alt="Photo depicts distal end of a locking loop, or pigtail, catheter. The catheter coil is straightened over a stylet and trocar for placement (a), and then locked into the loop configuration using the suture upon removal of the stylet and trocar (b)."/>
Figure 1.7 Distal end of a locking loop, or pigtail, catheter. The catheter coil is straightened over a stylet and trocar for placement (a), and then locked into the loop configuration using the suture upon removal of the stylet and trocar (b).
Vascular Access
Vascular access is critical in emergency patients, especially those undergoing surgery. Peripheral venous catheters are most commonly used, since they are relatively inexpensive, widely available, and can be placed quickly in emergency situations. However, they do not usually allow for repeated blood sample collection and are not appropriate for hyperosmolar fluids, including total or partial parenteral nutrition (TPN, PPN). These catheters can also be dislodged, soiled, and if a small‐bore catheter is used, they will not permit rapid administration of large volumes of fluids or medications. Vessels commonly used for peripheral catheters in small animal patients are the cephalic or accessory cephalic veins, lateral saphenous vein, or distance branches the medial saphenous vein [88]. Clipping of the hair and sterile preparation of the site are preferred, but not possible in all emergency situations. Failure to adequately prepare the skin prior to catheter placement has been associated with increased positive bacterial cultures compared with those that were aseptically placed [89]. In severely hypovolemic patients for whom these vessels cannot be cannulated percutaneously, surgical cut‐down to facilitate vascular access can be performed quickly and safely in small animal patients. Catheters placed without adequate skin preparation and sterile technique or with an emergency surgical cut‐down procedure should be considered temporary and removed once additional vascular access is obtained and the patient is more stable to prevent infection.
When repeated blood sample collection is anticipated, or for administration of multiple fluids or medications simultaneously, including TPN or PPN, central venous catheterization should be considered. Central catheters can have up to four lumens, which is convenient for concurrent administration of several intravenous therapies. If administration of parenteral nutrition is anticipated, one lumen should be reserved specifically for this use and labeled accordingly. Central catheters are generally placed in larger vessels, including the jugular vein and medial and lateral saphenous veins. They are most commonly placed using the Seldinger, or over the wire, technique (Video 1.3). Surgical cut‐down for vascular access for Seldinger technique or venotomy and through the needle (BD Intracath, Argon Medical Devices, Franklin Lakes, NJ) catheters can also be used. Regardless of the technique for placement, since a large vessel is being accessed, adequacy of primary and secondary hemostasis must be confirmed prior to placement [88, 90]. Strict aseptic technique must be followed. It is also important to have adequate patient restraint, which generally requires sedation or anesthesia, since maintenance of positioning and discomfort of vessel dilation is not well tolerated by many awake patients. The catheter is secured to the skin with sutures, and the insertion site covered by a protective wrap.
When intravenous catheterization is not possible, which is often the case in neonatal and small pediatric patients, intraosseous (IO) catheterization provides a rapid, safe method for delivery of fluid therapy and medications. This is because the capillary network within the marrow cavity is in direct communication with the nutrient and emissary veins that drain into the central circulation. Crystalloids, colloids, blood products and medications, including those for cardiopulmonary resuscitation, can be administered via the IO route and can be absorbed rapidly enough to be effective for the treatment of hypovolemic shock and cardiopulmonary arrest [91–96]. Sites commonly used for IO catheterization include the trochanteric fossa of the femur, proximal tibia, tibial tuberosity, wing of the ileum, the ischium and greater tubercle of the humerus [88, 92], with the trochanteric fossa and tibia used most commonly. Contraindications of placement of an IO catheter include fracture of the bone intended for cannulation, pneumatic bones in birds, and evidence of infection near the intended catheter site. Bone growth is not impacted by IO catheterization [95]. IO catheterization can be achieved with a variety of techniques, including standard hypodermic needles and spinal needles, IO infusion needles, a spring‐loaded penetration injection gun (Vet B.I.G Bone Injection Gun (15‐G), WaisMed Ltd, Houston, TX) and an automatic rotary insertion drill (EZ‐IO (15‐G Pediatric Needle Set), Vidacare Corporation, San Antonio, TX.). In a cat cadaveric study comparing these devices, the injection gun was found to be faster and easier to use, but there were no differences detected between insertion site (humerus or tibia), complications or success between the injection gun, rotary drill or manual IO catheter [96].
Direct arterial blood pressure measurement should be considered in any hemodynamically unstable patient. It allows for continuous, accurate pressure determination in the face of hypotension, hypertension, and arrhythmias. Indwelling arterial catheters can also be used to obtain blood samples, particularly for arterial blood gas analysis. Arteries generally accessible for percutaneous placement of an arterial catheter include the dorsal metatarsal artery (most commonly used), the coccygeal artery in the tail, the auricular artery in the dorsal pinna, the femoral artery, and the radial artery [88,97–99]. Maintenance of arterial catheters in all locations, except for the dorsal metatarsal artery, is difficult in mobile patients and is generally reserved for use in sedated or anesthetized patients. Femoral, dorsal metatarsal, and coccygeal artery catheters can also become contaminated with urine and/or feces, so consideration of these issues is important prior to catheter placement. Cats tend to have poor collateral circulation. It is not recommended to leave arterial catheters in cats for longer than six to eight hours because of concern for ischemic injury to the tissues distal to the catheter [97]. Contraindications for arterial catheterization include lack of close monitoring capabilities, thrombocytopenia, thrombocytopathia, and coagulopathy.
Once the course of the artery is determined by palpation and the site is aseptically prepared, an over‐the‐needle catheter is used to puncture the artery from an angle of 15–30 degrees above the vessel. Pulsatile blood flow will be observed in the hub of the catheter upon successful arterial cannulization. If percutaneous placement of an arterial catheter is not possible, access to the dorsal metatarsal or femoral artery can be achieved with a surgical cut‐down or ultrasound guidance [98]. Care must be taken to avoid damaging the artery, femoral vein, or sciatic nerve during the initial skin incision and approach to the femoral artery. The catheter is secured with tape and/or sutures depending on the catheter type placed and placement method use. Once the arterial catheter is in place, it can be used to collect arterial blood samples after an adequate pre‐sample of blood is taken (generally 3–6 ml of blood into syringes with small amounts of heparinized saline). Clear labeling of an arterial catheter is imperative to ensure that only heparinized saline is injected into the artery. Blood collected from the artery as a pre‐sample and medications should never be injected into the arterial catheter. The catheter can also be connected to non‐compliant tubing with heparinized saline and a pressure transducer for continuous arterial blood pressure monitoring.
Analgesia, Sedation and Anxiolytics
The need for sedation and anxiolytics in the stressed or scared veterinary patient and timely analgesics for those in pain cannot be overstated. This is particularly true in patients needing emergency surgery, as many conditions requiring emergency surgical intervention create significant discomfort or pain. Anxiety and stress are present in many patients with respiratory compromise, especially those with upper airway obstruction, and should be addressed immediately to provide relief for the patient and more accurate patient assessment. As with other body systems,