9 Gas Laws & Gas Cylinders

PAO2 = FiO2 x (PB - PH2O) - (PaCO2/RQ) RQ = 0.8

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

Cgas = Pgas / KH

0.003ml O2 dissolved in 100ml blood per 1mmHg PO2 applied PAO2 = 100mmHg PaO2 = 0.3ml O2

0.067ml CO2 dissolved in 100ml blood per 1mmHg PCO2

CaO2 = ((1.34ml O2/gm Hgb) x (15gm Hgb/100ml blood) x (% saturation)) + (0.003 x PaO2)

= CaO2 content x CO

Gas pressure inversely proportional to volume at constant temperature P1 x V1 = P2 x V2

Gas volume directly proportional to absolute temperature (°K) at constant pressure V1/T1 = V2/T2

Gas pressure directly proportional to absolute temperature (°K) at constant volume P1/T1 = P2/T2

(P1xV1)/T1 = (P2xV2)/T2

Equal gas volumes at same temperature and pressure contain the same number molecules or atoms V1/n1 = V2/n2

1 mole gas @ STP = 6.02 x 10^23 molecules GMW 1 mole O2 = 32g 2kg tank N2O (44g) = 45.45 Mole

22.4L @ STP

Avogadro + Boyle + Charles + Dalton PV/T = Rn PV/nT = R PV = nRT V = nRT/P R (constant) = 62.36 L⋅mmHg/Mol⋅K

E tank 14.7psi / 5L (PSI/14.7) x 5L L/flow = min Holds 660L 1900psig

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

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

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

Work requires energy (heat) Endothermic reaction Area surrounding rapidly expanding gas will feel cold Gas cylinder release - cold regulator

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

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

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