Transfusion and Anaemia in Critically Ill Adults (BSH 2013)

 

General ITU – Threshold <70, Target 70-90

Sepsis – early Target 90-100, later Target 70-90

Neuro – TBI Target 70-90, SAH Target 80-100, Stroke Target >90

IHD – Stable Target >90, ACS Target >80

 

Intro

 

-       20-30% of patient admitted to ITU have an Hb <90g/l

-       After 7 days, 80% of ITU patients have an Hb <90g/l

-       ITU accounts for 10% of annual blood use

 

Pathophysiology

 

-       Global oxygen delivery (DO2) is a product of cardiac output and arterial O2 concentration

-       Tissue hypoxia can occur as the result of a problem at any stage in the oxygen cascade – airway, pulmonary, cardiac, vascular flow etc.

-       Anaemia reduces oxygen carrying capacity

-       When tissue DO2 falls, compensatory mechanisms increase oxygen extraction up to a point

-       Once compensation is overwhelmed, O2 transport becomes directly proportional to O2 supply and tissue hypoxia becomes much more likely to occur.

-       Healthy individuals can maintain O2 supply down to a Hb of 40-50g/l

 

Transfusion Triggers

 

-       General ITU Population

o   TRICC Study 1999

o   Liberal <100g/l trigger v.s. Restrictive <70g/l trigger

o   Restrictive group received 54% fewer RBC units, and 33% no blood at all

o   No global difference in mortality

o   Patients <55 y.o. and those who were less ill (APACHE <20) had lower mortality with restrictive strategy. NNT = 13.

-       TRACS (cardiac surgery) and FOCUS (elective hip surgery) made the same conclusions

 

Alternatives to Red Cell Transfusion

 

Blood Sampling Techniques to reduce iatrogenic blood loss

-       Typically approx.. 40ml blood loss per day

-       Use of paediatric bottles reduces blood loss without affecting assay quality.

 

Erythropoietin

-       Critically ill patients do not produce a physiological increase in Epo production

-       Epo is not licensed for critically ill patient with anaemia due to no difference in patient outcomes and a concern over increased VTE risk

 

Iron Therapy

-       Evidence of absolute iron deficiency is absent in most ITU patients

-       Iron supplementation not recommended due to lack of randomized trials and concern over increased susceptibility to infection

-       Typical Iron profile in ITU

o   Serum iron – decreased

o   Total Iron Binding Capacity – Decreased

o   Ferritin – Increased

o   Transferrin – Decreased

o   Soluble Transferrin – Normal

 

Adverse Effects of RBC Transfusion in Critical Care

 

TACO

-       Acute respiratory distress with pulmonary oedema, tachycardia, increased BP and a positive fluid balance after blood transfusion

TRALI

-       Onset of pulmonary oedema within 6 hours of blood transfusion, hypoxia and bilateral pulmonary infiltrates on CXR.

-       Results from anti-neutrophil antibodies (leukoagglutinins) present in the donor plasma

RBC Storage Duration

-       Red cell storage process depletes 2,3 DPG, impairing oxygen release

-       Also depletes nitric oxide and causes membrane changes with decreased deformability, which combined limit capillary transit.

-       However no evidence to support need for ‘fresher’ blood in ITU patients

 

Severe Sepsis Patients

 

Early hours of sepsis

-       Low SVCO2% and high lactate indicative of tissue hypoxia

-       Transfusion to Hb approx. 100g/l associated with improved survival, but in trials that had many intensive interventions being tested at once.

Later stages of sepsis

-       As per TRICC trial, can use <70g/l as transfusion trigger

 

Neuro Critical Care

 

Difficult – increase Hct à increased oxygen carrying capacity, but also viscosity which may in itself reduces delivery to cerebral microvasculature.

 

Traumatic brain injury

-       Target 70-90g/l, increased to >90g/l if cerebral ischaemia present

SAH

-       Target 80-100g/l

Ischaemic Stroke

-       Target >90g/l

 

Ischaemic Heart Disease on ITU

 

Stable Angina – Hb >70g/l but transfusion >100g/l has uncertain benefit

ACS – Hb >80-90g/l