This study had three main findings. First, 55% of critically ill ventilated patients experienced constipation and 14% experienced diarrhea within the first week of ICU admission. Second, more patients had normal defecation from the fourth day, and diarrhea increased from the fifth day of ICU admission. Third, neither constipation nor diarrhea was associated with mortality, but diarrhea was associated with length of ICU stay.
In previous studies, 34-58% of patients had constipation, which was comparable with the result of this study (7, 8). The incidence of constipation varied among previous studies because of inconsistent definitions of constipation (9). Although many previous studies have used the definition of no defecation ≥3 days, Prat and colleagues reported that patients who had no defecation ≥6 days had more adverse outcomes than other patients (12). Therefore, in the current study, we confidently defined constipation as ≥6 days without defecation from ICU admission.
The incidence of diarrhea also varies widely among many studies, from 10-78% (9). In addition to the reasons for the different definitions as described above, this is also attributable to the method of data collection. The longer the number of days for which data are collected, the greater the chance that the patient will experience diarrhea, and thus the incidence could be higher. However, in our study, the effect was removed by conditioning the event to diarrhea occurrences during the first week of ICU admission. A previous study investigating GI symptoms during the first week of ICU admission reported that 22% of patients experienced diarrhea, indicating that diarrhea is common in ICU patients (13). However, because our study included only patients who used MV for more than 48 hours, there are no other studies with the same study population, which make our findings difficult to compare to those of past studies.
Similar to the previously-mentioned meta-analysis study (11), diarrhea was associated with length of ICU stay. The mechanism is not obvious, but diarrhea could cause impaired nutritional intake, electrolyte abnormalities, and dehydration, which may interfere with the critically ill patient’s recovery. Taito and colleagues suggest that, because the causality between diarrhea and ICU length of stay is unknown and the reverse causality described above cannot be ruled out, further studies are needed to evaluate the association between early-onset diarrhea and ICU length of stay (11). Our study study is one of the few that have addressed this issue by defining the occurrence as within the first week of ICU admission.
The meta-analysis also reported that diarrhea was associated with mortality, which was different from the results of our study (11). However, as mentioned above, many studies do not limit the observation period. Therefore, while late-onset diarrhea may be relevant, from the results of our study we can at least say that early-onset diarrhea was not associated with prognosis.
Constipation was not associated with patient outcomes, but over half of the critically ill patients in our study experienced constipation. Even though EN is started on the third day in many patients, having no defecation ≥6 days is distressing for patients. Taken together, our findings suggest that prevention of both constipation and diarrhea is essential for critically ill patients. One method of constipation and diarrhea prevention could be a bowel management protocol; however it has been shown that the use of laxatives for constipated patients increases the risk of diarrhea occurrence (9). Hence, we propose the use of an intervention involving a gut immune protection bundle with the addition of symbiotics using a combination of dietary fiber and beneficial bacteria, all of which are known to be effective against diarrhea (14). Furthermore, this intervention may be more effective if it is introduced before the fifth day after ICU admission when the occurrence of diarrhea was observed to increase. If diarrhea does occur, it is also important to take prompt action against electrolyte abnormalities and dehydration. In particular, appropriate monitoring of laboratory values and early detection of dehydration as well as electrolyte supplementation and fluid management are required (15).
When investigating constipation or diarrhea typically one would divide them directly into two groups representing those with and without occurrence of the event; however, if we compare a group with constipation and a group without constipation, for example, patients with diarrhea may be included in the group without constipation. Previous studies have not excluded these patients and, as such, the study design might have distorted the results. We were able to eliminate this misclassification bias by dividing the participants into three groups: normal defecation, constipation, and diarrhea. Furthermore, this study is novel in that it describes the status of EN and defecation during the first week of ICU admission, which has not been done in previous studies (11). Especially, investigation on the timing of the commencement of diarrhea is particularly lacking in the literature, thus our study could be a valuable resource.
This study has several limitations. First, all data were collected retrospectively based on electronic medical records, thus, unrecorded data could be not retrieved. At the facility under observation, information on the administration of injectable drugs was available, but information on the administration of oral drugs was not incorporated into the electronic medical record. Consequently, the use of intestinal peristalsis promoting drugs, a risk factor for diarrhea, was unknown and could not be analyzed. In addition, the formulation and administration method of EN was based on the judgment of clinicians and as such was varied. To solve these problems, we plan to conduct a daily prospective observational study after the EN protocol is implemented. Second, our findings are limited by the small number of diarrhea cases; there were 12 patients with early onset of diarrhea during the one-year observation period. It would be necessary to observe at least four years of data to eliminate chance errors. Third, since this study was conducted at a single university hospital, these results may not be generalizable to community hospitals or other institutions. Therefore, to increase the generalizability of the findings the number of research facilities may need to be increased in future studies. Finally, because the recorded details of the nature and amount of defecation were dependent on the subjective evaluation of the nursing staff, they may have overestimated or underestimated the occurrence or severity of the diarrhea. We aimed to avoid this by using a semi-quantitative tool, but it might be better to introduce a more systematic instrument such as the Bristol stool form scale or King’s stool chart (16-18).