What is the sequence of blockade in spinal anaesthesia?

The sequence of blockade in spinal anaesthesia is as follows:

1. Sympathetic fibres: These fibres are responsible for controlling the blood vessels and sweat glands. They are blocked first, leading to vasodilation and sweating below the level of the block.

2. Motor fibres: These fibres control muscle movement. They are blocked next, leading to paralysis below the level of the block.

3. Pain and temperature fibres: These fibres transmit pain and temperature sensations. They are blocked last, leading to analgesia (loss of pain sensation) and thermanesthesia (loss of temperature sensation) below the level of the block.

The level of the block depends on the site of injection of the local anaesthetic. For example, a spinal anaesthetic injected at the L3-L4 level will produce a block that affects the lower limbs, while an anaesthetic injected at the T10-T12 level will produce a block that affects the abdomen and legs.