Flushing and Locking Vascular Access Devices: SASH Protocol and Evidence
Evidence-based guide to vascular access device flushing and locking: SASH protocol (Saline-Administer-Saline-Heparin), pulsatile flush technique, positive pressure locking, heparin vs saline evidence, flush volumes, and device-specific protocols.
Flushing and Locking Vascular Access Devices: SASH Protocol and Evidence
Flushing and locking are fundamental maintenance practices for all vascular access devices. Proper technique maintains catheter patency, prevents medication interactions within the catheter lumen, and reduces the risk of intraluminal thrombosis. Improper flushing — too little saline, no pulsatile technique, no positive pressure — is the primary cause of catheter occlusion, one of the most common CVAD complications.
Parent guide: Infusion Therapy Safety: Complete Reference
The SASH Protocol
SASH stands for Saline-Administer-Saline-Heparin and describes the standard sequence for accessing and de-accessing a vascular access device lumen.
SASH Sequence
S — Saline flush (before administration):
- Purpose: Confirm catheter patency before medication administration; prevent medication interaction with residual lock solution in catheter
- Volume: 10 mL normal saline for CVADs; 3–5 mL for PIVs
- Technique: Pulsatile (push-pause), positive pressure
A — Administer medication:
- Infuse prescribed medication per orders
S — Saline flush (after administration):
- Purpose: Clear catheter lumen of residual medication; prevent drug-drug interactions in the catheter
- Volume: 10 mL normal saline for CVADs; 5–10 mL for PIVs
- Technique: Pulsatile, positive pressure
H — Heparin lock (or Saline lock — see below):
- Purpose: Maintain catheter patency between uses; prevent blood reflux into catheter tip
- Volume and concentration: Device-specific (see below)
Variant: SAS (Saline-Administer-Saline): Used when heparin is not indicated (e.g., Groshong-valved catheters, some peripheral IVs with saline lock).
Pulsatile Flushing Technique
Why Pulsatile?
Continuous, steady flushing produces laminar flow (smooth, non-turbulent) in the catheter lumen — it pushes fluid through without creating adequate turbulence to mechanically clear the lumen walls. Pulsatile (push-pause) flushing creates turbulent flow at each “push” cycle — this turbulence washes the catheter lumen walls, disrupts early fibrin adherence, and clears residual medication and blood cells from the tip and lumen.
Technique
- Fill a 10 mL syringe with normal saline
- Connect to catheter hub (after scrub-the-hub)
- Push 2 mL of saline — brief forceful push
- Pause 0.5–1 second — stop plunger movement
- Push 2 mL — brief forceful push
- Pause
- Continue in 2 mL increments with brief pauses until flush volume is complete
The rhythm: Quick push → pause → quick push → pause. The turbulence at the restart of each push cycle is what provides the cleaning effect.
Syringe Size Matters
ALWAYS use syringes ≥10 mL for CVAD flushing. Smaller syringes (3 mL, 5 mL) generate higher pressure per unit plunger displacement. With small syringes and an occluded or kinked catheter, the generated pressure can exceed the catheter’s rated burst pressure, causing catheter fracture or embolism.
Rule: If you can flush with easy plunger movement, the catheter is patent. If you feel resistance, STOP — do not force the flush. Investigate the cause of resistance before proceeding.
Positive Pressure Locking
The problem: When a syringe is disconnected from a catheter hub, the act of removing the syringe creates a small negative pressure (suction) that draws blood back into the catheter tip. This blood can clot in the catheter lumen, causing withdrawal occlusion or complete occlusion.
Positive pressure technique: Maintain forward pressure on the syringe plunger as you clamp the catheter or disconnect the connector.
Technique
With a clamp: Push the last 0.5–1 mL of saline while simultaneously closing the clamp on the catheter — the clamp closes before the saline flow stops, trapping positive pressure in the catheter.
With a Luer connector: While maintaining forward pressure on the plunger, rotate the syringe to disconnect. The disconnection happens with the plunger under pressure — not after releasing pressure.
Pressure displacement connectors (positive-pressure needleless connectors): These connectors are designed to create a small positive displacement of fluid into the catheter upon disconnection, theoretically reducing blood reflux. Evidence for their superiority is mixed; they do not eliminate the need for proper flushing technique.
