How to operate a 3 way Stopcock

3-way stopcocks are great for efficiently draining air and effusions from the body cavities. In this video we demonstrate how to operate a 3-way stopcock. 


We will use this same set-up for several different emergency procedures, including thoracocentesis (for pneumothorax, hemothorax and other pleural effusions), therapeutic abdominocentesis (for ascites/abdominal effusion/peritoneal effusion) and autotransfusion. You will need:

  • a 3-way stopcock
  • an extension set (we usually use a 30 cm regular extension set)
  • a syringe (60cc, 35cc, 20cc or 12cc depending on the size of the patient)
  • nitrile or latex gloves (the person operating the 3-way stopcock should always be wearing gloves).

Attach the different components. Attach the 3-way stopcock to the syinge and extension set. The size of your syringe will depend upon the size of the patient. For large dogs, a 60cc syringe would be appropriate, while for very small dogs and cats, you may choose to use a 20cc or 12 cc syringe.

Ensure that the connections are secure and make sure that there are no leaks. It is important to make sure that all of the connections are very secure, and that there are no leaks in the 3-way stopcock. If there is a leak, it can create the false impression that your are drawing air out of the patient's body cavity, when in reality air from the room is being aspirated into the syringe through an insecure connection. To test for leaks, clamp the extension set, turn the valve to the right, and aspirate back on the syringe. If there are no leaks, you should not be able to aspirate any air back into the syringe, and negative pressure should be maintained.

To operate the 3-way stopcock: To operate a 3-way stopcock when it is attached to a patient, remember:

  1. The port attached to the extension set will be pointing toward the patient
  2. The port on the right side of the 3-way stopcock will be used for evacuating fluid from the syringe and pushing it into your collecting bowl or sample tubes.
Remember: the direction that the valve is pointing towards always means "OFF."
  • If the valve is pointing TOWARD THE PATIENT, it will be "OFF" to the patient, and fluid (or air- if you are dealing with a pneumothorax) will be able to flow between the syringe and the side port.
  • If the valve is POINTING TOWARD THE RIGHT, it will be "OFF" to the side port, and fluid (or air) will be able to travel between the patient and the syringe.
So, when aspirating back from the patient, make sure that the extension set is unclamped, and the valve should be turned to the right. This enables you to draw fluid or air from the patient and into the syringe. To empty the syringe when it is full, turn the valve towards the patient (or "OFF" to the patient) and push the fluid (or air) out of the syringe. As you do this, you should be able to detect fluid (or air) coming out of the side port of the 3-way stopcock and into your collecting bowl. If you accidentally empty the syringe while the valve is still pointing toward the right, then you will simply push the fluid (or air) back into the patient, which is counterproductive. If you are the one operating the 3-way stopcock, it is very important to communicate with the person advancing the needle or catheter into the patient. Clearly state when fluid or air is flowing into the syringe, or when you are getting negative pressure. Say "ok good that is flowing," when you are able to aspirate easily. Say "negative," "negative pressure," or "not getting anything" when you encounter resistance to flow. If this is your first time, practice a couple rounds to get comfortable with operating the valve. Then put your skills to work and go save your patient!

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