Introduction
Post-operative ileus (POI) is the temporary impairment in gastrointestinal motility following surgery. It has a multifactorial origin and is an important cause of morbidity after abdominal surgery. Many strategies have been developed in order to identify the predictive factors of POI which may enable preventive measures.
This study aimed at identifying the perioperative risk factors(RF) associated with POI in patients undergoing colorectal surgery(CRS). 
Materials and Methods
This was a retrospective observational study. Sample consisted of 57 patients undertaking CRS in general surgery unit of Hospital de Santo António dos Capuchos. Data were extracted from intraoperative records and electronic processes. Cases were stratified by the occurrence of clinician-diagnosed POI.
POI was defined by the absence of cramps, passage of flatus or stool on or after 72 hours post-surgery.
Results were analyzed using SPSS17.0. Frequencies (Chi-square), univariate (Mann-Whitney test) and regression analysis were done to identify significant associations and RF.
Results and Discussion
From a total of 57 patients, 28,1% developed POI. The associated variables were:time (t) of nasogastric(NG) tube decompression (p<0,001, OR 1,07; IC 95%:1,03-1,12), t of bowel rest (p<0,001, OR 1,05; IC 95%:1,02-1,08), t to ambulation (p<0,001, OR 1,06; IC 95%:1,02-1,10), and opioids (OP) administration route (p=0,024). Development of POI was higher after epidural(EP) OP (OR 5,06; IC 95%:1,24-20,59). 
POI developed in 3 (17,6%) patients receiving intravenous (IV) tramadol(T), 10 (30,30%) receiving EP morphine(M) and 3 (50%) receiving EP sufentanil. In patients receiving IV M by PCA (7) none developed POI.
The retrospective character and the reduced sample size limited the capacity to identify other potentially associated variables and to determine the weight of each factor in the development of POI.
Conclusion
Prospective studies which allow the stratification of POI risk in the pre-operative period and the adoption of effective measures that enable POI prevention are needed.
Development of POI is related to many variables. Early ambulation and oral feeding, and reduced time of NG decompression should be encouraged. Regarding the anaesthetic technique, the OP type and administration route have to be considered. Of IV OP, T and IV PCA M showed a trend towards lower incidence of POI. For the EP route, M showed the best results. IV T and IV PCA M should be considered for patients undertaking CRS.

Post-operative ileus: what are the associated risk factors?