ANSWERS

1. How should volatile agents be stored?
   Volatile agents (eg. Fluothane and Halothane) should be stored in their original packaging at room temperature. The amber bottles in which they are supplied, plus the protective cardboard outer helps to prevent degeneration by light. Volatile agents should never be left on a windowsill as heat will cause evaporation and may represent an explosion hazard. The lid must be tightly applied in order to prevent spillage and evaporation, both of which pose a risk to staff who should not inhale the vapours.
2. How should gas cylinders be stored?
   Gas cylinders should be stored outside of the surgery, ideally in a shed or storage box designated solely for this purpose. The area should be cool, clean and dry to prevent any damage to the cylinders. Full cylinders should be marked clearly as such; most have a red seal which is removed once the cylinder is in use. Hazard warning signs stating that gases are stored and the prohibition of smoking must be clearly displayed.
3. How should anaesthetic circuits be cleaned and stored?
   • Turn off the anaesthetic gases and close the cylinders.
   • Remove the anaesthetic circuit from the machine detaching it from the common gas outlet.
   • Disassemble the circuit and gently clean tubes, connectors and rebreathing bags in mild detergent to remove organic matter such as blood and saliva.
   • Rinse well.
   • A disinfectant solution may then be used to kill bacteria, but thorough rinsing must be performed following this procedure.
   • Hang tubes and bags to dry in a warm environment, remembering that rubber rebreathing bags are perishable and should not be exposed to extremes in temperature.
   • Carefully check each component of the circuit for damage before reassembling when dry.
   • Circuits should be stored in a clean, dry and dust free environment.
4. What is the procedure for the cleaning of endotracheal tubes?
   First use a detergent solution to remove organic matter such as blood and saliva. Special brushes are available which may be passed through the entire tube to ensure that the inside is thoroughly cleaned and that there are no blockages. Rinse well before hanging to dry. Remember that endotracheal tubes have a limited life and that the rubber balloons are particularly prone to damage. Always inflate the balloon before storage to ensure that there are no punctures or blockages.
   NB. Some practices use a cold sterilising solution such as Novasapa following cleaning with a detergent. Again, this should be rinsed off thoroughly.
5. Explain the importance of good ventilation and an efficient scavenge system when inhalation agents are employed.
   Exposure to anaesthetic gases is a serious risk to personnel and is associated with neoplasia, neuropathy, infertility and bone marrow toxicity. In pregnant women a high incidence of abortion and congenital abnormalities have been reported. It is therefore an absolute necessity that a suitable scavenge system is employed (active types are considered the most efficient). Good ventilation is also essential, particularly in the recovery area where the patients exhale waste gases.
6. 6) What items should be close to hand on the anaesthetic trolley and why?
   • Lubricant - to aid the passing of the endotracheal tube; clumsy intubation may result in laryngospasm.
   • 2.5cm White open weave bandage - to securely tie in the endotracheal tube.
   • Cuff inflator - to inflate the balloon of the endotracheal tube and prevent the patient from breathing around it.
   • Oesophageal stethoscope - for monitoring the patient's heart during anaesthesia.
   • Rectal thermometer - to monitor the temperature of the patient during anaesthesia.
   • Monitoring sheet - to record details of the anaesthetic and the depth of the patient throughout the procedure.
   • Full/in-use/empty cylinder labels - to ensure that the correct gas cylinder is always in use.
   • Spanner - to tighten cylinders to the hanger yolk and prevent leakage.
   • Cylinder washers - to create a seal between the cylinder and hanger yolk, again preventing leakage.
   • Curved scissors, antiseptic solution, swabs, spirit, scalpel blade and intravenous catheters - to gain venous access for the administration of fluids and/or drugs in an anaesthetic emergency.
   • Emergency drugs - see Module 8.
7. List 6 important checks to be made to the anaesthetic machine prior to use.
   • Ensure that the scavenge system is attached.
   • Check the gas supply and flow meters.
   • Ensure that the vaporiser is full.
   • Check the emergency oxygen (oxygen flush) and emergency air intake valve.
   • Check the over pressure valve.
   • Check the nitrous oxide cut out device.

   Practical Task 2 - Safety Aspects of the Anaesthetic Machine and Circuits covers this subject in detail.

8. In addition to your answers to Q7, list 6 actions that should be carried out on a daily basis to maintain equipment used in gaseous anaesthesia.
