How should you clamp a syringe during flushing with a negative/neutral pressure cap?

• A. Clamp syringe while maintaining positive pressure, e.g., during the last mL of saline
• B. Remove clamp entirely
• C. Keep syringe unclamped throughout
• D. Do not clamp at all

Answer: (A)

When flushing with a negative/neutral pressure cap, you want to keep the system under a little positive pressure as you seal it. Clamping the syringe while you continue to press the plunger (maintaining positive pressure) during the last portion of saline push helps push out any remaining fluid and prevents the line from drawing back blood or air as you disconnect or cap the system. This brief moment of positive pressure at the end of the flush minimizes backflow and keeps the closed system intact. If you release pressure or keep the syringe unclamped, negative pressure can cause blood to reflux into the catheter or air to be drawn into the line, which compromises safety.