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Blast injuries: A case report
Blast Injuries: A Case Report Erik J. Usher, RN, CEN, EMS-RN, NREMT-P, CFRN
In the past, blast injuries were associated strictly with war and catastrophic industrial accidents. Unfortunately, these injuries are on the front lines of each ED and EMS system in the form of pipe bombs and terrorist plots. Domestically and internationally, the incidence of blast injuries is sporadic and infrequent. The injuries often are the result of fireworks—10,000-12,000 ED visits annually for this reason.1 What does this trend mean for the air medical transport industry? We need to be aware of the multiple sequelae of blast injuries other than just the obvious. It also means we need to be cognizant of the safety aspect of a potentially volatile explosive in the aircraft.
Case Report On December 31, 1999, late in the evening, Airlife 7 was dispatched to a rural ED approximately 100 nautical miles from University Medical Center in Las Vegas, the nearest Level I trauma center. Our patient was a 55-year-old man who was in the process of making explosives when one detonated in his shed. He was thrown across the room, struck a wall, and briefly loss consciousness. Local EMS rapidly transported the patient in full cervical spine precautions to the nearest ED, where he was evaluated and stabilized for transport. Initial ED evaluation cleared the spine and chest radiographically. Concurrent resuscitation involved intravenous administration of normal saline to a total of 5 L and liberal analgesia with a total of 100 mg of intravenous morphine sulfate. We were dispatched approximately 2 hours after the accident with a flight time of 58 minutes. On our arrival, the patient was awake, alert, and oriented, talking in full sentences with no airway compromise. Vital signs were BP 158/98, RR 24, HR 118, and an SaO2 of 99% on 15 L/min O2. Although the primary survey was unremarkable, during further examination, we noted this patient sustained several firstdegree burns to the face, including circumoral erythema. He was reported to have an open globe injury to the left eye that the flight crew had not seen because of heavy sterile dressings. The left tympanic membrane also was ruptured. The anterior aspect of the chest and abdomen had multiple avulsed areas, each measuring approximately 0.5-1.0 cm in length and width and presumably caused by shrapnel, none of which entered the pleural or abdominal cavity. Both hands, macerated beyond repair, were amputated at the radial/ulnar-metacarpal junction, and sterile pressure wraps were securely placed by a local orthopedic surgeon. While preparing the patient for transport, we interviewed his wife regarding the circumstances surrounding the accident. She said the patient was in an enclosed shed for approximately 40
15 minutes after the explosion. When she opened the door, she noted “a lot of smoke.” High flow oxygen was continued as our team began the flight back to Las Vegas. The return flight forced us to reach an altitude of approximately 9800 feet to clear the local topography. At this point, the patient became acutely restless with a rapid deterioration in both respiratory and neurologic status. His Glasgow Coma Score deteriorated from a 15 to 3 with an intermittent gag reflex. He was hyperventilated with a bag/valve/mask and successfully orally intubated with the aid of etomidate 20 mg intravenously. After intubation, hypotension persisted despite fluid therapy, so we began intravenous dopamine at 7 mcg/kg/min with an increase blood pressure from 60/doppler to 110/68. Neurologic status improved after approximately 10 minutes in the trauma center, requiring paralytics. Follow-up radiographs at the trauma center demonstrated free air in the abdomen and a pulmonary contusion. Surgical evaluation revealed a ruptured small bowel. The patient’s hands, eye, and small bowel all were repaired surgically. He was extubated on day 3 and discharged with physical therapy and surgical follow-up.
