Review of High Altitude Simulation Test (HAST) in Pediatric and Adult Patients with Sickle Cell Disease
Authors: Pandhi Aashima , Ramdhan Rebecca , Zhu Yuxi , Anim Samuel , Owusu-Ansah Amma T. , Brown Tracie 
Published: December 2024

Background: Sickle cell disease (SCD) is an autosomal recessive hemoglobinopathy characterized by complications like vaso-occlusive episodes (VOE), splenic and hepatic sequestration, acute chest syndrome (ACS), priapism, increased risk of ischemic stroke and pulmonary arterial hypertension. Air travel has emerged as one of the most popular and convenient forms of travel over the recent decades. High altitude exposure with air travel can produce a hypoxic environment which is known to trigger complications in these patients which can be further exacerbated by dehydration, temperature changes and increased stress. There is limited data about recommendations for patients with SCD during air travel. The Canadian Pediatric Society position statement published in 2007 recommends that patients with SCD use supplemental oxygen. The National Heart, Lung and Blood institute recommends that individuals dress warmly, stay hydrated and move about the cabin. The results of an online cross-sectional survey circulated through Canadian Hemoglobinopathy Association and American Society of Pediatric Hematology Oncology showed that though air travel was considered a major risk factor for complications, only 18 % of health care providers recommended supplemental oxygen. The High altitude simulation test (HAST) is a simple way to simulate the hypoxia of high altitude and hence can be used to assess the need for supplemental oxygen during air travel. There is limited data for HAST in SCD individuals. A single institution, retrospective cross-sectional study assessed the prevalence of high-altitude hypoxia in adults with SCD who underwent testing and described their demographics. Due to patient-reported symptom exacerbation during or after air travel, some individuals with SCD have completed the HAST to determine their oxygen needs during travel. Our study is unique because it includes pediatric patients in which HAST has not been previously described in the literature.

Methods: After institutional IRB approval, a retrospective chart review of 16 individuals with SCD who underwent HAST was performed. Descriptive statistics were used to characterize demographic and clinical features by using frequencies with proportions and medians with interquartile ranges for categorical and continuous variables, respectively.

Results: Of the 16 individuals referred for HAST, 10 (63%) completed testing, of which 8 (80%) met criteria for supplemental oxygen during air travel (positive test). 100% of the pediatric patients who underwent testing had a positive test. While anticipated travel was the most common reason for referral (87.5%), other reasons included facial swelling and pain in flight and development of VOE post-travel. Patients referred had a median (IQR) VOE frequency of 2 (1-3) in the two years prior to the HAST and 3 (1-4) lifetime ACS episodes. Asthma, baseline hypoxemia and obstructive sleep apnea were the most common associated co-morbidities among those referred.

In the group with a positive test, 7 (88%) individuals had HgbSS disease, 7 (88%) were females, 2 (25%) required nocturnal oxygen and 2 (25%) had a prior intubation for ACS. The median hemoglobin was 9.7 g/dl (8.23-9.43), reticulocyte count was 12% (9 -28), total bilirubin was 2.65 mg/dl (1.68-4.00), SpO2 was 97% (95-98) and white blood cell count was 9.65 X 103 u/L (8.50-10.78) in this group. The individual with history of facial swelling and pain in flight did not have recurrence of symptoms with use of supplemental oxygen with subsequent travel.

Conclusions: Both pediatric and adult individuals with SCD may be predisposed to VOE during or after air travel. Our study showed that 80% of all patients and 100% of pediatric patients who underwent HAST qualified for supplemental oxygen. A large prospective study of adults and children with SCD will provide data to develop a prediction model that informs patient selection for HAST referral.