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Arterial Catheterization
CHAPTER 201 ARTERIAL CATHETERIZATION Elisa M. Mazzaferro,
MS, DVM, PhD, DACVECC
KEY POINTS • Arterial catheters can be placed into the dorsal pedal, radial, femoral, coccygeal, and auricular arteries. • Arterial catheters can be used for direct blood pressure monitoring and procurement of arterial blood samples for blood gas and other analyses. • Arterial catheters are generally well tolerated but can easily become dislodged with excessive patient movement. • Use of arterial catheters should be avoided whenever possible in patients with severe coagulation abnormalities due to the risk of arterial hemorrhage.
The placement of an indwelling arterial catheter is a necessary and useful procedure for many critically ill veterinary patients. Arterial catheters can be used for frequent collection of arterial blood samples when evaluating an animal’s arterial oxygenation and ventilation and for direct arterial blood pressure monitoring. To avoid complications associated with hemorrhage or arterial thrombosis, the animal’s coagulation status should be considered before placement of a catheter into any artery. If severe thrombocytopenia (<50,000 platelets/µl) or prolonged activated partial thromboplastin time and prothrombin time are present, the patient is at a greater risk of hemorrhage from the site of arterial catheterization. Arterial catheters are most frequently placed in the dorsal pedal artery.1 Alternate locations for arterial catheter placement include the auricular artery on the dorsomedial surface of the ear pinna2 and the femoral, coccygeal, radial, and brachial arteries.3 With practice, arterial catheterization and maintenance is not technically difficult and can provide information that helps guide lifesaving treatment interventions in the most critically ill veterinary patients.3
PATIENT PREPARATION Although arterial catheters can be placed in an awake patient, placement is generally easier in an anesthetized animal. The dorsal pedal artery is the most suitable site for an awake patient given the restraint necessary. The site of arterial catheterization should be chosen based on the patient’s anatomy and consideration of underlying diseases, such as vomiting, diarrhea, or aural hematomas. For example, placement of a radial artery catheter may be inappropriate in a vomiting patient due to the risk of catheter contamination. Similarly, placement of a femoral, coccygeal, or dorsal pedal artery catheter is inappropriate in a patient with severe diarrhea. Auricular catheters are challenging to maintain in an awake patient and tend to better suited to an anesthetized patient. Because of the increased risks of auricular, femoral, coccygeal, and radial catheter dislodgement in ambulatory patients, dorsal pedal catheters are preferred, whenever possible.1 1040
PERCUTANEOUS ARTERIAL CATHETER PLACEMENT Once the proposed site of arterial catheterization has been chosen, the operator should become familiar with the animal’s anatomy, palpating over the artery as it courses along the leg, tail, or ear and feeling carefully for the arterial pulse. The designated site of catheterization should be clipped, then aseptically cleaned with an antimicrobial scrub before catheter placement. The operator should wash his or her hands carefully and ideally wear gloves to maintain aseptic technique during the procedure. Because arterial catheter placement relies largely on palpation of the pulse, it may not always be practical to wear gloves. Careful hand cleaning before catheter placement is recommended if gloves are not worn.
