CENTRAL VENOUS CATHETERS (CVCs) are used in many clinical areas for the administration of I.V. fluids, blood component transfusions, and medications; blood sampling; and hemodynamic monitoring. The evidence-based Surviving Sepsis Campaign guidelines have been instrumental in the reemergence of central venous pressure (CVP) monitoring as an effective tool in the care of patients with sepsis. Aggressive management of cardiac preload, afterload, and contractility is emphasized in the guidelines, and CVP monitoring is recognized as a key assessment parameter. In fact, one of the elements of the Severe Sepsis Bundle is maintaining adequate CVP.1
Since 2004, when the guidelines for sepsis management were first released, CVP monitoring has become the standard of care for patients with sepsis, increasing the number of CVC insertions.2 The information provided by CVP monitoring can mean earlier recognition of fluid imbalances and cardiac dysfunction.
This article reviews CVP monitoring, including indications, limitations, contraindications, recommended practices, complications, and nursing considerations.
CVP indicates right heart function
Central venous access for CVP monitoring is obtained by inserting a catheter into a vein, typically the subclavian or jugular vein, and advancing it toward the heart until the catheter tip rests within the superior vena cava near its junction with the right atrium. Normally, CVP ranges from 3 to 8 cm H2O or 2 to 6 mm Hg.3
CVP is important because it reflects changes in the cardiovascular system. CVP directly reflects right atrial (RA) pressure (provided the vena cava isn't obstructed), and indirectly, right ventricular end-diastolic pressure. As a consequence, CVP is a good indicator of right heart function.3 If the right ventricle is failing, for example, CVP will rise.
Keep in mind, however, that CVP is a poor indicator of left ventricular function. Left ventricular failure generally increases CVP, but if the right heart is functioning normally, CVP may remain normal despite high pulmonary artery pressures and pulmonary edema. Factors that influence CVP include the volume of blood returning to the right heart, vascular tone, cardiac contractility, and patient position.3
Indications for CVP monitoring include hypotension refractory to fluid resuscitation and severe sepsis.1 In patients with sepsis-induced tissue hypoperfusion, delivery of oxygen and nutrients to tissues is inadequate. Monitoring CVP provides an indicator of the patient's response to treatment. The CVC can also be used for other purposes; for example, to provide parenteral nutrition, infuse large fluid volumes, administer caustic or vasoactive drugs, and initiate transvenous cardiac pacing.4,5
Relative contraindications to CVC placement include injury proximal to the insertion site, anatomic distortion, presence of medical devices such as pacing lead wires, and uncorrected bleeding disorders.6
In adults, the most commonly used sites for nontunneled CVCs are the subclavian vein and the internal and external jugular veins.7 (See Veins used for CVP monitoring.) Whenever possible and if not contraindicated, the subclavian vein is preferred.2
Another option, femoral access, is avoided unless no other alternative is available in an emergency. Although easily accessible, the femoral site is associated with high rates of complications, including infection and iliofemoral thrombosis. If inserted in an emergency, a femoral catheter should be removed as soon as possible to reduce catheter-associated complications.6–8 For a comparison of common catheter insertion sites in adults, see CVC access sites: Pros and cons.
New CDC guidelines for preventing infection
The CDC recently released updated guidelines for the Prevention of Intravascular Catheter-Related Infections, 2011.8 Grading of recommendations includes Category 1A recommendations (which are strongly recommended for implementation and strongly supported by well-designed experimental, clinical, or epidemiologic studies) and Category 1B recommendations (which are strongly recommended for implementation and supported by some experimental, clinical, or epidemiologic studies and a strong theoretical rationale; or an accepted practice supported by limited evidence). Besides avoiding femoral access in adults (1A), the CDC recommendations regarding CVCs include:
* maintaining sterile technique for insertion and care (1B)
* wearing sterile gloves for CVC insertion (1A)
* using maximal barrier precautions (including cap, mask, sterile gown, sterile gloves, and sterile full body drape) for CVC insertion (1B)
* promptly removing any I.V. catheter when no longer needed (1A).
Before assisting with CVC insertion, perform proper hand hygiene either by washing your hands with conventional soap and water, or with alcohol–based hand rubs. Proper hand hygiene should be performed before and after palpating the catheter insertion site, as well as before and after inserting, replacing, accessing, repairing, or dressing any intravascular catheter.8
The Institute for Healthcare Improvement has created a care bundle for patients with CVCs, the Central Line Bundle.2 Care bundles are a group of best practices that have been shown to substantially improve patient outcomes when used together rather than applied individually. These evidence-based bundles are considered the stand ard of care.
