Physics and Gases Flashcards
3 components of pressure regularators
tightly wound spring attached to diaphragam which is connected to a valve controlling high pressure gas input.
PSI of central oxygen tank
55 psi, primary source for anesthesia machine
Pipeline pressure
- psi. Pipeline gauge located on pipeline side of check valve to avoid checking pressure within machine. Has both pressure regulators for pipeline and cylinder
secondary gas source for anesthesia maachine
e-cylinders. Pressurized to 2200 psi and have a regulator bc they need lower pressures. Separate regulators for each cyclinder
Regulator in O2 reserve cylinder reduces pressure from ___ to ___
2200 to 45 psi, second stage will reduce to 14
Regulator in nitrous reserve cylinder reduces pressure from ___ to ___
745 to 45 psi, second stage will reduce to 26
what happens if 2 cylinders are open at same time what will gauge read
cylinder w higher pressure
Oxygen e-cylinder (color, pressure at room temp, physical state)
green, 2000, gasN
Nitrous oxide (color, pressure at room temp, physical state)
blue, 745, liquid/vapor
Carbon dioxide (color, pressure at room temp, physical state)
Grey, 840, liquid/vapor
Air (color, pressure at room temp, physical state)
yellow, 1800, gas
Entonox (color, pressure at room temp, physical state)
blue, 2000, gas
heliox (color, pressure at room temp, physical state)
Brown, 2000, gas
Full e-cylinder of O2
660 L
Full e-cylinder nitrous
1600L at 750 psi. Volume cannot be determined by pressure guage. Pressure will remain at 750 until it has all been vaporized which means 20% of intial volume remains when there’s a drop in pressure
laminar flow, relationship to pressure gradient
directly proportional to pressure gradient (flow related to pressure), R is a constant, F=deltaP/R
turbulent flow, relation to pressure
nonlinear relationship between flow and pressure. flow rate is proportional to square root of pressure gradient
reynolds number
Re = densityvelocitydiameter/viscosity, point at which a fluid transitions from laminar to tubrelnt
Poueuille equation
Q = delta Ppir^4/ 8viscosity*length
describes relationship between variables that affect flow rate and laminar fluids
Bernoulli’s equation
sum of all energies per unit volume remains constant at all points along line of fluid when laminar
P1 + 1/2(densityvelocity^2) = P2 + 1/2(densityvelocity^2)
Venturi effect
when a fluid passes through a tube with varying diameters, lateral pressure exerted by fluid drops because of increase in velocity when there’s constriction
hyperechoic
strong reflection, white dot
bones, tendons, ligaments, diaphragm, nerves, liver angiomas, tumor, blood vessels, fibrosis, liver steatosis
weaker - solid organs, thick fluid, gray
anechoic (no reflection)
cysts, ascites, fluid
ultrasound transducer frequency and wavelength
increase frequency, increases image resolution, decreases ability of waves to penetrate
12Mhz waves - good resolution, not deep
3Mhz goes deep, but bad resolution
doppler effect
change in frequency of a wave due to relative motion between wave source and receiver
desflurane boiling point
22.8C
desflurane vapor pressure
700
Nitrous boiling pt
-88C
nitrous vapor pressure
38770
sevo boiling point
58.5C
sevo vapor pressure
157
iso boiling point
48.5C
iso vapor pressure
240
halothane boiling point
50.2C
halothane vapor pressure
244
Highest boiling pt to lowest boiling point gases
Sevo > Halothane > Iso > Des»_space; Nitrous
Highest vapor pressure to lowest vases
Nitrous»_space; des > halothane > iso > sevo
Daltons law of partial pressures
partial pressure of a gas in a mixure of gases is the pressure that gas would exert if it occupied the total volume
P = (barometric pressure - water vapor pressure)*F (F is fractional concentration of gas)
alveolar gas equation
used to predict alveolar PO2 based on the alveolar PCO2
PaO2 = PIO2 - (PaCO2/R) + correction
Henry’s law
used to determine concentration of a gas that has been dissolved in solution. at equilibrium, partial pressure of a gas in liquid phase equals partial pressure in gas phase. Henry’s law is used to convert the partial pressure of gas in liquid phase to conc of gas in liquid phase. solubility used to describe tendence of a gas to equilibrate with a solution
Cx = Px * solubility
variable bypass vaporizers
consist of the conc control dial, bypass chamber, vaporizing chamber, filler port, filler cap
splits fresh gas flow into two portions - first (20%) going into vaporizing chamber where it is saturated with the anesthetic vapor and the second portion going to bypass chamber.
