Machine, Breathing Systems and Monitoring Flashcards
Three roles of the anaesthetic machine
- create an artificial atmosphere
- maintain general anaesthesia
- emergency life support (positive pressure ventilation)
Essential components of anaesthetic machine
- supply of gas
- measurement of gas
- anaesthetic vaporisers
- breathing circuit
- resuscitation apparatus
Gasses and their outlet colours
OXYGEN - white
NITROGEN - black
AIR - white and black blocks
N2O - blue
ENTENOX (50% EACH OF N20 AND O2) - blue and white blocks
CO2 - grey
VACUUM SYSTEM - yellow
Forms of gases when compressed
LIQUID (therefore must weigh to determine level)
- nitrous oxide
- carbon dioxide
GAS (therefore must see pressure to determin levels)
- Oxygen
- Nitrogen
- Air
Name of the mechanism that alerts one when oxygen supply fails
Ritchie Whistle
Minimum ammount of oxygen required during anaesthesia
30%
Reasons for higher oxygen requirement during anaesthesia
- increased ventilation/perfusion mismatch during anaesthesia
- exhaled gases are saturated with water vapour, therefore dilution occurs
Formula for minute volume
Minute Volume = Tidal Volume x Respiratory Rate
Tidal volume usually = 8 mg.kg-1
Resp rate usually = 9 breaths.minute-1
Functions of anaesthetic breathing system
- provide sufficient peak inspiratory flow
- prevent rebreathing of expired alveolar gas
- prevent contamination of inspired gases by atmospheric air
- minimal resistance to breathing
Define: Dead Space, Total Dead Space, Physiological Dead Space
DEAD SPACE: portion of tidal volume that does not participate in alveolar gas exchange (contains very little CO2, therefore is re-breathable)
TOTAL DEAD SPACE = Apparatus Dead Space + Physiological Dead Space
PHYSIOLOGICAL DEAD SPACE = Anatomic Dead Space + Alveolar Dead Space
T-Piece Breathing Systems: Advantage and Disadvantages
ADVANTAGES
- compact
- reduced dead space
- reduced resistance (because no valves)
- good for controlled ventilation
DISADVANTAGES
- potential for hypercapnea if fresh gas flow too low
- wasteful in spontaneous ventilation
Modifications to T-Piece Breathing Systems
- Jackson-Rees: reservoir bag to R-limb
- Mapleson-D: spring-loaded valve to bag inlet
Magill Breathing System
Wasteful of Fresh Gas during controlled ventilation.
Coaxial breathing system
Circle Breathing System: Advantages and Risks
ADVANTAGES
- economy of gas and volatile agents
- conservation of heat and moisture
- prevention of atmospheric pollution
RISKS
- disconnections
- unidirectional valves stuck in open position –> CO2 rebreathing
- expiratory valve stuck in closed position –> pneumothorax
Components of Soda Lime (CO2 reabsorber)
calcium hydroxide
sodium hydroxide
water
ethyl violet (pH sensitive dye)
Equation of Soda Lime
- H2O + CO2 —> H2CO3
- 2NaOH + CO2 —> Na2CO3 + 2H2O + heat
- Na2CO3 + Ca(OH)2 —> CaCO3 + 2NaOH
Risks of CO2 absorbers
- react with volatiles to form carbon monoxide
- formation of “Compound A”
Clinical Monitoring Used
- respiration
- oxygenation
- circulation
- temperature
- depth of anaesthesia
- renal function
- muscle power
- blood glucose
Stages of Anaesthesia
STAGE I: induction to loss of consciousness (LOC)
STAGE II: LOC to automatic breathing
STAGE III-1: automatic respiration to eyeball paralysis
STAGE III-2: eyeball paralysis to intercostal paralysis
STAGE III-3: commencement to completion of intercostal paralysis
STAGE III-4: complete intercostal paralysis to diaphragmatic paralysis
STAGE IV: diaphragmatic paralysis, apnoea, death
Stages ideal for anaesthesia
Stage III levels 2-3
Specialised Monitoring Used
- blood pressure (manual, automatic, direct)
- ECG
- pulse oximetry
- capnography
- CVP
- peripheral nerve stimulation
- bi-spectral index
- temperature
Bi-Spectral Monitor Values
100: Awake EEG
0: Electrical silence
65-85: sedation
40-65: general anaesthesia
