Thrombolysis in the air. Air-ambulance paramedics flying to remote communities treat patients before hospitalization

PROBLEM ADDRESSED: First Nations* communities in the North have a high prevalence of coronary artery disease and type 2 diabetes and face an increasing incidence of myocardial infarction (MI). Many conditions delay timely administration of thrombolysis, including long times between when patients first experience symptoms and when they present to community nursing stations, delays in air transfers to treating hospitals, uncertainty about when planes are available, and poor flying conditions.

OBJECTIVE OF PROGRAM: To develop a program for administration of thrombolysis on the way to hospital by air ambulance paramedics flying to remote communities to provide more rapid thrombolytic therapy to northern patients experiencing acute MIs.

COMPONENTS OF PROGRAM: Critical care flight paramedics fly to northern communities from Sioux Lookout, Ont; assess patients; communicate with base hospital physicians; review an exclusion criteria checklist; and administer thrombolytics according to the Sioux Lookout District Health Centre/Base Hospital Policy and Procedure Manual. Patients are then flown to hospitals in Sioux Lookout; Winnipeg, Man; or Thunder Bay, Ont.

CONCLUSION: This thrombolysis program is being pilot tested, and further evaluation and development is anticipated.

Intubation success rates by air ambulance personnel during 12-versus 24-hour shifts: does fatigue make a difference?

OBJECTIVES: To determine whether the skill performance and psychomotor agility, as measured by the endotracheal intubation success rate, of air ambulance medical personnel would be affected by the potential fatigue incurred when increasing the length of their shifts from 12 to 24 hours. METHODS: This was a retrospective review of all flight and intubation records from a large air medical transport system from 1997, when 24-hour shifts were in place, and six months (March-August) of 1996, during which 12-hour shifts were scheduled. Records of all intubation efforts during both periods, including multiple attempts per patient, and outcomes of all attempts, were recorded. Results of successes and failures were tabulated for both ultimate intubation outcome per patient and all attempts per patient for each calendar day and for the 12 hours between 19:00 and 07:00 when fatigue might play a role. Results from the two study periods were compared using Fisher's exact test. RESULTS: During the six months of 1996, 190 of 199 (95.5%) patients were ultimately successfully intubated. These patients required 237 attempts (80.1% successful). During 1997, 362 of 376 (96.3%) patients were successfully intubated, and required 438 attempts (82.6% successful). There was no statistically significant difference in the number of ultimately successful intubations (p = 0.66) or total intubation attempts (p = 0.37) between 1996 and 1997. Analysis of intubations between 19:00 and 07:00 revealed 81 of 84 (96.4%) patients successfully intubated in 1996, with 81 of 103 (78.6%) attempts successful. During 1997, 173 of 180 (96.1%) patients were ultimately successfully intubated, with 173 of 212 (81.6%) attempts successful. Again, there was no significant difference in the number of successful intubations (p = 0.99) or intubation attempts (p = 0.55) between 1996 and 1997.

CONCLUSION: Psychomotor agility of air ambulance medical personnel, as measured by the success rate of endotracheal intubation, was not affected by the potential additional fatigue incurred as a result of increasing shift length from 12 to 24 hours.

Emergency room surgical workload in an inner city UK teaching hospital.

Abstract
Background
Emergency admissions may account for over 50% of surgical admissions. The impact on service provision and implications for training are difficult to quantify. We performed a cohort study to analyse these workload patterns.

Methods
Data on emergency room (ER) surgical admissions over six months was collected including patient demographics, referral sources, diagnosis, operation and length of stay and analysed according to sub-speciality and age-groups.

Results
There were 1392 (median age 41 (IQR 28–60) years, M:F = 1.7:1) emergency surgical admissions over six months; 45% were under 40 years of age and 48% patients self-referred to the ER. The commonest diagnoses were abscesses (11%), non-specific abdominal pain (9.7%) and neuro-trauma (9.6%). The median length of stay was 4 (IQR 2–8) days; with older (>80 years) patient staying significantly longer than those <40 years of age (median 8 vs 2 two days, P < 0.0001, Kruskal-Wallis test). Vascular patients remained in hospital longer than trauma or general surgery patients (median 14 vs 3 days, P < 0.0001, Kruskal-Wallis test). A high proportion (43.5%) of the patients required operative intervention and service implications of various diagnoses and operative interventions are highlighted.

Conclusion
With the introduction of shortened training period in Europe and World over, trainees may benefit from increased exposure to trauma and surgical emergencies. Resource planning should be based on more comprehensive, prospective data such as these.

