Slow onset

The slow onset of epidurals makes them unsuitable for routine use in establishing anaesthesia, and is generally seen as a disadvantage.

However, their slow onset can make them an option for establishing regional anaesthesia in patients with cardiac outflow obstruction, e.g. aortic stenosis, hypertrophic obstructive cardiomyopathy, in whom spinal anaesthesia is contra-indicated by its associated rapid vasodilatation.

A gradual incremental epidural top-up (or CSE with decreased spinal dose), with invasive arterial monitoring, can permit simultaneous titration of vasopressor treatment to avoid precipitous hypotension.

Less dense/less predictable block

Epidurals do not always produce such dense anaesthesia as spinals.

Additionally, there may be ‘missed segments’ – dermatomes that remain partially or completely unblocked.

Both these are reasons for combining epidural analgesia with general anaesthesia.

Hypotension

Although hypotension is a side effect, it is usually slower in onset than with spinals, although its magnitude can be as great.

Post-dural puncture headache

This is more common than with spinals.

It occurs in around 1 % of epidurals and results from accidental puncture of the dura, which may not always be recognized at the time of insertion.

If the dura is breached with a 16 G epidural needle, there is around a 70 % chance of PDPH in young and mobile patients.

Leg weakness

Some patients find leg weakness in the post-operative period unacceptable, which may limit the acceptability of epidural analgesia to them.

It is not inevitable and can be reduced by decreasing the concentration and/or volume of the local anaesthetic used. It is also less likely if a high vertebral site is chosen for epidural insertion.

Lower level of block

Epidurals do not always block all dermatomes below the upper level, unlike spinals. Whilst this can be an advantage, e.g. in permitting motor power to be retained in the legs, it can be a disadvantage if the lower level of block is not sufficient to provide analgesia sufficiently low down.

Urinary retention, Itching, Shivering

Urinary retention: blockade of the sacral nerves can induce urinary retention, necessitating bladder catheterization. The use of intrathecal opioids increases this risk.

Itching: intrathecal opioids can induce itching. Typically, the face (and often specifically the tip of the nose) is most affected. It can be severe, requiring rescue medication, such as naloxone or antihistamines.

Shivering: shivering is a relatively common side-effect of spinal anaesthesia. The mechanism is not known. Usually it is no more than troublesome, although if severe, it can be distressing and can interfere with patient monitoring.

High block, Nausea and vomiting

High block: if the block ascends higher than clinically desirable, the patient may experience unpleasant symptoms, particularly:

• Hypotension; owing to blockade of the peripheral and cardiac sympathetic innervation
• Difficulty breathing; this is usually subjective and is due to paralysis of the intercostal muscles. Diaphragmatic breathing remains effective. The ability to cough is commonly impaired

Unless the block progresses to total spinal, these symptoms can usually be managed conservatively.

Nausea and vomiting: these symptoms can be produced by spinal anaesthesia in two ways:

• As a side effect of hypotension in susceptible patients
• As a side effect of adding intrathecal opioids