Influence of two different levels of intra-abdominal hypertension on bacterial translocation in a porcine model

Abstract

Background: The purpose of the present study was to quantify bacterial translocation to mesenteric lymph nodes due to different levels of intra-abdominal hypertension (IAH; 15 vs. 30 mmHg) lasting for 24 h in a porcine model.

Methods: We examined 18 anesthetized and intubated pigs (52.3 ± 4.7 kg) which were randomly allocated to three experimental groups (each n = 6) and studied over a period of 24 h. After preparation and establishing a steady state, the intra-abdominal pressure (IAP) was increased stepwise to 30 mmHg in six animals using a carbon dioxide (CO2) insufflator (IAP-30 group). In the second group, IAP was increased to 15 mmHg (IAP-15 group), while IAP remained unchanged in another six pigs (control group). Using a pulse contour cardiac output (PiCCO®) monitoring system, hemodynamic parameters as well as blood gases were recorded periodically. Moreover, peripheral and portal vein blood samples were taken for microbiological examinations. Lymph nodes from the ileocecal junction were sampled during an intra-vital laparotomy at the end of the observational period. After sacrificing the animals, bowel tissue samples and corresponding mesenteric lymph nodes (MLN) were extracted for histopathological and microbiological analyses.

Results: Cardiac output decreased in all groups. In IAP-30 animals, volumetric preload indices significantly decreased, while those of IAP-15 pigs did not differ from those of controls. Under IAH, the mean arterial pressure (MAP) in the IAP-30 group declined, while MAP in the IAP-15 group was significantly elevated (controls unchanged). PO2 and PCO2 remained unchanged. The grade of ischemic damage of the intestines (histopathologically quantified using the Park score) increased significantly with different IAH levels. Accordingly, the amount of translocated bacteria in intestinal wall specimens as well as in MLN significantly increased with the level of IAH. Lymph node cultures confirmed the relation between bacterial translocation (BT) and IAP. The most often cultivated species were Escherichia coli, Staphylococcus, Clostridium, Pasteurella, and Streptococcus. Bacteremia was detected only occasionally in all three groups (not significantly different) showing gut-derived bacteria such as Proteus, Klebsiella, and E. coli spp.

Conclusion: In this porcine model, a higher level of ischemic damage and more BT were observed in animals subjected to an IAP of 30 mmHg when compared to animals subjected to an IAP of 15 mmHg or controls.

Figure 1

CFU in ileocecal MLN of pigs exposed to IAH for 24 h. Mean ± standard error of the mean of cultivable CFU in mesenteric lymph nodes taken from the ileocecal region according to the different levels of IAP (IAP-15/IAP-30: animals with an IAP of 15 mmHg or 30 mmHg, respectively, lasting for 24 h). Please take into consideration the logarithmic scale of the axis of ordinates. Asterisk denotes significant difference to control (IAP-15: p < 0.04; IAP-30: p < 0.01).

Figure 2

Translocated bacteria in bowel wall specimens of pigs exposed to IAH for 24 h. Histological specimens (Gram-stained) of bowel walls of pigs exposed to an IAP of 15 mmHg (B) and 30 mmHg (A, C) for 24 h. Boxes in A1, B1, and C1 (magnification: each ×400) mark extracts which are magnified in A2, B2, and C2 (magnification: each ×1,000). Bowel wall layers are labeled 'M' (tunica mucosa), 'S' (tela submucosa), and 'Musc' (tunica muscularis). 'L': intestinal lumen, 'G': Gruenhagen's space (according to Park's classification [26], ischemic damage to the gut is accompanied by proportionally increasing lifting of epithelia. In this way, the developing space between the mucosa and submucosa is named after Gruenhagen). Histomorphological damage shown in A and B correlates to Park score 1 (B (IAP-15): subepithelial space at villous tips) and 2 (A (IAP-30): extended subepithelial spaces). Cocci as well as rods passed Gruenhagen's space (see arrows) and invaded the tela submucosa (A, B: translocation score 2 to 3). Bacteria shown in C even crossed the tela submucosa and started invading the tunica muscularis (see arrows).

Figure 3

Translocated bacteria in MLN specimens of pigs exposed to IAH for 24 h. Histological specimens (Gram-stained, each ×1,000) of MLNs of pigs exposed to an IAP of 15 mmHg (D) and 30 mmHg (A, B, C) for 24 h. Cocci (A, D) as well as rods (B, C, D) were detectable (see arrows).

Figure 4

Bacterial counts in MLN of pigs exposed to IAH for 24 h. Median (minimum to maximum) of bacterial counts per mesenteric lymph node of the small and large bowel (ileum and colon) of pigs exposed to an IAP of 15 mmHg (IAP-15) or 30 mmHg (IAP-30) for 24 h. Results given as sum as well as distinguished between Gram-positive and Gram-negative bacteria. Asterisk denotes significant difference between bacterial counts in MLN of treatment group pigs and controls (P < 0.05).