6.2 Intravenous Catheter Care and Fluid Therapy Monitoring

Intravenous Catheter Care and Fluid Therapy Monitoring

Intravenous (IV) catheterization and fluid therapy are cornerstone interventions in small animal veterinary medicine. They allow for the direct administration of fluids, medications, and nutritional support into the systemic circulation. Because catheters bypass the body's primary protective barrier (the skin), strict aseptic preparation and meticulous ongoing care are required to prevent complications such as phlebitis, thrombosis, and catheter-associated sepsis. Additionally, continuous monitoring of fluid administration is essential to ensure therapeutic efficacy and to recognize signs of life-threatening fluid overload early.

IV Catheter Placement Preparation

The preparation for IV catheter placement must be treated as a minor aseptic procedure. The veterinary assistant is responsible for gathering supplies and preparing the patient’s skin.

Materials and Supplies Gathered

Before beginning, assemble the following materials:

• Clippers with a clean, functional No. 40 clipper blade (surgical shave).
• Skin prep solutions: Typically 2% chlorhexidine gluconate scrub and 70% isopropyl alcohol, or povidone-iodine scrub.
• IV Catheters: A selection of sizes. Over-the-needle (OTN) catheters are most common.
  • 18-gauge (Green): Used for large dogs or emergency resuscitation where rapid fluid delivery is required.
  • 20-gauge (Pink): Standard for medium to large dogs.
  • 22-gauge (Blue): Standard for small dogs and cats.
  • 24-gauge (Yellow): Used for puppies, kittens, and toy breeds.
• T-Connector (T-port) or Injection Cap: Pre-flushed with sterile saline to remove air bubbles.
• Heparinized or Normal Saline Flush: 3 mL syringe filled with sterile flush.
• Adhesive Medical Tape: Prepared strips of 1-inch and 1/2-inch surgical tape.
• Dry Sterile Gauze and antiseptic ointment (optional, depending on clinic protocol).

Skin Preparation Workflow

1. Shaving the Site: Shave a generous rectangular area over the chosen vein (most commonly the cephalic vein on the cranial aspect of the forelimb, or the lateral saphenous vein in dogs / medial saphenous vein in cats). The shave must extend 360 degrees around the limb. This ensures that the adhesive tape adheres directly to the skin and does not trap hair, which harbor bacteria and moisture, leading to infection.
2. Aseptic Skin Scrub: Perform a surgical scrub of the shaved skin. Apply a chlorhexidine-soaked gauze sponge to the center of the shaved area (over the vein) and scrub outward in a circular or spiral pattern toward the edges. Never return to the center with a gauze sponge that has touched the outer edges. Follow the scrub with an isopropyl alcohol rinse using the same center-to-perimeter technique. Repeat this alternating cycle (scrub-alcohol-scrub-alcohol) a minimum of three times to achieve proper skin antisepsis.

Catheter Maintenance and Daily Care

Once placed, a catheter must be monitored constantly. If a patient is on active IV fluids, the site must be checked at least every 4 hours. If the catheter is "patented" (not connected to continuous fluids but kept for vascular access), it requires scheduled maintenance.

Daily Inspection and Troubleshooting

The veterinary assistant should unwrap and inspect the insertion site daily, assessing for:

• Phlebitis: Inflammation of the vein, characterized by redness (erythema), local heat, pain upon palpation, and firmness of the vein (resembling a cord).
• Thrombophlebitis: Formation of a blood clot within the inflamed vein. The catheter must be removed immediately, and a new one placed in a different vein.
• Extravasation / Infiltration: Fluid leaking into the surrounding subcutaneous tissue. This is characterized by a cool, firm swelling around the catheter site. If this occurs, the catheter has migrated out of the vein and must be pulled.
• Subcutaneous Swelling (Paw Edema): Often referred to as "fat paw." This occurs when the tape securing the catheter is wrapped too tightly, obstructing lymphatic and venous return. The tape must be loosened or replaced.

Catheter Flushing Protocol

To maintain patency (preventing blood clots from blocking the catheter tip), the catheter must be flushed:

• Every 4 to 6 hours when not connected to continuous IV fluids.
• Before and after administering any IV medication.
• Flush Method: Inject 1 to 3 mL of sterile normal saline (or heparinized saline, typically 10 units of heparin per mL of saline). The injection should feel smooth and require minimal pressure. If you encounter resistance, do not force the flush, as this can dislodge a blood clot into the circulation. Stop, check for kinks in the catheter or T-connector, and notify the veterinarian.

Tape Hygiene

The tape securing the catheter must remain clean and dry. If the tape becomes soiled with blood, urine, or vomit, or if the patient gets it wet during drinking, the catheter must be removed and replaced at a new site. Wet tape acts as a wick, pulling bacteria from the external environment directly down the catheter tract into the bloodstream.

Fluid Therapy Monitoring

Fluid therapy is prescribed to replace deficits (dehydration), provide maintenance requirements, and offset ongoing losses (vomiting/diarrhea). The veterinary assistant monitors the delivery system and the patient's physical response.

Flow Rate and Equipment Checks

• IV Infusion Pumps: If a pump is used, verify the programmed rate (in mL/hour) against the veterinarian's orders at least once per hour. Check for alerts such as "Occlusion," "Air in Line," or "Low Battery."
• Gravity-Drip Systems: If a pump is unavailable, check the drip rate manually. Calculate the drops per minute based on the drip set calibration (e.g., macro-drip sets deliver 10, 15, or 20 drops/mL; micro-drip sets deliver 60 drops/mL, standard for pediatric or small patients under 10 kg).
• Fluid Volume Monitoring: Monitor the fluid level in the bag. Record the volume administered and verify that the patient is receiving the calculated hourly volume.

Monitoring for Fluid Overload (Hypervolemia)

Fluid overload occurs when a patient receives fluids faster than their cardiovascular and renal systems can process them. This is a life-threatening veterinary emergency. Cats, pediatric patients, and animals with pre-existing heart disease (e.g., congestive heart failure) or kidney failure are at the highest risk.

The veterinary assistant must monitor and immediately report the following signs of fluid overload:

• Tachypnea and Dyspnea: An increased respiratory rate (tachypnea) and increased effort (dyspnea) are the earliest signs of pulmonary edema (fluid in the lungs) or pleural effusion (fluid around the lungs).
• Coughing: A soft, moist cough, particularly in dogs.
• Serous Nasal Discharge: Clear, watery fluid leaking from the nostrils.
• Chemosis: Swelling (edema) of the conjunctiva around the eyes, appearing as a jelly-like swelling.
• Auscultation Findings: Wet crackles (harsh, popping sounds) heard when listening to the lungs with a stethoscope.
• Sudden Weight Gain: Hospitalized patients on fluid therapy must be weighed at least twice daily. A rapid increase in body weight (greater than 5-10% in 24 hours) indicates that the fluid is being retained in the tissues rather than excreted.