Chapter 15 Technical Aspects of Fluid Therapy
Hospitalized veterinary patients frequently require parenteral fluid therapy for several days, sometimes with complex combinations of intravenous fluids and drugs that require specialized catheters and delivery techniques. This chapter will provide an overview of the technical aspects of delivering fluids and mediations to patients by parenteral routes, with emphasis on intravenous techniques. There have been only a few reports of clinical studies comparing therapy methods or identifying complications in veterinary patients, and many of the principles described in this chapter are adapted from human medical practice, extrapolated from experimental work on animal models, or based on the author’s experience in a veterinary teaching hospital intensive care unit.
The most frequently used routes of parenteral therapy are intravenous, intraosseous, and subcutaneous. Intraperitoneal administration of fluids is potentially hazardous and offers no significant advantages over other routes; therefore it is not discussed further. The route of parenteral fluid administration is chosen based on the underlying disorder and its severity, therapeutic goals, fluid composition, and characteristics of the patient, including species, size, age, and accessibility of veins.
Subcutaneous fluid administration (hypodermoclysis) is a convenient and inexpensive route of maintenance fluid therapy for patients that do not require vascular access for other purposes. It should be reserved for relatively stable animals because peripheral vasoconstriction in illness may limit absorption of fluids and prevents successful use of the subcutaneous route. The fluid should be nearly isotonic (200 to 400 mOsm) to limit discomfort and complications. Although sodium-free or low-sodium fluids are tolerated by many human patients, the composition of fluid administered subcutaneously should ideally be comparable with that of extracellular fluid because electrolyte-free or hypertonic fluids are associated with higher complication rates.2,24,68 In humans, subcutaneous fluids can be supplemented with potassium at a concentration up to 40 mEq/L and in the author’s experience this concentration is usually well-tolerated by companion animals.70
The potential for pain, inflammation, and electrolyte imbalances from a large volume of subcutaneous electrolyte-free fluid may be a realistic concern in small animals; therefore it is prudent to avoid subcutaneous administration of large volumes of low-sodium fluids to cats and small dogs. Other potential complications include infection resulting in subcutaneous cellulitis and skin necrosis from caustic or hypertonic fluids or fluids administered under high pressure into an unyielding subcutaneous space.
The volume administered at any single site is limited by the distensibility of subcutaneous tissue. Therefore fluids are usually administered in the subcutaneous space over the dorsal neck and cranial trunk, where loose connective tissue is abundant. Although the addition of hyaluronidase to fluids for hypodermoclysis therapy in humans increases the rate of absorption of fluid, there is no evidence that the addition of this enzyme improves patient tolerance.12,68 However, it may be of value in dogs and cats with limited distensibility of their subcutaneous tissue when rapid administration is necessary because of time constraints. The fluid should be warmed to body temperature before administration to limit patient discomfort and enhance local blood flow and absorption. The skin should be cleansed with a cotton ball and alcohol to remove debris from the surface. Fluid may be administered with a syringe and 22-gauge needle in small animals or by gravity flow with a fluid administration set through a 20- to 18-gauge needle in larger animals. One company markets a subcutaneous catheter (Endo-Sof, Global Veterinary Products, New Buffalo, Mich.) designed to be implanted for repeated use. Although the catheter material is inert and can stay in place for a long time, failure to adhere to strict aseptic technique will result in bacterial contamination.
Intravenous administration is the route of choice when blood volume expansion is desired. It is clearly superior to subcutaneous administration for any critically ill patient with poor perfusion of tissues. Indications for vein cannulation include administration of fluids, drugs, total parenteral nutrition, blood products, intravenous anesthetics, and as a precaution against the need for venous access in the event of an emergency.
Intraosseous fluid administration provides access to the vascular space via the capillary beds of the medullary vascular system. It is an excellent alternative to the intravenous route in neonates, (in whom vascular access is technically difficult) or animals with circulatory collapse. This route is best suited for rapid, short-term administration of fluids, blood products, or drugs in emergency situations.
