What is new in monitoring splanchnic macro- and microcirculation

In this Euroanesthesia #EA18 lecture Joel Starkopf (Tartu, Estonia) discusses the recent advances in monitoring of the macro- and microcirculation in splanchnic region

How to assess and optimise macro- and microcirculation in splanchnic region

Joel Starkopf (joel.starkopf@ut.ee)
Department of Anaesthesiology and Intensive Care, University of Tartu, Tartu University Hospital, Estonia

Splanchnic comes from Greek word, splanchnikos (σπλαγχνικός), which means inward parts, organs, usually used to describe organs in the abdominal cavity (visceral organs). Splanchnic circulation is blood flow to the abdominal gastrointestinal organs including the stomach, liver, spleen, pancreas, small intestine, and large intestine, and it takes about approx 20…30% of cardiac output, and 20…30% of O2 consumption of the body. Splanchnic area is important reserve for blood mobilisation in case of haemorrhage/hypovolemia, but also serves are area for significant oedema formation in venous congestion (right heart failure, liver failure). The microvessels in the villi of the gut mucosa present the counter-current exchange of solutes, moving from arteriole to venule without traversing the entire length of the villus, which makes the tip of the villus highly susceptible to damage from hypoxia and hypotension. Prolonged hypoperfusion will therefore primarily cause mucosal sloughing at the tip of the villi, leading to barrier disruption, one of the putative mechanisms in cascade of MOF.

How to assess macrocirculation in splanchnic area? Hepatic vein catheterisation and Fick principle, dye-extraction methods (uptake of indocyanine green by liver), and ultrasound combined with laser Doppler flowmetry are methods available for splanchnic blood flow assessment. None of the methods is applicable in today’s clinical routine. Surrogate parameters include general blood flow assessment by cardiac output measurement, intra-abdominal pressure and abdominal perfusion pressure measurements (APP=MAP-IAP). Clinical signs such as pain, abdominal distention, bowel paralysis, feeding intolerance, diarrhoea, and melaena reflecting the compromised blood flow to visceral organs. For detection of mesenteric ischaemia novel biomarkers have been tested.

How to assess splanchnic microcirculation? Gastric tonometry detects gastric luminal pH, which is taken equal to intramucosal pH, and thereby reflects the status of gastric microcirculation. The method has limitations such as time needed to equilibrate CO2 between the balloon and the lumen; interference form acid secretion and enteral feeding. Assessment of microcirculation at sublingual area with hand-held videomicroscopes (HVM) is increasingly used. Over 600 articles about clinical and experimental use of HVM are published. The consensus statement of ESICM is recently released, suggesting further developments are needed prior to integration of vidoemicroscopy into routine clinical practice. Whether sublingual area specifically reflects the events taking place in splanchnic area of microcirculation, or indicates the whole body reaction, is not fully clear. In patients with ileostoma, intestinal microcirculation can be assessed with videomicroscope directly applied on mucosa of stoma.

How to optimize macrocirculation in splanchnic area? The changes in critical states, and effects of therapies such as vasopressors, inotropes and fluids should be recognized. Takala and co-authors have shown that both splanchnic blood flow and oxygen demand are increased in sepsis and other inflammatory distributive shock states, while cardiogenic shock is associated with reduced blood flow and increased oxygen extraction ratio, respectively. Effect of vasopressors in sepsis is variable, albeit mostly increasing the splanchnic blood flow, while in low flow states the inotropes uniformly improve splanchnic circulation. Enteral nutrition increases splanchnic blood flow and oxygen demand, therefore, caution with nutrition should be taken in cases where perfusion of gut is thought to be compromised. Parenteral nutrition, in contrast, does not influence splanchnic flow nor oxygen demand. Importantly, increase in IAP (and reduction in APP) is associated with reduced ICG-disappearance rate, suggesting decrease in hepatosplanchnic blood flow in IAH.

How to to optimize microcirculation in splanchnic area? The usability of microcirculatory indices as target for mhemodynamic optimisation remains questionable. In one hand, it is shown, that impaired microcirculation is associated with poor outcome. On contrast, the studies are demonstrated little coherence between macro- and microcirculation in response to various treatments (fluids, vasopressors, inotropes), which leaves many questions unresolved yet.

The aspects of assessment and optimisation can be summarised by the following table.

Take home message:

Splanchnic blood flow

• Takes up to one third of cardiac output in normal physiology
• Is increased postprandially, and in septic shock

Splanchnic microcirculation

• Indirect assessment via clinical signs and biomarkers
• Role for sublingual videomicroscopy in the future?

Optimisation of splanchnic blood flow

• Fluid management
• Intra-abdominal pressure and abdominal perfusion pressure are important
• Vasopressors and inotropes, depending on status
• Hypovolemia and hypotension vs venous congestion
• Little coherence between macro- and microcirculation

References:

• Takala J. Determinants of splanchnic blood flow. BJA British Journal of Anaesthesia 77(1):50-8
• Verbrugge FH, et al. Abdominal contributions to cardiorenal dysfunction in congestive heart failure. J Am Coll Cardiol. 2013 Aug 6;62(6):485-95. doi: 10.1016/j.jacc.2013.04.070.
• Jakob SM, et al. Increased splanchnic oxygen extraction because of routine nursing procedures. Crit Care Med. 2009.
• Hofmann D, et al. Increasing cardiac output by fluid loading: effects on indocyanine green plasma disappearance rate and splanchnic microcirculation. Acta Anaesthesiol Scand. 2005 Oct;49(9):1280-6.
• Treskes N, et al. Diagnostic accuracy of novel serological biomarkers to detect acute mesenteric ischemia: a systematic review and meta-analysis. Intern Emerg Med. 2017 May 6.
• Ince C, et al. Second consensus on the assessment of sublingual microcirculation in critically ill patients: results from a task force of the European Society of Intensive Care Medicine. Intensive Care Med. 2018;44(3):281-299.
• Gatt M, et al. Changes in superior mesenteric artery blood flow after oral, enteral, and parenteral feeding in humans. Crit Care Med. 2009 Jan;37(1):171-6. doi: 10.1097/CCM.0b013e318192fb44.
• Malbrain ML et al. Relationship between intra-abdominal pressure and indocyanine green plasma disappearance rate: hepatic perfusion may be impaired in critically ill patients with intra-abdominal hypertension. Ann Intensive Care. 2012 Dec 20;2 Suppl 1:S19
• Correa-Martín L, et al. Tonometry as a predictor of inadequate splanchnic perfusion in an intra-abdominal hypertension animal model. J Surg Res. 2013 Oct; 184(2):1028-34. doi: 10.1016/j.jss.2013.04.041. Epub 2013 May 10.
• Wu CY, et al. Effects of different types of fluid resuscitation for hemorrhagic shock on splanchnic organ microcirculation and renal reactive oxygen species formation. Crit Care. 2015; 19:434
• Andersson A, et al. Gut microcirculatory and mitochondrial effects of hyperdynamic endotoxaemic shock and norepinephrine treatment.Br J Anaesth. 2012;108(2):254-61.