessment included oximetry (96%), spirometry (95%), hypoxic challenge (45%) and walk test (10%). Of the patients, 11% did not fly. In those who flew, unscheduled respiratory healthcare use increased from 9% in the 4 weeks prior to travel to 19% in the 4 weeks after travel. However, when compared with self-reported data during the preceding year, medical consultations increased by just 2%. In patients flying after careful respiratory specialist assessment, commercial air travel appears generally safe.

Flight assessment in patients with respiratory disease: hypoxic challenge testing vs. predictive equations

Predictive equations have been proposed as a simpler alternative to hypoxic challenge testing (HCT) for determining the risk of in-flight hypoxia. To assess agreement between hypoxic challenge testing (HCT) and predictive equations for assessment of in-flight hypoxia. Retrospective study. Patients with chronic obstructive pulmonary disease (COPD) (n = 15), interstitial lung disease (ILD) (n = 15) and cystic fibrosis (CF) (n = 15) were studied. Spirometry was recorded prior to hypoxic inhalation and oxygen saturations (SpO2) were recorded before, after and during hypoxic inhalation. Blood gases were analysed before and after hypoxic inhalation and when SpO2 = 85%. An HCT was performed using the Ventimask method. The PaO2 at altitude was estimated for each group using four published predictive equations, which use values of PaO2 (ground) and lung function measurements to predict altitude PaO2. Results were interpreted using the BTS recommendations for prescription of in-flight oxygen post HCT. The Stuart Maxwell test of overall homogeneity was used to assess agreement between HCT results and each of the predictive equations. Ground PaO2 was significantly greater in patients with CF than either ILD or COPD (p < 0.05). PaO2 in all three groups significantly decreased following HCT. With the exception of equation 3, significantly fewer patients in each group would require in-flight O2 if prescription was based on HCT, compared to predictive equations (p < 0.05). Predictive equations considerably overestimate the need for in-flight O2, compared to HCT.

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.

Assessing the risk of hypoxia in flight: the need for more rational guidelines.

This study aimed to test the hypothesis that advice currently given by respiratory physicians to potentially hypoxic patients planning air travel varies and is not evidence-based. A prospective observational study was performed, surveying respiratory physicians in England and Wales. Sixty-two per cent responded. Nearly two-thirds worked in district general hospitals, a quarter in university hospitals, and the rest in tertiary referral (specialist) centres or a combination thereof. Most provide advice routinely; most of the remainder do on request or if concerned. Assessments comprise spirometry, blood gas level measurement, oximetry, predictive equations and hypoxic challenge tests. Twenty-five per cent of physicians measuring blood gas levels recommend in-flight oxygen when arterial oxygen tension (Pa,O2) <7.3 kPa, 50% when Pa,O2 is 7.3-8.0 kPa. Over two-thirds using spirometry recommend oxygen when the forced expiratory volume in one second <40% of the predicted value. Half recommend oxygen when arterial oxygen saturation (Sa,O2) <90%, 33% when Sa,O2 is 90-94%. Fewer than 10% of district hospital physicians (and none in other hospitals) use predictive equations. More than half of specialists but fewer than 10% of district hospital physicians perform hypoxic challenge tests. The risk of hypoxia at altitude is recognized by most respiratory physicians in England and Wales, but assessment methods and criteria for recommending oxygen vary widely. This suggests that most current advice is not evidence-based. Evidence-based guidelines are required.

Accuracy of fiberoptic central venous saturation catheter below 50%.

The fiberoptic central venous flotation catheter has gained widespread clinical acceptance for continuous monitoring of mixed venous oxyhemoglobin saturation. There are obvious research applications to this device, especially in monitoring very low central venous saturations in response to hypoxic challenge and cardiopulmonary exercise testing. However, the accuracy of this device has not been established in such low saturation ranges in humans. This study examines the tracking characteristics of the Opticath (Oximetrix, Mountain View, CA) pulmonary arterial catheter in comparison to simultaneously drawn blood specimens in which oxyhemoglobin saturation was determined by direct spectrophotometric oximetry. The results show that the catheter follows saturation established by bench oximetry quite closely between 50 and 80%, the range most commonly encountered in the clinical setting. However, at saturations below this range, the catheter consistently underestimates direct spectrophotometry. Since accuracy is extremely important for research purposes, two equations that can be used to correct catheter readings for mixed venous saturations less than 50% are presented.

Estimation of changes in alveolar-arterial oxygen gradient induced by hypoxia.

The alveolar-arterial oxygen tension difference provides a useful clinical indication of ventilation-blood flow mismatching in the lungs. In some clinical situations involving alveolar hypoxia (e.g., patients with chronic obstructive lung disease flying in commercial aircraft or normal humans at high altitudes) it would be useful to know this tension difference to predict the likely arterial PO2 under such potentially stressful conditions. Such estimates would require multiple arterial punctures performed under a variety of trying circumstances, conditions usually far distant from a suitable analytic facility. Consequently, we induced controlled hypoxia in 23 healthy humans and calculated changes in the alveolar-arterial oxygen tension difference during the hypoxic challenge test. We plotted this difference as a function of the alveolar oxygen tension over a range from 35 to 110 mm Hg. In addition to a series of control studies in which multiple arterial blood samples were obtained, we calculated arterial PO2 by converting the arterial oxyhemoglobin saturation (measured with an ear oximeter) into partial pressure of oxygen. During hypoxic procedures in which levels of oxygenation fell on the steep section of the oxyhemoglobin dissociation curve, fixing PCO2 at constant predetermined levels allowed accurate predictions of arterial PO2. We were able to demonstrate that the alveolar-arterial oxygen tension difference narrowed with decreasing alveolar oxygen tension, and that measurement with an ear oximeter provided data that allowed a reasonable estimate of the tension difference during hypoxic conditions.