Catheter product designs currently available include winged needle, over-the-needle, through-the-needle, and those placed through an introducer or over a guide wire (Table 15-1). Selection is influenced by operator experience, availability, cost, and patient requirements. Smaller diameter catheters and those made of soft material are less traumatic to veins than large or stiff catheters. For routine maintenance therapy, the smallest gauge catheter that provides adequate flow should be used. If rapid administration of fluid is required, the largest gauge size possible should be used (Table 15-2). The maximal fluid flow rate increases as the radius of the catheter lumen is increased. For small catheters (<14 gauge), this relationship is linear, whereas for larger catheters, flow rate increases geometrically with size and is proportional to the lumen radius raised to the fourth power (r4).25 Short over-the-needle catheters are preferred for rapid intravenous access in emergencies because they can be inserted rapidly and are available in sizes up to 8.5 French.
|Winged steel needle||Can be inserted rapidly with little to no skin prep||Suitable for short-term use only|
|High risk of extravasation|
|Over-the-needle (OTN)||Well suited for peripheral vein||Most brands cannot use for central access|
|Inexpensive||Cannot be tunneled very far subcutaneously|
|Technically easy to use||Stiff materials more damaging to veins|
|Multiple veterinary distributors||Unreliable for aspirating blood|
Fluid flow affected by limb position
|Over-the-needle with guide wire||Can be inserted into small/difficult veins||Same as OTN|
|Arterial catheters useful for dorsal pedal artery||More expensive than OTN|
|Through-the-needle (TTN)||Can be used for central access||Technically more difficult to insert|
|Useful for repeated blood collection||Greater potential for hemorrhage than OTN type|
|Can be tunneled subcutaneously||More expensive than OTN|
|Made of softer/less irritating material|
|Less likely to produce thrombophlebitis over time|
|Through introducer sheath with or without guide wire||Can be used to achieve central venous access||Same as TTN, plus:|
|Can insert relatively large/multilumen catheter||Requires drape/sterile field/sterile gloves|
|Can create a long subcutaneous tunnel|
|Catheter material may be very soft (silicone, polyurethane)|
|Can be placed in veins too difficult for TTN-style catheter|
|Weight||Jugular Vein (Through-the-Needle)||Limb Vein (Over -the-Needle)|
Winged needle catheters may be used for short-term (single dose) administration of fluid or drugs into a peripheral vein. They are available in needle sizes of 27 to 16 gauge and with various lengths of plastic tubing bonded to the needle and connecting to a Luer adapter. Plastic wings at the needle hub facilitate handling and securing the needle. The risk of needle puncture of the vessel wall and subsequent extravasation is high because the sharp needle bevel is left exposed within the lumen of the vein. Therefore these catheters are best used only for collection of blood or for single infusions of nonirritating drugs or fluids under direct supervision. They are usually positioned in the cephalic vein, where there is less risk of displacement by patient movement. They must be located sufficiently distal to the elbow so that joint flexion will not displace the needle through the vessel wall. Although these are not useful for long-term fluid administration, they have two major advantages for emergency or critical care patients: (1) they may be inserted rapidly with little or no skin preparation; and (2) in many operators’ experience they are the most effective device to obtain percutaneous venous access in cats (and occasionally small dogs) with poor peripheral perfusion, via cannulation of the medial cutaneous saphenous vein under direct visualization through the thin skin of the medial thigh.
Over-the-needle catheters are well suited for easy insertion into peripheral veins in companion animals. The wide range of available gauge sizes allows flexibility in vein selection and maximal flow rates. Some are designed for arterial cannulation (e.g., Arrow Radial Artery catheter, Arrow International, Reading, Pa.) and incorporate a wire guide stylet that facilitates placement. Multilumen catheters (e.g., the Arrow Twin Cath, Arrow International) allow infusion of incompatible solutions through a single catheter. In the past 15 years there has been an industry-wide move toward catheters that incorporate safety mechanisms to limit the risk of operator injury and exposure to patient blood. Safety catheters irreversibly retract or cover the needle after the vein is punctured and can be used for only one attempt.