Dorsal Pedal Artery Catheterization For placement of a catheter in the dorsal pedal artery, the patient should be positioned in lateral recumbency with the leg containing the proposed catheter site located down, adjacent to the table. The fur should be shaved on the anterior portion of the limb from the level of the tarsus distally along the length of the metatarsal bones. The artery is usually palpable just distal to the hock, in between the second and third metatarsal bones.1 Once the artery has been palpated and the site clipped and aseptically prepared, a 24- to 20-gauge over-the-needle catheter can be placed percutaneously or via a percutaneous facilitation technique. Percutaneous facilitation refers to the practice of making a small nick in the skin using the bevel of a 20-gauge needle. Care should be taken not to penetrate the artery during this process because arterial spasm is common and can make further attempts at arterial catheterization unsuccessful until a palpable pulse returns. Whether the overthe-needle catheter is placed directly through the skin or through a nick incision created by percutaneous facilitation, the needle and catheter should be inserted through the skin at a 15- to 30-degree angle over the palpable pulse.1 The needle and catheter should be directed dorsally and laterally to the metatarsals over the site of a palpable pulse in small maneuvers, with careful observation for a flash of blood in the catheter hub. Once a flash of blood is seen in the hub of the catheter, a judgment must be made as to if the catheter itself is within the artery or if a very small advancement is required. The catheter should then be pushed off the stylet into the artery. Pulsatile arterial blood should be observed as soon as the stylet is withdrawn from the catheter if arterial catheterization has been successful.1 If the catheter snags or does not feed easily, the catheter can be gently pulled over the stylet and another attempt made at catheterization. In some cases, when the original attempt at catheterization has failed, the catheter can be left in its original place and a second attempt made proximally if an arterial pulse is still palpable (Figure 201-1). Leaving the original catheter in place prevents hematoma formation, which may preclude further attempts at arterial catheterization. Should all attempts at arterial catheterization fail, a pressure
CHAPTER 201 • Arterial Catheterization
FIGURE 201-1 If percutaneous catheterization is unsuccessful, the original catheter can be left in place and an attempt can be made to place the catheter into the artery more proximally. This technique helps to prevent hematoma formation during catheter placement.
bandage should be placed for a minimum of 15 minutes to prevent hemorrhage and hematoma formation.1 Once the dorsal pedal artery catheter is in place, a Luer-Lock Tport or male adapter flushed with heparinized saline should be attached to the catheter hub to prevent further blood loss. The catheter should be flushed with heparinized saline, then secured in place with lengths of 1 2 - and 1-inch white adhesive tape. The catheter hub and adjacent skin and fur should be carefully wiped dry of any blood and other liquids or debris before tape is placed around the catheter hub and distal extremity. The tape should be secured tightly around the catheter hub to prevent dislodgement of the catheter. Additional lengths of 1-inch tape should be secured under the catheter hub and around the distal extremity. Some operators use a combination of surgical glue, suture, and tape to secure the catheter in place,1 although this is not always necessary. The site of catheter insertion should be covered with bandage material and then labeled “Arterial catheter, not for IV infusion” to prevent inadvertent injection of fluids or drugs into the arterial line.3
A
B FIGURE 201-2 A, For auricular artery catheterization, the pinna is supported by a roll of gauze held beneath it. The artery is directly visualized, and the catheter is inserted through the skin into the artery. B, When a flash of blood is evident in the hub, the catheter is carefully advanced into the artery.
Femoral Artery Catheterization Except for anatomic landmarks, percutaneous placement of a femoral artery catheter is similar to placement of a catheter into the dorsal pedal artery. The patient is placed in lateral recumbency, and the medial thigh clipped and aseptically scrubbed from the inguinal region distally to the stifle. The femoral artery pulse is palpable on the medial thigh ventral to the inguinal region and proximal to the stifle. The use of ultrasonography to facilitate identification of the femoral artery has been described and decreases the total time for catheter placement from 10 minutes to 1 minute.4 The over-theneedle catheter should be placed at a 20- to 30-degree angle through the skin and inserted in a proximal direction, with careful observation for a flash of blood in the catheter hub. Once a flash of blood is seen, the catheter should be advanced off the stylet into the femoral artery. As the stylet is removed from the catheter, pulsatile arterial blood will be visible if the catheter has been placed into the artery. A flushed Luer-Lock T-port or male adapter should be attached to the catheter hub. Once the catheter has been flushed with heparinized saline, a piece of butterfly tape should be placed securely around the catheter hub. The length of butterfly tape can be secured to the patient’s skin with sutures on either side of the catheter hub. An additional length of 1-inch white tape should be placed under the catheter and around the limb circumferentially to secure the catheter in place. Bandaging material should be used to cover the catheter. As for all arterial catheters, the bandage should be carefully labeled “Arterial catheter, not for IV Infusion” to prevent inadvertent infusion of drugs or fluids into the arterial line.