Introduction
Emergency surgical admissions account for 46% to 57% of all surgical admissions [1-3] but workload estimates are difficult to achieve because of the unpredictability and variability of such admissions. There are no contemporaneous studies concerning the nature and volume of emergency surgical admissions. The impact of the emergency surgical workload on surgical practice is not only determined by overall volume but also by patient demographics, appropriateness of referral, centralisation, diagnoses, and required surgical operations. [4] The changing patterns have implications for surgical training, workforce planning and service provision. [2] The Royal London Hospital, a multi-specialty inner city teaching hospital which provides London's only Air Ambulance caters to a young, ethnically & socio-economically diverse, mainly immigrant population. [5] Health services in London are to be reconfigured, with fewer centres catering to larger populations and this similar exercise is being carried out in different parts of the world for macro- and micro-economic reasons without adequate data on volume, length of stay and problems for various specialties in hospitals. [6] This study sought to identify the current patterns and common problems related to emergency room (ER) admissions from a single hospital.

Methods
All ER surgical admissions over six months (12 January – 11 July 2007) to accident and emergency department were recorded prospectively. Orthopaedic trauma only (not polytrauma) and urological admissions were excluded since they were managed by orthopaedic and urology departments respectively; patients referred internally (already in-patient for another medical condition) from other specialties were also excluded since they did not effect the surgical department's bed occupancy rates. Information was obtained from hand-over lists and the Electronic Patient Record (EPR) viewer, an intranet-based patient record of Barts and The London NHS Trust. All data were anonymised and recorded in password protected spreadsheets. Information regarding time of operation was extracted from theatre logs. The final diagnosis was determined after investigations and/or operation and all patients were followed-up till discharge. One overnight stay was classified as 1 day of stay for length of stay calculations. Statistical analysis (ANOVA and Kruskal-Wallis test for data with and without normal distribution respectively) were performed on SPSS 14.0 for Windows (SPSS UK Ltd, Surrey, UK).

Air Medical Transport of Cardiac Patients

The air medical transport of cardiac patients is a rapidly expanding practice. For various medical, social, and economic indications, patients are being flown longer distances at commercial altitudes, including international and intercontinental flights. There are data supporting the use of short-distance helicopter flights early in the course of a cardiac event for patients needing emergent transfer for percutaneous coronary intervention or aortocoronary bypass. When considering elective long-distance air medical transport of cardiac patients for social or economic reasons, it is necessary to weigh the benefits against the potential risks of flight. A few recent studies suggest that long-distance air medical transport is safe under certain circumstances. Current guidelines for air travel after myocardial infarction do not address the use of medical escorts or air ambulances equipped with intensive care facilities. Further research using larger prospective studies is needed to better define criteria for safe long-distance air medical transport of cardiac patients.

aeromedical transportair ambulanceair medical transportcardiac transportmyocardial infarctionpatient transport
The use of air medical transport services provided by private and insurance company-affiliated air ambulance companies has risen significantly over the past 15 years. In 1992 alone, the 250 US-based and 12 internationally based air medical transport operators belonging to the Association of Air Medical Services performed > 160,000 transfers over a wide range of distances.1 For a combination of medical, social, and economic reasons, cardiac patients with increasing acuity of illness are being transported distances spanning the globe.

Air medical transport is performed using rotary wing aircraft (ie, helicopter) or fixed-wing aircraft (eg, engine propeller or jet air ambulance, or medical escort on a commercial airline). Rotary-wing aircraft are used for emergency transport over short distances, whereas fixed-wing aircraft are used for transport over longer distances (eg, > 150 miles).2 For long-distance transport that is elective (ie, for economic and/or social reasons), patients in relatively stable condition may be medically escorted aboard a commercial aircraft. Elective long-distance transport of patients in less stable condition (eg, early post-myocardial infarction [MI], receiving mechanical ventilation, or receiving IV vasopressors or antiarrhythmic agents) and emergency long-distance transport is performed using fixed-wing air ambulances. The type of fixed-wing aircraft used for air ambulance transport generally depends on the distance to be traveled, with single- or twin-engine propeller aircraft reserved for shorter flights, whereas jets may even be used to transport across continents. The quality of air ambulance services may vary across companies. Generally, air ambulances should be configured to function as flying ICUs with a full range of pharmaceuticals, and compact portable medical equipment including IV pumps, cardiac and hemodynamic monitor, defibrillator, ventilator, pulse oximetry, and blood gas analyzer. The medical crew should include an intensive care trained physician, nurse, and/or medic.

When air medical transport is considered elective (eg, repatriation of patients from foreign countries where quality medical care is available), the risks and benefits should be considered. The social benefit of returning patients to their country is treatment in their language near their family and support system. For patients with travel insurance, if the anticipated cost of hospitalization exceeds the cost of air medical transport, insurance companies may prefer to repatriate patients to local health-care systems as soon as possible. Although the apparent benefits often justify the cost of air medical transport (whether paid for by the patient or an insurance company), the potential risks are less clearly defined. The transport of a patient with a recently stabilized coronary syndrome, in a hypoxic environment without possibility of surgical backup, is a potentially hazardous situation that demands rigorous patient selection.

This article aims to review the subject of air medical transport of patients with cardiac disease. The issues to be discussed include the history of air medical transport, the physiology and potential risks of flight, the data available regarding air transport of cardiac patients, the present state of technology available in an air ambulance, and the current guidelines regarding air travel for cardiac patients.

