The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Matthew J. O'Brien1, Gail P. Brittan1, Sue P. Murphy1, Mary Jo Biebl-Yahnke1, Peggy A. Zingler1

Background: Gas delivery methods used to perform High Altitude Simulation Testing (HAST), are not well standardized. Additionally, some methods allow assessment of oxygen titration during altitude simulation better than others. Comparing the pros and cons of the various methods may assist in the standardization of this diagnostic procedure. Although performed infrequently, this diagnostic test can be valuable in helping to define if a patient with compromised pulmonary function will require supplemental oxygen when exposed to high altitude conditions. Objective information regarding the most appropriate oxygen flow rate when at altitude can also be helpful. Evaluation methods used or suggested include: Hypobaric or Altitude chamber, venti-mask device using a setting of 35 or 40% O2-driven with a 100% Nitrogen gas, mouthpiece/2-way valve assembly, neoprene mask/2-way valve assembly, mouthpiece/demand valve and canopy enclosure.

These six variations are compared and a value assigned based on the pros and cons: 1=poor, 2=fair, 3=good, 4=excellent.
Assessments were based on: Patient Comfort, Ease of Communication, Safety, Gas Supply Requirements, Stability of FIO2 During Testing, Relative Cost, and Ease of Nasal Cannula O2 Delivery.
FIO2 stability was monitored using a zirconium oxygen analyzer (Medical Graphics Corporation).

Scores listed on the table indicate that the Hypobaric chamber method yields the lowest score due to cost, patient access, and patient comfort (score=14). Methods utilizing mouthpieces and nose clips also scored lower primarily because of patient comfort. The Venti-mask, neoprene mask with 2-way non-rebreather valve and the canopy method all scored higher due to patient comfort, communication and the ability to deliver nasal cannula oxygen during testing. Scores: Venti-mask=23, Neoprene mask=24, Canopy=25

Patient comfort and the ability to deliver and titrate oxygen during the evaluation are features of the last 3 methods. Air entrainment methods using 100% Nitrogen offer high flow and an inexpensive gas source, however users must ensure there are no obstructions to the entrainment sites which can cause an abrupt reduction in the FIO2 delivered to the patient. Always analyze and monitor what is being delivered to the patient. Canopy devices used for indirect calorimetry can be adapted to deliver reduced FIO2s and offer the most comfortable environment for HAST testing.