Auricular Artery Catheterization Catheterization of the auricular artery can be performed in dogs with large ears, such as hounds and hound mixes. The auricular artery is catheterized on the lateral side of the of the ear pinna.2 This type of catheter is usually placed while the patient is under heavy sedation or general anesthesia. The auricular artery pulse can be palpated on the dorsal aspect of the lateral pinna and the vessel traced toward the ear tip. The fur over the artery should be clipped and the site aseptically scrubbed. With the patient placed in sternal or lateral recumbency, the ear is pulled gently so that the pinna is held perpendicular to the skull. The tip of the ear should be bent ventrally toward the operator with the operator’s fingers supporting the pinna from below. The artery is now bent at a perpendicular angle so that it can be traced from the point of a palpable pulse to the ear tip, and the over-the-needle catheter (22 to 24 gauge) can be placed through the skin directly into the artery, with careful observation for a flash of blood in the hub of the catheter (Figure 201-2). Once a flash of blood is seen in the catheter hub, the catheter can be gently fed off of the stylet into the artery. The catheter should be flushed with heparinized saline solution, and a Luer-Lock male adapter or T-port inserted into the catheter hub to prevent further hemorrhage. The skin adjacent to the catheter hub should be dried carefully, and several drops of surgical glue should be placed adjacent to the catheter hub to help secure it to the skin. The catheter can be held in place with lengths of 1 2 -inch tape secured around the catheter hub and under the
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catheter. The ear can be supported from below with rolled 4 × 4-inch gauze squares or rolls of gauze. Because the weight of the bandage is cumbersome, awake and alert patients may attempt to shake their heads, potentially causing catheter dislodgement. For this reason, the use of an auricular artery catheter is often limited to obtunded, comatose, or anesthetized patients.
Radial Artery Catheterization Catheterization of a radial artery is technically more difficult than catheter placement in other anatomic locations but can be performed in large dogs. The patient should be placed in lateral recumbency and the palmar aspect of the forelimb clipped just proximal to the large carpal pad and just distal to the accessory carpal pad, where the arterial pulse is palpable. The clipped area should be aseptically scrubbed. The operator should hold the patient’s paw in one hand, palpating the arterial pulse with a thumb or forefinger. With the other hand, an over-the-needle catheter should be inserted through the skin at a 15- to 20-degree angle toward the palpable arterial pulse. The operator should watch carefully for a flash of blood in the catheter. As soon as a flash of blood is visible, the catheter should be pushed off of the stylet into the artery. Once in place, the catheter should be flushed with heparinized saline and capped with a Luer-Lock T-port or male adapter. The skin adjacent to the catheter hub should be dried. A length of 1 2 -in white adhesive tape should be secured around the catheter hub and the patient’s distal extremity. Additional lengths of 1-inch white adhesive tape should be placed under the catheter hub and then around the patient’s limb, with the catheter pushed proximally to secure the catheter in place. The catheter can be bandaged with layers of bandage material. As for all arterial catheters, the bandage should be carefully labeled “Arterial catheter, not for IV infusion” to prevent infusion of drugs and other substances into the artery.
Coccygeal Artery Catheterization The coccygeal artery pulse is easily palpable on the ventromedial aspect of the tail just distal to the tail base. The fur over the palpable pulse should be clipped, then the site aseptically scrubbed. The patient can be positioned in dorsal or lateral recumbency, depending on operator preference. The arterial pulse should be palpated in between coccygeal vertebrae, and the over-the-needle catheter should be inserted through the skin at a 15-degree angle and pushed cranially toward the tail base until a flash of blood is seen in the catheter (Figure 201-3). Once a flash of arterial blood is visualized, the catheter should be fed off of the stylet and then flushed with heparinized saline. A Luer-Lock T-port or male adapter should be fixed to the
catheter hub to prevent hemorrhage. The skin adjacent to the catheter hub should be wiped clean and dry, and a length of 1 2 -inch white adhesive tape should be secured to the catheter hub and around the patient’s tail. Additional lengths of 1-inch white adhesive tape should be placed under the catheter hub to push it cranially and secure it in place. The catheter can be wrapped with bandage material to maintain cleanliness. Because coccygeal catheters easily become contaminated with feces during defecation and can become dislodged with patient movement, coccygeal artery catheter use is limited largely to intraoperative procedures.
