8.6.2 Blood savings and transfusion

 Blood transfusion is main topic of a separate chapter (see Chapter 28) and will be discussed here  briefly: overall patient blood management, risks of transfusion and recommendations in cardiac surgery.

 Comprehensive blood savings management

Blood transfusion is only one component of an integrated blood-saving strategy that considers the patient's blood as an irreplaceable asset deserving maximum protection. It is based on five principles [5,9,25].

  • Correction of preoperative anaemia and/or coagulopathy ;
  • Saving the patient's blood cells and coagulation factors, limiting blood loss;
  • Rational administration of blood products, restrictive transfusion thresholds ;
  • Use of algorithms based on laboratory tests performed in the operating room;
  • Improvement of tissue DO2 by hemodynamic and ventilatory optimization.

This strategy includes measures that are listed in Table 8.9 and detailed in Chapter 28 (Comprehensive Blood Management Strategy) [2,8]. 

tab8.9

Preoperative anaemia deserves special mention because it is as easy to correct as it is dangerous for survival. Moderate anaemia (100-120 g/L) is associated with 40% increased morbidity [25] and 16% increased mortality [13]. It is present in about 30% of cases [13]. Preoperative treatment is straightforward, as most cases are due to iron deficiency anaemia: iron, folic acid, vitamin B12, possibly EPO; transfusion is not a consistent option, as a single blood bag increases perioperative risk by 2-3 times [24]. In addition to this baseline anaemia, there is intraoperative blood loss and blood loss from laboratory tests, which averages 450 mL in cardiac surgery and 1,000 mL for 2 weeks in intensive care [15].

The purpose of transfusion is to improve O2 transport to the tissues (DO2 ), not to correct haemoglobin (Hb) levels. It is based on haemodynamic imbalance, ischaemic organ dysfunction and the patient's cardiopulmonary reserve. However, Hb is a practical benchmark that is still widely used and allows simple criteria to be defined. Provided the patient is normovolaemic and the source of bleeding is controlled, transfusion is indicated for the following Hb values [1,2,3,4,12].

  • In a healthy individual with normal haemodynamics, transfusion is indicated if the Hb is < 60 g/L.
  • Perioperatively, a Hb value of 70-80 g/L is a reasonable threshold for transfusion.
  • In at-risk populations (coronary ischaemia, ventricular failure, stroke, nephropathy, advanced age), the transfusion threshold may be raised to 80-90 g/L; the same applies to febrile, septic or ARDS patients.
  • Transfusion is unlikely to improve DO2 when Hb is ≥ 100 g/L, except in cyanogenic heart disease (R-L shunt, pulmonary hypertension) or severe ARDS.

One blood bag increases Hb level by about 1 g/L and the Ht by 3% in an adult. Red blood cell transfusion affects coagulation. It improves platelet function by increasing thromboxane production and ADP release, and increases thrombin production [20]. In addition, the marginalisation of platelets in blood stream by mass of erythrocytes that remain in the middle of the stream increases the chances of thrombocyte attachment to the vessel wall [22]. 

Transfusion-related risks

About 1-4% of transfused patients develop complications. Risks of blood product transfusion can be grouped under several headings (see Chapter 28 Risks) [4].

  • Transfusion reaction: allergy, febrile reaction, circulating volume overload (1-5%).
  • Reaction related to blood bag components (hyperkalaemia, hypocalcaemia, etc).
  • Immunomodulation (leukocyte-related reactions): Transfusion-Related Acute Lung Injury (TRALI), cancer recurrence, inflammatory reaction, graft-versus-host disease (1:104 ).
  • ABO haemolytic reaction (1:105 ).
  • Transmission of bacterial, viral or prion-related diseases (1:106 ).
  • Economic risk (cost, supply difficulties).

