Abstract
OBJECTIVE:
Microvascular dysfunction occurs early in the pathogenesis of cardiovascular disease. Damage to the glycocalyx is a known cause of microvascular dysfunction, it causes a disturbed perfusion, inflammation and coagulation of the microcirculation. Cardiopulmonary bypass(CPB) during coronary artery bypass graft(CABG) can degrade the glycocalyx. It is known that pulsatile flow during CPB is associated with earlier recovery of the glycocalyx compared to non-pulsatile flow, but the effect of anaesthesia and cardioplegia has not yet been investigated. We aim to investigate the impact of anaesthesia and type of cardioplegia on glycocalyx thickness.
METHODS:
14 patients who underwent CABG with pulsatile or non-pulsatile CPB between May and July 2017 in the Maastricht University Medical Center (MUMC+) were included. The sublingual microcirculation was measured with the GlycocheckTM software at 7 time points, before the surgery, during surgery, on the intensive care unit (ICU) and the day after the surgery. The main outcome parameter is the perfused boundary region (PBR), this is an inversed parameter of the glycocalyx thickness. Other outcome parameters are density of the vessels and red blood cell(RBC) filling percentage. Mixed model analysis was used for statistical analysis.
RESULTS:
The induction of anaesthesia results in an increased RBC filling percentage (p = 0,037) and an increased density of the vessels (p = 0,028). Anaesthesia showed no effect on the PBR. No significant differences in PBR are seen between the two cardioplegia groups. A strong linear correlation is demonstrated between the PBR and the RBC filling percentages of the vessels between 5 and 25 µm with a Pearson’s correlation coefficient of 0,818.
CONCLUSIONS:
In conclusion, this study does not indicate that the induction of anaesthesia results in an impaired glycocalyx. During CPB no different glycocalyx alterations were seen in the different cardioplegia groups. Further research in a bigger population is necessary to investigate the microcirculatory alterations indicated through anaesthesia and the different cardioplegia fluids. However a PBR increase and a decrease in RBC filling percentage were noticed after the start of the CPB.
Introduction
Cardiovascular disease is the main cause of death in developed countries. (1) Microvascular dysfunction occurs early in the pathogenesis of cardiovascular disease. (2) A known cause of microvascular dysfunction is damage to the glycocalyx. The glycocalyx is a thin, gelatinous layer lining the luminal side of microcirculatory vessels, consisting of a meshwork of proteoglycans, glycosaminoglycans and plasma proteins. It is carbon rich and the layer is attached to the endothelium through backbone molecules. (3) It has an anti-inflammatory, anti-thrombotic function and it prevents leakage of plasma fluids into the interstitium. Furthermore the glycocalyx regulates the production of nitric oxide (NO), which causes vasodilatation. (4) Under normal circumstances the glycocalyx regulates the microvascular perfusion by regulating the vasomotor tone, but perfusion is impaired when glycocalyx integrity is disturbed . Degradation of the glycocalyx is one of the earliest changes in the pathogenesis of vascular disease. (5) When the glycocalyx is damaged, glycocalyx thickness reduces and blood interacts with the exposed endothelium provoking inflammation and coagulation. (6, 7)
A previous studies has shown that cardiopulmonary bypass (CPB) has a negative effect on the sublingual microcirculation during cardiac surgery and causes glycocalyx degradation. (8) In the absence of CPB during coronary artery bypass graft (CABG), there is almost no reduction seen in the microcirculatory perfusion and glycocalyx. (9, 10) Pulsatile flow during CPB improves the recovery of microvascular density and glycocalyx thickness postoperative compared to non-pulsatile flow. These effects are not only related to macrocirculatory parameters such as blood pressure and heart rate, but the glycocalyx could have an effect as well. While these studies studied the effect of CPB, the effects of anaesthesia and cardioplegia on microcirculation and glycocalyx integrity are still unknown.
The goal of this study is to investigate the impact of anaesthesia and cardioplegia on the glycocalyx. We hypothesize that there is a small effect of anaesthesia on the glycocalyx. A study from De Backer (2009) showed an effect on the microcirculation, the perfused small vessel density and proportion of perfused small vessels decreased after the induction of anaesthesia. Which might also have an effect on the glycocalyx. (11) We also hypothesize that microcirculatory alterations observed during CPB differ due to the type of cardoplegia fluid that is used, as some types of cardioplegia are accompanied by hemodilution, while others have almost no hemodilution.