Flush Volumes by Device Type
Per INS 2021 Standard 42:
| Device | Pre-Use Flush | Post-Medication Flush | Lock Solution |
|---|---|---|---|
| Peripheral IV (PIV) | 3–5 mL NS | 3–5 mL NS | Saline lock or remove |
| Midline catheter | 5–10 mL NS | 10 mL NS | Saline (10 units/mL heparin per institutional policy) |
| PICC — open-ended | 10 mL NS | 10 mL NS | Heparin 10 units/mL, 3–5 mL |
| PICC — valved (Groshong) | 10 mL NS | 10 mL NS | NS only (5–10 mL) — no heparin |
| Non-tunneled CVC | 10 mL NS | 10 mL NS | Heparin 10 units/mL, 3–5 mL per lumen |
| Tunneled CVC (Hickman) | 10 mL NS | 10 mL NS | Heparin 100 units/mL, 3 mL |
| Tunneled CVC (Groshong) | 10 mL NS | 10 mL NS | NS only — weekly when not in use |
| Implanted port | 10 mL NS | 10 mL NS | Heparin 100 units/mL, 5 mL; monthly when not accessed |
| Hemodialysis catheter | Per dialysis unit protocol | — | Heparin 5,000 units/mL (fill lumen dead space) |
Heparin Lock: Evidence and Controversy
The Question
For open-ended CVADs (Hickman, non-tunneled CVC, PICC), is heparin lock superior to saline lock for preventing catheter occlusion?
Evidence
The evidence is nuanced:
For short-term CVADs (PICC, non-tunneled CVC): Multiple RCTs and meta-analyses comparing heparin 10–100 units/mL lock vs. saline lock have found no statistically significant difference in occlusion rates for most CVADs in adults, when proper pulsatile flushing technique is used. INS 2021 states that evidence supports saline-only flushing as acceptable for PICCs and short-term CVCs.
For long-term CVADs (tunneled catheters, ports): Evidence is less definitive; heparin lock (100 units/mL for tunneled catheters; 100 or 500 units/mL for ports) is the prevailing institutional practice and is recommended by INS for long-dwell devices.
For pediatric PICCs and hemodialysis catheters: Heparin lock remains standard; the evidence base is less developed for alternatives in these populations.
Practical Recommendation
Follow institutional policy. Where institutional policy permits saline-only locking for PICCs based on updated evidence, this is acceptable with proper pulsatile flushing technique. For tunneled catheters and ports, heparin lock remains standard.
Never use heparin lock in:
- Heparin allergy
- HIT (heparin-induced thrombocytopenia) — use saline or alternative lock (citrate per protocol)
- Neonates (heparin-free protocols increasingly used due to systemic heparin concerns)
Frequency of Flushing When Device Is Not in Use
PIV
- If PIV is not in use but still patent, flush every 8–12 hours (per institutional policy) to maintain patency
- Most institutions require PIV assessment and flush at every nursing shift
PICC and Non-Tunneled CVC
- Flush and lock every 12–24 hours when not in continuous use
- At minimum, flush and lock after each discrete infusion episode
Tunneled CVC
- If not in daily use: flush and lock at least daily or per institutional policy
- Groshong valved tunneled CVC: saline flush weekly minimum when not in use
Implanted Port (Not Accessed)
- Maintenance flush every 4–6 weeks when not in use (requires port access with Huber needle; this is a nursing procedure at a designated flush appointment)
Related Resources
Related guides:
Related policies:
References
- Gorski LA, et al. (2021). INS Infusion Therapy Standards of Practice (Standard 42). J Infus Nurs, 44(Suppl 1).
- López-Briz E, et al. (2014). Heparin versus 0.9% sodium chloride locking for prevention of occlusion in CVCs: Cochrane review. Cochrane Database Syst Rev, (9):CD008462.
- Bertoglio S, et al. (2012). Efficacy of normal saline versus heparinized saline solution for locking catheters: a multicentre randomized study. J Clin Oncol, 30(9):e35–e38.
- Muñoz-Mozas G, et al. (2018). Saline vs heparin in maintaining PICC patency. J Vasc Access, 19(1):14–18.