Use of Human Fibrinogen Concentrate in Pediatric Cardiac Surgery Patients

Background: Bleeding after cardiac surgery can cause increased morbidity and mortality. This is a particularly serious problem in pediatric patients, especially neonates and infants, who may receive multiple units of blood products intraand postoperatively. The aim of this study is to demonstrate that the use of human fibrinogen concentrate (HFC) during cardiopulmonary bypass (CPB) decreased operative blood loss and the need for perioperative blood component therapy in neonatal, infant and other high-risk bleeding patients. Materials and methods: We have been using HFC in high-risk bleeding patients since April 2013.The drug is administered one time during the rewarming phase of CPB at a dose of 70 mg/kg, just prior to the termination of CPB. We conducted a retrospective cohort study of 100 pediatric cardiac surgery patients. The first 50 patients (HFC-treated group) that received the drug were compared to a group selected from the pre-HFC era (Pre-HFC group).We looked at total blood loss during the perioperative period, total transfusion requirements, including individual component therapy, duration of ventilation, length of stay (LOS) in the cardiac intensive care unit and LOS in the hospital. Thrombotic events were also compared between groups. Results: There was no significant difference in the age, weight and type of surgical operation between groups. There was significantly less fresh frozen plasma (FFP) (61 cc/kg vs. 39 cc/kg) and cryoprecipitate (11 vs. 2.8 cc/kg) used in those patients receiving HFC. There was a significant reduction in plasma fibrinogen at the time of rewarming compared with the preoperative value (225 vs. 114 mg/dL). However, there was no difference in the incidence of thrombotic events. Conclusion: HFC in a dose of 70 mg/kg significantly reduced the need for transfusion with cryoprecipitate and FFP in infants undergoing complex surgical repairs. Plasma fibrinogen concentration is significantly reduced during CPB.

acute problem in pediatric patients, particularly neonates and infants [3,4].Wolf et al. reported that early postoperative bleeding was independently associated with increased mortality in infants after cardiopulmonary bypass (CPB) [5].Their study demonstrated that the quartile with the greatest bleeding in the first twelve hours had a 25-fold increased mortality risk (10% vs. 0.4%) compared to the quartile with the least bleeding.Iyangar et al. reported transfusion with packed red blood cells (PRBC), fresh frozen plasma(FFP) and cryoprecipitate increased pulmonary complications and hospital length of stay (LOS) in pediatric cardiac surgery patients [6].Other authors have reported similar adverse events from transfusion therapy in pediatric cardiac surgery patients [7][8][9].
Fibrinogen (Factor I) is a plasma glycoprotein manufactured in the liver.Thrombin catalyzes the conversion of fibrinogen to fibrin, a step that is essential for clot formation, and fibrinogen also promotes platelet activation and agglomeration.The normal concentration of fibrinogen in the plasma is 1.5-4.0g/L or 150-400 mg/dL [10][11][12].Treatment options for augmenting fibrinogen include FFP, cryoprecipitate and/or human fibrinogen concentrate (HFC).FFP is issued as a single unit (200-250 mL), while cryoprecipitate is issued as a pooled sample of four to six units (10-20 mL).The concentration of fibrinogen in cryoprecipitate is typically 15 g/L, which is greater than the concentration of fibrinogen in FFP.FFP and cryoprecipitate have several limitations, including the need for ABO compatibility, the need for thawing, a variable fibrinogen content, the risk of transfusion-related complications (i.e., transfusion-related acute lung injury [TRALI] and transmission of infectious agents) and the presence of relatively high concentrations of citrate, which can acutely lower ionized calcium, leading to decreased myocardial contractility and hypotension [13,14].
The fibrinogen of children less than 12 months old with congenital heart disease is qualitatively dysfunctional [15].Moreover, the coagulation systems of neonates and children undergoing CPB are profoundly affected by haemodilution [16] and by consumption [17].Neonates and young infants undergoing complex cardiac repairs often receive multiple units of blood products, both in the operating room (OR) and intensive care unit (ICU) [18].Reducing the total volume of transfused blood products and reducing the unit donor exposure can reduce transfusion-related morbidity and mortality.

Introduction
Bleeding after cardiac surgery is a dangerous complication that can cause increased morbidity and mortality [1,2].This is an especially normalized ratio (INR) and partial thromboplastin time (PTT), preoperative and rewarming fibrinogen and the incidence of clinical thrombosis.We also compared, between groups, the duration of: CPB, aortic cross clamp (AXC), regional low flow perfusion (RLFP), and deep hypothermic circulatory arrest (DHCA).The number of patients that experienced deep hypothermia (low temperature < 20˚C) and the lowest intraoperative temperature achieved were also compared.

