While an epidural or a spinal are the currently preferred anaesthetics for Caesarean birth, there are some medical circumstances that mean it is sometimes not possible for them to be given, and therefore a general anaesthetic is necessary.
These reasons can include:
There is not enough time to put in an epidural
The epidural is not working effectively
The woman has had a back injury
The woman has an illness or complication that makes an epidural or spinal more risky
The woman strongly prefers a general anaesthetic
There is not enough time to put in an epidural. If the Caesarean needs to be done quickly, usually because of a medical emergency the woman will need a general anaesthetic, because it can work within a minute or two.
Epidurals can take about 5 to 10 minutes to insert and a further 20 minutes to 1/2 an hour until they are working effectively Spinals take about 5 minutes to insert and a further 5 minutes to work effectively. A spinal may be an option if there is a little more time available.
The epidural is not working effectively. In about 12 to 15% of cases an epidural does not numb the nerves enough to make the operation painless (the woman's sensation is tested with a piece of ice or a tip of a pointed object before the operation starts). It may be that you are still aware of contraction pains, meaning it is definitely not working! If this is the case, the anaesthetists will try to put in a spinal anaesthetic, or a general anaesthetic will be used.
The woman has had a back injury. Generally back injuries, lumbar disc operations, inherited abnormalities of the spine or bone diseases of the spine do not prevent women from being able to have an epidural or a spinal anaesthetic. However, these factors can increase the chances of an epidural not being fully effective, or present difficulties for the anaesthetist being able to insert an epidural or spinal needle.