[Factors influencing the level of spinal anesthesia: (II). Patient characteristics and technique of injection].

The extent 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 factors involved in patient characteristics and technique of injection; the age of the patient, the volume of cerebrospinal fluid, the rate of injection, the site of injection, and the position of the patient. Each of the factors does not seem to have a major impact on the level of sensory block as compared with characteristics of anesthetic solutions discussed in the previous review, but this has not been fully understood. Recent studies have shown that the management of posture to control the level of spinal anesthesia is not so easy as previously thought. It is my conclusion that knowledge of these factors is essential in the performance of reliable and safe spinal anesthesia.