Perfusion management
Patients under 10 kg in body weight had the CPB pump primed with one unit of PRBC and 200 cc FFP.In patients, over 10 kg a pure crystalloid prime was used.Target hemoglobin (Hg) while on CPB was 9 g/dL, but the transfusion trigger for additional units of PRBC was 7 g/dL.Heparin management for all patients was based on the following tests using the HEPCON ® HMS PLUS system.First, a baseline activated clotting time (ACT) with a projected heparin dose-response is performed.The initial heparin bolus is determined based on a desired ACT target of 480 seconds and a projected patient The purpose of this retrospective analysis is to demonstrate that the use of HFC during CPB decreased operative blood loss and the need for perioperative blood component therapy in neonatal, infant and other high-risk bleeding patients.

Materials and Methods
This is a retrospective cohort study reviewed and approved by the Western Institutional Review Board.

Patient population
HFC has been used on over 50 neonates, infants and other highrisk bleeding patients scheduled for elective cardiac surgery at Miami Children's Hospital since April 23, 2013.

Human fibrinogen concentrate administration
The drug was administered prophylactically, one time, prior to the termination of CPB, during the rewarming phase, in a dose of 70 mg/kg; this is the dose recommended by the manufacturer in adult patients if the fibrinogen level is not known.

Endpoints
The first 50 patients (Group 2 or HFC-treated) that received the drug, during the time period from April 23, 2013 to February 26, 2014, were compared to a group of patients treated from October 1, 2012 through April 22, 2013 (Group 1 or Pre-HFC).The two cohorts were comparable in terms of age, diagnosis, procedure, and identity of the surgeon.We looked to determine if there was a statistical difference between the groups for the following primary parameters: postoperative blood loss (chest and mediastinal tube drainage), and the amount and type of blood components transfused during surgery, including during CPB, and for the first 24 hours after surgery.Secondary endpoints included duration of postoperative ventilation in hours, LOS in the cardiac intensive care unit (CICU), the LOS in the hospital, postoperative prothrombin time (PT), international

Data analysis and data monitoring
Data was analyzed as mean ± standard deviation (SD), median and range, and proportions.Fifty charts were reviewed for each group.
The Statistical Package for Social Sciences (SPSS 21 ® ) was used to organize, validate and analyze the collected data.Indicators of central tendency and dispersion were calculated.Group comparisons were made using both parametric (t-tests) and non-parametric (Mann-Whitney U) tests for continuous variables.Chi-Square or Fisher's exact test, when appropriate, were used for categorical variables.A determining level of 0.05 was selected for all tests of significance.

Demographic characteristics
There was no significant difference in the age, weight and type of surgical operation between groups.One patient from Group 1 was eliminated due to being a statistical outlier.In Group 1, 46 out of 50 patients were less than 10 kg and in Group 2, 42 out of 50 patients were less than 10 kg.There was no variation in the duration of AXC, RLFP, and DHCA times.There was no difference in the number of patients that experienced deep hypothermia (χ 2 = 0.83, p > 0.05) and no difference in the lowest temperature achieved between groups (U = 1091, p > 0.05, r = -0.09).There was a significantly longer duration of CPB in the HFC-treated patients (Group 2), (U = 938, p < 0.05, r = -0.20)(Table 1 and Table 2).

Primary endpoints
The transfusion requirements in blood product type and amount are stratified into four groups: those given during CPB administered by the perfusionist; those products administered by anesthesia after termination of CPB; those products given by the ICU physicians once the patient leaves the OR; and then the total amount of all the blood products given during the three phases.With the above noted, there was a significant difference in the following parameters.There was significantly less FFP (U = 563, p < 0.01, r = 0.47) and cryoprecipitate (U = 411, p < 0.05, r = 0.68) given during CPB in the HFC-treated patients (Group 2).There was also significantly less FFP (U = 871, p < 0.05, r = 0.26) and cryoprecipitate (U = 722, p < 0.001, r = 0.49) given by anesthesia after termination of CPB in the HFC-treated patients (Group 2).Interestingly, the HFC-treated patients (Group 2) received significantly more Cell Saver than patients in Group 1 (U = 882, p < 0.05, r = 0.24).There was significantly less FFP (U = 730.5,p < 0.01, r = 0.36) and cryoprecipitate (U = 325.5,p < 0.01, r = 0.36) used in total in those patients receiving HFC (Group 2).Additionally, there was no difference in overall blood loss (U = 1039, p > 0.05, r = -0.13)or total transfusion requirements for other components (Table 3 and figure 2).

