Circulatory Effects of Peridural Block: I. Effects of Level of Analgesia and Dose of Lidocaine

Effects of different levels of peridural analgesia on cardiovascular dynamics, blood gases and limb blood flow were studied in normovolemic man. Lidocaine, 2 per cent, was injected to achieve successively greater levels of analgesic block. During analgesia to T4 or below, MABP, TPR, and CO remained within normal limits; with T2-3 block, TPR decreased 15 per cent and CO increased 22.6 per cent, resulting in a 5 per cent increase in MABP; with blocks extending to T1 or higher, TPR decreased 18.7 per cent while CO remained slightly above normal, resulting in a 16.3 per cent reduction in MABP. Blood flow in the leg increased progressively to 292 per cent with T2-3 block, while blood flow in the arm decreased as much as 58 per cent. However, after extension of the block above T1, blood flow in the arm increased to 125 per cent above normal, while blood flow in the leg declined to 219 per cent above normal. The data suggest that cardiovascular responses to peridural block, unlike responses to subarachnoid block, are not the result of sympathetic blockade alone, but involve several other factors, including the dose of local anesthetic. When several doses of lidocaine result in arterial blood levels ranging from 4 to 7 µg/ml, most subjects develop increased CO. This may be sufficient to offset vasodilating effects of high sympathetic block so that MABP remains normal.