Chronic intestinal ischemia and splanchnic blood-flow: Reference values and correlation with body-composition

Normal Splanchnic Blood Flow in a Patient with Severe Stenosis of the Celiac Artery and Superior Mesenteric Artery

The diagnosis of chronic mesenteric ischaemia is typically based on angiographic findings along with a classic symptomatology. Only a few methods are available for functional testing to establish the diagnosis, such as indirect measurement of the splanchnic blood flow and hepatic vein oxygenation. The present case is a 76-year-old woman with weight loss and intermittent abdominal pain who was clinically suspected of chronic mesenteric ischaemia based on severe stenosis of the celiac artery and superior mesenteric artery. Measurement of the total splanchnic blood flow and hepatic vein oxygenation, however, showed a normal perfusion after meal stimulation, as well as an increased hepatic vein oxygenation, indicating normal flow reserves. This was likely due to a richly developed Riolan's anastomosis arising from the inferior mesenteric artery. The present case advocates the need for functional testing when diagnosing chronic mesenteric ischaemia.

Improvement of the splanchnic blood flow and hepatic vein oxygenation following revascularization in patients with chronic mesenteric ischaemia

OBJECTIVES

Chronic mesenteric ischaemia (CMI) is an underdiagnosed but severe condition. Access to functional testing is often limited and the diagnosis is usually based primarily on symptoms and imaging. One of the functional tests available is measurement of the splanchnic blood flow (SBF). The purpose of the present investigation was to evaluate if changes in the splanchnic perfusion after revascularization can be detected by measuring the SBF and hepatic vein oxygenation.

MATERIALS AND METHODS

The SBF was measured in 10 patients before and after revascularization of the mesenteric arteries by either percutaneous transluminal angioplasty (n = 9) or open revascularization (n = 1). The SBF was measured indirectly using Fick's principle and using the tracer Tc-99m Mebrofenin along with assessment of hepatic blood oxygenation, before and after a standard meal, following catheterization of a hepatic vein and the femoral artery.

RESULTS

Nine of 10 patients (90%) achieved a profound increase in SBF after revascularization (mean increase in postprandial response to meal stimulation from 71 ± 95 to 531 ± 295 ml/min, p = 0.001), and an increase in postprandial hepatic vein oxygen saturation (from 52 ± 14% to 59 ± 13%, p = 0.006). The symptoms of the patients diminished accordingly. One patient had no symptom relief, and no increase in postprandial SBF, but an angiographic result with no significant stenosis postrevascularization.

CONCLUSIONS

Revascularization increased the SBF and hepatic vein oxygen saturation significantly concurrent with symptom relief and according with the angiographic successful result in the vast majority of patients. A satisfying angiographic result post vascular intervention does not rule out CMI.

Chronic mesenteric ischaemia: the importance of the individual mesenteric artery

BACKGROUND

Chronic mesenteric ischaemia (CMI) is a vastly underdiagnosed condition that typically leads to postprandial abdominal pain and weight loss. The aim of the study was to explore the involvement of various mesenteric vessels in total splanchnic blood flow (SBF) and hepatic vein oxygenation.

METHODS

Single-blinded comparative trial of 476 patients clinically suspected of CMI. Routine investigation included measurement of hepatic vein oxygen saturation, indirect measurement of the total splanchnic blood flow (SBF), using Fick's principle and the tracer [^99m Tc]Mebrofenin, before and after a meal, and digital subtraction angiography.

RESULTS

A total of 176 of the 476 patients (36%) had at least one angiographically significant stenosis (lumen reduction ≥70%). In patients with a significant one-vessel disease, the percentage having CMI according to SBF was 10% for a celiac trunk stenosis (n = 60), 50% for a superior mesenteric stenosis (n = 24) and 6% for an inferior mesenteric artery stenosis (n = 34). In patients with a significant two-vessel disease, the percentage with CMI according to SBF response was 92%, 18% and 79%, for no significant stenosis of the celiac trunk (n = 13), superior mesenteric artery (n = 17) and inferior mesenteric artery (n = 19), respectively.

CONCLUSION

Patients with significant one- or two-vessel stenosis involving the superior mesenteric artery have a higher likelihood of CMI according to flow criteria and a greater postprandial decrease in hepatic vein saturation on average than patients with no involvement of the superior mesenteric artery.

