Material and Methods
This was a observational longitudinal study and was conducted in accordance with the principles of the Declaration of Helsinki. The study was approved by the Ethics Committee for Clinical Research at local hospital (11.01.2019, 29620911-929-67). Ninety consecutive adult patients of the American Society of Anesthesiologists (ASA) Class II-III who underwent elective cardiac surgery with CPB over a 2-months period were included in this study. Patients undergoing emergency or re-do surgery, off-pump surgeries, transplant surgeries, vascular surgery were excluded from the study. Patients with insulin dependent diabetes mellitus (IDDM), those with a history of ejection fraction under 40% or pulmonary, renal or hepatic failure, those with hematologic disorder, those under 18 years old or those using alcohol, or any medication suppressing stress response as corticosteroids, vitamin C, or n-acetylcysteine, were not included the study. Since IDDM has a different pathogenesis, it was excluded from the study, considering that it may interact more negatively with tissue perfusion parameters. NIDDM patients discontinued their oral antidiabetic medications 24-hour before surgery. So the aim of this study is to evaluate the degree of stress response and related tissue oxygenation parameters in NIDDM patients whose documented preoperative normoglycemia with oral antidiabetic drug use and patients without DM.
Pulse oximetry, five channel electrocardiography, invasive blood pressure monitoring, bispectral index monitoring (BIS™, Covidien, MN, ABD) and invasive internally calibrated pulse wave analysis (ProAQT; Pulsion Medical Systems, Feldkirchen, Germany; PPVProAQT, COProAQT) were performed. As baseline measurement, patients received an initial hemodynamic assessment based on stroke volume, cardiac output (CO), and mean arterial pressure. DO2 (CO x arterial content of O2), VO2 (CO x [arterial-venous content of O2]), and O2ER calculations were performed with these calculated CO values by pulse wave analysis. However, when the CPB was initiated, pump flow was used as CO value due to inaccurate pulse wave analysis measurements during CPB.
Patients with no history of DM prior to surgery, may exhibit transient elevation of blood glucose >180 mg/dL during cardaiac surgery and cardiopulmonary bypass, they may have insulin resistance. We treated with a single or intermittent dose of intravenous insulin to maintain glucose ≤ 180 mg/dL at these patients. After a single dose insulin push therapy, blood glucose levels were re-evaluated and intravenous insulin regimen was started when necessary as recommended by Duggan et al.12 An endocrinology consultation was obtained in the postoperative period in case DM was detected in some of these patients. In patients with NIDDM, the bolus dose calculated with the formula (blood glucose value - 100/40) was applied when blood glucose was above 180 mg/dl. Then blood glucose value/100 units/hour infusion dose was started.12 Blood glucose levels were monitored with half an hour intervals.
Following adequate activated clotting time (>480 sec), cannulation were performed and CPB was initiated. CPB was performed in moderate hypothermia (28-31°C). Hemoglobin concentrations were kept above 7.5 g/dl during operation.
Blood samples were collected from the radial artery and internal jugular vein. Although jugular venous (ScvO2) and mixed venous oxygen saturation values differ slightly, it is acceptable to use ScvO2 instead of mixed venous oxygen saturation.13 Blood glucose and gas analysis were performed at four time points: after the induction of anesthesia before the surgery as baseline values (T1), at the 5-10thminute of CPB (T2), at the 30-40th minute of CPB (T3), and while the sternum was closing (T4). At these four time points, hemodynamic parameters, central venous oxygen saturation (ScvO2), lactate level, oxygen delivery (DO2), oxygen consumption (VO2), oxygen extraction rate (O2ER), mean arterial pressure (MAP) and urine output values were recorded.