Effects of cardiac preload reduction and dobutamine on hepatosplanchnic blood flow regulation in porcine endotoxemia

Hepatic blood flow regulation but not oxygen extraction capability is impaired in prolonged experimental abdominal sepsis

Impaired oxygen utilization has been proposed to play a significant role in sepsis-induced liver dysfunction, but its magnitude and temporal course during prolonged resuscitation is controversial. The aim of this study is to evaluate the capability of the liver to increase oxygen extraction in sepsis during repeated acute portal vein blood flow reduction. Twenty anesthetized and mechanically ventilated pigs with hepatic hemodynamic monitoring were randomized to fecal peritonitis or controls (n = 10, each). After 8-h untreated sepsis, the animals were resuscitated for three days. The ability to increase hepatic O₂ extraction was evaluated by repeated, acute decreases in hepatic oxygen delivery (Do₂) via reduction of portal flow. Blood samples for liver function and liver biopsies were obtained repeatedly. Although liver function tests, ATP content, and Do₂ remained unaltered, there were signs of liver injury in blood samples and overt liver cell necrosis in biopsies. With acute portal vein occlusion, hepatic Do₂ decreased more in septic animals compared with controls [max. decrease: 1.66 ± 0.68 mL/min/kg in sepsis vs. 1.19 ± 0.42 mL/min/kg in controls; portal venous flow (Qpv) reduction-sepsis interaction: P = 0.028]. Hepatic arterial buffer response (HABR) was impaired but recovered after 3-day resuscitation, whereas hepatic oxygen extraction increased similarly during the procedures in both groups (max. increase: 0.27 ± 0.13 in sepsis vs. 0.18 ± 0.09 in controls; all P > 0.05). Our data indicate maintained capacity of the liver to acutely increase O₂ extraction, whereas blood flow regulation is transiently impaired with the potential to contribute to liver injury in sepsis.NEW & NOTEWORTHY The capacity to acutely increase hepatic O₂ extraction with portal flow reduction is maintained in sepsis with accompanying liver injury, but hepatic blood flow regulation is impaired.

A clinical approach to acute mesenteric ischemia

PURPOSE OF REVIEW

To summarize current evidence on acute mesenteric ischemia (AMI) in critically ill patients, addressing pathophysiology, definition, diagnosis and management.

RECENT FINDINGS

A few recent studies showed that a multidiscipliary approach in specialized centers can improve the outcome of AMI. Such approach incorporates current knowledge in pathophysiology, early diagnosis with triphasic computed tomography (CT)-angiography, immediate endovascular or surgical restoration of mesenteric perfusion, and damage control surgery if transmural bowel infarction is present. No specific biomarkers are available to detect early mucosal injury in clinical setting. Nonocclusive mesenteric ischemia presents particular challenges, as the diagnosis based on CT-findings as well as vascular management is more difficult; some recent evidence suggests a possible role of potentially treatable stenosis of superior mesenteric artery and beneficial effect of vasodilator therapy (intravenous or local intra-arterial). Medical management of AMI is supportive, including aiming of euvolemia and balanced systemic oxygen demand/delivery. Enteral nutrition should be withheld during ongoing ischemia-reperfusion injury and be started at low rate after revascularization of the (remaining) bowel is convincingly achieved.

SUMMARY

Clinical suspicion leading to tri-phasic CT-angiography is a mainstay for diagnosis. Diagnosis of nonocclusive mesenteric ischemia and early intestinal injury remains challenging. Multidisciplinary team effort may improve the outcome of AMI.

Defense mechanisms to increasing back pressure for hepatic oxygen transport and venous return in porcine fecal peritonitis

