Measurement of central venous pressure from a peripheral intravenous catheter in the lower extremity.

Objectives: The measurement of central venous pressure (CVP) is used to assess intravascular status. Although this is usually accomplished by placement of a central venous catheter (CVC), there are circumstances when placement of a CVC may be technically difficult or impossible. The current study investigates the feasibility of measuring CVP from a peripheral intravenous catheter.

Methods: CVP was simultaneously measured from a CVC and from a peripheral intravenous site. The continuity of the peripheral intravenous catheter with the central venous system was evaluated by noting the change in the pressure measured from the peripheral catheter during a sustained inspiratory effort and during occlusion of the extremity (arm or leg) above the catheter.

Results: The cohort for the study included 37 adult patients. In 8 of the 37 patients (22%), there was no increase in the peripheral venous pressure (PVP) in response to a Valsalva maneuver or occlusion of the extremity above the intravenous site. For the upper extremity intravenous sites without a PVP increase, the PVP-CVP difference was 11.2 [+ or -] 6.2 mm Hg versus 2.7 [+ or -] 2.2 mm Hg in the patients in whom the PVP increased with these maneuvers (P < 0.0001). For the lower extremity intravenous sites without a PVP increase, the PVP-CVP difference was 7.6 [+ or -] 4.0 mm Hg versus 2.6 [+ or -] 1.9 mm Hg in the patients in whom the PVP increased (P < 0.0001). No variation in the accuracy of the technique was noted, depending on the size of the intravenous cannula, its location (upper versus lower extremity), CVP value, or patient positioning (supine, prone, lateral).

Conclusions: Provided that the PVP increases to a sustained inspiratory breath and occlusion above the intravenous site, there is a clinically useful correlation between the PVP and the CVP.

Key Words: central venous catheter, central venous pressure, lower extremity venous access 

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The measurement of central venous pressure (CVP) may be indicated as a means of assessing intravascular volume or cardiovascular performance. Although generally safe, complications may occur with central approaches to the venous circulation including arterial puncture, pneumothorax, and infection. (1,2) In addition, in rare circumstances, attempts to obtain central venous access may fail or more commonly during surgery, may not be possible related to patient positioning or inaccessibility under surgical drapes. During the 1940s, it was demonstrated that the pressure in the venous system of the upper extremity was only slightly higher than right atrial pressure. (3) Previous studies in adults (4-6) and children (7,8) have demonstrated a clinically useful correlation between CVP measurements obtained from a central venous catheter (CVC) and those obtained from a peripheral intravenous cannula. However, in these studies, the peripheral intravenous catheter was placed in either the upper extremity or the external jugular vein. This study prospectively evaluates the measurement of CVP from a CVC with those obtained from a peripheral intravenous cannula placed in either the upper or lower extremity.

Materials and Methods

This study was approved by the Institutional Review Board of the University of Missouri, and verbal informed consent was obtained from the patient. Patients undergoing a surgical procedure in which central venous access was deemed necessary were considered eligible for inclusion. After anesthetic induction and endotracheal intubation, central venous access was obtained by using a 7F single- or triple-lumen catheter with placement through the external jugular, internal jugular, or subclavian vein. Data were not included unless the postoperative or intraoperative radiograph demonstrated that the tip of the central venous catheter was at the junction of the superior vena cava and right atrium. The peripheral venous pressure (PVP) was obtained from a peripheral intravenous site by using a standard intravenous catheter (22 to 14 gauge). The continuity of the peripheral intravenous catheter with the central venous system was evaluated by showing a change in the PVP during a sustained inspiratory effort and during occlusion of the extremity (arm or leg) above the catheter. If no change was noted, the data were still collected, but the lack of response was noted on the data sheet. Venous pressure was measured from both the central venous catheter and the peripheral intravenous catheter, using standard pressure transducers, which were zeroed at the phlebostatic axis. Simultaneous measurements of the venous pressure from the central and peripheral catheters were performed every 15 minutes during the surgical procedures. Measurements were not taken during the rapid administration of fluids or medications. All measurements were recorded at end expiration.