Previous SectionNext SectionHistory of Air Medical Transport
The origins of rotary-wing air medical transportation date back to 1944 when the US military first used helicopters for air medical evacuation of the injured in Burma.2 US military helicopter evacuation dramatically expanded during the Viet

Safety of Air Medical Transport
The safety of air medical transport depends on both aviation and medical aspects. Aviation aspects have been a particular concern with air medical rotary-wing aircraft that have shown a tendency to crash and result in fatal and nonfatal injuries.5 Poor weather was identified as the greatest hazard to emergency medical service helicopter operations in a study by the National Transportation Safety Board published in 1988. Helicopter air ambulance accident rates have since declined considerably.5 The Association of Air Medical Services, an international organization established in 1980, also encourages safety, quality assurance, and quality improvement.18

The medical safety aspects of air transport relate to the stability of a patient’s condition, the potential for exacerbation of that condition by physiologic or physical factors related to air transport, and the quality of technology and medical personnel available. It must also be considered that depending on the type, location, and duration of transport, the delay in making an emergency landing for definitive treatment in a hospital may be substantial. The following review of the literature summarizes the data on the safety of air medical transport of cardiac patients. Data regarding short-distance emergency helicopter transport, long-distance emergency air ambulance transport, long-distance elective commercial transport, and long-distance elective air ambulance transport are discussed separately.

Short-Distance Emergency Helicopter Transport
The majority of data on air medical transportation of cardiac patients come from short-distance emergency helicopter flights. Five major reports describing the air medical transfer of patients early in the course of acute MI19 20 21 22 23 are summarized in Table 1 .

Kaplan et al19 report on 104 patients with suspected acute MI transferred by helicopter for emergency reperfusion within 36 h of symptom onset. While there were no in-flight deaths, in-flight complications (serious hypotension or new arrhythmias requiring treatment) occurred in 13 patients (12%). Physicians were required to exercise medical skill or judgement during 26% of the transports. Similarly, Bellinger et al20 describe 250 patients transported by helicopter within 12 h of onset of symptoms of acute MI for emergent cardiac catheterization. Of the 240 patients who received thrombolytics, 72% had therapy instituted before or in-flight. Complications included hypotension in 25 patients (10%) and arrhythmias in 25 patients (10%). The in-flight arrhythmias consisted of third-degree AV block (eight patients) and nonsustained ventricular tachycardia (seven patients), and did not result in any significant morbidity.

Topol et al21 reported on 150 patients with evolving MI transported by helicopter to a tertiary care institution for acute intervention. No patients died or experienced hemodynamic instability or bleeding complications during transfer. Fifty-five patients received thrombolytic therapy initiated prior to transfer. Arrhythmic complications (ventricular tachycardia and third-degree AV block), although increased in the population receiving thrombolytics, were infrequent (8 of 150 patients) and transient.

Fromm et al22 compared 95 acute MI patients transported by helicopter within 12 h of initiation of thrombolytic therapy to 119 nontransported acute MI patients similarly treated. In-flight complications included medically managed hypotension in 18 patients, but no episodes of cardiac arrest or cardioversion. There was no increase in bleeding complications compared to the nontransported control population. In a study by Spangler et al23 of 192 acute MI patients transferred by helicopter, 110 patients received thrombolytic therapy prior to transfer and the remainder received thrombolytic therapy after transfer. Patients with inferior MI treated with thrombolytics prior to flight were more likely to experience symptomatic bradycardia and hypotension requiring atropine compared to patients treated after the flight, but there was no in-flight mortality in either group.

The first randomized study to suggest outcome benefit from helicopter transport is the recently published Air Primary Angioplasty in Myocardial Infarction Study.24 The study randomized 138 patients with high-risk, acute MI at centers without coronary angioplasty capabilities to either on-site thrombolysis or transfer for primary angioplasty by the most expedient means (air or ground transport). Of the 71 patients transferred, 21% were by helicopter (mean distance, 57 miles) and 79% were by ground ambulance (mean distance, 26 miles). Despite a delay in time from arrival to treatment (155 min vs 51 min), patients randomized to transfer had decreased hospital stay (6.1 days vs 7.5 days, p = 0.015) and 38% reduction (8.4% vs 13.6%, p = 0.331) in major cardiac adverse events (death, reinfarction, or stroke)

