Hypotension

Hypotension is the most common side effect of spinal anaesthesia. Caused by sympathetic blockade leading to peripheral vasodilatation, and usually treated in the first instance with vasoconstrictors such as phenylephrine or metaraminol. These may be given as prophylaxis or as treatment and can be given as an infusion or as intermittent boluses.

IMPORTANT! In patients with fixed cardiac output states (e.g. aortic stenosis or hypertrophic obstructive cardiomyopathy), sudden hypotension and decreased systemic resistance can be fatal. Spinal is not usually a suitable technique in such patients.

Post-dural puncture headache (PDPH)‏

Post-dural puncture headache is caused when cerebrospinal fluid leaks from the thecal sac, causing a low pressure headache. Incidence reduces with decreasing needle diameter and with use of needles with 'atraumatic' tips, such as the Sprotte or Whitacre. Following a single pass with a small gauge atraumatic needle, the incidence is less than 0.5 %. The incidence increases with the number of attempts at spinal needle placement.

Finite duration of block

Spinal anaesthesia typically lasts 2–4 h. If surgery lasts beyond the length of effective anaesthesia, there is no way of prolonging single shot spinal blockade.

Leg weakness

Although newer local anaesthetic agents can produce some degree of differential block (sensory block without motor block), motor block is generally unavoidable with spinal anaesthesia. Some patients may find this disagreeable or distressing. At the very least, it limits the speed of mobilization, which may be relevant in minor surgery.

It also limits the usefulness of spinals in day surgery, although low-dose modifications of the technique can be used successfully.

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.

High block

If the block ascends higher than clinically desirable, the patient my experience unpleasant symptoms, particularly:

• Hypotension; resulting from 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.

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.

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