Evaluation of Impedance Cardiography as an ... - Wiley Online Library

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ORIGINAL PAPER

Evaluation of Impedance Cardiography as an Alternative to Pulmonary Artery Catheterization in Critically Ill Patients Invasive pulmonary artery catheterization has historically been the method of choice for the evaluation of hemodynamic status. Impedance cardiography (ICG) is an accurate, noninvasive technique to obtain hemodynamic status information without the risk and cost associated with invasive methods. The purpose of this prospective, observational study was to determine whether the availability of ICG could decrease the need for placement of a pulmonary artery catheter in critically ill patients in coronary care units. After the need for hemodynamic data was determined, ICG parameters were provided to the attending physician who then decided whether pulmonary artery catheter insertion was still necessary. Of 107 subjects enrolled in the study, 14 (13%; 95% confidence interval, 7.3%–21.0%) were judged by the treating physicians to have indications for hemodynamic monitoring. In these subjects, the provision of ICG data allowed the physician to avoid placement of a pulmonary artery catheter in 10/14 patients (71%; 95% confidence interval, 41.9%–91.6%). When ICG was utilized, clinicians reported that the information was helpful in 10/10 patients (100%; 95% confidence interval, 74.1%–100.0%) and improved outcome in 6/10 patients (60%; 95% confidence interval, 26.2%–87.8%). ICG can replace the pulmonary artery catheter in coronary care unit patients, and clinicians utilizing ICG believe it aids medical decision making and improves patient outcomes. (CHF. 2004;10(2 suppl 2):17–21) ©2004 CHF, Inc.

T

he flow-directed, balloon-tipped pulmonary artery catheter (PAC) was introduced in clinical medicine as a diagnostic and monitoring tool for patient-specific, hemodynamic goaldirected therapy.1 Acute decompensated heart failure (HF) presents as a hemodynamic crisis, and therapeutic interventions are aimed directly at improving hemodynamics, including reducing cardiac preload and afterload and augmenting contractility. Unfortunately, physicians cannot accurately assess hemodynamic profiles based on history and physical examination.2–5 Therefore, critically ill patients hospitalized with HF may require the use of a PAC to identify the need for and monitor the effectiveness of therapeutic interventions, often referred to as tailored therapy.6,7 Some studies have shown an improvement in outcomes with PAC-guided therapy,8–13 whereas others have chal-

lenged the utility, safety, and economics of the PAC and suggested it does not improve outcomes while increasing complications and cost.14–17 A noninvasive method to obtain hemodynamic measurements in hospitalized HF patients would be desirable, and by virtue of its lower cost and risk, might increase the appropriate use of hemodynamics to guide therapy. Impedance cardiography (ICG) is a noninvasive method for obtaining hemodynamic parameters, including measurements of flow (stroke volume and cardiac output), afterload (systemic vascular resistance), work (left cardiac work), contractility (velocity index and acceleration index), fluid status (thoracic fluid content [TFC]), and electromechanical timing intervals (preejection period, left ventricular ejection time, and systolic time ratio).18 ICG accuracy has been validated in numerous clinical states, including

heart failure,19–21 pulmonary hypertension,22 mechanical ventilation,23 and postcoronary artery bypass.24,25 The purpose of this study was to determine whether the availability of ICG in coronary care units (CCUs) could decrease the need for PAC placement, and whether the information from ICG was helpful in the course of treatment.

Methods

This was an observational, prospective study conducted with a convenience sample of patients admitted to the CCU at a single institution over a 21-day period. Inclusion criteria for the study were patients admitted to the CCU with the potential need for PAC monitoring. Exclusion criteria were: PAC already placed; height 7 ft 8 in; weight 341 lb; presence of severe aortic regurgitation, atrial fibrillation, atrial

Marc A. Silver, MD; Pamela Cianci, MSN; Sharon Brennan, RN; Helen Longeran-Thomas, RN; Faheem Ahmad, MD From the Department of Medicine and the Heart Failure Institute, Advocate Christ Medical Center, Oak Lawn, IL Address for correspondence: Marc A. Silver, MD, Clinical Professor of Medicine, University of Illinois; Chairman, Department of Medicine, and Director, Heart Failure Institute, Christ Hospital and Medical Center, Room 319 South, 4440 West 95th Street, Oak Lawn, IL 60453 E-mail: [email protected] ICG as an alternative to PAC