Over-the-needle catheters are useful for short procedures such as anesthesia and for intravenous fluid administration for 48 to 72 hours. These catheters are usually positioned in the cephalic, accessory cephalic, medial and lateral saphenous, or femoral veins. Any other accessible superficial vein may be satisfactory (e.g., ear veins in rabbits or dogs with pendulous ears).
There are several disadvantages associated with over-the-needle catheters. They may fray or splinter at the tip during insertion and cause excessive injury to the vein with a high risk of thrombosis. They are difficult to secure adequately and may slide in and out of the skin with limb movement. This action increases the risk of trauma to the vein and may also facilitate entry of skin surface bacteria through the catheter wound and into the vein. When they are located in distal limb veins, fluid flow through these catheters is often affected by limb position (e.g., elbow flexion often stops gravity flow of fluids through a cephalic vein catheter). Several brands of these catheters are composed of stiff Teflon or irritating polypropylene and are not suited for extended dwell periods in an external jugular vein or in veins that cross a joint where motion enhances catheter-induced vessel trauma.
Through-the-needle catheters are long (6 to 36 inches) and are often used to gain deep or central venous access from peripheral sites. These catheters are generally known as midline catheters in human medicine because they are designed to obtain access to proximal limb veins from distant venipuncture sites. Because of the anatomy of the external jugular and lateral saphenous veins in companion animals, these catheters work well to obtain central venous access. This allows the catheter tip to be positioned in a large central vein with rapid blood flow, allowing safe administration of viscous or hypertonic solutions. It is often difficult to thread these catheters past the elbow and axillary regions of the forelimb; thus they are of limited usefulness in cephalic veins.
Through-the-needle style catheters are usually long and provide several advantages over short, over-the-needle style catheters. Body position and movement do not affect the rate of fluid flow when the tip of the catheter is positioned in a deep or central vein. Multiple blood samples may be withdrawn easily from these catheters. They may be anchored securely to the skin and tunneled extensively through subcutaneous tissue and are therefore less likely to conduct surface bacteria into a vein than are shorter catheters.51,57 However, small vein cannulation is often more difficult than with over-the-needle catheters, and the risk of catheter or air embolization during catheterization is greater.
Central venous catheters designed for insertion into a human internal jugular or subclavian vein use almost always use a guide wire placement technique to increase the likelihood of successful cannulation. Because they are composed of soft material, they either incorporate a wire stylet or are threaded over a preplaced guide wire using the technique of Seldinger.72 Some of the catheters marketed for use in humans are suitable for use in dogs and cats (e.g., Arrow Pediatric Central Venous Catheterization Sets, Arrow International). Some guide wire catheters are marketed specifically for use in dogs and cats (e.g., Mila International, Florence, Ky.; Global Veterinary Products). The guide wire technique allows central vein access via insertion into veins that may not be successfully cannulated otherwise. Other peripherally inserted central catheters (PICCs; Mila International, Global Veterinary Products) are inserted through a short, larger introducer sheath with or without a guide wire. A major advantage of these catheter designs is the availability of double or even triple lumen products that allow greater vascular access through a single catheter.
Catheter composition affects handling characteristics during insertion and influences the potential for thrombosis and phlebitis. Widely used catheter materials include polyvinyl chloride (PVC), polyethylene, polypropylene, polyurethane, silicon elastomer (Silastic), tetrafluoroethylene (TFE Teflon), and fluoroethylene-propylene (FEP Teflon) (Table 15-3). These materials are chemically inert, but leaching of plasticizers and stabilizing agents from some plastics probably contributes to the development of phlebitis, especially in small veins with low blood flow.63,75,85 Silicone elastomer catheters are the most chemically inert, whereas PVC, polypropylene, and polyethylene are the most reactive. Teflon and polyurethane are intermediate in reactivity. Some catheters composed of more irritating material are coated with silicone elastomer to reduce their reactivity. Catheter thrombogenicity is related not only to chemical reactivity but also to the stiffness of the material and the smoothness of its surface.18,33 Teflon is the stiffest material; polypropylene, PVC, and polyethylene are more flexible. Stiff catheters are easier to pass through the skin and subcutaneous tissues but are more prone to kinking and more likely to damage vessel walls and cause thrombophlebitis. Polyurethane elastomer (e.g., Vialon, Becton Dickinson, Franklin Lakes, N.J.) and silicone elastomer catheters are much softer and more flexible. Silicone elastomer catheters are so flexible that they are difficult to introduce into a vein without a stylet or guide wire.
