Topics / Anaesthesia / Obstetric Anaesthesia

Summary This article attempts to clarify the differences between pre-loading, co-loading as well as the different fluids available to prevent hypotension caused by spinal anaesthesia.

Basics

Spinal anaesthesia can cause severe hypotension due to a pharmacological sympathectomy. This results in peripheral vasodilation and venous pooling of the blood. These changes causes a decrease in the venous return and a decrease in the cardiac output.

However, there are various methods available in order to prevent this drop in blood pressure. Two important ones are known as pre-loading and co-loading.

Pre-loading

In this method, we administer intravenous fluids (10-20 ml/kg around 15-20 minutes) to the patient before we begin with spinal anaesthesia. This pre-loading with fluids will counteract the hypotensive effects caused by spinal anaesthesia.

Co-load

Is a similar method as above, used for the same effect. However, the fluids are given as a rapid bolus infusion in the period just following the spinal anaesthesia. This method is often seen as more physiologically appropriate as the volume of fluids administered coincides with the time in which the blood vessels are undergoing maximal vasodilation.

Fluid of Choice

Crystalloids are commonly used to pre-load and co-load the patient. However, some criticism of this fluid type is that there is a rapid redistribution of these fluids into the extravascular space. Crystalloids may exit the intravascular space within a 1 hour period. Therefore, not being very efficacious. (shorter intravascular half-life)

Colloids may also be used. They are better at preventing the occurrence of hypotension because they remain in the intravascular space for a longer period of time. However, it is sometimes not used because these fluids are more costly, may derange coagulation and there is also a risk of anaphylaxis. (longer intravascular half-life)

Conclusion

Pre-loading is not superior to co-loading irrespective of the type of fluid that is used. This means that in an urgent situation, one should not “waste” time trying to pre-load the patient when similar results may be achieved with co-loading the patient.
Colloids are more efficient than crystalloids in the prevention of hypotension. However, the decision to use them over crystalloids will depend on the costs and other complications associated with colloids.

Read more about this topic: “Co-loading or pre-loading for prevention of hypotension after spinal anaesthesia! a therapeutic dilemma” by Sukhminder Jit Singh Bajwa, Ashish Kulshrestha, and Ravi Jindal.