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Congestive Heart Failure (ISSN 1527-5299) is published bimonthly (Feb., April, June, Aug., Oct., Dec.) by CHF, Inc., Three Parklands Drive, Darien, CT 06820-3652. Copyright ©2004 by CHF, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers. The opinions and ideas expressed in Congestive Heart Failure do not necessarily reflect those of the Editor and Publisher. For copies in excess of 25 or for commercial purposes, please contact Sarah Howell at [email protected] or 203.656.1711 x106.

decision-making process and results is shown in Figure 2. Of the 107 patients enrolled, 14 (13%) were initially judged as appropriate candidates for hemodynamic monitoring using a PAC. After the ICG data were made available to the treating physician, ICG was used in lieu of a PAC in 10 of 14 patients (71%). ICG data were rated as helpful in clinical decision making by the physician in all 10 of these cases (100%), and rated as helpful in improving the patient outcome in 6 of 10 patients (60%). In each of the four patients (29%) in whom PAC monitoring was still preferred after the provision of ICG data, the reason provided was unfamiliarity with ICG technology.

Discussion

Figure 1. Impedance cardiography sensor placement

flutter, or frequent premature ventricular contractions (≥6/min). Upon enrollment, the attending physician identified whether the patient needed hemodynamic monitoring via PAC. Once identified, ICG measurements were obtained in the supine position (BioZ ICG Monitor, Model 4110–101, CardioDynamics, San Diego, CA). The ICG method requires four sets of dual sensors, two sets attached at the base of the neck and two sets attached at the side of the patient’s chest at the level of the xiphoid process in the mid-axillary line (Figure 1). The outer sensors transmit an alternating electrical current that is not felt by the patient; the inner sensors measure the changes in electrical impedance due to changes in the thoracic cavity. Changes in impedance are measured and used to calculate real-time hemodynamic parameters. All ICG measurements were performed by nurses or technicians trained to use the device. A report listing the following ICG hemodynamic parameters was provided to the treating physician: stroke volume/stroke index, cardiac output/cardiac index, systemic vascular resistance/systemic vascular 18

ICG as an alternative to PAC

resistance index, and TFC. Upon provision of the ICG data, the physician determined whether ICG could be used alone to provide hemodynamic information or if PAC insertion and monitoring were still required. If ICG information was sufficient, the physician documented its influence on patient care. When ICG was not used as the primary measurement for hemodynamics, the reason was documented. Data are expressed in absolute and relative percent terms, and 95% confidence intervals were determined by a Monte Carlo simulation of 100,000 iterations.

Results

One hundred seven patients entering the CCU were screened for the need for invasive PAC placement and monitoring. The mean age was 71 years. Primary cardiac diagnosis was either decompensated HF or acute myocardial infarction. Some patients had a secondary diagnosis of pulmonary disease. The study results with 95% confidence intervals are listed in Table I, and a flow diagram illustrating the

There has been considerable debate about whether the benefits of PAC justify the risks associated with invasive monitoring. The central question is whether the hemodynamic information obtained by the PAC outweighs the potential for infection and other complications associated with an indwelling right heart catheter. Physicians who utilize PAC monitoring in patients hospitalized with HF maintain that the information is helpful in their disease management decisions for a particular patient. However, due to the lack of proven benefit of the PAC in prospective trials and the cost and risk associated with the procedure, many physicians treating hospitalized HF have reduced or eliminated their use of hemodynamic monitoring in such cases. Although ICG does not provide pulmonary artery or pulmonary artery wedge (PAW) pressures, it does provide reliable and reproducible measures of cardiac index, stroke volume, systemic vascular resistance, and other hemodynamic parameters. In this study, ICG data allowed physicians to avoid performing PAC placement in 10 of the 14 patients in whom they originally deemed invasive monitoring necessary. Thus, 71% of patients who would otherwise have been subjected to the risks of right heart catheterization, including march . april 2004 . supplement 2


Table I. Study Results VARIABLE

NO.

