- Equipment 5
- valves
- incompetent inspiratory
- exhaled CO2 goes into inpiratory limb, causing rebreathing
- prolonged phase III, then slanting of the inspiratory phase, which may reach zero
- incompetent expiratory
- on inpiration, CO2 is taken from the expiratory limb
- prolonged phase II and slanting of the inspiratory segment, which never reaches zero
- suction
- carbon dioxide absorption
- soda lime
- components
- 80% Ca(OH)2
- 4% NaOH/KOH
- 16% water
- indicator dye
- phenolphthalein
- ethyl violet
- trace of silicates
- granules of 4-8 mesh (will pass through mesh with 4-8 strands per inch in each axis)
- reactions
- CO2 + H2O —> H2CO3
- H2CO3 + 2 NaOH —> Na2CO3 + 2 H20 + heat
- Ca(OH)2 + Na2CO3 —> CaCO3 + 2 NaOH + heat
- (+ some Ca(OH)2 + heat —> CaO + H2O
- OVERALL: CO2 + Ca(OH)2 —> CaCO3 + H20
- benefits
- low flows
- humidification + warming of gases
- 1kg absorbs 120 - 250L of CO2
- warms (up to 44 C) and humidifies circuit (up to 29 g/m3)
- cons
- compound A
- a penta fluoro iso propenyl fluoro methyl ether
- more likely when soda lime is dry and KOH rather than NaOH
- renal, hepatic and brain damage in rats
- CO
- volatiles with -CHF2 group
- des, iso and enflurane (‘DIE!’)
- when soda lime become dried out
- Baralyme
- calcium hydroxide and barium hydroxide
- compound A forms 5x faster
- Amsorb
- no CO or compound A formation
- Flow
- direct
- gas meter
- vitallograph
- water displacement spirometer
- indirect
- pressure
- constant resistance, variable pressure
- pneumotachograph
- resistance in circuit measured with a differential pressure transducer
- small bore tubes encourage laminar flow
- heating element prevents condensation
- constant pressure drop, variable resistance
- bobbin rotameter
- density important at top, turbulent flow
- viscosity important at bottom, laminar flow
- tin oxide coating to prevent static
- variable orifice
- accurate within 2%
- read falsely high in hyperbaric conditions
- Wright peak flowmeter
- Quantiflex mixer flowmeter
- one dial for desired O2 percentage
- other dials for FGF
- reduces risk of hypoxic mixtures
- can easily change gas flows while keeping proportions the same
- mechanical movement
- Wright’s spirometer
- 150 revs per litre of gas flow
- accurate within 5% w. 4 - 24 L/min
- minimum flow 2L/min to work
- heat transfer
- pitot tube
- ultrasound
- USS speed increased if flow in same direction
- pollution
- Scavenging
- passive
- to air
- pressure relief valves
- high: + 5cmH20
- low: -0.5cmH20
- often also have a reservoir bag
- Cardiff charcoal aldasorber
- does not absorb nitrous
- difficult to tell when exhausted
- require replacement every 12 hours
- heating causes release of agents back to the atmosphere
- active
- 4 components: collection system, transfer system, receiving system, disposal system
- operating theatres change the air at least 20x/hour to reduce ambient gas concs