Equipment and Monitoring Flashcards
Tell me about the Bourdon Gauge…
Aneuroid gauge which can be used to measure pressure, and indirectly temperature.
Robust and flexible coiled metal tube linked to a cog and a pointer - when high pressure enters the tube it uncoils and the pointer moves across a calibrated scale
Calibrated and colour coded for different gases, pipeline or cylinder - can’t be used to nitrous oxide.
Can be attached a liquid containing bulb that will expand with temperature change and uncoil the tube.
Tell me about the Wright respirometer…
A vane encircled by housing containing angled slits; gas inlet and outlet, calibrated dial
Measures gas volumes.
Gas enters and exerts a rotational force on the vane. Via a set of gears, the spin moves a pointer on a calibrated scale; 150 revolutions per 1L of gas
Simple and cheap, but overreads at high flow and underreads and low flow.
Only measures flow in one direction, so need two to measure insp and exp.
Error of 5-10%, vulnerable to water vapour condensation
Modern versions use a infrared beam to count rotations.
Tell me about pneumotachographs…
Devices used to measure gas flow - constant orifice variable pressure.
Types; screen, Fleisch and Pitot tubes. Hot wire similar.
E.g. Screen - gauze across a widening in the tube, resistance causes drop in pressure across the screen, measured by a differential pressure transducer.
Hot wire - two thin metal strips at 90deg to each other heated to constant temperature; resistance is temperature dependent so as gas flows and wire cools, resistance changes proportional to flow.
Tell me about scavenging…
Designed to reduce environmental anaesthetic gas concentrations
Can be active or passive
Active systems use a pump to generate negative pressure and require an open system to prevent negative pressure reaching the patient
Passive systems use the positive pressure generated by patient’s expiration to transmit gas via a closed system
Four components:
1. Collecting - connects to the APL valve via a 30mm connector
2. Transfer - corrugated plastic hose connects collecting to receiving
3. Receiving - reservoir or length of tubing
4. Disposal - active is high flow low pressure vacuum to draw exhaust gases
- passive tubing directly vents to the atmosphere through an external wall
Activated charcoal adsorbers are passive - absorb halogenated anaesthetic agents but not nitrous oxide; saturated after 12 hours.
Tell me about the BPEG classification of pacemakers…
Agreed nomenclature; 5 letters each relating to a separate function.
I - chamber being paced - V, A, D, O
II - chamber being sense - V, A, D, O
III - mode of response - T, I, D, O
IV - programmable functions - R, C, M, P, O
V - anti-tachycardia function - O, P, S, D
e.g. DDDR is dual chamber paced, sensing, triggered or inhibited, rate modulated
How can gas flow be measured?
Medical or patient gas flow.
Medical gas flow - rotameters
Patient gas flow - mini Wright peak flow, or a device within a breathing system such as a pneumotachograph
Variable pressure variable orifice - Watersight
Variable pressure constant orifice - Pneumotachograph
Constant pressure variable orifice - Bobbin rotameters, Wright peak flow
Others; hot wire, pitot tubes, ultrasonic
Tell me about the Manley ventilator…
The Manley ventilator is a minute volume divider and has two bellows and three valves.
The total flow set at the flowmeters is the minute volume; therefore the Manley is classed as a minute volume divider.
The tidal volume is preset.
It does have the appropriate connections compatible with anaesthetic gas scavenging systems.
In spontaneous ventilation it acts as a Mapleson D breathing system (not Mapleson E), which requires high fresh gas flows to prevent rebreathing
What are the main classes of electrical equipment?
I: outer causing connected to earth; a fault melts the fuse and cuts off supply
II: double insulation, doesn’t need an earth connection
III: electrical supply derived from separated extra safety voltage (SELV), low enough that risk of shock is low, microshock may still occur.
I and II subclassified:
B: body - maximal leakage 500μA
BF: body floating - isolating capacitor or transformer, leakage 500μA
CF: cardiac floating - least likely to cause microshock, 50μA
COSHH recommended maximum allowed air concentrations…
NO - 100ppm
Iso/des/sevo - 50ppm
Halothane - 10ppm
8 hour time weighted average
Flow rates through cannulae…
Blue 22G 30mL/minute
Pink 20G 55mL/minute
White 17G 135mL/minute
Grey 16G 180mL/minute
Orange or brown 14G 270mL/minute