SURGICAL CUTDOWN FOR ARTERIAL CATHETER PLACEMENT If percutaneous placement of an arterial catheter is unsuccessful, surgical cutdown can be performed to allow direct visualization and catheterization of the artery. Patient anatomy largely limits surgical cutdown procedures for arterial catheter placement to the dorsal pedal and femoral arteries. Sterile technique should be used at all times. The area over the dorsal pedal or femoral artery should be clipped and aseptically scrubbed, then draped with sterile field towels secured with towel clamps. A small bleb of 2% lidocaine should be inserted in the skin, with care taken to avoid iatrogenic intravenous or arterial administration of the local anesthetic. The skin over the arterial pulse should be incised, with close attention to avoiding laceration of the artery and vein underneath the skin. The artery should be visible directly under the skin, surrounded by perivascular fascia. The dorsal pedal artery is usually visible on top of the metatarsal bones.3 Several drops of lidocaine should be placed directly over the artery to prevent arterial spasm as the perivascular fascia is bluntly dissected away from the vessel with a curved mosquito hemostat. Once the fascia has been removed from around the artery, a length of suture can be placed around the artery to help lightly elevate it parallel with the skin incision. It is very important to remove every bit of the perivascular fascia before attempting catheter placement.1 Once the artery has been gently elevated from the incision, the over-the-needle catheter can be inserted directly into the vessel, with care taken to not penetrate through the other side. Excessive traction on the artery can cause arterial spasm, which makes catheterization difficult. A flash of blood will be observed in the hub of the catheter once the catheter has been introduced into the lumen of the artery. The catheter can then be fed off of the stylet, flushed, and capped with a Luer-Lock T-port or male adapter. The suture that was used to elevate the artery can be used to secure the catheter around the catheter hub. The skin over the catheter should be closed with nonabsorbable suture, and the catheter taped in place, bandaged, and labeled as with any other arterial catheter.
MAINTENANCE OF THE ARTERIAL CATHETER
FIGURE 201-3 A coccygeal artery catheter can be placed on the ventral surface of the tail, just caudal to the tail base, in between coccygeal vertebrae.
Depending on the mobility of the patient, arterial catheters can be connected to a continuous flushing system with heparinized saline, or intermittently flushed every 1 to 4 hours.3 In extremely small patients, care needs to be taken to avoid excessive heparinization. Like other vascular catheters, arterial catheters should be examined on a daily basis for signs of erythema or infection. The bandage should be changed daily or more frequently as needed due to soiling. Small volumes of flush solution should be injected to maintain catheter patency. However, other infusions (drugs, fluids, or blood products) should never be administered into an arterial line. Because patient dislodgement of an arterial line can result in significant hemorrhage, it is ideal for patients with indwelling arterial catheters to be under constant supervision. If this is not possible, then measures should be
taken to reduce the likelihood of catheter dislodgement, such as application of an Elizabethan collar.
system. The arterial blood sample should be analyzed immediately or placed on ice for arterial blood gas analysis.
THREE-SYRINGE TECHNIQUE The three-syringe technique should be employed whenever a blood sample is obtained from an arterial catheter. In this technique, the catheter is first flushed with 1 2 ml of heparinized saline. The same syringe is then used to withdraw 3 ml of blood from the catheter, and it is saved in an aseptic manner, to be infused back into the patient through a peripheral venous catheter, where possible. The desired volume of arterial blood is then withdrawn into an appropriate syringe. The catheter is then flushed with 2 to 3 ml of heparinized saline and clamped off or reconnected to the continuous flushing
REFERENCES 1. Hughes D, Beal MW: Emergency vascular access, Vet Clin North Am Small Anim Pract 30(3):491-507, 2000. 2. Waddell LS: Direct blood pressure monitoring, Clin Tech Small Anim Pract 15(3):111-118, 2000. 3. Beal MW, Hughes D: Vascular access: theory and techniques in the small animal emergency patient, Clin Tech Small Anim Pract 15(2):101-109, 2002. 4. Ringold SA, Kelmer E: Freehand ultrasound guided femoral arterial catheterization in dogs, J Vet Emerg Crit Care 18(3):306-311, 2008.
