1 Define central venous catheterization

Central venous catheterization involves inserting a catheter into the venous circulation and advancing it so its distal orifice is positioned immediately adjacent to or within the right atrium of the heart (Figure 25-1).

Figure 25-1 Placement of the central venous catheter.

2 What are the perioperative indications for placement of a central venous catheter?

Guiding fluid replacement

Evaluating cardiac function

Providing access for the following:

Aspiration of air emboli that can occur during neurosurgical procedures

Drug infusion

Blood and fluid infusion

Introducing a pulmonary artery catheter or transvenous pacemaker

Blood sampling

3 What are the nonoperative indications for placement of a central venous catheter?

Hyperalimentation

Temporary hemodialysis

Long-term chemotherapy

Frequent therapeutic plasmapheresis

4 What is the best approach to central venous cannulation?

Numerous access points are available for introduction of a catheter into the venous circulation. All approaches carry risks, and none will work successfully for every patient. Therefore it is important to become familiar with several approaches: subclavian vein, internal jugular vein, antecubital external jugular vein, and femoral vein. It is also of interest that peripheral venous pressure when measured at the antecubital vein closely mirrors the central venous pressure (CVP).

5 Describe the subclavian vein approach

The subclavian approach is commonly used because of the ease of access to the vessel. The subclavian vein is best cannulated from the subclavicular approach with the patient in the Trendelenburg position. The skin puncture is made just lateral to, and one fingerbreadth below, the costoclavicular ligament, which can be identified by a notch two thirds of the length down the clavicle. The needle is directed along the posterior border of the clavicle in the direction of the sternal notch until venous blood is aspirated.

6 Describe the internal jugular vein approach

There are several approaches to the internal jugular vein, three of which are briefly described here. The patient is put in the Trendelenburg position.

Low anterior: Locate the point at which the sternal and clavicular heads of the sternocleidomastoid muscle join. Introduce the needle at this point and direct it at a 30-degree angle to the skin. Advance the needle toward the ipsilateral nipple until venous blood is aspirated.

High anterior: Palpate the carotid artery at the level of the cricothyroid membrane. Introduce the needle just lateral to the carotid pulsation and advance it toward the ipsilateral nipple at a 30-degree angle until venous blood is aspirated. This approach frequently requires penetration of the sternocleidomastoid muscle by the introducer needle.

Posterior: Locate the junction of the posterior border of the sternocleidomastoid muscle and the external jugular vein. Introduce the needle just posterior to this point and advance it along the deep surface of the muscle toward the ipsilateral corner of the sternal notch until venous blood is aspirated.

7 Describe the external jugular vein approach

When the patient is in a Trendelenburg position, the external jugular vein frequently can be visualized where it crosses the sternocleidomastoid muscle. The needle is advanced in a direction paralleling the vessel and is introduced into the vein approximately two finger widths below the inferior border of the mandible. Difficulty may arise in advancing the catheter or guidewire into the central circulation from the external jugular vein approach because the patient’s anatomy frequently directs the catheter into the subclavian rather than the innominate vein. It is also frequently difficult to pass the guidewire or catheter past the clavicle.

8 When is the femoral vein approach used?

The femoral vein is not a preferred approach because of the high risk of infection. Femoral venous cannulation may be undertaken when subclavian or internal jugular catheterization is unsuccessful. Femoral lines should be removed as soon as it is practical.

9 Review the different types of central venous catheters

Single-lumen catheters may have single distal port or multiport tips. Triple-lumen catheters have three channels and lumens at slightly different positions on the distal cannula, providing ports for simultaneous drug infusion, blood drawing, and CVP monitoring. They are available in 7.5- and 9-Fr sizes. A percutaneous introducer sheath is designed for insertion of a pulmonary artery catheter into the central circulation. It is a large-bore catheter (9 Fr) and has a side port that can be used for CVP monitoring or for fluid infusion. Some catheters are heparin coated.

10 How is a catheter introduced into the central venous circulation?

Before cannulation is attempted, Trendelenburg positioning will increase venous pressure at the target vessel. As the needle is advanced toward a vessel, slight and constant aspiration is required. Occasionally during needle advancement the vessel walls will collapse on themselves so the needle passes through the entire vessel and blood can be aspirated by slowly withdrawing the needle, all the while gently aspirating. Finally, thorough knowledge of adjacent vital structures is important to avoid unwarranted complications.

