Thu11November0840AM 3

A 74-year-old male is scheduled for a resection of a tongue carcinoma, radical neck dissection and the creation of an osteocutaneous flap to cover the tissue defect. The duration of surgery is expected to be 12 hours.

Which of the following is the most appropriate humidifier to include in the anaesthetic circuit for this patient?

(Please select 1 option)

Cold waterbath

Ultrasonic nebuliser

Warm waterbath Incorrect answer selected

Gas driven nebuliser

Heat and moisture exchanger (HME) This is the correct answer

Explanation

The absolute humidity of fully saturated gas at 37°C is 44 g/m3. Efficient humidification is essential to preserve action of the cilia in the tracheal and maintain mucous flow.

The efficiency of humidification devices varies.

Nebulisers produce water vapour in the form of microdroplets. Gas driven nebulisers produce water droplets in the range of 2-4 µm most of which are deposited in the upper airways and bronchioles (absolute humidity 60 g/m3).

Ultrasonic vaporisers produce droplets of <2 µm, capable of reaching the alveoli (absolute humidity 90 g/m3). Whilst efficient, these vaporisers can cause over-hydration with flooding of the lungs and increases in airway resistance.

The cold and hot water baths produce an absolute humidity of 10 and 40 g/m3 respectively. The hot water humidifier in particular can lead to airway burns if water traps are not used and are prone to bacterial colonisation.

The heat and moisture exchangers (HME) retain heat and moisture from the expired respiratory gases and return them during inspiration. They are cheap and disposable, produce an absolute humidity of 25 g/m3 (relative humidity 60-80%) and incorporate antiviral and bacterial filters. They are the most appropriate humidification devices used for routine anaesthesia being almost as effective as the nose.

Answer Statistics

1

1%

2

7%

3

9%

4

84%

Times answered: 248