High (Hypoxic) Altitude Simulation
Studies in the PFT Laboratory
Katrina Hynes, BS RRT
Asst. Supervisor – Mayo Clinic Pulmonary Function Labs
Adjunct Faculty – University of Minnesota Rochester
Background: In-Flight Regulations
• Standard for airline cabin
pressurization is regulated by the FAA.
• (SAE ARP1270)
• The most important factor in this
standard is that cabin altitude pressure
not exceed more than 8000 ft. altitude
in normal conditions.
Background: In-Flight Regulations
• The FAA allows for brief drops in air
pressure for safety purposes only, such
as to avoid bad weather conditions. The
minimum air pressure is equal to
10,000 ft.
• Average 6214 ft (range 0 – 8915 ft)
• Cottrell JJ Chest 1988 (92) 81-4
Background: In-Flight Regulations
• The Air Carrier Access Act of 1986
required the U.S. Department of
Transportation to develop regulations
to ensure that persons with disabilities
are treated without discrimination in
any way, consistent with the safe
carriage of all passengers.
• Air Carrier Access Act, 49 USC §41705 (1986).
High Altitude Simulation Test (HAST)
for Pulmonary Patients - Evidence
• A. Normal subjects
• B. Subjects with
COPD
• Subjects with
restrictive lung dz
Cramer D. Ward S. Geddes D. Assessment of
oxygen supplementation during air travel.
Thorax. 51(2):202-3, 1996 Feb.
High Altitude Simulation Test (HAST)
for Pulmonary Patients - Evidence
• SpO2 measured with 4 L and following 5
min at FIO2 .21 in 3 pts with COPD
•Kramer et. al. Chest, Volume 108(5).November 1995.1292-1296
High Altitude Simulation Test (HAST)
for Pulmonary Patients - Evidence
• 18 retired servicemen (age 68 +/- 6) with severe
COPD (FEV1 31% +/- 10%)
• Altitude simulation 8000 ft. in a hypobaric
chamber.
• PaO2G at sea level of 72.4 +/- 9 mm Hg, PaO2Alt
of 47.4 +/- 6 mm Hg after 45 minutes of
hypobaric exposure.
• PaO2Alt = 0.453 [PaO2G] + 0.386 [FEV1%
predicted] + 2.440 (r = 0.847)
Annals of Internal Medicine. 111(5):362-7, 1989 Sep 1.
High Altitude Simulation Test (HAST)
for Pulmonary Patients - Evidence
• Surveyed physicians
in England
• 268 respondents
• No consensus exists
regarding assessment
methods or criteria for
recommending
oxygen
•R.K. Coker, M.R. Partridge. Eur
Respir J 2000; 15: 128±130
High Altitude Simulation Test (HAST)
Guidelines
• Managing passengers with respiratory disease
planning air travel: British Thoracic Society
recommendations - Evidence Based
• Thorax 2002;57:289–304
Purpose of recommendations (6)
• To enhance safety for passengers with lung
disease traveling by air and reduce the number
of in-flight medical incidents due to respiratory
disease.
High Altitude Simulation Test (HAST)
BTS Guidelines
• To increase recognition among
healthcare professionals that patients
with respiratory disease may require
clinical assessment and advice before
air travel.
• To provide an authoritative up to date
literature review of available evidence.
High Altitude Simulation Test (HAST)
BTS Guidelines
• To provide consistent, practical, and
comprehensive advice for healthcare
professionals managing such patients.
• To formulate key research questions
• To promote the development of methods
for monitoring the size of the problem
High Altitude Simulation Test (HAST)
BTS Guidelines
• Evidence definitions
High Altitude Simulation Test (HAST)
BTS Guidelines
Ten Indications
• Severe COPD or asthma; [B]
• Severe restrictive disease (including
chest wall and respiratory muscle
disease), especially with hypoxemia
and/or hypercapnia; [C]
High Altitude Simulation Test (HAST)
BTS Guidelines
• Patients with cystic fibrosis; [C]
• History of air travel intolerance with
respiratory symptoms (dyspnea, chest
pain, confusion or syncope); [C]
• Co-morbidity with other conditions
worsened by hypoxemia
(cerebrovascular disease, coronary
artery disease, heart failure); [C]•
High Altitude Simulation Test (HAST)
BTS Guidelines
• Pulmonary tuberculosis; [C]
• Within 6 weeks of hospital discharge
for acute respiratory illness; [C]
• Recent pneumothorax; [B]
• Risk of or previous venous
thromboembolism; [B]
• Pre-existing requirement for oxygen or
ventilator support. [C]
High Altitude Simulation Test (HAST)
BTS Guidelines
Recommended assessment
• History and examination with particular
reference to cardiorespiratory disease,
dyspnea, and previous flying experience;
[C]
• Spirometry [C]
• SpO2 by pulse oximetry or ABG’s [C]
High Altitude Simulation Test (HAST)
BTS Guidelines
• Blood gas tensions are preferred if
hypercapnia is known or suspected. [C]
• In those who are screened who have
resting sea level oximetry between 92%
and 95% with additional risk factors,
hypoxic challenge testing is
recommended [C]
High Altitude Simulation Test (HAST)
BTS Guidelines
High Altitude Simulation Test (HAST)
BTS Guidelines
High Altitude Simulation Test (HAST)
• Gong H. at el coined the term Hypoxic
Altitude Simulation Test (1984)
• Premise: Altitude hypoxia is a primary
stress or threat to patients with
cardiopulmonary disorders and FIO2 at
altitude can be replicated according to
known pressure-altitude relationships
• Monitored SpO2 and ECG
High Altitude Simulation Test
(HAST)- Methods
• Ideal test:
Hypobaric chamber
• Variable altitudes
• Oxygen titration
• Unaffordable and
impractical
High Altitude Simulation Test
(HAST)- Methods
• Modified body
plethysmograph
• Exit port for gas
flow
• Controlled
environment
• Oxygen titration?
