Manometry of a vascular catheter using intravenous tubing

If the proceduralist is unsure whether the vein or artery has been cannulated, saline filled tubing can be attached to the needle or catheter (panel A) and opened to the atmosphere (panel B). In the event of venous cannulation, the fluid column would decrease to approximate the venous pressure in the vein (normally less than 14 cmH2O) as shown in panel B. In the event of arterial cannulation, the fluid column would likely be dramatically higher (eg, more than ~55 cmH2O in an infant with a mean pressure of 40 mmHg or ~110 cmH2O in an adult with a mean pressure of 80 mmHg, inset) with the blood flowing up and often out of the tubing.