24. Disconnection monitors

Question 1

Which monitors are essential for
the induction and maintenance
of general anaesthesia

Answer 1

1
> Trained anaesthetist

2
> Anaesthetic machine that has been 
checked, 
airway equipment,
emergency drugs, 
self-inflating bag and 
alternative oxygen supply to be
immediately available

3
> ECG, blood pressure and oxygen saturations

4
> FiO2, EtCO2 with capnography and inhalational agent concentration
(±MAC)

5
> Ventilating volumes and airway pressures

6
> Temperature monitoring and peripheral nerve stimulation if muscle relaxant used

7
> Depth of anaesthesia monitoring
(e.g BIS or entropy) if total intravenous
anaesthesia or muscle relaxant used

Question 2

Which monitors would alert you to a disconnection in the

breathing circuit?

Answer 2

1

> The vigilant anaesthetist is the most important monitor!

2
In order to know which monitors would alarm,
three important factors
must be considered:

• Where in the circuit has the
disconnection taken place

• Whether the patient is breathing spontaneously
or being ventilated

• What alarm parameters have been set

3> Point of disconnection –
working from the patient end to the anaesthetic
machine,
a disconnection in the breathing circuit can occur between:

• The catheter mount and the airway device
• The HME filter and the catheter mount
• The breathing circuit and the HME filter
• The anaesthetic machine and the breathing circuit

4
> Spontaneously breathing –
working from the machine end to the patient,
if the disconnection has occurred
proximal to the point at which EtCO2
sampling takes place
(i.e. the EtCO2 sampling line is still connected
and
in continuity with the patient)
hen an EtCO2 trace would still be present
but the patient would
not be receiving fresh gas flow with inhalation
agents from the anaesthetic machine.

Inspired oxygen concentration and
volatile concentrations would
remain unaffected but the corresponding
expired concentrations would be zero.

> Ventilated patient –

whether the disconnection occurs
 proximal or distal
to the EtCO2 sampling port is 
irrelevant as the patient is apnoeic. 
The EtCO2 measurement and
 trace would be lost,
 tidal volumes and minute
ventilation would fall, and
 airway pressures would drop triggering alarms
(provided they have not been switched off).

The ventilator would also alarm as the bellows would not be able to fill.
Expired inhalational agent concentration,
MAC and
expired oxygen concentrations would also
drop.

Question 3

What would be the potential consequences of a disconnection in the breathing circuit?

Answer 3

1
> If disconnection occurs in the presence 
a trained, vigilant anaesthetist,
then theoretically it should be
 identified rapidly with no significant
consequences.

2
> However, if it takes longer to identify,
then a spontaneously breathing
patient would continue to
breathe room air and
over time would wake up
(provided he or she were not receiving total intravenous anaesthesia).

3
> A ventilated patient, following a disconnection, would remain apnoeic,
oxygen saturations would fall
(the time at which this occurs would
depend on the original FiO2 the patient was receiving),

would become hypoxic and,
if not corrected, there would be
 associated ECG changes
(most likely bradycardia), 
hypotension and eventually 
the patient would
suffer a cardiac arrest.

Therefore, depending on the outcome of the
disconnection,

this event could be classified as a critical incident
or a
serious incident requiring investigation (SIRI).