Letter to the Editor:
To the Editor:
I would like to add yet another factor in considering the potential problems resulting from the “Beach Chair” position, namely, that like the brain, the spinal cord is a structure that autoregulates its blood flow in a similar fashion, normally between mean arterial blood pressures of 60 and 120 mmHg.1 Below the lower and above the upper limit of autoregulation, flow becomes pressure dependent and spinal cord ischemia may be exacerbated if the spinal cord perfusion pressure is sustained below the lower limits of autoregulation. The adequacy of spinal cord blood flow has important structural components associated with arterial input, and a number of authors have shown a paucity of radicular arteries in the cervical spinal cord in autopsy material.2,3 Thus, Manners4 noted in a post mortem review of 215 spinal cords, that 45 had only 1 radicular cervical artery. In addition, the lower cervical spinal cord is a vulnerable “watershed” area as it is farthest from collateral pathways.5
Confirmation of the clinical response can be seen in Jellinger’s analysis of the distribution of chronic, ischemic cord lesions in 60 cases of advanced arteriosclerosis.6 In the Manners postmortem review just mentioned, he described 25 spinal cord infarctions in geriatric cases in which the selective site for small softening was at the C5-C8 levels, with the greatest numbers of infarcts being at the C6 segment. In essence we are dealing with a region of the spinal cord, the cervical area, having the highest functional metabolic demand with a very marginal blood flow. With our large geriatric population coming to surgery, these spinal cord vascular-rheological considerations are critical in the management of these patients and the utmost care should be manifest in the use of deliberate hypotension as emphasized by the Letters to the Editor by Cullen and Kirby7 and Munis8 in prior issues of the
APSF Newsletter. While we may think that the cerebral perfusion pressure in a given patient may be adequate for the brain, the same perfusion pressure may be inadequate for the metabolic requirements of the spinal cord and cause an ischemic state which, if prolonged, could lead to dire neurological consequences. A more complete review of the factors concerning autoregulation and spinal cord perfusion pressure can be seen in the paper by Albin and coworkers.9
Maurice S. Albin, MD, MSc (Anes)
Professor, Department of Anesthesiology
University of Alabama at Birmingham, Birmingham, AL
- Hickey R, Albin MS, Bunegin L, et al. Autoregulation of spinal cord blood flow: Is the cord a microcosm of the brain? Stroke 1986;17:1183-1189.
- Turnbull IM, Breig A, Hassler O. Blood supply of the cervical cord in man. A microangiographic study. J Neurosurg 1966;24:951-960.
- Fried LC, Doppman JL, Di Chiro G. Direction of blood flow in the primate brain. J Neurosurg 1970;33:326-330.
- Manners T. Vascular lesions in the spinal cord in the aged. Geriat 1966;2:151-160.
- DiChiro G, Fried LC. Blood flow currents in spinal cord arteries. Neurology 1971;21:1088-1096.
- Jellinger K. Spinal cord arteriosclerosis and progressive vascular myopathy. J Neurol Neurosurg Psychiatr 1967;30:195-201.
- Cullen DJ, Kirby RR. Beach chair position may decrease cerebral perfusion, catastrophic outcomes have occurred. APSF Newsletter 2007;22:25,27.
- Munis J. The problems of posture, pressure and perfusion. APSF Newsletter 2007;22:82-83.
- Albin MS, Bunegin L, Gilbert J, et al. Anesthesia for spinal cord injury. Problems in Anesthesia 1990;4:138-154.