Current Guidelines Regarding Air Travel
The current guidelines regarding long-distance flight and cardiac patients are limited to unescorted commercial airline travel. The American College of Cardiology (ACC) and American Heart Association (AHA) recommend that following uncomplicated MI, patients in stable condition (without fear of flying) may travel by air within the first 2 weeks, provided they are accompanied by companions, carry sublingual nitroglycerin, and request airport transportation to avoid rushing.39 Patients who are in unstable condition, are symptomatic, or who experienced a complicated MI (requiring cardiopulmonary resuscitation, experiencing hypotension, serious arrhythmias, high-degree block, or congestive heart failure), are recommended to wait a period of at least 2 weeks following stabilization before commercial air travel. The guidelines of the Aerospace Medical Association (AsMA) state that unescorted commercial airline flight is contraindicated within 3 weeks of uncomplicated MI, within 6 weeks of complicated MI, within 2 weeks of coronary artery bypass surgery, or within 2 weeks of cerebrovascular accident.40 Other cardiovascular contraindications to commercial airline flight include unstable angina, severe decompensated congestive heart failure, uncontrolled hypertension, uncontrolled ventricular or supraventricular tachycardia, Eisenmenger syndrome, and severe symptomatic valvular heart disease. The American Medical Association (AMA) guidelines indicate that travel by commercial aircraft is contraindicated within 4 weeks after MI, within 2 weeks after cerebrovascular accident, and for anyone with severe hypertension or decompensated cardiovascular disease.7 Table 3 summarizes the current guidelines regarding airline travel for patients with cardiac conditions.

With the advent of fixed-wing air ambulances equipped with intensive care facilities, cardiac patients are being transported earlier than these recommendations for unescorted commercial air travel. Although it seems reasonable that patients could be safely transported sooner under these circumstances, there are no established peer reviewed guidelines at present regarding the early transport of hospitalized cardiac patients by fixed-wing air ambulance.

Previous SectionNext SectionConclusions
Elective long-distance air medical transport of cardiac patients occurs with increasing frequency, as a result of medical, economic, and social pressures to return a patient to their country or medical system. Despite the benefits of early air medical repatriation, there are potential risks involved in transporting cardiac patients. These risks are related to the adverse effects of hypoxia and gas expansion at altitude, the effects of anxiety about flying, and the potential for complications related to movement of the patient.

There are data supporting the use of short-distance helicopter flights early in the course of a cardiac event for patients needing emergent transfer for percutaneous coronary intervention or aortocoronary bypass. When considering elective long-distance air medical transport of cardiac patients for social or economic reasons, it is necessary to weigh the benefits against the potential risks of flight. A few studies28 29 30 suggest that elective long-distance air medical transport by commercial airline is safe for patients in stable condition 2 to 3 weeks after MI, particularly when patients are accompanied by a medical escort. Another study31 suggests that, once patients are chest pain free for 48 to 72 h after MI, they may safely undergo elective long-distance air medical transportation with the use of fixed-wing air ambulances.

Modern-day air ambulances have true intensive care capabilities, allowing transport of critically ill patients receiving mechanical ventilation, inotropes, and even intra-aortic balloon pumps. There exists compact technology to analyze blood gases and electrolytes during flight, and all forms of IV medications are at the disposal of the flight physician, allowing for a great deal of flexibility. Thrombolytic therapy, pacing, and defibrillation have been shown to be both effective and safe during flight, and may be used in event that an acute myocardial infarction occurs during transport. Bypass circuits and left ventricular assist devices represent the current extremes of cardiac support during flight, used only by devoted centers with fully trained flight crews. More common usage of such devices during long-distance voyages in the future will certainly depend on rigorous training of flight physicians and support staff.

The current guidelines of the ACC/AHA, AsMA, and AMA concerning air travel after acute MI address unescorted travel by commercial airline only. Although it appears reasonable that patients can be transported earlier with the use of air ambulances, there are no established peer-reviewed guidelines at present regarding the early tra

Words cannot begin to describe my thankfulness to Angel Flight and all who are involved in this charity.

Twelve months ago I was terrified as to the outcome and complexity of getting a liver transplant, not to mention the fact that I had to get from the middle of Michigan to Rochester, Minnesota, in record time. Everything had to be synchronized—from the moment the hospital received the liver to my arrival within two hours.

Well, it’s been three months since I got “the call” from Mayo Clinic saying they had a liver waiting for me! It was pretty emotional for me and my family because there were so many times that we did not know if I would ever have the transplant or be healthy enough to endure the wait. What made it even more divine was the fact that the day they called me was also my birthday. I could not have been given a more perfect gift.

I want to thank you for being an intricate part of my transplant. Angel Flight is all that your name implies and far more. From the pilot who unselfishly donated his time, to the people who took the call to set everything up, this would not have succeeded if it weren’t for their generosity and kindness. Thank you for taking time for another and giving me a second chance at life. May God richly bless Angel Flight…a place in Heaven is reserved just for you!

Before the mid-1980’s, little was known about mitochondrial disease. Patients were likely to be misdiagnosed as having cerebral palsy, Parkinson’s or other disorders.


Such was the case with Emily, a 14-year-old girl from Ellicott City, Md., whose parents were told she had cerebral palsy. Emily, who exhibited symptoms at birth, is fully dependent and unable to walk, eat, or talk.


“Her disorder is in the muscular dystrophy family,” says her mother, Kathy.


Kathy is a former pediatrician who stays home to care for Emily and two other children who also have the illness but with milder symptoms. Kathy herself has mitochondrial disease and says her symptoms include muscle twitches, GI problems, a weakened immune system and allergies.


