Mechanical Ventilation at Altitude

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Mechanical Ventilation at Altitude
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Altitude
Armstrongs Line 63,500 FT
Space Equivalent Zone FL 500 and above
Physiologically Deficient Zone 10,000 ft FL 500
AGL
Physiologic Zone Sea Level 10,000 ft
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Hypoxia

• Function of Daltons Law (Ptotal P1 P2P3)
• PIO2 Patm x FIO2
• 159.6 760 x 0.21
• 118.2 563 x 0.21
• Water vapor pressure is 47 mmHg
• PAO2 at seal level 112
• PAO2 at 8,000 feet 71

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Altitude and Inspired PO2
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Normal cabin altitude in commercial aircraft
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Altitude Physiology
The gas laws explain the physiologic effects of
altitude

• Boyles Gas Law
• P1/P2 V2/V1
• The volume of gas is inversely proportional to
  its pressure as temperature remains constant
• i.e. a volume of gas increases as pressure
  decreases
• In flight gases expand at altitude
• Body is adaptable up to 10,000 feet above sea
  level

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18,000 feet 0.5 ATA
8,000 feet Normal cabin pressure
Sea level 1ATA 760 mm Hg
33 FSW 50 of sea level volume 2ATA
66 FSW 33 of sea level volume 3ATA
99 FSW 25 of sea level volume 4 ATA
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Barometric Pressure
GAS EXPANSION
(BOYLES LAW)
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Trapped GasesBarometric Pressure Changes

• Related to Boyles law
• i.e. volume of gas changes inversely with
  pressure
• Can be found in
• Ear, sinuses, teeth, GI tract.
• Any closed space that normally or pathologically
  contains air/gases
• Symptoms occur on ascent or descent but usually
• Ears during descent
• GI tract during ascent
• Sinuses during descent

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Trapped GasesBarometric Pressure Changes

• Consider that many need to valsalva to clear
  their ears
• eye injuries, nasal injuries, head injuries
• may want to premedicate with vasoconstrictor
• Patients who are known to have trouble clearing
  their ears should have a nasal vasoconstrictor
  available
• NEVER FLY WITH A COLD
• Patients with altered level of consciousness may
  manifest trapped gases with significant agitation
• Check their ears!!

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• Adult volunteers in a hypobaric chamber
  (n502)
• Altitudes of 650, 4000, 6000, 7000, and 8000
  feet
• Measured oxygen saturation (pulse oximetry)
• Determined Environmental Symptoms
  Questionnaire
• Evaluation of adverse events

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N Engl J Med 3571 www.nejm.18 org july 5, 2007
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N Engl J Med 3571 www.nejm.18 org july 5, 2007
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N Engl J Med 3571 www.nejm.18 org july 5, 2007
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N Engl J Med 3571 www.nejm.18 org july 5, 2007
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N Engl J Med 3571 www.nejm.18 org july 5, 2007
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• Adverse effects were more common at 7,000 and
  8,000 feet vs. lower altitudes
• Average SpO2 reduction was 4.4 at 8,000 feet
• 7.4 of participants developed acute mountain
  sickness

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12 fall in SpO2 31 fall in PaO2
Schäcke G. Basics for preventive occupational
survey when working in oxygen depleted
atmosphere. Presented at the 28th International
Congress on Occupational Health, Milan, June
1116, 2006. abstract.
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Flying with Pulmonary Disease

• BTS recommendations for patients with
  pulmonary disease during air travel.

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Flying with Pulmonary Disease

• The hypoxia altitude simulation test (HAST)
• Patients breathe 15 oxygen
• Monitoring includes
• Continuous ECG to evaluate for ectopy or
  arrhythmias.
• Arterial blood gas measurement before and during
  the simulation.
• The patient usually wears a nasal cannula
  underneath the reservoir mask, so that if the
  Pao2 drops, the test is repeated with
  supplemental oxygen.

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Flying with Pulmonary Disease

• Other issues
• The normal response to increased altitude is
  hyperventilation
• This is no problem in people without lung disease
  (increase in MVV of 10)
• However in COPD the same change represents a 50
  increase in MVV!
• SpO2 alone cannot tell the story in COPD

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Flying with Pulmonary Disease

• Equation for determining the need for oxygen at
  altitude
• PaO2 (Alt) (0.519)PaO2(SL)(11.85xFEV1)1.76
• Where PaO2Alt Predicted PaO2 at altitude
• PaO2(SL) - PaO2 measured at sea level
• FEV1 forced expiratory volume in 1 second

Dillard TA, et alHypoxemia during air travel in
patients withchronic obstructive pulmonary
disease. Ann Intern Med 1989 111 362367.
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Effects of Altitude on Ventilator Performance

• Evaluation of the Mark VIII in an aircraft
• Lung model and paralyzed animal up to 34,000 feet

Kirby RR. Function of the Bird Respirator at
altitude. Aerospace medicine 196940463-469.
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A change in ambient pressure results in slower
emptying of the expiratory timer cartridge and a
slower respiratory rate
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Effects of Altitude on Ventilator Performance

• Evaluation of Oxylog 1000
• Six normal volunteers

Roeggla M. Emergency mechanical ventilation at
moderate altitude. Wilderness and Environ Med
19956283-287.
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Effects of Altitude on Ventilator Performance

• Lung model study
• At 2040 meters tidal volume increased by 28
• At 9120 metres tidal volume increased by 106.
• A lesser change, but in the opposite direction,
  occurred in respiratory rate.
• The net effect was a linear increase in minute
  volume with altitude.
• At 2040 and 9144 metres minute volume increased
  by 13 and by 45, and rate decreased by 10 and
  30 respectively.

