Major bleeding during cardiac surgery is an outcome that warrants the use of blood transfusions and reinterventions, both of which are risk factors for mortality (Moulton et al., 1996; Makar et al., 2010; Vivacqua et al., 2011). Acute coagulation defects are a common complication in cardiac surgery and can arise as a result of tissue injury and hypotension, with haemodilution, hyperfibrinolysis, and inflammatory responses all helping to sustain bleeding (Levy et al., 2005; Karkouti et al., 2010; Makar et al., 2010; Chee et al., 2016). An added complication is that this patient group are likely to have comorbidities and ongoing anticoagulant treatment for the prevention of heart disease, or anticoagulants administered during surgery to prevent clot formation (such as heparin) (Scrutinio & Giannuzzi, 2008).
Many studies have found that both preoperative and postoperative fibrinogen levels are negatively correlated with blood loss during cardiac surgery (Kozek-Langenecker et al., 2017). In one study of 1,954 patients undergoing cardiac surgery, a preoperative plasma fibrinogen level of less than 2.5 g/L was independently associated with increased risk of postoperative bleeding when compared with a preoperative plasma fibrinogen level of 4.6 g/L or more (Walden et al., 2014) (Figure 8).
A systematic review and meta-analysis of 20 research articles covering a total of 5,972 cardiac surgery patients indicated that low pre- and postoperative fibrinogen levels are associated with greater blood loss in cardiac surgery (Gielen et al., 2014). The authors identified a significant negative pooled correlation between:
Some studies focus on distinct clinical settings. For instance, Liu et al. carried out a retrospective study of 125 patients with type A acute aortic dissection, a tear in the inner layer of the ascending aorta that redirects blood to create a false lumen (Liu et al., 2018). The findings indicated that a fibrinogen level of less than 2.17 g/L was independently associated with higher in-hospital mortality in these patients (adjusted odds ratio 5.527; 95% confidence interval 1.660–18.401; p=0.005).
Low postoperative fibrinogen is also a risk factor for excessive bleeding following cardiopulmonary bypass (CPB). In a prospective, multi-centre observational cohort study of cardiac surgery patients undergoing CPB (n = 1,956), plasma fibrinogen levels measured at the time of ICU admission was correlated with excessive bleeding, defined as the 24–hour chest tube output exceeding the 90th percentile of the distribution (n = 189) (Kindo et al., 2014). Fibrinogen levels were 2.5 g/L for the control group compared to 2.1 g/L for the group that experienced excessive bleeding (p<0.0001). On admission to intensive care, there was a significant negative correlation between fibrinogen levels and excessive bleeding (r = -0.237; p<0.0001). In this study, the authors recommend a cut-off of 2.2 g/L fibrinogen level at the point of admission to intensive care for predicting postoperative bleeding (Kindo et al., 2014).
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