Elsevier

Resuscitation

Volume 80, Issue 8, August 2009, Pages 893-897
Resuscitation

Clinical paper
Continuous cardiac index monitoring: A prospective observational study of agreement between a pulmonary artery catheter and a calibrated minimally invasive technique,☆☆

https://doi.org/10.1016/j.resuscitation.2009.04.015Get rights and content

Abstract

Introduction

Continuous cardiac index (CCI) monitoring can provide information to assist in hemodynamic support. However, pulmonary artery catheters (PAC) pose logistic challenges in acute care settings. We hypothesized that CCI measured with a calibrated minimally invasive technique (LiDCO/PulseCO, UK) would have good agreement with the PAC.

Methods

We performed a prospective observational study in post-operative cardiac surgery patients. All patients had a PAC with CCI monitoring capability. We connected the LiDCO apparatus to a radial artery line and performed a one-time calibration with a lithium dilution indicator. In order to test the least invasive method possible, we used a peripheral intravenous (IV) line for indicator delivery rather than the conventional central line technique. We recorded paired PAC/LiDCO-PulseCO CCI measurements every minute for 3 h. We blinded investigators and clinicians to minimally invasive data with an opaque shield over the monitor. We assessed agreement with Bland-Altman analysis.

Results

We obtained 1485 paired measurements in 8 subjects. The mean CI was 2.9 L/min/m2. By Bland-Altman plot, PAC and LiDCO measurements showed minimal bias (−0.01), but the 95% limits of agreement (±2SD) of ± 1.3 L/min/m2 were relatively wide with respect to the mean.

Conclusions

This calibrated minimally invasive (i.e. radial arterial line and peripheral IV) technique demonstrated low bias compared with CCI measured by PAC. However, the relatively wide confidence limits indicate that differences in the two measurements could still be clinically significant.

Introduction

Quantitative resuscitation can improve outcomes for critically ill patients.1, 2, 3 As cardiac index can be an important target of a quantitative resuscitation strategy,2 continuous cardiac index (CCI) monitoring may provide important information to guide early hemodynamic support. However, in settings where early resuscitation is commonly performed (e.g. emergency department), pulmonary artery catheterization (PAC) may pose logistic challenges due to its invasive nature and the necessary equipment required for the procedure. Even when available, the elapsed time from the decision to insert a PAC until the time that hemodynamic values are obtained is typically 90 min or more,4 making the PAC less than optimal for the early resuscitation period. Furthermore, there are concerns of potential increased morbidity associated with PAC use.5, 6 Validating a less invasive technique for CCI monitoring would be pertinent for emergency medicine and critical care practice.

There are less invasive systems that use pulse contour or pulse power analysis of a peripheral arterial line to determine cardiac index. One can be calibrated with a lithium indicator dilution (LiDCO/PulseCO, UK). In previous studies, this technique has shown good agreement with a PAC for serial cardiac index measurements.7, 8 However, most of these studies used intermittent measurements (rather than continuous) and a central venous catheter for indicator delivery. Central venous catheterization poses logistic challenges of its own for the earliest phase of resuscitation.9 In addition, continuous data may be more useful in a population undergoing multiple rapid treatments. Thus, validating a calibrated minimally invasive technique that would not require central venous catheterization could potentially make continuous cardiac index monitoring feasible in a broader scope of acute care settings.

We hypothesized that CCI measured with a minimally invasive calibrated pulse power analysis technique would have good agreement with CCI measured with a PAC. Our purpose was to test this hypothesis using the least invasive method possible for calibration (i.e. peripheral intravenous line and peripheral arterial line thus obviating the need for central venous catheterization), continuous rather than intermittent cardiac index measurement, and a one-time initial calibration set which would be an important practical aspect for translation to early resuscitation settings.

Section snippets

Methods

Study Design: Prospective observational study.

Setting: Intensive Care Unit (ICU) of an urban academic medical center (Cooper University Hospital, Camden, NJ, USA).

Human Subjects Protection: The Institutional Review Board approved this study. All participants gave written informed consent.

Participants: We enrolled a convenience sample of adults undergoing cardiac surgery. We selected cardiac surgery patients for this study on the grounds that (1) they often demonstrate dynamic changes in cardiac

Results

We obtained 1485 paired measurements in eight subjects whose mean age was 63 years. The subjects underwent one to four vessel coronary artery bypass grafting with a mean time on cardiopulmonary bypass pump of 70 min. All subjects were mechanically ventilated for the duration of the study. All subjects received intravenous vasoactive agents including nitroglycerin (100%), nicardipine (25%), nitroprusside (25%), fenoldopam (12%), and milrinone (12%) (Table 1). Initial mean heart rate, central

Discussion

In this prospective observational study, we found moderate agreement between the minimally invasive LiDCO/PulseCO technique and the pulmonary artery catheter for continuous cardiac index monitoring using the analysis method of Bland and Altman.12 However, interpretation of the agreement requires consideration of the clinical relevance of the limits of agreement (LOA). The relatively wide LOA could indeed be clinically significant in some circumstances.

Our study differs from prior studies in

Conclusions

This calibrated minimally invasive technique for continuous cardiac index measurement demonstrated moderate agreement with CCI measured by PAC. However, the relatively wide limits of agreement indicate that differences between the two measurement techniques could still be clinically significant. The peripheral calibration of the minimally invasive technique and the continuous measurement aspect may contribute to the wide limits of agreement.

Funding sources

This was an investigator-initiated study which was performed without financial or other support from any commercial interest.

Author contributions

JVM had full access to all of the data in the study and takes full responsibility for the integrity of the data and the accuracy of the analysis. JVM, RPD, JEP, SMH, ST were responsible for study concept and design. JVM, LR, VL, PP acquired the data. JVM, PP, SMH, ST were responsible for analysis and interpretation of data. JVM, SMH, RCA, ST were responsible for drafting the article. RPD, JEP, LR, VL, RCA, SMH, ST were responsible for critical revision of the article for insight, impact,

Conflict of interest statement

Dr. Trzeciak has previously received industry research support from Biosite and Eli Lilly, and currently receives research support from Novo Nordisk and INO Therapeutics. The other authors declare that they have no competing financial or personal interests that could inappropriately bias their work.

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    Citation Excerpt :

    Literature about the reliability and clinical value of PWA monitors has been variable. A high degree of correlation between CO obtained by the PWA method and PAC has been demonstrated in different clinical settings, including cardiac surgery, burn surgery, neurosurgery, and septic patients.107–112 In a study by Hamzaoui and colleagues,113 the reliability of PiCCO in subjects with rapidly changing vascular tone was found to be good with frequent calibrations.

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A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2009.04.015.

☆☆

This study was presented in abstract form at the 2008 Society for Academic Emergency Medicine annual meeting, Washington, D.C.

1

Currently with UMDNJ-Robert Wood Johnson Medical School, Robert Wood Johnson University Hospital, New Brunswick, NJ, USA.

2

Currently with the University of Pennsylvania, Philadelphia, PA, USA.

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