MS, DVM, PhD, DACVECC
KEY POINTS • Arterial catheters can be placed into the dorsal pedal, radial, femoral, coccygeal, and auricular arteries. • Arterial catheters can be used for direct blood pressure monitoring and procurement of arterial blood samples for blood gas and other analyses. • Arterial catheters are generally well tolerated but can easily become dislodged with excessive patient movement. • Use of arterial catheters should be avoided whenever possible in patients with severe coagulation abnormalities due to the risk of arterial hemorrhage.
The placement of an indwelling arterial catheter is a necessary and useful procedure for many critically ill veterinary patients. Arterial catheters can be used for frequent collection of arterial blood samples when evaluating an animal’s arterial oxygenation and ventilation and for direct arterial blood pressure monitoring. To avoid complications associated with hemorrhage or arterial thrombosis, the animal’s coagulation status should be considered before placement of a catheter into any artery. If severe thrombocytopenia (<50,000 platelets/µl) or prolonged activated partial thromboplastin time and prothrombin time are present, the patient is at a greater risk of hemorrhage from the site of arterial catheterization. Arterial catheters are most frequently placed in the dorsal pedal artery.1 Alternate locations for arterial catheter placement include the auricular artery on the dorsomedial surface of the ear pinna2 and the femoral, coccygeal, radial, and brachial arteries.3 With practice, arterial catheterization and maintenance is not technically difficult and can provide information that helps guide lifesaving treatment interventions in the most critically ill veterinary patients.3
PATIENT PREPARATION Although arterial catheters can be placed in an awake patient, placement is generally easier in an anesthetized animal. The dorsal pedal artery is the most suitable site for an awake patient given the restraint necessary. The site of arterial catheterization should be chosen based on the patient’s anatomy and consideration of underlying diseases, such as vomiting, diarrhea, or aural hematomas. For example, placement of a radial artery catheter may be inappropriate in a vomiting patient due to the risk of catheter contamination. Similarly, placement of a femoral, coccygeal, or dorsal pedal artery catheter is inappropriate in a patient with severe diarrhea. Auricular catheters are challenging to maintain in an awake patient and tend to better suited to an anesthetized patient. Because of the increased risks of auricular, femoral, coccygeal, and radial catheter dislodgement in ambulatory patients, dorsal pedal catheters are preferred, whenever possible.1 1040
PERCUTANEOUS ARTERIAL CATHETER PLACEMENT Once the proposed site of arterial catheterization has been chosen, the operator should become familiar with the animal’s anatomy, palpating over the artery as it courses along the leg, tail, or ear and feeling carefully for the arterial pulse. The designated site of catheterization should be clipped, then aseptically cleaned with an antimicrobial scrub before catheter placement. The operator should wash his or her hands carefully and ideally wear gloves to maintain aseptic technique during the procedure. Because arterial catheter placement relies largely on palpation of the pulse, it may not always be practical to wear gloves. Careful hand cleaning before catheter placement is recommended if gloves are not worn.