John, 7, has autism and Crohn’s disease. Kelly, 17, has severe ADHD. Both suffer from muscular problems due to low muscle tone and weakness.


Through advanced research, scientists have learned more about abnormalities in the molecular powerhouse known as the mitochondria, which converts glucose and oxygen into energy.


But due to an inherited condition, the mitochondria can fail, causing cells to lose energy and become damaged and even die.


Last summer Emily was able to take two Angel Flights —first to be evaluated and diagnosed, and then to undergo surgery.


“She seemed to enjoy the flight,” Kathy notes. “The pilots couldn’t have been more wonderful. There was no other way we could have gotten down there.”


Emily suffers from severe scoliosis and, following diagnostic tests, was deemed to be a good candidate for the spinal fusion surgery.


The complex seven-hour surgery required inserting rods and screws in her back.


“She was in the hospital for a week,” her mom says. “She is still on bed rest. It’s a long recovery.”


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Flying High - Nice Heart.

Known as “the silent epidemic” because its symptoms are mild or nonexistent, Hepatitis C is extremely rare in children, with a lower than 1 percent occurrence, compared to up to a 40 percent prevalence in adults.


Like other boys his age, the seventh grader from Johnson City enjoys playing sports. His favorites are soccer, basketball and baseball. He’s also an avid reader. But unlike others, Garrett takes part in a clinical drug trial that produces discomforting flu-like symptoms. He is under the care of Dr. William Balistreri, one of the world’s most foremost authorities on pediatric gastroenterology and liver disease.


As one of some 112 child participants nationwide, Garrett is treated with the drug pegylated interferon along with ribavirin, a regimen currently FDA-approved for adults. He must also travel to see Dr. Balistreri in Cincinnati once a month.


To get to Dr. Balistreri, though, means a long journey from the Volunteer State to the Cincinnati Children’s Hospital Medical Center in Ohio.


At one time, Garrett and his father Tom, a retired Army Veteran who served in both Desert Shield and Desert Storm, made the journey as often as once a week for one month, and then traveled there every three weeks.


To drive or fly that distance so often would be time-consuming and expensive, so Garrett and his father are thankful that Angel Flight® provided the frequent lifts needed to transport them to Cincinnati. Tom said his son was “apprehensive at first” about flying, but that Garrett “is getting used to it,” and that the pilots have been helpful and friendly.


André Hawkins is the Clinical Research Coordinator in the Division of Gastroenterology, Hepatology and Nutrition at the hospital, and he realizes what a huge role Angel Flight plays in Garrett’s treatment. Garrett and other children enrolled in clinical studies “wouldn’t be able to participate otherwise,” notes André.


Angel Flight gets Garrett where he needs to be—and back home again

Doctor

The Atmosphere

The atmosphere is conveniently divided into concentric layers according to the thermal features of each layer.




Characteristics of atmospheric layers

Composition of the Atmosphere

The composition of the atmosphere does not vary to any appreciable extent with altitude. Each component of the atmosphere is diminished to the same extent with altitude. Most small variations present in air at low altitudes are man-caused with an increase in carbon monoxide. The ozone layer screens out harmful levels of ultra-violet radiation.


Gas Approximate
Percent

Oxygen 21

Nitrogen 78

Carbon dioxide 0.03

Neon/Helium/Krypton
Xenon/Hydrogen/Argon } Trace



Troposphere
This is the layer nearest to the earth's surface, throughout which most medical missions will be flown.

The upper boundary of the troposphere depends upon the surface and air temperatures below it. The intensity of the temperature depends upon the axis the earth presents to the sun. Thus the upper boundary is approximately 60,000 ft at the equator and approximately 25,000 ft at the poles.

Characteristics of the Troposphere
Presence of weather and turbulence
Temperature decrease with altitude
Presence of water vapour
Constant composition of the atmosphere
Atmospheric pressure decreases with altitude
Adverse weather and turbulence can be avoided by the ability of an aircraft to fly above the troposphere. There is less strain upon the aircraft and crew and it is more economical on fuel supply.

Temperature falls approximately 2oC for every 1,000 ft of altitude gained (the temperature lapse rate) and continues to do so until the upper limit of the troposphere is reached. The lower the temperature of the air, the less it's capacity for holding water vapour. Thus the capacity decreases with altitude until the tropopause is reached, above which water vapour is essentially absent. This adds to the importance of adequately humidifying therapeutic oxygen when it is administered, since cylinder oxygen is also dry.

Stratosphere
The stratosphere starts at the upper boundary of the troposphere i.e. the tropopause. The upper boundary of the stratosphere was designated at 265,000 ft when it was believed that temperatures were constant to this height. It is now known that above 90,000 ft the temperature increases progressively to 150,000 ft and then decreases to the outer-most boundary of the stratosphere.

