[Methods for measuring spinal cord blood flow]

Spinal cord blood flow measurement by arterial spin labeling

The assessment of spinal cord (SC) hemodynamics, and especially SC blood flow (SCBF), plays a key role in the pathophysiological description and understanding of many SC diseases such as ischemia, or spinal cord injury. SCBF has been previously measured in animals with invasive techniques such as autoradiography or labeled microspheres; no MR technique, however, has been proposed so far. The possibility of quantitatively measuring SCBF in mice using MRI was investigated using a presaturated FAIR (flow-sensitive alternating inversion recovery) arterial spin labeling (ASL) technique. SCBF measurements were performed at the cervical level of the mouse as well as on the brain so as to use cerebral blood flow (CBF) values as internal references. With a spatial resolution of 133 x 133 microm(2) for the SCBF maps, absolute regional perfusion values could be measured within the different structures of the SC (gray matter, white matter, and cerebrospinal fluid area). Similar perfusion values were found in SC gray matter (330+/-90 mL/100g/min) and in brain (295+/-22 mL/100g/min for thalamus). This result, in agreement with SCBF/CBF measurements performed with non-MR techniques, opens new perspectives for noninvasive longitudinal and in vivo animal studies. Application to human experiments may also be possible.

[Neurotoxicity of intrathecally administrated agents]

Spinal anaesthetics can induce histopathologic lesions and regional haemodynamic alterations in the spinal cord. There are numerous causes of neurologic lesions, including direct trauma of the spinal cord and nerve roots during puncture or catheter insertion, compromised spinal cord perfusion and direct neurotoxic effect. Histopathologic lesions are localized either in meninges (meningitis or arachnoiditis) or in neuraxis (myelitis or axonal degeneration). Neurotoxicity can result from decrease in neuronal blood supply, elicited by high concentrations of the solutions, long duration exposure to local anaesthetics, and the use of adjuvants. They have been implicated in the occurrence of cauda equina syndrome after continuous spinal anaesthesia using hyperbaric solution of lidocaine and tetracaine given through small diameter catheters. Selective spinal analgesia is induced by spinal opioids without motor blockade except for meperidine. Complications occurred in patients after high doses of morphine, which were related to one of its metabolites, morphine-3-glucuronide. Preservative-free opioid solutions are to be preferred for spinal anaesthesia. There is no report of neurotoxicity neither in animal studies, nor in humans, using spinal clonidine. In order to reduce the incidence of neurotoxicity, some safety rules should be followed. The lowest efficient dose of local anaesthetics must be given. Incomplete blockade should not necessarily lead to a reinjection. Large volume of hyperbaric lidocaine or repeated injections of such solutions must be avoided as well as preservative-containing solutions. The administration of new compounds by the spinal route must be supported by data of spinal neuropharmacology and the lack of neurotoxicity must have been previously checked with animal studies.