Predictive Validity of Acoustic Gastrointestinal Surveillance (AGIS) in Post-Operative Feeding

Using advances in low-cost sensor technologies and computer-aided analysis, the
investigators have developed a disposable, non-invasive device for the continuous monitoring
of abdominal sounds, called an AGIS sensor (Acoustic Gastro-Intestinal Surveillance).
Following abdominal surgery, the standard protocol employed by most hospitals is to feed
patients on their first post-operative day. However, one in every four patients is unable to
tolerate feeding because of delayed recovery of bowel function, a condition called
post-operative ileus (POI). Following abdominal surgery, monitoring for POI is typically
limited to incidental interactions with the attending physician or other staff, which occur
only intermittently throughout the day. The AGIS system specifically addresses postoperative
digestion monitoring by offering continuous analysis of GI signals, automated processing of
the signals, and immediate reporting of the patient's progress to caretakers.

The AGIS system is a compact, rapidly deployable unit that is comfortable for subjects and
convenient in application. The AGIS sensor includes a standard microelectronic microphone
for measurement of abdominal vibration and acoustic signals. The material in contact with
the subject is standard 3M Tegaderm wound bandage adhesive material which is disposable,
avoiding the need for cleaning and disinfection.

The AGIS sensor includes fine, flexible and convenient cables that connect to the AGIS
Gateway, a low voltage battery powered device with a size approximately of a smartphone. The
AGIS Gateway monitors the AGIS sensor signals and provides a measurement of intestinal
motility and reports an AGIS Feeding Index score. The score is calculated using the number
of acoustic events detected by AGIS per minute.

The investigators recently performed a proof-of-concept, cross-sectional study to test
whether the AGIS monitoring system could distinguish healthy control participants from
patients recovering from GI surgery. Seven healthy control participants were fed a breakfast
and monitored with AGIS for two hours following the meal, allowing the investigators to
obtain acoustic data and calculate a normal range of AGIS scores. The investigators also
placed the sensor on patients recovering from abdominal surgery. The investigators monitored
each patient for two hours and compared their AGIS scores to those of healthy controls using
ANOVA with post-hoc comparisons. AGIS successfully discriminated among healthy control,
patients tolerating food, and patients with POI.

Although the investigators' pilot data indicate that AGIS can distinguish patients from
healthy controls, and can further distinguish between patients with POI vs. those tolerating
food, the investigators do not yet know if AGIS can reliably predict which patients will
fail to tolerate postoperative feeding. The investigators propose to test the predictive
validity of the AGIS system in a pragmatic, observational study of patients scheduled for
abdominal surgery.

Hypothesis: Using AGIS signals recorded on the day of abdominal surgery, AGIS can predict
which patients will fail to tolerate postoperative feeding vs. which can be safely fed; AGIS
will achieve an overall accuracy of 80% or greater.

Study Design: The investigators will place the AGIS sensor on GI patients for 20 minutes
during the immediate pre-operative phase to establish a baseline AGIS motility rate.
Following abdominal surgery, the surgeons will place the AGIS sensor on the patient in the
operating room, and will begin recording for 60 minutes as the patients is transferred and
recovers in the post-anesthesia care unit. AGIS recordings will be collected continuously
throughout the remaining of the patient's hospital stay. As this is an observational study,
physicians and nurses will not be made aware of the AGIS readings. Patients will be managed
according to standard practice. The investigators' goal will be to determine the accuracy of
AGIS in predicting post-operative feeding tolerance in the context of usual care and without
the "Hawthorne effect" potentially impacting care decisions. Investigators blinded to the
AGIS recordings will abstract all data and outcomes.

Inclusion Criteria:

1. 18 years of age or older

2. Patient scheduled to undergo abdominal surgery

Exclusion Criteria:

1. Cannot consent or has no surrogate who can consent.

2. Cognitive inability to follow directions to maintain abdominal device in place

3. Any abdominal wall condition that disallows topical coverage as deemed by the
managing surgeons (e.g. open abdominal wound, oozing wound, advanced cellulitis,
necrotizing fasciitis, etc)