Continuous positive pressure ventilation during epidural blockade – effects on cardiac output distribution
It has been shown that when cardiac output (CO) decreases during continuous positive pressure ventilation (CPPV), its regional distribution adapts with a favouring of vital organs. Does epidural blockade modify this adaptation? Methods:
Regional blood flows were assessed by the microsphere technique (15 μm) in 17 anaesthetised pigs during spontaneous breathing and CPPV with 8 cm H2O end-expiratory pressure (CPPV8) before and after epidural blockade. The block was induced at either the Th6–7 (Thep) or the L6–S1 (Lep) level with 1 ml of lidocaine 40 mg · ml−1. Results:
When Lep was combined with CPPV8, mean arterial pressure and CO decreased significantly, and they decreased even more when combined with Thep. In contrast, the relative perfusion of the central nervous system, heart and kidneys remained stable during the four conditions studied. The adrenal perfusion during CPPV8 was obviated by epidural blockade. The absolute and relative perfusion of the skeletal muscle decreased during epidural blockade. The administered doses of epidural lidocaine did not affect blood flow in the spinal cord. Conclusions:
The locally mediated nutritive vasoregulation of vital organs outweighed the sympathetic blockade induced by epidural blockade. During Thep blockade the animals were less capable of responding to the haemodynamic changes induced by CPPV8, probably due to the blockade of the cardiac part of the sympathetic nervous system.