|Intra-abdominal hypertension (IAH) is defined as increased pressure within the confines of the abdominal cavity. As pressure rises, ischemia of the splanchnic organs will result from direct compression of the organs and vasculature. Intra-abdominal pressure (IAP) is also transferred across the diaphragm to the thoracic cavity, resulting in cardiac ischemia and reduced cardiac output. An abdominal compartment syndrome (ACS) develops if pressures are sustained above 20 mmHg, resulting in new or progressive organ failure.
Elevations in IAP can alter other cardiovascular parameters such as central venous pressure (CVP) used to assess fluid resuscitation. Increased intra-thoracic pressure will increase CVP through compression on the vena cavae, as well as the pulmonary tissues, increasing right ventricular afterload. However, venous return is variable and dependent on the IAP, resulting in further alterations of CVP measurements.
Identification of IAH in horses is complicated, as indirect methods of measurement such as intra-vesicular or gastric pressures are not accurate. Current recommendations for monitoring IAP are through direct, invasive measurement from the peritoneal cavity that risks complications including infection, hemorrhage, and trauma to splanchnic organs.
The effects of IAP on the hemodynamics of healthy horses were investigated with a pneumoperitoneum model to create an IAP of 20 mmHg. Our results indicate that CVP tends to increase as IAP increases up to 12 mmHg, whereas CVP fell as pressures increased further. Femoral venous pressures (FVP) were significantly increased with changes in IAP, and showed excellent correlation with pressures measured directly from the abdomen. Femoral blood flow and femoral vein diameter were not altered.
Serum biomarkers were also measured as an objective method to monitor IAP in the horse. Blood samples were obtained before, during and after abdominal insufflation. Concentrations of interleukin-10, intestinal fatty acid binding protein, and procalcitonin were determined using equine specific ELISA. The tests indicated that biomarkers were measurable throughout the experiment, but were not altered by IAP. The results of this study indicate that FVP may be used as an indirect measure of IAP in horses. However, moderate increases in IAP was not able to produce significant changes in biomarkers of ischemia and inflammation, as measured by commercial ELISA.
This thesis interpolates material from three papers by the author [reference 11, 12, 16]. Chapter 2 uses material from reference  and Chapter 3 uses material from reference , both coauthored with Reid Hanson. Meanwhile, Chapter 4 is based on reference , coauthored with Elizabeth Barrett, Valeria Albanese, and Reid Hanson.