Discussion Blast injuries carry a myriad of occult injuries. Surgical exploration may reveal injuries far worse than external evaluation presents. Blast injuries have three phases:2 • Heat and light reach the victim. • A pressure wave compresses body parts and knocks the victim to the ground. • Falling debris can become missiles that produce injury. These phases produce different types of injuries, denoted as primary, secondary, tertiary, and miscellaneous. The pressure wave generally is the cause of primary injuries,
Airlife of Las Vegas, Nevada, division of Mercy Air Service, Inc. Address for correspondence: Erik J. Usher, 12998 S. Las Vegas Blvd., Las Vegas, NV 89124 Key words: miscellaneous injuries, primary injuries, secondary injuries, tertiary injuries Copyright © 2001 by Air Medical Journal Associates 1067-991X/2001/$35.00 + 0 Reprint no. 74/1/118328 doi:10.1067/mmj.2001.118328
Air Medical Journal 20:5
affecting hollow gas-containing organs, such as the lungs and gastrointestinal (GI) tract.2 If we imagine the human body as a semirigid container being rapidly compressed by a pressure wave, we can make an educated guess at what type of injuries can be sustained. Ruptured tympanic membranes, ruptured globes, pulmonary contusions, pneumothoraces, ruptured bowels, and even central nervous system involvement may be seen. Primary injuries tend to be the most deadly because of their tendency to be present without any outward clues. Pulmonary manifestations should be of the utmost priority because these organs are most seriously affected by the blast and cause the most immediate threat to life.3 The blast causes widespread alveolar damage because of its effects on tissue-gas interfaces, producing interstitial and intra-alveolar hemorrhage and edema, parenchymal and pleural lacerations, and alveolarvenous fistulas.3 Central neurologic manifestations are of two main types. First are the shock wave effects, which produce a concussion syndrome and various types of intra- and extra-axial hemorrhage, and second are the effects of cerebral air embolism. As with dysbaric diving casualties, the specific neurologic manifestation of air embolism are myriad.3 Secondary injuries are caused by flying debris and direct explosive forces.2 These injuries tend to be the most visually impressive and most focused on because of their obvious nature. These injuries include lacerations, fractures, and burns.2 Tertiary injuries are essentially deceleration and blunt trauma wounds caused by the patient being thrown. These injuries also are visually impressive and equal to that of an ejected automobile occupant. Miscellaneous injuries encompass all those related to the blast, including but not limited to toxic inhalations, radiation exposure, asphyxiation from carbon monoxide (CO) and cyanide (CN), and any crush injuries from falling architecture.1 It is important for the prehospital provider to ascertain whether the explosion occurred in an enclosed space and whether the patient requires any decontamination or special isolation from miscellaneous injuries incurred at the scene. It is possible for the detonation to have released radiation or volatile chemicals from either an industrial accident or terrorist act. This contamination is of special consideration for air transport to decide if the chemicals could react to the jet-A fuel or oxygen that can create a second and equally devastating disaster. It is important to determine whether either of the tympanic membranes has ruptured.1 Lavonas’ studies note a close correlation between the presence of ruptured tympanic membranes and devastating pulmonary and GI injuries.1 Every emergency situation can be complicated by specialty patients. One particular subgroup is the obstetric patient, particularly in the second and third trimester. Although the fetus is in relatively little jeopardy from the primary injury because of the surrounding incompressible amniotic fluid, the uterine placental junction is at high risk for abruption and sheering as a result of the effect known as spalling.1 Spalling is denoted as a blast wave moving from a medium to high density (endometrial muscle) to that of a lower density (placenta) with subsequent damage at their interface.1 September-October 2001
Putting it All Together This case touches on a number of pathologies. Most of these injuries were related in one way or another to the blast, but several cascading events were directly related to alterations in physiology as a result of increased altitude. Because altitude physiology is the foundation of aviation medicine, it is always beneficial to reiterate the problems associated with increased altitude. This patient rapidly decompensated at approximately 9800 feet. This problem is best presented by reviewing the gas laws relative to this patient’s symptomatology. Boyle’s Law states that, at a constant temperature, a given volume of gas is inversely proportional to the pressure surrounding the gas. Translation: as altitude increases, barometric pressure decreases, gas in an enclosed space expands, and as altitude decreases, pressure increases and gas compresses.4 In this patient, the expanding gas in both his GI tract and residual respiratory volume increased intrathoracic pressure. This increase compressed the vena cava, which decreased preload and therefore fostered hypotension. The residual intraalveolar air expanded and subsequently decreased tidal volume, adding to hypoxia. The effects of Boyle’s Law can be minimized by inserting nasogastric tubes to decompress GI air and watching peak pressures with intubated patients and changing ventilator settings as