I think the Doctors know what they are doing when they try to get pregnant women to accept a blood transfusion!
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.
Definition
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.
A
im of Treatment Complications of Massive TransfusionThe 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.
The complications of massive transfusion are those of any blood transfusion plus :
- Blood Volume Replacement
The 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).
Oxygen consumption is given by :
Where CO = Cardiac Output, CaO2 and CvO2 are arterial and venous oxygen content respectively.
Oxygen delivery is :
The extraction ratio (ER) is the ratio of oxygen consumption to oxygen delivery, normally around 25%.
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.