Statistical analysis

The pressure values were rounded to the nearest 1 mm Hg. When calculating the difference between the pressure measured from the central venous catheter (CVP) and the pressure measured from the peripheral intravenous catheter (PVP), only positive numbers were used so that if the PVP measurement was less than the CVP measurement, then the absolute value (not the negative value) was used because it was our contention that the negative value could artificially lower the mean difference between the 2 pressure values and thereby bias the data. Using a difference of 5 mm Hg as a significant difference between the PVP and CVP readings and an anticipated standard deviation of 5 mm Hg, power analysis determined the requirement of a cohort of 28 patients, assuming an [alpha] value of 0.05 and a [beta] value of 0.05. If the [beta] value was increased to 0.10, then the power analysis resulted in a cohort of 23. All data are presented as mean [+ or -] SD, with a value of P less than 0.05 considered significant.

A two-tailed, unpaired t test was used to compare the PVP-CVP difference measured from upper versus lower extremity veins and the PVP-CVP difference between patients in whom there was an increase in the PVP with occlusion above the extremity and with a sustained inspiratory breath versus those in whom no change was noted. When multiple t tests were performed, a Bonferroni correction was used. One-way analysis of variance with a post hoc test (Tukey-Kramer multiple comparisons) was used to evaluate the PVP-CVP difference, using different-sized catheters and the PVP-CVP difference, based on the CVP value. A contingency table with a Fisher exact test was used to compare the frequency with which the PVP from the upper versus the PVP from the lower extremity intravenous site was less than or equal to 2 mm Hg and [less than or equal to] 5 mm Hg different from the CVP and to compare the accuracy of the technique when patients were supine versus other positions (lateral or prone).

Results

The cohort for the study included 37 adult patients (23 females, 14 males) ranging in age from 16 to 80 years and in weight from 80 to 123 kg. Thirty patients were in the supine position, 4 were prone, and 3 were lateral. The peripheral intravenous cannula was placed in the upper extremity in 11 patients and in the lower extremity in 26 patients. There were a total of 529 sample sets (PVP and CVP). The number of samples sets (PVP and CVP) obtained from the patients varied from 6 to 40. The size of the peripheral intravenous cannula from which the PVP was measured ranged from a 22 to a 14 gauge.

In 8 of the 37 patients (22%), there was no increase in the PVP in response to a sustained inspiratory effort or occlusion of the extremity about the intravenous site. This occurred in three cases when the intravenous cannula was in the upper extremity (3 of 11, or 27%) and in five cases when the intravenous cannula was in the lower extremity (5 of 26, or 19%, P = NS). There were 26 supine patients in whom there was an increase in the PVP in response to a sustained inspiratory effort or occlusion of the extremity about the intravenous site and 3 supine patients in whom there was no response of the PVP. There were three patients in other positions (lateral or prone) in whom the technique worked and four in whom the technique did not work (P = 0.0271). However, in patients who were positioned either prone or lateral and in whom there was an increase in the PVP in response to a sustained inspiratory breath and to occlusion above the intravenous site (n = 3), the PVP-CVP difference was 1.2 [+ or -] 1.3 mm Hg, compared with 2.7 [+ or -] 2.0 mm Hg (P = NS) in the 26 patients in the supine position in whom there was an increase in the PVP in response to a sustained inspiratory breath and to occlusion above the intravenous site.