warranted. Another consideration is to fly at lower altitudes with patients at risk, as long as terrain allows and safety is not compromised. Dalton’s Law says the pressure of a gaseous mixture is equal to the sum of the partial pressure of the gasses in that mixture.4 Translation: this describes the pressure exerted by a gas at various altitudes, with each gas present in the atmosphere contributing to the total atmospheric pressure. For example: the atmosphere is composed of: • Oxygen 20.95%, 159.22 mmHg • Nitrogen 78.08%, 593.408 mmHg • Other gasses 1%, 7 mmHg • Argon • Carbon monoxide • Hydrogen • Neon • Helium This combination equals a total atmospheric pressure of 760 mmHg and 100% at sea level.5 As altitude increases, gases exert less pressure, but the concentration of gases remain the same. At 18,000 feet, oxygen is still 21% but now only 80 mmHg. Nitrogen is still 78% but now only 296 mmHg; other gases are at 1% and still 7 mmHg, equaling 380 mmHg but still 100%. As altitude increases and barometric pressure decreases, gas expansion causes the available oxygen to decrease as gas molecules move farther apart. The result of this pressure change is hypoxia. This patient suffered the same effect that all people do at certain altitudes—hypoxia. This change happens to every person in the aircraft, although it is more prominent with concurrent injuries. The effects of Dalton’s Law may be minimized in several ways. The application of supplemental oxygen will increase the relative percentage of available oxygen. If safety and terrain 41
allow, a lower maximum altitude can minimize the effect, and a pressurized aircraft can alleviate the problem. Henry’s Law states that the amount of gas in a solution is proportional to the partial pressure of that gas over the solution.6 Translation: this law deals with gases dissolved in a liquid. An example of this law is a bottle of soda pop. With the cap on, the gases above the liquid create an equilibrium with the gases dissolved in the liquid. Removing the cap causes a pressure decrease in the gas above the liquid and allows the gas bubbles within the liquid to be released. If the bottle is shaken before removing the cap, the gas bubbles are removed much quicker.5 One clinical example of this phenomenon is decompression sickness or “the bends.” In this case nitrogen bubbles form in the blood and can settle in pulmonary vessels, joint spaces, and occasionally in portions of the central nervous system. This law usually is reserved for the patient being transported by air after diving within 24 hours. A scuba diver’s body absorbs nitrogen at a much greater rate at depth, and it takes time for this absorbed gas to be blown off. The problem is if an individual flies at an altitude of 8000 feet within 24 hours after diving, it would be like a nondiver flying at 40,000 feet—unpressurized! Charles’ Law deems that, at a constant pressure, the volume of a given gas is directly proportional to the absolute temperature of that gas.4 Translation: if the pressure of a gas remains constant, the volume will vary directly with the temperature. It is also important to note that, for each 1000 feet gained in altitude, the temperature decreases by 2° C. This patient also was subject to the effects of Charles’ Law. As we gained altitude, the temperature ambiently fell almost 14° C and therefore was subject to a slight decrease in barometric pressure. This accounted for a slight decrease in the size of trapped air molecules and a minor counter effects of Boyle’s Law. One way to combat the effects of Charles’ Law is to increase ambient heat and maintain the patient’s thermoregulation.
42
Graham’s Law says the rate of diffusion of a gas through a liquid medium is directly related to the solubility of the gas and is inversely proportional to the square root of its density or gram molecular weight.6 Translation: gas exchanges at a cellular level, with CO being 19 times more diffusible than oxygen. This, in combination with all the other laws associated with altitude physiology, may have pushed our patient to the point of respiratory failure. He also was in an enclosed smoky space for approximately 15 minutes, breathing CO, which is more diffusible than oxygen, and therefore relative hypoxia is already present with CO poisoning. In this case, the application of supplemental oxygen will benefit the patient and reduce the effects of Graham’s Law.
Conclusion High-energy blast injuries are becoming a more common occurrence in the modern ED and prehospital setting. It behooves EMS practitioners to familiarize themselves with the plethora of injuries associated with such catastrophic events. In addition to the kinematics involved, practitioners also should become familiar with the compounds and dangers associated with the manufacture of these incendiary devices.
References 1. Lavonas E. Blast injuries. EMEDICINE home page, 1999. Available from: www.edmedicine.com. 2. Merrick C, Goldberg R, editors. PHTLS basic and advanced pre-hospital trauma life support. 3rd ed. St. Louis: Mosby-Year Book, Inc.; 1994. 3. Tintinalli J, Ruiz E, Krome R, editors. Emergency medicine: a comprehensive study guide. 4th ed. New York: McGraw-Hill; 1996. 4. Ernsting J, Sharp GR, editors. The Earth’s atmosphere. In: Sharp GR, editor. Aviation medicine. London: Trimed Books Ltd.; 1978. 5. Samuels D, Bock, Campbell P, Merrill N, Chew Jr. J. Air medical crew national standard curriculum. Pasadena: ASHBEAMS; 1988. 6. Egan DF, et al. Gases, the atmosphere and the gas laws. In: Scanken CL, Egan DF, Wilkins RL, editors. Egan’s fundamentals of respiratory therapy. St. Louis: CV Mosby Co.; 1982.
