ELEMENTARY DEMONSTRATIONS 



127 



FIG. 103. Arterial cannula. 



inserted, and tied in with the second ligature. Lastly the ends of this 

 ligature are brought round the bulb of the cannula, and tied to make 

 the connection secure. 



The arterial cannula is J_ shaped and provided with a bulbous 

 enlargement. This shape is chosen both to hinder clotting and to 

 facilitate the washing out of 

 clots. One limb of the JL * s 

 fitted with a short piece of 

 rubber tube, and this is closed 

 by a piece of glass rod or a 

 clip. The other limb is con- 

 nected by a short length of 

 thick rubber tube (pressure 

 tubing) to a long length of 

 fine bored glass tubing. The 

 latter must be at least 5 feet 

 in length, and is held in the 

 vertical position by a clamp. The glass tube and cannula are filled 

 with 1 per cent, sodium citrate, and this decalcifies the blood and so 

 prevents clotting. The solution is coloured with methylene blue, and 

 a long strip of white paper scaled in centimetres is placed behind 

 the tube. 



By cutting through the attachment of the sterno-mastoid muscle, the 

 junction of the jugular with the subclavian veins is next exposed. The 

 innominate vein is picked up and cleaned with the aneurism needle. 

 Two ligatures are placed under it, and a clip on the part "nearest the 

 heart. One of the ligatures is tied round the junction of the jugular and 

 subclavian veins. As the vein is clipped before the ligature is tied, it 

 becomes distended with blood, and this facilitates the introduction of 

 the cannula. The straight vein cannula is connected with a short 

 length (1 foot) of glass tubing. The latter is clamped in the vertical 

 position, and is filled with sodium citrate solution. The cannula is also 

 filled with sodium citrate solution, and to retain the solution a clip is 

 placed on the rubber tube, which connects the cannula with the glass 

 tube. The positive pressure in the glass tube must not be more than 

 3 to 4 inches of the solution. 



The innominate vein is now slit and the cannula introduced. Then 

 the clip on the vein is removed, and the cannula is pushed down into 

 the superior vena cava. The clip on the rubber tube is next opened so 

 as to place the venous cannula in connection with the vertical tube. 

 The fluid in this will now oscillate with each respiration at a level of 

 about 2-3 inches. The clip on the artery is next opened. The fluid in the 



