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3 Three‐way tap

Jane Sturgess

Figure 3.1 Three‐way tap. Note the arrows on the limbs to indicate flow of fluid/air.

Figure 3.2 Equipment. Three‐way taps come individually or incorporated with extension tubing.

Figure 3.3 Different possible positions of a three‐way tap and combinations of equipment: (a) open to infusion and cannula; (b) open to infusion, air, and cannula; (c) as per b but capped off to air; (d) used for aspirating from cannula or injecting intravenously; (e) open to infusion, syringe, and cannula; (f) open to infusion and syringe – useful for aspirating fluid to then give bolus by turning three‐way tap round to position d; (g) used for giving two infusions simultaneously; (h) off to all ports.

Description of the three‐way tap

The three‐way tap is shaped like a T, and when examined closely you can see each ‘arm’ of the ‘T’ has a small arrow or line on it (Figure 3.1). The arrow indicates that flow can happen through it, as long as the arrow is pointing at something that permits flow – like a fluid line, a vein, or air.

Another way to look at the three‐way tap is to imagine it like a road traffic roundabout with three exits. Flow can happen only when there is an exit attached to an open secondary route (giving line, fluid circuit, air). If the exit has a bung on it imagine it like a roadblock: flow does not occur.

The top of the ‘T’ with no arm (and no arrow), or the aspect of the ‘roundabout’ with no exit, stops flow and acts as an off switch.

It may come individually or be incorporated with extension tubing (Figure 3.2).

Potential uses of the three‐way tap (Figure 3.3)

1 To aspirate fluid from a fluid giving set

2 To aspirate fluid from a drain (e.g. ascitic drain, pleural drain)

3 To aspirate blood from invasive lines (e.g. central venous pressure [CVP] or arterial line)

4 To aspirate air from a fluid giving set

5 To aspirate air from a drain (examples as 2)

6 To permit intermittent pressure measurements with a manometer in a fluid system (e.g. cerebrospinal fluid [CSF] pressure, invasive blood pressure, intra‐abdominal pressure)

7 To inject drugs into a fluid‐filled system (e.g. intravenous fluid giving set, CSF injection, epidural catheter, external ventricular drain)

8 To inject drugs, treatments into other spaces (e.g. pleurodesis)

9 To permit the infusion of more than one fluid or drug at the same time via the same cannula

Safe use of a three‐way tap

The three‐way tap acts as an interface between the patient and the therapy; either as a middle point between lines into or drains from the patient, and a giving/monitoring set, or a drain collection device.

Look at the tap, identify the arms, and decide which way to turn it before going ahead with the procedure. It is also worth planning to use a bung if you need to stop flow through one of the arms (even if for a short time or as a temporary measure). Whilst planning how to turn the taps during the procedure, you should also decide how you need to leave the tap when the procedure is finished; should flow be permitted to continue, or does it need to be stopped.

If an arm of the T, or a road exit is pointing to an open exit with no device or bung attached it is ‘open to air’. This presents a significant risk of either (i) air entering the patient and causing a serious complication, for example, air embolus, pneumothorax, pneumocephalus OR (ii) fluid leaving the patient in an unplanned and/or uncontrolled manner, for example, bleeding, fast and excessive loss of CSF, ascites, or pleural fluid.

It is important to use a clean technique when using or manipulating the three‐way tap for infection control to protect the patient and to avoid cross‐contamination of any samples taken.

After the procedure

Make sure there are no arms left open to air.

When deciding how to leave the tap at the end of a procedure it is worth thinking about what measure you will use to determine whether and when to change your plan – this measure may be determined by time, by patient’s symptoms (increasing breathlessness), by pressure measurement (CSF pressure greater than 15 cmH₂O), by volume of fluid in the drain etc.

Your first plan may be to permit flow or to stop flow.

Anatomical pitfalls

1 If the fluid/air you hope to drain is at high pressure or high volume it will automatically flow to the outside – take care if this is unplanned, or you wish to drain only a predetermined amount (e.g. pleural effusion, CSF, ascites). Be prepared to replace large fluid losses with the appropriate intravenous replacement fluid (blood, albumin, crystalloid).

2 If the fluid/air you hope to drain is at low pressure (negative intrapleural pressure on inspiration, or central vein with three‐way tap system above the level of the heart) or low volume, fluid may flow into the patient inadvertently causing complications such as pneumothorax or air embolism – take care.

3 Using a syringe to aspirate a low volume, low pressure system can collapse the tissues if too great a negative pressure is applied. This can either make the drain or line fail or give a false negative result to your aspiration, leading to unnecessary repeated tests (with associated risks) or a false diagnostic conclusion (with associated risks, and delay in diagnosis).

Top tips

1 Look at the tap and plan how to turn it before you start – which ways do you need fluid/air to flow and at what time points of the procedure?

2 Plan how to stop flow – you can either turn the tap so that the top of the T with no arm faces the direction you want to stop flow from (usually the patient); you can put a bung onto the Luer lock that has an arm with an arrow pointing towards it; or you can quarter turn the tap so that none of the arms point towards a line – it will lie at an angle to the giving system.

3 If aspirating low volume or low pressure fluid consider using a small syringe in the first instance and be prepared with a choice of larger syringes. It is easy to switch to a larger syringe during the procedure if the fluid/air flows easily.