There are many potential hazards that may arise from anaesthesia; these include:

• Anaesthetic gas pollution (scavenge systems are essential).
• Self-injection with harmful drugs (proper restraint of patients during induction helps to prevent accidents).
• Explosions and fire (some electrical items should not be used in the presence of volatile anaesthetics).

In addition to the dangers to personnel, every animal undergoing an anaesthetic is at a certain degree of risk. Patients with pre-existing disease affecting the respiratory or cardiovascular system and those suffering from shock are classed as high risk cases and no matter how carefully they are monitored throughout the procedure that risk will always be present. However, dangers associated with equipment and apparatus can be virtually eliminated by frequent thorough safety checks, careful use and regular maintenance and servicing.

In the practical examination you may be asked to set up an anaesthetic circuit; remember that in practice you would never simply attach a piece of equipment to the anaesthetic machine without having at least first checked the gas supply and that of the vaporiser. It doesn't take a minute just to twist the vaporiser control and check that it dials correctly (remember to set it back to zero), nor is it time-consuming to press the emergency oxygen flush. It is sensible to keep a list of all the necessary checks and soon they will become second nature.

THE ANAESTHETIC MACHINE

1) Scavenge system - Before even thinking about touching the machine, check that the scavenge system is in place. A scavenge system is required by law to protect all involved in anaesthesia and should ALWAYS be used. Check any piping and casing for cracks or damage. If a fluabsorber (activated charcoal) is used it must be weighed regularly to ensure that it is replaced when spent. Other systems are passive, active-passive and active. The latter is the most efficient of all types.

2) Gas supply and flowmeter - Ensure that all cylinders are closed and fitted securely to the hanger yolk. The flowmeter control valves must also be closed since a rush of gas could cause the floates to hurtle upwards and cause damage. Press the oxygen flush to remove any residual gases from the machine and check that the pressure gauges read zero. Rotate the spindle of the oxygen cylinder slowly in an anti-clockwise direction and note the reading of the pressure gauge. Open the flowmeter control and ensure that the bobbin is freely floating; dirt or non-vertical positioning can cause inaccuracies and indicate the need for urgent servicing of the machine. Close the flowmeter and press the oxygen flush. Replace the cylinder if necessary and label as "in use" or "full" accordingly. If the machine holds a spare cylinder, this should also be tested. The nitrous oxide cylinders are checked in the same way but remember that the oxygen MUST be on or the alarm will sound. A scavenge pipe connected directly to the free gas outlet will prevent pollution.

3) Vaporiser - Ensure that the vaporiser is full before use. Calibrated vaporisers are agent specific and the port should be filled with a key-ended tube to prevent spillage and the use of the wrong anaesthetic. Rotate the dial to ensure that it moves correctly and then set to zero. Check that the filling port is tightly closed.

4) Oxygen flush - The oxygen flush (or emergency oxygen) is usually activated by a button located prominently on the front of the anaesthetic machine. Oxygen arrives directly from the cylinder and bypasses the vaporiser. Press the button and check for the high flow of oxygen from the common gas outlet.

5) Over pressure valve - The over pressure valve is useful for testing the system for leaks. Press the oxygen flush and occlude the common gas outlet. An alarm should sound when the valve is opens. If the alarm does not sound, gas is likely to be escaping elsewhere.

6) Nitrous oxide cutout device - Ensure the curtailment of nitrous oxide flow by opening both the oxygen and nitrous oxide flow valves and then closing that of the oxygen. Both floates should fall simultaneously and an alarm should sound.

7) Emergency air intake valve - The emergency air intake valve is opened by the inspiratory effort of the patient should gas flow from the machine stop. Room air then enters the system. Test the valve by attaching a length of pipe to the common gas outlet and then apply suction. The valve will open once a sufficient vacuum is present and an alarm will sound.

CIRCUITS

1. Check tubing for cracks, holes and dirt. Circuits should be hung when not in use and not kinked or squashed. Coaxial systems (where one pipe resides within another) may be difficult to assess.
2. Check reservoir bags for leaks; rubber is particularly perishable, especially if cleaned or stored incorrectly. Other rubber articles such as masks and endotracheal tubes should also be examined. Inflate the cuffs of endotracheal tubes prior to use.
3. Ensure that all connectors are removed prior to cleaning and correctly replaced. Again, check for cracks and other damage.
4. Check that any valves open and close freely.
5. If Waters canisters are used, the soda lime must be replaced once spent.

The importance of good maintenance of anaesthetic equipment cannot be stressed enough. Professional servicing should be carried out every 6 months and it is advisable to keep a file containing guarantees, instructions and service records for reference. All items should be cleaned and stored according to the manufacturer's instructions. If you are unsure of any aspect regarding the equipment be it how to use it, clean it, store it or whether it is damaged - ALWAYS ASK; you may prevent an accident.