Blood loss in cardiovascular surgery in the OR and ICU was higher in proportion to the CPB time, particularly in the > 3 h group, i.e., 6.2 and 3.1 times, respectively, higher than in the < 2 h group. Differences in platelet counts and fibrinogen levels among groups were not significant, but ROTEM™ measurement use showed a significant reduction in EXTEM and FIBTEM A10 at CPB termination, which are said to reflect the platelet counts and fibrinogen polymerization [9].
Based on the study, we suggest that blood transfusion management using ROTEM™ might be necessary if CPB time is > 3 h, such as aortic surgery, to add EXTEM and FIBTEM parameters as transfusion algorithms. Therefore, if CPB time can be predicted to be > 3 h perioperatively, we would measure not only CBC and fibrinogen but also parameters by POC, i.e., ROTEM to determine whether the amount of preparation, such as FFP and PCs, would be enough or not preoperatively.
Haensig et al.[12] also reported that POC was effective if CPB time was > 115 min. However, Girdauskas et al.[13] reported that POC was more useful for the surgery with deep hypothermic circulatory arrest (DHCA), with an average CPB time of approximately 200 min. In brief, they suggested that longer CPB time was more valuable for the measurement of POC coagulation test, which reduced the incidence of massive transfusion. However, only few studies investigated the relationship between CPB time, bleeding volume, and platelet function using POC, such as ROTEM.
Based on this study, two possible causes of reduced EXTEM and FIBTEM A10 were identified as represented by ROTEM. The first one was decreased antithrombin level. As shown in Fig. 2, when CPB exceeded 3 h, antithrombin was significantly lower than those in the other CPB time groups. The low antithrombin level might reduce the effectiveness of heparin, resulting in platelet activation and consequently reducing platelet function following the CPB termination [14]. The second reason was based on DHCA. As shown in Table 1, most surgery types with > 3 h CPB were aortic surgeries such as total and hemi-arch replacement that required DHCA which could be reflected not by ASA physical status but EuroSCORE II as well. Moreover, the body temperature in DHCA was approximately 25 °C–29 °C in our hospital, requiring longer time for cooling and rewarming. It is generally said that platelet function is markedly impaired by hypothermia because of inactivation of enzyme insides the platelet [15]. Its hemostatic inability is known to be reversible; therefore, sufficient rewarming can also recover the platelet function. We regularly terminate CPB when the rectal temperature exceeded 36 °C in DHCA cases; however, recovery of rectal temperature did not always coincide with the recovery of platelet function, showing time discrepancy. Based on these perspectives, the minimum temperature of DHCA tended to be higher in recent years. Therefore, if DHCA cases were excluded from patients in the CPB of > 3 h group, the group that only included mainly re-do or multi-valve replacement surgeries, decreased platelet function might not occur that often.
The measurement cost of POC test should also be considered because these tests are expensive, amounting to 20–30 US$ for each test. Moreover, the most recent POC tests have been changed into cartridge type for easy-to-go measurement and maintenance, i.e., ROTEM Sigma™ including EXTEM, INTEM, Heptem, and Aptem, amounting to approximately 100 US$.
Several studies have already investigated the usefulness of POC tests to reduce perioperative bleeding, transfusions, and cost for cardiac surgery and trauma patients [16]. Moreover, a recent multicenter study investigated a higher number of patients, i.e., 7402 cardiac surgeries with routine POC algorithm, who have been proven to have reduced major bleeding and PRBCs transfusion and PC [17].
By contrast, based on the results of our study, routine protocol for applying the POC test did not seem to be cost effective [18]. Therefore, patients with longer CPB time, with higher risk factors i.e., higher EuroSCORE II, and who used antiplatelet medications and coagulants should be carefully selected for the measurement of POC test because of high cartridge costs. Cardiac surgeries with CPB time of < 3 h do not require routine POC test but require sufficient usual laboratory CBC and coagulation tests including Fib.
Limitations of this study include the small number of patients as an observational study. The influence of DHCA for the > 3 h group could not be excluded. We noted that patients undergoing DHCA were weaned from CPB at a lower temperature, and this might affect platelet counts and function represented by the ROTEM measurements [19]. If patients with DHCA were excluded, platelet dysfunction may have been lower than that of our data. Only elective cardiac cases were included in this case-control study, and those who underwent emergency aortic dissection were excluded. Longer periods of hospital courses, including any complications, i.e., length of artificial ventilation, kidney injury, and neurological deficits, should also be considered.