The key components of the Central Line Bundle are hand hygiene, maximal barrier precautions, chlorhexidine skin antisepsis, optimal catheter site selection with subclavian vein as the preferred site for nontunneled catheters, and daily review of line necessity, with prompt removal of unnecessary lines.2 For a review of potential complications associated with CVC insertion, see On alert for complications.
CVP readings can be obtained with either a transducer or a water manometer. Transducers are commonly used in critical care areas because they're a part of monitoring equipment and provide continuous readings.9 For a summary of best practices for measuring CVP using a transducer, see How to measure CVP.
Mak ing waves
CVP is measured at end-diastole. The CVP/RA waveform has five components: three positive (upward) deflections (the a, c, and v waves) and two negative (downward) deflections (the x and y descents). See How the RA waveform corresponds to the ECG for details.
Although normal CVP is 2 to 6 mm Hg, it's important to remember that CVP in isolation is meaningless and must always be interpreted in conjunction with other clinical data, such as vital signs, heart and lung sounds, and other physical assessment findings.
Possible causes of increased CVP include vasoconstriction, increased blood volume, right ventricular failure, tricuspid insufficiency, pericardial tamponade, pulmonary embolism, obstructive pulmonary disease, and positive pressure ventilation. Decreased CVP may indicate hypovolemia, vasodilation (as from sepsis or vasodilating medication), or increased myocardial contractility.3,10
When monitoring a patient's CVP, ensuring correct use of the equipment, collecting accurate data, and tracking trends are crucial nursing responsibilities. Immediately investigate if you find a change in the waveform compared to the patient's baseline waveform, or if the pressure reading suddenly and drastically changes. Here are possible reasons for common problems.
* A smaller-than-usual waveform can be caused by air bubbles in the system, thrombus formation, lodging of the catheter against the vessel wall, kinking of the catheter, incorrect calibration, or a loose connection in the tubing or transducer.
* An erratic waveform can result from movement of the catheter tip within the vessel lumen (the catheter may require repositioning).
* An absent waveform may indicate a large leak in the system (usually noted by reflux of blood in the tubing); a loose, cracked, or defective transducer; air in the transducer; stopcock turned to the wrong position; or thrombus occlusion of the catheter tip.
Keep the pressure on
In recent years, CVP monitoring has become increasingly common and important, in part due to recommendations of the Surviving Sepsis Campaign. Many EDs and ICUs routinely utilize CVP monitoring in critically ill patients for rapid assessment of volume status. By becoming proficient in the use of this valuable assessment tool, you can provide optimal patient care.
On alert for complications3,10
Potential complications associated with CVC insertion include:
* localized infection
* vessel laceration
* right ventricular perforation
* hematoma at insertion site
* malpositioned catheter
* air embolism.
How the cvp waveform corresponds to the ecg3,10
The a wave is produced by RA systole (contraction) and occurs 80 to 100 ms after the P wave on the ECG.
The x descent is the downslope of the a wave and reflects RA relaxation.
The c wave occurs with tricuspid valve closure; isovolemic ventricular contraction forces the tricuspid valve to bulge upward into the RA. The c wave follows the QRS on ECG.
The v wave occurs as the RA continues to fill during against a closed tricuspid valve in late ventricular systole. The v wave correlates with the peak of the T wave on ECG.
The y descent, which is the downslope of the v wave, occurs when the tricuspid valve opens and blood from the RA empties rapidly into the right ventricle at the onset of RV diastole.
The z point coincides with the middle to end of the QRS complex. It occurs just before closure of the tricuspid valve and is a good indicator of right ventricular end diastolic pressure. The z point is useful when a waves aren't visible, as in atrial fibrillation.
Measuring CVP with a transducer3,11
* Perform hand hygiene.
* Place the patient in a supine position and explain the procedure to patient. (If the patient can't tolerate being supine, make sure all CVP readings are taken with the patient in the same alternate position.)
* Locate the phlebostatic axis at the intersection of the mid-axillary line and fourth intercostal space (see illustration).
* If an I.V. solution is being infused through the CVP monitoring line, temporarily stop it and flush the line to prevent artifacts.
* Turn the three-way stopcock off to the patient and remove the cap from the three-way port to open the system to air.
* Press the zero button on the monitor and look for a display indicating the equipment has been zeroed.
* Replace the cap on the stopcock and turn the stopcock on to the patient.
* Observe the CVP waveform and document the CVP reading and patient position.
* Resume the I.V. infusion if indicated.
Source for illustration: Woods SL, Froelicher ESS, Motzer SU, Bridges EJ. <italic>Cardiac Nursing</italic>. 6th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins 2010:461.