The maintenance of an adequate level of FVIII is essential for the perioperative management of patients with HA. The recommended level of FVIII to achieve adequate hemostasis during surgery differs depending on the surgical procedure and associated bleeding risk. It is usually considered the risk of perioperative coagulopathy and bleeding is lower in EVAR than in laparotomic aortic repair, but we set a peak target level for FVIII at 100% during surgery, considering the possible risk of conversion from EVAR to laparotomy. Gautier et al. have published a similar case report and described EVAR was advantageous to the standard laparotomic surgery in respect to less need for FVIII concentrate in the perioperative period [3]. But they experienced the development of a hematoma at the femoral artery access site on the first postoperative day.
There are 3 laboratory tests to evaluate FVIII level: FVIII:C1, a 2-stage coagulation method, and a chromogenic assay [4]. Although FVIII:C1 is most broadly used in many hospitals, including ours, because it is simple and is also recommended as a perioperative assay by the guidelines [2], it may underestimate the FVIII level in heparinized blood because some of intrinsic coagulation factors other than FVIII are inhibited by heparin-bound antithrombin [5]. Thus, evaluation of the FVIII level by FVIII:C1 is not accurate during heparinization or in case of insufficient heparin reversal. The APTT or ACT assay could be a surrogate for FVIII:C1, as indicated in the guidelines [2], but these are also affected by heparin. TEG and ROTEM can perform several different assays simultaneously: intrinsic activation, extrinsic activation, intrinsic activation with heparinase, and functional fibrinogen assay. Because total evaluation of these test results could make it comprehensive to understand the cause of perioperative coagulopathy, they have been also examined for the usefulness in the evaluation and treatment of hemophilia patients [6, 7]. Hence, we expected the CKH assay would be useful to estimate the FVIII level even in the presence of heparin owing to heparinase which neutralizes heparin in the blood sample. Unfortunately, our results indicated heparinase used in CKH could not fully neutralize heparin in the blood sample because R-CKH was prolonged during heparinization and returned within the normal range after heparin reversal. Although the blood concentration of heparin in our case was calculated as 1 unit/ml (estimated blood volume, 70 ml/kg), it has been reported heparin activity could be accurately quantified in the range of 0.05 to 0.8 U/ml [8]. CKH would not be suitable for estimation of the FVIII level during heparinization at a concentration higher than 0.8 U/ml, but it could be valid in residual heparin after heparin reversal by protamine. HEPTEM in ROTEM, a similar assay to CKH, has been proved not to be affected by heparin up to 8 U/ml [9]. ROTEM might be better for the estimation of the FVIII level in hemophilic patients during perioperative heparinization.
Maintenance of the FVIII level is also important for appropriate heparin management in cardiovascular surgery. ACT is the mainstay assay for heparin titration during endovascular procedures, but it is also strongly affected by FVIII deficiency, which results in a prolonged value despite the absence of heparin. The prolonged ACT owing to insufficient FVIII replacement can result in underdosing of heparin and inadequate anticoagulation. The use of TEG could facilitate distinguishing between FVIII deficiency and the effect of low-dose heparin (less than 0.8 U/ml) [8], which might contribute to the appropriate heparin management. If the surgical procedure requires medium- or high-dose heparin, TEG could not prove if the FVIII level is adequately maintained during heparinization. In such a situation, the combination of ROTEM and ACT might be more helpful for the appropriate heparin management. However, TEG could be useful for the estimation of the FVIII level at least after heparin reversal, because the TEG results after protamine indicated appropriate heparin reversal without inappropriate FVIII level: there was clinically negligible difference between R-CK and R-CKH, and normal values in all TEG assays and ACT after protamine.
An advantage of implementation of a viscoelastic monitor including TEG is a more comprehensive diagnosis for coagulopathy rather than routine coagulation tests such as APTT or ACT. Although our TEG data after protamine administration indicated normal coagulation properties, including appropriate heparin reversal and adequate FVIII replacement, this advantage would be more important in cardiac surgery [10], in which coagulopathy is more severe owing to the use of cardiopulmonary bypass [5]. The CRT and CFF assays could be performed even in the presence of a certain level of heparin and showed maximally activated clot strength and fibrin mesh strength. In combination with the CK and CKH assays, they could provide more detailed information regarding coagulopathy and aid in making more appropriate decisions regarding coagulation management [11].
We described coagulation assessment by TEG for a patient with HA undergoing EVAR. Both the maintenance of adequate FVIII level and heparinization are important in cardiovascular surgery, and routine coagulation tests, such as APTT and ACT, do not distinguish heparin anticoagulation from FVIII deficiency. Although we expected a kaolin-activated assay with heparinase included in the TEG global hemostasis test could be useful for the estimation of the FVIII level during heparinization, it could neither fully eliminate the effect of heparin nor reflect the FVIII level during heparinization in EVAR. TEG could provide more detailed information about perioperative coagulopathy owing to heparinization or coagulation factor deficiency than APTT or ACT, at least before heparinization or after protamine administration. ROTEM might be more helpful for the estimation of the FVIII level than TEG during perioperative heparinization. Nevertheless, the implementation of viscoelastic monitors that include intrinsic activation assays with and without heparinase, in combination with routine coagulation tests such as APTT or ACT, could be helpful for coagulation management for patients with hemophilia who need heparinization during surgery.