Many brands of catheters are made radiopaque by the addition of heavy metal salts (barium or bismuth) to the plastic. When mixed uniformly into the material, these salts increase the roughness of the catheter surface and increase the risk of thrombosis.33 If embedded within the wall of the catheter, or if the catheter is coated with another, less thrombogenic material (e.g., silicon elastomer), this risk is lower. Heparin coating may significantly reduce catheter thrombus formation, at least for 1 to 2 days.67,74 Some manufacturers have developed antibiotic-coated catheters that appear to reduce the risk of catheter-associated sepsis.27,43,45 Examples of antiseptics either coated onto or impregnated into catheters include chlorhexidine-silver sulfadiazine and rifampicin-miconazole.27,43
Peripheral vein cannulation is most often performed in the cephalic and accessory cephalic veins of the thoracic limbs and the lateral saphenous vein of the pelvic limbs. Other suitable veins include the medial saphenous (cats), the femoral veins (in some cats and dogs), and the ear veins in dogs with pendulous ears. These veins may fill very slowly in animals with poor peripheral perfusion and can be difficult to visualize or palpate. In this setting, the saphenous veins may be superior (lateral in dogs, medial in cats) because the relatively thin skin overlying them allows better visualization and control over catheter insertion. Catheterization may be facilitated by the vascular access procedures described in the following sections.
Short-term administration of fluids may be accomplished using any vein, and choice of vein in this setting depends primarily on operator experience and catheter design. Central venous catheterization is preferred in patients that require long-term fluid administration or parenteral nutrition, administration of hypertonic solutions or irritating drugs, frequent blood sampling, or central venous pressure (CVP) monitoring. Central venous access is most easily accomplished by cannulation of the external jugular or saphenous veins. The right external jugular is preferred over the left because this vein joins the cranial cava in a straighter line through the brachycephalic trunk than does the left, facilitating catheter passage into the cranial vena cava.
The risk of infection is increased in the presence of bandage contamination. Catheters inserted into peripheral veins that are likely to be soiled by vomiting, diarrhea, or urine pose a greater threat. Therefore the saphenous veins are not ideal choices in animals with diarrhea or polyuria, and the cephalic vein is not a good choice in an animal with frequent vomiting. There is a greater threat of infection of catheters inserted through a cut-down incision or through skin that is wounded or infected. Therefore unhealthy skin is avoided, and catheters inserted through incisions are removed as soon as possible, ideally within 6 hours.
Catheters located in limb veins are particularly accessible to the animal’s teeth, and some animals chew at and damage or remove the catheter. Catheters located in an ear vein may prompt scratching and head shaking that eventually dislodge the device. Some form of restraint, such as an Elizabethan collar, may be necessary to prevent damage to catheters located at these sites. The risk of catheter damage is considerably lower when the jugular vein is used and bandaged adequately. Surprisingly, most sick dogs and cats do not disturb properly positioned, carefully bandaged intravenous catheters. Animals that chew or scratch at their catheters frequently do so because of excessive irritation. Catheters and bandages that were tolerated initially and subsequently provoke chewing or scratching should be carefully inspected for evidence of tightness, wetness, or infection.
There is a risk of thrombosis whenever a vein is cannulated. Thrombosis is more likely in small veins with low blood flow or when the intravascular portion of the catheter traverses a mobile joint. Some specific diseases such as preexisting phlebitis, glomerulonephritis, protein-losing enteropathy, autoimmune hemolytic anemia, and any disorder that causes systemic inflammation are complicated by increased risk of serious thrombosis and pulmonary thromboembolism.21,37,42,62 Intravenous catheterization in these animals is probably accompanied by a higher risk of clinically significant thrombosis than in other diseases. It may be advisable to avoid venous catheterization in these animals when possible. When catheterization is unavoidable, one should use short, soft, small diameter catheters that are removed as soon as possible. Compared with catheterization of peripheral veins, catheterization of the jugular vein in companion animals is probably not an independent risk factor for venous thrombosis and pulmonary thromboembolism, but the consequences of thrombosis in that location are more apparent and severe. Cats with aortic saddle thrombi have poor blood flow to their pelvic limbs and devitalization of those tissues. Pelvic limb vein catheterization in these animals is associated with a high risk of venous thrombosis and infection and must be avoided.