Transfusion is directly related to postoperative morbidity and mortality after cardiac surgery. A comparative analysis of  patients survival who receive 1-2 blood bags compared to those who are not transfused in a group of 3,254 cases shows an overall increase in mortality of 16% in transfusion recipients; death risk is multiplied 1.7 times (HR 1.67) at 6 months, but the difference is no longer significant at 5 years (HR 1.06) [21]. However, the "collateral damage" of transfusion seems to be present in the long term. In a series of 1,915 cardiac surgery patients followed up at 5 years, transfusion (34% of the group) resulted in a 70% increase in mortality (HR 1.7) in the long term, even after adjustment for comorbidities and associated factors; in multivariate analysis, transfusion remained an independent determinant of mortality [7]. A 10-year follow-up study of 10,289 CABG patients showed a significant reduction in survival of transfused patients that was proportional to the number of blood bags received (Figure 8.22A) [14]. In this study, the long-term risk of 3 blood bags is equivalent to that of reoperation, common trunk disease or low ejection fraction; the risk of 6 units of blood is the same as that of renal failure or ventricular failure. An analysis of the 7-year outcome of 8,724 patients showed an odds ratio of 3.38 and 3.35 respectively for infections and ischaemic complications (MI, stroke, renal failure) in transfused patients compared to non-transfused patients (Figure 8.22B) [18]. However, these observations mainly concern polytransfused patients; indeed, the administration of 1-2 bags of leukoreduced blood does not seem to affect long-term vital prognosis [16].

 08 22

Figure 8.22: Effect of transfusions on postoperative mortality in cardiac surgery. A: Reduction in 10-year survival of transfused patients in proportion to the number of blood bags received during coronary artery ECC [12]. 1: No transfusion (yellow line). 2: transfusion of 3 units (blue line). 3: transfusion of 6 or more units (red line). B: Increased mortalityaftercardiac surgery in transfused patients compared to non-transfused patients. The difference occurs mainly in the first six months, but the curves continue to diverge slightly in the long term [18].

Recent comparisons between restrictive (Hb < 70 g/L) and liberal (Hb > 90 g/L) transfusion thresholds show no difference in short-term or long-term mortality, which means that the restrictive attitude is safe [4]. In cardiac surgery, however, the situation seems different. The restrictive strategy tends to increase cardiovascular mortality (OR 1.64), although it does not alter rate of complications or morbidity [17]; in non-surgical acute coronary syndrome, it increases risk morbidity (OR 1.78) [6]. Cardiac surgery patients are therefore a fragile population that deserves a transfusion threshold of 80-90 g/L Hb rather than a low threshold (Hb 70 g/L) appropriate for a non-cardiovascular population. The apparent discrepancy between the latter two studies and those cited above is that, for the same Hb level, transfused patients have a poorer prognosis than those who were not transfused. In other words, acute anaemia is dangerous, and transfusion to correct it makes the situation worse. The conclusion is to avoid preoperative anaemia at all costs and to keep intraoperative blood loss to a minimum.

Recommendations for cardiac surgery

A few simple measures can significantly reduce the consumption of blood products and change patients prognosis [19].

  • Treat preoperative anaemia. Too many patients arrive in the operating room with an Hb of 100-110 g/L. An Hb level of < 120 g/L in women and < 130 g/L in men is responsible for increased perioperative morbidity and mortality [23], and this risk is doubled in case of transfusion [10,11]. Treatment with iron, vitamin B12, folic acid and, if necessary, erythropoietin (EPO) can normalise the values preoperatively and allow surgery to be performed with a better reserve.
  • Restrict transfusions: restrictive threshold (Hb < 80 g/L, Hb < 90 g/L in the elderly or at risk).
  • Limit blood loss: rigorous haemostasis, normovolaemic pre-ECC haemodilution, blood recovery, ultrafiltration.
  • Avoid intraoperative coagulopathy: normothermia, acid-base balance, calcium, antifibrinolytics. Routine use of thromboelastography to assess coagulation factor deficiencies and selectively compensate for them: protamine, tranexamic acid, fibrinogen, PCC, factor XIII.
  • Improve tolerance to anaemia: FiO2 0.8-1.0, muscle relaxation, deep anaesthesia, normovolaemia.

 

 Blood transfusion 
  Red blood cell transfusion aims at improving tissue DO2 . Indications (normovolaemic patients and controlled bleeding):
- Transfusion is indicated if Hb is < 60 g/L
- Perioperatively, transfusion is usually indicated if the Hb is < 70-80 g/L
- In populations at risk (coronary ischemia, ventricular failure, stroke, nephropathy, advanced age), the threshold for transfusion can be raised to 80-90 g/L
 
Transfusion is unlikely to improve DO2 when Hb is ≥ 100 g/L, except in cyanotic heart disease (R-L shunt, pulmonary hypertension) or ARDS.
 
Transfusion increases the risk of infection, ARDS and renal failure. Like anaemia, it increases postoperative morbidity and mortality by about 15% (relative). Acute anaemia is dangerous, and transfusion to correct it makes the situation worse. It is important to avoid preoperative anaemia and to limit intraoperative blood loss.

 

 © CHASSOT PG, MARCUCCI Carlo, last update November 2019.

 

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