Minimising aspiration risk is the most important end-point in any fasting guideline. The approximate incidence of fatal aspiration associated with an anaesthesiologist giving anaesthesia in Australia is 1 in 3 million 37.
On induction ideally the stomach is empty. If you suspect the patient has a “full stomach” conventional practice is to raise the pH of the contents by administering 20mls of “foul tasting” sodium citrate. Animal studies show that damage to the lungs is minimised if a more alkaline solution is aspirated.41
Sodium citrate, along with maltodextrin, forms the basis of Dex. Sodium citrate was incorporated so that the patient's gastric contents become more alkaline after drinking Dex. Dex aims to minimise risk associated with aspiration by rapidly emptying from the stomach and raising the pH of the residual gastric volume.
Dex properties that facilitate gastric emptying include:
i) Low osmolality
ii) High pH
iii) Low viscosity
Duodenal osmoreceptors and acidic pH receptors trigger neural and hormonal feedback loops, preventing gastric emptying when activated. Dex is designed to avoid activating these negative feedback loops, so that the 200ml of fluid rapidly passes into the duodenum.
The rapid gastric emptying of Dex has been shown to be similar to that of water, and had been confirmed by both scintigraphy and MRI.
Registrar Intubation Tips
Gastric contents can enter the lungs via two mechanisms:
Actively (thoraco/abdominal muscle contraction)
Passive prevention manoeuvres:
Tilt bed head up 30 degrees (prevents passive gastric content flow)
Do not bag/mask early (may inflate stomach with air - displace gastric contents)
Active prevention manoeuvres:
Deep rapid paralysis (prevent thoraco/abdominal muscle contraction)
If you are not paralysing patient - use deep induction dose (perhaps with vasopressor)
Bag/mask only when the patient is deep or paralysed- then intubate
In the latest mortality report from ANZCA,37 of the 9,054,216 anaesthetics calculated over a 3 year period, there were 5 deaths due to aspiration:
2 deaths - No anaesthesiologist involved
3 deaths – no airway protection used in high risk upper GI endoscopy patients