Jennifer A. Leinicke

Operative Management of Rib Fractures in the Setting of Flail Chest:A Systematic Review and Meta-Analysis

Objective: To perform a systematic review and meta-analysis of studies comparing operative to nonoperative therapy in adult FC patients. Outcomes were duration of mechanical ventilation (DMV), intensive care unit length of stay (ICULOS), hospital length of stay (HLOS), mortality, incidence of pneumonia, and tracheostomy. Background: Flail chest (FC) results in paradoxical chest wall movement, altered respiratory mechanics, and frequent respiratory failure. Despite advances in ventilatory management, FC remains associated with significant morbidity and mortality. Operative fixation of the flail segment has been advocated as an adjunct to supportive care, but no definitive clinical trial exists to delineate the role of surgery. Methods: A comprehensive search of 5 electronic databases was performed to identify randomized controlled trials and observational studies (cohort or case-control). Pooled effect size (ES) or relative risk (RR) was calculated using a fixed or random effects model, as appropriate. Results: Nine studies with a total of 538 patients met inclusion criteria. Compared with control treatment, operative management of FC was associated with shorter DMV [pooled ES: −4.52 days; 95% confidence interval (CI): −5.54 to −3.50], ICULOS (−3.40 days; 95% CI: −6.01 to −0.79), HLOS (−3.82 days; 95% CI: −7.12 to −0.54), and decreased mortality (pooled RR: 0.44; 95% CI: 0.28–0.69), pneumonia (0.45; 95% CI: 0.30–0.69), and tracheostomy (0.25; 95% CI: 0.13–0.47). Conclusions: As compared with nonoperative therapy, operative fixation of FC is associated with reductions in DMV, LOS, mortality, and complications associated with prolonged MV. These findings support the need for an adequately powered clinical study to further define the role of this intervention.

p38 MAPK regulates Bax activity and apoptosis in enterocytes at baseline and after intestinal resection

Increased apoptosis in crypt enterocytes is a key feature of intestinal adaptation following massive small bowel resection (SBR). Expression of the proapoptotic factor Bax has been shown to be required for resection-induced apoptosis. It has also been demonstrated that p38-α MAPK (p38) is necessary for Bax activation and apoptosis in vitro. The present studies were designed to test the hypothesis that p38 is a key regulator of Bax activation during adaptation after SBR in vivo. Enterocyte expression of p38 was deleted by tamoxifen administration to activate villin-Cre in adult mice with a floxed Mapk14 (p38-α) gene. Proximal 50% SBR or sham operations were performed on wild-type (WT) and p38 intestinal knockout (p38-IKO) mice under isoflurane anesthesia. Mice were killed 3 or 7 days after operation, and adaptation was analyzed by measuring intestinal morphology, proliferation, and apoptosis. Bax activity was quantified by immunoprecipitation, followed by Western blotting. After SBR, p38-IKO mice had deeper crypts, longer villi, and accelerated proliferation compared with WT controls. Rates of crypt apoptosis were significantly lower in p38-IKO mice, both at baseline and after SBR. Levels of activated Bax were twofold higher in WT mice after SBR relative to sham. In contrast, activated Bax levels were reduced by 67% in mice after p38 MAPK deletion. Deleted p38 expression within the intestinal epithelium leads to enhanced adaptation and reduced levels of enterocyte apoptosis after massive intestinal resection. p38-regulated Bax activation appears to be an important mechanism underlying resection-induced apoptosis.