Characteristics of the Stratosphere
Weather is absent
No change in temperature with altitude (at those used for aeromedical flights)
Lack of water vapour
Ozone present from 60,000 to 150,000 ft
Atmospheric pressure continues to decrease with altitude
Thermosphere (Ionosphere)
The thermosphere starts at the upper boundary of the stratosphere, i.e. the stratopause. This is from 265,000 ft and extends to 430 miles above the earth. It has a progressive rise in temperature with altitude to almost 2000oC. It is also known as the ionosphere since particles present are ionised.


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Physiology of the Aviation Environment

The influences of the aviation environment upon human physiology has a direct relationship to the physics of mechanical inertia, gravity and the pressure and temperature changes associated with alteration of altitude.

Two major concerns dominate the medical care when altitude is gained:
The partial pressure of oxygen within the alveoli is significantly reduced. This may lead to hypoxia unless it is compensated for by oxygen enrichment therapy.


The volume of gases trapped within body cavities or medical equipment will expand and contract according to altitude.
These problems may be partially overcome by flying at low altitudes where cabin pressure remains close to that on the ground. However, low altitude flying has severe disadvantages in terms of turbulence and adverse weather conditions. Low altitude flying is also more hazardous and accrues decreased aircraft performance, speed and fuel consumption.

It is therefore sometimes preferable to fly a patient at higher altitudes, if necessary in pressurised craft, with adjustments being made to compensate for the apparent altitude. Even in these instances it is still necessary for the patient to experience the changes associated with ascent and descent during take-off and landing.

Gas Expansion

There are two laws of physics with govern the volume of gases and the changes that occur with altitude:

Charles' Law


"At a constant pressure, the volume of a given mass of gas
is directly proportional to its absolute temperature."


i.e. Volume = Constant

Temperature (oK)

In other words, at constant pressure, as temperature increases the volume of a given mass of gas increases. As temperature falls, so the volume of gas decreases.


Boyle's Law


"At a constant temperature, the volume of a given mass of
gas is inversely proportional to the pressure to which it is subjected."


i.e. Pressure x Volume = Constant

In other words, at constant temperature, as pressure increases, the volume of a given mass of gas decreases. As pressure falls, so the volume of the gas increases.

The effects of altitude upon ambient temperature and pressure have been considered. From the known temperatures and pressures at various altitudes, the expected expansion of gases at particular altitudes can be calculated. The gas-volume expansions are only approximate, because of the large number of variables related to local conditions, but they are adequate for the medical flight attendant.


Altitude (ft) Altitude (m) Gas volume

0 0 1.0
5000 1500 1.2
10000 3000 1.5
15000 4500 1.9
18000 5400 2.0
20000 6000 2.4


When the effects of altitude upon closed or semi-closed body cavities are considered, a further factor must be taken into account. The expected fall in partial pressure of water vapour normally associated with increasing altitude does not occur since body cavities maintain a saturated level of water vapour be secretion of moisture from the lining mucosae.

The gases within open cavities such as the open mouth or unobstructed nasopharynx, are free to maintain equilibrium with cabin pressure. There is therefore no danger of excessive positive or negative pressures occurring.

However, a semi-closed cavity has a restricted communication with cabin air that may or may not allow pressure equalisation. This will depend upon the degree of restriction of gases from maintaining an equilibrium, for example the facial sinuses via the ostia, and the middle ear via the eustachian tube. Communications between body cavities and the cabin pressure have the best chance of allowing pressure equalisation to occur when the rate of ascent or descent is not too severe. A closed cavity of course, has no communication with the cabin atmosphere.

When a cavity is semi-closed or closed, changes in pressure within those cavities associated with changes in altitude may be harmful and/or painful if equilibrium with cabin pressure cannot be achieved. The positive pressure or negative pressure (vacuum) that can develop in a semi-closed or closed cavity will also depend upon the rigidity of the cavity wall. The ability to accommodate increases or decreases in volume by expanding or collapsing will reduce the pressure changes associated with changes in gas volume.

Situations where collection of gas can give rise to problems associated with altitude include:

Gas In The Body
Ear and sinus cavities
Pneumothorax
Penetrating eye injuries
Dental cavities
Gastrointestinal conditions
Gas introduced into cavities during diagnostic procedures
Gas introduced into tissues during trauma


Gas in Equipment
Orthopaedic air splints
Pneumatic, anti-shock trousers
Air in intravenous fluid

Flight Attendant

In order to cope with the varied responsibilities and unusual circumstances encountered during aeromedical work, both physical and mental fitness is essential. The work involves a lot of man-handling, during both loading and unloading patients, with awkward manoeuvres and sometimes over difficult terrains. Therefore the attendant must not have any disabilities, either temporary or chronic.

Weight
Excess weight is associated with many physical disorders that may preclude flight duty. It is also important with regard to payload and aircraft balance with movement within the cabin.

Motion Sickness
Despite efforts to avoid turbulent air conditions, some disturbing motion must be anticipated. Even those with the most stable vestibular apparatus and strongest stomachs may experience motion sickness on occasions.

