This is the way to look at the amount of acid entering the lower part of the oesophagus which might cause problems due to reflux. A naso-gastric catheter is inserted which records the amount of acid entering the oesophagus. This information can then be downloaded onto a computer and event markers such as sleeping, feeding and discomfort experienced can be recorded and then used in conjunction with the acid trace on the computer to determine the importance of any acid reflux causing problems and to determine the extent and severity of the gastro-oesophageal present.