For the three upper extremity intravenous sites without a PVP increase to a sustained inspiratory breath or occlusion above the intravenous sites, the difference between the PVP and CVP was 11.2 [+ or -] 6.2 mm Hg versus 2.7 [+ or -] 2.2 mm Hg in the other eight patients (P < 0.0001) (Table 1). For the five lower extremity intravenous sites without a PVP increase to a sustained inspiratory breath or occlusion above the intravenous sites, the difference between the PVP and CVP was 7.6 [+ or -] 4.0 mm Hg versus 2.6 [+ or -] 1.9 mm Hg in the other 21 patients (P < 0.0001) (Table 1). When there was an increase in the PVP with a sustained inspiratory breath or occlusion above the intravenous site, there was no difference between the PVP-CVP gradient when comparing upper extremity (2.7 [+ or -] 2.2 mm Hg) and lower extremity intravenous sites (2.6 [+ or -] 1.9 mm Hg) (Table 1). When comparing the number of PVP measurements that were less than or equal to 2 mm Hg and [less than or equal to] 5 mm Hg difference from the CVP, there was no difference noted between peripheral intravenous sites in the upper versus the lower extremity (Table 2). The relation between the PVP-CVP difference (central versus peripheral) and the size of the peripheral intravenous catheter is listed in Table 3.

When considering the three upper extremity intravenous sites that produced no PVP increase in response to a sustained inspiratory breath or occlusion above the intravenous site, the intravenous catheter was in a forearm vein, median cubital vein, or the dorsum of the hand. Two of these patients were prone and one was supine. These three catheters were 16 gauge. Of the lower extremity intravenous catheters whose PVP did not increase in response to a sustained inspiratory effort or occlusion above the intravenous site, the catheter was in the saphenous vein in all five patients. Three of the patients were in the supine position and two were in the lateral position. The intravenous catheter was either a 16 gauge (n = 3) or 18 gauge (n = 2).

When comparing the PVP-CVP difference in patients in whom there was an increase in the PVP with a sustained inspiratory breath or occlusion above the intravenous site across the different-sized intravenous catheters used, there was no clinically significant difference noted when using a 14, 16, 18, or 22 gauge catheter (Table 3). The mean difference was 0.8 mm Hg between the group with the highest PVP-CVP gradient (3.1 mm Hg in those patients who had an 18 gauge catheter) and the group with the lowest PVP-CVP gradient (2.3 mm Hg in those patients who had a 16 gauge catheter). Although this value did reach statistical significance, we postulate that this is a type I error, as there were no other differences noted when using larger (14 gauge) and smaller (22 gauge) catheters. Likewise, no clinically significant accuracy of the technique was noted when comparing the PVP-CVP difference in patients, in whom there was an increase in the PVP with a sustained inspiratory breath or occlusion above the intravenous site, based on the baseline CVP value (Table 4).

Discussion

The current study demonstrates that CVP can be measured from a lower extremity peripheral intravenous site in adult patients, provided that there is continuity with the central venous compartment demonstrated by an increase in the PVP measured from the peripheral intravenous site in response to a sustained inspiratory effort and by occlusion of the extremity above the site of the catheter. This correlation was noted regardless of the size of the intravenous catheter and the position of the patient. Although there were a limited number of 22 gauge catheters used in the current study, in our previous study evaluating this technique in infants and children, we noted a similar correlation of the PVP with the CVP when using 24, 22, and 20 gauge peripheral intravenous catheters. (7) One caveat of the current study is that we did not specifically address the issue of patient positioning and therefore only 7 of the 37 patients were in the lateral or prone positioning. There were significantly fewer patients in the lateral or prone position compared with the supine position in whom continuity from the peripheral to the central venous system could be demonstrated by noting an increase in the PVP in response to a Valsalva maneuver and with occlusion of the extremity above the intravenous cannula. However, if the continuity of the peripheral to the central venous system was demonstrated, then the PVP-CVP was not different between the supine patients and those in other positions (lateral or prone).

Knowledge of the relation between the central and peripheral measurement of CVP dates back to the middle 20th century. (3) Recent studies rejuvenated this relatively lost work to find sites that could be easily, less invasively, and more cost-effectively used to measure the CVP than a central venous catheter. Parker et al (6) evaluated the correlation of external jugular venous pressure, as it is in relatively direct communication with the central venous system, with CVP. The cohort for their study included 24 patients undergoing major surgery, who were mechanically ventilated in the supine position. They noted a mean difference between external jugular venous pressure and central venous pressure of 0.3 mm Hg (95% confidence interval, -4.1 to +3.5 mm Hg), with the CVP varying from 0 to 22 mm Hg.