Secondary Endpoints
There was no difference in the duration of ventilation and LOS in both the CICU (U = 990, p > 0.05, r = 0.17) and hospital (U = 1013, p > 0.05, r = 0.15).No distinctions were obvious in Factor VII use or heparin concentration of 3.0-4.5 mg/kg.Second, heparin levels and ACT tests were run every 30 minutes or more frequently as needed.Reversal is with 1.2 mg protamine for every 100 International Units (IU) of residual heparin activity as documented by the HEPCON.Third, a low range heparin assay to confirm heparin reversal or need for additional protamine is conducted after CPB.

Transfusion protocol
A ROTEM-based transfusion protocol was used in both groups (Figure 1); in Group 2 this was done after the administration of HFC.From that point forward the same transfusion protocol was used in both groups.It is our practice to employ rotational thromboelastometry (ROTEM) to guide component transfusion therapy, as described by Romlin et al. [19].Therefore, nearing the conclusion of CPB, ROTEM is used to guide component transfusion therapy.It is our institutional practice to begin to correct the dilutional coagulopathy while still on CPB, but just prior to its termination.The goal is to commence correction of the CPB-induced coagulopathy and hypofibrinogenemia.The component therapy could include plateletpheresis, FFP and/or cryoprecipitate depending on the ROTEM results.Ongoing hypofibrinogenemia was corrected with cryoprecipitate in both groups.Further ROTEM tests were done as needed, both in the OR and in the CICU.PRBC were transfused based on the Hg level reported on the iStat blood gas machine; transfusion triggers were Hg less than 10 g/dL.

Adverse event surveillance
The incidence of thrombotic events was also analyzed.A thrombotic event was defined as venous or arterial vessel occlusion secondary to placement of a vascular catheter documented by ultrasound (US), an aortic to pulmonary artery shunt occlusion, a Sano shunt occlusion, a thrombus in a major vessel or thrombosis while on cardiopulmonary support (CPS).Patients are routinely assessed for adequate peripheral circulation.Any patient demonstrating signs or symptoms of arterial or venous occlusion has an US done to confirm the diagnosis.Signs and symptoms of venous occlusion in the affected extremity include pain, edema, erythema, and distended peripheral veins.Signs and symptoms of arterial occlusion in the affected extremity include pain, pallor, loss of pulses, parathesia, paralysis and dose, nor the need for mediastinal exploration (χ 2 = 1.69, p > 0.05).
There was a significantly higher PT in the HFC-treated group (Group 2) compared with Group 1 (U = 770, p < 0.01, r = 0.27).There was no difference in postoperative INR (U = 10.5, p > 0.05, r = 0.14) and PTT (U = 14, p > 0.05, r = 0.11) between groups.On the contrary, there was a significant reduction in plasma fibrinogen at the time of rewarming compared with the preoperative value in the Group 2 patients.The rewarming fibrinogen level was below the normal range in 33 of the 34 patients that had the test performed.However, there was no difference in the incidence of thrombotic events (χ 2 = 0.25, p > 0.05).See table 4 and table 5.

