Diagnostic Accuracy Study of a Point-of-Care Test for Coagulation Function

Laboratory evaluation of blood clotting is widely used in perioperative medicine, either by conventional technique (prothrombin time - PT/INR, Activated Partial Thromboplastin Time - aPTT, fibrinogen dosage and platelet count) or by the Point of Care method (Thromboelastogram ) - notably in surgical procedures with the possibility of severe volume loss (cardiovascular, oncological, trauma, etc.).

The prothrombin time (PT) is a general assessment of the integrity of the extrinsic and common pathway of coagulation. It determines the time of formation of the fibrin clot. The INR/RNI (International Normalized Ratio) is calculated from the PT and is intended to establish valid comparisons regardless of the type of PT reagent (known as thromboplastin) used by different clinical laboratories. The INR is indicated for evaluating the integrity of the extrinsic (factor VII*) and common pathway (fibrinogen and factors II*, V and X*), and for monitoring the anticoagulant effect of an anti-vitamin K agent (warfarin), capable of inhibiting the synthesis of vitamin K dependent factors (II, VII, IX, X, proteins C and S).

Today, due to its safety, sensitivity and speed, the thromboelastogram is recommended as the method of choice for assessing hemostasis in a surgical setting. However, because it is still not widespread in many centers, mainly due to its high cost, many hospitals are limited to the use of traditional laboratory methods which, despite their undeniable reliability, require more time for their execution and release of results.

In cardiac surgery with cardiopulmonary bypass (CPB), the use of prime solution to fill the CPB circuit results in hemodilution of coagulation factors, with factor I (fibrinogen) being one of the most affected, but not the only one. Each abnormality detected requires a specific action. Thus, the activated clotting time (ACT) is normalized with the administration of protamine. Thrombocytopenia and/or platelet dysfunction, with platelet concentrate infusion. Abnormalities in clotting factors, with administration of the specific factor, eg fibrinogen, either by factor concentrate, cryoprecipitate or plasma. It is at this moment that a quick assessment of hemostasis, in a global and individualized way at the same time, is necessary.

More than a decade ago, devices appeared on the market designed to help patients using warfarin to maintain their anticoagulation within parameters established for each case, providing safety, speed and comfort. Using a reagent strip and a drop of blood, evaluating the INR has become as simple as evaluating capillary blood glucose for diabetic patients. In just a few seconds, INR assessment can show significant changes in the extrinsic coagulation pathway, an important step to help with rapid decision-making in surgical environments. The Coaguchek Device, validated and used for outpatient management of patients using Warfarin, presents valuable characteristics for this purpose (simplicity, speed, safety), also important in the context of intraoperative decision-making. There are few reports in the literature on the use of the Coaguchek device in surgery and on the reliability of the data obtained through its use.

To evaluate this correlation, the main objective of the present study is to evaluate the effectiveness of the portable INR meter in a surgical setting and comparing it with conventional laboratory methods. The proposal is a cross-sectional diagnostic study in patients scheduled electively to undergo cardiac surgery with cardiopulmonary bypass at Hospital de Base in the Federal District.

All patients will receive standard monitoring associated with hemodynamic monitoring with invasive blood pressure and central venous access. Balanced general inhalation anesthesia will be administered to all patients. Hemodynamic support with dobutamine, noradrenaline, nitroprusside, nitroglycerin, vasopressin, or milrinone will be offered according to perioperative needs. The same commercial brand of heparin and protamine will be used to all the patients.

Laboratory tests, including samples for the Coaguchek device strip, will be collected 10 minutes before heparin administration and 10 minutes after the end of the protamine infusion. The laboratory exams that will be collected are: arterial blood gases, venous blood gases, electrolytes, complete blood count, coagulogram (TAP, aPTT, INR) and fibrinogen.

The sample size was calculated for the limits of agreement by Bland and Altman (1986)1, according to the method developed by Lu et al. (2016).2 Based on previous studies3-5, we assumed a mean difference between the POC test and the laboratory test of 0.126 units with a standard deviation of 0.132. Furthermore, based on clinical criteria, we consider that an absolute difference greater than 0.5 units will be clinically relevant. In other words, the maximum difference (Δ) between the tests (so as not to change the clinical approach) would be up to ± 0.5 units; that is, (-Δ ,Δ) equals (-0.5,0.5). Assuming a 5% ɑ level and 95% confidence intervals around the Bland-Altman limits of agreement, 43 participants were needed to ensure a statistical power of 90% to detect agreement between the two methods. All calculations were performed using the Stata 16 program (StataCorp, Texas, United States). We decided to increase the sample to 50 patients for cases of loss to follow-up or failures in annotations.