Healthy animals undergoing short-term catheterization for elective procedures (e.g., anesthesia for ovariohysterectomy) rarely develop phlebitis or sepsis from sloppy technique during catheter placement. In contrast, sick animals with compromised immunity may not tolerate even a minor breach of aseptic technique, and intravenous catheters may quickly become colonized and serve as a point source for bacteremia and septic phlebitis. With the exception of emergency venous access, these patients require careful aseptic technique for skin preparation and catheter insertion. If an intravenous catheter is to remain in place for more than a few hours, the skin must be prepared as for any surgical procedure. Every effort must be made to be thorough but gentle because abraded or scarified skin is not healthy and will support colonization by pathogenic bacteria. Key points include avoiding clipper burn and avoiding rough cotton gauze for skin cleansing:
1. A wide clip centered on the intended venipuncture site is performed. A No. 40 blade is used to obtain a close cut. The clipper blade must be well lubricated and held parallel to the skin (not raked across it) to limit clipper burn, and the coat is clipped sufficiently far from the point of insertion so that there is no risk the catheter will touch hair during the procedure. If it is not possible to clip a sufficiently wide area, consider wrapping the appendage or neck with a temporary bandage to hold down the hair coat and keep it out of contact with the catheter.
2. Wash your hands and apply a germicidal lotion (e.g., Avagard [3M, St. Paul, Minn.], Citrus II [Beaumont Products, Kennesaw, Ga.], IC Lotion [R&R Lotion, Scottsdale, Ariz.], or Purell [GOJO Industries, Akron, Ohio]). Don a clean examination glove on the dominant hand using a “no touch” technique. Treat this glove as though it were sterile, and do not touch its fingers with your bare hand when removing it from the container.
3. Local anesthesia with subcutaneous lidocaine often facilitates catheterization. Although some animals react to the transient sting of injected lidocaine, this is often less stressful than the sensation produced by a large-gauge catheter being forced through the skin. Local anesthesia also provides the option of making a facilitation incision at the venipuncture site (see the Percutaneous Facilitation Procedure section). If local anesthesia is desired, it should be done immediately after clipping to allow time to take effect while the skin is prepared. The skin is wiped once with an alcohol-soaked cotton ball, and the venipuncture site is anesthetized with 0.1 to 0.5 mL of lidocaine/bicarbonate 9:1 mixture administered subcutaneously. By mixing nine parts of lidocaine with one part of sodium bicarbonate solution, the sting of lidocaine is reduced.53,64 If made in advance, the lidocaine/bicarbonate mixture should be used within 1 month because the lidocaine in this mixture degrades at a rate of approximately 11% per week.82
4. The skin must be cleaned for at least 2 and preferably 3 minutes with cotton balls freshly soaked with the surgical scrub of choice. Do not use containers of premade antiseptic-soaked gauze or cotton balls; people reaching into the container with their bare hands contaminate these. Most antiseptic soaps require continuous wet contact for that entire time to be effective. This means that there is no rinsing with alcohol or water between scrubs until the full 2 to 3 minutes have elapsed. Frequent changing of the cotton balls facilitates removal of surface debris. The following antiseptic agents are useful:
5. Residual soap solution is removed from the skin and surrounding hair with cotton balls or gauze sponges soaked in alcohol, hydrogen peroxide, sterile water, or sterile saline solution. Soap left on the skin and coat will cause dermatitis—remove all of it.