   • Replenish any items used from the emergency box.
   • Check circuits, rebreathing bags, endotracheal tubes and connectors for damage and replace if necessary.
   • Remove and replenish empty gas cylinders.
   • Check the status of soda-lime if used and replace if necessary.
   • Thoroughly clean circuits (see Q3).
   • Thoroughly clean the anaesthetic machine and trolley (see Q9).
9. How should the anaesthetic machine be cleaned?
   • Before the day's procedures all surfaces of the anaesthetic machine should be damp dusted in order to maintain sterility in the theatre.
   • Between use, any organic material such as blood or saliva should be removed with a damp cloth and detergent (care must be taken not to use too much water as this may cause damage to the machine); ensure that patients do not ingest soap bubbles!
   • At the end of the day, the gas cylinders should be turned off, circuits disconnected and everything removed from the anaesthetic trolley; clean all surfaces including the vaporiser and cylinders with detergent to remove organic matter and then use a suitable disinfectant such as Trigene diluted to the correct strength.
     NB. If used, Schraeder probes should be removed from the wall socket and the pipes neatly coiled.
10. How frequently should professional servicing of the anaesthetic machine be performed?
    Every six months. A service logbook should be kept and the anaesthetic machine itself must be labelled with a sticker showing the date of the last service and when the next one is due.
11. Describe a pulse oximeter.
    The pulse oximeter is a photoelectric instrument that measures the oxygen saturation of a patient's blood and shows a digital display of the pulse rate. The machine should never be relied upon as a sole source of reassurance however. The patient is connected to the machine by a probe which usually attaches to the tongue, lip or ear, and by measuring the absorption of selected wavelengths of light arterial oxygen saturation is interpreted. Always refer to the manufacturers' instructions as to operation and maintenance and ensure that batteries are not allowed to run low.
12. Describe a laryngoscope.
    A laryngoscope consists of a handle, blade and light source. It is used to depress the base of the tongue and evert the epiglottis during intubation.
13. Describe the 4 types of scavenge system in use in veterinary practice; which is the most efficient? The types are listed below in order of efficiency (with the most efficient first):
    • Active - consisting of a transfer, receiving and disposal system involving an active suction unit such as a fan or pump.
    • Active-passive - the use of a wide bore tube from the expiratory valve of the circuit which passes the gas to a forced ventilation system.
    • Passive (to outside) - reliant upon the patient's respiratory efforts to transfer the gases via a wide bore tube to the outside.
    • Passive (to charcoal absorber) - as above but the gases are chemically absorbed rather than transferred to the outside (nitrous oxide is not absorbed by this method).
14. How would you gauge the content of gas cylinders, soda lime canisters, charcoal absorbers and volatile agent levels?
    • Gas cylinders - may be weighed, monitor the pressure/contents gauge once the cylinder is attached to the anaesthetic machine.
    • Soda lime canisters - observe for colour change (be careful, because some soda lime changes from pink to white when spent, some changes from white to mauve).
    • Charcoal absorbers - must be regularly weighed.
    • Volatile agent - Monitor the measuring gauge on the vaporiser of the anaesthetic machine.
15. Describe the function of the following parts of the anaesthetic machine/circuit: i) Expiratory valve ii) Flow meter iii) Oxygen flush iv) Reducing valve v) Vaporiser
    • Expiratory valve - a valve which allows the escape of gas in a semi-closed system.
    • Flow meter - a calibrated device which controls the amount of gas administered to the patient.
    • Oxygen flush - also known as emergency oxygen; delivers fresh oxygen directly to the common gas outlet.
    • Reducing valve - a valve sited between the cylinder and flow meter allowing delicate control of the gas flow.
    • Vaporiser - an agent specific calibrated device which allows volatile liquid to vaporise; the vapour concentration is adjusted by selecting the desired percentage on the dial.
16. What is meant by "co-axial" and which circuits possess this property?
    Co-axial means a tube within a tube. The Lack and Bain systems are examples of coaxial circuits. In the Lack, the outer limb is inspiratory and surrounds an inner expiratory tube. In the Bain, the outer limb is expiratory whilst the inner is inspiratory.
17. What is the Magill circuit also known as?
    Mapleson A.
18. In which circuit might a Jackson Rees modification be employed?
    Ayres T piece; the Jackson Rees modification is the inclusion of an open ended reservoir bag on the expiratory limb.