Respiratory Infections
Acute upper respiratory tract infections may possible be damaging to both patients and other crew members. The hazards of blocked sinus ostia and eustachian tubes associated with altitude effects and pressure changes should be considered. If the crew person is unable to clear their ears, during a cold for example, he or she should be temporarily grounded.

Immunisations
Crews whose duties may take them to countries with serious endemic diseases should be up to date with appropriate immunisations. An immunisation record should be carried with the passport.

Drugs and Alchohol
Companies operating aircraft for aeromedical usage must follow regulations regarding the ingestion of medications and alcohol by crew members in the hours prior to flight duty. Restrictions may vary between companies and countries of operations. One should bear in mind the deterioration in performance related to alcohol and drug levels. Flight work is both physically and mentally demanding and the onset of fatigue is hastened. This is compounded by drugs and alcohol. Therefore common-sense should be exercised at all times.

Appearance and Conduct
The flight attendants will by necessity be presenting themselves to patients in the home and hospital environment. They should therefore appear as clean and well groomed professionals. Tobacco and alcohol breath, strong perfumes and aftershaves may be upsetting to patients within the confined aircraft environment.

Communications
Communications with other agencies should be polite and in a professional manner. Where possible correct terms should be utilised as this will reduce confusion, make communications brief and concise, to portray a better image.

Stress
Given that air ambulances are regularly dispatched to the more seriously ill patients, the crew is exposed to a higher degree of work stress. Coupled with this fact must be the noise, smell and vibration factors which can be equally fatiguing. The crew has also to function quickly, accurately, safely and professionally, often under difficult circumstances, be it under the very hot conditions of summer or the wet and cold conditions in the winter. With all these stresses to be considered it is very important that the crew are mentally and physically fit. If a crew member is not fit, safely is jeopardised, patient care is compromised, and crew mates are over-exercised!


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Hypoxia

Hypoxia is the state of oxygen deficiency at the tissue level. This differs from anoxia, which is the state of complete absence of oxygen at the tissue level, which rarely occurs.

Traditionally 4 types of hypoxia have been described:

1. HYPOXIC HYPOXIA - In which the partial pressure of oxygen in the arterial blood is reduced

2. ANAEMIC HYPOXIA - In which the arterial partial pressure of oxygen is normal, but there is reduced amount of haemoglobin to carry the oxygen

3. STAGNANT HYPOXIA - In which the arterial partial pressure of oxygen is normal but the blood flow to the tissues is inadequate to supply sufficient oxygen

4. HISTOTOXIC HYPOXIA - In which the delivery of oxygen to the tissues is adequate but the action of a toxic agent prevents the tissues from utilising the oxygen supply

Except for emergency decompression of the cabin, patients travelling in pressurised aircraft will not have to tolerate cabin altitudes of more than 8000 ft. Some unpressurised flights may have to climb above 8000 ft to traverse mountainous areas. For this reason, the effects of diminished oxygen tension in the atmosphere up to 15000 ft should be appreciated.

Helicopter emergency missions will usually be performed between 1000 - 1500 ft but when necessary, lower altitudes can be utilised.

A patient with a respiratory condition may be rendered with an arterial partial pressure of oxygen (PaO2) of 64 mmHg (8.4kPa) when breathing room air at sea level. This is the same PaO2 to be expected in a healthy individual at approximately 6000 ft altitude, all other conditions being equal. Thus one may consider that this patient has an oxygen status whilst on the ground, equivalent to 6000 ft. The patient may therefore require supplementary oxygen therapy at 6000 ft, equivalent to that required by a physiologically healthy individual at 12000 ft.

The carbon monoxide inhaled by cigarette smokers, reduces the oxygen carrying capacity of the blood, to the extent that the smoker may be considered to be at an equivalent altitude of 2000 ft when at sea level.

The Patient's Equivalent Altitude
When preparing a patient for air transport it is useful to be able to judge the patient's oxygen status in terms of an 'altitude equivalent'.

In order for the value of the altitude equivalent to be of use, one must take into account whether or not it was calculated whilst the patient was receiving any ventilatory support to improve the oxygen status, such as mechanical assistance or therapeutic oxygen. The height of the patient above sea level when the estimate was made, and how long the patient has been at that altitude must also be considered.

In order to make an accurate calculation of a patient's 'altitude equivalent' it is necessary to know their PaO2. Apart from a proportion of patients who are undergoing aeromedical interhospital transfers, the majority of patients have an unknown PaO2.

Two methods can be used to estimate the altitude equivalent of an hypoxic patient. The first involves relating the patient's cerebral function to the changes that are known to occur with healthy individuals at altitudes. This will not take into account any cerebral deficiencies the patient may have due to factors other than hypoxia.

