Accuracy of Central Venous Pressure Measuremet From the Abdominal Inferior Vena Cava

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506 PEDIATRICS Vol. 89 No. 3 March 1992

EXPERIENCE

AND

REASON-Briefly

Recorded

‘In Medicine one must pay attention not to plausible theorizing but to experience and reason together. ...I

agree that theorizing is to be approved, provided that it is based on facts, and systematically makes its deductions from what is observed. . ..But conclusions drawn from unaided reason can hardly be serviceable; only those

drawn from observed fact.’ Hippocrates: Precepts. (Short communications of factual material are published here. Comments and criticisms appear as letters to the Editor.)

Accuracy

of Central

Venous

Pressure

Measurement

From

the

Abdominal

Inferior

Vena

Cava

Measurement of central venous pressure can be a

valuable adjunct to clinical care. Although the femoral

vein has become an increasingly common site for

central venous catheterization of critically ill

chil-dren,’ most authorities25 state that central venous

pressure should be recorded from intrathoracic

loca-tions. Because it is recommended that central venous

catheters not enter the heart,6 the femoral route is

practical only if intra-abdominal pressure

measure-ments accurately reflect central venous pressure. We

report a study validating measurement of central

ye-nous pressure from the abdominal inferior vena cava

in infants and children.

METHODS

Records of pediatric cardiac catheterizations at University

Med-ical Center (Tucson, AZ) were reviewed, and 20 consecutive cases that met the following criteria were selected for study: (1) right heart catheterization performed through a femoral vein; (2) age 21 years at the time of catheterization; (3) not receiving assisted ventilation at the time of catheterization; (4) no known potential obstruction to blood flow from inferior vena cava to right atrium, ie, congenital or acquired interruption of the inferior vena cava, atrial baffle repair of transposition of the great arteries, or caval

conduit (eg, for cavopulmonary anastomosis); (5) availability of

pressure recordings from right atrium and abdominal inferior vena cava made by fluoroscopically controlled rapid catheter pullback; and (6) sinus rhythm at the time of pressure recording. Cardiac catheterizations were performed for evaluation and/or treatment of congenital heart disease, and informed consent was obtained in all cases. We conducted this study in the cardiac catheterization laboratory in preference to the intensive care unit because the superior catheter and recording systems available in the catheteri-zation laboratory, as well as fluoroscopic observation of catheter position, minimized variation in recorded pressure due to factors other than catheter position.

All recordings included tracings of phasic and electronically derived mean pressure from the right atrium and abdominal infe-rior vena cava near the confluence of the iliac veins. Right atrial pressure at end expiration was considered the true central venous pressure, because at end expiration intrathoracic (and presumably intrapericardial) pressure is equal to atmospheric pressure. Respi-ratory phase was inferred from the right atrial pressure recording, and mean pressure at end expiration was measured to the nearest 0.5 mm Hg in both atrial and caval recordings. In certain cases, electronically derived mean pressure values at end expiration were lower than expected from inspection of end-expiratory phasic

Received for publication Feb 11, 1991; accepted Mar 19, 1991.

Reprint requests to (T.R.L.) Pethatric Cardiology, Arizona Health Sciences Center, Tucson, AZ 85724.

pressure tracings. In these cases, mean pressure at end expiration was measured by planimetry of the phasic pressure tracing as shown in Fig 1. The magnitude of respiratory variation in electron-ically derived mean pressure in each tracing was also noted.

Accuracy of central venous pressure measurement in the abdom-inal inferior vena cava was determined by comparing mean caval pressure to mean right atrial pressure at end expiration. Both the standard error of the estimate (from linear regression) and the absolute error of the technique (caval pressure - atrial pressure)

were calculated. We also calculated ‘limits of agreement’ between inferior caval and right atrial pressure as suggested by Bland and Altman.7 We considered that accuracy within 2 to 3 mm Hg would be adequate for clinical use.

RESULTS

Patients selected for review included 10 infants,

aged 15 days to 15 months (median 7 months), and

1 0 older children, aged 5 to 1 8 years, median 9 years.

Catheters used for pressure recordings were 60 to 65

cm long for infants and 90 to 1 10 cm long for children,

with a minimum internal diameter of 0.032 in. (0.8

mm). All catheters had multiple side holes, which

prevented spurious pressure recordings from

entrap-ment of the catheter tip. Planimetry was used to

measure end-expiratory mean pressure in 5 patients,

and planimetered mean pressure was found to be 0.5

1 second

p -S

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I

Fig 1. Phasic and electronically derived mean pressures from the right atrium of an infant subject are shown. Four inspirations (large negative deflections in the phasic pressure tracing) are shown, and each pair of vertical dashed lines indicates one cardiac cycle at end expiration. Note that electronically derived mean pressure is sub-stantially higher than phasic pressure during inspiration and ap-pears lower than phasic pressure during expiration. Planimetry of phasic right atrial pressure during these three end-expiratory car-diac cycles yields a mean pressure of 6.8 mm Hg, nearly 2 mm Hg higher than electronically derived mean pressure.