4. One catheter injection cap, intravenous tubing set, syringe filled with drug or intravenous solution, catheter “T” piece, or other needleless injection site device (e.g., Interlink connectors, Baxter Healthcare, Deerfield, Ill.; CLAVE or CLC 2000 connectors, ICU Medical, San Clemente, Calif.; Abbott Laboratories, Abbott Park, Ill.) (Figure 15-1)
1. Because this device is intended for short infusions and because the stainless steel needle may be less likely to drag surface contamination into the wound, skin preparation may be minimal. Although not essential, clipping the hair at the injection site facilitates visualization of the vein for needle placement. Whether the coat is clipped, wipe the area once with alcohol-soaked cotton balls or gauze to remove dander and flatten the coat.
3. Flush the catheter with intravenous fluid or drug solution to purge air from the system. Disconnect the syringe from the tubing, and hold the catheter by its “wings” in your dominant hand. To prevent fluid from draining out of the system, hold the tubing coiled in the same hand, with the Luer adapter end held level with the needle tip.
6. Blood flows into the catheter tubing when the vein is entered. Advance the needle fully into the vein. Lift the needle slightly as it is advanced, a technique that is important for any venipuncture, to minimize the risk of penetrating the vessel wall (Figure 15-2).
8. Attach the syringe with drug solution or intravenous fluid to the tubing, and fill the catheter with solution. Alternatively, an intravenous fluid line may be attached if immediate fluid administration is desired. Examine the skin near the end of the catheter for any evidence of extravasation at the start of the infusion.
9. If the catheter has two pliable wings, lay them flat on the skin surface, and wrap a single piece of white tape over them and around the limb. This tape should be applied snugly but not tightly enough to occlude the vein. The tape does not cover the point of entry.
10. If the needle is to remain in place and unobserved, it may be prudent to apply a gauze sponge with antiseptic ointment to the skin penetration site, and secure this to the limb with a second piece of 1-inch white tape.
Figure 15-2 Technique for placement of a needle into a superficial vein. Once the vein has been entered, the bevel remains oriented toward the skin, and the shaft of the needle is lifted up against the superficial wall of the vessel as the needle is advanced. The needle bevel functions like the curved tip of a ski and prevents the point from catching on the vessel wall.
3. A small incision through the skin facilitates insertion of large-gauge catheters (Figure 15-3, A) or placement of the catheter through tough skin (see the Percutaneous Facilitation Procedure section). The techniques for direct and indirect insertion are the same as noted previously. Indirect catheterization is strongly preferred because this forms a subcutaneous tunnel between the point of entry through the skin and the point of entry into the vein that serves as a barrier to bacterial migration.52,56
4. An assistant restrains the animal and occludes the proximal vein. Grasp the catheter firmly at the junction of the needle and catheter hubs, ensuring that the catheter does not loosen and partially slide off the needle during manipulation. Never touch the skin at the point of insertion, and never touch the needle/catheter shaft. The needle bevel is directed up during the procedure. Advance the needle, first subcutaneously and then into the vein. Penetration of the vein often is heralded by a distinct “pop” as the needle punctures the tough vessel wall and by the flow of blood into the needle hub (Figure 15-3, B).
5. Advance the needle and catheter as a unit for another 3 to 5 mm. This ensures that both the needle and catheter tips are within the lumen of the vein. During this maneuver, hold the needle shaft as parallel to the long axis of the vein as practical, and lift the catheter tip away from the deep wall of the vein (as described for winged needle catheterization, see Figure 15-2). Once the catheter tip has entered the vessel, slide the catheter off the needle and into the lumen of the vein (Figure 15-3, C). If the catheter material is very soft and flexible, an alternative technique is to retract the needle 5 mm back into the catheter and advance the catheter and needle in unison all the way into the vein.
9. If a cephalic or lateral saphenous vein is cannulated, wrap the catheter hub with a strip of 1.5-to 2.5-cm (0.5 or 1 inch) white tape, and extend this strip around the limb. The tape should be pressed tightly onto the catheter hub but loosely anchored to the limb (Figure 15-3, E-G). The goal is to secure it to the limb, yet avoid wrapping it too tightly. When cannulating the medial saphenous or femoral vein (or any vein at a large, flat surface), the catheter hub should be anchored to the skin with a suture to limit in-and-out movement during flexion and extension of the limb. To provide a secure anchor without strangulating skin, place a single loop of suture material through the skin under the catheter hub, and create a slightly loose loop incorporating skin only by tying a secure square knot. Then tie the free ends of this anchor tightly around the catheter hub with a surgeon’s knot.
