Why does the blood pressure drop down during injections of anaesthetics in spinal anaesthesia?

Spinal medications: Can cause a sympathectomy. This results in vasodilation and a drop in the systemic vascular resistance. This can drop your blood pressure.

Sympathetic block: Spinal anesthesia causes vasodilatation. Blood pressure should not drop if the patient was pre-hydrated and anesthesiologist administers appropriate medication to diminish this side effect.

Vasodilatation: Once the spinal anesthetic is set up there is a vasodilatation that occurs in your blood vessels. This essentially means that the blood you have in your body is now occupying a larger space. Because of this your blood pressure has a tendency to decrease. This is easily treated with medications.