Gastric volume and acidity at caesarean section.

The pulmonary acid aspiration (Mendelson's) syndrome may present after regurgitation and inhalation of acid gastric content during obstetric anesthesia. The stomach contents of 70 mothers were aspirated at caesarean section after pre-operative gastric 'emptying' and alkaline ingestion. The acidity of the gastric aspirate was analysed and volumes were measured. The patients were divided into 5 groups according to the time when gastric aspiration was carried out. A 'safe' gastric pH (pH greater than 3.5) was found in all patients up to 2 hours after antacid ingestion (groups 1-3). However, 2 1/2 hours after antacid ingestion (group 4y, 50% of patients had gastric volumes in excess of 25 ml and a pH of less than 3.5. We therefore recommend that, if general anaesthesia is to be induced or is in progress 2 hours after antacid therapy, the alkaline regimen should be resumed after repeated gastric aspiration.