Phys, Machines, Monitors Flashcards
The risk of radiation exposure
Inversely related to the square of the distance from radiation source
Risk = 1/square root of feet’s
Hagen-poiseuille’s equation
It investigate the steady flow of liquid through a capillary tube. (Describes the glow of fluids through IV cath)
States the flow (Q) of fluid is related to a number of factors:
Inversely to
- Viscosity (n) of fluid (increases with increasing H/H and decreases temp -> hence the benefiting using warmers)
- Length (L) -> shorter increases flow
Directly
- Pressure gradient across the tubing (P) -> elevating IV bags or squeezing it
- Diameter (r) of tube (increases flow rate by 16 folds)
Turbulent gas flow increases with increasing … and ….
In other words; Turbulent flow resistance depends on …. and …
Gas density and gas flow rate
- decreasing gas desensitized with helix instead of air helps to relieve airway obstruction (e.g. tracheas stenosis)
- decreasing gas flow rate as taking slower deep breaths also helps ventilation in obstructed patient
So decreasing density (decreasing resistance) and flow rate (decreasing Reynolds’s number) improves gas flow.
Reynold’s number > 2100, has become turbulent
Laminar has flow resistance depends on ….
Gas viscosity
What property of Heliox increases flow to laminar?
By reducing Reynolds number due to its lower density, heliox changes the turbulent to laminar
Heliox 70% and O2 30% mixture ( it has lower density than O2 but it’s viscosity is the same as O2)
The density of the gas … at high altitude, but viscosity….
Decreases and viscosity remains the same.
So the high flow will be affected in high altitude and the flowmeters will over read higher flows because the higher the flow the density decreases in high altitude
Where there is no effect at low flows as the flow is laminar and depends on viscosity which is unaffected by high altitude
Colors of cylinders
Green Blue Yellow Gray Black Brown
O2 N2O Air CO2 Nitrogen Helium
Volumes and pressured
O2
Air
N2O
625 L. 2000 PSI
625 L. 2000 PSI
1590 L 750 PSI
Characteristics of N2O cylinder
Stored as both liquid and compressed gas
As vaporized nitrous leaves the cylinder, more nitrous is vaporized.
Therefore, the pressure in the cylinder remains the same as long as there is any nitrous remaining in cylinder.
When the pressure begins to decrease, approximately 400L of nitrous remains in the cylinder
Dead space in circle system starts from … and can be reduced by placing a ….
From the Y piece
By placing a septum in the Y piece
The ideal position of circle system structure position from expiratory to inspiration
Expiratory unidirectional valve > pop off valve > circle absorber > fresh gas flow > inspiratory unidirectional valve
Best action When major crossover of O2 and N2O pipelines suspected
D/C patient from machine and ventilate with ambu bag with room air.
Maintain anesthetic with TIVA
(Turning on the backup O2 cylinder is not an option because it could be filled with N2O earlier before the suspicion)
Action when pipeline O2 fails and your backup O2 cylinder is low with O2
Turn of the ventilator and start manual ventilation
Because continuousventilationwith even low flows will empty the O2 early from the back up cylinder
What’s the most important safety feature in machine to prevent the delivery of hypoxia mixture
The inspired O2 analyzer
The best monitor to detect the expired limb disconnection during spontaneous ventilation is
Inspired oxygen analyzer
Mapleson’s A circuit vs Mapleson’s D circuit
A: prevents rebreathing during SPONTANEOUS ventilation
D: prevent rebreathing during CONTROLLED ventilation ( in order to prevent rebreathing during spontaneous, fresh gas need to be increased 3 times the minutes ventilation)
Bellows and circuit disconnection
Ascending va descending bellows
Ascending-> rose during expiration, will not fill during circuit d/c and therefore identify any disconnection
Descending-> falls during expiration, continues to raise and fall in event of circuit d/c and therefore can’t recognize a circuit d/c
When there is hope in the bellows, what effect or change seen on FIO2 in
O2 powered ventilation
Air powered ventilation
Increase in FIO2
Decreases
What is the saturated vapor pressure and what it depends on?
It’s the pressure exerted on the wall of the container at equilibrium
Depends on Temp of liquid and liquid physical characteristics (not on the barometric pressure).
Vaporizer output and its relationship to fresh gas flow?
The vapor output will decrease weather in low or high fresh gas flow rate
Vaporizer output at high altitude increases or decreases?
Increases (except Desflurane) as the potency decreases due to decrease in density of vapor, therefore no need to change the dial.
Desflurane remains the same as its electrically heated (boiling point for Desflurane is 23 degree and its heated to 39)
When Desflurane vaporizer alarms?
- agent level less than 20 ml
- tilting of vaporizer grater than 10 degrees
- power failure
To agents has the same saturated vapor pressure?
Halothane + isoflurane (~240 mmHg)
So they are the least error to occur in terms of vapor output if mistakenly filled with wrong agent
When is the sub-ambient pressure alarm identified? and what common cases of negative pressure?
The sub-ambient pressure alarm is intended to identify a breathing system pressure of
What dose the US echogenicity measures?
Measures acoustic reflect acne, ability of tissue to reflect the US wave.
Hyperechoic are -> bones, tendons, and nerves are hypo or hyper depends on its location
Arteries and veins are anechoic
What dose US acoustic impedance means?
Resistance to US wave propagation.
Denser the material it has more acoustic impedance and appears more white in the screen.
