Chemistry Physics
Class Notes
7/14/1999
Do study questions for quiz
Density – r’ship between wt and vol of substance
- D = M/V expressed in in gm/L
Densities – Room air is 1.3 gm/L
- H is .09
- H2O 1.0 gm/cc
- ice .92gm/cc, which is why it floats
Vander Waals forces (VDW f) these forces occur when the shape and pattern of their charges are aligned so 1 end is relatively + and the other end is relatively - a 2 pole system
VDWf must be overcome to have change from a a liquid to a vaporGMW not really related to anesthesia but its taught anyway
Its expressed in gm per gm/L,
so O2 is expressed as 32gm per 1.429gm/L = 22.4L
Avagadro's hypothesis says 1 mol of any gas will = 22.4L, and real gasses can be calculated to = 22.4L, 1 mol of O2 weighs 32gm and fills a 22.4L container
Diffusion rate is proportional to differences in PaP
A way to figure out the PaO2 is to multiply 5 x %O2 administered, this is approximate, as the A-a gradient, N, H2O vapor in lungs and CO2 contribute their own Pa P which alter the #’s. It is possible to figure an approximate PaO2 if it is known that a person receiving 100% O2 should have a sat of 500%, we’ll learn it later
We need to know pressure volume for ventilator patients as RT shheres and ARDs
Face mask O2 delivers @ 4% O2 / L, and venturi masks entrain some RA to adjust O2 delivery
Need to know about full cylinder containers – pressure & volume
Anesthesia bag – requires flow in order to maintain size, so if the bag is flat then there is 1) no flow or 2) a poor seal
Page 11 - vapor pressure – flask with 100% O2 + desflorane and Halo(243vp)at 273 C and 1 atm
Also think of how to calc the numbers when a % is given, and calc mmHg from % derived or given
Need to know what vp is because it exerts mmHg – Dalton says all the pressures will add up to 760mmhg
Problems that will be asked – at STP there is a flask of O2 and halo is added. What is the PaO2 in the flask. When Pa P are asked for the answer is in mmHg
Think of 760 as 100%, and 243 as 32% Pa Halo
243/760 == .32 = 32% of halo in flask, there are 2 ways to figure it out
1. 100% - 32% = 68%, 68% of 760mmHg(mult .68 x 760) = 517mmHg
just think of adding enough halo to exert a pressure which will change the PaO2
Critical pressure is the pressure needed to liquefy a gas at its critical temp.
Adiabatic deals with expansion or compression of gasses
Gasses cool with adiabatic expansion and heat with adiabatic compression
When cylinder is opened into a vacuum and no heat loss or gain is noted this is considered to be adiabatic???????????????
When opening a cylinder of compressed gas into free air, the gas molecules expand into the free air so the heat can dissipate into the air around it. Condensation is seen on the valve, and this is good. Joules-Thompsons effect condensation occurs because the molecules that come out cool the molecules just around the valve which causes condensation. ??????????????
If gas is released from a pipe thru a small orifice and there is no room for those molecules to go, and there is a potential for a large temp increase in the container (pipe), therefore it can heat and explode. This would happen if the temp raises over the combustibility of the gas. (BOOM)
HUMIDIFICATION – refers to the presence of water molec in the gaseous state in a mixture of gas. Gas water molec are considered vapors at temps < the critical temp of water
Humidity – absolute – the water content of gas expressed as the wt of water per volume of gas, which is usually expressed as x mg of water / L air
At a given temp and pressure
Ambient temp is the air temperature of the air around us. Ie the ambient temp of a frig is considered when keeping milk form souring
Humidification helps prevent drying and heat loss. Causes are:
Cascades not used in OR because they're cumbersome and they promote bacterial growth
Hypothermia – physio effect causes
Cool and warm patient effects the Av dissociation curve
Cold – shifts to the left causing: hbg to hold onto O2(hbg has inc affinity for O2) and wont release it ti the tissues –
A-a gradient: A= alveolar a= arterial gradient means the difference between the two. Partial pr of inspired O2 is PiO2, which is 760 mmhg – 47 mmHg
Formula PaO2 = FIO2 { PiO2 - (paCO2 / RQ) } RQ = .8
Alveolar PaO2 of the A-a gradient of O2 = .21{(760-47) – (40/.8)} is @100
Medical gas cylinders handout chap 99
CO2 is used for insufflations during lap, and tourniquet placement
Helium is used to get laminar flow movement. – ENT cases use it in cuff so when laser is used the tracheal burns wont occur, or can fill balloon with NS or water and a blue dye, which alerts if the cuff is broken
And helio-ox good for asthma pts who need laminar flow to dec turbulance on airways
The testing of tanks is to 5/3 of capacity , so O2 is tested at nearly double to ensure tank integrity.
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