Other investigators have previously evaluated more peripheral sites as a means of estimating CVP by using peripheral intravenous catheters placed in the upper extremity. Munis et al (5) compared the correlation of PVP with CVP in 1,026 paired measurements from 15 patients. The average CVP was 10.19 [+ or -] 3.72 mm Hg, whereas the average PVP was 13.19 [+ or -] 3.68. The correlation coefficient of CVP versus PVP was 0.819. They also noted that the technique was effective regardless of patient positioning (supine, lateral, or prone) and that the continuity of the PVP to the CVP could be demonstrated by the fact that the PVP increased when the arm above the catheter was occluded (a technique that we used in our current study). Unlike in our study, none of the patients failed to show an increase in the PVP with occlusion of the arm above the peripheral intravenous site.

Further validation of this technique is provided by Amar et al (4) in a study that included patients during mechanical ventilation in the intraoperative period (n = 100) and during spontaneous ventilation in the postanesthesia care unit (n = 50). In the intraoperative group, the mean PVP was 9 [+ or -] 3 mm Hg, the mean CVP was 8 [+ or -] 3 mm Hg, with a correlation coefficient (r value) of 0.86. Bland-Altman analysis revealed a bias of -1.6 mm Hg and a precision of 1.7 mm Hg. In 10 patients, there was an identical increase of 5 [+ or -] 2 mm Hg of the PVP and CVP after a 2-L fluid challenge. A similar correlation between the PVP and CVP was noted during spontaneous ventilation in the postanesthesia care unit with a bias of -2.2 mm Hg, a precision of 1.9 mm Hg, and a correlation coefficient of 0.88. The authors reported no difference in the correlation of PVP with CVP when stratified according to the size of the intravenous catheter.

This technique has also been applied to the pediatric population. (7,8) We have previously evaluated this technique in a cohort of 30 pediatric patients ranging in age from 1 to 12 years. As was noted in the current study, in 5 of the 30 pediatric patients, there was no increase in the PVP in response to a Valsalva maneuver and with occlusion of the extremity above the intravenous site. In these patients, there was a poor correlation between PVP and CVP (16 [+ or -] 5 mm Hg versus 5 [+ or -] 3 mm Hg in the remaining 25 patients, P < 0.0001). We also noted that there was no difference between the PVP-CVP gradient regardless of whether the intravenous catheter was in the upper or lower extremity (5 [+ or -] 3 mm Hg versus 6 [+ or -] 4 mm Hg).

Milhoan et al (8) studied the correlation between upper extremity (hand or antecubital vein) PVP and PA pressures in patients ranging in age from 1 to 24 years of age who had undergone cavopulmonary or Fontan connections. They found the mean PVP to be 17.5 [+ or -] 5.6 mm Hg, with a mean PA pressure of 16.1 [+ or -] 5.4 mm Hg. The difference was 1.5 [+ or -] 1.5 mm Hg, with a correlation coefficient of 0.97.

Conclusion

The current study provides additional information regarding the potential value of using PVP to estimate CVP in adult patients. Although previous studies in adults have demonstrated this correlation, (4,5) the current study is the first in adults to demonstrate the efficacy of this technique, using PVP measurements from the lower extremity. In addition, unlike previous studies, we have not found this technique to be effective in 100% of the patients. We suggest that the continuity of the peripheral and the central circulation needs to be demonstrated by use of Valsalva maneuver and occlusion above the intravenous site. With both of these maneuvers, there should be an increase in the PVP. If an increase in pressure is not noted, then the peripheral catheter probably is not continuous with the central circulation, and use of values from this site would not be advisable. Factors that may interfere with the continuity of the venous system from the periphery to the central compartment include occlusion of the vessel above the intravenous site due to patient positioning, soft tissue or muscular obstruction, venous valves, or even a pathologic process leading to obstruction. If continuity between the peripheral and central venous system is demonstrated, we found the correlation of PVP with CVP to be accurate regardless of the size of the intravenous cannula, its location (upper versus lower extremity), CVP value, or patient positioning (supine, prone, lateral). This technique may be used to estimate CVP in situations such as patient inaccessibility during a surgical procedure, technical problems, or patient-related factors that preclude placement of a CVC. The technique can also be used to immediately estimate CVP while there is preparation for placement of a CVC.

