This is interesting. An experimental study demonstrates how Lidocaine, from a spinal block, can be manipulated using a weak magnetic field, if the Lidocaine is mixed with a ferrofluid.
The most serious compilation of spinal blocks is the notorious ‘high spinal block’, which is a consequence of the local anaesthetic spreading to far in the cranial direction. In the worst case scenario, the T1-T4 cardioaccelerator nerves are knocked out, resulting in bradycardia, hypotension or even cardiac arrest. The incidence of cardiac arrest after spinal block may be as high as 6,4 in 10.000.
To prevent this from happening we try to inject the smallest possible volumes of local anesthetic. We could also use hyperbaric solutions as it allows for gravity to concentrate the anaesthetic where we want it. By positioning the patient correctly we could concentrate the anaesthetic effect to the dependent nerve roots, thereby reducing volume and risk of cranial spread. That never worked for me. God knows I tried.
In this recent study from Anesthesia & Analgesia they injected local anaesthetic into simple a model of the spine made out of plastic tubing filled with 0,9% sodium chloride. They used two different solutions. One solution contained standard hyperbaric lidocaine with methylene-blue. The second contained hyperbaric lidocaine, methylene-blue and a ferrofluid, which should allow for manipulation with a magnetic field.
Indeed, the ferrofluid solution was locked in place by the magnetic field. The non-magnetic hyperbaric lidocaine would spread upwards and downward and then sink in the ‘subarachnoidal space’ as expected. The ferrofluid solution remained suspended, without spreading, and responded to movements of the magnetic field instead of gravity.