Chapter 61 Peripheral Venous Catheterization
Peripheral venous access is a cornerstone of the treatment of the emergency or critically ill patient. Patients often require temporary venous access for medications, fluid and electrolyte replacement, or transfusion of blood products. Medications and fluids with osmolalities 600 mOsm or less may be administered safely via a peripheral vein.1 Site selection depends on the available vessels, condition of the vessels and patient, expense, and the urgency of the situation. Vascular access traditionally involves the insertion of a catheter into the cephalic, saphenous, or auricular vein; however, any visible vessel is a potential candidate for catheterization. Various techniques are used to insert catheters, including percutaneous, facilitative relief holes, and venous cutdowns.
A variety of catheters are commercially available (Figure 61-1). The length and gauge (diameter) of the catheter to be used are dependent on the species and size of the patient, the veins available and their condition, and the needs of the patient.
Both the radius and the length of the catheter determine the maximum flow rate. A large-gauge, short catheter is needed if fluids are to be administered rapidly, such as in a severely hypovolemic patient. If a slow infusion is acceptable, then a small-gauge catheter might be appropriate. A smaller catheter-to-vein ratio is considered more “vein friendly.”
The winged needle (butterfly) is for short-term use when the animal is not moving around very much. Applications might include blood collection or administration of nonirritating medications. Common needle size ranges from 25 to 19 gauge. The needles have plastic wings on the shaft to facilitate placement or taping in place. Plastic tubing of various lengths extends from the needle to the syringe connector port. These catheters are easy to place but difficult to maintain because of the ease with which the indwelling sharp needle punctures the vessel wall, allowing for subcutaneous infiltration of fluids or medications.
The over-the-needle catheter is the most commonly used type. It is inexpensive and easy to place. The needle point extends a millimeter or so beyond the catheter tip. Over-the-needle catheters are available in a variety of lengths and gauges and are made of various materials (Teflon, polypropylene, polyvinyl chloride, and polyurethane).
Catheters passed through the needle are called through-the-needle or inside-the-needle catheters. Through-the-needle catheters are usually longer (8 to 12 inches) than over-the-needle catheters and come in a variety of diameters. These catheters are used primarily in the jugular vein but can be used peripherally in the medial or lateral saphenous veins. These catheters can be inserted to the level of the posterior vena cava, allowing for administration of hyperosmotic solutions. They can also be inserted into the cephalic vein but are often difficult to pass beyond the axilla into the larger anterior vena cava. A plastic sleeve prevents catheter contamination during insertion. Once the catheter is placed, the needle is withdrawn from the skin puncture site and covered with a needle guard to prevent the needle from shearing the catheter.
Arrow International (Reading, PA) produces a double-lumen over-the-needle catheter called a TwinCath. The TwinCath is more expensive than regular single-lumen catheters, but it allows simultaneous infusions of otherwise incompatible fluids via one catheter. Catheter placement is identical to that of any single-lumen over-the-needle catheter.
The cephalic vein is located on the anterior antebrachium. It crosses from the medial aspect of the leg an inch or so proximal to the carpus to join the brachial vein proximal to the elbow, which ultimately joins the external jugular vein. An accessory cephalic vein on the anterior aspect of the metacarpus passes over the carpus and joins the cephalic vein.2 If possible, it is best to avoid the insertion of the catheter over the carpus, because it will be difficult to secure.
The cranial branch of the lateral saphenous obliquely crosses the lateral aspect of the distal tibia.2 The lateral saphenous vein is larger than the medial saphenous in the dog, and the medial saphenous is larger than the lateral and is more commonly catheterized in the cat.