DENSITIES OF CEREBROSPINAL-FLUID AND SPINAL ANESTHETIC SOLUTIONS IN SURGICAL PATIENTS AT BODY-TEMPERATURE

Purpose: To determine the densities of cerebrospinal fluid (CSF) in pa tients for surgery under spinal anaesthesia. The densities of the CSF were compared with the densities of local anaesthestic solutions and t heir mixtures with commonly used spinal opioids. Method: One ml of CSF was collected from 131 consecutive patients that consented to the stu dy at the time of spinal anaesthesia, Densities were; measured at 37 d egrees C in a Density Meter that displayed density to the fourth decim al point and was accurate to 0.00003 g . ml(-1). The densities of a se lection of spinal anaesthetic drugs were also measured. Results: The m ean CSF density in the study population was 1.00059 +/- SD 0.00020. In men of all ages, the mean CSF density was 1.00067 +/- 0.00018 g . ml( -1); in postmenopausal women 1.00060 +/- 0.00015 g . ml(-1); in premen opausal non-pregnant women 1.00047 +/- 0.00076 g . ml(-1); and in preg nant women 1.00033 +/- 0.00010 g. ml(-1). There were differences betwe en the CSF densities in pregnant-women compared with men (P = 0.0001), postmenopausal women (P = 0.0001) and non-pregnant premenopausal wome n (P = 0.03). Local anaesthetic solutions that contain sugar (glucose or dextrose) were all hyperbaric. In the absence of sugar, all local a naesthetic solutions were hypobaric except for lidocaine CO2 which was slightly hyperbaric; Opioids were all hypobaric except meperidine whi ch was hyperbaric. Conclusion: Pregnant women have slightly lower CSF densities than do men and postmenopausal women, and non-pregnant preme nopausal women. In the absence of sugar all spinal anaesthetic solutio ns measured were hypobaric except for lidocaine CO2 and meperidine, bo th of which were hyperbaric.