Does a height-related CS spinal anaesthetic dose improve reliability?
Research type
Research Study
Full title
A randomised controlled trial comparing an individualised, height – related dose of intrathecal 0.5% hyperbaric bupivacaine with a standard fixed dose of 2.6ml, for elective Caesarean section.
IRAS ID
279712
Contact name
Helen B.K. Brar
Contact email
Sponsor organisation
County Durham and Darlington NHS FT
ISRCTN Number
ISRCTN13247823
Duration of Study in the UK
2 years, 0 months, 1 days
Research summary
The preferred technique for anaesthesia for a planned Caesarean section is a ‘spinal’ block. This involves an injection of local anaesthetic (0.5% hyperbaric bupivacaine). This local anaesthetic is injected between the vertebral column bones of the lower back, into the fluid which surrounds nerves supplying the areas which need to be numb. The effects of the local anaesthetic work very quickly, and the patient is able to remain fully awake during the operation. This has safety benefits for both the mother and the baby.
It is important that the sensory level at which the mother becomes numb, is high enough for the operation to be carried out without undue pain. This needs to be just below the level of the armpits. A low sensory block may result in unpleasant sensations or pain being felt during the operation. This may require supplementation with additional painkillers through the vein, or even conversion to a general anaesthetic.
However, if the sensory level is too high, undesirable side effects may occur. The most common effect of a ‘high’ block is a drop in blood pressure, which can produce nausea and vomiting. Reduced blood supply to the placenta from low blood pressure that is not treated promptly, may result in distress to the unborn baby. Significantly high blocks can proceed to cause arm weakness, difficulty in breathing and talking, and loss of consciousness (a ‘total’ spinal block). A total spinal block is an unpleasant experience for both the mother and her partner, if present.
Currently, there are a few standard doses for the spinal anaesthetic that individual anaesthetists can choose to use. These doses vary according to individual anaesthetists and individual centres. However, these doses do not necessarily fully take into account individual patient factors such as height, which can alter the extent of the spinal block.
This study aims to compare an individualised dose of local anaesthetic specific to each mother’s height, with a single standard volume dose.
In the author’s centre, a height – volume table has evolved over 11 years, and has shown promising results. This table has been modified slightly, based on a mathematical formula, to be used in this study (see appendix 1).
The focus on height alone for determining dose (and excluding weight, as has been investigated in other studies), arises from the fact that the vertebral column encompassing the spinal cord and emerging spinal nerves, remains at a fixed length despite any increase in weight, and it would be assumed that a taller mother would need more local anaesthetic to achieve the same height of block.
This height – related concept has already been applied to determine the size of other internal organs, such as the lungs and windpipe.
All other common variables known to affect block height, such as speed of injection, level of injection and aspiration of fluid during injection, will be standardised between the two groups, such that the only difference between the two groups is the volume injected.
REC name
West Midlands - Edgbaston Research Ethics Committee
REC reference
20/WM/0271
Date of REC Opinion
10 Dec 2020
REC opinion
Further Information Favourable Opinion