Saturday, July 15, 2006

Transfusion for Massive Blood Loss

Transfusion for Massive Blood Loss
Presented below is a description of massive blood loss and the inherent problems associated with large volume blood transfusions. Following this is a suggested protocol for guiding management of the patient receiving a massive transfusion for haemorrhage.
Massive transfusion is arbitrarily definied as the replacement of a patient's total blood volume in less than 24 hours, or as the acute administration of more than half the patient's estimated blood volume per hour.
Aim of Treatment
The aim of treatment is the rapid and effective restoration of an adequate blood volume and to maintain blood composition within safe limits with regard to haemostasis, oxygen carrying capacity, oncotic pressure and biochemistry.
Complications of Massive Transfusion
The complications of massive transfusion are those of any blood transfusion plus :
Blood Volume ReplacementThe complications of massive transfusion are exacerbated by inadequate or excessive transfusion. Traditionally transfusion of hypovolaemic patients has been directed towards maintaining a haemoglobin concentration of 10g/dl. The use of haemoglobin as the only indicator (or 'transfusion trigger') may result in unnecessary administration of blood products, with their concommittant risks.
Transfusion requirements should be based on the patient's physiologic needs, defined by their oxygen demand (consumption).
The most appropriate monitor of tissue oxygen supply is the tissue oxygen tension, reflected by the PvO2, or mixed venous partial pressure of oxygen (normally 6 kPa, 45mmHg). Patients with a low PvO2 can be classed as stable or unstable depending on haemodynamics, ventilation, acid base status and urine output. If they are stable, no therapy is indicated until a true critical level is reached (PvO2 around 3 kPa, 23mmHg). If unstable, treatment must be intituted.
Thus transfusion should be guided by haemodynamic stability, PvO2 and ER. Obviously during trauma resuscitation, haemodynamic stability is the key indicator.
In summary :
If Hb > 10g/dl transfusion is rarely indicated.
If Hb < 7g/dl transfusion is usually necessary.
With Hbs between 7 and 10 g/dl, clinical status, PvO2 and ER are helpful in defining transfusion requirements.
ThrombocytopeniaDilutional thrombocytopenia is inevitable following massive transfusion as platelet function declines to zero after only a few days of storage. It has been shown that at least 1.5 times blood volume must be replaced for this to become a clinical problem. However, thrombocytopenia can occur following smaller transfusions if disseminated intravascular coagulation (DIC) occurs or there is pre-existing thrombocytopenia.
Coagulation Factor DepletionStored blood contains all coagulation factors except V and VIII. Production of these factos is increased by the stress response to trauma. Therefore only mild changes in coagulation are due to the transfusion per se, and supervening DIC is more likely to be responsible for disordered haemostasis. DIC is a consequence of delayed or inadequate resuscitation, and the usual explanation for abnormal coagulation indices out of proportion to the volume of blood transfused.
Oxygen Affinity ChangesMassive transfusion of stored blood with high oxygen affinity adversely affects oxygen delivery to the tissues. Evidence for this is as yet not forthcoming, but it would seem wise to use fairly fresh red cell transfusions (<1 week old). Use of fresh (<24 hours) blood is not indicated. 2,3 DPG levels rise rapidly following transfusion and normal oxygen affinity is usually restored in a few hours.
HypocalcaemiaEach unit of blood contains approximately 3g citrate, which binds ionized calcium. The healthy adult liver will metabolise 3g citrate every 5 minutes. Transfusion at rates higher than one unit every five minutes or impaired liver function may thus lead to citrate toxicity and hypocalcaemia. Hypocalcaemia does not have a clinically apparent effect on coagulation, but patients may exhibit transient tetany and hypotension. Calcium should only be given if there is biochemical, clinical or electrocardiographic evidence of hypocalcaemia.
HyperkalaemiaThe plasma potassium concentration of stored blood increases during storage and may be over 30mmol/l. Hyperkalaemia is generally not a problem unless very large amounts of blood are given quickly. On the contrary, hypokalaemia is more common as red cells begin active metabolism and intracellular uptake of potassium restarts.
Acid/Base DisturbancesLactic acid levels in the blood pack give stored blood an acid load of up to 30-40mmol/l. This, along with citric acid is usually metabolised rapidly. Indeed, citrate is metabolised to bicarbonate, and a profound metabolic alkalosis may ensue. The acid-base status of the recipient is usually of more importance, final acid/base status being dependent on tissue perfusion, rate of administration amd citrate metabolism.
HypothermiaHypothermia leads to reduction in citrate and lactate metabolism (leading to hypocalcaemia and metabolic acidosis), increase in affinity of haemoglobin for oxygen, impairment of red cell deformability, platelet dysfunction and an increased tendency to cardiac dysrhythmias.
Acute Respiratory Distress Syndrome (ARDS)The aetiology of ARDS is as yet not fully understood, but various risk factors have been identified. Both under- and over-transfusion are associated with an increased risk of ARDS, as is albumin < 30g/l. Microaggregate filters should be used during massive transfusion except when giving fresh whole blood or platelets.
Protocol for Management of Massive Transfusion
Sequence of ComponentsProfound hypotension should be treated speedily. Administer crystalloid or colloid infusions rather than delay fluid administration. Initial red cell replacement is in the form of packed red cells.
Laboratory SamplesAt the start of resuscitation, blood should be taken for group and crossmatch, coagulation tests, full blood count and biochemistry. These must be properly labelled and identified in all situations.
Blood Bank ArrangementsRoutine procedures should be followed until it becomes obvious that massive transfusion is likely. The blood bank should be informed as soon as possible that a major trauma is arriving or in the building.
For extreme emergencies group O blood should be supplied first. Rhesus D negative blood should be supplied to all women of childbearing age. Type specific (ABO Rh D matched) blood should be available in 5 minutes and the switch should be made promptly so as not to deplete stores of group O blood. Continue transfusing blood on this basis until time is available to crossmatch on the original serum sample. If an antibody screen is negative and more than one blood volume has been administered there is no point attempting compatibility tests except to exclude ABO mismatches.
MonitoringDuring massive transfusion, regular monitoring of haemoglobin, platelet count, prothrombin time (PT), partial thromboplastin time (PTT) and fibrinogen levels should take place and be used to guide component replacement.
ComponentsComponent replacement should occur only in the presence of active bleeding or if interventional procedures are to be undertaken.
Platelet concentrates (1 pack/10kg) are given if platelet count falls below 50. Each platelet concentrate also provides around 50ml of fresh plasma.
Fresh frozen plasma (12ml/kg)is administered if PT or PTT are running higher than 1.5 times control levels.
Cryoprecipitate (1-1.5 packs/10kg) is given for Fibrinogen levels < 0.8g/l.
For massive uncontrolled traumative haemorrhage, maintenance of full haeostatic ability is usually unrealistic. The priority is for definitive surgical arrest of haemorrhage from major vessels. Combinations of stored whole blood, packed cells, colloids & crystalloids are given to maintain blood volume or pressure at adequate levels and haemoglobin at around 7g/dl or haematocrit at 0.25. Conserve limited supplies of fresh blood, plasma or platelets until the bleeding is controlled.
When blood loss has lessened (0.5l/hour) and major vessels have been controlled, it becomes worthwhile correcting haemostasis.


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