Virginia Research Day 2022

Medical Student Research Biomedical

11 Elucidating The Role Of The Individual Components Of Perioperative Ileus: Anesthesia, Skin Incision, Laparotomy, And Intestinal Manipulation

John N. Pignataro; Tatiana M. Midkiff; Caitlyn P. Hodges; Natalie Jeong Min Kim; Anthony J.M. Bauer Corresponding author: Jpignataro1@liberty.edu

Liberty University College of Osteopathic Medicine

Background: Perioperative ileus is a major determinant of in-hospital recovery after surgery resulting in delayed enteral feeding, increased morbidity, prolonged hospitalization, and increased costs. The prevailing hypothesis is that anesthesia plays a major role. However, the mechanism(s) of perioperative ileus are not completely understood. Therefore, our goal was to elucidate the individual components of a surgical procedure in causing perioperative ileus and to investigate a novel vascular leak mechanism that potently disrupts perioperative gastrointestinal motility. Methods: Five groups of C57Bl/6 were used: controls, anesthesia (30 min isoflurane 2%), skin incision, laparotomy, and intestinal manipulation (IM) (N=4 each). After resuscitation a 90 min gastrointestinal transit assay (GIT) assessed motility by feeding FITC- dextran (70 kD) and plotting a distribution histogram with a calculated geometric center (GC). IM consisted of running the bowel with moist cotton applicators. A confocal system was used to image intact jejunal loops with the microvasculature labeled with isolectin-B4 (IB4-594λ=114.8 kDa) and dextran

skin incision, laparotomy and IM groups. Neutrophils were absent within the muscularis of all immediate groups. However, after IM a postoperative neutrophilic extravasation began 3-hr after resuscitation. The in vivo motility effect of exogenous serum was determined by intraperitoneal injection. Serum (250µl and 1000µl) caused an immediate dose dependent delay in transit GCs compared to lactate-Ringers (LR) (5.1±0.63, 3.6±0.32 vs. 9.9±0.53, respectively). Muscles exposed to serum showed a dose dependent inhibition of spontaneous contractions (0.25%=22.3±3.57, 0.5%=77.1±8.66 and 1.0%=95.1±6.81% inhibition, which was abolished by LNA (serum 0.5%=6.1±2.07%). Conclusions: Anesthesia cannot fully explain perioperative ileus. The data quantifies the individual components of perioperative ileus. Additionally, the data supports the novel hypothesis that surgery triggers an intestinal microvascular leak causing a significant delay in gastrointestinal transit via activation of nitrergic neuromuscular transmission in the absence of a cellular immune response.

fluorophores. Neutrophil transmigration into jejunal muscularis externa whole mounts was quantified using a Hanker-Yates (p<0.05). An organ bath assessed jejunal circular muscle contractility. Results: GIT was proportionally delayed by the invasiveness of the surgical procedure. Anesthesia caused an immediate small decrease in GC, which waned (control=10.4±0.57, imm=8.7±0.97, 3 hr=8.9±0.52 and 24- hr=10.2±1.2. Whereas skin incision, laparotomy and IM demonstrated significant, immediate delays in GCs of 7.8±1.41, 6.8±1.18 and 3.8±0.39, respectively. Analysis of the percent contribution for each perioperative ileus component yielded the following: anesthesia=25.75%, skin incision=13.64%, laparotomy=15.15%, and IM=45.45% of the delay in transit. Postoperative GIT remained delayed through 24 hours (GC=4.2±0.52). Live ex vivo 3D confocal imaging of control jejunal loops showed fluorophore containment within the microvasculature illuminating its 3D structure. Anesthesia did not cause an increase in vascular leak of the fluorophores. But an immediate leak was present in the

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