OF

SUBJECTS

% (95% CI)

107

Subjects enrolled Need for PAC determined

14/107

ICG data used as primary HD data

10/14

PAC placed after ICG data

… 13 (7.3–21.0) 71 (41.9–91.6)

4/14

ICG rated as aiding decision making

29 (8.4–58.1)

10/10

ICG rated as helping improve patient outcome

100 (74.1–100.0)

6/10

60 (26.2–87.8)

CI=confidence interval; PAC=pulmonary artery catheter; ICG=impedance cardiography; HD=hemodynamic

Table II. Projected Procedural Cost Savings With Impedance Cardiography (ICG) PAC COST ($) ITEM

TYPICAL

LOW

HIGH

PAC

60

42

100

…

Central venous catheter insertion kit

23

14

28

…

Pressure tubing

3

2

6

…

Premixed heparin drip

2

1

3

…

Trifurcated transducer monitor set

25

11

35

…

Co-set apparatus

15

12

20

…

Sterile gown, mask, gloves, drapes, and dressing

13

8

21

…

Medication for procedural sedation

15

…

17

…

Fluoroscopy procedure and interpretation

25

…

75

…

Additional ICU days cost ($1000/d)*

ICG COST ($)

1800

1000

3000

…

24

30

30

…

Physician insertion cost (CPT 93501)

160

160

160

…

ICG disposable/procedural cost

…

…

…

20

ICG technician time (5 min × $30.00/h) × 2 d

…

…

…

6

ICG physician professional interpretation (CPT 93701–26)

…

…

…

8

2165

1280

3495

Nursing care time (site and catheter care) for 2 d (30 min/d × $30/h)

Total procedure cost

34

PAC=pulmonary artery catheterization; CPT=current procedural terminology; *days for typical, low, and high are derived from 25th, 50th, and 75th percentile differences between intensive care unit (ICU) bed days of PAC and non-PAC patients, from Connors AF, Peroff T, Dawson NV, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. JAMA. 1996;276(11):889–897. Adapted with permission from AACN Clin Issues. 1999;10(3):419–426.27

Table III. Projected Annualized Cost Savings by Percent Reduction and Pulmonary Artery Catheterization (PAC) Volume Per Month TOTAL ANNUAL SAVINGS ($) NO.

OF

PAC PROCEDURES PERFORMED

PER

MONTH

20%*

40%*

60%*

80%*

5

25,572

51,144

76,716

102,288

10

51,144

102,288

153,432

204,576

25

127,860

255,720

383,580

511,440

50

255,720

511,440

767,160

1,022,880

100

511,440

1,022,880

1,534,320

2,045,760

*Percentage of PAC procedures replaced with impedance cardiography

infection and pneumothorax, were managed successfully using only ICG. Others have suggested that ICG may offer enough similar information to ICG as an alternative to PAC

reduce the need for a certain percentage of some invasive procedures, and have estimated that when ICG is utilized in place of PAC, cost savings are between

$600 and $3088 per patient.26,27 As physicians become more comfortable with the use of ICG, it is likely that a significant portion of patients in CCUs will march . april 2004 . supplement 2

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Enrollment CCU patients with a potential need for HD monitoring (N=107)

Physician determination of need for HD monitoring

HD monitoring required (n=14) (13%)

HD monitoring not required (n=93) (87%)

ICG data provided/ physician determination of PAC requirement

PAC not required (n=10) (71%)

PAC required (n=4) (29%)

Figure 2. Flow chart of decision-making process and study results. CCU=coronary care unit; HD=hemodynamic; PAC=pulmonary artery catheter; ICG=impedance cardiography

be managed more safely and cost-effectively using noninvasive hemodynamic monitoring with ICG. Table II provides a procedural cost comparison between PAC placement and ICG, and Table III extrapolates those procedural costs to annualized savings. Significant portions of HF patients who are admitted to a hospital are not treated in a CCU or with hemodynamic parameters via the PAC. These patients may benefit from the use of ICG, which can easily be performed in an emergency department and subacute setting. The use of ICG in non20


critical-care treatment may also result in significant cost savings, due to more targeted treatment of hemodynamic instability, effective titration of medications, and determination of patient stability for discharge. In this study, the lack of PAW pressure did not appear to be a deterrent to utilizing ICG in place of PAC. Although isolated ICG measurements of TFC correlate poorly with PAW pressure, previous studies have shown that changing TFC levels can be utilized to monitor extravascular and intravascular volume changes.19 These