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0 10 20

ABDOMINAL VENA CAVAL PRESSURE (mm Hg)

EXPERIENCE AND REASON 507

to 2.5 mm Hg higher than electronically derived mean

pressure in these cases. All 5 patients in whom

plan-imetry was necessary were infants (P < .05, Fisher’s

Exact Test). Respiratory variation in electronically

de-rived mean pressure was 0.9 ± 0.1 mm Hg (SEM) in

the right atrium, which was significantly greater than

in the inferior vena cava (0.4 ± 0.1 mm Hg, P < .0001

by repeated-measures analysis of variance).

The relationship between mean pressure in the

abdominal vena cava and right atrium at end

expira-tion is shown in Fig 2. The correlation between the

two pressures was excellent (r = .994, P < .000 1),

with a standard error of the estimate of only 0.37.

Neither the slope (1 .002) nor the intercept (-0.0 18)

of the regression line was significantly different from

the line of identity (slope = 1, intercept = 0). The

mean difference between abdominal and atrial mean

pressure was 0.0 ± 0.36 mm Hg (SD), and in 13 of

20 patients the abdominal and atrial mean pressures

were identical. In the remaining 7 patients, mean

pressure in the abdominal vena cava was 0.5 mm Hg

higher than right atrial pressure in 4, and was 1 .0 and

0.5 mm Hg lower than right atrial pressure in 1 and

2 patients, respectively. “Limits of agreement’ were ±

0.72 mm Hg, substantially less than the 2 to 3 mm

Hg considered adequate for clinical use.

DISCUSSION

Although Bruner8 has stated that it should be

pos-sible, in theory, to measure central venous pressure

from any systemic vein, placement of central venous

pressure monitoring lines into the thorax is a nearly

universal recommendation.25 The subclavian and

jugular approaches to the superior vena cava carry

risks of pneumothorax, hemothorax, or carotid artery

puncture, especially in uncooperative pediatric

pa-tients. The femoral approach avoids these

complica-tions,’ as well as providing a convenient site for

cutdown should percutaneous catheterization fail.

However, the US Food and Drug Administration has

recommended that central venous catheters (except

C) = E E w (1) Cl) w -i I-= (9

Fig 2. Mean pressures at end expiration from the right atrium are

plotted against those from the abdominal inferior vena cava. Closed triangles represent single data points; duplicate and triplicate points are indicated by open triangles. The regression line is shown (right

atrial pressure = 1.002.vena cava pressure - 0.018 mm Hg, r =

.994, standard error of the estimate = 0.37, P < .0001), which was not significantly different from the line of identity.

pulmonary artery catheters) not be allowed to enter

the heart,6 because monitoring catheters within the

right atrium, regardless of insertion site, may cause

dysrhythmias,9 atrial thrombi,’#{176} or cardiac rupture.”

Because abdominal vena cava pressure accurately

reflects central venous pressure, the femoral approach

to central venous catheterization can provide equally

valid clinical information.

Our data show that, at end expiration, mean

pres-sure in the abdominal inferior vena cava is essentially

identical with mean central venous pressure.

Circu-latory pressures are most appropriately measured at

end expiration because, in the absence of assisted

ventilation or pericardial disease, intrapericardial

pressure is approximately equal to atmospheric

pres-sure so that measured pressure (intracavitary -

at-mospheric pressure) is closest to transmural pressure

(intracavitary - intrapericardial pressure) at end

ex-piration. Ideally, central venous pressure should be

measured on a beat-to-beat basis, and only

end-expiratory measurements accepted. Unfortunately,

the time constants used to produce electronically

de-rived mean pressures (especially by bedside

monitor-ing systems) result in contamination of end-expiratory

mean pressure by inspiratory and expiratory pressures

which will be most pronounced when respiratory rate

and effort are increased. This phenomenon explains

why all five patients who required planimetric

meas-urement of end-expiratory mean pressures were

in-fants (P < .05, Fisher’s Exact Test). Because we found

that respiratory variation in central venous pressure

was less pronounced in abdominal than in thoracic

tracings, abdominal measurements more closely

ap-proximate end-expiratory mean pressure than do

tho-racic measurements when substantial respiratory

var-iation is present.