Air Medical Journal 20:5
In the past, blast injuries were associated strictly with war and catastrophic industrial accidents. Unfortunately, these injuries are on the front lines of each ED and EMS system in the form of pipe bombs and terrorist plots. Domestically and internationally, the incidence of blast injuries is sporadic and infrequent. The injuries often are the result of fireworks—10,000-12,000 ED visits annually for this reason.1 What does this trend mean for the air medical transport industry? We need to be aware of the multiple sequelae of blast injuries other than just the obvious. It also means we need to be cognizant of the safety aspect of a potentially volatile explosive in the aircraft.
Case Report On December 31, 1999, late in the evening, Airlife 7 was dispatched to a rural ED approximately 100 nautical miles from University Medical Center in Las Vegas, the nearest Level I trauma center. Our patient was a 55-year-old man who was in the process of making explosives when one detonated in his shed. He was thrown across the room, struck a wall, and briefly loss consciousness. Local EMS rapidly transported the patient in full cervical spine precautions to the nearest ED, where he was evaluated and stabilized for transport. Initial ED evaluation cleared the spine and chest radiographically. Concurrent resuscitation involved intravenous administration of normal saline to a total of 5 L and liberal analgesia with a total of 100 mg of intravenous morphine sulfate. We were dispatched approximately 2 hours after the accident with a flight time of 58 minutes. On our arrival, the patient was awake, alert, and oriented, talking in full sentences with no airway compromise. Vital signs were BP 158/98, RR 24, HR 118, and an SaO2 of 99% on 15 L/min O2. Although the primary survey was unremarkable, during further examination, we noted this patient sustained several firstdegree burns to the face, including circumoral erythema. He was reported to have an open globe injury to the left eye that the flight crew had not seen because of heavy sterile dressings. The left tympanic membrane also was ruptured. The anterior aspect of the chest and abdomen had multiple avulsed areas, each measuring approximately 0.5-1.0 cm in length and width and presumably caused by shrapnel, none of which entered the pleural or abdominal cavity. Both hands, macerated beyond repair, were amputated at the radial/ulnar-metacarpal junction, and sterile pressure wraps were securely placed by a local orthopedic surgeon. While preparing the patient for transport, we interviewed his wife regarding the circumstances surrounding the accident. She said the patient was in an enclosed shed for approximately 40
15 minutes after the explosion. When she opened the door, she noted “a lot of smoke.” High flow oxygen was continued as our team began the flight back to Las Vegas. The return flight forced us to reach an altitude of approximately 9800 feet to clear the local topography. At this point, the patient became acutely restless with a rapid deterioration in both respiratory and neurologic status. His Glasgow Coma Score deteriorated from a 15 to 3 with an intermittent gag reflex. He was hyperventilated with a bag/valve/mask and successfully orally intubated with the aid of etomidate 20 mg intravenously. After intubation, hypotension persisted despite fluid therapy, so we began intravenous dopamine at 7 mcg/kg/min with an increase blood pressure from 60/doppler to 110/68. Neurologic status improved after approximately 10 minutes in the trauma center, requiring paralytics. Follow-up radiographs at the trauma center demonstrated free air in the abdomen and a pulmonary contusion. Surgical evaluation revealed a ruptured small bowel. The patient’s hands, eye, and small bowel all were repaired surgically. He was extubated on day 3 and discharged with physical therapy and surgical follow-up.
