Coagulation screening
Routine coagulation testing remains standard practice as part of the surgical pre-assessment at many institutions to identify any abnormality that might increase the risk of perioperative bleeding. However, a normal coagulation screen can be mistakenly reassuring. A coagulation screen includes a prothrombin time, an activated partial thromboplastin time (APTT), and a thrombin time. Ninety-five percent of the adult population is expected to lie within the normal ranges provided by the testing laboratory. The results of these tests may not accurately reflect the complex interactions of haemostasis in vivo, between vasculature, clotting factors, platelets and fibrinogen, and may not therefore correlate well with the actual perioperative bleeding risk [
14]. Prolongation of these tests may indicate a deficiency of one or more coagulation factors requiring specialist haematological advice and pre-operative management. Laboratory tests may also be prolonged by pre-analytic variables and phospholipid antibodies, neither of which cause bleeding [
15].
In advance of a surgical procedure, it is often feared that without undertaking a coagulation screen a bleeding disorder may be missed. The majority of patients with a moderate to severe congenital bleeding tendency will have exhibited bleeding following haemostatic challenges early in life, and/or have a positive family history, meaning that they are already aware of their underlying condition.
It is widely accepted that undertaking a structured personal bleeding history, for example using the International Society on Thrombosis and Haemostasis validated bleeding assessment tool (ISTH-BAT), combined with exploring a family history of bleeding and information on concomitant use of antiplatelet and antithrombotic medications, is an effective way of identifying individuals with an increased bleeding tendency [
16]. Selective laboratory testing can then be undertaken in those individuals identified with a high bleeding risk. Furthermore, in mild to moderate von Willebrand disease, one of the more common bleeding disorders, the coagulation screen may be normal, and the disorder may be missed if a detailed personal and family history is not taken. The limiting factor of this approach may be those individuals who have never undergone a significant operative challenge and, as such, not had a challenge of their haemostatic system.
Within the UK, the British Society for Haematology caution against the practice of unselected coagulation screening and advise selective screening in those with a positive personal or family bleeding history, patients on anticoagulants and those patients with a relevant medical history including cancer, liver disease, sepsis and disseminated intravascular coagulation [
17]. The National Institute for Health and Care Excellence in the UK also recommends a similar approach [
18]. There is no international consensus. US guidance suggests extra caution and recommends coagulation screening in higher-risk surgical cases. The Italian Society for Thrombosis and Haemostasis continues to recommend routine coagulation testing for all due to the lack of robust randomised controlled clinical trials [
19,
20].
However, in higher risk surgery such as cardiac surgery, undertaking a coagulation screen at baseline may still be recommended for those patients requiring CPB, when heparin anticoagulation monitoring can prove challenging if there is baseline coagulation abnormality. For example, factor XII (Hageman factor) deficiency or lupus anticoagulant will both lead to isolated APTT prolongation without a clinical bleeding risk, but will also prolong the baseline activated coagulation time (ACT). In these cases, ACT monitoring during bypass may not accurately measure the effect of heparin.
We undertake coagulation screening in patients who will require CPB or extra corporeal membrane oxygenation circuits. This allows us to offer an alternative heparin monitoring strategy using the anti-factor Xa assay for those patients with baseline APTT abnormalities. The anti Xa test is not affected by variables interfering with the ACT test. However, this assay may not be readily available with a fast enough turnaround time in all institutions.
Anaesthetic considerations
Pre-operative anaemia is common in cardiac surgery with a prevalence of between 10 and 50% (depending on definition) [
21]. Pre-operative anaemia is mostly the result of inadequate erythropoiesis due to iron deficiency, malnutrition, malabsorption, inflammation, bone marrow disorders, or chronic blood loss [
22]. Importantly, anaemic patients need to be identified, as early as possible, by the cardiologist, surgeon or anaesthetist [
23]. The International Consensus Conference on PBM 2018, defined the current status of the PBM evidence base for clinical practice and research purposes, and established four clinical and three research recommendations for pre-operative anaemia, including the strong recommendation to detect and manage anaemia sufficiently early before major elective surgery [
24].
Assessment of full blood count, ferritin, transferrin saturation, and the soluble transferrin receptor are recommended to identify any iron deficiency with or without anaemia [
22]. Anaemia is often found in cardiac surgery patients due to infection or chronic kidney disease resulting in functional iron deficiency. After iron supplementation, haemoglobin concentrations rise approximately 1–2 g/dL within 2–4 weeks. A multicentre observational study by the UK Association of Cardiothoracic Anaesthesia and Critical Care Research Network found that the development of an intravenous iron pathway is feasible, but appears limited to selected high-risk cardiac patients in routine NHS practice. Patients with anaemia who received intravenous iron supplementation before surgery were at higher surgical risk, were more likely to have a known previous history of iron deficiency or anaemia, had a higher rate of chronic kidney disease and were slightly more anaemic than those who did not receive any iron supplementation [
25]. A recent meta-analysis including four randomised controlled trials and seven observational studies suggested that administration of intravenous iron reduced the number of patients transfused and improved post-operative morbidity in adult cardiac surgery patients with pre-operative anaemia or iron deficiency [
26].
An ongoing multicentre interventional trial (NCT02632760) with 1000 participants is expected to provide definitive answers about the effects of intravenous iron before cardiac surgery with the primary outcome measure as the number of days alive and out of hospital up to 90 days post operatively. A recent trial of 505 patients with iron deficiency or anaemia undergoing cardiac surgery investigated the effects of ultra short-term treatment using a combination of iron, erythropoietin, vitamin B12, and folic acid. During the first 7 days, significant reductions were observed in red cell concentrate transfusions, as well as significant increases in haemoglobin concentration, reticulocyte count, and haemoglobin content of reticulocytes (RET-He) [
27]. Thus, iron supplementation, especially in combination with erythropoietin is recommended when the anaemia of chronic disease is accompanied by iron deficiency with complete depletion of iron stores [
28]. Importantly, diagnosing and (if indicated) correcting pre-operative anaemia should be mandatory ahead of planned cardiac surgeries. In urgent cases, patients should still receive ultrashort-term pre-operative treatment [
27].