The impact of sample site and storage on thromboelastography values

Abstract

Thromboelastography (TEG) provides information on the entire clotting system by measuring viscoelastic properties of whole blood during the coagulation process. The advantage of TEG over routine laboratory tests is the rapid assessment of coagulation and fibrinolysis while considering the role of all blood components. Since the use of TEG is expanding outside the operating rooms, we intended to get further evidence whether the use of different sample sites (arterial-venous) result in similar TEG values. Furthermore, we assessed the effect of citrate storage on TEG values. After approval by the Ethical Committee of the Northern Osthrobothnia Hospital District, we recruited 51 ASA II-IV surgical patients aged 18-85 years in Oulu University Hospital in 2013-2014. Written informed consent was obtained from all subjects. Patients with a known pre-existing bleeding tendency or who were taking aspirin, an antiplatelet agent, warfarin, or any other drug to influence coagulation were excluded. On arrival into the operating room, four arterial and four venous samples were drawn from each patient into 2.7-mL Vacutainer tubes containing 3.2% citrate before an intravenous line was inserted to avoid any influence of intravenous infusion or drugs on our results. Arterial samples were obtained from an arterial cannula inserted in the radial artery and venous samples were simultaneously drawn by a direct venipuncture from the antebrachial vein. The first sample from each site was discarded leaving three arterial and three venous samples for analysis. The Vacutainer tubes were labeled in the order of collection and compared respectively. Blood samples were analyzed 30 min, 60 min, and 120 min after collection. All samples were stored at room temperature and re-calcified before analysis. No other laboratory testing were taken. The TEG analyses were performed according to manufacturer's guidelines by a single trained study nurse. Kaolin was used as an initiator in each test. Two computerized TEG® analyses (TEG 5000 Thromboelastograph® Hemostasis System, Haemonetics Corporation, Niles, USA) with four separate channels were used. TEG parameters used for this study were reaction time (R) and maximum amplitude (MA). Patients acted as their own controls, ie blood samples were compared only with individual's own samples. The data was analyzed using SPSS for Windows (IBM Corp., released 2012: IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp.). The Bland–Altman method was used to quantify the mean bias between measurements with 95% limits of agreement and the percentage errors (mean, median) were calculated. The main results are shown in Table 1. Altogether, 306 blood samples were collected from 51 patients undergoing elective surgery. There were 25 men and 26 women with a mean age of 65 years (range: 30-81 years). The ASA risk score was 2 in 35 patients, 3 in 15 patients and 4 in 1 patient. The patients had the following comorbidities: hypertension (44%), coronary heart disease (8%), diabetes (20%), asthma (24%), and obesity (43%). The following surgical procedures were performed: Laparoscopic splenectomy (1), small bowel resection (1), cholecystectomy (2), laparoscopic fundoplication (2), laparoscopic rectocolpopexy (1), spondylodesis (18), decompression (10), laminectomy (4), foraminotomy (1), microdiscectomy (1), and robotic assisted prostatectomy (10). Forty-six complete series (3 arterial and 3 venous samples) were obtained. In five patients, at least one trace was excluded due to technical TEG channel failure. The TEG trace was abandoned if there was not any numeric value for the analysis. The other traces of these patients were used in the analysis. A total of 239 samples were used for comparisons. The mean R in all samples was 8.2 min (range 3.2-15.6 min, SD 1.8) and the mean MA was 65.2 mm (range 49.3-77.0 mm, SD 6.1). For arterial–venous comparison, 30 min samples were used. The mean percentage error between sample pairs was