Effect of thoracic epidural anaesthesia on ventilation-perfusion distribution and intrathoracic blood volume before and after induction of general anaesthesia.
BACKGROUND
Gas exchange is impaired during general anaesthesia due to development of shunt and ventilation-perfusion mismatching. Thoracic epidural anaesthesia (TEA) may affect the mechanics of the respiratory system, intrathoracic blood volume and possibly ventilation-perfusion (VA/Q) distribution during general anaesthesia.


METHODS
VA/Q relationships were analyzed in 24 patients undergoing major abdominal surgery. Intrapulmonary shunt (Qs/QT), perfusion of "low" VA/Q areas, ventilation of "high" VA/Q regions, dead space ventilation and mean distribution of ventilation and perfusion were calculated from the retention/excretion data of six inert gases. Intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) were determined with a double indicator technique. Recordings were made before and after administration of 8.5 +/- 1.5 ml bupivacaine 0.5% (n = 12) or 8.3 +/- 1.8 ml placebo (n = 12) into a thoracic epidural catheter and after induction of general anaesthesia.


RESULTS
Before TEA, Qs/QT was normal in the bupivacaine group (2 +/- 2%) and the placebo group (2 +/- 3%). TEA covering the dermatomal segments T 12 to T 4 had no effect on VA/Q relationships, ITBV and PBV. After induction of general anaesthesia Qs/QT increased to 8 +/- 4% (bupivacaine group, P < 0.05 and to 7 +/- 2% (placebo group, P < 0.05). ITBV and PBV decreased significantly to the same extent in the bupivacaine group and the placebo group.


CONCLUSIONS
TEA has no effect on VA/Q distribution, gas exchange and intrathoracic blood volume in the awake state and does not influence development of Qs/QT and VA/Q inequality after induction of general anaesthesia.
Hachenberg
T
T
Department of Anaesthesiology and Intensive Care Medicine, Ernst-Moritz-Arndt Universität Greifswald, Germany.
Holst
D
D
Ebel
C
C
Pfeiffer
B
B
Thomas
H
H
Wendt
M
M
Hedenstierna
G
G
D000767:Anesthesia, Epidural; D000779:Anesthetics, Local / Q000494:pharmacology*; D001810:Blood Volume / Q000187:drug effects; D002045:Bupivacaine / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011652:Pulmonary Circulation / Q000187:drug effects* / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000187:drug effects*
D000779:Anesthetics, Local; D002045:Bupivacaine