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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 2  |  Issue : 2  |  Page : 32-38

Cheetah noninvasive cardiac output: A viable alternative to arterial line and pulmonary artery catheter cardiac output techniques after cardiac surgery in Sub-Saharan Africa


1 Dr. Joe Nwiloh Heart Center, St. Joseph's Hospital, Adazi Nnukwu, Anambra State, Nigeria
2 Department of Anesthesia, University of Nigeria Teaching Hospital, Ituku-Ozalla, Enugu State, Nigeria
3 Department of Anesthesia, College of Medicine/University College Hospital, Ibadan, Oyo State, Nigeria
4 Wellstar Atlanta Medical Center, Atlanta, Georgia, USA
5 Department of Surgery, Lagos State University Teaching Hospital, Ikeja, Lagos, Nigeria

Date of Web Publication26-Apr-2018

Correspondence Address:
Dr. Jonathan Nwiloh
Dr. Joe Nwiloh Heart Center, St. Joseph's Hospital, Adazi Nnukwu, Anambra State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njct.njct_2_18

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  Abstract 


Objective: The objective of the study is to determine the utility and practicality of Cheetah noninvasive cardiac output monitoring (NICOM) as a means of hemodynamic monitoring of adult patients after open heart surgery (OHS) in Sub-Saharan Africa (SSA). Materials and Methods: This was a single-institutional prospective study of eight adult patients undergoing OHS with cardiopulmonary bypass between August 2015 and April 2016. Cardiac output (CO) was calculated utilizing three measuring techniques; (1) Cheetah NICOM through skin electrodes, (2) FloTrac Vigileo through an arterial line, and (3) Vigilance through an oximetry Swan Ganz catheter (pulmonary artery catheter). CO readings were grouped into four intervals; precardiopulmonary bypass, postcardiopulmonary bypass, and first 24 h and second 24 h in Intensive Care Unit (ICU). The CO recordings from the three techniques were then compared for correlation between the noninvasive and two invasive techniques. Results: The mean patient age was 46.3 ± 15.7 years and 4 (50.0%) were males. Seven (87.5%) patients had acquired heart disease and 1 (12.5%) congenital heart disease. Three (37.5%) patients had severe pulmonary hypertension and 2 (25.0%) patients required intra-aortic balloon pump postoperatively. Correlation was highest in the ICU after patients were fully warm. Correlation coefficients were r = 0.56, bias 0.39 ± 2.34 between NICOM and Vigileo and r = 0.53, bias 1.43 ± 2.26 between NICOM and Vigilance within the first 24 h in ICU. In subsequent second 24 h in ICU, r = 0.84, bias − 0.16± −1.81 between NICOM and Vigileo and r = 0.29, bias 5.68 ± 1.55 between NICOM and Vigilance were the correlation coefficients. There was either none or poor correlation between NICOM and both the Vigileo or Vigilance pre- and post-cardiopulmonary bypass as most patients were still relatively hypothermic. Conclusion: NICOM reliably calculated CO in normothermic patients after OHS, showing average-to-high positive correlations with the Vigileo and Vigilance. Its easy applicability and cheaper cost make it more readily adaptable in SSA with limited finances and skilled healthcare workforce.

Keywords: Cheetah noninvasive cardiac output monitoring, heart surgery, invasive cardiac output


How to cite this article:
Nwiloh J, Ufoegbunam P, Akinyemi A, Klein E, Nwokocha O, Okafor N, Ariyo I. Cheetah noninvasive cardiac output: A viable alternative to arterial line and pulmonary artery catheter cardiac output techniques after cardiac surgery in Sub-Saharan Africa. Niger J Cardiovasc Thorac Surg 2017;2:32-8

How to cite this URL:
Nwiloh J, Ufoegbunam P, Akinyemi A, Klein E, Nwokocha O, Okafor N, Ariyo I. Cheetah noninvasive cardiac output: A viable alternative to arterial line and pulmonary artery catheter cardiac output techniques after cardiac surgery in Sub-Saharan Africa. Niger J Cardiovasc Thorac Surg [serial online] 2017 [cited 2020 Dec 1];2:32-8. Available from: http://www.nigjourcvtsurg.org/text.asp?2017/2/2/32/231274




