Why Spinal Anesthesia Cause Hypotension?

    Every Therapeutic technique has come with adverse effects. But the therapeutic technique is allowed only if it gives more benefits than harm. Spinal anesthesia provide excellent pain relief during surgery especially in cesarean delivery (Read article on Pain relief methods during child birth). It allow surgeries while patient is conscious. Patient feels no pain below the level of spinal anesthesia. Spinal Anesthesia has lesser complications as compared to general anesthesia.

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Spinal Anesthesia has its own complications and side effects. One of the complications of of spinal anesthesia is hypotension.

Q: Why spinal anesthesia Cause Hypotension?

Our vessels are supplied with autonomic nerve fibers. These nerve fibers originate from spinal cord and supply the vessels of lower limbs. These nerve fibers maintain a muscular tone in the blood vessels and don’t allow vessels to over-dilate and prevent pooling of blood. This mechanism help to maintain blood pressure. Major pooling of the blood takes place in the vessels especially in veins of the lower limbs.

In spinal anesthesia we block the all the nerve impulses below the level of anesthesia. The autonomic nerve supply is also blocked in addition to sensory and motor blockage. Blockage of autonomic stimulation result in loss of vascular tone and vessels dilate. Vessels can’t maintain blood pressure, they dilate and pooling of blood takes place. This results in circulatory hypovolumia. As Blood pools in the vessels of lower limbs instead of circulating through out the body. When you measure blood pressure in such patient, It will give you lower readings. Because little amount of blood reach upper limb. Patient become pale, breathless, anxious and in the end unconscious. Tachycardia (increase in heart rate) is the first sign of hypotension. Spinal anesthesia may cause disastrous consequences in a person who already has low blood pressure, or is dehydrated.

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Q: How to Prevent Hypotension in Spinal Anesthesia?

Proper history, examination and investigations must be carried out before surgery. Opinion of anesthesiologist should be followed and only he should decide whether patient is fit for spinal anesthesia or not.

Preventive Measures:

• Measure the blood pressure before surgery and make sure that patient is not hypotensive (hypo = low).
• If patient is hypertension (hyper = high) and is on medication then closely monitor his blood pressure.
• Hydrate the patient, before, during and after the surgery if there is risk of hypotension.
• Monitor the heart rate, blood pressure and blood oxygen saturation during the surgery.
• Shift the patient to ICU after surgery and closely monitor his heart rate, oxygen saturation and blood pressure.