Enhanced facial grimacing when laparotomy involves cutaneous and visceral tissue injury

Abstract

Introduction: Laparotomy is a common surgical procedure that entails incision of the abdomen and is associated with varying degrees of postoperative pain. Laparotomies can be performed in mice and result in facial grimacing, which can be quantified using PainFace, a software platform that automates facial grimace analyses.

Objectives: We evaluated the extent to which incision of the ventral skin, peritoneum, and intestinal manipulation, all of which can occur as part of a laparotomy surgery, affects the magnitude and duration of facial grimacing in 2 strains of mice along with allodynia at the incision site in CD-1 mice.

Methods: White-coated CD-1 male and female mice and black-coated C57BL/6 male mice (8-12 weeks of age) were split into groups (n = 20 per group) that underwent laparotomies with varying manipulations.

Results: Mouse grimace scale scores were higher in both strains after surgery when the small intestine was manipulated in 2 different ways compared to groups that received a cutaneous incision alone or cutaneous and peritoneal incision.

Conclusion: These studies show that mice exhibit more pronounced facial grimacing when both cutaneous and visceral tissues are injured during laparotomy surgery. Consistent with clinical findings, our experiments suggest that postoperative pain could be reduced by minimizing visceral tissue injury during surgical procedures.

Keywords: C57Bl/6; CD-1; Grimace; Laparotomy; Pain; Visceral.

Figure 1.

Laparotomy surgery manipulations. SHAM, Fur shaved with a razor; EPIT, epithelium incision; PERI, peritoneum incision; SQUE, small intestine gently squeezed; PALP, small intestine palpated.

Figure 2.

Male (A–E) and female (F–J) CD-1 laparotomy surgical manipulation groups. PainFace used to analyze facial grimaces from each 30-min video. Mean mouse grimace scale (MGS) scores from (A and F) SHAM, (B and G) EPIT, (C and H) PERI, (D, I) SQUE, and (E and J) PALP groups at baseline (BL), 0.5-hour, 2-hour, and 4-hour time points. Error bars represent standard error of the mean (sem). Kruskal–Wallis test performed with Dunn post-hoc test. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Male, n = 15 to 20 per group. Female, n = 8 to 12 per group.

Figure 3.

Male C57BL/6 laparotomy surgical manipulation groups. PainFace used to analyze facial grimaces from each 30-min video. Mean mouse grimace scale (MGS) scores from (A) SHAM, (B) EPIT, (C) PERI, (D) SQUE, and (E) PALP groups at baseline (BL), 0.5-hour, 2-hours, and 4-hour time points. Error bars represent sem. Kruskal–Wallis test performed with Dunn post-hoc test. *P < 0.05, ***P < 0.001, ****P < 0.0001. n = 12 to 20 per group.

Figure 4.

Mechanical allodynia at incision site in female CD-1 mice. Mean sensitivity scores for SHAM, EPIT, PERI, SQUE, and PALP groups measured 3 hours after laparotomy relative to baseline (BL, combined values from all groups). Error bars represent sem. Kruskal–Wallis test performed with Dunn post-hoc test. *P < 0.05, **P < 0.01, ***P < 0.001. n = 6 to 7 per group.