Equipment Flashcards
How does a VIE work
Liquid O2 stored at -150 to -170 and 5-10 atms.
O2 vapour heated and passed through pressure regulator to pipelines at 400kPa
What happens in a VIE at times of increased use
Control valve allows liquid O2 to pass through pressure raising vaporiser and super heater to enter pipelines.
What happens in a VIE at times of decreased use
Pressure within system increases and a safety valve blows up if goes over 1700kPa
How do oxygen concentrators work
O2 extracted from air via differential adsorption through a zeolite medium.
Safety features of gas outlets
Schrader sockets, colour coded
O2 black, N2O blue, Air black and white, Suction yellow
Safety features of anaesthetic machine gas outlet
Colour coded hoses, NISTs
Safety features of gas cylinders
Bodok seal
Pin index system
Gas cylinder sizes
D 340L
E 680L
F 1360L
CD 460L
Pin index of air
Pin index of O2
Pin index of N2O
1 and 5
2 and 5
3 and 5
Pin index of air
Pin index of CO2
1 and 5
1 and 6
Pin index of entonox
7
Effect of altitude on concentration of anaesthetic gas
Concentration different ie (2x100/100 ) = 2% at 100kPa vs (2x100/50) = 4% at 50kPa therefore partial pressure is the same.
Ideal scavenging system (5)
- Simple and cheap
- Doesn’t affect oxygenation or ventilation
- Doesn’t affect breathing dynamics
- Can’t be connected to patient (30mm tube)
- Doesn’t pollute other parts of hospital
Components of active scavenging system
Collection and transfer (between APL and receiver), receiving unit (guards against excessive pressures), disposal through vacuum and copper pipe.
How does a Cardiff aldsorber work
Filters volatiles, doesn’t filter N2O, increases weight with use, heating releases gases
Limits of sevoflurane
60 ppm
Limits of N2O
100 ppm
Limits of isoflurane/ enflurane
50 ppm
Limits of halothane
10 ppm
Classify breathing systems
Open - ether mask
Semi open - Hudson, VM
Semi-closed - Mapleson
Closed - circle (with exp valve closed)
Advantages (4) of circle system
- Economical - can use low flows
- HME gases
- Suitable for SV and IPPV
- Scavenging
Disadvantages (3) of circle system
- Complex and risks of disconnection
- Rebreathing metabolised products (theoretical)
- Requires monitoring (volatiles and O2)
Components of soda lime
Mesh size
94% CaOH
5% NaOH/ KOH
0.2% silica and zeolite
4-8
Titan yellow colour change
Ethyl violet colour change
Pink –> white
White –> purple
Effect of granule size on CO2 absorption
Increased - decreased SA for absorption
Decreased - increased resistance to flow
Features of HME
Passive, exhaled gases fully saturated with water pass over mesh and causes water to condense on its surface allowing warmth and humidification of fresh gas.
15 and 22mm fittings
Side port analysis
How do nebulisers add humidification
Risks of ultrasonic nebs
Add water particles, not vapour
Risk of over saturation of airway
Types of oxygen analysers
- Electrochemical
a) Galvanic fuel cell
b) Polarographic cell - Physical
a) paramagnetic
b) mass spectrometer
How does galvanic fuel cell work
Gold cathode and lead anode
Lead anode acts as battery
In KOH solution
Measures voltage generated in proportion to concentration of oxygen.
How does paramagnetic oxygen analyser work
Nitrogen dumbbells between two magnets with mirror in the middle.
Oxygen attracted to magnetic field displaces dumbbells. The mirror reflects light which is detected by photocell. Current prop to O2 conc.
Disadvantages of galvanic fuel cell (4)
Slow
Temp sensitive
Drifts
Expires
Features of IR spectroscopy
Molecules of 2 or more elements can absorb IR radiation.
Ionised and charged particle goes through accelerator. Particles deflected based on mass:charge ratio and detected.
IR peaks of
CO2
N2O
Volatiles
4.3 micrometres
4.6 micrometres
3.3 and 8-9 micrometres
Describe graph of current of charging circuit of defibrillator at point of switch closure
Time x axis
Current y axis
Exponential decline
Describe graph of voltage of charging circuit of defibrillator at point of switch closure
Exponential increase
Sterilisation definition
Eliminates all microbes (assurance 1x10^6)
Disinfection definition
Removes all but bacterial spores
Cleaning
Removes visible soil
Methods of sterilisation (4)
Steam
Ethylene Oxide
Ozone
Hydrogen Peroxide
Methods of disinfection (3)
Thermal wash
Chemical
Pasteurisation
What does a pulse oximeter measure
Proportion of Hb saturated O2 in pulsatile blood
What is the Beer-Lambert law
Beer’s law = absorption is directly proportional to the concentration
Lambert’s law = absorption is directly proportional to the length
How does a pulse ox work
2x light emitting diodes, one red one infrared light, sequence of on/off and off cycle.
