![]() These open during yawning or swallowing, or during Valsalva maneuvers (forcing positive pressure to open the eustachian tube by blowing against a closed nasopharynx). The Eustachian tube helps equilibrate the pressure in the middle ear with the external atmosphere via the levator and tensor veli palati muscles. Posterior to this is an ossicular structure that remains open. The anterior aspect is a mucosa-lined structure adjacent to the nasopharynx that is flat at rest. This anatomy further divides into two separate parts. The middle ear begins behind the tympanic membrane (TM) and communicates via the eustachian tube with the nasopharynx. The middle and inner ear are air-filled spaces that are essential for both hearing and spatial orientation. Such areas include the inner ear, lungs (specifically relative to pneumothoraces), and potentially any air-filled instruments like a balloon cuff on an endotracheal tube (ET). The increase in the volume occupied by gas at higher altitudes can have adverse effects on various body sites sensitive to changes in air volume and pressure. An understanding of flight physiology is essential, as even an increase of 1000 to 1500 feet above sea level can cause gas expansion leading to clinical significance in the critically ill. Additional physiological factors of high altitude transport, the details of which are beyond the scope of this discussion, include decreasing temperatures, dehydration, and gravitational forces.Ī typical helicopter pre-hospital transport reaches altitudes of 1000 to 3500 feet above ground level, while airplane transport typically transports at altitudes of 10000 to 40000 ft above sea level. In-flight hypoxia as altitude increases can have a marked clinical significance in the transport of the critically ill. One report demonstrated a decrease of 32 mm Hg, from 159 at sea level to 127 at the height of 6200 feet. Īnother physiological factor that changes with altitude is the decrease in the partial pressure of oxygen as height above sea level increases this leads to a reduction in FiO2 (fraction of inspired oxygen) at a higher altitude compared to sea level. Fortunately, acceptable cabin altitude levels, or the atmospheric height experienced inside a flight cabin, have been safely increased over time due to aircraft and technologic improvements. This setting is possible through in-cabin pressurization, thereby decreasing barotraumatic risks that would be in effect at higher altitudes. Federal regulations, such as those promulgated by the FAA, require cabin pressure to be below atmospheric pressure equal to the pressure at 8000 feet above sea level. These physiological factors affect both helicopter pre-hospital transport and aeromedical airplane transport. These changes are demonstrated by the fact that atmospheric pressure at 10000 feet is 10.1 pounds per square inch (psi) (68 kPa), compared to 14.7 psi (101 kPa) at ground level. Boyle’s law explains that “the volume of a gas is inversely proportional to the pressure to which it is subjected.” Based on this law, pressure decreases with increased altitude, thereby causing an increase in the volume of gas. An understanding of flight and altitude physiology is essential to prevent pre-hospital fight-induced barotrauma. Known triggers of urticaria should be avoided.Physiologic parameters at high altitudes vary from those at sea level. Doxepin, calcium channel blockers, or immunosuppresive drugs may be needed for symptoms that are not well controlled with antihistamines. Patients should avoid identified allergens. The use of both H 1 and H 2 receptor blockers has been recommended but has not been proven more effective. Treatmentĭrugs that block histamine-1 (H 1) receptors (antihistamines) are the primary treatment for urticaria. Angioedema is frequently associated with urticaria. It affects people of all ages but is most common between the ages 20 and 40. Urticaria is a primary sign of local and systemic anaphylactic reactions. The mast cell degranulation is due to an immunoglobulin E–mediated reaction to allergens (e.g., foods, drugs, or drug additives), heat, cold, and, rarely, infections or emotions. ![]() Urticaria is caused by vasodilation and increased permeability of capillaries of the skin due to the release by mast cells of vasoactive mediators. Synonym: hives See: illustration allergy angioedema Etiology The wheals appear primarily on the chest, back, extremities, face, or scalp. ![]() An allergic reaction marked by multiple discrete swellings on the skin (wheals) that are intensely itchy and last up to 24 hr.
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