gases mix at patient outlet side of vaporizer
amount of liquid anesthesitc equations
3 * FGF (L/min) * volume % = liquid of volatile anesthetic/hr
desflurane vaporizer
vapor pressure is 3-4x that of other gases
Tec 6, two independent gas circuits arranged in parallel. fresh gas enters at inlet, passing through a fixed restrictor R1 and exits the vaporizer gas outlet. Vapor circuit arises at desflurane sump which is electrolly heated to 39C above boiling point. Sump is a reservoir for desflurane vapor. Downstream is shutoff valve. Output controlled by adjusting concentration control valve R2 which is variable restrictor. Pressure supplying R1 and R2 are equal and is called working pressure.
pharmacologic effect of inhalation agent determined by
determined by partial pressure of anesthetic in the brain, at equilibriu,, brain partial pressure = anesthestic pp in arterial blood
two variables of alveolar concentration (FA)
- delivery of agent to lungs
- uptake of agent by blood
rate of rise of FA increases with ____ rate of anesthestic delivery
higher rate
rate of rise of FA decreases with ____ degree of anesthetic blood uptake from lungs
greater
if volatile is not as blood soluble, does increased ventilation help rate of rise
No because of minimal blood uptake. FA will rise rapidly irresepective of ventilation
Low blood solubility = _____ rate of rise FA
faster
High blood solubility = _____ rate of rise FA
slower, can be helped with increased ventilation
higher solubility = _____ rate of blood uptake from lungs
higher
lower solubility = ____ rate of blood uptake from lungs
lower
higher cardiac output = ____ induction
slower induction. greater volume of blood, perfuses lungs and removes inhaled anesthetic more, increased uptake decreases concentration of anesthetic in lungs, lowers alveolar arterial and prain partial pressure
changes in CO affect FA of _____ soluble agents more
highly. any significant reduction in CO decreases blood uptake
vessel rich group
brain, heart, splachnic, liver - less than 10% of body weight, receives 75% of CO. complete equilibrium within 4-8 min
muscle group
muscle and skin - 50% body weight, 20% CO, responsible for most of uptake beyond 8 min and requires 2-4hr for equilibrium
fat group
poorly perfused, great affinity for anesthetic
factors that enhance FA
increased ventilation, decreased CO, low blood solubility
blood solubity affect on FA
low blood solubility –> increased FA
ventilation affect on FA
increased ventilation –> increased FA
CO affect on FA
decreased CO –> increased FA
increasing FI _____ rate at which FA approaches FI
increases
factors that enhance FA increase or decrease rate of rise in FA/FI
increase
Nitrous oxide affect on CO and SVR
crease
also does not inhibit hypoxic pulmonary vasoconstriction
Nitrous affect on uterine tone and skeletal muscle relaxation
no affect
nitrous oxide can cause a ___ in volume
increase. volume depends on 2 variables - time and inspired concentration
Contraindications for nitrous
intenstinal obstruction, pneumo, vascular air embolus, COPD, laparoscopy, introcular air, tympanoplasty, pneumocephalus, enotraceal tube cuffs
FA/FI ratio rises ____ when CO is doubled
rises slower, more so for soluble agents than insoluble agents
acoustic impedence is product of what and what
density and propagation speed
