Central Venous Pressure Catheterization And Monitoring

Central venous catheterization should be performed (1) when rapid delivery of cardiac medications to the coronary circulation is required during cardiopulmonary resuscitation (CPR);15 (2) for access when peripheral veins are inadequate; and (3) when measurement of central venous pressure is desired. Hypovolemic shock by itself is not, however, an indication for central venous catheterization. Many patients who require large-volume infusions or transfusion with multiple units of blood can be managed with large-bore peripheral IVs. Determination of central venous pressure is indicated when (1) massive volume repletion is administered to elderly patients or those with heart disease, (2) fluid administration is being monitored in patients with visceral trauma and severe head injuries, and (3) pericardial tamponade is suspected.

A variety of sites and techniques are available to access the central circulation. Most commonly, a catheter is placed in the upper vena cava via the internal jugular or subclavian vein; less commonly, via the external jugular vein. The femoral vein may also be used, but it requires subsequent immobilization of the leg and the procedure is accompanied by a higher rate of infection and thrombosis. Emergency physicians should become skilled in at least two approaches for central venous catheterization, using one as primary while reserving the other as a backup.

Use of peripheral veins to access the central circulation and measure central venous pressure has the indisputable advantage of avoiding the risk associated with direct puncture of the subclavian and internal jugular veins. However, low flow is inevitable due to the long course of the catheter from the extremity to the superior vena cava. Peripheral sites also fail frequently due to catheter malposition and kinking. In the arm the brachial-basilic system must be used, since catheters in the cephalic system often become kinked in the plexus of veins at the shoulder. Smooth passage and correct tip positioning are more likely if the patient is sitting with his or her head angulated sharply toward the catheterized arm, the arm is held abducted, and the catheter is wire-guided. In emergency situations, however, this time-consuming approach to the central circulation is often impractical. The femoral and axillary veins are safe and reliable alternatives. However, in the presence of cardiac arrest, internal jugular or subclavian lines are highly desirable for drug administration.

Anatomy

A brief review of anatomy is warranted (Fig 17-1 and Fig 17-3). The major veins of the upper thorax are deeply and centrally placed and well protected by the clavicles, sternum, and strap muscles. The internal jugular veins join the subclavian veins to form the brachiocephalics (innominates), which, in turn, join to become the superior vena cava. The sternocleidomastoid muscle attaches separately by two heads to the sternum and clavicle; the triangle formed by these two heads and the clavicle is just above the internal jugular vein. The right internal jugular has a straight path into the superior vena cava, whereas all the other major tributaries curve. Both external jugular veins enter the subclavian veins at close to right angles. The subclavian veins lie immediately posterior to the junction of the medial and middle thirds of the clavicle and are anterior and inferior to the artery; the pleura are immediately posterior and inferior to the subclavian vessels ( Fig 17:4). The internal jugular vein usually lies anterolateral to the carotid. The basilic and brachial veins join to form the axillary vein. The cephalic vein joins the axillary vein more superiorly, just before it becomes the subclavian vein. The axillary vein continues the distal subclavian vein and runs medial to the axillary artery from the distal arm. The femoral vein is medial to the femoral artery. The relative locations of components of the neurovascular-lymphatic bundle in the groin from lateral to medial can be recalled by the mnemonic NAVEL (nerve, artery, vein, empty space, lymphatic).

FIG. 17-3. Relationship of major torso veins to other anatomy.
FIG. 17-4. Coronal section through the midclavicle.

Equipment and General Technique for Central Venous Catheterization

All equipment should be at the bedside, including a central venous (CV) pressure manometer if CV pressure monitoring is desired. Catheter-through-needle devices, whose large 14-gauge insertion needles are prone to complications and whose 16-gauge catheters allow maximum gravity-assisted flow of 100 to 150 mL/min, have been largely supplanted by wire-guided (Seldinger) catheters.6 Their use allows use of a small needle to place any size catheter into a vessel.

The patient should be placed in a neutral to maximum of 30° head rotation and 15° Trendelenburg's position, and the entire route of the neck should be prepped so that all three approaches are possible in case the primary approach fails. The right side is preferred over the left, since (1) the lung apex is slightly lower, (2) there is a straight relationship between the right internal jugular vein and the superior vena cava, and (3) the left-sided thoracic duct cannot be injured. With unilateral chest trauma in the absence of suspected vessel injury, the attempt should be on the injured side in order to protect the uninjured hemithorax in the event of complications from the procedure.