High central venous pressure (CVP) acutely decreases venous return. How this affects hepatic oxygen transport in sepsis remains unclear. The aim of this study was to evaluate the effects of repeated increases in CVP via standard nursing procedures (NPs) on hepato-splanchnic and renal oxygen transport in a prolonged porcine sepsis model. Twenty anesthetized and mechanically ventilated pigs with regional hemodynamics monitored were randomized to fecal peritonitis or controls (n = 10 pigs/group). Resuscitation was started after 8 h of observation and continued for 3 days. NPs were performed at baseline and 8 h, 32 h, 56 h, and 72 h after resuscitation started. NPs increased CVP by 4-7 mmHg in both groups. In controls, this was associated with less decrease in hepatic arterial (Q_ha; 62 ± 70 mL/min) than portal venous flow (Q_pv; 364 ± 151 mL/min). Portal venous oxygen content and hepatic O₂ delivery (Do₂) and consumption (V̇o₂) decreased by 11 ± 6 mL/dL and 0.9 ± 0.3 and 0.4 ± 0.3 mL·min^-1·kg^-1, respectively. In septic animals, hepatic Do₂ decreased more in response to increasing CVP (1.5 ± 0.9 mL·min^-1·kg^-1), which was attributable to a larger fall in both Q_ha (88 ± 66 ml/min) and portal O₂ content (14 ± 10 mL/dL, all P < 0.05). This resulted in numerically lower hepatic V̇o₂ since O₂ extraction did not increase significantly. In control conditions, a smaller decrease in Q_ha compared with Q_pv helped to limit the reduction in hepatic V̇o₂ in response to acute CVP increase. In sepsis, the contribution of Q_ha to maintain hepatic Do₂ was reduced, which jeopardized hepatic V̇o₂ further. Renal arterial flow was similarly affected by CVP increase as Q_ha.NEW & NOTEWORTHY Sepsis impairs intrinsic mechanisms to attenuate effects of increasing back pressure on hepatic oxygen transport.

Mesenteric vascular dysregulation and intestinal inflammation accompanies experimental spinal cord injury

Cervical and high thoracic spinal cord injury (SCI) drastically impairs autonomic nervous system function. Individuals with SCI at thoracic spinal level 5 (T5) or higher often present cardiovascular disorders that include resting systemic arterial hypotension. Gastrointestinal (GI) tissues are critically dependent upon adequate blood flow and even brief periods of visceral hypoxia triggers GI dysmotility. The aim of this study was to test the hypothesis that T3-SCI induces visceral hypoperfusion, diminished postprandial vascular reflexes, and concomitant visceral inflammation. We measured in vivo systemic arterial blood pressure and superior mesenteric artery (SMA) and duodenal blood flow in anesthetized T3-SCI rats at 3 days and 3 wk postinjury either fasted or following enteral feeding of a liquid mixed-nutrient meal (Ensure). In separate cohorts of fasted T3-SCI rats, markers of intestinal inflammation were assayed by qRT-PCR. Our results show that T3-SCI rats displayed significantly reduced SMA blood flow under all experimental conditions (P < 0.05). Specifically, the anticipated elevation of SMA blood flow in response to duodenal nutrient infusion (postprandial hyperemia) was either delayed or absent after T3-SCI. The dysregulated SMA blood flow in acutely injured T3-SCI rats coincides with abnormal intestinal morphology and elevation of inflammatory markers, all of which resolve after 3 wk. Specifically, Icam1, Ccl2 (MCP-1), and Ccl3 (MIP-1α) were acutely elevated following T3-SCI. Our data suggest that arterial hypotension diminishes mesenteric blood flow necessary to meet mucosal demands at rest and during digestion. The resulting GI ischemia and low-grade inflammation may be an underlying pathology leading to GI dysfunction seen following acute T3-SCI.

Dynamic contrast-enhanced ultrasound of slaughterhouse porcine livers in machine perfusion

The aim of this study was to enable investigations into novel imaging and surgical techniques by developing a readily accessible, versatile liver machine perfusion system. Slaughterhouse pig livers were used, and dynamic contrast-enhanced ultrasound was introduced to optimize the procurement process and provide real-time perfusion monitoring. The system comprised a single pump, oxygenator, bubble trap and two flowmeters for pressure-controlled perfusion of the vessels using an off-the-shelf perfusate at room temperature. Successful livers exhibited homogeneous perfusion in both the portal vein and hepatic artery with dynamic contrast-enhanced ultrasound, which correlated with stable oxygen uptake, bile production and hepatic resistance and normal histology at the end of 3 h of perfusion. Dynamic contrast-enhanced ultrasound revealed perfusion abnormalities invisible to the naked eye, thereby providing context to the otherwise systemic biochemical/hemodynamic measurements and focal biopsy findings. The model developed here is a simple, cost-effective approach for stable ex vivo whole-organ machine perfusion.