Hypoxia Altitude Simulation Test (HAST)

Background

  • Approximately 741 Million Passengers Traveled on US Commercial Airlines in 2006 (Chest, 2008) [MEDLINE]
  • Approximately 1 Billion Passengers Travel Worldwide Each Year (Chest, 2008) [MEDLINE]
  • Respiratory Complaints are Among the Most Common Necessitating Emergency Calls on Airlines
  • Commercial Aircraft are Pressured to Approximately 8,000 Feet: corresponds to a FIO2 of 15.1%

Indications

  • Screening for Altitude-Associated Hypoxemia in Patients with Cardiopulmonary Disease: HAST aims to identify patients who fall on the steep portion of the hemoglobin dissociation curve and are, therefore, at risk for significant oxygen desaturation at altitude
    • British Thoracic Society Recommendations for Screening Based on Ground SpO2
      • SpO2 >95%: no further testing or supplemental oxygen with air travel is required
      • SpO2 92-95%: HAST is recommended to determine the need for supplemental oxygen with air travel
        • These recommendations recognize that pulse oximeters have large confidence intervals of 2-4%
      • SpO2 <92%: supplemental oxygen is recommended with air travel
    • Aerospace Medical Association Medical Guidelines Task Force Guidelines for Screening Based on Ground pO2
      • Ground pO2 <70 mm Hg: HAST is recommended (Aviat Space Environ Med, 2003)[MEDLINE]

Technique

Procedure

  • HAST is as Predictive as Measuring Oxygenation in a Hypobaric Chamber (Considered the Gold Standard Test)
  • Testing of SpO2 (or pO2) with the Patient Breathing 15.1% Oxygen (Simulating 8,000 ft = 2,400 m, Pb 565 mm Hg) via a Tight Fitting Mask/Mouth Piece or in a Body Box
    • Concomitant EKG Monitoring
  • Patient Also Wears a Nasal Cannula Beneath the Mask, Allowing Repeat Testing with Supplemental Oxygen

HAST Interpretation

  • pO2 >55 mm Hg During HAST: no supplemental oxygen is required
  • pO2 50-55 mm Hg During HAST: considered borderline -> measurement with activity can then be obtained
  • pO2 <50 m Hg During HAST: testing with supplemental oxygen (usually 2L/min) is performed

Clinical Data

  • Comparative Study of 6MWT and Hypoxia Altitude Simulation Test (HAST) in Patients with Either Interstitial Lung Disease or COPD (Aviat Space Environ Med, 2007) [MEDLINE]
    • Oxygen Desaturation Induced by the 6MWT Correlated with that After HAST (r = 0.52)
  • Study of Algorithm Using Resting/6WMT SpO2 and HAST in COPD Patients (Thorax, 2012) [MEDLINE]
    • Baseline SpO2 <92%: supplemental oxygen is required for air travel
    • Baseline SpO2 92-95%
      • 6MWT SpO2 <84%: supplemental oxygen is required for air travel
      • 6MWT SpO2 ≥84%:
        • HAST SpO2 ≤85%: supplemental oxygen is required for air travel
        • HAST SpO2 >85%: no supplemental oxygen is required for air travel
    • Baseline SpO2 >95%
      • 6MWT SpO2 <84%
        • HAST SpO2 ≤85%: supplemental oxygen is required for air travel
        • HAST SpO2 >85%: no supplemental oxygen is required for air travel
      • 6MWT SpO2 ≥84%: no supplemental oxygen is required for air travel

References

  • Aerospace Medical Association. Medical guidelines for airline travel, 2nd ed. Aviat Space Environ Med 2003; 74:A1–A19 [MEDLINE]
  • Walking capacity and fitness to fly in patients with chronic respiratory disease. Aviat Space Environ Med 2007;78:789–792 [MEDLINE]
  • Hypoxia altitude simulation test. Chest. 2008 Apr;133(4):1002-5. doi: 10.1378/chest.07-1354 [MEDLINE]
  • The hypoxia altitude simulation test: an increasingly performed test for the evaluation of patients prior to air travel. Chest. 2008 Apr;133(4):839-42. doi: 10.1378/chest.08-0335 [MEDLINE]
  • Flying with respiratory disease. Respiration. 2010;80(2):161-70. doi: 10.1159/000313425. Epub 2010 Apr 16 [MEDLINE]
  • Air travel and chronic obstructive pulmonary disease: a new algorithm for pre-flight evaluation. Thorax. 2012 Nov;67(11):964-9. doi: 10.1136/thoraxjnl-2012-201855. Epub 2012 Jul 5 [MEDLINE]