Discussion
This is one of the first reports of the use of HFC in pediatric  using a multiple regression model, that preoperative fibrinogen concentration is an independent predictor of postoperative bleeding volume [21].In this same study, the investigators also demonstrated that fibrinogen concentration, even when within the normal range, is a limiting factor for postoperative hemorrhage, i.e., fibrinogen values are inversely correlated with the risk of transfusion, even when within the normal range.The prophylactic infusion of HFC has been shown to reduce bleeding after adult coronary artery bypass graft (CABG) surgery without evidence of hypercoagulability [22].Moreover, FIBTEM (fibrin-based extrinsically activated test with tissue factor and the platelet inhibitor cytochalasin D)-guided HFC administration was associated with reduced transfusion requirements and reduced postoperative bleeding within the first 24 hours in adult patients undergoing aortic valve operations and ascending aortic reconstructions [23].In children, there is a paucity of data regarding the use of HFC in pediatric cardiac surgery patients.However, Galas et al. did report that in bleeding pediatric cardiac patients the use of HFC was "as efficient and safe as cryoprecipitate" [24].Also, the American Society of Anesthesiologists (ASA) Practice Guidelines for Perioperative Blood Management, published in February 2015, recommends that "in patients with excessive bleeding, consider the use of fibrinogen concentrate" [25].
Thrombosis is a reported complication in HFC-treated patients, but the risk appears to be low [26].However, Jakobsen et al. reported an increased risk of neurological thromboembolic complications and renal failure in their retrospective review of 1,876 adults undergoing CABG treated with fibrinogen concentrate [27].Our analysis did not demonstrate an increased incidence of thrombotic events in HFCtreated patients, although the sample size was considerably smaller than that reported by Jakobsen et al.Virtually all of the thrombotic events were femoral arterial or femoral venous occlusions after percutaneous catheter insertion.There was one right atrial thrombus in Group 1.In Group 2, there was one shunt occlusion and one shunt occlusion and thrombosis on CPS the same patient.All the other thrombotic events were related to percutaneous central venous catheters or arterial catheters.This incidence is high, but not inconsistent with other reports in the literature [28][29][30].Furthermore, we did not examine any of the patients for end-organ damage due to thrombotic events by conducting brain MRIs or abdominal ultrasounds.This is certainly a limitation of this study.
The concentration of fibrinogen in HFC is standardized, in distinction to the variability that exists with FFP or cryoprecipitate.HFC is stored as a lyophilized powder at room temperature that permits fairly rapid reconstitution without unnecessary delays for cross matching or thawing [31].Moreover, infusion volumes are low and the drug also does not contain any citrate.One unit of cryoprecipitate (10-20 cc of volume) contains 250-350 mg of fibrinogen [32]; the cost is $186 per unit whereas HFC costs $0.85 per mg.Thus, an equivalent dose of HFC at 250-350 mg would cost $212-$287.HFC is more expensive, but the reduced donor exposure might justify the increased cost.cardiac surgery patients.It demonstrated that using HFC one time at a dose of 70 mg/kg reduced the need for transfusion with FFP and cryoprecipitate during and after separation from CPB, while in the OR and overall, but not when in the ICU.This was despite the fact that the HFC-treated group had a significantly longer CPB time, which would normally predict a higher transfusion risk [20].The reduced need for cryoprecipitate was certainly expected, since the HFC-treated patients were receiving a substantial dose of fibrinogen.The reduced need for FFP was not as intuitively obvious.It is noteworthy that in our analysis 82% (Group 1) and 81% (Group 2) of the blood products were administered in the OR, either by perfusion or anesthesia; less than 20% of the total was given by the ICU staff.This is a reflection of our programmatic philosophy of delivering a stable, non-bleeding patient to the ICU.This could also explain why there was no difference in the ICU component of the transfusion therapy.This analysis corroborates previous studies demonstrating that the fibrinogen level at rewarming is typically 60% lower than the preoperative baseline value.Since the fibrinogen level can be used to dose HFC, quantifying the fibrinogen level at the time of administration can be potentially important.However, we had difficulty getting this lab value back in a timely enough fashion to utilize the fibrinogen level to dose the HFC.We believe this would be preferable to dosing based on weight.We also did not record unit donor exposure during this time period, so we did not include this in our analysis, but using HFC in lieu of cryoprecipitate necessarily must reduce unit donor exposure, since cryoprecipitate is issued as a pooled sample of 4-6 units, necessitating a 4-6 unit donor exposure from that one therapeutic intervention.
Our analysis partially corroborates the findings of studies in adult patients regarding a reduced transfusion requirement for FFP and cryoprecipitate, but did not demonstrate significantly less perioperative blood loss or a lower transfusion requirement for PRBC or platelets.We did not expect the administration of HFC to decrease the need for transfusion with platelets.Moreover, it is possible, given the profound dilutional coagulopathy that occurs in neonates and young infants undergoing CPB, that a dose of 70 mg/kg is not sufficient to produce similar results.Perhaps a greater dose, or multiple doses, is required.Further studies will need to be conducted.One potential bias for this observational, retrospective analysis was patient selection in the pre-HFC group.We went back serially in time and, based on the patient demographic characteristics and planned surgery, included any patient we considered at high risk for bleeding and only then did we examine the record.Another limitation of this analysis is that we encountered numerous missing values for some of the variables of interest, particularly the preoperative coagulation studies.Therefore, the analysis had to be performed using only valid paired values.Furthermore, the postoperative PT was significantly longer in the HFC-treated group (Group 2), the only variable that was significantly worse for this cohort.We attribute this to the smaller amount of FFP this group received.Even though the PT was longer in Group 2, this did not lead to further bleeding.Since this is a retrospective observational study, results should be interpreted with caution.We are recommending a prospective, randomized controlled trial for more accurate comparison and generalizable conclusions.This analysis has demonstrated an intriguing result, one deserving further study.Like recombinant coagulation factor VIIa (rFVIIa), which has been shown to be useful in preventing re-exploration for uncontrolled bleeding in children undergoing cardiac surgery with CPB [33][34][35], HFC can potentially be another useful drug in pediatric cardiac surgery patients.A prospective, randomized, controlled trial is planned.
In conclusion, HFC given during the rewarming phase of CPB in a dose of 70 mg/kg significantly reduced the need for transfusion with cryoprecipitate and FFP in infants undergoing complex surgical repairs placing them at risk for perioperative bleeding.There was also no increased risk of thrombotic complications in this series.

Table 1 :
Demographic data