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This is the time for critical oxygen desaturation to occur in the apnoeic patient. Critical oxygen desaturation is 88–90%. This is the upper inflection point of the oxygen-haemoglobin dissociation curve, beyond which further desaturation will occur very rapidly. Safe apnoea time can be increased from about 1 min breathing air, to as much as 8 min after breathing 100% O2, in a healthy patient.



A short-acting beta-2 agonist. It is used to:

  1. Treat and prevent bronchospasm in conditions such as asthma and COPD. It relaxes the smooth muscle of the airways.

  2. Treat hyperkalaemia.

  3. Inhibit premature labour.


  1. Metered inhaler, commonly called a ‘puffer’ (100 mcg/dose).

  2. Salbutamol powder.

  3. Nebuliser solution 2.5–5 mg in nebules. A salbutamol puffer, with a spacer, is just as effective as nebulised salbutamol.1

  4. IV salbutamol. This solution can also be used subcut. Do not give nebuliser solution IV.

  5. Oral Ventolin syrup 2 mg/5 mL.




  1. Metered inhaler—1–2 inhalations up to every 4 h.

  2. Nebulised solution—adults and children > 12 yrs 2.5–5 mg q 4–8 h. Can be used up to every 20 min, depending on severity of bronchospasm.

  3. IV/subcut salbutamol. In adults/children > 40 kg, give a LD of 200 mcg IV, over 1 minute, then an infusion of 5 mcg/min to a maximum of 20 mcg/min. In children < 40 kg, give a LD of 5–7.5 mcg/kg (maximum 300 mcg) over 10 min then an infusion of 1 mcg/kg/min to a maximum of 5 mcg/kg/min (maximum 80 mcg/h). If only a peripheral line is available, use ≤ 200 mcg/mL dilution of salbutamol.

If giving subcut to adults, use 500 mcg q 4 h as needed. For children, use 8 mcg/kg q 4 h as needed.

Uterine relaxation to halt/delay premature labour

Load 25 mg salbutamol into 1000 mL Hartmann's solution. Infuse 60–100 mL over 10–20 min then run the solution at 0.6 mg/h (24 mL/h), increased at 10 min intervals until there is a response. Then increase rate more slowly until contractions cease. The usual dose is 0.6–2.7 mg/h (24–108 mL/h). Once contractions have stopped for 1 h, reduce the rate by decrements of 50% every 6 h. Maximum treatment duration is 48 h. Oral salbutamol 6 mg q 6 h can be used for maintenance therapy.


Beta-2 agonists reduce potassium levels by causing potassium to enter skeletal muscle cells. Salbutamol is effective given IV or by nebuliser. Give 10–20 mg via nebuliser over 30 min in the adult.2

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