Spinal Anaesthesia Hypotension in Caesarean
On this page
Direct answer
Hypotension after spinal anaesthesia for caesarean section results from sympathetic blockade that dilates arterioles and veins, reducing venous return and cardiac output. It is the most common maternal complication of spinal anaesthesia for caesarean. It is prevented or treated with left uterine displacement, fluid co-loading and a vasopressor, while the block is kept to about the T4 level.
What you must remember
- Mechanism: Sympathetic blockade dilates arterioles and veins, lowering systemic vascular resistance and venous return.
- Aortocaval compression: The gravid uterus compresses the aorta and inferior vena cava in the supine position, adding to the fall in preload.
- Block level: Hypotension and bradycardia become more likely as the block extends above about T4.
- Left uterine displacement: A left tilt relieves aortocaval compression and improves venous return.
- Fluids: Crystalloid co-loading reduces the severity of hypotension but does not abolish it.
- Vasopressors: Phenylephrine or ephedrine, given as a bolus or infusion, is a more reliable way to correct hypotension than fluids alone.
Managing hypotension once it appears
Hypotension is commonly defined as a fall of about 20 per cent from baseline systolic pressure, and early treatment protects uteroplacental perfusion. The steps below set out the order of response.
- Recognise the fall: Measure blood pressure every one to three minutes after the block and act on a drop from baseline.
- Displace the uterus: Ensure a firm left tilt so that the uterus is off the great vessels.
- Give a vasopressor: Start a bolus or infusion of phenylephrine or ephedrine, titrated to the blood pressure.
- Check the fetus: Confirm the fetal heart rate, since maternal hypotension can reduce placental perfusion.
- Review the block: If hypotension persists, check the block level and the dose used.
Fluids alone are not enough once the block is established, so exam answers should move quickly to a vasopressor.
Monitoring should continue after the first correction, because hypotension can return as the block evolves and the patient is repositioned. Fluid and vasopressor doses are adjusted to the measured pressure, not fixed in advance.
Where the exam tries to catch you
Spinal hypotension questions usually test the mechanism, the prevention strategy and the correct block level.
- Trap: Relying on a large crystalloid bolus instead of a vasopressor Correct: Fluids reduce hypotension but are less effective than vasopressors once the block is established.
- Trap: Aiming for a higher block to improve surgical conditions Correct: Caesarean needs a block to about T4, and higher levels increase the risk of hypotension and respiratory compromise.
- Trap: Tilting the patient to the right to relieve compression Correct: Left uterine displacement relieves aortocaval compression, since the uterus is pushed to the left.
Frequently asked questions
What causes hypotension after spinal anaesthesia for caesarean?
Sympathetic blockade dilates arterioles and veins, reducing systemic vascular resistance and venous return. The pregnant uterus also compresses the aorta and inferior vena cava in the supine position, which worsens the fall. Spinal hypotension is therefore both vascular and mechanical.
Which vasopressor is used for spinal hypotension in caesarean?
Phenylephrine and ephedrine are the commonly used vasopressors, given as boluses or infusions to correct hypotension. Phenylephrine is widely used for prophylactic infusion. The choice depends on local protocol and the maternal heart rate.
What block level is needed for caesarean section?
A sensory block up to about T4 is generally required for caesarean section under spinal anaesthesia. Higher levels increase the risk of hypotension, respiratory compromise and bradycardia. The dose and baricity of the local anaesthetic determine the block level.
How often should blood pressure be monitored after the spinal?
Blood pressure should be measured frequently, typically every one to three minutes from the start of the block until the surgery is well advanced. Frequent measurement allows early treatment of hypotension. The exact frequency follows institutional protocols.