Anaesthesiology
Fluids and Blood Products
Perioperative fluids for MBBS and NEET-PG: crystalloids versus colloids, venous access, resuscitation targets, blood products and transfusion reactions, mapped to NMC codes AS9.
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Fluids and Blood Products
Perioperative fluids for MBBS and NEET-PG: crystalloids versus colloids, venous access, resuscitation targets, blood products and transfusion reactions, mapped to NMC codes AS9.
This chapter covers perioperative fluid therapy and the use of blood products, from the compartments of body water to the choice between crystalloid and colloid. It sets out peripheral and central venous access, resuscitation targets, and the indications, complications and safe practice of transfusion.
High-yield: Fluids and Blood Products
- Total body water is about 60% of body weight, split into two-thirds intracellular and one-third extracellular fluid.
- Crystalloids such as normal saline and Ringer's lactate distribute through the extracellular space, so only about a quarter to a third stays in the vasculature.
- Colloids such as albumin stay in the intravascular space longer, but crystalloids are first-line for most resuscitation.
- Normal saline in large volumes causes a hyperchloraemic metabolic acidosis, so balanced solutions such as Ringer's lactate are often preferred.
- Ringer's lactate is avoided as a diluent for blood because its calcium can promote clotting in the giving set.
- Maintenance fluid replaces daily losses, while resuscitation fluid replaces an acute deficit and is given as rapid boluses titrated to response.
- Adequate fluid resuscitation is judged by heart rate, blood pressure, capillary refill, urine output and, where available, lactate clearance.
- A urine output of at least about 0.5 millilitres per kilogram per hour indicates adequate renal perfusion in an adult.
- The largest peripheral cannula gives the fastest flow, as flow rises with the fourth power of the radius and falls with catheter length.
- Central venous access is used for vasopressors, parenteral nutrition, central pressure monitoring and difficult peripheral access.
- Packed red cells are transfused to improve oxygen-carrying capacity, generally guided by a restrictive threshold around a haemoglobin of 7 grams per decilitre.
- Fresh frozen plasma replaces clotting factors, platelets treat thrombocytopenic bleeding, and cryoprecipitate is a source of fibrinogen.
- The commonest cause of a fatal haemolytic transfusion reaction is an ABO-incompatible transfusion from a clerical or identification error.
- Massive transfusion can cause hypocalcaemia from citrate, hyperkalaemia, hypothermia and a dilutional coagulopathy, which must be anticipated and corrected.
Fluids and blood products
- **Crystalloids:** Normal saline, Ringer's lactate. First-line for resuscitation; spread through extracellular space.
- **Packed red cells:** Raise oxygen-carrying capacity. Restrictive threshold around haemoglobin 7 g/dL.
- **FFP, platelets, cryoprecipitate:** Clotting factors; thrombocytopenic bleeding; source of fibrinogen.
- **Massive transfusion risks:** Hypocalcaemia, hyperkalaemia, hypothermia, dilutional coagulopathy.
NMC competencies in this chapter
- **AS9.1:** Intravenous access in a simulated environment
- **AS9.2:** Central venous access in a simulated environment
- **AS9.3:** Principles of perioperative fluid therapy
- **AS9.4:** Blood products and their perioperative use
Frequently Asked Questions
What is the difference between a crystalloid and a colloid?
Crystalloids such as saline and Ringer's lactate are salt solutions that spread through the extracellular space, while colloids carry larger molecules that stay in the vasculature longer. Crystalloids are first-line for most resuscitation.
Why is a large short cannula better for rapid fluids?
Flow through a cannula rises with the fourth power of its radius and falls with its length, so a wide, short peripheral cannula delivers fluid far faster than a long, narrow central line.
When are red cells transfused?
To restore oxygen-carrying capacity in anaemia or blood loss. Most guidance uses a restrictive threshold around a haemoglobin of 7 grams per decilitre, individualised to the patient and clinical setting.
What causes a fatal haemolytic transfusion reaction?
Most fatal acute haemolytic reactions are due to ABO-incompatible transfusion caused by a clerical or patient-identification error, which is why checking at the bedside is so important.
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