The second method involves a diagnostic oxygen challenge. Physical examination of the patient with regard to skin and mucous membranes, pulse and blood pressure and peripheral circulation, degree of breathlessness and oxygen saturation will give some indication of the degree of hypoxia present. If oxygen is provided in increasing concentrations until the majority of signs indicating hypoxia have disappeared, the minimum percentage of oxygen required can be related to the range of altitude where that percent of oxygen is required to compensate for hypoxia.

The point of working out the patient's equivalent altitude is that it will provide some indication of the degree of supplemented oxygen required at those altitudes to be experienced. It will become obvious which patients will require IPPV assistance in order to cope with the planned altitudes.

Oxygenation

Partial Pressures
If a vessel is occupied by more than one gas, the total pressure exerted is the sum of the pressures exerted independently by each gas. Each gas exerts a PARTIAL PRESSURE.

Dalton's Law
The maximum pressure exerted by a vapour in a closed space at a given temperature, depends only on that temperature and is independent of the pressure of other vapours or gases (provided they have no chemical action upon it).


When several vapours of gases (having no chemical action upon each other) are present in the same space, the pressure exerted by the mixture is the sum of the pressures that would be exerted by each of its constituents if separately confined within the same space.
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Physiological Effects of Hypoxia Secondary to Altitude
Before compensatory increases in ventilation come to have any effect, the reduced oxygen tension of altitude produces symptoms. Early symptoms may be mild and may be missed if there is a rapid rate of ascent. The symptoms related to hypoxia with altitude are described below with the associated O2 saturation to be expected at each altitude.

18000 - 20000 ft
(02 sat > 70%) Unconsciousness occurs with minimal warning but sometimes preceded by anoxic convulsions. Death will assume if O2 support is not provided or aircraft does not return to lower altitude.

16000 - 18000 ft
(02 sat > 72%) Severe handicaps. Unable to perform flying duties or attend to others. Physical effort precipitates coma.

14000 - 16000 ft
(02 sat > 80%) Deterioration in neuromuscular control. Psychomotor performance becomes unreliable. Slow thought processing. Emotional states may manifest similar to those exhibited with alcoholic intoxication. Light-headedness. Severe headaches. Paraesthesiae interfering with touch and grasp sensation. Physical exertion may provoke syncope.

10000 - 14000 ft
(02 sat > 85%) Loss of critical judgement, unreliability of mental calculations. Diminished ability to concentrate on particular tasks. Severe fatigue. Euphoria may mask these effects from the subject making them oblivious to the above handicaps.

8000 - 10000 ft
(02 sat > 90%) Reduced mental and physical abilities. Day vision may be impaired. Headaches and fatigue may occur.

5000 - 8000 ft
(02 sat > 92%) Ability to perform skilled tasks impaired. Reduced capacity to perform physical tasks. Fatigue may occur.

4000 - 5000 ft
(02 sat > 95%) Diminished night vision. A resting subject performing minor mental tasks may show no change in performance. The ability to perform mental tasks may be impaired.

SEA LEVEL - 4000 ft
(02 sat > 93%) No hypoxia symptoms.

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These factors are especially important during patient transport by jet aircraft, of less import in slower aircraft and may be negligible in helicopter operations.

Tradition
When patients are moved horizontally they are traditionally moved longitudinally. This applies to patient movements within hospital and by road ambulances. If road ambulances were able to accommodate patient stretchers in a sideways orientation, although the effects of acceleratory forces in the direction of travel would be minimised, severe cornering would produce centrifugal forces deleterious to the patient.

Cross-Plane Orientation
Placement of the patient across the cabin instead of fore and aft has some advantages. The effects of the forces resulting from acceleration and deceleration no longer act along the longitudinal axis of the patient and are therefore less detrimental to the vital functioning of the body. When an aircraft makes a standard turn, it converts much of the centrifugal force to one acting downward in relationship to the floor of the aircraft. This reduces shifts of body fluids in a head-foot direction when the patient is orientated cross-plane. In this respect the skill of the pilot has a direct influence upon the patient. These effects upon the physiology of patients carried by helicopters are minimal since the forces involved are much smaller.

Attitude of Aircraft
The dominant attitude of fixed wing aircraft is nose up on ascent and landing. A plane does not always follow it's nose when on a downward path except when diving. Normal descents involve the maintenance of a near-horizontal attitude. The final glide is usually nose up until the landing wheels make ground contact and the nose wheel has landed. Aircraft with tail wheels maintain a nose-up attitude. Much finer control is possible during take-off, cruising and landing in helicopter operations. Essentially the patient's stretcher is in a horizontal position when the helicopter is on level ground. Take-off and landing may produce a nose-down attitude of between 5o and 20o but with careful manoeuvring this can be achieved in a near-horizontal attitude. In flight, normal cruising will produce approximately a 5o nose-down attitude.

Medical Conditions
Any alteration in the attitude of the aircraft will be translated to the patient in terms of a head-up or head-down tilt. This disposition may be important in certain clinical conditions. For example it is often desirable to avoid a head-down tilt in patients with cardiac conditions. Conversely, patients with raised intracranial pressure should ideally be placed with a small degree of head-up tilt.


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