α1-acid glycoprotein and albumin in the spinal fluid of pregnant women

Abstract Pregnant women at term need a smaller dose of local anaesthetic to produce the same spinal anaesthesia as non-pregnant women. The aim of the study was to see whether the concentrations of binding proteins were reduced in spinal fluid in pregnant women. The concentrations of the binding proteins α 1 -acid glycoprotein (AAG) and albumin were measured in plasma and spinal fluid from 20 pregnant and 20 non-pregnant women, ASA 1. Mean spinal fluid albumin was 3.13 micromol/1 in non-pregnant and 1.97 micromol/1 in pregnant women (95% confidence interval of the difference: 0.62 – 1.50). Mean spinal fluid AAG was 0.152 micromol/1 in non-pregnant and 0.081 micromol/1 in pregnant women (95% confidence interval of the difference: 0.030 – 0.100). The concentrations in plasma were also reduced in late pregnancy. All the changes were statistically significant. Since only a minor fraction of bupivacaine seems to be protein bound in spinal fluid these differences may have only a little influence on the free fraction and cannot be solely responsible for the increased sensitivity of pregnant women to spinal anaesthesia.