PHYSIOLOGIC CHANGES IN FLIGHT AND HIGH ALTITUDE ENVIRONMENTS

Ruthanne Taylor, DNP, FNP-BC

Medical Provider

US Embassy Prague

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PRIMARY FACTORS TO CONSIDER IN AIR MEDICAL TRANSPORT

• 1. Boyle’s Law

• 2. Partial Pressure of Oxygen

• 3. Oxyhemoglobin Dissociation Curve in High Altitude Environments

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BOYLE’S LAW

• Boyle’s law tells us that: In a closed space, AS PRESSURE DECREASES, VOLUME INCREASES.

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BOYLE’S LAW

• The volume of gas in an enclosed space will increase by 35% at 8,000 feet (2,400 Meters) which is the approximate altitude setting in most commercial aircraft.

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PARTIAL PRESSURE OF OXYGEN

• At Sea Level, the Partial Pressure of Oxygen is 98mmHg which leads to a PaO2 of 98mmHg and O2 saturations of 98-100% in healthy individuals.

• At 8,000 feet, the Partial Pressure of Oxygen is 55mmHg which leads to a PaO2 of 90mmHg and O2 saturations around 90% in healthy individuals.

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THE EFFECT OF ALTITUDE ON VOLUME

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THE OXYHEMOGLOBIN DISSOCIATION CURVE

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OXYHEMOGLOBIN DISSOCIATION CURVEAS AFFECTED BY ALTITUDE

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OXYHEMOGLOBIN DISSOCIATION CURVE

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SO WHAT? HOW DOES ALTITUDE AFFECT OUR PATIENTS?

• What are the implications for the human body as it is moved to higher altitudes, and therefore, lower pressure environments?

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GAS EXPANSION

• Volume of trapped gas expands by 35% at 8000 ft

• Difficult to monitor and reverse

• Can lead to:

• Tension pneumothorax

• Wound dehiscence

• Intracranial hemorrhage

• Ocular damage

• Recent surgery as well as head and chest trauma represent greatest risks

• Reason for most transport contraindications11

THE FLIGHT ENVIRONMENT

• Cabin pressure in Commercial and Air Ambulance aircraft with pressurized environments is equivalent to 5000-8000 feet above sea level.

• At this altitude, a healthy individual has a typical O2 saturation of 94-95%

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AIRCRAFT ENVIRONMENT

• Oxygen saturation can be helped with:

• Supplemental oxygen

• Preflight blood transfusion in the case of blood loss or anemia

• Low altitude flight is beneficial (when this is a controllable factor)

• Bringing oxygen on board commercial aircraft is not possible any longer. Only oxygen concentrators are allowed.

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UNPRESSURIZED AIRCRAFT

•What about helicopters?

•What about unpressurized small aircraft?

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ABSOLUTE CONTRAINDICATIONS TO AIR MEDICAL TRANSPORT

• Unsafe flying conditions

• Terminal patient

• Certain acute communicable infections

• Combative, uncontrollable patient

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ABSOLUTE CONTRAINDICATIONS TO AIR MEDICAL TRANSPORT

Premature infants and neonates are particularly susceptible to the environmental changes in aircraft, and should always be transported by NICU specialist teams.

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RELATIVE CONTRAINDICATIONS

• Cardiovascular disease

• Wait 2 weeks after an MI if possible

• Acute pulmonary edema

• Consider lower altitude flight (when controllable)

• Pulmonary diseases

• Acute asthma or COPD exacerbation

• Oxygen probably unnecessary if pO2 > 92% and/or patient can walk 50 yards without distress

• Pneumothorax

• Chest tube with Heimlich valve

• Wait 72-96 hours if Chest Tube has been removed17

RELATIVE CONTRAINDICATIONS

• Hemorrhagic stroke

• Delay travel for 7 days if possible

• Anemia

• Severe (Hb < 7.0 g/ml) or acute blood loss (Hct < 30%)

• Sickle cell crisis can be precipitated

• Gastrointestinal disease

• Bowel obstruction/ ileus

• Unreduced incarcerated hernia

• Volvulus or intussusception

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RELATIVE CONTRAINDICATIONS

• Recent surgery

• Laparotomy: 10 days

• Laparoscopic: 3-5 days

• Thoracotomy: 14 days

• CABG: 10-14 days

• Angioplasty: 3-5 days

• Middle ear: 10 days

• Cataract: 1 day

• Spinal anesthesia: 1 day

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RELATIVE CONTRAINDICATIONS• Extremity fractures

• Bivalve all fresh casts

• Avoid air splints

• Hare traction or Sager Splint, not suspended weights

• Skull fractures

• Risk of intracranial air with sinus fractures

• Must fly at low altitude

• Mandibular fractures

• Use elastic bands, not wires

• Spinal injuries

• Immobilize on Stryker stretcher

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RELATIVE CONTRAINDICATIONS• Retinal disease

• S/P retinal detachment repair- delay 2-6 weeks depending on how fixed

• Supplemental oxygen for retinal disease

• Gas gangrene

• Dental abscess

• Acute psychosis or delirium

• Decompression sickness

• Delay flying for 12-24 hours after diving

• Pregnancy with imminent delivery21

PSYCHIATRIC PATIENT CONSIDERATIONS

• Patients with some neurological or psychiatric disorders become very upset by changes to familiar routines, confusion over procedures, enforced crowding with strangers, or lack of privacy.

