expert commentary

IJ.M.S. 44 Horgan et al. February, 1991

fuse oesophageal spasm) or gastrointestinal (cholelithiasis, peptic ulcer) pathologies. Clearly a definitive test to establish the presence of abnormal reflux is needed.

The normal subject experiences acid reflux from the stom- ach into the distal oesophagus for up to 2% of his day, but these normal physiological reflux episodes are cleared by oesoph- ageal peristalsis and reflex swallowing. It is against this background of normal physiological reflux that abnormal re- flux must be diagnosed . . . .

24 hour pH monitoring of the distal oesophagus has now become established as the most reliable diagnostic technique in the investigation Of suspected gastro-oesophageal reflux 3. However the test is not without disadvantages, such as the prolonged test period, the relative patient intrlerance, and the frequent need for overnight hospitalisation of the patient. A shorter period of pH-metry would in theory be more accept- able to both patient and staffprovided its reliability was estab- lished.

Fink and McCallurn 6 have reported on the usefulness of shorter periods of pH-metry. They concluded that a 12 hour period of monitoring was highly accurate for diagnosis of reflux and furthermore that a 3 hour postprandial period of testing shows a 77% diagnostic sensitivity. These results were based on a study of 16 patients, and all time periods were analysed as part of an overall 24 hour test. It has recently been reported that an 8 hour period ofpH-metry is as accurate as a 24 hour period s , and in this study testing periods were assessed on consecutive days.

We have found the use of three hour pH monitoring of the distal oesophagus to be easy to perform, more acceptable to the patient, less expensive than longer testing periods, and more suitable to an out patient diagnostic unit needs.

In this present report, we have oncb more reaffirmed the usefulness of 8 hour pH-metry in refluxers with significant elevations above controls in values for the total number of reflux episodes (p<0.001) and the percent time pH<4 (p<0.03). The mean value for the % time pH<4 (3 hours: 0.01 + 0.05 SEM) in our control subjects is less than those reported in the literature. De Meester et al 7 cites 4.2% as the maximum normal value for the 24 hours of testing, while others have rec- ommended lower figures (1.9%) 6. For the shorter time period (3 hours) of testing, Fink et al6 reported a normal figure (% time pH<4) of 0.7% + 0.4% (SEM), a higher figure than in our study, but taken immediately after eating which tends to stimulate reflux and elevate the resulting measured values. It would therefore appear fl~at an investigating unit must decide how pH metry is to be employed in their hands, a set protocol must be followed rigidly, and standard maximum normal values (mean +2 x standard deviation) established from an asymptomatic control population.

We conclude that (i) eight hour oesophageal pH-metry has a continuing place in research or clinical aspects of gas- trooesophageal reflux (ii) three hour pH-metry is a practical inexpensive, and accurate method of diagnosing reflux with high patient acceptance that can be utilised as a screening test in an out patient seuing (iii) with negative 3 hour pH-metry, or atypical symptomatology, a longer period of monitoring should be arranged.

References I. BenneU, J. R. pH measurement in the oesophagus. In: Baillieres

Clinical Gastroenterology. 1, 4: 1987. 2. Evans, D. F. Tw~aty-four ambulatory oesophageal pH monitoring: an

update. Br J Surg. 74: 157-161. 1987. 3 De Meester, R. R. The limitations of 24 hour pH monitoring

ofthe oesophagus. In De Meester, T. R. and Skinner D. B.: Esophageal disorders: pathophysiology and therapy. Raven Press New York 1985.

4 Choiniere, L., Miller, L., ]lves, R., Cooper J. D. In: De Me.ester, T. R. and Skinner, D. B., e.d; Esophageal Disorders: Pathophysiology and therapy. Raven Press, New York. 1985.

5. Horgan, P. G., Waldron, D., Saleh, H. et al. Distal oesophageal pH monitoring gastroesophageal reflux. Irish Med. J., 83, 4, 142-144, 1990.

6 Fink, S. M., McCal/um, R. W. The value of short term pH monitoring in gastrooesophageal reflux. IAMA; 252:1160-4, 1984, 1990.

7. De Meester, T. R. Technique, indications and clinical use of 24 hour oesophageal ph monitoring. 1. Cardiovasc Surg. 79; 656-670. 1985.

EXPERT COMMENTARY

The Role of 3 hour Oesophageai pH Monitoring in Gastro-Oesophageai Reflux

Patrick J. Byrne, Oesophageal Function Laboratory, St. James's Hospital.

This is a study comparing 3 hour pH monitoring with 8 hour pH monitoring, with reference to a previous study by the same first author which claimed that 8 hour monitoring is adequate.

The authors point out that manometric localisation of the lower oesophageal sphincer is ideal but in this study the probe was placed by pH change alone. This technique is satisfactory in the majority of cases but a simultaneous reflux event can cause errors. There is reference to a previous study that claims 8 hour monitoring is as accurate as 24 hour monitoring. However, definition of a positive result in an individual patient for acid reflux, is not clear for this or the previous study.

The results are presented for the total period and only two parameters are presented, i.e. the number of events and % time that the pH < 4.0. The 8 hour study had 36 events with an avarage duration of 1.47 minutes per event compared to 37 events for the 3 hour study with an average duration of 4.76 minutes per event. This would suggest that the 3 hour study had greater acid exposure than the 8 hour study. Cuschieri's 1 normal data for 24 hour studies is 2.13 mins/event. It is also important to point out that pH data is not normally distributed and non parametric statistics should be used for anaylsis.

I agree with the authors' caution in suggesting 3 hour pH monitoring only as an initial screening before 24 hour studies. One of the problems is the period of acclimatisation to the probe. Other studies have shown that there is an increased rate of swallowing during the first 4-6 hours 2 and this might explain the findings in this study. Nevertheless, there is now a tendency to carry out short term studies, especially with am- bulatory manometry during physiological manoeuvre. 3 hour pH monitoring could therefore, find a niche, if carried out with ambulatory manometry. There is a need, however, to docu- ment a larger number of asymptomatic normal volunteers for 3 hour pH monitoring, and to compare all of the relevant parameters with the results of 24 hour pH monitoring.

References 1. Cheadle, W. G., Vitale, G. C., Sadek, S. A., Cuschicri, A. Computer-

rised ambulatory esophageal pH monitoring in 50 asymptomatic sub- jects. Results and clinical implications. Amer. L Surg. 1988: 155, 503.

2. Emda, C., Garner, A., Blum, A. L. Technical aspects of intraluminal pH-metry in man: Current status and recommendations. Gut 1987: 28, 1177.