Respiratory function during cervical and thoracic extradural analgesia in patients with normal lungs.

Lung volumes, expired gas volumes, tests of ventilatory capacity and blood-gas tensions were measured in women before and after induction of cervical or thoracic extradural analgesia using 2% mepivacaine. Inspiratory capacity, vital capacity, total lung capacity and FEV1 all decreased significantly 30 min after both cervical and thoracic extradural blocks. The changes observed during cervical block were significantly greater than those observed during thoracic extradural analgesia. Expiratory reserve volume and functional residual capacity decreased significantly after thoracic extradural block, but did not change after cervical extradural block. Reduction in expired minute volume was observed in the two groups. PaCO2 and alveolar-arterial oxygen tension difference increased, and PaO2 decreased significantly 25 min after both blocks. These results demonstrate that pulmonary ventilation is slightly impaired by the two blocks and to the same degree, but ventilatory reserve and capacity are markedly impaired by cervical extradural block.