End-tidal carbon dioxide during thoracotomy. Its relation to blood level in adults and children.

The concentration of carbon dioxide in end-tidal gas was compared with the tension in arterial or superior vena caval blood during thoracotomy in twelve patients. In six adults requiring pulmonary resection, one-lung anaesthesia did not change the difference between the two measurements. In six children in whom a systemic to pulmonary arterial anastomosis was being created to improve pulmonary blood flow impaired by cyanotic congenital heart disease, occlusion of the pulmonary artery caused in increase in the blood-end-tidal carbon dioxide gradient. This change was particularly marked in two neonates and was of sufficient magnitude to render end-tidal monitoring unreliable in these circumstances.