To Örebro University

Major abdominal surgery may be followed by postoperative complications, especially in the elderly and patients with co morbidities as diabetes mellitus and obesity. Some of the most feared complications as anastomotic leakage, abdominal infections, abdominal compartment syndrome (ACS) and intestinal ischemia can lead to sepsis, systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS) with high morbidity and mortality. This thesis evaluates intraperitoneal microdialysis (IPM) as a method for early detection of surgical complications. IPM measures extracellular metabolites as lactate, pyruvate, glycerol and glucose. The lactate/pyruvate (l/p) ratio describes the current relationship between aerobic and anaerobic metabolism. Glycerol is a degradation product of lipolysis from fat and a part of the cell membrane and released when cell injury occurs. In Paper I, evaluation of IPM in patients with and without diabetes mellitus and obesity during 48 hours after abdominal surgery did not show any difference in l/p ratio and glycerol levels compared to a control group. Paper II investigated the first two days after abdominal surgery in patients with major complications using IPM. L/p ratio was higher and glycerol was lower. Paper III used IPM in the immediate postoperative period in patients after endovascular repair for ruptured abdominal aortic aneurysm (rEVAR). Patients who required decompression due to intraabdominal hypertension (IAH) with organ failure had higher l/p ratio and glycerol. Paper IV investigated the effects of Aortic Balloon Occlusion (ABO) and Superior Mesenteric Artery (SMA) occlusion for one hour followed by three hours reperfusion in an animal model. ABO had a pronounced effect on the hemodynamic state. I.p l/p ratio increased during ischemia and decreased on reperfusion while glycerol increased on reperfusion and the effect was less pronounced in the SMA group. In conclusion, IPM monitoring of l/p ratio and glycerol indicates serious postoperative complications at an early stage. The l/p ratio increases or is continuously high while glycerol seems to have a more complex pattern. Diabetes and obesity do not influence the results.

Intra-abdominal hypertension (IAH) and the progression to abdominal compartment syndrome (ACS) are known complications of vascular and abdominal surgery, trauma, sepsis, and burns. ACS is associated with high mortality. In ACS, hypoperfusion, hypoxia, onset of inflammatory pathways and increased levels of oxygen reactive species are believed to cause tissue damage and initiate organ failure. Early detection of IAH is central in order to stop the pathological processes. Microdialysis is a method to determine extracellular metabolic changes through analysis of glucose, pyruvate, lactate and glycerol. Microdialysis is known to be feasible in the abdomen to detect early signs of postoperative complications. The ratio of lactate and pyruvate (l/p ratio) reflects the intracellular relationship between aerobic and anaerobic metabolism. Glycerol is elevated when cells have increased energy needs and in cell damage. Our hypothesis was that IAH and ACS cause early metabolic changes in the abdomen which could be determined by microdialysis, and possibly serve as clinical markers for organ failure due to IAH. In Paper I methodology was established using a porcine model with CO2 pneumoperitoneum. Using the model in Paper II and III, we showed that metabolic changes (elevated l/p ratio and glycerol) occurred early in the abdomen as IAH was induced and also restituted after decompression. Decrease in urine output, circulatory changes and impaired mucosal circulation indicated that the model mimicked ACS well. In a clinical study (Paper IV), patients that underwent endovascular surgery for rAAA and later needed decompression due to IAH with organ failure, had more pronounced early metabolic alterations than patients without severe IAH. In conclusion, early abdominal metabolic changes due to IAH are seen experimentally in a model and in patients after rAAA. These changes can be measured with microdialysis and they could, if the results are verified in further studies,be used as clinical markers for IAH and ACS.