  Introduction Top


A reliable method of estimating cardiac function and performance is essential to guide patient management after open heart surgery (OHS). The balloon-tipped flow directed Swan Ganz pulmonary artery catheter (PAC) which measures cardiac output (CO) by thermodilution has been the gold standard since first introduced into clinical practice in 1971.[1],[2] Nevertheless, due to its invasiveness and associated complications, other less invasive methods such as transesophageal echocardiogram (TEE) and FloTrac have evolved over time. However, TEE's utility is limited primarily to intraoperatively and not practical postoperatively in the ICU. The FloTrac Vigileo through an arterial line provides continuous display of CO both intraoperatively and postoperatively and has been validated to correlate closely with the PAC.[3] Similarly, the Cheetah noninvasive cardiac output monitoring (NICOM) which is completely 100% noninvasive uses bioreactance from skin electrodes to continuously display real-time CO intraoperatively and postoperatively.[4] Although previous studies of NICOM from the developed nations have demonstrated correlation with the PAC and FloTrac in several clinical scenarios,[5],[6] there is no study to the best of our knowledge from resource-poor countries seen in most of Sub-Saharan Africa (SSA).


  Materials and Methods Top


We prospectively enrolled eight adult patients undergoing OHS at Dr. Joe Nwiloh Heart Center, St. Joseph's Hospital, Adazi-Nnukwu, Anambra State, Nigeria, between August 2015 and April 2016 into the study. The protocol was approved by our institutional review board, and informed consent was obtained from each patient. The number of enrolled patients was limited by the available consumables for Cheetah NICOM. All patients were treated by our standard adult OHS protocol which included placement of an arterial line and a Swan Ganz PAC. Patients in addition had placement of the Cheetah NICOM skin electrodes on the anterior chest wall although they could also be placed on the posterior chest wall. CO measurements were recorded as close as simultaneously possible using the following three methodologies.

  1. Cheetah NICOM (Cheetah Medical Inc., Portland, OR, USA) - Uses bioreactance to calculate CO based on analysis of relative phase shifts of an oscillating current that occurs when this current traverses the thoracic cavity. Technique requires the connection of four double electrode sensors placed on the thorax
  2. FloTrac Vigileo (Edwards Lifesciences, Irvine, CA, USA) - Uses a software algorithm to calculate CO based on arterial pulse pressure, stroke volume, vessel compliance, and peripheral vascular resistance. Requires a specific pressure transducer which is attached to an arterial catheter and then connected to the Vigileo monitor
  3. Vigilance (Edwards Lifesciences, Irvine, CA, USA) - Provides continuous and comprehensive display of hemodynamic parameters including CO when used with a Swan Ganz PAC and mixed venous oxygen saturation (SvO2) when used with an Edwards oximetry catheter.


CO and cardiac index were displayed continuously by all three devices, with selected readings intermittently charted and then grouped into four interval periods; (1) before sternotomy and cardiopulmonary bypass, (2) postcardiopulmonary bypass and chest closure, (3) first 24 h in Intensive Care Unit (ICU), and (4) second 24 h in ICU. The CO measurements were usually terminated within 48 h postoperatively in most patients. The recorded values between these devices at the different intervals were compared using linear regression. All the data were entered into an Excel Spreadsheet and then imported into Sigma Plot (Systat Software, Inc., San Jose, CA, USA) for statistical analysis. Categorical variables were reported as frequencies and percentages, while continuous variables were reported as median, mean ± standard deviation. Correlation coefficient to measure the strength of association between two variables was calculated using the Pearson's Product Moment correlation. Bland–Altman analysis was used to determine the bias and variability differences between the NICOM versus the Vigileo and NICOM versus Vigilance.


  Results Top


There were eight patients with 4 (50.0%) males and mean age 46.3 ± 15.7 years. The preoperative demographics, diagnosis, and surgical procedures are summarized in [Table 1], [Table 2], [Table 3]. Two patients with mitral valve disease had severe pulmonary hypertension, and one patient with atrial septal defect had systemic pulmonary hypertension with bidirectional shunting. Patients were placed on inotropes and pressors as needed to maintain adequate hemodynamics. In addition to inotropes, two patients required mechanical heart support with intra-aortic balloon pump (IABP) postcardiopulmonary bypass to maintain adequate hemodynamics. For the purposes of the study, we selected CO values taken simultaneously close as possible between the devices during each of the four interval periods for analysis. The values for NICOM were then compared individually with Vigileo and Vigilance for correlation. The recorded values for each interval period are shown in [Table 4]. The obtained values precardiopulmonary bypass was plotted in scatter charts [Figure 1] and [Figure 2]. The correlation coefficient between the NICOM and Vigilance was r = 0.25 indicating a weak positive association while r = 0 between the NICOM and Vigileo indicating no relationship. Postcardiopulmonary bypass scatter charts [Figure 3] and [Figure 4] show r = 0.30 between NICOM and Vigilance and r = 0.20 between NICOM and Vigileo, both indicating weak positive associations. The first 24 h ICU scatter charts show r = 0.53 between NICOM and Vigilance and r = 0.56 between NICOM and Vigileo both indicating moderate positive associations. The corresponding Bland–Altman plot also shows all the CO values within two standard deviations (STD) of the bias 0.395 between the NICOM and Vigileo and only three CO values outside of two STD of the bias 1.439 for Vigilance [Figure 5] and [Figure 6]. The second 24 h ICU scatter charts show r = 0.29 between NICOM and Vigilance indicating a weak positive association and r = 0.84 between NICOM and Vigileo indicating a strong positive association. The corresponding Bland–Altman plots shows only two values outside of two STD of the bias −0.166 for the NICOM and Vigileo [Figure 7] and [Figure 8].
Table 1: Preoperative demography