Material and methods
Patient population
This observational study was approved by the Medical Ethical Testing Committee (METC) of Maastricht University Medical Center (MUMC+), Maastricht, the Netherlands. Patients (≥18 years) who underwent coronary artery bypass graft (CABG) between May and July 2017 with pulsatile and non- pulsatile CPB were included. All procedures were elective; emergency surgeries were not included. Written informed consent was obtained from all included patients. Exclusion criteria were oral injuries and procedures without CPB. Some patients were lost to follow-up, because the operation was cancelled or rescheduled.
Operative techniques
A standardized anaesthesia protocol for CABG with CPB is utilised in MUMC+. The induction of anaesthesia is performed with sufentanil forte, midazolam and rocuronium. For the maintenance of the anaesthesia continuous infusion of propofol and sufentanil forte is used. After the induction, the patients receive a bolus of tranexamic acid and cefazoline. Cefazoline is applied as a prophylactic antibiotic.
A median sternotomy incision was performed on all patients. Before the start of the CPB heparin is given. A CPB-device (Maquet Netherlands BV, Hilversum, the Netherlands) and Terumo tubes (Terumo Europe NV, Leuven, Belgium) were utilised. 7500 IE heparin was used for priming of the CPB. Cannulation is only started if the activated clotting time (ACT) is above 300. The arterial cannula is placed in the ascending aorta and the venous cannula in the right atrium. Two types of cardioplegia are used during CABG, blood and St. Thomas II. The St. Thomas II cardioplegia is hypothermic and the blood cardoplegia is normothermic. St. Thomas II exists of 16 mM potassium chloride, 10 mM sodium bicarbonate and 16 mM magnesium chloride. Blood cardioplegia predominantly consists of 26 mM potassium chloride. (12, 13) At the end of the surgery, after the removal of the CPB, protamin was administered to reverse the effect of heparin.
Microcirculatory measurements and analyses
The sublingual microcirculation was measured with the GlycocheckTM software (Glycocheck BV, Maastricht, the Netherlands). This technique uses Sidestream Darkfield Imaging(SDI) for the analysis of the microcirculation. (14) The GlycocheckTM produces green light, which, in contrast to all surrounding tissue, is absorbed by the haemoglobin in the red blood cells. This creates bright images with dark spots at spaces where there are red blood cells. The software then automatically detects the dynamic lateral red blood cell (RBC) movements. (15) The main outcome parameter from the GlycocheckTM is the perfused boundary region (PBR). The PBR is an inverse parameter of the glycocalyx, it is the RBC permeable part of the glycocalyx (Fig. 1). When the PBR is high the glycocalyx integrity decreases and the blood can have contact with the endothelium. Other outcome parameters are the RBC filling percentage of the vessels and the density of the vessels.
Figure 1. Perfused Boundary Region
The Perfused Boundary Region is the RBC permeable part of the glycocalyx. The PBR increases when the glycocalyx integrity decreases.
The patients were measured at seven time points: 1) the day before the surgery 2) before the induction of anaesthesia 3) after the induction of anaesthesia 4) after the start of the CPB 5) after stop of the CPB 6) after arrival on the intensive care unit (ICU) 7) the day after the surgery. At each time point, three consecutive measurements were made and mediated, to ensure the validity of the measurements. Not every patient has three measurements at one time point. When a patient has two measurements, those values are mediated. When a patient has one measurement at a certain timepoint, this was seen as a missing value. Care was taken to search for places with a high vascular density and few vascular loops. Pressure artefacts were avoided.
Preoperative and intraoperative characteristics
Patient characteristics such as age, gender, body mass index (BMI), hypertension and diabetes mellitus were registered. Perioperative data was collected such as temperature, surgical time, aortic cross-clamp time and the heparin doses. At the seven time points lab values (pH, lactate, potassium, sodium etc.) and vital parameters (blood pressure, heart rate, respiratory rate and the oxygen saturation) were registered.
Statistical analyses
Statistical analysis were performed using SPSS statistical software (23.0; IBM, New York, USA). Mixed model analysis evaluated the data, the groups were divided in blood and St. Thomas II cardioplegia. Mann-Whitneys U test and Fisher’s exact test analysed the patient characteristics. A p-value < 0,05 was considered statistically significant.
Results
17 Patients were included in this study, one was lost to follow-up and two were excluded because of oral injuries.
Baseline characteristics
The patient characteristics and some intraoperative data are shown in Table 1. The blood cardioplegia group has significantly less blood administration then the St. Thomas II cardioplegia group. Furthermore there were no differences among the two groups.