References

1. Sznajder I, Zveibil FR, Bitterman H, et al. Central vein catheterization: failure and complication rates by three percutaneous approaches. Arch Intern Med 1986;146:259-261.

2. Domino KB, Bowdle TA, Posner KL, et al. Injuries and liability related to central vascular catheters, Anesthesiology 2004;100:1411-1418.

3. Winsor T, Burgh GE. Use of the phlebomanometer: normal venous pressure values and a study of certain clinical aspects of venous hypertension. Am Heart J 1946;31:387-406.

4. Amar D, Melendex JA, Zhang H, et al. Correlation of peripheral venous pressure and central venous pressure in surgical patients. J Cardiothorac Vasc Anesth 2001;15:40-43.

5. Munis JR, Bhatia S, Lozada LJ. Peripheral venous pressure as a hemodynamic variable in neurosurgical patients. Anesth Analg 2001;92:172-179.

6. Parker JL, Flucker CJR, Harvey N, et al. Comparison of external jugular and central venous pressures in mechanically ventilated patients. Anaesthesia 2002;57:584-605.

7. Tobias JD, Johnson JO. Measurement of central venous pressure from a peripheral vein in infants and children. Pediatr Emerg Care 2003;19:428-430.

8. Milhoan KA, Levy DJ, Shields N, et al. Upper extremity peripheral venous pressure measurements accurately reflect pulmonary artery pressures in patients with cavopulmonary or Fontan connections. Pediatr Cardiol 2004;25:17-19.

Paul Cox, BS, Joel O. Johnson, MD, PHD, and Joseph D. Tobias, MD

From the University of Missouri School of Medicine and the Departments of Anesthesiology and Child Health, University of Missouri, Columbia, MO.

Reprint requests to Dr. Joseph D. Tobias, University of Missouri, Department of Anesthesiology, 3W40H, One Hospital Drive, Columbia, MO 65212. Email: [e-mail]

Accepted October 4, 2004.

RELATED ARTICLE: Key Points

* For the technique to work, one must demonstrate continuity between the peripheral and central venous system by demonstrating an increase in the peripheral venous pressure in response to a sustained inspiratory breath (Valsalva maneuver) and with occlusion above the intravenous site.

* The correlation between the central venous pressure and the peripheral venous pressure was not affected by the size of the intravenous catheter, the location of the peripheral intravenous cannula (upper versus lower extremity), or the central venous pressure value.

* This technique may be used to estimate central venous pressure if situations arise such as patient inaccessibility during a surgical procedure, technical problems, or patient-related factors that preclude placement of a central venous catheter. The technique can also be used to immediately estimate central venous pressure while there is preparation for placement of a central venous catheter.

Table 1. Peripheral venous pressure versus central venous pressure
values (a)

                                                  Number of sample sets
                         Difference               (PVP vs CVP) and
Patient group            (mean [+ or -] SD)       number of patients

1: PVP from upper         2.7 [+ or -] 2.2 mm Hg      88 and 8
   extremity vs CVP: +
   response to Valsalva
2: PVP from upper        11.2 [+ or -] 6.2 mm Hg      53 and 3
   extremity vs CVP: no
   response to Valsalva
3: PVP from lower         2.6 [+ or -] 1.9 mm Hg     302 and 21
   extremity vs CVP: +
   response to Valsalva
4: PVP from lower         7.6 [+ or -] 4.0 mm Hg      86 and 5
   extremity vs CVP: no
   response to Valsalva

Patient group                           P

1: PVP from upper        <0.0001 vs group 2; NS vs group 3
   extremity vs CVP: +
   response to Valsalva
2: PVP from upper        <0.0001 vs group 1
   extremity vs CVP: no
   response to Valsalva
3: PVP from lower        <0.0001 vs group 4; NS vs group 1
   extremity vs CVP: +
   response to Valsalva
4: PVP from lower        <0.0001 vs group 3
   extremity vs CVP: no
   response to Valsalva

(a) PVP, peripheral venous pressure; CVP, central venous pressure.

