Page 494 - Cardiac Nursing

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470 P A R T III / Assessment of Heart Disease
CVP. An increased CVP is usually an indication of later stages of CVP is measured at end-diastole, although consideration
LV failure, although the CVP may remain normal even in the must also be given to the effect of the maximal pressure. Useful
presence of high PA pressures and pulmonary edema. clinical information can also be obtained by examining the
CVP/RAP waveforms. There are five mechanical components (a,
Complications c, v waves and x and y descent) of the CVP waveform. A dual-
channel strip chart recorder should be used to identify the corre-
Complications associated with CVP monitoring include local- sponding venous pressure waves with the electrical events on the
ized infection, arrhythmias, vessel laceration, RV perforation, ECG (Display 21-3). The mean CVP is determined by bisecting
thrombophlebitis, hematoma formation at the insertion site, and the a, c, and v waves so that there are equal areas above and below
pneumothorax or a malpositioned catheter. 134 The most com- the bisection or measured at the leading edge of the c wave (also
mon predictor of complications, particularly pneumothorax, is known as the “z” point). The z point reflects the final pressure in
the number of needle insertions required to access the vein. the RA just before the onset of RV systole and the closure of the
There is an increased risk of arterial puncture, but fewer malpo- AV valves; thus, this point represents the RV end-diastolic pres-
sitioned catheters, with the jugular approach. 134 Conversely, sure (preload). Alternatively, if the a and c waves cannot be visu-
there may be a decreased risk of infection with a subclavian ver- alized, draw a straight line through the Q wave or the upstroke of
7
sus jugular or femoral insertion. 35,135 the arterial pressure waveform to identify end-diastole. If there
are large A and V waves, the CVP measurement should be made at
Measurement Technique the z point or the base of the a wave if the z point cannot be iden-
tified. 142 If there is a large A or V wave, the peak A or V wave pres-
The CVP system is referenced by placing the air–fluid interface of sure indicates increased upstream hydrostatic pressures (e.g., he-
the stopcock at the level of the phlebostatic axis (see
in Fig. 21-1) patic, renal). The CVP tracing may be useful in the diagnosis of
or at a point 5 cm below the sternal angle. With correct referencing, wide-complex tachyarrhythmias of unknown origin, tricuspid re-
the hemodynamically stable patient can be positioned up to gurgitation (large V wave that begins with the onset of systole), re-
45 degrees for CVP measurements. 136 striction of RV filling due to ventricular stiffness or volume overload
An area of confusion when measuring the CVP from a triple lu- (y ( descent 4 mm Hg—these patients are not likely to respond
men catheter is the question of which port to transduce. There are with increased CO if given a fluid bolus), 143 pericardial tamponade
no research-based recommendations regarding port selection. The (loss of x and y descent) (Fig. 21-10), and constrictive pericarditis.
differences in pressures measured from the various ports are small
( 1.5 mm Hg). 118 When the distal port is used there is limited
effect from fluids administered via the more proximal ports. 137 Be- PA PRESSURE MONITORING
cause of the potential for a clinically significant change in pressure
depending on the port transduced, it seems prudent to transduce Indications
consistently one port, and if a change in the site of monitoring is
necessary, to annotate the change on the flowsheet. Between 1993 and 2004, the use of PA catheters has decreased
65%, 144 with the greatest decrease occurring after the publication
Interpretation of CVP Data of a study of 5,735 patients in 1996, which suggested that PA
catheter use may increase morbidity and mortality. 145 Since this
There has been increased use of CVP to guide therapy due to the study, several consensus conferences 146–148 identified patient pop-
decreased use of PA catheters and results of a study in patients ulations for which PA pressure monitoring may be beneficial or
with acute lung injury, which suggests that outcomes from ther- additional outcome studies are needed and that there is a need for
apy guided by central venous catheter measurements are similar to standardized education of critical care providers.
those guided by PA pressure measurements. 138 Assessment of the In response to the consensus conference recommendations a
dynamic changes in the CVP in response to a fluid bolus or res- number studies have been completed. Several studies found no
piration are more sensitive and specific indices of fluid respon- improvement or worsening of patient outcomes from PA catheter
siveness than absolute CVP or PAOP values. guided therapy in general, vascular, or cardiothoracic surgical pa-
The absolute CVP may be useful in guiding differential diag- tients. 149–153 The Pulmonary Artery Catheter in the Management
nosis. For example, if the PAOP is increased and greater than the of ICU Patients (PAC-Man) study 154 evaluated use of a PA
CVP, the differential diagnosis should focus on the left heart. If catheter versus transesophageal echocardiography (TEE) monitor-
both the PAOP and CVP are increased, the differential diagnosis ing in patients with acute respiratory distress syndrome (ARDS),
should include diffuse coronary heart disease or cardiomyopathy, HF, or multiorgan dysfunction. No specific treatment guidelines
pericardial constriction or tamponade, or over distention of the or endpoints were used. There was no significant difference be-
right heart. If the CVP is increased and greater than the PAOP, tween groups in ICU or 28-day mortality; although in the PA
consideration should be given to right HF or pulmonary vascular catheter group, 80% of the patients had treatment changes made
disease. 139 In patients with severe HF, CVP 10 mm Hg had a within 2 hours of catheter insertion. The Sepsis Occurrence in
positive predictive value of 85% for a PAOP 22 mm Hg and Acutely Ill Patients (SOAP) study 155 was an observational study
was useful in evaluating 80% of the patients studied. 140 Evalua- that evaluated the association between PA catheter use and out-
tion of left heart function should always include consideration of come. Although the patients with PA catheters had a higher mor-
right heart function. Correct interpretation of the CVP requires tality rate, when confounding factors such as acuity, age, organ
knowledge of the patient’s CO. For example, the treatment would dysfunction, and comorbidities were controlled for, the use of a
be different for a patient with a low CVP and normal CO versus PA catheter was not associated with increased 60-day mortality.
low CO. 141 An interesting aspect of the secondary analysis of the SOAP study