Although a catheter can be inserted through a large-bore needle, the most common technique involves passing it over a guidewire, commonly referred to as the Seldinger technique. An 18- or 20-G needle is introduced into the vessel, and a guidewire is threaded through the needle and into the vein. The needle is removed, leaving the guidewire in place. The catheter is then passed over the guidewire and into the vessel. Finally the guidewire is removed. The obvious benefit of the Seldinger technique rests in the use of a smaller-gauge introducer needle.

11 In attempting a central venous puncture, dark blood returns. Does this satisfy you that you are indeed within a vein?

Arterial blood may be dark because the patient is cyanotic, cardiac output is inadequate, or the patient may have methemoglobinemia, for example. The flow of blood also may be nonpulsatile in cardiac failure. The best way to determine whether you are indeed in a vein is to thread a short, small-gauge catheter (e.g., 18- or 20-G) over the wire, remove the wire, and transduce the small catheter.

12 How is central venous pressure measured?

The central venous catheter is attached to a fluid-filled manometer or electronic pressure transducer. The pressure at the distal orifice is transmitted through the fluid path within the catheter and, if a manometer is used, supports the fluid column within the manometer. If the base of the fluid column is placed at the level of the right atrium, the height of the fluid column represents the pressure (in centimeters of H₂O) at the distal orifice of the catheter, the CVP. More commonly the catheter is attached to a pressure transducer that converts the pressure transmitted via the catheter into an electrical signal that is displayed (in millimeters of mercury) on a real-time display screen (1 mm Hg = 1.3 cm of H₂O). When measuring CVP, it is crucial to place the pressure transducer or base of the manometer at the same (atrial) level each time because a variance of only a few centimeters from that level will result in a significant measurement error since the range of CVP is only 0 to 13 cm of H₂O. In contrast, variation in the transducer position during arterial pressure measurement will result in a much smaller error since the range of arterial pressures is 0 to 200 mm Hg, and an error in transducer positioning for pulmonary artery pressure measurement would fall somewhere in between.

13 At what point on the body should central venous pressure be measured?

The ideal point at which to measure CVP is at the level of the tricuspid valve. It is at this point that in the healthy heart hydrostatic pressures caused by changes in body position are almost zero. This phenomenon exists because, as the pressure at the tricuspid valve changes (e.g., if it increases from position change), the right ventricle will fill to a greater degree, right ventricular output will transiently increase, and the change in pressure at the tricuspid valve will be brought back toward zero. The opposite will occur if pressure at the tricuspid valve decreases.

An external landmark for the tricuspid is a point 2 inches behind the sternum, roughly the anterior axillary line, at the fourth intercostal space. Ongoing adjustment is necessary to ensure that the transducer or manometer is consistently at this level whenever the patient’s position or bed height is changed (Figure 25-2).

Figure 25-2 Positioning of the patient for central venous catheter measurement.

14 Where should the distal orifice of the catheter be positioned?

When pressure measurements guide fluid management, the tip of the catheter can be positioned within either the atrium or the vena cava near the caval-atrial junction.

For monitoring the waveform of the CVP tracing, position the catheter within the atrium. By so positioning, the waveform will not be damped and will accurately reflect the pressure changes within the right atrium.

Placement of the catheter for aspiration of air emboli during neurosurgical cases requires positioning of the catheter (preferably multiport) tip in the right atrium near the superior vena cava–atrial junction. Embolized air flows past this point and accumulates in the superior aspect of the atrium. Positioning the catheter tip at the superior vena cava–atrial junction allows for optimal aspiration.

15 How can you judge the correct positioning of the distal orifice of the catheter?

Before insertion, measure the distance from the point of insertion to the right atrium (external landmark—immediately to the right of the third costal cartilage), giving a rough estimate of the length of inserted catheter necessary.

Advancing the catheter under fluoroscopy is the most accurate method for positioning the catheter tip but is time consuming and cumbersome.

