In cardiac surgery,anesthesia induction causes significant haemodynamic changes. However, haemodynamic management routinely uses blood pressure and cardiac output targets, and this is supported by blood analyses but for this rarely employs microvascular monitoring . However, macrohaemodynamics management following cardiac surgery is limited in predicting the microcirculation . The microcirculation can be assessed by the use of vascular occlusion testing (VOT) .NIRS is an easily applicable, non-invasive method for assessing tissue oxygenation and microvascular reactivity .The aim of the our study was to evaluate the effects of anaesthesia induction on microvascular reactivity using VOT.
Prior to induction of anaesthesia, we performed the first VOT with NIRS.Thereafter, all patients received a standardised anaesthesia induction with fentanyl (5 mcg/kg), rocuronium (1 mg/kg), midazolam (0,1 mg/kg).Then,tracheal intubation, positive pressure ventilation was started to maintain end-tidal CO2 tension of 30-35 mmHg.Maintenance of anesthesia was performed using intermittent midazolam, fentanyl, and rocuronium.The second VOT was performed 20 min after induction of anaesthesia (before skin incision). Comparisons of data before and after induction were made by using the paired samples t test.
VOT variables before and after induction of anaesthesia are shown in Table . Baseline StO2 was higher after induction of anaesthesia (78,8 vs. 85,1%, P = 0.03). Oxygen consumption was significantly lower after induction, as indicated by the higher minimum StO2 (54,8 vs.66,6 % p=0,001) and the slower occlusion slope (0,22 vs.0,16 p=0,001). After induction of anaesthesia, reperfusion time was significantly longer (22,4 vs.28,7) and reperfusion slope was significantly slower (1,82 vs.1,27 p=0,001).
In our study of pediatric cardiac surgery patients, significant microcirculatory alterations were observed after induction of anaesthesia.The clinical evaluation of microcirculatory reactivity seems to be of great interest, but currently its assessmentis considered technically challenging. Among a variety of non-invasive techniques,NIRS coupled with VOT has been proposed to be an easy-to-perform and reliable tool to assess microvascular reactivity. The occlusion slope reflects oxygen consumption in the tissue; thus, a slower occlusion rate indicates lower metabolic rate, impaired regional perfusion distribution or impairment in oxygen utilisation by mitochondria. After reperfusion, previously closed capillaries favourably open and blood flow in previously patent capillaries increases, causing a hyperaemic response. Thus, a slower reperfusion slope and a diminished degree of flow reperfusion indicate impaired microvascular reactivity.
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