When the procedure is performed electively, preceding the approach for catheter placement with a 22-gauge needle attached to a 5- or 10-mL syringe filled with lidocaine facilitates local anesthesia and allows the operator to "locate" the vein. After landmarks are identified, an 18-gauge needle is then inserted into the vein ( Fig.. 17-5A). Gentle, continuous negative pressure on the syringe should be maintained until free flow of blood is obtained. The syringe is removed and a fingertip is used to occlude the hub before wire insertion (Fig 17-5B). This often forgotten or ignored maneuver is important to prevent aspiration of air, particularly in internal jugular or subclavian vein catheterizations. The needle is then removed ( Fig 17-5C), leaving just the wire in the vein. A small skin incision (1 to 2 mm) is often made over the wire (Fig 17,:5.C>) to facilitate smooth entry of the catheter, which is threaded over the wire and into the vein with a twisting motion ( Fig 17-.5.E). The wire is then removed, leaving only the catheter in place (Fig 17-5F). If a large-bore catheter is necessary, the apparatus is used with a venodilator. In this situation, the venodilator is removed with the wire, leaving the large-bore 8.5-Fr catheter sheath in place.

FIG. 17-5. Seldinger technique of catheter insertion (wire-guided). (From Conahan TJ III, Schwartz AJ, Geer RT: Percutaneous catheter introduction: The Seldinger technique. JAMA 237:446, 1977. With permission.)

The principal advantages of wire-guided catheters are (1) use of a small (and thus safer) needle for insertion; (2) the step-up capability with a venodilator, allowing for the higher flow rates often required in trauma resuscitation; (3) the flexibility of exchanging standard intravenous catheters, central venous catheters, and Swan-Ganz catheters without repeated stabs; and (4) the use of J wires to access the central circulation from the external jugular vein.

Ultrasound visualization of the central vein while puncture is attempted reduces the number of punctures necessary for cannulation and the time required to establish central access while also reducing the incidence of complications. The technique is particularly helpful when the traditional landmark-based techniques fail or are impractical due to vascular anomalies or body habitus, or when patients with a coagulopathy require central venous access. 78

Complications

The three most common serious complications of direct puncture of a central vein are pneumothorax, arterial puncture, and local infection. With subclavian puncture, the incidence of pneumothorax is 2 to 4 percent, significantly greater than with either internal jugular approach. The incidence of arterial puncture, 3 to 7 percent, is similar for all approaches. In children, success rates for subclavian venous catheterization are higher than for internal jugular venous catheterization and the complication rate is lower. Other, less common complications include hydrothorax, chylothorax (left side), hydromediastinum, air or catheter embolism, thrombosis, dysrhythmia, nerve injuries, osteomyelitis of the clavicle, catheter tip perforation of the superior vena cava (causing hydromediastinum or hydrothorax) or right atrium (causing hydropericardium), knotting with other catheters, and puncture of endotracheal tube cuffs.9 Care in executing the procedure and in the selection of patients who will benefit from central venous catheterization will minimize the occurrence of complications.

Technique of Commonly Used Approaches

EXTERNAL JUGULAR VEIN The external jugular vein is a superficial, readily accessible vessel that lies in the subcutaneous tissue over the sternocleidomastoid muscle. The vein courses inferior and joins the subclavian vein under the clavicle ( Fig 1.7-3). Central venous access via this route has an increased success rate (57

to 95%) if a J wire-guided catheter assembly is used. Success is enhanced by introducing the wire through a 16-gauge catheter rather than through a needle, using a J tip with no more than a 3-mm radius, exaggerating head tilt with marked traction on the skin of the neck, and—when initial attempts with wire through needle techniques are met with resistance at the level of the clavicle—twisting the tip of the J wire 180° before making a second attempt. It is also recommended that a small syringe (insulin or TB syringe) be attached to the introducing needle-catheter assembly for both stabilization and to maintain negative pressure. The external jugular vein is very pliable and collapses easily during initial skin puncture. Gently withdrawing the needle back while maintaining suction improves chances of catheterization.

The main disadvantage of the external jugular catheterization is difficulty in securing the catheter in the neck. The venous valves within its course may impede catheter placement as well. The constant movement of the patient makes most external jugular lines short-lived. Also, turning of the neck impedes flow of the infusion, making the line unreliable for fluid or medications unless it is constantly watched.

INTERNAL JUGULAR VEIN There are three traditional approaches to catheterization of the internal jugular vein. The central approach may be the most popular. After the patient is placed in Trendelenburg position, the needle should puncture the skin 1 cm below the apex of a triangle at the midpoint formed by the tendinous and muscular heads of the sternocleidomastoid muscle. The palpation and definition of the margin of the carotid artery is not as important as in the anterior approach but is helpful in locating the vein and to avoid puncture of the artery. Held at a 60° angle with the plane of the skin, the needle is directed slightly lateral to the axis of the body (lateral to the pulsation of carotid artery). Common helpful landmarks for needle direction include the ipsilateral nipple and a plane parallel to the medial border of the lateral head of the sternocleidomastoid muscle. Blood return should be obtained within 3 cm, since the vein is very superficial here. If the attempt fails, the needle should be withdrawn completely before the next attempt.