studies have demonstrated sensitivity in monitoring changes in response to diuretic therapy28–31 as well as thoracentesis and pericardiocentesis.32,33 One case report showed a similar relative reduction in TFC as with PAW pressure in response to treatment.34 Physicians rated ICG information as helpful in their decision-making process in all patients and believed it improved patient outcome in 60% of cases. Whether ICG actually influenced a change in intended treatment in these patients was not evaluated. However, a recent study in dyspneic patients demonstrated that ICG data changed the attending physician’s therapeutic plan a substantial 24% of the time.35 These results suggest the potential for broad utilization of ICG technology, although there are certain limitations to this study. This was a small, behavioral study without defined end points to describe patient outcomes. There was no control group to compare patient care decision-making interventions based on the two different methods of hemodynamic monitoring and the findings are limited to the treatment of medical CCU patients. The Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE) is a multicenter, randomized controlled trial designed to test outcomes of PACguided therapy compared with that guided by clinical assessment alone in hospitalized HF patients.36 The BioImpedance cardioGraphy (BIG) substudy of ESCAPE will examine the diagnostic and prognostic role of ICG hemodynamic data collected in a blinded fashion. The data from ESCAPE and BIG will help define the future role of hemodynamic-guided therapy and ICG in the treatment of advanced HF. The results of this study indicate that noninvasive hemodynamic parameters obtained by ICG can be used in a significant portion of patients who would otherwise require PAC placement. Clinicians using ICG believed the information was helpful in guiding therapeutic decisions and improving patient outcomes. march . april 2004 . supplement 2


REFERENCES 1 Swan HJ, Ganz W, Forrester J, et al. Catheterization of the heart in man with use of a flow-directed balloon-tipped catheter. N Engl J Med. 1970;283(9):447–451. 2 Shah MR, Hasselblad V, Stinnett SS, et al. Hemodynamic profiles of advanced heart failure: association with clinical characteristics and long-term outcomes. J Card Fail. 2001;7(2):105–113. 3 Speroff T, Connors AF Jr, Dawson NV. Lens model analysis of hemodynamic status in the critically ill. Med Decis Making. 1989;9(4):243–252. 4 Eisenberg PR, Jaffe AS, Schuster DP. Clinical evaluation compared to pulmonary artery catheterization in the hemodynamic assessment of critically ill patients. Crit Care Med. 1984;12(7):549–553. 5 Stevenson LW, Perloff JK. The limited reliability of physical signs for estimating hemodynamics in chronic heart failure. JAMA. 1989;261:884–888. 6 Stevenson LW, Miller LW. Cardiac transplantation as therapy for heart failure. Curr Probl Cardiol. 1991;16:217–305. 7 Drazner MH, Solomon MA, Thompson B, et al. Tailored therapy using dobutamine and nitroglycerin in advanced heart failure. Am J Cardiol. 1999;84:941–943. 8 Rivers E, Nguyen B, Havstad S, et al. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med. 2001;345(19):1368–1377. 9 Ivanov RI, Allen J, Sandham JD, et al. Pulmonary artery catheterization: a narrative and systematic critique of randomized controlled trials and recommendations for the future. New Horiz. 1997;5(3):268–276. 10 Steimle AE, Stevenson LW, Chelimsky-Fallick C, et al. Sustained hemodynamic efficacy of therapy tailored to reduce filling pressures in survivors with advanced heart failure. Circulation. 1997;96:1165–1172. 11 Hamilton MA, Stevenson LW, Child JS, et al. Sustained reduction in valvular regurgitation and atrial volumes with tailored vasodilator therapy in advanced congestive heart failure secondary to dilated (ischemic or idiopathic) cardiomyopathy. Am J Cardiol. 1991;67:259–263. 12 Stevenson LW, Steimle AE, Fonarow G, et al. Improvement in exercise capacity of candidates awaiting heart transplantation. J Am