Discussion Blast injuries carry a myriad of occult injuries. Surgical exploration may reveal injuries far worse than external evaluation presents. Blast injuries have three phases:2 • Heat and light reach the victim. • A pressure wave compresses body parts and knocks the victim to the ground. • Falling debris can become missiles that produce injury. These phases produce different types of injuries, denoted as primary, secondary, tertiary, and miscellaneous. The pressure wave generally is the cause of primary injuries,
Airlife of Las Vegas, Nevada, division of Mercy Air Service, Inc. Address for correspondence: Erik J. Usher, 12998 S. Las Vegas Blvd., Las Vegas, NV 89124 Key words: miscellaneous injuries, primary injuries, secondary injuries, tertiary injuries Copyright © 2001 by Air Medical Journal Associates 1067-991X/2001/$35.00 + 0 Reprint no. 74/1/118328 doi:10.1067/mmj.2001.118328
Air Medical Journal 20:5
affecting hollow gas-containing organs, such as the lungs and gastrointestinal (GI) tract.2 If we imagine the human body as a semirigid container being rapidly compressed by a pressure wave, we can make an educated guess at what type of injuries can be sustained. Ruptured tympanic membranes, ruptured globes, pulmonary contusions, pneumothoraces, ruptured bowels, and even central nervous system involvement may be seen. Primary injuries tend to be the most deadly because of their tendency to be present without any outward clues. Pulmonary manifestations should be of the utmost priority because these organs are most seriously affected by the blast and cause the most immediate threat to life.3 The blast causes widespread alveolar damage because of its effects on tissue-gas interfaces, producing interstitial and intra-alveolar hemorrhage and edema, parenchymal and pleural lacerations, and alveolarvenous fistulas.3 Central neurologic manifestations are of two main types. First are the shock wave effects, which produce a concussion syndrome and various types of intra- and extra-axial hemorrhage, and second are the effects of cerebral air embolism. As with dysbaric diving casualties, the specific neurologic manifestation of air embolism are myriad.3 Secondary injuries are caused by flying debris and direct explosive forces.2 These injuries tend to be the most visually impressive and most focused on because of their obvious nature. These injuries include lacerations, fractures, and burns.2 Tertiary injuries are essentially deceleration and blunt trauma wounds caused by the patient being thrown. These injuries also are visually impressive and equal to that of an ejected automobile occupant. Miscellaneous injuries encompass all those related to the blast, including but not limited to toxic inhalations, radiation exposure, asphyxiation from carbon monoxide (CO) and cyanide (CN), and any crush injuries from falling architecture.1 It is important for the prehospital provider to ascertain whether the explosion occurred in an enclosed space and whether the patient requires any decontamination or special isolation from miscellaneous injuries incurred at the scene. It is possible for the detonation to have released radiation or volatile chemicals from either an industrial accident or terrorist act. This contamination is of special consideration for air transport to decide if the chemicals could react to the jet-A fuel or oxygen that can create a second and equally devastating disaster. It is important to determine whether either of the tympanic membranes has ruptured.1 Lavonas’ studies note a close correlation between the presence of ruptured tympanic membranes and devastating pulmonary and GI injuries.1 Every emergency situation can be complicated by specialty patients. One particular subgroup is the obstetric patient, particularly in the second and third trimester. Although the fetus is in relatively little jeopardy from the primary injury because of the surrounding incompressible amniotic fluid, the uterine placental junction is at high risk for abruption and sheering as a result of the effect known as spalling.1 Spalling is denoted as a blast wave moving from a medium to high density (endometrial muscle) to that of a lower density (placenta) with subsequent damage at their interface.1 September-October 2001
Putting it All Together This case touches on a number of pathologies. Most of these injuries were related in one way or another to the blast, but several cascading events were directly related to alterations in physiology as a result of increased altitude. Because altitude physiology is the foundation of aviation medicine, it is always beneficial to reiterate the problems associated with increased altitude. This patient rapidly decompensated at approximately 9800 feet. This problem is best presented by reviewing the gas laws relative to this patient’s symptomatology. Boyle’s Law states that, at a constant temperature, a given volume of gas is inversely proportional to the pressure surrounding the gas. Translation: as altitude increases, barometric pressure decreases, gas in an enclosed space expands, and as altitude decreases, pressure increases and gas compresses.4 In this patient, the expanding gas in both his GI tract and residual respiratory volume increased intrathoracic pressure. This increase compressed the vena cava, which decreased preload and therefore fostered hypotension. The residual intraalveolar air expanded and subsequently decreased tidal volume, adding to hypoxia. The effects of Boyle’s Law can be minimized by inserting nasogastric tubes to decompress GI air and watching peak pressures with intubated patients and changing ventilator settings as warranted. Another