Table 2. Peripheral venous pressure values that were less than or equal
to 2 or 5 and equal to or greater than 6 mm Hg different from the
central venous pressure value (a)

                               PVP vs CVP difference
Patient group                (mm Hg) and No. of values (b)

1: PVP from upper extremity     [less than or equal to]2      49
   vs CVP: + response to        [less than or equal to]5      72
   Valsalva                  [greater than or equal to]6      16
2: PVP from upper extremity     [less than or equal to]2       0
   vs CVP: no response to       [less than or equal to]5       4
   Valsalva                  [greater than or equal to]6      49
3: PVP from lower extremity     [less than or equal to]2     157
   vs CVP: + response to        [less than or equal to]5     278
   Valsalva                  [greater than or equal to]6      24
4: PVP from lower extremity     [less than or equal to]2       7
   vs CVP: no response to       [less than or equal to]5      27
   Valsalva                  [greater than or equal to]6      59

                                 No. of
Patient group                  sample sets            P

1: PVP from upper extremity        88          <0.0001 vs 2; NS vs 3
   vs CVP: + response to                       <0.0001 vs 2; 0.0087 vs 3
   Valsalva
2: PVP from upper extremity        53          <0.0001 vs 1
   vs CVP: no response to                      <0.0001 vs 1
   Valsalva
3: PVP from lower extremity       302          <0.0001 vs 4; NS vs 1
   vs CVP: + response to                       <0.0001 vs 4; 0.0087 vs 1
   Valsalva
4: PVP from lower extremity        86          <0.0001 vs 3
   vs CVP: no response to                      <0.0001 vs 3
   Valsalva

(a) PVP, peripheral venous pressure; CVP, central venous pressure.
(b) Value could be counted more than once. If the PVP-CVP difference was
1 mm Hg, it would be counted in both the less than or equal to 2 mm Hg
and the less than or equal to 5 mm Hg groups.

Table 3. Peripheral venous pressure-central venous pressure difference
according to gauge of intravenous cannula (a)

                No. of patients  PVP-CVP
                and sample       difference
Catheter gauge  sets             (mm Hg)

14               3 and 27        2.9 [+ or -] 2.0
16              11 and 199       2.3 [+ or -] 1.9
18              11 and 104       3.1 [+ or -] 2.1
20               8 and 148       2.7 [+ or -] 2.2
22               2 and 29        2.9 [+ or -] 2.1

(a) PVP, peripheral venous pressure; CVP, central venous pressure.
Data include only patients in whom there was an increase in the PVP in
response to a Valsalva maneuver and with occlusion above the intravenous
site. The catheter gauge from 2 patients was not recorded so these data
include only 35 of the 37 patients. When analyzed using analysis of
variance and a post hoc test, the only statistically significant
difference (P < 0.01) was between the 16 and 18 gauge groups.

Table 4. Peripheral venous pressure-central venous pressure difference
according to central venous pressure value (a)

                                                          CVP equal to
                      CVP less than or                    or greater
                      equal to 7 mm Hg  CVP 8-14 mm Hg    than 15 mm Hg

PVP-CVP difference    4.0 [+ or -] 2.3  1.7 [+ or -] 1.3  1.1 [+ or -]
  from upper                                                1.4
  extremity IV sites
PVP-CVP difference    3.0 [+ or -] 1.8  2.3 [+ or -] 2.0  1.8 [+ or -]
  from lower                                                1.8
  extremity IV sites

(a) PVP, peripheral venous pressure; CVP, central venous pressure; IV,
intravenous.
Data in this table include only patients whose PVP increased due to a
Valsalva maneuver and with occlusion above the peripheral IV site.