US probe frequency? High vs low in terms wavelengths, resolution, and depth of penetration
The high frequency has shorter wavelength with high resolution but limited depth penetration
Low frequency has larger wavelength and deeper penetration but low resolution
EtCO2 tracing in following situations
Expiratory valve stuck malfunctioning (if valve open vs closed)
EtCO2 will show rebreathing shape when expiratory valve stuck is open
And will show bronchospasm if expiratory valve stuck closed
EtCO2 trace when inspiratory valve malfunction in spontaneous vs controlled ventilation?
Rebreathing trace if spontaneous and you’ll see prolonged inspiration trace if controlled ventilation
Trace of EtCO2 during sample line leak?
EtCO2 lower initially due to dilution with air, and later peaks up due to raise in CO2
Lead one voltage is btw …
Lead 2 voltage is btw …
Lead 3 voltage is btw …
LA and RA
LL and RA
LL and LA
How to obtain V5 lead using three lead ECG?
Place RA over manubrium
Place LA over V5 position
Place LL at its neutral position
Which lead is used to monitor atrial activity?
Lead 2
Which leaves the transducer zeroed at? How much mmHg change for every 10 cm change in transducer position?
Leveled at RA
For every 10 cm change in position, BP will change ~ 7.5 mmHg
pH 15 20 ( for every 20 cm change, BP will change by 15 mmHg)
When compering radial artery pressure peaks to aortic pressures the … + … are higher where … + … lower
The radial artery will have higher systolic and pulse pressure.
Where diastolic and mean are lower
This is because the pressure waves propagates from aorta to distal vessels and meet resistance in small vessels resulting in amplification of the wave form due to pulse wave reflection
MCC of brachial artery catheter?
Median nerve injury
Direct arterial pressure measurement principle
Fluid filled tubing transducer system converting mechanical energy into electrical energy
Transducer system uses strain gauge and Wheatstone bridge circuit
What dose arterial wave form depends on ? And which one is more important?
1) natural frequency of transduction system (it is the frequency at which it tends to oscillate and amplify the arterial wave form)
2) damping coefficient (it is the tendency of fluid system to extinguish motion).
At higher natural frequency, damping coefficient has little effect on arterial pressure wave.
Over damping of arterial pressure resulting pressure reading? Causes?
Higher diastolic but no change in MAP
- high viscosity of fluid
- small tube diameter
- long tube length
- soft high compliance tubing
- air bubble in tubing
Hyper resonance or underdamped system of arterial pressure will read ? Causes?
Higher systolic but unchanged MAP
- stuff (low compliance tubing)
- big catheter (18 g instead of 20 g in radial artery)
Indirect BP measurement;
- artificially higher when …
- artificially lower when …
- falsely low when …
Width of cuff should be … of circumference or .. of the arm diameter
… is measured and SBP and DBP are …
- too small
- too big cuff
- If cuff deflated rapidly
40%
20%
MAP is calculated where SBP + DBP are derived
Compression of indirect BP to arterial?
Mercury sphygmomanometry is most accurate
Over read at low pressures and it under reads at high pressures.
Causes of overestimation/underestimate of CO with thermodiulation technique?
- loss of injectate
- incomplete filling the injectate syringe
- clot in the thermister
- catheter location too distally
When it underestimate then check the temperature it might be too proximal
CO measurement by thermodiulation method is inaccurate in which conditions?
- AF
- intracardiac shunt
- Tricuspid regurgitation
Difference between serum osmolality measurement vs calculation?
Calculation is a formula (2x Na + gluc/18 + BUN/2.8)
The measurement used by osmometer that includes other substance than Na/glucose and BUN(depression of freezing point)
So if osmolar difference between measurement and calculations, might present alcohol or other ingested substance contributing to osmolar difference
Line isolation monitors what? When it alarms?
Monitor the integrity of underground power source in the OR
Alarms when leakage is > 2 mAmp
When second fault occurs it poses shock hazard to patient and OR personnel
What to do when line isolation monitor alarms?
If before procedure then postpone the surgery or move the case.
If during the case then electrical devices systematically unplugged starting with recently plugged in.
What’s the maximum allowable microshock in OR?
At which micro and macro shocks results in Vfib?
Dose the line isolation monitor prevent macro or micro shocks?
10 microampere
At 100 microampers (micro)and 100 miliamperes (macro) results in Vfib
Line isolation monitor prevents only the mAcro shacks.
How much O2 last in a tank with 1100 psi running on 6L/min flow?
The full O2 tank has 660L in a 2000 psi
Relation is Linearly proportional
625/2000=×/1100
Solve for x = 343L
Now divide the volume over flow and you get the time
343L/6 = 57 min
Calculation for remaining O2 in a tank?
Flow I Full ~600 I Half ~300
6L. 100 min. 50 min
5L. 120 min. 60 min
4L. 150 min. 75 min
3L. 200 min. 100 min
Gas cylinders color
Green Blue Grey Yellow Blue Brown
O2-> green NO or Entonox (mixture of O2 + O2) -> blue CO2 -> Grey Air -> yellow Entonox -> blue O2/helium -> brown
Physical state of gases in cylinder
All are gases except NO and CO2 which is liquid/vapor
Pressure of gases in cylinder at room Temp in psi
O2/Entonox/Heliox -> 2000 psi
NO -> 745 psi
CO -> 840 psi
Air -> 1800 psi
