Equipments Flashcards
How is oxygen manufactured?
Fractional distillation of air or the use of an oxygen concentrator in which zeolite mesh absorbs Nitrogen. Leaving about 97% oxygen.
Storage of oxygen?
- Gas in cylinders
- Liquid in VIE
Properties of the oxygen cylinder ?
- Black body and white top
- Stored at 13,700kPa or 137bar
- Varies between 12000-17000kpa
State all the possible cylinder sizes?
C - 170 L
D - 340 L
E - 680 L
F - 1,360 L
G - 3,400 L
J - 6800 L
What are the properties of VIE?
- Pressure 10 - 17bar
- Safety valve
- Pressure regulator to 4bar
- Liquid oxygen at -160 to -180 degrees
- Inner stainless steel
- Outer pure steel
- Insulating perlite
- Evaporator
What is the VIE?
- Allows storage of cryogenic liquids
- Oxygen, Nitrogen & Argon
What is the critical temperature of oxygen?
- 118 degrees
What are the physiochemical properties of oxygen?
- Boiling point -182 degrees
- Critical temperature- -118
- Critical pressure 50bar
Define critical temperature?
This is the temperature above which vapour of the gas cannot be liquified regardless of the pressure applied
What’s the critical pressure of a gas?
The critical pressure of a gas is the pressure require to liquify the gas at its critical temperature.
What is negative pressure ventilation?
Occurs within a chamber and this pressure is applied to the thorax
Positive pressure ventilation by functions?
- Trigger
- Limit
- Cycle
What is tigger ventilation?
- The event starting each breath
- No spont effort - Time - Set RR
- Spont effort - Minimum flow
What is limit controlled ventilation?
The factor that controls respiratory flow.
Ventilation by cycle control ?
- changing from insp to exp
- cycling signals include; Time, volume & flow
Classification of breathing systems?
- Open
- Semi-open
- Semi -closed
- Closed
What are the properties of Mapleson-A system?
- Efficient during SV
- Inefficient during CV
- FGF must equal patient’s alveolar MV to avoid re-breathing of CO2
- The co-axial version is called a Lack circuit
Why is Mapleson-A inefficient during CV?
Gas is forced from through the APL valve due to high pressure in the system. Thus system becomes inefficient
Scavenging and the Lack circuit (Co-axial Mapleson-A) ?
This makes gas scavenging much easier
What are the characteristics of Mapleson B circuit?
- Inefficient with both SV & CV
- During exhalation a mixture of FGF & alveolar gases pass via the APL valve
- During inspiration mixed FGF & retained alveolar gas is inspired
- FGF 2-3 times pts MV
What are the characteristics of Mapleson C circuit?
- Inefficient for SV & CV
- Used in the emergency setting
What are the characteristics of the Mapleson D system?
- Consists of a co-axial bain modification
- Inefficient for both SV & CV
- More fresh gas will be available with longer expiratory pauses
- At least 2 times the mV is required to prevent re-breathing (In both CV & SV)
What are the characteristics of the Mapleson D system?
- Consists of a co-axial bain modification
- Inefficient for both SV & CV
- More fresh gas will be available with longer expiratory pauses
- At least 2 times the mV is required to prevent re-breathing (In both CV & SV)
What are the characteristics of Mapleson F?
- Modified T-piece by jackson & Rees
- This is a low resistance circuit
- Used in paediatric anaesthesia
What are the safety features of an anaesthetic machine ?
- Vigilant & well-trained anaesthetist
- Power supply & back-up battery
Gas supply safety features of an anaesthetic machine ?
- Color coded pipes
- Non-interchangeable specific valves (wall)
- Non-interchangeable Screws Threads - NIST (Machine)
- Back-up cylinders connected via pin index system
Gas flow measurement and control safety features?
- Flow control - Needle valve reduces pressure from 4 bar to 1 bar
- Flow meter - O2 is the last flow meter added to the fresh gas
- Modern electronic flow meters
- Anti-hypoxic mixture devices
Vaporizer as a safety features?
- Electronic
- Color coded
- Agent specific
Other anaesthetic machine safety features ?
- Oxygen failure warning alarm
- APL valve
- Soda lime
- Common gas outlet
What is Saturated Vapor Pressure?