Dorsal Pedal Artery Catheterization For placement of a catheter in the dorsal pedal artery, the patient should be positioned in lateral recumbency with the leg containing the proposed catheter site located down, adjacent to the table. The fur should be shaved on the anterior portion of the limb from the level of the tarsus distally along the length of the metatarsal bones. The artery is usually palpable just distal to the hock, in between the second and third metatarsal bones.1 Once the artery has been palpated and the site clipped and aseptically prepared, a 24- to 20-gauge over-the-needle catheter can be placed percutaneously or via a percutaneous facilitation technique. Percutaneous facilitation refers to the practice of making a small nick in the skin using the bevel of a 20-gauge needle. Care should be taken not to penetrate the artery during this process because arterial spasm is common and can make further attempts at arterial catheterization unsuccessful until a palpable pulse returns. Whether the overthe-needle catheter is placed directly through the skin or through a nick incision created by percutaneous facilitation, the needle and catheter should be inserted through the skin at a 15- to 30-degree angle over the palpable pulse.1 The needle and catheter should be directed dorsally and laterally to the metatarsals over the site of a palpable pulse in small maneuvers, with careful observation for a flash of blood in the catheter hub. Once a flash of blood is seen in the hub of the catheter, a judgment must be made as to if the catheter itself is within the artery or if a very small advancement is required. The catheter should then be pushed off the stylet into the artery. Pulsatile arterial blood should be observed as soon as the stylet is withdrawn from the catheter if arterial catheterization has been successful.1 If the catheter snags or does not feed easily, the catheter can be gently pulled over the stylet and another attempt made at catheterization. In some cases, when the original attempt at catheterization has failed, the catheter can be left in its original place and a second attempt made proximally if an arterial pulse is still palpable (Figure 201-1). Leaving the original catheter in place prevents hematoma formation, which may preclude further attempts at arterial catheterization. Should all attempts at arterial catheterization fail, a pressure
CHAPTER 201 • Arterial Catheterization
FIGURE 201-1 If percutaneous catheterization is unsuccessful, the original catheter can be left in place and an attempt can be made to place the catheter into the artery more proximally. This technique helps to prevent hematoma formation during catheter placement.
bandage should be placed for a minimum of 15 minutes to prevent hemorrhage and hematoma formation.1 Once the dorsal pedal artery catheter is in place, a Luer-Lock Tport or male adapter flushed with heparinized saline should be attached to the catheter hub to prevent further blood loss. The catheter should be flushed with heparinized saline, then secured in place with lengths of 1 2 - and 1-inch white adhesive tape. The catheter hub and adjacent skin and fur should be carefully wiped dry of any blood and other liquids or debris before tape is placed around the catheter hub and distal extremity. The tape should be secured tightly around the catheter hub to prevent dislodgement of the catheter. Additional lengths of 1-inch tape should be secured under the catheter hub and around the distal extremity. Some operators use a combination of surgical glue, suture, and tape to secure the catheter in place,1 although this is not always necessary. The site of catheter insertion should be covered with bandage material and then labeled “Arterial catheter, not for IV infusion” to prevent inadvertent injection of fluids or drugs into the arterial line.3
A
B FIGURE 201-2 A, For auricular artery catheterization, the pinna is supported by a roll of gauze held beneath it. The artery is directly visualized, and the catheter is inserted through the skin into the artery. B, When a flash of blood is evident in the hub, the catheter is carefully advanced into the artery.
Femoral Artery Catheterization Except for anatomic landmarks, percutaneous placement of a femoral artery catheter is similar to placement of a catheter into the dorsal pedal artery. The patient is placed in lateral recumbency, and the medial thigh clipped and aseptically scrubbed from the inguinal region distally to the stifle. The femoral artery pulse is palpable on the medial thigh ventral to the inguinal region and proximal to the stifle. The use of ultrasonography to facilitate identification of the femoral artery has been described and decreases the total time for catheter placement from 10 minutes to 1 minute.4 The over-theneedle catheter should be placed at a 20- to 30-degree angle through the skin and inserted in a proximal direction, with careful observation for a flash of blood in the catheter hub. Once a flash of blood is seen, the catheter should be advanced off the stylet into the femoral artery. As the stylet is removed from the catheter, pulsatile arterial blood will be visible if the catheter has been placed into the artery. A flushed Luer-Lock T-port or male adapter should be attached to the catheter hub. Once the catheter has been flushed with heparinized saline, a piece of butterfly tape should be placed securely around the catheter hub. The length of butterfly tape can be secured to the patient’s skin with sutures on either side of the catheter hub. An additional length of 1-inch white tape should be placed under the catheter and around the limb circumferentially to secure the catheter in place. Bandaging material should be used to cover the catheter. As for all arterial catheters, the bandage should be carefully labeled “Arterial catheter, not for IV Infusion” to prevent inadvertent infusion of drugs or fluids into the arterial line.