With a specialized central venous catheter, the tip can be used as an electrocardiogram (ECG) electrode. After insertion the catheter is filled with electrolyte solution (normal saline or 8.4% NaHCO₃), and the V lead of the ECG is attached to a proximal connection. The catheter is advanced toward the right atrium. The P-wave axis and voltage on the V lead tracing indicates the catheter tip position. As the catheter tip passes the area of the sinoatrial node, the P wave becomes equal in height to the R wave of the ECG. The catheter tip passing the mid-atrial position is demonstrated by a decreasing or biphasic P wave. Low atrial positioning is indicated by an inverted P wave or absence of the P wave.

16 Describe the normal central venous pressure waveform and relate its pattern to the cardiac cycle

The normal CVP waveform shows a pattern of three upstrokes and two descents that correspond to certain events in the cardiac cycle (Figure 25-3).

The a wave represents the increase in atrial pressure that occurs during atrial contraction.

The x′ descent is the decrease in atrial pressure as the atrium begins to relax.

Before total relaxation is completed, the c wave occurs, which is caused by the bulging of the tricuspid valve into the atrium during the early phases of right ventricular contraction.

The x descent follows the c wave and is a continuation of the x′ descent. The x descent is caused by a drop in pressure brought about by a downward movement of the ventricle and tricuspid valve during the later stages of ventricular contraction.

The v wave represents the increase in atrial pressure that occurs while the atrium fills against a closed tricuspid valve.

The y descent represents a drop in pressure as the ventricle relaxes, the tricuspid valve opens (because atrial pressure is higher than ventricular pressure at this point in time), and blood passively enters the ventricle.

Figure 25-3 Normal central venous pressure waveform.

17 What influences central venous pressure?

CVP is directly related to returning blood volume, venomotor tone, and intrathoracic pressure and inversely related to cardiac function. The following perioperative events may change these variables:

Anesthetic-induced vasodilation and cardiac depression

Hypovolemia, hemorrhage, and rapid fluid replacement

Positive-pressure ventilation and positive end-expiratory pressure

Increased abdominal pressure (pneumoperitoneum)

Sympathetic activation caused by agonist drugs and surgical stress

Intraoperative ischemia may cause diastolic dysfunction or heart failure

18 Is central venous pressure an indicator of cardiac output?

Cardiac output is primarily a function of venous return (in the absence of frank heart failure), along with modulation by heart rate, cardiac contractility, and peripheral vascular resistance. Since CVP does not solely reflect intravascular volume, it must be considered within the clinical context to be valuable. For instance, although a rising CVP suggests an increased intravascular volume and improved venous return to the thorax, CVP will also increase in conditions such as right heart failure, cardiac tamponade, tension pneumothorax, pulmonary embolism, and increasing intra-abdominal pressure. These events are associated with decreasing cardiac output.

19 How does central venous pressure relate to right ventricular preload?

CVP has long been thought to reflect right ventricular preload or more specifically right ventricular end-diastolic volume. End-diastolic volume is a key parameter in the Frank-Starling law of the heart. Recently it has been shown that CVP does not necessarily correlate with ventricular volume, cardiac performance, or the response of the heart to volume infusions in both normal and compromised patients. The likely reason for this is a large spread and nonlinearity in diastolic ventricular compliances among individuals and incomplete knowledge of transmural pressures.

Despite the previous findings, it is widely held that CVP measurement is useful to the clinician as a guide to intravenous fluid replacement, especially at the upper and lower range of CVP. Thus a low (0 to 2 mm Hg) or decreasing CVP may indicate a need for fluid administration, whereas an increasing or elevated CVP (above 12 mm Hg) may indicate overresuscitation or a patient with impaired cardiac performance. The response of CVP to a fluid bolus has also been shown to be useful in assessing fluid status. In Figure 25-4 it can be seen that a 200-ml fluid bolus in the hypovolemic patient will result in a small but transient increase in CVP, whereas the same bolus in the normovolemic patient will result in a larger but still transient increase. However, in the hypervolemic patient with right ventricular failure, the same bolus results in a sustained increase in CVP. The CVP is best used to monitor a trend; an isolated determination is of limited value.

Figure 25-4 Central venous pressure and fluid status.

