By: 2 August 2012

A simple technique using local anaesthetic mixed with magnetised “ferrofluids” may provide a new approach to preventing a rare but serious complication of spinal anaesthesia, reports Anesthesia & Analgesia.
With further research, the magnet technique may provide a second means – in addition to gravity – of preventing “high spinal block,” which occurs when spinal anaesthetics spread to the upper portions of the spinal cord. The preliminary studies were performed by Dr Robert H. Thiele of University of Virginia Health Sciences Center, Charlottesville.
Although it is very rare – occurring at a rate of about 0.6 per 1,000 cases – high spinal block is a serious complication of spinal anaesthesia. It occurs when injected anaesthetics travel too high in the spinal cord, interfering with the spinal cord fibers governing heart function. This can result in sharp drops in heart rate and blood pressure, with a risk of cardiac arrest and death.
Anaesthesiologists currently prevent high spinal block by modifying the anaesthetic dose and by positioning the patient so that gravity distributes the anaesthetic to the lower portions of the spinal cord. “However, in certain instances, gravitational forces alone may not be sufficient to control block height,” the researchers write. They evaluated a different approach: using magnetised anaesthetic fluid and a weak magnetic field to control the spread of fluids.
Dr. Thiele and colleagues created a simple model of the spine using fluid-filled plastic tubing. They then prepared a local anaesthetic solution with or without the addition of a water-based ferrofluid to magnetise the fluid. In this model, both fluids ran downward by gravity.
However, when a magnet placed outside the tubing, below the level of the needle, it halted the downward flow of magnetised fluid. In fact, when the magnet was moved, the fluid moved “uphill,” against gravity. (A video demonstration can be viewed online at
Dr Thiele and coauthors believe that a similar technique using magnetised local anaesthetic solution and exterior magnets could help to control the spread of spinal anaesthesia during surgical procedures, thus providing a simple but effective additional safeguard against high spinal block. It might also be useful in controlling the spread of anaesthetics in other situations, for example, spinal anaesthesia on one side of the body.
Of course, much more research is needed before a concept demonstrated in plastic tubing can be applied in patients. Among the questions to be answered is the safety of the magnetic fluid – the ferrofluid used in the experiments is not approved for use in humans, although magnetic particles are used in other medical treatments.
Other issues include the quality of anaesthesia and practical matters related to applying a magnetic field in the operating room. Pending further study, the new magnetic technique “may allow anaesthesia providers a second means of controlling block spread,” the researchers write.