High Altitude Simulation Test
(HAST)- Methods
• Standard gas mixture
cylinder
• Directional valve
• Demand valve
High Altitude Simulation Test
(HAST)- Methods
• Blender driven with
100% N2 and .21
•Variable FIO2
• Oxygen analyzer
• Reservoir
• Directional valve
• CPAP mask
High Altitude Simulation Test
(HAST)- Methods
• Non-rebreathing mask
•Gas source
• Venti-mask
•Driven with 100% nitrogen
40% setting =
approximately 14-15%
•Set to 35% =
approximately 15-16%
“Laboratory Assessment of Fitness to Fly in Patients with Lung
Disease: A Practical Approach.” A.G.Robson, et al
Eur Respir J 2000; 16: 214-219
High Altitude Simulation Test
(HAST)- Methods
• Alternative altitudes
• Alternative Indications
•Bengdag, China: 14,100 •Athletic training
ft
•Bogota, Colomba: 8355
ft
•Quito, Ecuador: 9222 ft
•Telluride, USA: 9086 ft
High Altitude Simulation Test
(HAST)- Methods
• Determining the standard gas mixture at
your altitude or for varying altitudes
• Factor = [1-6.873E-6 X Alt(Feet)]^5.256
• Bag FIO2 = ((760 X factor)/PBaro) X 0.21
Inspired Oxygen Concentration
High Altitude Simulation
0.25
0.2
0.15
Series1
0.1
0.05
0
0
2000
4000
6000
Altitude
8000
10000
12000
Mottram CD
10th Ed.
Ruppel’s
Manual PFT
Chap 5
High Altitude Simulation Test
(HAST)- Methods
• Rochester, MN average barometric
pressure = 740 mmHg
• Standard gas mixture for 8000 ft is
16.1%
• Denver = 5,280 ft (“mile high city”)
• Bag FIO2 = ((760 X factor)/PBaro) X 0.21
• Bag FIO2 = ((760 X .82495)/740) X 0.21
• Bag FIO2 = 17.8%
High Altitude Simulation Test
(HAST)- Methods
• http://www.go2altitude.com
High Altitude Simulation Test
(HAST)- Methods
• Walking
•BTS recommends walking if SaO2 87-90%
• O2 Titration
•Hypobaric
chamber
•Body box
•Mask???
CHEST 2011; 140(1):84–90
• 16 patients with COPD were exposed to alveolar
hypoxia in a hypobaric chamber (HC) at 2,438
m (8,000 ft) and with a HAST (method: mask)
• Conclusion: oxygen titration using an NC during
a HAST causes accumulation of oxygen within
the facemask and underestimates the oxygen
dose required
High Altitude Simulation Test
(HAST)- Methods
• BTS Guidelines – oxygen
recommendations
• Guideline threshold for advising in-flight
oxygen: 82–84%
• 2 l/min via nasal cannula will improve
hypoxemia but not quite to sea level
values
• 4 l/min > sea level values
Thorax 2012;67:964–969
• 100 patients with COPD
High Altitude Simulation Test
(HAST)- Equipment
• Hypoxia gas delivery system
and appropriate mixture
• Electrocardiograph and blood
pressure system
• Ratings of Perceived Exertion
scale (RPE)
• Pulse Oximeter or ABG’s
High Altitude Simulation Test
(HAST)- Protocol
• Obtain resting room air variables
• ECG, RPE, B/P, SpO2
• Place on hypoxic mixture for 20
minutes or early termination criteria
• Obtain hypoxic gas mixture variables
• ECG, RPE, B/P, SpO2/ABG’s
High Altitude Simulation Test
(HAST)- Protocol
• Early termination criteria
• Change in baseline rhythm (i.e. VT,
SVT, PSVT)
• ST – T wave depression > 1 mm
• SpO2 < 80%
• Subject intolerance
High Altitude Simulation Test
(HAST)- Reporting
High Altitude Simulation Test
(HAST)- Reimbursement
“Show me the Money”
High Altitude Simulation Test
Current Procedural Terminology (CPT)
• 94452: High Altitude Simulation Test
(HAST), with physician interpretation
and report
• 94453: High Altitude Simulation Test
(HAST), with physician interpretation
and report; with supplemental oxygen
titration.
Air Travel with Oxygen
• Does your airline accept passengers who
require supplemental oxygen?
• How much notice do you require before
the flight?
• What documentation is required from my
doctor?
• What do you charge for supplying oxygen
and how is the charge determined?
Air Travel with Oxygen
• Do you allow passengers to bring their
empty oxygen equipment?
• Are there specific seat requirements?
• What liter flow options are available?
• Do you provide nasal cannulas or
masks?
Air Travel with Oxygen
What to check once you’re on board?
• Oxygen cylinders are full
• The oxygen equipment is working
properly
• The flow meter has been set to the
proper liter flow per minute
• You have access to all of your
medicines, including inhalers
Questions?