Mon22November0925AM 5

Preoxygenation prior to a rapid sequence induction is mandatory.

Which one of the following options is the most appropriate index of the adequacy of preoxygenation in these circumstances?

(Please select 1 option)

Expired partial pressure of carbon dioxide (EtCO2)

Arterial oxygen saturation (SpO2)

Expired fraction of oxygen (FEO2) Correct

Central cyanosis

Arterial partial pressure of oxygen (PaO2)

Explanation

An expired fraction of oxygen (FEO2) of greater than 90% is judged to be adequate prior to induction of general anaesthesia. The key point of preoxygenation is the denitrogenation of the functional residual capacity (FRC). This is the determining factor of oxygen desaturation during apnoea.

This process depends on three key factors:

Inspired volume

Inspired oxygen concentration (FiO2), and

Respiratory rate.

The two principal preoxygenation techniques include the application of a tight fitting face mask connected to an appropriate anaesthetic circuit with an adequate fresh gas flow.

Slow technique: Normal tidal volume breathing for two to five minutes (TVB 2-5 min). Denitrogenation is 95% complete after three minutes.

Fast technique: The patient takes four to eight deep vital capacity breaths at FiO2 of 1.0 (100%) for 30 to 60 seconds (4-8 DB 30-60 s).

It is not practical to measure PaO2 during preoxygenation.

A pulse oximeter reading of 100% (SpO2) or measured SaO2 does not necessarily indicate optimised oxygenation as it does not take into account tissue reserves. The absence of central cyanosis is a very crude clinical sign of hypoxia.

Whilst the end-tidal CO2 might determine the alveolar partial pressure of oxygen (PAO2) and therefore PaO2, it is not a primary index of oxygenation.

Answer Statistics

1

3%

2

9%

3

86%

4

1%

5

3%

Times answered: 259