Effect of acute hypovolaemia on lignocaine absorption and cardiovascular response following epidural block in dogs.

The effect of acute hypovolaemia (15% blood loss) on the absorption of lignocaine from the epidural space and on the cardiovascular response to epidural analgesia was studied in 10 dogs. After bleeding the net rate of systemic drug absorption was significantly reduced compared with the rate under normovolaemic conditions. Maximum blood concentrations of the drug were lower by about 30%. This finding emphasizes the importance of blood flow as a determinant of the pharmacokinetics of local anaesthetics. After bleeding, epidural injection of lignocaine caused considerable cardiovascular depression. Significantly greater decreases in arterial pressure and cardiac output occurred compared with those observed under normovolaemic conditions. These results emphasize the view that epidural anaesthesia should not be used in the presence of moderate hypovolaemia.