Background
Despite implementation of enhanced recovery after surgery (ERAS) and laparoscopic techniques postoperative ileus (POI) remains frequent after colorectal surgery impacting the patient, their recovery and healthcare resources. Presently there are no tests that reliably predict or enable early POI diagnosis. Volatile organic compounds (VC) are products of human and microbiota cellular metabolism and we hypothesised that a detectable alteration occurs in POI.

Methods
This was a prospective observational study of patients undergoing laparoscopic colorectal resection within an established ERAS programme. Standardised end expiratory breath sampling was performed on the morning of surgery and the first three post‐operative mornings. VC concentrations were analysed using Selected Ion Flow Tube Mass Spectrometry and GastroCH4ECK®. Feasibility data, bowel preparation, post‐operative oral intake, POI and 30‐day morbidity were recorded.

Results
Of the 75 potentially eligible patients, 58 (77%) agreed to participate. Per‐protocol breath sampling was successfully completed in 94%. There were no analytical failures. Baseline and post‐operative VC levels were broadly comparable and were not altered by bowel preparation or post‐operative oral intake. POI developed in 14 (29%) patients. Pre‐operative ammonia concentration was higher in POI patients (830ppb vs. 510ppb, P=0.027). There was an Increase in acetic acid at day two in patients who developed POI (99ppb vs 171ppb, p=0.021).

Conclusion
Repeated VC breath sampling and analysis is feasible in the peri‐operative setting. Morning of surgery ammonia concentration may be a potential predictor of POI.