The vascular endothelium plays a key role in this inflammatory reaction and in the microcirculatory changes that occur during cardiac surgery.1 Microcirculation is the main site of many essential functions such as coagulation, immunological functions, inflammatory response, regulation of homeostasis and vasomotor tone control. Cardiac surgery under cardiopulmonary bypass is known to induce a systemic inflammatory response syndrome.1 Many factors such as surgical trauma, blood loss, transfusion, hypothermia, hypoperfusion and cardiopulmonary bypass itself may promote this inflammatory reaction.
First, cardiopulmonary bypass is responsible for morphological modifications resulting in impairment in capillary perfusion and compromising the density of perfused capillaries.2 Perfusion heterogeneity in a patient is responsible for poorly perfused areas and areas of hypervelocity in capillaries which may constitute an arteriovenous shunt.2 These alterations are associated with peri-operative lactataemia independently of haemodynamic parameters.
Second, cardiopulmonary bypass is associated with functional alterations and a decrease in microvascular reactivity as shown by various methods, including but not limited to laser-Doppler during local thermal stimulation or iontophoresis of acetylcholine, in vitro acetylcholine stimulation and near-infrared spectroscopy during a vascular occlusion test. Endothelium-dependent vasoconstriction and heat induced vasodilation are altered in cardiac surgery patients.3–5 Previous studies have shown strong individual variability in microcirculatory profiles, particularly before surgery. The large SDs in baseline measurements imply significant heterogeneity among these study populations.
Microvascular alterations are involved in acute organ dysfunctions such as acute lung injury, acute kidney injury, hepatocellular injury, myocardial ischaemia without obstructive coronary artery disease, delayed wound healing, encephalopathy and long-term cognitive impairment and disability. In several acute pathological conditions, microcirculatory impairment was identified as an independent predictor of mortality.6–9
Microcirculatory impairment could thus play an important role in cardiac surgery outcome. De Backer et al. reported that a decrease in the proportion of perfused vessels after cardiac surgery was correlated with both peak lactate and changes in the Sequential Organ Failure Assessment (SOFA) score. Nam et al. showed that a decrease in microvascular reactivity after cardiac surgery was independently associated with the volume of postoperative bleeding.4 In a study using a vascular occlusion test and near-infrared spectroscopy to measure microvascular reactivity, Kim et al.5 reported higher complication rates and longer hospital stay lengths in patients with lower microvascular reactivity recovery on postoperative day 1. Postoperative restoration of microvascular reactivity correlates with clinical outcomes in cardiac surgery patients.
Disrupted microcirculation has been observed in a number of chronic diseases, including but not limited to hypertension, diabetes mellitus, atheromatous plaques, coronary artery disease, obesity, depression and chronic renal disease, common conditions in cardiac surgery patients. To our knowledge, Feng et al.10 are the only authors to have taken one of these pre-operative conditions into account. They have shown that poorly controlled diabetes resulting in impaired arteriolar function before and after cardiac surgery under cardiopulmonary bypass was associated with increased expression and activation of protein kinase C and enhanced oxidative stress. However, neither the impact of these pre-operative conditions on pre-operative microcirculatory function nor the outcomes after cardiac surgery, especially in relation to cognitive function, have ever been studied.
