Effect of decreased cerebrospinal fluid proteins on the spread of local anaesthetic drugs in pregnancy.

Cerebrospinal fluid (CSF) and plasma protein concentrations were determined in 60 ASA-I female patients, 30 non-pregnant women, who were to undergo lower abdominal or lower limb surgery (group I, controls) and 30 pregnant women at term, who were posted for lower segment caesarean section (group II). All patients received spinal analgesia. Time of onset of analgesia and level of analgesia achieved were compared in two groups. A significant fall (16.6%) was noted in the plasma proteins in pregnant (6.10 +/- 0.6 g/dl) women as compared to non-pregnant patients (7.30 +/- 0.44 g/dl; P less than 0.01). CSF proteins also showed a significant fall (43.2%) in pregnant (25.80 +/- 5.52 mg/dl), as compared to non-pregnant women (45.43 +/- 7.66 mg/dl; P less than 0.001). Dose of local anaesthetic drug required was significantly less (44%) in pregnant (3.21 +/- 0.29 mg/segment) as compared to non-pregnant women (5.73 +/- 0.74 mg/segment; P less than 0.01). Time of onset of block was significantly less in pregnant than in non-pregnant patients after the injection of drug (2.86 +/- 0.42 sec and 3.41 +/- 0.43 sec respectively; P less than 0.01). No correlation was found between plasma proteins and CSF proteins. CSF protein concentration also did not correlate with dose of local anaesthetic drug, or with time of onset of block. It is suggested that fall in CSF protein concentration may be another contributory factor in the reduced dose requirement of local anaesthetic drug for subarachnoid block during pregnancy.