Development of a Physiologically Based Pharmacokinetic Modelling Approach to Predict the Pharmacokinetics of Vancomycin in Critically Ill Septic Patients

BACKGROUND AND OBJECTIVES

Sepsis is characterised by an excessive release of inflammatory mediators substantially affecting body composition and physiology, which can be further affected by intensive care management. Consequently, drug pharmacokinetics can be substantially altered. This study aimed to extend a whole-body physiologically based pharmacokinetic (PBPK) model for healthy adults based on disease-related physiological changes of critically ill septic patients and to evaluate the accuracy of this PBPK model using vancomycin as a clinically relevant drug.

METHODS

The literature was searched for relevant information on physiological changes in critically ill patients with sepsis, severe sepsis and septic shock. Consolidated information was incorporated into a validated PBPK vancomycin model for healthy adults. In addition, the model was further individualised based on patient data from a study including ten septic patients treated with intravenous vancomycin. Models were evaluated comparing predicted concentrations with observed patient concentration-time data.

RESULTS

The literature-based PBPK model correctly predicted pharmacokinetic changes and observed plasma concentrations especially for the distribution phase as a result of a consideration of interstitial water accumulation. Incorporation of disease-related changes improved the model prediction from 55 to 88% within a threshold of 30% variability of predicted vs. observed concentrations. In particular, the consideration of individualised creatinine clearance data, which were highly variable in this patient population, had an influence on model performance.

CONCLUSION

PBPK modelling incorporating literature data and individual patient data is able to correctly predict vancomycin pharmacokinetics in septic patients. This study therefore provides essential key parameters for further development of PBPK models and dose optimisation strategies in critically ill patients with sepsis.

Functional testing in the diagnosis of chronic mesenteric ischemia

Chronic mesenteric ischemia (CMI) results from insufficient oxygen delivery or utilization to meet metabolic demand. Two main mechanisms may lead to mesenteric ischemia: occlusion in the arteries or veins of the gastrointestinal tract, or reduced blood flow from shock states or increased intra-abdominal pressure, so-called non-occlusive mesenteric ischemia. Severe stenoses in the three main mesenteric vessels as demonstrated with CT-angiography or MR-angiography are sufficient to proof mesenteric ischemia, for example in patients who present with weight loss, postprandial pain and diarrhea. Still in many clinical situations mesenteric ischemia is only one of many possible explanations. Especially in patients with a single vessel stenosis in the celiac artery or superior mesenteric artery with postprandial pain, mesenteric ischemia remains a diagnosis of probability or assumption without functional proof of actual ischemia. This review is aimed to provide an overview of all past, present and future ways to functionally proof CMI.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in the stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to loss of appetite or dietary restriction.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to the loss of appetite or dietary restriction.

New vasoactive peptides in cirrhosis: organ extraction and relation to the vasodilatory state

BACKGROUND

Patients with cirrhosis have substantial circulatory imbalance between vasoconstrictive and vasodilating forces. The study of circulatory vasoactive peptides may provide important pathophysiological information. This study aimed to assess concentrations, organ extraction and relations to haemodynamic changes in the pro-peptides copeptin, proadrenomedullin and pro-atrial natriuretic peptide (proANP) in patients with cirrhosis.

MATERIALS AND METHODS

Fifty-four cirrhotic patients and 15 controls were characterized haemodynamically during a liver vein catheterization. Copeptin, proadrenomedullin and proANP were measured in hepatic and renal veins and the femoral artery.

RESULTS

We found no differences in concentrations of copeptin and proadrenomedullin between patients and controls. ProANPs were higher in cirrhotic patients, median 138 pm (25/75 percentiles 101-194) compared with controls, median 91 pm (25/75 percentiles 82-153) P=0·02. ProANPs were higher in the femoral artery and renal vein, median 140 pm and 116 pm (25/75 percentiles 109-191 and 92-164, respectively), compared with controls, median 99 and 81 (25/75 percentiles 85-146 and 66-123) P=0·02 and P=0·007, respectively. We found no extraction of copeptin, proadrenomedullin or proANP over the liver. Copeptin correlated with portal pressure (R=0·50, P<0·001). Proadrenomedullin correlated with portal pressure (R=0·48, P<0·001) and heart rate (R=0·36, P<0·01). ProANP correlated with cardiac output (R=0·46, P<0·002) and portal pressure (R=0·32, P<0·02). All propeptides correlated with Child score (R>0·31, P<0·03).

CONCLUSIONS

Pro-atrial natriuretic peptide is elevated in cirrhosis. Copeptin, proadrenomedullin and proANP are related to portal pressure and seem associated with systemic haemodynamics. These propeptides may participate in development and perpetuation of vasodilatation and hyperdynamic circulation in cirrhosis.