Auricular Artery Catheterization Catheterization of the auricular artery can be performed in dogs with large ears, such as hounds and hound mixes. The auricular artery is catheterized on the lateral side of the of the ear pinna.2 This type of catheter is usually placed while the patient is under heavy sedation or general anesthesia. The auricular artery pulse can be palpated on the dorsal aspect of the lateral pinna and the vessel traced toward the ear tip. The fur over the artery should be clipped and the site aseptically scrubbed. With the patient placed in sternal or lateral recumbency, the ear is pulled gently so that the pinna is held perpendicular to the skull. The tip of the ear should be bent ventrally toward the operator with the operator’s fingers supporting the pinna from below. The artery is now bent at a perpendicular angle so that it can be traced from the point of a palpable pulse to the ear tip, and the over-the-needle catheter (22 to 24 gauge) can be placed through the skin directly into the artery, with careful observation for a flash of blood in the hub of the catheter (Figure 201-2). Once a flash of blood is seen in the catheter hub, the catheter can be gently fed off of the stylet into the artery. The catheter should be flushed with heparinized saline solution, and a Luer-Lock male adapter or T-port inserted into the catheter hub to prevent further hemorrhage. The skin adjacent to the catheter hub should be dried carefully, and several drops of surgical glue should be placed adjacent to the catheter hub to help secure it to the skin. The catheter can be held in place with lengths of 1 2 -inch tape secured around the catheter hub and under the
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PART XXII • PROCEDURES
catheter. The ear can be supported from below with rolled 4 × 4-inch gauze squares or rolls of gauze. Because the weight of the bandage is cumbersome, awake and alert patients may attempt to shake their heads, potentially causing catheter dislodgement. For this reason, the use of an auricular artery catheter is often limited to obtunded, comatose, or anesthetized patients.
Radial Artery Catheterization Catheterization of a radial artery is technically more difficult than catheter placement in other anatomic locations but can be performed in large dogs. The patient should be placed in lateral recumbency and the palmar aspect of the forelimb clipped just proximal to the large carpal pad and just distal to the accessory carpal pad, where the arterial pulse is palpable. The clipped area should be aseptically scrubbed. The operator should hold the patient’s paw in one hand, palpating the arterial pulse with a thumb or forefinger. With the other hand, an over-the-needle catheter should be inserted through the skin at a 15- to 20-degree angle toward the palpable arterial pulse. The operator should watch carefully for a flash of blood in the catheter. As soon as a flash of blood is visible, the catheter should be pushed off of the stylet into the artery. Once in place, the catheter should be flushed with heparinized saline and capped with a Luer-Lock T-port or male adapter. The skin adjacent to the catheter hub should be dried. A length of 1 2 -in white adhesive tape should be secured around the catheter hub and the patient’s distal extremity. Additional lengths of 1-inch white adhesive tape should be placed under the catheter hub and then around the patient’s limb, with the catheter pushed proximally to secure the catheter in place. The catheter can be bandaged with layers of bandage material. As for all arterial catheters, the bandage should be carefully labeled “Arterial catheter, not for IV infusion” to prevent infusion of drugs and other substances into the artery.
Coccygeal Artery Catheterization The coccygeal artery pulse is easily palpable on the ventromedial aspect of the tail just distal to the tail base. The fur over the palpable pulse should be clipped, then the site aseptically scrubbed. The patient can be positioned in dorsal or lateral recumbency, depending on operator preference. The arterial pulse should be palpated in between coccygeal vertebrae, and the over-the-needle catheter should be inserted through the skin at a 15-degree angle and pushed cranially toward the tail base until a flash of blood is seen in the catheter (Figure 201-3). Once a flash of arterial blood is visualized, the catheter should be fed off of the stylet and then flushed with heparinized saline. A Luer-Lock T-port or male adapter should be fixed to the
catheter hub to prevent hemorrhage. The skin adjacent to the catheter hub should be wiped clean and dry, and a length of 1 2 -inch white adhesive tape should be secured to the catheter hub and around the patient’s tail. Additional lengths of 1-inch white adhesive tape should be placed under the catheter hub to push it cranially and secure it in place. The catheter can be wrapped with bandage material to maintain cleanliness. Because coccygeal catheters easily become contaminated with feces during defecation and can become dislodged with patient movement, coccygeal artery catheter use is limited largely to intraoperative procedures.