Think about a pot of boiling water covered with a lid? vapor in equilibrium with water
This is the partial pressure the vapor of a liquid will exert when the liquid and the vapor of that liquid are in equilibrium.
What is a vaporizer?
It is a device which produces the required concentration of an anaesthetic agent to the patient
Why do we need a vaporizer?
This is because the SVP for anaesthetic agents is much higher than required to produce anaesthesia at room temperature.
Classification of vaporizers?
Draw diagram
- Variable bypass vaporizers
- Measured flow vaporizers
Characteristics of the variable bypass vaporizer?
- FGF is split into two streams
- One stream enters the vaporizer chamber and the other bypasses
- The two streams rejoin to deliver the required concentration
- Conc. is controlled by using a flow splitting valve
Differences between VBV & MFV?
- VBV - Variable Bypass Vaporizer
- MFV - Measured flow vaporizer
MFV - Vapor is added to FGF
Example: TEC6 Desflurane vaporizer
Disadvantages of VBV?
- Flow dependent
- Low vapor conc. at high flows
- Overfilling vaporizer may increase conc
- Vapor leak via bypass chamber
- Increased vapor conc during IPPV (Bumping effect)
- No temperature compensation
What is latent heat of vaporization ?
This is the energy required to convert 1kg of a substance from liquid form to gaseous form. SI unit = Joule.kg-1
Vaporizers at high altitudes?
- No adjustment is required
- Partial pressure remains the same at high altitudes
- SVP remains constant at high altitudes
What is Beer’s law?
Absorbance of light passing through a medium is proportional to the concentration of the medium and its molar extinction coefficient.
What is Lambert’s law?
The absorbance of light passing through a medium is proportional to the path length
What is a pulse oximeter?
Used to measure the percentage saturation of haemoglobin with oxygen saturation utilizing Beer-Lambert’s law
Principles of pulse oximetry ?
- Uses absorption of infrared light
- Absorption by oxy & deoxy forms of Hb
- Red = 660nm and infrared= 940nm
- The pulsatile vessels cause two wave-forms
What is the isobestic point?
- Equal light absorption
- Value is 805nm (wave length)
Deoxy-Hb ?
- Absorbs more red light
What are the principles of capnography?
- Diatomic gas molecules
- Each diatomic gas absorbs radiation of particular wavelength
- Reference and sample chamber windows are made of crystal (silver bromide or sapphire) as glass absorbs infrared.
- Analyzer is calibrated using air
- Change in atmospheric pressure affects capnography
- Water vapor trap is required
- Hygroscopic tubing is needed
See page 42 EDAIC pass for capnography traces
see book
Components of an arterial line?
- Intra-arterial cannula
- Column of heparinized saline + Pressure 300mmHg
- Transducer
- Short, wide stiff tubing
Information from an intra-arterial BP monitor?
- BP
- HR
- Contractility (systolic Upstroke)
- SVR - Shape of the dicrotic notch
- Stroke volume - Measuring area under the curve
- Cardiac output
- Respiratory swing
Indications for Intra-arterial BP monitoring ?
- Trauma, surgery and inotropic support
- Frequent blood sampling
- Obese patients
- Arrhythmias
What are the early complications of IABP?
- Haematoma
- Ischaemia
- Pain
- Radial nerve injury
What are the late complications of IABP?
- Ischaemia
- Thrombosis
- Infection
What is the Allen’s test ?
Used to confirm adequate blood supply to the lower limb if the radial artery is occluded
What is the natural frequency?
This is the frequency at which the system will oscillate if disturbed and left alone.
It is proportional to the square root of length and diameter and inversely proportional to the compliance and density
What is the frequency of IABP?
- Above 40 hertz
What is resonance?
The tendency of a system to oscillate
What is damping?
The tendency of a system to resist oscillation
How is the effect of resonance removed from an IABP monitoring system?
Ensuring the natural frequency of the system is 10 times that of the fundamental frequency
What are the causes of damping?
- Air embolism
- Clots
- Kinked cannula
What are the characteristics of an over damped system ?
- Underestimating SBP
- Overestimating DBP
- MAP unchanged
What are the characteristics of an under damped system ?
- overestimates SBP
- Underestimates DBP
- MAP is unchanged
What happens when you flush the IABP monitor ?
It should oscillate 2-3 cycles before settling
What is the value for optimal damping?
0.64
What is the value for critical damping
value 1 - No oscillation