Gas and Pressure Flashcards
Gauge measurements
Fsw - feet of sea water
psi - pounds per square inch
Absolute Pressure measurement
Ata - atmospheres absolute
mmHg
Equivalent pressure measurements
1 atmosphere 760 mmHg 14.7 psi 33 fsw 10 meters of sea water (msw) 0.99 bar 760 torr 101 kilopascals (kPa) 0.1 Megapascals (mPa)
Formula for ata to mmHg
mmHg = ata x 760
Formula ata to fsw
fsw = (ata -1) x 33
Formula ata to psi
psi = (ata - 1) x 14.7
Formula fsw to ata
ata = (fsw + 33) / 33
Formula psi to ata
ata = (psi + 14.7) / 14.7
Absolute temp for F
Fahrenheit to Rankine (R)
R = F + 460
Absolute Temperature for C
Celsius to Kelvin
K = C + 273
Boyle’s Law
Pressure and volume. Inverse relationship
Gay-Lussac’s Law
Pressure-temperature.
Charles’ Law
Volume-Temperature
Significant shrinkage
Dalton’s Law
Partial pressure of gases. The total pressure of a mixed gas is equal to the sum of the partial pressures of each of the component gases.
Henry’s Law
Dissolved gas in solution. The amount of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas over the liquid.
Pascal’s Law
Hydraulics. A bubble deep in the body tissues responds to the pressure applied outside the body.
Graham’s Law
Gas diffusion. Gas moves from area higher pressure to an area of lower pressure.
Pulmonary oxygen toxicity
Identified by Lorraine Smith (1899)
Difficulty breathing, cough, chest tightness, substernal burning,reduction in vital capacity.
Time/dose relationship
Unit pulmonary toxicity dose
UPTD = 100% oxygen at 1 ata for 1 min = 1 UPTD
Max UPTD dose in 12 hours
1440
Central nervous system (CNS) toxicity
Identified by Paul Bert 1878
Convulsion, nausea, dizziness, muscle twitching, abnormal vision or hearing, anxiety, confusion
Time/dose relationship
Threshold for CNS toxicity breathing 100% oxygen
1.6 ata - several hours
2 ata - 4 hours
3 ata - 1 hour
Max oxygen dose - 100% O2 at 3 ata (2280 mmHg)
Variables that shorten time to oxygen toxicity seizure
Elevated CO2, fever, exercise, upright position
Preventing oxygen toxicity
Intermittent air breathing (air breaks), limit inspired po2 to 2280 mmHg
Nitrogen narcosis
Only occurs when breathing air
Sx - euphoria, mood change, idea fixation, slowed reactions, judgement errors, unconsciousness
Can affect inside attendant
Threshold is approximately 4 ata (100 fsw)
Isobaric counter-diffusion
When gas inside a bubble is replaced by another gas. Occurs because of pressure gradients of the two gases.
Solubility of nitrogen in fat
5xs more soluble in fat than water
The amount of time it takes half of nitrogen in tissue to be eliminated is called
Half-time
Number of half times required for nitrogen to be completely eliminated in a tissue.
6 units of half time
Critical ratio
When ratio of nitrogen to ambient pressure hits critical ratio, bubbles form.