19. List circuits suitable for cats and small dogs.
    • Ayres T piece.
    • Ayres T piece with Jackson Rees modification.
    • Coaxial Lack.
    • Bain Mapleson E.
    • Bain Mapleson F.
20. List circuits suitable for medium to large dogs.
    • Magill.
    • Coaxial Lack.
    • Parallel Lack.
    • Bain Mapleson D.
    • To & Fro system.
    • Circle system.
21. What are the gas flow rates required for closed circuits?
    5-10 mls/kg/minute (more than 10mls may be necessary if used as low flow circuits).
22. What is meant by the term "circuit factor"?
    The circuit factor is a term used to describe the amount by which the calculated tidal volume of the patient is multiplied by in order to administer the correct amount of gas. Each type of circuit has its own circuit factor, apart from the closed systems (To & Fro and Circle system) - see Q21.
23. State the circuit factors for the following circuits: Ayres T piece, Bain (Mapleson D, E and F), Lack, Magill.
    • Ayres t piece = 2.5-3
    • Bain (Mapleson D, E and F) = 2.5-3
    • Lack = 1-1.5
    • Magill = 1-1.5
24. Describe the modified Lack circuit, and explain how it differs to the standard Lack circuit.
    There are 2 types of Lack system. The standard Lack consists of a double tube (described as coaxial) through which the animal breathes. The outer tube is the inspiratory limb and connects to a reservoir bag, whilst the inner tube is the expiratory limb. The modified Lack is also known as the parallel Lack and consists of a parallel configuration of the inspiratory and expiratory limbs. This avoids the problems of coaxial systems including disconnection, fracture or kinking of the inner limb.
25. Nitrous oxide can be safely used in semi-closed (non-re-breathing) circuits, but must be used with caution in closed (re-breathing) circuits. What must be measured if nitrous oxide is employed within a closed circuit and why?
    It is essential that the carbon dioxide level of the blood is monitored since hypercapnia (hypercarbia) is a risk.
26. What is intermittent positive pressure ventilation?
    This is a technique used to "breathe" for the patient should natural respiration cease. The rebreathing or reservoir bag is filled with oxygen and squeezed intermittently to fill the patient's lungs. If an open-ended bag is used, the end needs to be occluded. A modest amount of carbon dioxide may be necessary to promote the return of natural breathing.
27. Describe how the Bain Mapleson D, E and F circuits differ.
    • The Mapleson D possesses a closed reservoir bag and is suitable for cats and small dogs.
    • The Mapleson E does not possess a reservoir bag and is suitable for animals larger than 10kg.
    • The Mapleson F possesses an open-ended reservoir bag and is suitable for animals larger than 10kg.
28. What is meant by the term "tidal volume"?
    Tidal volume is the amount of gas inspired and expired in one breath. It is expressed in mls and is estimated at 10-15mls/kg. Larger animals tend to require 10mls/kg whilst cats and toy breeds require 15mls/kg.
29. What is meant by the term "minute volume"?
    Minute volume is the amount of gas inspired and expired over the duration of one minute. It is expressed in mls which may then be converted to litres. It is calculated by multiplying the TIDAL VOLUME by the respiratory rate.
30. How would you work out the gas flow rate for a 4kg cat with a respiratory rate of 20 breaths per minute (an Ayres T piece is to be used)?
    • First estimate the TIDAL VOLUME which is 10-15mls/kg 15 x 4 = 60mls.
    • Next calculate the MINUTE VOLUME (tidal volume x respiratory rate) 60 x 20 = 1200mls or 1.2L.
    • Finally multiply the minute volume by the CIRCUIT FACTOR 1.2 x 2.5 = 3L.
31. How would you work out the gas flow rate for a 20kg dog with a respiratory rate of 10 breaths per minute (a Magill circuit is to be used)?
    • First estimate the TIDAL VOLUME which is 10-15mls/kg 10 x 20 = 200mls.
    • Next calculate the MINUTE VOLUME (tidal volume x respiratory rate) 200 x 10 = 2000mls or 2L.
    • Finally multiply the minute volume by the CIRCUIT FACTOR 2 x 1.5 = 3L.
32. If nitrous oxide is to be used, what ratios of oxygen to nitrous are suitable?
    • 50% Nitrous and 50% Oxygen.
    • 66% Nitrous and 33% Oxygen.