Elsewhere my associates and I1 have reported on the concentration of procaine in the subarachnoid space during spinal anesthesia in patients in the Trendelenburg position. The reports were based on the analysis of samples taken at various intervals of time from three groups of adult patients, at the site of injection, from a site three interspaces above and from the cisterna magna. The first group of 122 patients received 150 mg. of procaine hydrochloride dissolved in 3.5 cc. of cerebrospinal fluid; the second group of 156 patients received 300 mg. dissolved in 3.5 cc., and the third group of 143 patients received 300 mg. dissolved in 7 cc. All injections were made between the second and the third lumbar vertebra, and the patients were immediately placed in the Trendelenburg position. After this samples were taken.
At the moment of injection the concentration at the site of injection is at