9 Gas Laws & Gas Cylinders Flashcards
PAO2 Equation
PAO2 = FiO2 x (PB - PH2O) - (PaCO2/RQ) RQ = 0.8
Alveolar/Arterial Ratios
Alveolar-arterial oxygen difference/gradient
(A - a)DO2 or PAO2 - PaO2
Normal 5-15mmHg
Arterial-alveolar ratio
PaO2/PAO2
Normal > 0.75
PaO2/FiO2
Normal >200
Henry’s Law
Cgas = Pgas / KH
Dissolved PaO2
0.003ml O2 dissolved in 100ml blood per 1mmHg PO2 applied
PAO2 = 100mmHg
PaO2 = 0.3ml O2
Dissolved CO2
0.067ml CO2 dissolved in 100ml blood per 1mmHg PCO2
Arterial O2 Content Equation
CaO2 = ((1.34ml O2/gm Hgb) x (15gm Hgb/100ml blood) x (% saturation)) + (0.003 x PaO2)
O2 Delivery
= CaO2 content x CO
Boyle’s Law
Gas pressure inversely proportional to volume at constant temperature
P1 x V1 = P2 x V2
Charles’ Law
Gas volume directly proportional to absolute temperature (°K) at constant pressure
V1/T1 = V2/T2
Gay-Lussac’s Law
Gas pressure directly proportional to absolute temperature (°K) at constant volume
P1/T1 = P2/T2
Combined Gas Laws
(P1xV1)/T1 = (P2xV2)/T2
Avogadro’s Law
Equal gas volumes at same temperature and pressure contain the same number molecules or atoms
V1/n1 = V2/n2
Avogadro’s Number
1 mole gas @ STP = 6.02 x 10^23 molecules
GMW 1 mole O2 = 32g
2kg tank N2O (44g) = 45.45 Mole
1 Mole Gas = x L
22.4L @ STP
Ideal Gas Law
Avogadro + Boyle + Charles + Dalton PV/T = Rn PV/nT = R PV = nRT V = nRT/P R (constant) = 62.36 L⋅mmHg/Mol⋅K
Oxygen Tank
E tank
14.7psi / 5L
(PSI/14.7) x 5L
L/flow = min
Holds 660L
1900psig
Nitrous Oxide Tank
Pressure gauge (psig) does not change until N2O unable to move from liquid to gas state (no liquid present)
Open valve → releases gas ↓pressure
Liquid N2O changes to gas state ↑pressure
Equilibrates on pressure gauge Ø change
*Weigh tank to determine N2O remaining
Able to hold more volume w/ less psi than E cylinder tank d/t ↑ Moles (liquid more dense than gas)
Mass N2O present / GMW (44g) = # Moles (n) N2O
V = nRT/P
Holds 1590L
745psig
Joule-Thomson Effect
Decrease in temperature as heat loss result when gas expands freely into space
Compression & expansion
Normal conditions compression/expansion occurs slowly enough that heat transfer (exothermic/endothermic reactions) not felt of observed
Heat change dissipates into the environment
Compression
Exothermic reaction
↑ kinetic energy when compressed
Heat lost to the environment
Anesthesia machine gas compression via narrow valve = heat
Ignition possible, especially in high O2 environment
Expansion
Work requires energy (heat)
Endothermic reaction
Area surrounding rapidly expanding gas will feel cold
Gas cylinder release - cold regulator
Adiabatic Compression/Expansion
Rapid compression (exothermic) heat liberation does not have time to dissipate
Things in vicinity or in contact w/ gas will heat up
Rapid expansion (endothermic) surrounding area will feel cold
OR insulated area where compression/expansion occurs ჻ heat trapped and unable to dissipate
Concentration Effect
Accelerating alveolar gas concentration by increasing inspired concentration
Alveolar fraction (FA) / Inspired fraction (FI)
Optimal FA/FI ratio = 1
How quickly anesthetic gas enters bloodstream & crosses the blood-brain barrier
Patient who receives higher concentration will feel anesthetic effects sooner
2nd Gas Effect
Large volume uptake (highly soluble) gas N2O delivered at high concentration to accelerate alveolar partial pressure increase of anesthetic (ex: Isoflurane)
Concurrent gas administered w/ anesthetic
Oxygen + anesthetic + nitrous oxide
N2O highly soluble and quickly absorbed into blood → leaves void in alveolus
Effect: Concentrates anesthetic gas & suctions in more gas from airways = ↑ anesthetic
Result: Able to anesthetize patient more quickly d/t ↑ anesthetic concentration in the alveolus
