19.1 Peripheral IV Cannulation, Venipuncture, Saline Locks & Maintaining Infusions

19.1 Peripheral IV Cannulation, Venipuncture, Saline Locks & Maintaining Infusions

CPCF Appendix A minimum entry-to-practice skill #27A requires the Primary Care Paramedic to conduct peripheral intravenous cannulation and to maintain peripheral IV access devices and infusions of crystalloid solutions without additives. Skill #19 additionally requires peripheral venipuncture. These are core PCP psychomotor skills and they carry a disproportionate share of the procedural questions on the examination, because every step has a defensible reason behind it.

Indications, and the Discipline of Not Cannulating

Establish access when there is a reasonable prospect of needing it: volume replacement, intravenous medication, a patient with a condition liable to deteriorate, or a transport during which either may become necessary. Cannulating every patient is not good practice — each attempt is painful, carries infection and infiltration risk, and consumes time that is sometimes better spent moving.

Absolute and relative site contraindications — these appear repeatedly on examinations:

• A limb with an arteriovenous fistula or graft (Section 14.6) — never
• A limb on the side of a mastectomy with axillary node clearance, or with lymphoedema
• A limb with a dialysis catheter, or the affected limb after a stroke where sensation and circulation are impaired
• Through infected, burned, or traumatized skin, or distal to a fracture
• A limb with impaired circulation, or one that will be immobilized in a splint
• Veins over a joint where flexion will occlude or dislodge the catheter, unless nothing else is available

Site Selection

Work distal to proximal — a failed proximal attempt makes every site distal to it unusable.

Choose a vein you can feel, not one you can see. A palpable, bouncy, compressible vein that refills after pressure is far more reliable than a visible but thrombosed cord. Avoid valves — felt as small firm bumps — and avoid areas where a vein bifurcates.

Catheter Gauge

Flow rate is governed by Poiseuille's law: flow rises with the fourth power of the radius and falls with length. A short wide catheter therefore flows dramatically faster than a long narrow one — which is why a short 14 G peripheral cannula outperforms a long central line for rapid volume. For resuscitation, choose the largest catheter the vein will comfortably accept; for a stable patient needing only medication, a smaller catheter is kinder and lasts longer.

Technique

1. Explain the procedure and obtain consent (indicators A3.3 and H3.3).
2. Hand hygiene, then gloves. A point-of-care risk assessment determines whether eye protection is also needed (Section 8.4).
3. Prepare everything before you start: catheter, extension set or saline lock primed with saline, flush, dressing, tape, sharps container, tourniquet, antiseptic.
4. Apply the tourniquet about 10 to 15 cm proximal to the intended site, tight enough to occlude venous return but not the arterial pulse — you must still feel a distal pulse.
5. Encourage filling: dependent positioning, gentle tapping, warmth, opening and closing the fist. Avoid vigorous slapping, which causes spasm.
6. Clean with an appropriate antiseptic using friction and allow it to dry completely — the drying is the disinfection, and cannulating through wet antiseptic stings and does not disinfect. Do not re-palpate the cleaned site.
7. Anchor the vein by applying distal traction on the skin with the non-dominant thumb.
8. Insert bevel up at 10 to 30 degrees to the skin, shallower for superficial veins.
9. Watch for flashback in the chamber, then lower the angle and advance a further 1 to 2 mm so that the catheter tip — not just the needle tip — is inside the lumen.
10. Advance the catheter off the needle into the vein while holding the needle still. Never re-insert the needle into an advanced catheter — it can shear the catheter and embolize a fragment.
11. Release the tourniquet, occlude the vein proximal to the catheter tip, remove the needle, and dispose of it directly into the sharps container — never recap.
12. Attach the primed extension or lock, flush gently with saline, and watch and feel the site. Resistance, swelling, pain, or blanching means the catheter is not in the vein.
13. Secure with a transparent dressing that leaves the site visible, loop and tape the tubing so that a pull on the line does not pull on the catheter, and document the gauge, site, attempt number, date and time, and who inserted it.

Limit attempts. Two attempts per clinician is a widely used convention before handing over or escalating to an alternative route. Every additional attempt costs time, veins, and patient trust.

Peripheral Venipuncture (Blood Sampling)

Skill #19 includes peripheral venipuncture for diagnostic sampling. Prehospital blood draws — most often at the moment of cannulation — save a repeat needle at hospital and can shorten time to results.

• Draw before flushing, so the sample is not diluted by saline.
• Order of draw matters when multiple tubes are used, because additive carryover between tubes invalidates results. Follow the sequence your service and receiving laboratory specify.
• Fill tubes to the marked line — an under-filled citrate tube gives a falsely prolonged coagulation result.
• Invert gently the specified number of times; shaking haemolyses the sample, which falsely elevates potassium and can trigger an unnecessary hyperkalaemia response.
• Label at the patient's side, immediately, with two identifiers. Never label in advance.
• Record the time of collection and hand the samples over explicitly.

Saline Locks and Maintaining Infusions

A saline lock is a short extension with a needle-free connector that keeps the catheter patent without a running infusion. It preserves access, reduces the risk of accidental fluid overload, and is the correct choice when no continuous fluid is needed.

Skill #27A also requires maintaining infusions of crystalloid without additives, including on interfacility transfers:

• Verify before departure: the fluid type, the volume remaining, the prescribed rate, the drip set calibration, and the catheter site.
• Calculate the drip rate:

Drops per minute = (Volume in mL  x  Drop factor)  /  Time in minutes

Example: 500 mL over 4 hours (240 minutes) with a 20 drops/mL set: (500 x 20) / 240 = approximately 42 drops per minute.

Common drop factors are 10, 15, or 20 drops/mL for macrodrip sets and 60 drops/mL for microdrip.

• Check the site at least every 15 minutes during transport and after every patient movement.
• Do not add anything to a bag you did not prepare, and do not adjust a prescribed rate outside your authorization — escalate to medical direction.
• Keep the bag above the patient; gravity is the driving force, and the bag dropping below the insertion site allows blood to back up and clot the line.

Complications and Their Recognition

[!CAUTION] Sharps safety is a competency, not a housekeeping matter. Never recap a needle, activate the safety mechanism before disposal, use a sharps container at the point of use rather than carrying an exposed needle across the room, and never pass an uncapped needle to another person. A needlestick is a life-altering occupational exposure and must be reported immediately (Section 8.1).