Peripheral intravenous catheter placement is the single most commonly performed invasive procedure by veterinary technicians. Studies show that first-attempt success rates among experienced vet techs exceed 85%, but that rate drops significantly when catheter gauge, site selection, or patient restraint are suboptimal. Using a Fluid Therapy Calculator before placement ensures you choose the right catheter for the prescribed fluid plan.
Catheter gauge determines maximum flow rate and is selected based on patient size, intended use, and vein diameter. A larger gauge number indicates a smaller catheter diameter. For rapid fluid resuscitation, the largest gauge the vein can accommodate is preferred because flow rate is proportional to the fourth power of the catheter radius (Poiseuille's law).
| Catheter Gauge | Patient Weight | Typical Use | Max Flow Rate |
|---|---|---|---|
| 24 ga | < 2 kg (neonates, kittens) | Maintenance fluids, medication delivery | ~22 mL/min |
| 22 ga | 2-5 kg (cats, small dogs) | Maintenance fluids, blood sampling | ~36 mL/min |
| 20 ga | 5-25 kg (medium dogs) | General purpose, moderate fluid rates | ~65 mL/min |
| 18 ga | > 25 kg (large dogs) | Rapid resuscitation, blood transfusion | ~105 mL/min |
The cephalic vein on the dorsal aspect of the forelimb is the most commonly used site in both dogs and cats. It is superficial, easily stabilized, and allows patients to remain ambulatory. The lateral saphenous vein (dogs) or medial saphenous vein (cats) on the hindlimb is an excellent alternative when cephalic veins are compromised or when bilateral forelimb access is needed.
The jugular vein is reserved for central venous catheterization, large-volume blood draws, or when peripheral access is impossible. Jugular catheters allow higher flow rates and central venous pressure monitoring but carry increased risks of infection and require more rigorous aseptic technique. The auricular (marginal ear) vein in dogs with pendulous ears can be used for short-term access in emergencies but is not ideal for sustained fluid therapy.
Before approaching the patient, gather all supplies to minimize restraint time and stress. You will need: appropriately sized over-the-needle catheter, clippers with a #40 blade, chlorhexidine or alcohol prep pads, T-port or injection cap, pre-flushed extension set (0.9% NaCl), white tape and/or transparent adhesive dressing (Tegaderm or VetWrap), heparinized saline flush (2-3 mL), gauze squares, and examination gloves. Having a second catheter immediately available prevents delays if the first attempt fails.
Step 1: Restrain and position. Place the patient in sternal recumbency. The restrainer holds off the cephalic vein at the proximal antebrachium with one hand while stabilizing the dorsal paw with the other, extending the carpus slightly to straighten the vein.
Step 2: Prepare the site. Clip a generous area (approximately 3 x 5 cm) over the dorsal antebrachium. Perform a surgical scrub using chlorhexidine (3 alternating scrubs) or swab with 70% isopropyl alcohol.
Step 3: Visualize and palpate. The vein should be visible and turgid after occlusion. Palpate to confirm its course. In dark-skinned patients, palpation may be more reliable than visualization.
Step 4: Insert the catheter. With the bevel up, enter the skin at a 15-30 degree angle just distal to where you want the catheter tip to reside. Advance until a flash of blood appears in the stylet hub. Reduce the angle to nearly parallel with the vein and advance the catheter-stylet unit 1-2 mm further to ensure the catheter tip (not just the stylet) is intraluminal.
Step 5: Thread the catheter. Stabilize the stylet and advance the catheter off the stylet into the vein with a smooth, steady motion. Never reinsert the stylet into a partially advanced catheter, as this risks shearing off catheter material. Remove the stylet and immediately cap or connect the extension set.
Step 6: Flush and secure. Flush with 1-2 mL of heparinized saline, watching for subcutaneous swelling. Secure with white tape in a butterfly configuration, then wrap with conforming bandage (VetWrap) ensuring you can still monitor the insertion site.
Warning: Never forcefully advance a catheter that meets resistance. Forced threading can perforate the vein wall, lacerate the intima, or cause a catheter embolism. If you cannot advance smoothly, remove the entire assembly and attempt at a new site proximal to the failed attempt (never distal, as the vessel may leak).
Peripheral catheters should be flushed with 1-3 mL of heparinized saline (1-2 units/mL) every 4-6 hours when not in continuous use. Assess the site at least every 4 hours for swelling, pain, erythema, discharge, or warmth. Per AAHA guidelines, peripheral catheters should be replaced or rotated every 72 hours to minimize infection risk. Change the bandage whenever it becomes soiled or wet.
Blown vein (perivascular infiltration): Subcutaneous swelling during or after flushing indicates the catheter has exited the vessel lumen. Remove immediately and apply gentle pressure for 30-60 seconds. Reattempt proximal to the site or on the opposite limb.
Phlebitis: Inflammation of the vein wall presents as erythema, warmth, pain, and a palpable cord along the vein. Remove the catheter, apply a warm compress, and document. Risk factors include hypertonic solutions, irritating drugs (diazepam, phenobarbital), prolonged dwell time, and poor aseptic technique.
Catheter kinking: Most commonly occurs at a joint (carpus). Ensure proper placement away from flexion points and use adequate tape to prevent migration. Splinting the limb may help in active patients.
Catheter occlusion: If the catheter will not flush, do not force. Attempted forceful flushing risks dislodging a thrombus. Remove and replace the catheter. Use the Triage/Emergency Specialist for guidance on difficult vascular access cases, and reference the Vital Signs Reference to assess patient stability.
Catheter placement proficiency improves dramatically with practice. New vet techs should aim for supervised placement of at least 50 catheters before working independently. Practicing on training models and cadavers builds muscle memory for angle, depth, and threading technique.
- Select gauge by patient size — 24 ga for neonates, 22 ga for cats, 20 ga for medium dogs, 18 ga for large dogs and resuscitation.
- Cephalic is first-line — saphenous and jugular are alternatives when cephalic access is compromised.
- Enter at 15-30 degrees bevel up — reduce angle after flash, advance catheter-stylet 1-2 mm before threading.
- Never reinsert the stylet — if threading fails, remove the entire assembly and start fresh at a new site.
- Flush every 4-6 hours — replace peripheral catheters every 72 hours to reduce infection risk.