11. If the catheter is to remain in place for more than 6 hours, it should be covered with a short, light bandage that extends 6 to 12 cm (2 to 4 inches) above and below the point of insertion (Figure 15-3, G-J).
Figure 15-3 Catheterization of the cephalic vein with an over-the-needle style catheter. A, The skin has been clipped widely, the insertion site blocked with a 9:1 lidocaine/bicarbonate mixture, and the skin has been aseptically prepared as described in the text. An 18-gauge injection needle is used to create a facilitation incision in the skin. The skin at that site must never be touched. B, The tip of the needle-catheter assembly is advanced into the skin puncture and proximally, parallel to the long axis of the vein, through the subcutis as far as practical before entering the vein. The catheter shaft is not allowed to contact the distal limb hair. The catheter is angled toward the vein and advanced into it. The goal should be to “snag” the outer layer of the vein with the needle tip. The flow of blood into the clear needle hub depicted here confirms venipuncture. C, The needle is held stationary, and the catheter is advanced fully to the Luer hub, or as deeply as possible without crossing a joint. D, The needle is removed, and an injection plug or “T” piece is connected to the Luer fitting. Any air is aspirated, and the system is purged with heparinized saline. E, The end of a 1-cm-wide (0.4 inch) strip of white porous tape is secured around the catheter hub, and then the remainder of the tape is wrapped firmly, but loosely, around the limb. F, A 5- × 5-cm (2- × 2-inch) gauze with antiseptic ointment is laid over the skin insertion site and secured with more porous white tape. G, In this example, a 0.5-inch-wide (1-cm) strip is applied as a “yoke” around the hub, with the long ends directed proximally. Incorporation of those ends into the bandage will help prevent the catheter from becoming partially withdrawn. H and I, The catheter and adjacent limb are wrapped with 5- to 8-cm-wide (2- to 3-inch) cotton cast padding, applied heavily enough to provide some support to the catheter and prevent a tourniquet effect. A layer of stretch gauze is applied more snugly over the cast padding. A final layer of stretch bandaging material (with or without adhesive) is applied, more snugly still, over the stretch gauze. The “T” piece extension is secured to the stretch bandage material with white tape to prevent any traction on the Luer connection. It may be connected to an intravenous administration set, needleless connector, or a new locking Luer syringe filled with heparinized saline. The bandage is initialed and dated.
3. Proper positioning is critical for successful cannulation of the external jugular vein. In animals with thin skin and large, easily distended veins, the procedure is easily accomplished with the animal restrained in lateral recumbency. In this position, the external jugular vein is usually located directly lateral to the trachea. Sternal recumbency or a sitting position is preferred in animals that resist being restrained on their side and in those with thick skin or small, poorly distensible veins. In both the sternal and sitting positions, the animal should be held with its pelvic limbs directed away from the side chosen for venipuncture (Figure 15-4, A). This maneuver makes the neck more convex on that side and reduces the depth of the jugular furrow. An assistant elevates the head, and the nose should be initially held in a horizontal position and directed away from the intended site at a 30- to 45-degree angle with the median plane. If the animal has abundant loose skin on the neck, elevating the nose tenses the skin and facilitates identification of the vein. It is helpful to experiment with different head and nose positions until the optimal position is found. If you are right handed, occlude the vein at the thoracic inlet with the thumb of the left hand, and use your left index finger to palpate the vein. The patient’s right external jugular vein is preferred because it may be easier to advance the catheter into the cranial vena cava from this side. The puncture site should be 1 to 2 cm (about 0.5 to 0.75 inch) lateral to the vein and in the cranial half of the neck.
4. As with over-the-needle catheters, a small skin incision facilitates insertion of large-gauge catheters and eases access through tough skin (Figure 15-4, B). The techniques for direct and indirect insertion are the same as noted previously. Indirect insertion is strongly preferred because this forms a subcutaneous tunnel between the point of entry through the skin and the point of entry through the vein that serves as a barrier to bacterial migration. Never touch the skin at the point of insertion, and never touch the needle/catheter shaft.
