British Journal of Anaesthesia vol:104 issue:2 pages:143-149
Background. The safety of epidural anaesthesia in patients at risk for right ventricular
pressure overload remains controversial. We compared the haemodynamic effects of vascular
and cardiac autonomic nerve block, induced by selective lumbar (LEA) and high thoracic epidural
anaesthesia (TEA), respectively, in an animal model subjected to controlled acute right
ventricular pressure overload.
Methods. Eighteen pigs were instrumented with epidural catheters at the thoracic (T) and
lumbar (L) level and received separate injections at T2 (1 ml) and L3 (4 ml) with saline (s) or
bupivacaine 0.5% (b). Three groups of six animals were studied: (i) a control group (LsþTs), (ii)
LEA group (LbþTs), and (iii) TEA group (LsþTb). Haemodynamic measurements including
biventricular pressure-volumetry were performed. Right ventricular afterload was then
increased by inflating a pulmonary artery (PA) balloon. Measurements were repeated after
30 min of sustained right ventricular afterload increase.
Results. LEA decreased systemic vascular resistance (SVR) and did not affect ventricular function.
TEA had minor effects on SVR but decreased left ventricular contractility while baseline
right ventricular function was not affected. Control and LEA-treated animals responded similarly
to a PA balloon occlusion with an increase in right ventricular contractility and heart rate.
Animals pretreated with a TEA did not show this positive inotropic response and developed
low cardiac output in the presence of right ventricular pressure overload.
Conclusions. In contrast to LEA, TEA reduced the haemodynamic tolerance to PA balloon
occlusion by inhibiting the right ventricular positive inotropic response to acute pressure