In the lateral or posterior approach, the head is turned slightly away from the selected side; after the patient is placed in Trendelenburg postion, the needle is inserted at the posterior margin and deep to the sternocleidomastoid muscle two to three fingerbreadths above the clavicle and directed toward the suprasternal notch ( Fig

1.7.-6). Frequently, the external jugular vein crosses the lateral wall of the sternocleiomastoid muscle at this point. If it does, the needle should be inserted at the junction of the crossing at a 90° angle to the external jugular vein. Blood should be aspirated within 4 to 5 cm. The carotid artery is just behind this path, albeit slightly posterior, and may be at increased risk for puncture.

FIG. 17-6. A. Posterior approach for internal jugular venipuncture. B. Central approach. C. Anterior approach. (From Textbook of Advanced Life Support, 2d ed. Dallas, American Heart Association, 1990, pp 149-150. With permission.)

The anterior approach and its variants may well be the most technically difficult. After the carotid is identified, the needle is entered at the midpart of the medial border of the sternocleidomastoid. With the fingers over the carotid, the needle is directed 30 to 45° from the midline plane toward the ipsilateral nipple. This approach has the greatest likelihood of carotid puncture and appears to be the least favored of the IV cannulation approaches.

SUBCLAVIAN VEIN The subclavian vein is still the most commonly used site for central venous access. The right side is preferred because the pleural dome is lower on that side. The fact that the point of insertion is in a broad, flat area of the chest makes it ideal for use when central venous access will be required for a prolonged period. The patient is placed in the Trendelenburg position. If the patient is a child, a towel is placed under the thoracic spine. This may also be helpful in some adults.

The infraclavicular subclavian approach is the most commonly taught technique. There is no universal agreement on exactly where the needle should enter ( Fig

1.7.-7.). The bisection of the middle and medial thirds of the clavicle is an appropriate landmark. Another is a point just lateral and inferior to the junction of the clavicle and first rib. For this latter approach the needle is aimed at the bisection of the junction. Using the former landmark, the skin is penetrated about 1 cm inferior to the clavicle and directed inferomedially. With the index or middle finger of the other hand in the suprasternal notch, the needle is aimed at the superior and most posterior portion of the ipsilateral clavicular head ( Fig 17-7). Inferomedial orientation of the needle bevel facilitates entry of the wire or catheter into the brachiocephalic vein.

Vessel entry occurs at a depth of 3 to 4 cm.

For the supraclavicular subclavian approach, the patient's head is turned slightly away from the involved side. The needle enters just above the clavicle, 1 cm lateral to the insertion of the clavicular head of the sternocleidomastoid muscle and 1 cm posterior to the clavicle. It is then directed to bisect the angle formed between the sternocleidomastoid and the clavicle, at an angle of 10° above the horizontal, with the tip pointing just caudad to the contralateral nipple. Keeping the bevel up prevents trapping of the wire or catheter against the inferior wall of the vessel. Vessel puncture occurs at a depth of 2 to 3 cm.

FEMORAL VEIN Femoral vein catheterization is used when the vessels of the upper body are not suitable, and when access is required above and below an injury. Although femoral vein catheterization is somewhat easier than subclavian or internal jugular catheterization, the insertion site is difficult to sterilize and keep clean, and patient movement may make it difficult to keep the line secured.

The patient should be supine with the ipsilateral hip in a neutral to slightly externally rotated position. The approximate position of the femoral vein can be determined by dividing the distance between the anterior superior iliac spine and the pubic tubercle into three equal segments ( Fig 17-2). The femoral artery usually lies at the junction of middle and distal thirds. If the femoral pulse is palpable, the needle puncture site should be 1.5 cm medial and 1.5 cm inferior to the inguinal ligament. Once venous blood is obtained, the guide wire is inserted though the needle, the needle is removed, and the catheter is inserted over the wire.

This access can be used for the measurement of central venous pressure, for intravenous pacing, for Swan-Ganz pulmonary artery catheterization, and to administer large volumes of fluids rapidly; the increased risk of infection and thrombosis make it less than ideal as a route for hyperalimentation. It is not an ideal central access site for administration of ACLS medications.

AXILLARY VEIN The axillary vein (Fig 17-2) is used for central venous access when the femoral, subclavian, and jugular veins are unavailable. This useful technique is unfortunately rarely used by emergency physicians. With practice, the success rate for central access via the axillary vein is similar to that for puncture of the internal jugular or subclavian vein. There is no risk of pneumothorax and the method has the advantage that, when arterial puncture occurs, direct pressure can be applied.

Patients are placed supine with head-down tilt and the arm abducted to 45°. In this position the axillary vein follows a straight course from the arm to the subclavian vein. An insertion point is chosen approximately 2.5 cm inferior to the axillary pulse and lateral to the midclavicular line. The introducer needle is then inserted along a line formed by the insertion point and suprasternal notch, at an angle of 30° to the skin, and directed parallel to the course of the artery toward the chest wall. In children and thin adults, the artery is easily palpable.

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