Transfusion strategy: impact of haemodynamics and the challenge of haemodilution

Abstract

Blood transfusion is associated with increased morbidity and mortality and numerous reports have emphasised the need for reduction. Following this there is increased attention to the concept of patient blood management. However, bleeding is relatively common following cardiac surgery and is further enhanced by the continued antiplatelet therapy policy. Another important issue is that cardiopulmonary bypass leads to haemodilution and a potential blood loss. The basic role of blood is oxygen transport to the organs. The determining factors of oxygen delivery are cardiac output, haemoglobin, and saturation. If oxygen delivery/consumption is out of balance, the compensation mechanisms are simple, as a decrease in one factor results in an increase in one or two other factors. Patients with coexisting cardiac diseases may be of particular risk, but studies indicate that patients with coexisting cardiac diseases tolerate moderate anaemia and may even benefit from a restrictive transfusion regimen. Further it has been shown that patients with reduced left ventricular function are able to compensate with increased cardiac output in response to bleeding and haemodilution if normovolaemia is maintained. In conclusion the evidence supports that each institution establishes its own patient blood management strategy to both conserve blood products and maximise outcome.

Figure 1

Unadjusted long term survival following standard cardiac surgery procedures (CABG, AVR, and MVR) divided on perioperative blood transfusion [24]. Patients dying within first 30 days postoperatively were excluded from analysis.

Figure 2

The fraction of patient not receiving perioperative blood transfusion in European cardiac centers (survey from 2005: 119 European institutions covering 117,800 cardiac procedures).

Figure 3

Variables and factors influencing and determining organ oxygenation and the measurement possibilities.

Figure 4

Factor and relations between the oxygen delivery and oxygen consumption.

Figure 5

Oxygen consumption dependency of oxygen supply and influence of oxygen extraction fraction.

Figure 6

Perioperative changes in haematocrit and total haemoglobin. SCENARIO A: optimal perioperative management; impact of accurate blood conservation, use of cell-saver/retransfusion of machine blood and autotransfusion. SCENARIO B: nonoptimal perioperative handling; no use of cell-saver/retransfusion of machine blood and postoperative autotransfusion.

Figure 7

Variances in cardiac index and SvO₂ in elective patients the night before surgery [91].