5. Fully retract the catheter into the sterile sheath so that it is not visible at the needle bevel. Grasp the device firmly at the hub of the needle, and penetrate the skin with the bevel of the needle facing away from the skin surface. When possible, advance the needle subcutaneously parallel to the vein for at least 2 cm (0.75 inch) before introducing it into the vein (Figure 15-4, C). Penetration of the vein is usually heralded by a distinct pop as the needle punctures the tough wall of the vessel. A flashback of blood entering the needle hub is usually, but not always, seen (Figure 15-4, D). The catheter may then be manipulated through the sterile sheath and advanced through the needle.
6. If you suspect successful venipuncture but do not see a flashback, try advancing the catheter through the needle. If the catheter is not easily advanced, it is likely that the catheter has entered subcutaneous tissue. In that case, withdraw the entire assembly in unison. Do not pull the catheter back through the needle until the needle is withdrawn because of the risk of shearing on the needle bevel. Inspect the needle and catheter for damage; if none is present, it may be used for another attempt. Any subsequent attempts can be made through the original skin wound.
7. Because the needle forms a hole in the vessel wall that is larger in diameter than the catheter, postcatheterization hemorrhage is occasionally a problem. This can be minimized by holding the venipuncture site above the level of the heart to reduce venous pressure, such as by performing jugular vein cannulation with the animal in a sitting position. Accurate needle positioning minimizes laceration of the vein, and rapid application of a sterile dressing and bandage provides direct compression and tamponade.
10. Attach the “T” piece, injection cap, or needleless connection device to the Luer hub. If using a “T” piece, first attach a syringe with heparinized saline solution to it, and purge all air from the lumen. If you use an injection cap, purge the air from its dead space by filling it with sterile solution. Attach the device, aspirate any air from the catheter, and confirm catheter patency by successful aspiration of blood. Purge the catheter with the solution (Figure 15-4, G).
11. If the catheter was inserted completely, withdraw it 1 to 2 cm (0.5 to 0.75 inch) from the skin, and dry this exposed section with a sterile gauze sponge. Wrap a 2.5- to 5-cm (1 to 2 inches) “butterfly” of waterproof white tape around the catheter and needle guard. This piece of tape should bridge the needle guard and the exposed portion of catheter to where it enters the skin (Figure 15-4, H). Through-the-needle catheters frequently fail because of kinking at the point of exit from the needle guard or the point of entry into the skin. The tape prevents this by forming a protective “sandwich” around the catheter as it exits the needle guard or hub.
12. If the catheter was too long, leave an appropriate length outside the skin, and incorporate it into a “sandwich” of white tape as described previously. If there is sufficient length, it may be coiled into a loop that is completely encased between the two layers of tape.
13. Dry the Luer connection at the junction of the needle and catheter hubs with a sterile gauze sponge, and compress them together firmly. If desired, a drop of cyanoacrylate adhesive may be applied to the surfaces before forcing them together (Figure 15-4, I). This connection may also be bridged with a “sandwich” created by two strips of 1-inch white tape that cover the first “butterfly” strip of tape and extend from the suture site all the way to the injection cap (Figure 15-4, J).
16. Anchor the catheter with a strip of porous white tape. If a jugular vein is cannulated, firmly apply the tape to the base of the needle guard, and then wrap it in a manner that pulls the catheter in a dorsal direction on the ipsilateral side to help prevent the catheter from slipping ventrally later (Figure 15-4, L). The goal is to secure the catheter to the skin, not to wrap it on tightly.
17. Apply layers of cast padding, stretch gauze, and elastic bandage material, wrapping up (dorsally) on the ipsilateral side in the case of a jugular vein catheter. While wrapping the catheter bandage, hold the limb or neck in a natural position (partially flexed limb or nose pointed down) to prevent binding (Figure 15-4, M-O).
18. If the catheter is intended to be positioned into the anterior vena cava or the intrathoracic portion of the caudal vena cava, a lateral thoracic radiograph should be obtained to confirm ideal location of the catheter tip.