Can historical assumptions be used to assess fitness to fly for other respiratory compromised patients? An evaluation of physiological parameters to risk stratify patients planning air travel

Cliff, Ian James (2022) Can historical assumptions be used to assess fitness to fly for other respiratory compromised patients? An evaluation of physiological parameters to risk stratify patients planning air travel. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Introduction: The risks associated with commercial flight for respiratory compromised patients is well known. Many of the assumptions are based on studies that have included patients with Chronic Obstructive Pulmonary Disease (COPD) and have often been extended to other respiratory and non-respiratory disorders. The primary aim of this thesis is to examine the differences in physiological parameters and Hypoxic Challenge Test (HCT) outcomes in patients with Motor Neurone Disease (MND), Interstitial Lung Disease (ILD) and COPD. The secondary outcome is to investigate whether physiological parameters can predict HCT pass or failure in ILD, MND and COPD patient groups. Methods: Respiratory patients who were referred into a 'fitness to fly' service (n=225) with COPD (n=51), MND (n=118) and ILD (n=56) completed baseline lung function and an HCT as part of risk stratification for planned air travel. Descriptive statistics were obtained, and analysis was performed using one-way ANOVA, Kruskal-Wallis, and Chi-Squared tests, as appropriate. Data from patients requiring in-flight oxygen was compared to patients who did not, per the British Thoracic Society recommendations 2011 (Ahmedzai et al., 2011). Univariate analysis and logistic regression were performed to evaluate independent physiological parameters for HCT failure. Results: Demographic data relating to age, smoking history and BMI were significantly different between the patient groups. Spirometric data showed significant differences in Forced Expiratory Volume in one second (FEV1) absolute, per cent predicted and standardised residuals, however, there was no significant difference in Forced Vital Capacity (FVC) absolute or per cent predicted. Resting capillary blood gases (CBGs) (FiO2 21%) showed significant differences between patient groups in all parameters except for pH. Responses to the hypoxic mix during the HCT (FiO2 15%) showed differences in all CBG values except pH. This was also mirrored in the corrective values (FiO2 28%). The difference between the PaO2 at rest (21%) and during the HCT (15%) is higher in the MND and ILD groups (2.66 and 2.74 kPa respectively) versus the COPD group (2.2kPa). The HCT fail rate was greatest for the COPD group. In the MND group there was no significant difference between the pass (n=94) and fail (n=24) groups for age, gender, smoking history, or BMI. There was a significant difference for all spirometry data (Forced Expiratory Volume in one second - FEV1, FVC - Forced Vital Capacity and FEV1/FVC ratio – absolute, per cent predicted and standardised residuals). Moreover, the resting blood gases (FiO2 21%) data showed a significant difference for all parameters except pH (<0.001). The Regression analysis showed limited predictive value of spirometry and/or resting blood gas data except for PaCO2 and base excess (BE). In the ILD group, demographic data relating to age, gender, smoking history, and BMI were comparable. Spirometric data showed differences in per cent predicted for FEV1 and FVC. There was no difference in any of the parameters relating to static lung volumes, transfer factor or 6MWT. Furthermore, there was no difference between the group for resting blood gases (21%). The Regression analysis showed limited predictive value for spirometry. Conclusions: In this exploratory examination, the physiological data supports significant differences between the disorders for most data. The assumptions and algorithms based on the study of COPD patients cannot be assumed for MND or ILD, and these groups need to be specifically studied to better understand their response to the commercial cabin environment. The predictive value of spirometic paraments and resting blood gases are limited in assessing hypoxaemia during a commercial flight in MND and ILD patients, except for parameters relating to respiratory failure. Despite the significant difference between the two groups, routine physiological data was limited in the predictive regression equations. The recommended safest approach in managing these groups of patients is to perform an HCT in all patients intending to use air travel, until more evidence-based data is available.