• What will be the effect of such irritants as parking, luggage transport, long lines, security checks that may involve physical searches, confusing announcements, gate changes, cancelled flights, cramped seating, taxiway delays, turbulence, airsickness, inconvenient or delayed access to toilet facilities, lost luggage, disruption of schedules by weather, aircraft delays or missed connections, and other realities of air travel?

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COMMERCIAL AIRLINE EVACUATIONS

• Much cheaper

• Longer flying range means…

• More destination options

• Fewer refueling stops

• Less chance of injury exacerbation from multiple take-offs and landings

• Stretcher travel

• Six seats in business class

• Access to electrical outlets?23

PRACTICAL PROBLEMS

• Arranging can be a bear

• Non-covered service

• Assistance companies solicit competing bids

• Ambient noise

• Low humidity (10-20%)

• Prolonged immobilization

• Airframe vibration

• Planes (and helicopters) do crash

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PRACTICAL PROBLEMS

• Airlines have the right to refuse boarding to travelers that appear acutely ill or debilitated

• Limitations on what can be carried on board, i.e. oxygen, IV fluid, medications.

• Customs and Passport Control Issues

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AIR AMBULANCE EVACUATIONS

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AIR AMBULANCE EVACUATIONS

• There are no governmental standards for flight team qualifications

• There is a Commission on Accreditation of Medical Transport Services, accredited services have met stringent requirements for crew training, crew rest, equipment and supplies carried, on-board safety, patient restraint systems, and vehicle/aircraft maintenance.

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INFECTIOUS DISEASE

• CDC has authority to quarantine passengers:

• Pandemic influenza

• SARS

• Cholera

• Diphtheria

• TB (infectious stage)

• Plague

• Smallpox

• Yellow fever

• Viral hemorrhagic fevers28

DEEP VEIN THROMBOSIS PREVENTION

• Low Molecular Weight Heparin – Enoxaparin (Lovenox) 40mg SQ before flight. Administer once a day.

• Factor Xa Inhibitors – Only one approved for DVT prophylaxis

• Fondaparinux (Atrixa) 2.5mg SQ every day, first dose prior to flight

• Direct Thrombin Inhibitors and NOAC – Off label use

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FURTHER READING

• ISO Document on Travel Thrombosis - MED website

• Bartholomew, J. Shaffer, J. and McCormick, G. Air Travel and Venous Thromboebolism: Minimizine the Risk. Cleveland Clinic Journal of Medicine. Volume 78 Number 2 February 2011

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USEFUL WEB SITES

• Virtual Naval Hospital- http://www.vnh.org

• Aerospace Medical Association- http://www.asma.org/publications/

• Commission on Accreditation of Medical Transport Services

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CASE SCENARIO

• A 38 y.o. security guard sustained a gunshot wound (GSW) to the right chest during an attempted attack on the consular visitor’s entrance. He is short of breath and bleeding from a sucking open wound between his 5th and 6th ribs.

• Temp 36.7 Pulse 67 Respirations 30 BP 110/770

• Local ER facilities are limited, but a UN surgeon is available.

• Next commercial flight to DOS medevac center is in 72 hours.

• Vetted Air Ambulance provider can be at your location in 24 hours.

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DIAGNOSIS?

Potential Complications?

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HOW WOULD YOU MANAGE THE CASE?

• What are the most immediate concerns?

• What do you have in your health unit to manage these concerns?

• What steps do you need to take, in order of priority, to get the patient where they need to be for definitive treatment?

• What concerns do you have in the air transport environment?

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THINGS TO CONSIDER

• What is the immediate threat environment?

• Is there a facility within driving distance that can manage this case?

• Are locally available services capable of providing the highest medical standard of care during transport?

• How long will it take to make arrangements for commercial or private air ambulance transport?

• Do you need to send a medical attendant?

• Logistics? Passports, visas, luggage, family members.

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WHAT IF THIS OCCURRED AT A REMOTE SITE IN YOUR COUNTRY?

• Would there be pressure to use a helicopter service?

• How might an unpressurized aircraft (airplane or helicopter) environment affect this patient?

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HOW WOULD YOU MANAGE THE CASE?

• Is there a local hospital that can manage the case?

• What can you do in the Health Unit prior to transport to this hospital, or prior to medevac?

• What would you want to consider in your choice of commercial versus air ambulance transport?

• What companies have you evaluated in advance of this scenario?

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