TRANSPORT PHYSIOLOGY

REACH Air Medical Services

REACH Mission

We will be available and prepared to provide customer-oriented, high-quality patient care, in a safe and efficient manner. In every situation, we will do what is right for the patient.

Objectives

• Describe the significance of gas laws pertinent to the transport environment.

• Describe the stresses of flight and their effects on transport teams and their patients.

• Identify specific interventions to combat the different stressors to the transport team and their patients.

• Identify the signs and symptoms of hypoxia.

• Identify appropriate interventions to mitigate the adverse effects of barometric pressure change in transport.

Flight Physiology Terms

• Ambient Pressure– The pressure of existing and adjacent

environment• Physiological Zone

– The area from sea level to 10K feet• Cabin Altitude

– The altitude measured inside the cabin of an aircraft

• Cruising altitude– The actual, level-off altitude outside

the aircraft above sea level

Flight Physiology Terms

• Atmosphere– The gaseous layer around the earth,

composed mainly of nitrogen and oxygen

• Altimeter– An instrument used to measure aircraft

altitude

• Barometer– An instrument used to measure atmospheric

pressure

• Barometric Pressure– The pressure of the air in certain

environment, measured by a barometer

Boyle’s Law

• Statement of Law– At a constant temperature, the

volume of a gas is inversely proportional to it’s pressure.

• Example– Trapped gas in the body

Dalton’s Law

• Statement of Law– Total pressure of a mixture of gases

equals the sum of the partial pressure of each gas in the mixture

• Example– Hypoxia

Henry’s Law

• Statement of Law– Gas dissolved in a liquid is directly

proportional to the weight of the gas above the liquid.

• Example– Soda can– Decompression sickness

Charles’ Law

– Statement of Law• The pressure of gas is directly

proportional to its temperature (volume remains constant)

– Example• Storage of oxygen containers

Graham’s Law

• Statement of Law– A gas will diffuse from an area of high

concentration (or pressure) to an area of low concentration.

• Example– Gas exchange at the cellular level

Stresses of Transport• Hypoxia• Trapped Air• Thermal changes• Decreased Humidity• Noise• Vibration• Fatigue• Gravitational,

acceleration/deceleration forces

Hypoxia

An oxygen deficiency sufficient to cause an impairment of function

• Causes– Inadequate supply of oxygen– Inadequate oxygen transport

capability– Inability of body to use oxygen

Stages of Hypoxia• Indifferent Stage

– Physiologic zone: 0 – 10 K feet– Increased HR and RR– Decrease in night vision @ around 5 K

Stages of Hypoxia

• Compensatory Stage– 10 K – 15 K feet– Increased HR, RR, BP, Respiration

Depth– Drowsiness– Poor judgement– Impaired coordination– Impaired efficiency

Stages of Hypoxia

• Disturbance Stage– 15 K – 20 K feet– Characterized by

• Dizziness, sleepiness, tunnel vision, cyanosis, slowed thinking and decreased muscle coordination.

– Which can cause…• Impaired flight control• Impaired handwriting• Impaired speech• Decreased coordination

Stages of Hypoxia

• Critical Stage– 20 K - 30 K feet– Mental confusion and incapacitation– Unconsciousness– Circulatory failure– Cardiovascular collapse– Death

Types of Hypoxia• Hypoxic Hypoxia• Anemic Hypoxia• Stagnant Hypoxia• Histotoxic Hypoxia

Hypoxic Hypoxia

• Deficiency in alveolar oxygen exchange.

• Causes– Reduction of pO2 in inspired air

– Ineffective gas exchange in an area of the lung

• Result– Inadequate oxygen supply in arterial

blood

Hypoxic Hypoxia

Altitude Pressure Oxygen

sea level 760mmHg 160mmHg

1000 ft. 732 132 8000 ft. 564 11818000 ft. 380 8034000 ft. 187 39

• Reference Protocol:– Atmospheric Pressure, Limits for Specific Disease

Processes

Hypoxic Hypoxia

• Treatment– Supplemental 02– Altitude restriction– BIPAP– Advanced airway management– Fix problem

Anemic Hypoxia

• Reduction of 02 carrying capacity – Decrease in circulating Hgb– Reduction of functional / avail Hgb

• Treatment– Maximize available 02– Consider transfusion

Stagnant Hypoxia

• 02 deficiency secondary to poor circulation– Heart failure– Hypovolemia– Shock (any source)

• Treatment– Maximize 02 supply– Maximize 02 delivery

• Consider volume• Consider pump

Histotoxic Hypoxia

• Inability to utilize 02 at cellular level– “Poisoned tissue”

• Causes– Sepsis– Alcohol– Cyanide– Carbon monoxide

• Treatment– Cause specific

Trapped Air

• Expands with increase in altitude and contracts on descent

• Trapped air will expand!• Air expansion can cause rupture!• One liter of gas at sea level will expand

to the equivalent of three liters of gas at 28,000 ft.

• Even with pressurization of the cabin the body can act like a closed container.

Trapped Air

• Cranium• Sinuses• Ears• GI Tract• Thorax• Medical

Devices

Trapped Air

– Middle ear• Eustachian tube is far easier to open for

expanding gases than it is to open when gas contracts. Therefore rupture is more likely on descent when the eustachian tube is blocked.

– Bowel gas, sinus and pleural space gases• Causing abdominal pain, increased

intracranial pressure and possible pneumothorax

Trapped Air

• Pneumothorax– Vent the chest!

• Bowel Obstruction– NGT– Vent to atmosphere or place on

suction• Pneumocranium

– Lowest altitude possible

Trapped Air

• Colostomy– BEWARE!– Vent to atmosphere

• ETT cuff– If high altitude for long periods of time

replace cuff air with saline or sterile H20

• IV Bags– Remove all air prior to flight

• Glass Bottles– Do not use!

• Air Splints / MAST Pants– Monitor for increased pressure with altitude

Other Barometric Pressure Issues• Dive Injuries

– Transported altitude < 1000 ft. – Divers should be discouraged from

flying within 24 hours of dives > 66 feet.

• Dental work– Should not fly within 24 hrs.

Thermal Changes

• Temperature decreases with altitude

• Consider when “packaging” patient• Consider flight crew dress

Decreased Humidity

• Decreased humidity with increased altitude– ETT’s plug more easily– Corneas will dry out– Dehydration

Noise

• Ear protection• Cannot auscultate BS during flight• Cannot auscultate BP during flight• Creates acceleration of other

senses

Vibration

• Constant low vibration– Traction devices must not have

hanging weights– Diligent check of equipment settings– Screws and bolts loosen over time– Palpation of pulses– Additional stress and fatigue on crew,

patient, and equipment

Fatigue

• Operational stressors• Personal stressors

– D rugs– E xhaustion– A lcohol– T obacco– H ypoglycemia

Gravitational Forces

• Helicopter G forces are minimal, fixed wing aircraft may experience increased forces

• Maneuvering– Visual Disturbances– Disturbances in consciousness

• Acceleration/Deceleration • CNS depressants and narcotics are

potentiated.

Key Points

Patient

• All patients receive supplemental 02!• Assess and address all pulmonary needs

prior to departure• Assess and address circulatory

deficiencies prior to flight• Release trapped air• NGTs should never be clamped• Hematocrit should be > 21 and HGB

should be > 7

Crew• Well rested• Avoid smoking• Remain in seat with restraints to avoid

vibration• Avoid gas producing foods ( check on

your partner!)• Avoid chewing gum on ascent• Avoid flying with cold or ear infection• Avoid effects of ETOH for 12 hours

before flight

Conclusion