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Archive for the ‘Ventilator alarms’ Category

Ventilator alarms.

These are very important items, and should be used whenever a ventilator is used, even if the ventilator is being constantly attended to, such as in the operating theatre.
They come in two forms.

a. The type that is included with a ventilator, you tend to only find these on the more modern ventilators, they are connected such that the machine can’t be used unless the alarm is in operation.
NOTE>>>>>>>>>>>However do remember that you whilst you can only operate the machine with the alarms being on, that is not much good if they are not correctly set to suit the needs of the patient on the machine at the time.

b. The stand-alone type, these may be used with any ventilator that does not have a built-in one, and as a rule, it is possible to use the ventilator and not turn them on.
This makes them less satisfactory, however, they are very useful where your ventilators are not fitted with alarms.

How they work.
Most will rely upon being connected into the patient circuit and receiving a pressure wave each time the patient receives a breath.
This pressure wave will operate a pressure switch this, in turn, will be connected to the electronics of the alarm, thus telling the alarm each time the patient gets a breath.
The more recent type that are fitted to the machines will rely much more on electrical signals generated within the ventilator.

What they do.
Some of the alarms will protect the patient from a number of different problems that could occur with a ventilator.
The most simple are called disconnection alarms and will simply guard against the possibility of the patient becoming disconnected from the machine, in these the electronic circuits will be able to detect a pressure wave from the patient tubes.
If the patient becomes disconnected then obviously there will be no pressure wave as all the air from the ventilator will spill out into the room. This will trigger the alarm after a short delay.

The electronics are made so that when the alarm is switched on an internal clock begins to count, should it not detect a pressure waveform within a set time limit it will sound an alarm.
This time limit will be about 10 seconds.
If all is well, the internal clock will start to count and when the pressure in the patient tubes rises above a set level the pressure wave is detected in the alarm and it resets the electronics which starts to count again.
The set pressure level in the alarm through which the pressure waveform from the ventilator must pass will be about 15 Cm H2O.
Here is a list of some of the things which a sophisticated alarm will be monitoring.

Overpressure.
If the pressure generated by the ventilator goes above the level you have set the alarm will trigger and on newer models it will dump the excess pressure, this protects the patient’s lungs from damage.

Disconnection or low pressure. (Cycle fail.)
Should the pressure fail to reach a set level in a set time the alarm will trigger and alert the staff of a possible disconnection, a large leak or simply that the machine is giving low pressures.
Some new machines combine overpressure and cycle fail into one control. Thus you set the control to the pressure reached, there is built into the electronics a window of 8 Cm H2O, that is 4 each side of the set position. This means that if the machine cycles to more than 4 above the set pressure the alarm goes off if it fails to reach 4 below the set pressure it will also alarm off.
This makes it easy to set and much less likely to be set wrong.

PEEP. (Positive end-expiratory pressure)
This is used when a PEEP. has been set on the machine, it will alarm if the level of PEEP drops below that which you have set.

CPAP.(Continuous positive airway pressure)
This is used when CPAP is being used and will alarm if the CPAP. level drops below that which you have set.

Minute volume.
This will alarm is the set minute volume drops below a given level.

Oxygen pressure
This is used on machines that are plugged into a wall gas supply, in this case, oxygen.
It will alarm if the oxygen input pressure (normally around 60 psi) to the ventilator falls below a set level.

FIO2 level (Fractionally Inspired Oxygen)
This is the level of oxygen set on a machine that has an oxygen mixer as part of it. It will alarm if the set level deviates from the high and low alarm settings.

Air pressure.
This is also used on machines that are plugged into a wall gas supply, in this case, air. It will alarm if the air input pressure (normally around 60 psi) falls below a set level.

Pressure differential.
If the input pressure difference between Air and Oxygen is greater than the set level it will alarm.

Power failure
This sets off an alarm if the electricity supply to the ventilator is cut off.

Lastly, and I repeat this again because it is most important, a ventilator should NEVER, I repeat NEVER, be used without at least a disconnection alarm fitted and CORRECTLY adjusted.

MAINTENANCE.
The greatest part of maintenance will involve checking the accuracy of them, making sure that if it is set to alarm at say 35 Cm H2O pressure, that it does do that, making sure that if the delay period is 21 second, for example, that that is what you get.
These are simply function and accuracy checks.
On some, you may need to replace a battery from time to time.
On the whole, they are quite reliable items that give little trouble.
You will get the most trouble from the staff using them, endless complaints that they don’t alarm off or alarm all the time.
You must take each complaint most seriously, failure of one of these to operate at a needed moment could be a serious matter, check it very well, leave it running on a ventilator with a 2 Ltr bag on the patient `Y’ piece ( so that the pressure on the ventilator is cycling correctly ) for a couple of hours before you say it is OK.
It might be that there IS a problem and the alarm is only doing its job, the alarm may indicate a problem with the ventilator perhaps a leak in the internal tubes for example, or the machine failing to cycle from time to time.
So although your experience tells you it is operator error, never take it for granted.
If there are problems with the unit they will be things like :
a. A leak in the pressure tube to it, or inside the unit.

b. a faulty pressure switch inside.

c. flat batteries ( if they are fitted ).

d. an electronic problem.

e. Incorrect adjustment, this last one is the most common and is caused by the user not setting it to suit the needs of the patient on the machine at the time.

You sometimes have to be a bit careful telling staff that they are at fault if it is in use at the time and you are called to look, the first thing to do is to watch the pressure gauge for a moment to get an idea of the pressures involved, then check the adjustment of the alarm, most times a little adjustment is all that is needed, sometimes nothing needs to be said to the operator, this saves upsetting anyone.
Lastly, I must repeat again, the ventilator alarm is a very important piece of equipment, people’s lives may depend upon it.
If you have a ventilator without an alarm and you are not able to get one, put a clear note on the machine for all to read saying so.

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