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Table 2: Preoperative diagnosis

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Table 3: Procedures performed

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Table 4: Analyzed recorded cardiac outputs

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Figure 1: Comparison of noninvasive cardiac output monitoring and Vigilance precardiopulmonary bypass.

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Figure 2: Comparison of noninvasive cardiac output monitoring and Vigileo prebypass.

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Figure 3: Comparison of noninvasive cardiac output monitoring and Vigilance postbypass.

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Figure 4: Comparison of noninvasive cardiac output monitoring and Vigileo postcardiopulmonary bypass.

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Figure 5: Comparison of noninvasive cardiac output monitoring and Vigilance Intensive Care Unit.

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Figure 6: Comparison of noninvasive cardiac output monitoring and Vigileo in Intensive Care Unit.

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Figure 7: Comparison of noninvasive cardiac output monitoring and Vigilance after 24 h.

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Figure 8: Comparison of noninvasive cardiac output monitoring and Vigileo after 24 h.

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  Discussion Top


After the initial wave of enthusiasm and wide spread deployment of the Swan Ganz catheter in critically ill patients, subsequent studies showing questionable benefits in clinical outcomes coupled with recognition of potential associated complications has led to a more selective usage.[7],[8] Its utilization has therefore gradually decreased significantly over the last two decades and is now limited in most Institutions to patients undergoing OHS.[3] Because of these concerns, especially the known complications associated with the PAC, less invasive techniques of determining CO in clinical practice have subsequently evolved. The FloTrac Vigileo through an arterial line calculates CO and other hemodynamic parameters from the arterial pulse pressure waveforms using special software algorithm. The Vigileo allows continuous CO display and does not require any calibration. Several studies have validated the correlation in CO measurements between the Flora and PAC thermodilution. Cannesson et al.[3] in a review of 11 patients after cardiac surgery comparing CO by PAC and FloTrac found clinically acceptable agreements between them. The FloTrac CO is however invalidated in the presence of an IABP which causes diastolic blood pressure augmentation, thus interfering with the arterial wave form analysis used for computation. While the FloTrac still requires placement of a radial or femoral arterial line, it is significantly less invasive with minimal morbidity compared to the PAC technique. The accuracy of the completely 100% noninvasive thoracic bioimpedance technique has evolved and improved over time. The newer generation device such as the Cheetah NICOM has been demonstrated in several validation studies to have good correlation with invasive techniques in clinical settings. Squara et al.[4] in their review of 110 patients requiring PAC in the immediate postoperative period after cardiac surgery found that the NICOM when compared to PAC most often had acceptable accuracy in a wide range of circulatory scenarios. Similarly, another review by Marqué et al.[9] of 29 patients compared CO measurements by PAC, FloTrac Vigileo, and NICOM during the immediate postoperative period after cardiac surgery. They concluded based on their findings that the NICOM and Vigileo had equivalent monitoring capabilities. Our review equally showed positive correlations between the NICOM and both invasive techniques although correlation was higher with the Vigileo. We in addition observed that there were stronger positive correlations in the ICU than in the operating room. This we believe may be attributable to the long anesthesia preparatory period, with patients temperatures trending downward, as most were often hypothermic before sternotomy and initiation of moderate hypothermic cardiopulmonary bypass. We furthermore noticed that prebypass hypothermia appeared to interfere with the skin electrodes sensors and following sternotomy with chest spreading, the distance of the skin electrodes increased from the heart, with both these two factors appearing to affect the CO reliability. These interferences and resultant disparities between the NICOM, Vigileo, and Vigilance however tend to decrease following rewarming and chest closure. The improvement continues into the ICU as the patients reach normothermia as evidenced by the stronger positive correlation with Vigileo and Vigilance, highest with the Vigileo during the second 24 h in the ICU. The Bland–Altman statistical analysis [10] which assesses the agreement between clinical measurements from two methods shows most of the values falling between two standard deviation of the bias between NICOM and Vigileo and NICOM and Vigilance in our patients once in the ICU and fully warm. Therefore, because the NICOM is very user-friendly, is easy to place, and avoids waiting for a physician to place an invasive vascular line, it can be deployed anywhere within the hospital. In addition, there is no risk of infection or vascular injury, especially in older patients associated with the other invasive techniques. The CO accuracy is also not affected by inotropes, vasopressors, or shock. The nurses can easily be trained to set it up and obtain baseline hemodynamic profile even before the patient gets to the anesthesia holding area or operating room. Concerted efforts to limit hypothermia once patient enters the operating room will also help maintain reliability of the CO measurements. We have since used the NICOM as the sole CO measuring tool to guide postoperative hemodynamic management in a patient undergoing isolated mitral valve replacement with satisfactory results.

