CCP 105 Fundamentals of Aero Medical Transport Flashcards
Hypoxic hypoxia
“pure hypoxia” occurs as a result of insufficient oxygen available to the lungs
could occur because inspired PO2 is lower than normal (high altitude) or it could be due to a respiratory problem (hypoventilation, diffusion impairment, V/Q mismatch, R to L shunt)
Histotoxic hypoxia
↓ in ATP production by the mitochondria due to a defect in the cellular usage of oxygen → the inability of cells to take up or use oxygen from the bloodstream, despite physiologically normal delivery of oxygen
example of histotoxic hypoxia is cyanide poisoning
Stagnant hypoxia
AKA hypoperfusion or “low flow” hypoxia
blood flow is abnormally low (shock or other “low-flow” states, like VTE)
decreased blood flow (hypoperfusion) is the primary limitation, thus, the problem resides with the cardiovascular system
Anemic hypoxia
occurs when the oxygen carrying ability of the blood decreases d/t a reduction in total hemoglobin
can be seen in the patient with chronic anemia who is being transferred for some other acute medical condition, who becomes hypoxemic during flight due to a reduction in total oxygen carrying capacity coupled with decreased ambient partial pressure O2 from altitude, and increased global metabolic demand from their acute disease process
Boyle’s Law
“Boyle’s balloons expand as they go up”
pressure (P) of a gas is inversely proportional to the volume (V) (temperature + volume of gas are constant)
can be expressed as P1·V1 = P2·V2
used to describe the effects of altitude on gases in closed cavities within the body. As altitude increases, ambient pressure decreases, and volume expansion occurs in enclosed spaces. For example, a 40 mL PTX can increase in volume by up to 16% at 1.5 km (approx. 5000 feet) from sea level
Grahams law of diffusion
“If you eat too many Graham crackers you’re not gonna fit into small places”
The rate of diffusion (or effusion) of a gas is inversely proportional to the square root of the mass of its particles.
When a gas has particularly large particles (or is particularly dense), it will mix more slowly with other gases, and oozes more slowly from its containers
Example: the diffusion of oxygen and carbon dioxide in the blood and the transfer of oxygen from blood into the cells. CO2 molecules are much more massive than O2 molecules, and CO2 has 22x the solubility of O2, thus, CO2’s diffusion rate is much faster than that of O2
Universal Gas Law
the state of a fixed mass of gas is determined by its pressure, volume and temperature (PV = nRT)
this is the mutant offspring of Boyle’s, Charles’s, Gay-Lussac’s and Avogadro’s principles.
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behaviour of many gases under many conditions, yet it has many limitations
Gay-Lussac’s Law
“Gay-Lussac feels hot when he’s under pressure!”
The pressure of a gas is directly proportional to its temperature.
for a constant volume, the pressure is directly proportional to absolute temperature
This law can be expressed by the equation P1/T1 = P2/T2
An example of this as seen in the aeromedical environment would be that as you increase in altitude, air pressure decreases and the ambient air temperature decreases. This cold response to high altitude can be a stressor during flight.
Henry’s Law
“Henry the homeless alcoholic. When he opens his beer, the gas equilibrates!”
for a constant temperature, the amount of dissolved gas in a liquid is directly proportional to the partial pressure of that gas (in contact with its surface)
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Gasses with a higher solubility will have more dissolved molecules than gasses with a lower solubility if they have the same partial pressure.
explains how gasses dissolve across the alveoli – capillary barrier. predicts how gasses behave during gas exchange based on the partial pressure gradients and solubility of oxygen and carbon dioxide
Daltons Law
“Dalton is a dick. Dalton goes everywhere with all his friends. When he is on a plane, as the plane goes up, him and all his friends spread out”
the sum of the partial pressure in a mixture of gases will equal the total pressure. Can be expressed as Ptotal=PA+PB+…
Dalton’s law explains the changes in the atmospheric content of specific gases at different altitudes.
At sea level, the partial pressure of oxygen is 21% (157 mmHg or 21 kPa). At the summit of Mount Everest with a barometric pressure of 33.7 kPa or 0.3 atm, and using Dalton’s law, the partial pressure of oxygen is only 7 kPa or 52 mmHg, leading to oxygen-hemoglobin saturation of less than 80% without supplementation
for CCP’s Dalton’s law can be used to calculate the expected partial pressure of oxygen that should be obtained via ABG when supplemental oxygen is given to a patient.
Fick’s Law of diffusion
“Fick is THICC”
describes how the spontaneous movement of solute particles is driven by a concentration gradient
describes the relationship between the rate of diffusion and the three factors that affect diffusion
the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane
The rate of diffusion will double if: surface area or concentration difference is doubled or thickness of the exchange membrane is halved.
For example, an elderly patient with COPD who has developed PNA will have decreased gas exchange at altitude because of decreased atmospheric pressure, decreased surface area of the alveoli, and increased membrane thickness, owing to both the long standing COPD and the exudate from the pneumonia
Charles Law
“Charles’ chest contracts when its chilly”
the Volume (V) of a gas is directly proportional to the temperature (T)
Charles’ law can be expressed as V1·T1 = V2·T2
This law is valid as long as the pressure and the amount of gas are constant
Charles’ Law can be seen in the aeromedical environment with respect to helicopter lift and air temperature. As the air heats up, volume increases, allowing the molecules to spread out, making the air less dense. Helicopters fly easier in cold weather because gas molecules are more compressed and allow more lift as the rotor blades spin. Gas molecules are farther apart in hot weather and provide less lift. Therefore, a helicopter or airplane is able to carry a smaller amount of weight on a hot, humid day than a cold, dry day