20 Does central venous pressure relate to left ventricular preload?

CVP possibly reflects right ventricular preload only. In patients whose left and right ventricles are functioning normally, CVP often parallels the left atrial pressure, which may reflect the preload of the left ventricle. However, in patients with pulmonary hypertension, lung disease, or right or left ventricular function abnormality, a pulmonary artery catheter provides better information with regard to the left side of the heart than does a central venous catheter.

21 Is there a single normal central venous pressure reading?

No single CVP is normal for all patients. Resting CVP may range from 0 to 10 mm Hg in different individuals and varies little over time. The reason for this spread is not clear, although it is not necessarily related to blood volume. In the operating room there are frequent perturbations that can impact the CVP, and the correct interpretation of a changing CVP is often not obvious. Because of this it becomes important to use all available clinical signs, including fluid resuscitation, urine output, blood pressure, and effects of anesthetic agents to determine an appropriate range of CVP for that patient.

22 Are there noninvasive alternatives to central venous pressure that better indicate volume status?

In recent years as it has become clear that CVP does not reliably correlate with preload and may be a useful indicator of the hemodynamic state only at the extremes, the more dynamic concept of fluid responsiveness has emerged for optimizing fluid therapy. Various techniques have been used to measure fluid responsiveness. For example, respiratory variation in systolic pressure during positive-pressure ventilation will decrease as volume is infused in a hypovolemic patient, or an esophageal Doppler can be used to measure increased descending aortic flow velocity (which mirrors cardiac output) as fluid is infused.

23 How can an abnormal central venous pressure waveform be used to diagnose abnormal cardiac events?

It may be used to assist in diagnosis of pathophysiologic events affecting right heart function. For example, atrial fibrillation is characterized by absence of the normal a wave component. Tricuspid regurgitation results in a giant V wave that replaces the normal c, x, and v waves. Other events that can change the normal shape of the CVP waveform include junctional rhythm with cannon A waves, atrioventricular dissociation, asynchronous atrial contraction during ventricular pacing, tricuspid stenosis, cardiac tamponade, increased ventricular afterload (from pulmonary hypertension or pulmonary embolus), and right ventricular ischemia and failure.

24 Can you use the central venous catheter for blood transfusions?

It depends on catheter size. For instance, 7-Fr triple-lumen catheters have narrow lumens, long lengths, and high resistance to flow, restricting the rate of blood administration and creating increased shear force on blood cells that can damage them. Nine French triple-lumen catheters have larger lumens and shorter lengths and are satisfactory for blood administration. Percutaneous introducer sheath used for pulmonary artery catheterization are short and have 9-Fr lumens and are excellent for blood administration. Always warm blood administered through central access to prevent hypothermia and arrhythmias.

25 Describe complications associated with placement of the central venous catheter

Considering the proximity of the carotid artery to the internal jugular vein, it is not surprising that carotid artery puncture is one of the more common complications associated with all internal jugular vein approaches.

Pneumothorax may occur and is more commonly associated with a subclavian, low anterior (internal jugular), or junctional approach (junction of the internal jugular vein and subclavian vein).

Hemothorax is associated primarily with the subclavian vein approach and occurs secondary to subclavian artery puncture or laceration.

The thoracic duct, as it wraps around the left internal jugular vein, can reach as high as 3 or 4 cm above the sternal end of the clavicle. This places the duct in a vulnerable position for puncture or laceration when a left internal jugular venipuncture is attempted.

Shearing and embolization of a catheter tip may occur when a catheter is withdrawn through a needle. Likewise a Seldinger guidewire can be sheared and embolized if attempts are made to withdraw it through an introducer needle. Therefore, if a catheter or wire cannot be advanced through an introducer needle, remove the parts in unison.

Air embolism is a risk, and to avoid this problem the patient should be positioned head down (if entry is at a point superior to the heart) until the catheter is inserted and the hub of the catheter is occluded.

Late complications include infection, vascular damage, hematoma formation, clot formation, dysrhythmia, and extravascular catheter migration.

26 Are any special precautions needed when removing a central venous catheter?

Before a subclavian or internal jugular catheter is removed, the patient should be placed in a head-down position to increase venous pressure at the point of removal and thereby prevent air aspiration into the vein. Following removal of the catheter, external pressure should be maintained on the area from which the catheter is withdrawn until clot formation has sealed the vessel.