Effects of rest temperature, contact activation, and sample technique on canine thrombelastography

Abstract

Objective To determine the effects of rest temperature, contact activation (CA), and sample collection technique on thrombelastography (TEG) using canine whole blood. Design Prospective, experimental study. Setting University‐based research facility. Animals Twelve healthy, adult, mixed‐breed dogs. Interventions Blood was collected by jugular venipuncture. Tubes containing 3.2% sodium citrate, with and without 75 μg/mL corn trypsin inhibitor (CTI), were filled by vacuum. Samples rested for 30 minutes at 3 temperatures: 37°C, room temperature (RT, 20–22°C), or warmed to 37°C 5 minutes prior to analysis (prewarmed). Samples were analyzed at 37°C. CTI‐treated samples were analyzed with and without 1:50,000 tissue factor (TF) as activator. Six dogs were also tested similarly using a needle/syringe collection technique. Measurement and Main Results Prewarmed samples exhibited greater MA compared to RT (55.5 ± 7.2 mm vs. 53.5 ± 6.0, P< 0.05), while 37°C samples exhibited a steeper angle (56.7 ± 10.4°C vs. 52.4 ± 8.6°C) and greater MA (55.9 ± 7.5 mm vs. 53.5 ± 6.0 mm) than RT samples (both P< 0.05). CTI‐treated samples were hypocoagulable (R time 45 min [7.5–56.8 min], angle 8.2°C [5.1–42.5°C], MA 29.2 ± 9.7 mm, P< 0.001), with TF activation returning all but the angle (42.5 ± 7.6°C) to values similar to citrated samples (angle = 56.7 ± 10.4°C, P = 0.017). Collection using a syringe/needle method revealed a shorter R time for prewarmed samples only (R time 4.7 ± 0.7 min, vs. 5.6 ± 0.8 min for vacuum‐collected samples, P = 0.008). Conclusions Even in the absence of exogenous activators, CA has an impact on canine TEG results. The effects of rest temperatures and sample collection technique on TEG appear to be minimal.

Retrospective comparison of thromboelastography results to postmortem evidence of thrombosis in critically ill dogs: 39 cases (2005–2010)

“…Because this study was conducted retrospectively, the timing of sample collection for TEG relative to death and necropsy was not standardized, which also may have affected results. 63 However, there was no association between necropsy evidence of thrombosis and duration of time between TEG and necropsy. In addition, only previously collected and processed tissue was available for retrospective histopathologic review, and evidence of thrombosis or infarction may have been missed in tissues that were not saved.…”

“…Thus, the relatively small number of cases in this study may have introduced Type II error. Because this study was conducted retrospectively, the timing of sample collection for TEG relative to death and necropsy was not standardized, which also may have affected results . However, there was no association between necropsy evidence of thrombosis and duration of time between TEG and necropsy.…”

Systematic evaluation of evidence on veterinary viscoelastic testing Part 2: Sample acquisition and handling

“…The second (LOE 3, Good) investigated TEG results in clinically healthy dogs using jugular vein blood samples obtained using a butterfly catheter and vacuum tube (discard tube used) with those obtained using direct venipuncture and syringe aspiration (no discard tube). Syringe‐drawn samples had significantly shorter R time; however, no other significant differences were observed …”

Viscoelastic pharmacodynamics after dalteparin administration to healthy dogs

“…11,12 In a recent study 13 in humans, investigators suggested that only those patients who had changes in thromboelastography tracings after treatment with LMWH benefited from that treatment, regardless of the AXA. Thromboelastography may be activated by stimulating the intrinsic pathway (through recalcification 16 or exposure of the sample to kaolin) or the extrinsic pathway (through the addition of tissue factor to the reaction). 14 The effect of LMWH (dalteparin) on a modified thromboelastography assay has been investigated in an in vitro study in dogs.…”