Pre-medication & peri-operative drugs

Question 1

drugs affect gastric pH

Answer 1

Regurgitation and aspiration of gastric contents (Mendelson’s syndrome) can be an important complication of general anaesthesia, particularly in obstetrics and during emergency surgery, and requires prophylaxis against acid aspiration. Prophylaxis is also needed in those with gastro-oesophageal reflux disease and in circumstances where gastric emptying may be delayed.

An H2-receptor antagonist can be used before surgery to increase the pH and reduce the volume of gastric fluid. It does not affect the pH of fluid already in the stomach and this limits its value in emergency procedures; an oral H2-receptor antagonist can be given 1–2 hours before the procedure. Antacids are frequently used to neutralise the acidity of the fluid already in the stomach; ‘clear’ (non-particulate) antacids such as sodium citrate are preferred.

Question 2

Anti-muscarinic drugs

Question 3

Sedative drugs

Question 4

Benzodiazepines

Question 5

Antagonists for central and respiratory depression