The practical conduct of anaesthesia

Equipment checks

Anaesthetic equipment should be up-to-date and maintained regularly and the instruction manuals available and accessible. An equipment check must be performed before an operating theatre session begins, because a common cause of problems is the use of a machine that has not been checked properly and which malfunctions. An adequate check of anaesthetic apparatus is an integral part of good practice; failure to check the anaesthetic equipment properly may amount to malpractice.

Operating theatre staff usually carry out checks when setting up an operating theatre for use or after apparatus has been serviced or repaired, but the ultimate responsibility for ensuring that the apparatus is safe for its intended use rests with the anaesthetist. Sophisticated tests may have been performed after major servicing, but key control settings may have been altered, and it is essential that the anaesthetist checks that the equipment is in proper working order and ready for clinical use. The final check is the sole responsibility of the anaesthetist who is to use the machine; it cannot be delegated to any other person. There is no justification for proceeding with an anaesthetic when faults have been identified in the equipment. If there is no record of an adequate preoperative check of equipment and a problem occurs as a result of equipment failure, it is very difficult to defend an allegation of negligence.

At its most basic, the function of an anaesthetic machine is to enable the anaesthetist to administer oxygen under pressure without leaks. If all else fails, this allows the anaesthetist to maintain cerebral oxygenation. Anaesthetic apparatus should be checked before the start of each operating session in a logical sequence, as recommended on the Association of Anaesthetists checklist ( Table 22.1 ). Further checks should be undertaken between cases ( Box 22.1 ). The primary intention of the anaesthetic machine check is to ensure that it is safe to use and will deliver gases under pressure without leaks. These checklists are available as laminated cards intended to be attached to all anaesthetic machines in the UK and Ireland.

In most industries in which complex equipment is used, full training is provided for users. It is not acceptable for anaesthetists to assume that they intuitively understand an anaesthetic machine they have not used before. Those new to the specialty require detailed instruction and training in the use of anaesthetic equipment, but even experienced anaesthetists need tuition in the use of new equipment.

Alternative means of ventilation

The early use of an alternative means of ventilation, namely a self-inflating bag that does not rely on a source of oxygen to function, may be lifesaving. A self-inflating bag must be immediately available in any location where anaesthesia might be given. An alternative source of oxygen should also be readily available.

Perform manufacturer's machine check

Modern anaesthesia workstations may perform many of the following checks automatically during start-up. Anaesthetists must know which are included and ensure that the automated check has been performed.

Power supply

The anaesthetic workstation and relevant ancillary equipment must be connected to the mains electrical supply (where appropriate) and switched on. The anaesthetic workstation should be connected directly to the mains electrical supply and only correctly rated equipment connected to its electrical outlets. Multisocket extension leads must not be plugged into the anaesthetic machine outlets or used to connect the anaesthetic machine to the mains supply. Hospitals should have backup generators, and many operating theatres have their own backup system. Backup batteries for anaesthetic machines and other equipment should be charged.

Gas supplies and suction

The gas supply master switch (if one is fitted) should be switched on. On some workstations it is necessary to disconnect the oxygen pipeline to check the correct function of the oxygen failure alarm, although on machines with a gas supply master switch, the alarm may be operated by turning the master switch off. Repeated disconnection of gas hoses may lead to premature failure of the Schrader socket and probe, and current guidelines recommend that the regular check of equipment includes a tug test to confirm correct insertion of each pipeline into the appropriate socket (see later). It is also recommended that the oxygen failure alarm is checked once a week by disconnecting the oxygen pipeline with the oxygen flowmeter turned on; the alarm must sound for at least 7 s. Oxygen failure warning devices are also linked to a gas shut-off device. Anaesthetists must be aware of both the tone of the alarm and which gases will continue to flow on the anaesthetic machine.

Breathing system and vaporisers

All breathing systems which are to be used must be checked and a two-bag test performed before use ( Box 22.2 ). Breathing systems should be inspected visually for correct configuration and assembly. All connections within the system and to the anaesthetic machine should be checked to ensure that they are secured by push and twist. It should be ensured that there are no leaks or obstructions in the reservoir bags or breathing system. A pressure leak test (between 20 and 60 cmH ₂ O) should be performed on the breathing system by occluding the patient end and compressing the reservoir bag.

Manual leak testing of vaporisers (see later) was previously recommended. It should only be performed on basic Boyle machines because it may be harmful to modern anaesthetic workstations. Manufacturer's recommendations should be reviewed before performing a manual test.

The anaesthetist should check that the vaporisers for the required volatile anaesthetic agents are fitted correctly to the anaesthetic machine, any locking mechanism is fully engaged and the control knobs rotate fully through the full ranges. Vaporisers should be adequately filled but not overfilled, and the filling port must be tightly closed. Tilting vaporisers can result in delivery of dangerously high concentrations of vapour, and therefore they must always be kept upright. All vaporisers must be turned off after they have been checked.

It may be necessary to change a vaporiser during use, although this should be avoided if at all possible. If a change is necessary, repeat the leak test because failure to do so is a common cause of critical incidents. Some anaesthetic workstations automatically test the integrity of vaporisers.

It is only necessary to remove a vaporiser from a machine to refill it if the manufacturer recommends this.

Carbon dioxide absorber

The contents and connections should be checked to ensure that there is an adequate supply of CO ₂ absorbent and that it is of an appropriate colour.

Alternative breathing systems

If a coaxial system is in use, an occlusion test should be performed on the inner tube and a check should be made that the adjustable pressure-limiting (APL) valve, where fitted, can be fully opened and closed.

Correct gas outlet

Special care must be exercised if the anaesthetic machine incorporates an auxiliary common gas outlet (ACGO). Incidents of patient harm have resulted from misconnection of a breathing system to an ACGO or incorrect selection of the ACGO.

Breathing systems

Whenever a breathing system is changed, either during a case or a list, its integrity and correct configuration must be confirmed. This is particularly important for paediatric cases, when breathing systems may be changed frequently during an operating list.

Ventilator

It is important to check that the ventilator is configured correctly and the ventilator tubing is attached securely. The controls should be set according to the intended use of the ventilator, and the system should be checked to ensure that adequate pressure is generated during the inspiratory phase. Ventilator alarms should be checked to ensure that they are working and correctly configured. The pressure relief valve should be checked to ensure that it functions correctly at the set pressure.

Scavenging

The anaesthetic gas scavenging system should be checked to ensure that it is switched on and functioning and that the tubing is attached to the appropriate exhaust port of the breathing system, ventilator or anaesthetic workstation.