Thomas G.Function of the Drager Oxylog
ventilator at high altitude. Anaesth Intensive
Care 199422276-80.
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Effects of Altitude on Ventilator Performance

• Evaluation of the effects of altitude at 2700 m
  compared to 171 m altitude on minute ventilation
  and blood gas analysis in healthy volunteers
  during mechanical ventilation with the Ambu Matic
  ventilator.
• At 2700 m altitude, the delivered minute volume
  increased by 13.8. paCO2 decreased by 9.2 (p lt
  0.01 for all reported changes).

Roeggla M. Emergency respirator therapy in
intermediate altitude with the Ambu Matic. Acta
Med Austriaca. 199623(5)168-9.
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Effects of Altitude on Ventilator Performance

• Comparison of the 3 Drager Oxlog transport
• ventilators in an altitude chamber
• Lung model study
• Changing resistance and compliance at a
  constant rate and tidal volume

Flynn JG. The performance of Drager Oxylog
ventilators at simulated altitude. Anesth
Intensive Care 200836549-552.
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Effects of Altitude on Ventilator Performance
Flynn JG. The performance of Drager Oxylog
ventilators at simulated altitude. Anesth
Intensive Care 200836549-552.
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Effects of Altitude on Ventilator Performance
Flynn JG. The performance of Drager Oxylog
ventilators at simulated altitude. Anesth
Intensive Care 200836549-552.
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Effects of Altitude on Ventilator Performance

• Evaluate performance of two ventilators used by
  CCATT for patient transport
• Lung model study in an altitude chamber

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Effects of Altitude on Ventilator Performance

• Volume and pressure control
• 0, 10, and 20 of PEEP
• 0.21 and 1.0
• Altitude of sea level, 4,000, 8,000, and 15,000
• Barometric pressure of 754, 657, 563, and 428 mm
  Hg
• Continuous monitoring of pressure volume and flow
• All data was recorded to a PC for later analysis

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Oxygen Supplementation Required above 10,000 feet
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Room air
FIO2 1.0
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Room air
FIO2 1.0
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Altitude Compensation with the Impact 754
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• Define oxygen requirements of critically
  ill/injured warfighters requiring mechanical
  ventilation and transport in a hypobaric/hypoxic
  environments
• Twenty-two mechanically ventilated patients
  were studied
• 117 hours of continuous recording
• All patients survived the 6-9 hour flight
• Mean oxygen usage was 3.24 1.87 L/min (range
  1.6 to 10.2 L/min).

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CCATT Monitoring Project

• Define oxygen requirements of critically
  ill/injured warfighters requiring mechanical
  ventilation and transport in a hypobaric/hypoxic
  environments

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CCATT Monitoring Project

• Define oxygen requirements of critically
  ill/injured warfighters requiring mechanical
  ventilation and transport in a hypobaric/hypoxic
  environments

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CCATT Monitoring Project
Mean oxygen use was 3.24 1.87 L/min (range 1.6
to 10.2 L/min).
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CCATT Monitoring Project
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CCATT Monitoring Project
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CCATT Monitoring Project

• Determine the effects of transport in a hypobaric
  environment by evaluating the number and duration
  of hypoxemic events (oxygen saturation lt 90) in
  critically ill/injured warfighters.
• Desaturation was defined as a recorded SpO2 of
  less than 90.
• Three episodes were seen
• 85 nadir with a 35 second length
• 86 nadir with a 115 second length
• 89 nadir with a length of 280 seconds.
• No interventions in mechanical ventilation were
  seen during these desaturation episodes with
  spontaneous resolution to a SpO2 of 90 in all
  cases.

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IED bilateral LE fx and soft tissue injury
arrives with bilateral tourniquets sbp 50 45
units blood products. no injury above inguinal
ligaments.
6-Aug-2006
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35 yo male U.S. Army. Max face trauma and
fractures with full facial burn. nasally
intubated. no other body trauma.
9-AUG-2006
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Summary

• Ventilation at altitude presents a number of
  physiologic and technical challenges
• Understanding the effects of altitude on
  barometric pressure and resultant changes in gas
  volume and PO2 are critical
• Appreciation of the gas laws predicts how
  ventilator performance responds at altitude
  (lowPB)