Photodetector produces current proportional to ratio of light and compared to reference table
What is the isobestic point
Point both wavelengths absorptions is the same, 590 and 810 nm
What wavelength and type does deoxyHb absorb more
Red
660nm
What wavelength and type does oxyHb absorb more
IR
940nm
Sources of pulse ox error
- Pulsatile
Poor perfusion
Dyes
CO poisoning
Methhaemagolbinaemia - Non pulsatile
Movement
Ambient light
Nail varnish
Diathermy
Wavelengths of light absorbed by COHb and Met Hb
CO Hb 660nm
MetHb both 660 and 940nm
How does CO2 monitoring work
IR absorption spectrophotometry
Sapphire lens, 4.3nm, detector compares reference and sample chamber
Other methods of CO2 monitoring
Raman spectrometry (argon laser)
Mass spectrometry
Photoacoustic spectrometry
Chemical colourmetry
What is resonance
Tendency to oscillate at bigger amplitude
How does BP change in the periphery
Higher systolic and lower diastolic
Non electric methods of temperature monitoring
Mercury (to -39)
ETOH (to -70)
Dial
Electrical methods of temperature monitoring
Theromocouple
Thermistor
Resistance wire
How does thermocouple work
Graphical relationship
Seebeck effect
Cu/ constantan metals. Voltage generated at junction of metals depending on temperature.
Positive linear
Advantages of thermocouple
Simple, cheap, tough, small
How does thermistor work
Semiconductor beads made of chromium or manganese oxides
Resistance decreases as temp increases (expo)
Advantages (3)
Disadvantages (2) of thermistor
- Accurate, cheap, quick, can be used in intravascular devices
- Ages, hysteresis
How does a resistance wire temperature monitor work
Graphical relationship
Platinum wire, resistance increases and temperature increases
Linear
Advantages (3)
Disadvantages (2) of resistance wire
- Accurate, precise, wide temp range
- Slow, hysteresis
Single twitch NMB monitor character
0.1-0.2ms at 1Hz
TOF character
4 stimuli at 2Hz
DBS character
2 bursts of 3 stimuli at 50Hz separated by 750ms
Can repeat after 20 secs
Tetanic stimulation character
5 seconds at 50Hz
3 second pause then can check PTC at 1Hz x 20
Correlation of PTC and TOF
> 15 = 2 TOF
What does a co-oximeter measure
OxyHb, DeoxyHb, MetHb, COHb
Cathode and anode of a polarographic clark electrode
Platinum cathode
Silver/ silver chloride anode
Solution of polarographic electrode
KOH/ KCl
What process occurs at cathode/ anode in Clark electrode
Cathode - reduction (gain electrodes)
Anode - oxidation (loss electrodes)
Equation at anode at cathode in Clark electrode
Anode - Ag + Cl = AgCl + e
Cathode - O2 + 2H2O + 4e = 4OH-
How does Serveringhaus (CO2) electrode work
Silver/ silver chloride electrode in pH sensitive glass surrounded by HCO3 buffer. CO2 moves through teflon/ rubber membrane. Moves equation to the right which increases H+ ions therefore decreases pH
Pros (2) and cons (2) of Severinghaus electrode
Pro - accurate, stable
Cons - rate governed by permeability of membrane and rate of reaction
Equation of H2O/ CO2
H2O + CO2 <–> H2CO3 <–> H+ + HCO3-
Components of pH electrode
Calibrated with 2x solutions of known pH.
Silver silver chloride measuring electrode in HCl
Mercury/ mercury chloride reference electrode in KCl with porous plug
How does a pH electrode work?
Electrode is a metal conductor in electron solution enclosed in a membrane with selective ion permeability.
Pourous plug minimises KCl diffusion into sample on reference electrode.
Metal conducts electrons, solution conducts ions. Difference between H+ in sample and HCl at generates EMF/ voltage.
How does an oesophageal doppler work
Measures velocity of blood flow via the change in frequency of reflected US waves. Velocity can be converted to flow by knowing diameter of aorta. Then can be X HR = CO.
Assumptions for use of doppler (4)
- 70% SV in descending aorta
- Diameter same throughout cycle
- Blood moving at the same velocity
- No blood flow in diastole
Measurements doppler gives
Peak velocity (contractility)
SV (area of peak)
FTc
CO
Increase in SV by 10% = fluid responsive
Explain dye dilution and thermodilution measurement of CO
Dye dilution (indocyanine green)(lithium) injected at known amount. Change in conc downstream proportional to flow. CO inversely proportional to AUC
Thermodilution injects known amount cold saline and thermistor detects temperature difference
Mechanism of electrical injury (3)
- Shock (macro and micro)
- Burns (direct/ fire)
- Interference (acting upon incorrect monitoring)
Limits of type 1 electrical equipment
B/BF - 0.1 mA –> 0.5 mA SFC
CF - < 0.05mA
Limits of type 2 electrical equipment
B/BF - 0.1mA –> 0.5mA SFC
CF - <0.01mA
Effect of increasing frequency of US waves
Increased resolution
Decreased penetrating capacity
What is the piezoelectric effect
Mechanical stress induced in crystalline substance when potential difference applied across it (or vice versa)
How does USS work?
Probe generates pulsed sound wave at desired frequency.
Sound waves penetrates to a depth determined by frequency.
Sound waves reflected back to transducer when reaches a barrier between media.
Sound energy converted to electrical energy to display image.
What is the doppler effect
Frequency of transmitted sound alters as it is reflected from moving object.
What is the doppler equation
Velocity = (F reflected - F origin) x speed of sound / 2Fo x cos angle between sound and object
Use of doppler effect
Doppler equation measures velocity.
If cross sectional area of vessel known can measure flow in CO monitoring
How does wet dry hygrometer work
2 mercury thermometers. One in bulb in water.
Latent heat of vaporisation causes bulb wet bulb to cool.
Amount of evaporation dependent on humidity of air.
(More evaporation = greater cooling).
Difference in temp correlates to humidity. (Bigger difference = less humid).
Relative humidity referenced against calibrated reference table.
