Monday, April 6, 2015

Study group discussion: Oxytocin

Question: Why does oxytocin cause volume overload?

Answer: It is similar to vasopressin in structure.

Vasopressin and oxytocin are similar in structure. So vasopressin is ADH. It retains water. Which will cause Intravascular volume expansion

There are a lot of compounds which have a similar structure and interesting clinical effects. Here are a few http://medicowesome.blogspot.in/2014/11/hormones-that-have-similar-structure.html

Doubt: Several pharmacology books said that oxytocin may cause hypertension. But Williams obstetrics says that it will cause serious hypotension if given as undiluted iv bolus. I'm confused.

Answer:
Bolus causes hypotension.
Normal infusion causes fluid retention.
Although unlike ergonovine, oxytocin does not produce hypertension.

So don't give bolus is the moral of the story. It can cause Placental hypoperfusion.

Question: How does it cause Placental hypoperfusion?

Answer: If your blood pressure drops, blood supply to all organs will be compromised. Comprehende?
Think of placenta as an organ. So Placental hypoperfusion!

Doubt: Does anyone know why iv bolus of oxytoxin will have adverse effect of hypotension and tachycardia?

Answer: In high doses... Oxytocin has vasodilator action which produces hypotension and reflex tachycardia.

From what I read, oxytocin decreases venous return and systemic vascular resistance. So that'll cause a compensatory tachycardia.

Source: http://www.ncbi.nlm.nih.gov/pubmed/18513945

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