The NICOM cost, though higher than desired, remains cheaper than the Vigileo and Vigilance, in addition to having zero morbidity. The skin electrodes are the only incurred cost for use as the monitor is provided free by the manufacturer. One of its major advantages over the other two methods as mentioned previously is the ease of deployment analogous to placing electrocardiogram electrodes, compared to the required skills to insert arterial or central venous lines for Vigileo and Vigilance, respectively. Given the paucity of trained and skilled personnel in resource-poor countries seen in most of SSA, the NICOM provides a simple and reliable method of measuring CO in low-to-moderate risk adolescents and adults undergoing OHS. The Vigileo requiring only an arterial line is equally a viable alternative to the PAC in these resource-poor countries with dearth of skilled workforce. Our study limitation includes being a single-institutional study with a small number of patients.


  Conclusion Top


This review of Cheetah NICOM demonstrates a moderate-to-high positive correlation with both the Vigileo and Vigilance in a small cohort of adult patients undergoing OHS at our Institution. This encouraging preliminary finding has prompted us to continue its use with more patients to further confirm its reliability and ability to be used as the sole CO measuring tool in our patients after OHS. Although the NICOM has been shown to be comparable to PAC in nonsurgical patients with pulmonary hypertension,[11] we still recommend PAC in surgical patients with severe left ventricular dysfunction, with severe pulmonary hypertension, or requiring mechanical heart assistance with the IABP.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Ganz W, Donoso R, Marcus HS, Forrester JS, Swan HJ. A new technique for measurement of cardiac output by thermodilution in man. Am J Cardiol 1971;27:392-6.  Back to cited text no. 1
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2.
Reuter DA, Huang C, Edrich T, Shernan SK, Eltzschig HK. Cardiac output monitoring using indicator-dilution techniques: Basics, limits, and perspectives. Anesth Analg 2010;110:799-811.  Back to cited text no. 2
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3.
Cannesson M, Attof Y, Rosamel P, Joseph P, Bastien O, Lehot JJ, et al. Comparison of floTrac cardiac output monitoring system in patients undergoing coronary artery bypass grafting with pulmonary artery cardiac output measurements. Eur J Anaesthesiol 2007;24:832-9.  Back to cited text no. 3
    
4.
Squara P, Denjean D, Estagnasie P, Brusset A, Dib JC, Dubois C, et al. Noninvasive cardiac output monitoring (NICOM): A clinical validation. Intensive Care Med 2007;33:1191-4.  Back to cited text no. 4
    
5.
Raval NY, Squara P, Cleman M, Yalamanchili K, Winklmaier M, Burkhoff D, et al. Multicenter evaluation of noninvasive cardiac output measurement by bioreactance technique. J Clin Monit Comput 2008;22:113-9.  Back to cited text no. 5
    
6.
Moshkovitz Y, Kaluski E, Milo O, Vered Z, Cotter G. Recent developments in cardiac output determination by bioimpedance: Comparison with invasive cardiac output and potential cardiovascular applications. Curr Opin Cardiol 2004;19:229-37.  Back to cited text no. 6
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7.
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;12:13-6.  Back to cited text no. 7
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8.
Vender JS. Resolved: A pulmonary artery catheter should be used in the management of the critically ill patient. Pro. J Cardiothorac Vasc Anesth 1998;12:9-12.  Back to cited text no. 8
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9.
Marqué S, Cariou A, Chiche JD, Squara P. Comparison between flotrac-vigileo and bioreactance, a totally noninvasive method for cardiac output monitoring. Crit Care 2009;13:R73.  Back to cited text no. 9
    
10.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307-10.  Back to cited text no. 10
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11.
Rich JD, Archer SL, Rich S. Noninvasive cardiac output measurements in patients with pulmonary hypertension. Eur Respir J 2013;42:125-33.  Back to cited text no. 11
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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