To adequately address the issue of the impact of pre-operative microcirculatory function on postoperative outcomes, we designed the MONS study (Preoperative Evaluation of Microcirculation for the Prediction of Complications after Cardiac Surgery under Extracorporeal Circulation), an observational prospective cohort study, registered at Clinical-Trials.gov (NCT 03631797), which is a powerful tool to investigate the prognostic value of pre-operative microcirculatory function in patients scheduled for cardiac surgery under cardiopulmonary bypass for the occurrence of postoperative complications. Sixty patients scheduled for an elective valvular or coronary cardiac surgery under cardiopulmonary bypass at our university hospital will be included. Patients with a dark skin phototype, undergoing emergency or combined (valve and coronary arterial bypass grafting) surgery, or signs of delirium or other forms of cognitive alteration before surgery will be excluded. Microcirculatory function will be evaluated in each patient before surgery using a laser speckle contrast imaging device (Perimed, Järfälla, Sweden) placed on the forearm. The microvascular perfusion changes induced by iontophoresis of acetylcholine and sulfate nitroprussiate, reactive hyperaemia after ischaemia caused by calibrated skin pressure (standardised device) and dermal response to local thermal stimulation (thermal hyperaemia) will be recorded. Primary judgment criteria will consist of late surgical re-intervention (>12 h) for evacuation of pericardial effusion (seeps), surgical wound disintegration or surgical site infection within 30 postoperative days, SOFA scores greater than 2 at 48 h, postoperative confusion (assessed using the Confusion Assessment Method or the Confusion Assessment Method for the Intensive Care Unit), acute kidney injury (stage ≥2 according to the Kidney Disease Improving Global Outcomes classification), acute lung injury [defined as PaO2 < 55 mmHg in ambient air, PaO2 : FiO2 ratio <250 or pulse oxygen saturation (SpO2) < 90% and need for oxygen therapy], atrial fibrillation over the course of the hospital stay (excluding patients with permanent atrial fibrillation pre-operatively) and hepatocellular injury (cytolysis >10 N, prothrombin rate and factor V decreased <60%). Secondary outcomes will include functional and psycho-cognitive evolution at 30 postoperative days as evaluated by changes in the modified Rankin scale, activities of daily living score, brief Geriatric Depression Scale and Mc Nair test.
Sophisticated pre-operative assessment is needed to provide a more accurate risk of complications. Thus, assessments aimed at identifying patients those in need of peri-operative critical care and improving care in the peri-operative period are of great importance. Data suggest that patients could require different haemodynamic goals. Individualised haemodynamic management strategy tailored to individual patient physiology may improve postoperative outcomes. Pre-operative microcirculation assessment may be a reliable tool in establishing this individualised strategy.
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1. Laffey JG, Boylan JF, Cheng DC. The systemic inflammatory response to cardiac surgery: implications for the anesthesiologist. Anesthesiology
2. Koning NJ, Simon LE, Asfar P, et al. Systemic microvascular shunting through hyperdynamic capillaries after acute physiological disturbances following cardiopulmonary bypass. Am J Physiol Heart Circ Physiol
3. Gomes V, Gomes MB, Tibirica E, et al. Postoperative endothelial dysfunction assessment using laser Doppler perfusion measurement in cardiac surgery patients. Acta Anaesthesiol Scand
4. Nam K, Oh H-M, Koo C-H, et al. Microvascular reactivity measured by vascular occlusion test is an independent predictor for postoperative bleeding in patients undergoing cardiac surgery. J Clin Monit Comput
5. Kim TK, Cho YJ, Min JJ, et al. Microvascular reactivity and clinical outcomes in cardiac surgery. Crit Care
6. Ince C, Mayeux PR, Nguyen T, et al. The endothelium in sepsis. Shock
7. Sakr Y, Dubois MJ, De Backer D, et al. Persistent microcirculatory alterations are associated with organ failure and death in patients with septic shock. Crit Care Med
8. De Backer D, Creteur J, Dubois MJ, et al. Microvascular alterations in patients with acute severe heart failure and cardiogenic shock. Am Heart J
9. Trzeciak S, Dellinger RP, Parrillo JE, et al. Early microcirculatory perfusion derangements in patients with severe sepsis and septic shock: relationship to hemodynamics, oxygen transport, and survival. Ann Emerg Med
10. Feng J, Liu Y, Chu LM, et al. Changes in microvascular reactivity after cardiopulmonary bypass in patients with poorly controlled versus controlled diabetes. Circulation
2012; 126 (11_Suppl_1):S73–S80.