Microcirculation and Anesthesia in Vascular Surgery

Ischemia/reperfusion (I/R) injury is a common problem in patients undergoing aortic clamping for vascular surgery and may lead to systemic inflammation and organ dysfunction. Increased production of pro-inflammatory molecules and oxidative stress induced by I/R are responsible for microvascular alterations similar to those observed during sepsis, which result in tissue hypoxia. Anesthetics can affect the microcirculation. Propofol causes vasodilation stimulating NO production and decreases microvascular density. A final arteriolar vasodilation could involve a greater oxygen delivery and better perfusion, but a massive dose-dependent vasodilation could lead to a shunt of blood flow with reduced oxygen availability. Volatile anesthetics cause dose-dependent vasodilation too and desflurane, unlike isoflurane and alothane, maintains myocardial, hepatic, intestinal and muscle blood flow. This prospective observational study aims to evaluate the effects of intravenous and balanced anesthesia on sublingual and peripheral muscle microcirculation in patients undergoing elective open abdominal aortic aneurysm repair. This study was approved by the investigator's local ethical committee of Azienda Ospedaliera Universitaria "Ospedali Riuniti" of Ancona, Italy. A written informed consent was obtained from all patients. Patients were eligible if they were scheduled for elective infrarenal abdominal aortic open repair with or without prosthetic aorto-aortic or aorto-bisiliac bypass under general anesthesia. Patients received balanced (desflurane + remifentanil) or total intravenous (TIVA, propofol + remifentanil, with target-controlled infusion) anesthesia according to the attending physician's decision, resulting in two study groups. Spectral entropy was used in monitoring anesthetic depth. A goal-directed hemodynamic management was applied in all patients. Hemodynamics was evaluated with Flotrac/Vigileo (Edwards Lifesciences) monitor according to routine clinical practice. Arterial and central venous blood gases were measured according to routine clinical practice. All measurements were collected before anesthesia induction (baseline) and at end-surgery. Changes in sublingual microvascular flow and density were assessed with incident dark field illumination imaging (Cytocam, Braedius, Amsterdam, NL). After gentle removal of saliva and other secretions with a gauze, the probe was applied to the sublingual region, avoiding excessive pressure. Three sequences of 10 seconds each were recorded in 3 different mucosal areas. Subsequently, clips were analysed offline by AVA software (Automated Vascular Analysis v3.0). The following parameters were calculated for small vessels: microvascular flow index, total vessel density, perfused vessel density, percentage of perfused vessels, flow heterogeneity index. Near infrared spectroscopy (InSpectra, Hutchinson Technology, MN, USA) was applied on the thenar eminence with a vascular occlusion test (VOT) to assess variations in the peripheral muscle tissue oxygenation and microcirculatory reactivity. A probe was applied on the thenar eminence, and, after a 3-minute period of stabilization, tissue O2 saturation (StO2) and tissue haemoglobin index (THI) were recorded. Then arterial inflow was arrested by inflating a sphygmomanometer cuff to 50mmHg above the systolic arterial pressure; the cuff was kept inflated until StO2 decreased to 40% and finally was released. StO2 modifications were continuously recorded during the reperfusion phase until stabilization. The following parameters were extrapolated: StO2 downslope, StO2 upslope, area of hyperemia. Statistics: normality of distribution will be assessed with Kolmogorov-Smirnov test. Data will be expressed as mean±standard deviation or median [1st-3rd quartile], as appropriate. Two-way ANOVA with Sidack's multiple comparisons test or Wilcoxon and Mann-Whitney U test were used to compare variables between the two time points into the same group and between two groups at time-matched points as appropriate. A p value <0.05 was used to indicate statistical significance.