In critical care use, pressure monitoring catheters

frequently have only a single opening from each

lumen, so catheter tip entrapment is an important

potential source of measurement error. This

possibil-ity should be excluded by free blood return and by

appropriate pressure pulse before abdominal or

tho-racic venous catheters are used for pressure

measure-ment. Appropriate atmospheric zero pressure level

should be established at the mid-thorax regardless of

the site of central venous pressure measurement.

Abdominal vena cava pressure may be significantly

higher than right atrial pressure whenever there is

obstruction to flow in the inferior vena cava or at the

cavoatrial junction. This may occur in patients with

congenital, thrombotic, or surgically acquired

inter-ruption or obstruction of the inferior vena cava or

patients with extrinsic compression of the inferior

vena cava (eg, by abdominal tumor); similar

precau-tions apply to intrathoracic pressure monitoring in

patients with superior caval obstruction. We did not

include in this study any mechanically ventilated

patients or patients with respiratory distress, although

our experience suggests that results are comparable:

Fig 3 shows superior and inferior vena cava pressure

tracings in a 6-month-old infant with bacterial sepsis

who required inotropic support and vigorous me-chanical ventilation for septic shock and severe

cap-illary leak, which resulted in edema, ascites, and

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508 EXPERIENCE AND REASON

I isec

mmHg t

Insp insp

30- j,

1f

mmHg SV

----L

-

--Fig 3. Simultaneous central venous pressure tracings from the

abdominal inferior vena cava at the level of the second lumbar vertebra (IVC, above) and from the superior vena cava (SVC, below) obtained from a 6-month-old patient with bacterial sepsis (see text). Inspirations (insp) are indicated by arrows. Although central venous pressure at peak inspiration is slightly higher in the abdomen than in the thorax (19 to 20 mm Hg vs 18 mm Hg), at end expiration both catheters indicate a central venous pressure of 12 mm Hg.

acquired respiratory distress syndrome. The presence

of ascites, pulmonary disease, and positive pressure

ventilation did not interfere with the accuracy of

central venous pressure measurement from the

ab-dominal inferior vena cava in this or any other patient

in our experience. Despite these potential limitations,

we have shown that the accuracy of central venous

pressure measurement in the abdominal inferior vena

cava is usually equal, and occasionally superior, to

measurement in the right atrium or thoracic great

veins.

SUMMARY

Central venous pressure measurements in the

ab-dominal inferior vena cava were compared with

measurements in the right atrium in 10 infants and

10 children during cardiac catheterization. At end

expiration, the mean pressures at these two sites were

within 1 mm Hg of each other in all 20 patients, with

a mean difference of 0.0 ± 0.36 mm Hg. The

abdom-inal inferior vena cava is a safe and convenient site

for measurement of central venous pressure, and our

study confirms that such measurements are accurate.

THOMAS R. LLOYD, MD

RICHARD L. DONNERSTEIN, MD

ROBERT A. BERG, MD University Heart Center

Steele Memorial Children’s Research Center

Sections of Cardiology and Pulmonary/Critical Care Dept of Pediatrics

University of Arizona College of Medicine Tucson, AZ

REFERENCES

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Percutaneous femoral venous catheterizations: a prospective study of complications. IPediatr. 1989;1 14:411-415

2. Chameides L, ed. Textbook of Pediatric Advanced Life Support. Dallas, TX: American Heart Association; 1988:39

3. McIntyre KM. Lewis AJ, eds. Textbook of Advanced Cardiac Life Support.

Dallas, TX: American Heart Association; 1983:260

4. Graef JW, ed. Manual of Pediatric Therapeutics. 4th ed. Boston, MA: Little, Brown; 1988:89

5. Seneff MG, Rippe JM. Central venous catheters. In: Rippe JM, Irwin RS, Alpert JS, Dalen JE, eds. Intensive Care Medicine. Boston, MA: Little, Brown; 1985:16-33

6. Precautions necessary with central venous catheters. FDA Drug Bull. July

1989:15-16

7. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307-310

8. Bruner JMR. Handbook of Blood Pressure Monitoring. Littleton, MA: PSG;

1978: 152-153

9. Daniels SR. Hannon DW, Meyer RA. Kaplan S. Paroxysmal

supraven-tricular tachycardia: a complication of jugular central venous catheters

in neonates. AJDC. 1984;138:474-475

10. Bagwell CE, Marchildon MB. Mural thrombi in children: potentially lethal complication of central venous hyperalimentation. Crit Care Med.

1989;17:295

1 1. Agarwal KC, Khan MAA, Falla A, Amato JJ. Cardiac perforation from

central venous catheters: survival after cardiac tamponade in an infant.

Pediatrics. 1984;73:333-338

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1992;89;506

Pediatrics

THOMAS R. LLOYD, RICHARD L. DONNERSTEIN and ROBERT A. BERG

Cava