Capnography: a sensitive method of early detection of air embolism.

Seven capnograms are shown demonstrating the invariable fall in the level of expired CO2 which occurs during the operation for the insertion of a Pudenz-Heyer drain for hydrocephalus. The fall occurs when contrast medium is injected down the heart catheter after withdrawal of the guide but never after subsequent injections unless air is present in the syringe. The effect is shown not to be due to a difference in temperature between the contrast medium and the body. A comparison is made with a capnogram recorded during the setting up of an I.V. transfusion in an infant in which a small quantity of air was seen to enter the circulation along the tubing of the butterfly needle. It is concluded that the fall in the capnogram seen during Pudenz-Heyer operations is due to air embolism. The severity of its effect is shown to be proportional to the volume of air injected in relation to body weight. The value of the capnograph as a sensitive monitor of air embolism is emphasised together with the fact that the fall in the capnogram precedes that of the blood pressure or any other recordable effect.