Validation of a Predictive Score for HAST
Validation of a Predictive Score for HAST
Patients with chronic lung diseases travelling by plane often suffer with symptoms related to
 lower oxygen levels they are exposed to while flying.

 Therefore, patients with respiratory conditions are routinely assessed to establish if they
 need supplemental oxygen in flight. A hypoxic altitude simulation test (HAST) is often part
 of this assessment and consists in having patients breathe a oxygen/nitrogen blend with a
 lower oxygen concentration compared to normal room air, simulating in-flight conditions.
 Oxygen levels are measured before and after the test through a blood sample (from the earlobe
 or an artery in the wrist) and with a finger probe. In-flight oxygen is required if the
 oxygen level in the blood is lower than 6.6 kPa. HASTs are time consuming, costly, and
 require a dedicated hospital appointment.

 Using historical data, the Investigators developed scores based on capillary blood gas (blood
 sample from the earlobe), diagnosis and sex to predict the outcome of the HASTs. The
 Investigators validated the proposed scores in a separate historic cohort of patients and
 showed it had good concordance with the HASTs results.

 In this study, the Investigators want to confirm prospectively if the score, based on blood
 results (venous and/or earlobe), can predict the outcome of the HASTs and therefore reduce
 the number of tests performed, travel time for patients, and costs for the NHS.

 All patients, aged 18 or older, who are having a HAST for clinical purposes at the
 cardio-respiratory lab at Leeds Teaching Hospital NHS Trust will be invited to take part in
 the study. The Investigators will record diagnosis, results of HAST and previous spirometry
 from the medical notes, perform a spirometry if not done in the previous 12 months and
 collect a blood sample (one tube, 4 mls). With these data, the Investigators will calculate
 the score and assess its agreement with the outcome of the HAST.

 Each participant's involvement in the study will last for approximately 90-120 minutes, which
 is the normal duration of a HAST.

 The Investigators aim to include up to 280 subjects in the study.
Over the last two decades, there has been a significant increase in the number of people
 flying on a regular basis. As a result, more individuals with chronic respiratory disease are
 being referred for formal assessment to assess if they require inflight oxygen.

 At cruising altitude, passengers are exposed to reduced atmospheric pressure equivalent to an
 altitude of 8000 ft, corresponding to a reduction of oxygen from 21% to approximately 15%.
 National and International recommendations on air travel suggest screening patients with
 chronic lung diseases for the need of in-flight oxygen supplementation. However, due to the
 paucity of available evidence, there is no consensus on which investigation should be
 performed and the precise risk factors associated with in-flight complications.

 The British Thoracic Society, which published the most recent and comprehensive
 recommendations on this topic, recommends that patients with respiratory diseases should be
 assessed clinically, and in specific situations, a hypoxic altitude simulation tests (HAST)
 should be performed. Unfortunately, the vast majority of these recommendations are level C at
 best, as current evidence is limited to a handful of prospective or retrospective analyses.

 A standard hypoxic altitude simulation test requires the patients to breathe a blend of 15%
 oxygen in nitrogen for 20 minutes. This simulates the oxygen tension at 8000 ft, the
 equivalent cabin pressure. Blood gas measurements are taken before and after the test. A fall
 in the pO2 below 6.6 kPa is considered indicative for use of in-flight oxygen.

 Often the HASTs yield negative results (i.e. no inflight oxygen required). These tests are
 heavy on resources, time consuming, costly, not widely available and require dedicate
 hospital appointment. Thus, predictors of outcomes of HASTs are needed to reduce the number
 of HASTs performed.

 Several studies have looked at predictors of oxygen desaturation during HAST in varying
 populations with the aim of better selecting patients who need the test. However, results
 have been inconclusive. Data on the role of baseline oxygenation, FEV1 and exercise test in
 predicting oxygen desaturation during the HAST are conflicting and most studies have been too
 small to provide decisive answers.

 The Investigators recently developed and validate, on historical data, three scores to
 predict negative HASTs, according to the BTS 2011 recommendations (i.e. scores predicting
 which patients do not need to undergo a formal assessment). All of these had good ROC AUC and
 agreement with the outcome of the HAST in the retrospective dataset.

 The Investigators hypothesise that the multivariable score (Model 1), based on a combination
 of CBG variables (bicarbonate and oxygen saturation) and baseline diagnosis (ILD and COPD)
 would be the best predictor of negative response in a formal HAST. Furthermore, the
 Investigator hypothesise that the score could be further simplified for the use in clinical
 practice by measuring the serum bicarbonate and oxygen saturation through a pulse oximeter
 (Model 1s). This is in light of the good arterio-venous concordance previously demonstrated
 for bicarbonate and of the good reliability of non-invasive measurement of oxygen saturation.
 Such a simplified score, if its predictive value is confirmed, would not only reduce the
 number of unnecessary HAST performed, but also minimise patients' discomfort and hospital
 appointments, reducing the costs for the NHS.

 In this prospective single centre study, the Investigators will assess the validity of the
 best performing score (Model 1) derived in our retrospective study for negative HAST. In
 addition, the Investigators want to verify whether the use of SpO2 in place of SO2 and of
 serum bicarbonate in place of capHCO3 would allow for similar results. The investigators also
 aim to evaluate the performance of the other predictive scores previously derived in our
 retrospective analysis, and, if none of these models are a good and effective predictor, we
 aim to develop a new model based on newly measured data.

 The Investigators aim to enroll up to 280 subjects, but interim analyses will be performed
 with the scope to early terminate the study if primary outcome is met.

 Demographic and baseline characteristics of patients will be analysed on the whole population
 and by the cohorts depending on the underlying diagnosis and the outcome of the HAST.

 Receiver operating characteristics (ROC) curves will be plotted to test the hypothesis that
 the scores are good predictors of negative HASTs. Diagnostic values of the scores will be
 expressed by sensitivity, specificity, positive and negative predictive values.
Inclusion Criteria:

 -  Age ≥18 years old (at the time of HAST)

 -  Clinically stable

 -  Hypoxic altitude simulation test, scheduled as part of the clinical care

 Exclusion Criteria:

 -  Inability to provide informed consent

 -  Being part of a clinical trial, which would exclude patients who are taking part in
 other studies including observational studies.