consideration is to fly at lower altitudes with patients at risk, as long as terrain allows and safety is not compromised. Dalton’s Law says the pressure of a gaseous mixture is equal to the sum of the partial pressure of the gasses in that mixture.4 Translation: this describes the pressure exerted by a gas at various altitudes, with each gas present in the atmosphere contributing to the total atmospheric pressure. For example: the atmosphere is composed of: • Oxygen 20.95%, 159.22 mmHg • Nitrogen 78.08%, 593.408 mmHg • Other gasses 1%, 7 mmHg • Argon • Carbon monoxide • Hydrogen • Neon • Helium This combination equals a total atmospheric pressure of 760 mmHg and 100% at sea level.5 As altitude increases, gases exert less pressure, but the concentration of gases remain the same. At 18,000 feet, oxygen is still 21% but now only 80 mmHg. Nitrogen is still 78% but now only 296 mmHg; other gases are at 1% and still 7 mmHg, equaling 380 mmHg but still 100%. As altitude increases and barometric pressure decreases, gas expansion causes the available oxygen to decrease as gas molecules move farther apart. The result of this pressure change is hypoxia. This patient suffered the same effect that all people do at certain altitudes—hypoxia. This change happens to every person in the aircraft, although it is more prominent with concurrent injuries. The effects of Dalton’s Law may be minimized in several ways. The application of supplemental oxygen will increase the relative percentage of available oxygen. If safety and terrain 41
allow, a lower maximum altitude can minimize the effect, and a pressurized aircraft can alleviate the problem. Henry’s Law states that the amount of gas in a solution is proportional to the partial pressure of that gas over the solution.6 Translation: this law deals with gases dissolved in a liquid. An example of this law is a bottle of soda pop. With the cap on, the gases above the liquid create an equilibrium with the gases dissolved in the liquid. Removing the cap causes a pressure decrease in the gas above the liquid and allows the gas bubbles within the liquid to be released. If the bottle is shaken before removing the cap, the gas bubbles are removed much quicker.5 One clinical example of this phenomenon is decompression sickness or “the bends.” In this case nitrogen bubbles form in the blood and can settle in pulmonary vessels, joint spaces, and occasionally in portions of the central nervous system. This law usually is reserved for the patient being transported by air after diving within 24 hours. A scuba diver’s body absorbs nitrogen at a much greater rate at depth, and it takes time for this absorbed gas to be blown off. The problem is if an individual flies at an altitude of 8000 feet within 24 hours after diving, it would be like a nondiver flying at 40,000 feet—unpressurized! Charles’ Law deems that, at a constant pressure, the volume of a given gas is directly proportional to the absolute temperature of that gas.4 Translation: if the pressure of a gas remains constant, the volume will vary directly with the temperature. It is also important to note that, for each 1000 feet gained in altitude, the temperature decreases by 2° C. This patient also was subject to the effects of Charles’ Law. As we gained altitude, the temperature ambiently fell almost 14° C and therefore was subject to a slight decrease in barometric pressure. This accounted for a slight decrease in the size of trapped air molecules and a minor counter effects of Boyle’s Law. One way to combat the effects of Charles’ Law is to increase ambient heat and maintain the patient’s thermoregulation.
42
Graham’s Law says the rate of diffusion of a gas through a liquid medium is directly related to the solubility of the gas and is inversely proportional to the square root of its density or gram molecular weight.6 Translation: gas exchanges at a cellular level, with CO being 19 times more diffusible than oxygen. This, in combination with all the other laws associated with altitude physiology, may have pushed our patient to the point of respiratory failure. He also was in an enclosed smoky space for approximately 15 minutes, breathing CO, which is more diffusible than oxygen, and therefore relative hypoxia is already present with CO poisoning. In this case, the application of supplemental oxygen will benefit the patient and reduce the effects of Graham’s Law.
Conclusion High-energy blast injuries are becoming a more common occurrence in the modern ED and prehospital setting. It behooves EMS practitioners to familiarize themselves with the plethora of injuries associated with such catastrophic events. In addition to the kinematics involved, practitioners also should become familiar with the compounds and dangers associated with the manufacture of these incendiary devices.
References 1. Lavonas E. Blast injuries. EMEDICINE home page, 1999. Available from: www.edmedicine.com. 2. Merrick C, Goldberg R, editors. PHTLS basic and advanced pre-hospital trauma life support. 3rd ed. St. Louis: Mosby-Year Book, Inc.; 1994. 3. Tintinalli J, Ruiz E, Krome R, editors. Emergency medicine: a comprehensive study guide. 4th ed. New York: McGraw-Hill; 1996. 4. Ernsting J, Sharp GR, editors. The Earth’s atmosphere. In: Sharp GR, editor. Aviation medicine. London: Trimed Books Ltd.; 1978. 5. Samuels D, Bock, Campbell P, Merrill N, Chew Jr. J. Air medical crew national standard curriculum. Pasadena: ASHBEAMS; 1988. 6. Egan DF, et al. Gases, the atmosphere and the gas laws. In: Scanken CL, Egan DF, Wilkins RL, editors. Egan’s fundamentals of respiratory therapy. St. Louis: CV Mosby Co.; 1982.
Air Medical Journal 20:5