Coll Cardiol. 1995;25:163–170. 13 Fonarow GC, Stevenson LW, Walden JA, et al. Impact of a comprehensive heart failure management program on hospital readmission and functional status for patients with advanced heart failure. J Am Coll Cardiol. 1997;30:725–732. 14 Connors AF, Peroff T, Dawson NV, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. JAMA. 1996;276(11):889–897. 15 Sandham JD, Hull RD, Grant RF, et al. A randomized controlled trial of the use of pulmonary artery catheters in high-risk surgical patients. N Engl J Med. 2003;348(1):5–14. 16 Richard C, Warszawski J, Anguel N, et al. Early use of the pulmonary artery catheter and outcomes in patients with shock and acute respiratory distress syndrome. JAMA. 2003;290(20):2713–2721. 17 Polanczyk CA, Rohde LE, Goldman L, et al. Right heart catheterization and cardiac complications in patients undergoing noncardiac surgery: an observational study. JAMA. 2001;286:309–314. 18 Yancy C, Abraham WT. Noninvasive hemodynamic monitoring in heart failure: utilization of impedance cardiography. Congest Heart Fail. 2003;9(5):241–250. 19 Drazner M, Thompson B, Rosenberg P, et al. Comparison of impedance cardiography with invasive hemodynamic measurements in patients with heart failure secondary to ischemic or nonischemic cardiomyopathy. Am J Cardiol. 2002;89(8):993–995. 20 Albert N, Hail M, Li J, et al. Equivalence of bioimpedance and thermodilution in measuring CO/CI in patients with advanced, decompensated chronic heart failure hospitalized in critical care. J Am Coll Cardiol. 2003;41(6 suppl):211A. 21 Silver MA, Lazzara D, Slaughter M et al. Thoracic bioimpedance accurately determines cardiac output in patients with left ventricular assist devices. J Card Fail. 1999;1(5). 22 Yung GL, Fletcher CC, Fedullo PF, et al. Noninvasive cardiac index using bioimpedance in comparison to direct Fick and thermodilution methods in patients with pulmonary hypertension. Chest. 1999;116(4):281S. 23 Ziegler D, Grotti L, Krucke G. Comparison of cardiac output measurements by TEB vs. intermittent bolus thermodilution in mechanical ven-

tilated patients. Chest. 1999;116(4):281S. 24 Sageman WS, Riffenburgh RH, Spiess BD. Equivalence of bioimpedance and thermodilution in measuring cardiac index after cardiac surgery. J Cardiothorac Vasc Anesth. 2002;16(1):8–14. 25 Van De Water JM, Miller TW. Impedance cardiography: the next vital sign technology? Chest. 2003;123(6):2028–2033. 26 Becker K Jr. Resolved: a pulmonary artery catheter should be used in the management of the critically ill patient. Con. J Cardiothorac Vasc Anesth. 1998;12(2 suppl 1):13–16. 27 Hendrickson K. Cost-effectiveness of noninvasive hemodynamic monitoring. AACN Clin Issues. 1999;10(3):419–426. 28 Taler SJ, Textor SC, Augustine JE. Resistant hypertension: comparing hemodynamic management to specialist care. Hypertension. 2002;39:982–988. 29 Taler S, Textor S, Augustine J, et al. Volume control in treatment of resistant hypertension: dissociation between cardiopulmonary volume, ANP and declining GFR. J Am Soc Nephrol. 2001;12(suppl):l492a. 30 Brodin LA, Jogestrand T, Larsen FF, et al. Effects of furosemide and slow-release furosemide on thoracic fluid volumes. Clin Cardiol. 1986;9(11):561–564. 31 Larsen G, Morgensen L, Tedner B. Influence of furosemide and body posture on transthoracic electrical bioimpedance in AMI. Chest. 1986;90:733–737. 32 Van de Water JM, Mount BE, Barela JR, et al. Monitoring the chest with impedance. Chest. 1973;64(5):597–603. 33 Peterson JR, Jensen BV, Drabaek H, et al. Electrical impedance measured changes in thoracic fluid content during thoracentesis. Clin Physiol. 1994;14:459–466. 34 Ventura HO, Pranulis MF, Young C, et al. Impedance cardiography: a bridge between research and clinical practice in the treatment of heart failure. Congest Heart Fail. 2000;6(2):40–47. 35 Peacock F, Summers R, Emerman C. Emergent dyspnea impedance cardiography-aided assessment changes therapy: the ED IMPACT trial. Ann Emerg Med. 2003;42(4):S82. 36 Shah MR, O’Connor CM, Sopko G, et al. Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE): design and rationale. Am Heart J. 2001;141(4):528–535.

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