[Factors influencing the level of spinal anesthesia: (I). Characteristics of anesthetic solutions].

The practitioner of spinal anesthesia needs to know the minimum block he or she can expect in order to guarantee the adequate anesthesia to perform a given operation. At the same time, the anesthesiologist needs to know the maximum extent of block, for which he or she must be prepared to avoid being caught unaware. The height of sensory block is determined by the cephalad distribution of the local anesthetic in the cerebrospinal fluid and uptake by neuronal tissue in sufficient amounts to produce the block. Out of many factors that have been considered to affect the distribution, this paper discusses characteristics of anesthetic solutions. It has been suggested that solutions that are marginally hyperbaric can safely produce relatively consistent blocks with an extent that is suitable for many operations performed under spinal anesthesia.