Red Cell Transfusion in Critical Care - BCSH guideline 2012 - 60% of ITU patients are anaemic
- 20-30% have a first Hb <90g/L
- After 7 days 80% have a Hb <90g/L
- 30-50% receive red cell transfusion
Association between anaemia and inferior outcome- Impaired erythropoiesis secondary to inflammation
- It is uncertain whether the lack of effectiveness of transfusion is because anaemia itself does not affect outcome or because the risks associated with current stored red cell transfusions out weigh physiological benefits
Pathophysiology of anaemia- Young adults can maintain oxygen supply at Hb of 40-50g/L by increasing cardiac output and oxygen extraction.
- Heart and brain have high oxygen extraction ratios which limit these compensatory mechanisms.
- Oxygen consumption is increased in the critically ill so anaemia may be less well tolerated.
Transfusion triggers- TRICC study – transfusion requirements in critical care (Herbert et al, 1999).
- Hb<90g/L randomised to either a
- High transfusion trigger of 100g/L (target 100-120g/L)
- Low transfusion trigger of 70g/L (target 70-90g/L)
- Non-significant trend to lower 30 day mortality (23% v. 19%) in the lower trigger group.
- Introduction of leucodepletion
- Storage age of red blood cells
- Selection bias- few patients with cardiac disease and high rate of clinician refusal.
- TRACS study (2010) – transfusion requirements after cardiac surgery
- Trigger HCT 24 versus 30%
- Mean maintained Hb 105 versus 91g/L
- No difference in 30 day mortality between high and low trigger
- No difference in mortality or morbidity
- Default transfusion trigger 70g/L (range 70-90)
- Transfusion trigger should not exceed 90g/L in most critically ill patients.
- Erythropoietin should not be used to treat anaemia in critically ill patients.
- In the absence of clear iron deficiency, routine supplementation is not recommended.
- Consider blood conservation sampling devices.
- Consider paediatric blood sampling tubes.
- Pre-transfusion clinical assessment to assess risk of TACO.
- Consider rate of transfusion, fluid balance and need for dieresis
- Assess for TRALI in patients presenting with dyspnoea and pulmonary infiltrates within 6 hours of transfusion.
- Adverse events should be investigated and reported for local risk management and national haemovigilance schemes.
- Insufficient evidence to support use of ‘fresher blood’ to the critically ill.
- In the early resuscitation phase of severe sepsis, with evidence of inadequate oxygen delivery (ScvO2<70%, SvO2<65%, lactate >4mmol/L), target of 90-100g/L should be considered.
- In traumatic brain injury, target haemoglobin 70-90g/L. If evidence of cerebral ischaemia, increase target to >90g/L.
- In subarachnoid haemorrhage, target Hb 80-100g/L
- In ischaemic stroke, target Hb >90g/L
- In stable angina, target Hb >70g/L. Transfusion to >100g/L has uncertain benefit.
- In acute coronary syndrome, maintain Hb 80-90g/L
- Red cell transfusion should not be used to assist weaning.
- Alternatives to red cell transfusion
- Critically ill do not generate erythropoietin in response to anaemia
- Combination erythropoietin and iron can modestly decrease transfusion requirements, but benefits negligible when transfusion trigger is 70g/L
- Possible decrease in mortality among trauma patients
- Not licensed for these patients.
- Iron studies typically demonstrate
- Reduced transferrin, iron to iron binding ratio and transferring saturation
- Iron is shifted into macrophages resulting in a functional iron deficiency, but evidence of absolute iron deficiency is absent in most.
- Excess iron may increase susceptibility to infection.
- Blood sampling techniques
- Typical daily blood loss associated with phlebotomy 40mls.
- Blood sampling conservation devices (Venous arterial blood management protection system). No published cost effectiveness.
- Paediatric sampling bottles
- Adverse consequences of transfusion specific to the critically ill
- Transfusion associated circulatory overload
- Acute respiratory distress with pulmonary oedema, tachycardia, hypertension with a positive fluid balance after blood transfusion.
- Incidence difficult due to different definitions
- 1 study suggested 1 in 357 units. (Rana et al, 2006)
- Transfusion related acute lung injury
- Pulmonary oedema within 6 hours of transfusion with a PaO2:FiO2 <300mmHg in room air, bilateral infiltrates and NO left atrial hypertension.
- Rana et al estimated 1 in 1271 units.
- Red cell storage duration
- 2,3 DPG depletion impairs oxygen release
- Reduced nitric oxide production, membrane changes, decreased deformability, increased adherence to endothelium limit capillary transit.
- Accumulation of bioactive substances, especially in non-leucodepleted cells.
- Rivers et al 2001 – goal directed resuscitation in early sepsis (first 6 hours)
- Transfusion trigger of HCT 30 (approx Hb 100g/L) was used together with dobutamine in patients with evidence of tissue hypoxia (ScvO2<70%)
- Reduced risk of death in hospital by 16%.
- Increasing haematocrit in brain injury is contentious, as increasing it improves oxygen carrying capacity but also increases viscosity which impairs cerebral blood flow.
- Delayed cerebral ischaemia is a major concern – current strategies focus on maintaining adequate cerebral perfusion pressure and avoiding raised intracranial pressure.
- No evidence on transfusion
- Anaemia is associated with unfavourable outcome, but no evidence that transfusion improves this.
- Evidence that both high and low haemoglobin are associated with unfavourable outcome.
- Impact of transfusion has not been evaluated.
- Anaemia is a risk factor, but it is unknown if transfusion modifies the risk.
- Coronary system has high oxygen demands
- Decreased oxygen content of blood per unit volume
- Coronary disease restricts blood flow
- Hypotension and tachycardia also reduce diastolic (when maximal coronary perfusion occurs) coronary blood flow.
- Chronic ischaemic heart disease
- A post hoc sub group analysis of the TRICC trial of patients with ischaemic heart disease showed a non-significant trend towards lower 30 day mortality in the liberal transfusion group. (Underpowered)
- FOCUS study of elderly patients undergoing hip fracture surgery found no difference in mortality or cardiovascular complications between a liberal and restrictive transfusion strategy, despite 40% of patients having IHD.
- TRACs study was similar in patients undergoing elective cardiac surgery and found no difference in mortality or severe morbidity.
- Anaemic patients developing acute coronary syndrome have worse outcomes and anaemia is more common as patients are older, widespread use of anti-platelets and blood loss during revascularisation procedures.
- Wu et al analysed 79000 patients presenting with acute MI. Transfusion improved 30 day mortality when haematocrit <0.33%
- Conflicting evidence from Rao et al and Yang et al who found that transfusion was associated with worse outcomes – but these were only cohort studies.
- Extubation failure is associated with a seven-fold increase in mortality.
- Failure to wean can be associated with an imbalance in oxygen supply and demand. Thus, it seems reasonable that improving arterial oxygen content could assist weaning.
- The two largest studies are only subgroup analyses of TICC and CRIT and only provide weak evidence, but these show no benefit (or possibly worse outcomes).
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