Archive for the ‘Humidifier’ Category


When someone is on a ventilator or even just being given oxygen by a mask, the oxygen that they get comes from a concentrator, from a liquid oxygen tank or from a gas cylinder, if it is from the concentrator then there is no real problem, however, if it is coming from one of the other sources you get two troubles, one is that the oxygen is very cold and the other is that it is very dry. This leads to problems in the lungs and airways, so what is needed is to warm and moisten the oxygen.
This is done with a humidifier.
Humidity is the amount of water vapour in a gas.
The absolute humidity is the mass of water vapour per litre of gas and is expressed as mg/L.

Maximum capacity is the maximum amount of vapour that a given volume of gas can hold.
Gases at maximum capacity are often referred to as being saturated. If the temperature of a gas drops, water will fall out of the gas as condensation.

Relative humidity (RH) is the ratio of the absolute humidity to the maximum capacity, expressed as a percentage.
There are various ways of doing this but most often they involve passing the oxygen over or through warm water, there are one or two other ways but less common.
The temperature of the water is regulated by a controllable thermostat, this controls a heating element, the temperature of the water obviously controls the temperature of the air reaching the patient.
Now the most important thing is that the air reaching the patient is never greater than body temperature, if it is then the lungs and airways can get burned.
For this reason the best of the humidifiers are electronically controlled.
The temperature sensor for the thermostat is in the gas pipes to the patient, this checks the temperature and controls the thermostat, the doctor will set the thermostat control to the required temperature then if it decides that the temperature is too hot it will turn down the heater, if it is too cold it will turn the heater up.
It is most important that the sensor is situated as close to the patient’s mouth as possible (on the inspiratory limb), to give accurate readings.
There will also be an alarm system that you can set that will sound off if for some reason the temperature goes above that which you have set.
The more simple ones won’t have all this, and for this reason you have to keep a closer eye on them.
The temperature that the patient gets will not be the same as the temperature of the water, the patient temperature depends upon a lot of things, the flow rate of the gas, the room temperature, and if the patient tube is heated or not, very long patient tubes between the humidifier and the patient will make a difference, the air will have longer to cool down as it passes through the tube, more sophisticated humidifiers will have a heated wire in the tube, this keeps the air passing along it warm and thus prevents excess condensation on the tube walls, and makes sure that the patient gets the humidification required.
Lastly, there is a safety gain by having a heated inspiratory tube going tho the patient in that you do not have to have the water temperature as hot to allow for the heat loss in the patient tubes.

So whatever temperature the water is at you must check the temperature at the patient end having set up your gas flow, you can use an ordinary thermometer which is put into the airflow.
In some places the humidifiers that I have just described are no longer used when only very low levels of humidity are needed.
What is used now is a thing called an artificial nose, it consists of a holder which connects into the patient circuit between the end of the tubes from the ventilator and the endotracheal tube, inside is a sponge which is kept moist, this will moisten the air as it passes through, another device often used is the same sort of thing except that it has rolled up paper in it this picks up the moist expired air, as the inspired air comes past it so it picks up the warmth and moisture, these can be used a few times, but obviously the inserts will have to be changed to avoid cross infection. Saves a lot on electricity as well, and there is no chance of the patient getting burned.
As far as the maintenance of humidifiers goes, there is not very much.
Repairing leaks to the water container, making sure, on some types, that there is a gas-tight seal. Lastly and most importantly that the electrical side is in good order, from two points of view

a. Not wanting to damage the patient

b. That you are mixing electricity and water, and that can be dangerous.
As a result it is most important that you do regular checks on these pieces of equipment, fill them up and run them for half an hour or so and check that the thermostat controls the temperature correctly.
Check the condition of the earthing and the wiring inside the control box.
Carry out an electrical safety check.
If they use temperature sensors to automatically control the temperature check that these are working correctly.

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