Methods of humidification

There are many devices that can be used to supply humidification (see Table 1.2). The best of these will fulfil the following requirements:

1 The inspired gas must be delivered to the trachea at a room temperature of 32–36ºC and should have a water content of 33–43 g/M3.
2 The set temperature should remain constant; large ranges of flow should not affect humidification and temperature.
3 The device should have a safety and alarm system to guard against overheating, over-hydration and electric shocks.
4 It is important that the appliance should not increase resistance or affect the compliance to respiration.
5 It is essential that whichever device is selected, wide-bore tubing, that is, tubing with a wide internal diameter (sometimes referred to as elephant tubing), must be used.

General considerations of oxygen administration
1 Oxygen is an odourless, tasteless, colourless, transparent gas that is slightly heavier than air.
2 Oxygen supports combustion, therefore there is always a danger of fire when oxygen is being used.

The following safety measures should be remembered:
(a) Oil or grease around oxygen connections should be avoided.
(b) Alcohol, ether and other inflammatory liquids should be used with caution in the vicinity of oxygen.
(c) No electrical device must be used in or near an oxygen tent.
(d) Oxygen cylinders should be kept secure in an upright position and away from heat.
(e) There must be no smoking in the vicinity of oxygen.
(f) A fire extinguisher should be readily available and all staff have a responsibility to be competent in its use.

Table 1.2 Devices for humidification
Device	Use	Benefits	Problems
Condensers (Swedish nose)	Perform function of nasopharynx	Retain heat and water from expired air and return to inspired air	Heated humidifiers may be preferable for long-term use
Cold water bubble humidifiers	Deliver partially humidified oxygen	Achieve about 50% humidity	Inefficient
Water bath humidifiers	Deliver adequately humidified oxygen	Achieve about 100% humidity	Overheating may damage trachea. Efficiency can alter with flow rate/surface area and water temperature. Condensation and collection of water in delivery tubes. Micro-contamination of stagnant water possible
Aerosol generators	Provide micro-droplets of water suspended in the gas	Can achieve highly saturated gas. Device not governed by temperature