Ret heterozygous mice have enhanced intestinal adaptation after massive small bowel resection

Intestinal adaptation is an important compensatory response to massive small bowel resection (SBR) and occurs because of a proliferative stimulus to crypt enterocytes by poorly understood mechanisms. Recent studies suggest the enteric nervous system (ENS) influences enterocyte proliferation. We, therefore, sought to determine whether ENS dysfunction alters resection-induced adaptation responses. Ret+/- mice with abnormal ENS function and wild-type (WT) littermates underwent sham surgery or 50% SBR. After 7 days, ileal morphology, enterocyte proliferation, apoptosis, and selected signaling proteins were characterized. Crypt depth and villus height were equivalent at baseline in WT and Ret+/- mice. In contrast after SBR, Ret+/- mice had longer villi (Ret+/- 426.7 ± 46.0 μm vs. WT 306.5 ± 7.7 μm, P < 0.001) and deeper crypts (Ret+/- 119 ± 3.4 μm vs. WT 82.4 ± 3.1 μm, P < 0.001) than WT. Crypt enterocyte proliferation was higher in Ret+/- (48.8 ± 1.3%) than WT (39.9 ± 2.1%; P < 0.001) after resection, but apoptosis rates were similar. Remnant bowel of Ret+/- mice also had higher levels of glucagon-like peptide 2 (6.2-fold, P = 0.005) and amphiregulin (4.6-fold, P < 0.001) mRNA after SBR, but serum glucagon-like peptide 2 protein levels were equal in WT and Ret+/- mice, and there was no evidence of increased c-Fos nuclear localization in submucosal neurons. Western blot confirmed higher crypt epidermal growth factor receptor (EGFR) protein levels (1.44-fold; P < 0.001) and more phosphorylated EGFR (2-fold; P = 0.003) in Ret+/- than WT mice after SBR. These data suggest that Ret heterozygosity enhances intestinal adaptation after massive SBR, likely via enhanced EGFR signaling. Reducing Ret activity or altering ENS function may provide a novel strategy to enhance adaptation attenuating morbidity in patients with short bowel syndrome.

Disruption of retinoblastoma protein expression in the intestinal epithelium impairs lipid absorption.

We previously demonstrated increased villus height following genetic deletion, or knockout, of retinoblastoma protein (Rb) in the intestinal epithelium (Rb-IKO). Here we determined the functional consequences of augmented mucosal growth on intestinal fat absorption and following a 50% small bowel resection (SBR). Mice with constitutively disrupted Rb expression in the intestinal epithelium (Rb-IKO) along with their floxed (wild-type, WT) littermates were placed on a high-fat diet (HFD, 42% kcal fat) for 54 wk. Mice were weighed weekly, and fat absorption, indirect calorimetry, and MRI body composition were measured. Rb-IKO mice were also subjected to a 50% SBR, followed by HFD feeding for 33 wk. In separate experiments, we examined intestinal fat absorption in mice with conditional (tamoxifen-inducible) intestinal Rb (inducible Rb-IKO) deletion. Microarray revealed that the transcriptional expression of lipid absorption/transport genes was significantly reduced in constitutive Rb-IKO mice. These mice demonstrated greater mucosal surface area yet manifested paradoxically impaired intestinal long-chain triglyceride absorption and decreased cholesterol absorption. Despite attenuated lipid absorption, there were no differences in metabolic rate, body composition, and weight gain in Rb-IKO and WT mice at baseline and following SBR. We also confirmed fat malabsorption in inducible Rb-IKO mice. We concluded that, despite an expanded mucosal surface area, Rb-IKO mice demonstrate impaired lipid absorption without compensatory alterations in energy homeostasis or body composition. These findings underscore the importance of delineating structural/functional relationships in the gut and suggest a previously unknown role for Rb in the regulation of intestinal lipid absorption.

Colonic Bleeding and Ischemia

Abstract Colonic bleeding is common, has multiple etiologies, and is a significant cause of hospitalization and mortality in adult patients. Most episodes of acute colonic bleeding resolve spontaneously with conservative management. The urgency of diagnostic workup and therapeutic intervention is dependent on acuity and severity of hemorrhage. Colonic ischemia results from colonic hypoperfusion and is a relatively rare condition. It can be roughly classified as occlusive and nonocclusive. Clinical presentation varies widely depending on the degree of ischemia. Diagnosis of colonic ischemia requires a combination of diagnostic techniques. Treatment is dependent on severity of disease and ranges from supportive care to surgical resection.