SURGICAL CUTDOWN FOR ARTERIAL CATHETER PLACEMENT If percutaneous placement of an arterial catheter is unsuccessful, surgical cutdown can be performed to allow direct visualization and catheterization of the artery. Patient anatomy largely limits surgical cutdown procedures for arterial catheter placement to the dorsal pedal and femoral arteries. Sterile technique should be used at all times. The area over the dorsal pedal or femoral artery should be clipped and aseptically scrubbed, then draped with sterile field towels secured with towel clamps. A small bleb of 2% lidocaine should be inserted in the skin, with care taken to avoid iatrogenic intravenous or arterial administration of the local anesthetic. The skin over the arterial pulse should be incised, with close attention to avoiding laceration of the artery and vein underneath the skin. The artery should be visible directly under the skin, surrounded by perivascular fascia. The dorsal pedal artery is usually visible on top of the metatarsal bones.3 Several drops of lidocaine should be placed directly over the artery to prevent arterial spasm as the perivascular fascia is bluntly dissected away from the vessel with a curved mosquito hemostat. Once the fascia has been removed from around the artery, a length of suture can be placed around the artery to help lightly elevate it parallel with the skin incision. It is very important to remove every bit of the perivascular fascia before attempting catheter placement.1 Once the artery has been gently elevated from the incision, the over-the-needle catheter can be inserted directly into the vessel, with care taken to not penetrate through the other side. Excessive traction on the artery can cause arterial spasm, which makes catheterization difficult. A flash of blood will be observed in the hub of the catheter once the catheter has been introduced into the lumen of the artery. The catheter can then be fed off of the stylet, flushed, and capped with a Luer-Lock T-port or male adapter. The suture that was used to elevate the artery can be used to secure the catheter around the catheter hub. The skin over the catheter should be closed with nonabsorbable suture, and the catheter taped in place, bandaged, and labeled as with any other arterial catheter.
MAINTENANCE OF THE ARTERIAL CATHETER
FIGURE 201-3 A coccygeal artery catheter can be placed on the ventral surface of the tail, just caudal to the tail base, in between coccygeal vertebrae.
Depending on the mobility of the patient, arterial catheters can be connected to a continuous flushing system with heparinized saline, or intermittently flushed every 1 to 4 hours.3 In extremely small patients, care needs to be taken to avoid excessive heparinization. Like other vascular catheters, arterial catheters should be examined on a daily basis for signs of erythema or infection. The bandage should be changed daily or more frequently as needed due to soiling. Small volumes of flush solution should be injected to maintain catheter patency. However, other infusions (drugs, fluids, or blood products) should never be administered into an arterial line. Because patient dislodgement of an arterial line can result in significant hemorrhage, it is ideal for patients with indwelling arterial catheters to be under constant supervision. If this is not possible, then measures should be
taken to reduce the likelihood of catheter dislodgement, such as application of an Elizabethan collar.
system. The arterial blood sample should be analyzed immediately or placed on ice for arterial blood gas analysis.
THREE-SYRINGE TECHNIQUE The three-syringe technique should be employed whenever a blood sample is obtained from an arterial catheter. In this technique, the catheter is first flushed with 1 2 ml of heparinized saline. The same syringe is then used to withdraw 3 ml of blood from the catheter, and it is saved in an aseptic manner, to be infused back into the patient through a peripheral venous catheter, where possible. The desired volume of arterial blood is then withdrawn into an appropriate syringe. The catheter is then flushed with 2 to 3 ml of heparinized saline and clamped off or reconnected to the continuous flushing
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