The accuracy and trending ability of cardiac index measured by the fourth-generation FloTrac/Vigileo system™ and the Fick method in cardiac surgery patients

Continuous cardiac output estimation using a new modified Fick method during off-pump coronary artery bypass graft surgery: a retrospective observational study

PURPOSE

Several technical aspects of the Fick method limit its use intraoperatively. A data-driven modification of the Fick method may enable its use in intraoperative settings.

METHODS

This two-center retrospective observational study included 57 (28 and 29 in each center) patients who underwent off-pump coronary artery bypass graft (OPCAB) surgery. Intraoperative recordings of physiological data were obtained and divided into training and test datasets. The Fick equation was used to calculate cardiac output (CO-Fick) using ventilator-determined variables, intraoperative hemoglobin level, and SvO2, with continuous thermodilution cardiac output (CCO) used as a reference. A modification CO-Fick was derived and validated: CO-Fick-AD, which adjusts the denominator of the original equation.

RESULTS

Increased deviation between CO-Fick and CCO was observed when oxygen extraction was low. The root mean square error of CO-Fick was decreased from 6.07 L/min to 0.70 L/min after the modification. CO-Fick-AD showed a mean bias of 0.17 (95% CI 0.00-0.34) L/min, with a 36.4% (95% CI 30.6-44.4%) error. The concordance rates of CO-Fick-AD ranged from 73.3 to 87.1% depending on the time interval and exclusion zone.

CONCLUSIONS

The original Fick method is not reliable when oxygen extraction is low, but a modification using data-driven approach could enable continuous estimation of cardiac output during the dynamic intraoperative period with minimal bias. However, further improvements in precision and trending ability are needed.

Perioperative hemodynamic monitoring in cardiac surgery

PURPOSE OF REVIEW

Cardiac surgery has traditionally relied upon invasive hemodynamic monitoring, including regular use of pulmonary artery catheters. More recently, there has been advancement in our understanding as well as broader adoption of less invasive alternatives. This review serves as an outline of the key perioperative hemodynamic monitoring options for cardiac surgery.

RECENT FINDINGS

Recent study has revealed that the use of invasive monitoring such as pulmonary artery catheters or transesophageal echocardiography in low-risk patients undergoing low-risk cardiac surgery is of questionable benefit. Lesser invasive approaches such a pulse contour analysis or ultrasound may provide a useful alternative to assess patient hemodynamics and guide resuscitation therapy. A number of recent studies have been published to support broader indication for these evolving technologies.

SUMMARY

More selective use of indwelling catheters for cardiac surgery has coincided with greater application of less invasive alternatives. Understanding the advantages and limitations of each tool allows the bedside clinician to identify which hemodynamic monitoring modality is most suitable for which patient.

Accuracy of Cardiac Output Measured by Fourth-Generation Flotrac and Lidcorapid, and Their Characteristics Regarding Systemic Vascular Resistance in Patients Undergoing Cardiac Surgery

OBJECTIVES

The clinical use of less-invasive devices that calculate the cardiac output from arterial pressure waveform is increasing. The authors aimed to evaluate the accuracy and characteristics of the systemic vascular resistance index (SVRI) of the cardiac index measured by 2 less-invasive devices, fourth-generation FloTrac (CI_FT) and LiDCOrapid (CI_LR), compared with the intermittent thermodilution technique, using a pulmonary artery catheter (CI_TD).

DESIGN

This was a prospective observational study.

SETTING

This study was conducted at a single university hospital.

PARTICIPANTS

Twenty-nine adult patients undergoing elective cardiac surgery.

INTERVENTIONS

Elective cardiac surgery was used as an intervention.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters, CI_FT, CI_LR, and CI_TD, were measured after the induction of general anesthesia, at the start of cardiopulmonary bypass, after completion of weaning from cardiopulmonary bypass, 30 minutes after weaning, and at sternal closure (135 measurements in total). The CI_FT and CI_LR had moderate correlations with CI_TD (r = 0.62 and 0.58, respectively). Compared with CI_TD, CI_FT, and CI_LR had a bias of -0.73 and -0.61 L/min/m², limit of agreement of -2.14-to-0.68 L/min/m² and -2.42-to-1.20 L/min/m², and percentage error of 39.9% and 51.2%, respectively. Subgroup analysis for evaluating SVRI characteristics showed that the percentage errors of CI_FT and CI_LR were 33.9% and 54.5% in low SVRI (<1,200 dyne×s/cm⁵/m), 37.6% and 47.9% in moderate SVRI (1,200-1,800 dyne×s/cm⁵/m), 49.3% and 50.6% in high SVRI (>1,800 dyne·s/cm⁵/m²), respectively.

CONCLUSIONS

The accuracy of CI_FT or CI_LR was not clinically acceptable for cardiac surgery. Fourth-generation FloTrac was unreliable in high SVRI. LiDCOrapid was inaccurate across a broad range of SVRI, and minimally affected by SVRI.

Validation of cardiac output estimation using the fourth-generation FloTrac/EV1000™ system in patients undergoing robotic-assisted off-pump coronary artery bypass surgery

The pulmonary artery catheter (PAC)-despite its invasiveness-remains the gold standard for cardiac output (CO) monitoring. The FloTrac system, a less invasive hemodynamic monitor has been developed, which estimates CO using arterial pressure waveform analysis without external calibration. Recently, an upgraded version of FloTrac system with improved algorithm to follow changes in vascular resistance was introduced into the market. The aim of this study was to assess the reliability of the CO estimated from the fourth-generation FloTrac/EV1000 system (CO_FT) compared to that measured with PAC using the thermodilution method (CO_PAC) during robotic-assisted off-pump coronary artery bypass (OPCAB) surgery. CO_FT and CO_PAC were obtained simultaneously at 4 predefined time points during robotic-assisted OPCAB: 5 min after the induction of general anesthesia (T1), after starting one-lung ventilation (T2), after capnothorax (T3), and after mini-thoracotomy was performed (T4). The agreement of data was investigated by Bland-Altman analysis. Thirty-four patients were initially enrolled. After exclusion, 32 patients and a total of 128 paired CO measurements were obtained. The overall bias was 1.46 L/min, the 95% limits of agreements were - 3.40 to 6.33 L/min, and the percentage error was 72.98%. Regression analysis of the systemic vascular resistance index (SVRI) and the bias between CO_PAC and CO_FT showed that the bias was moderately correlated with the SVRI (r² = 0.43; p < 0.0001). Despite a software upgrade, the reliability of the fourth-generation FloTrac/EV1000™ system during robotic-assisted OPCAB to estimate CO was not acceptable, especially in patients with low SVRI.

Comparison between Fourth-Generation FloTrac/Vigileo System and Continuous Thermodilution Technique for Cardiac Output Estimation after Time Adjustment during Off-Pump Coronary Artery Bypass Graft Surgery: A Retrospective Cohort Study

(1) Background: Previous studies reported limited performance of arterial pressure waveform-based cardiac output (CO) estimation (FloTrac/Vigileo system; CO-FloTrac) compared with the intermittent thermodilution technique (CO_int). However, errors due to bolus maneuver and intermittent measurements of CO_int could limit its use as a reference. The continuous thermodilution technique (CO_cont) may relieve such limitations. (2) Methods: The performance of CO-FloTrac was retrospectively assessed using continuous recordings of intraoperative physiological data acquired from patients who underwent off-pump coronary artery bypass graft (OPCAB) surgery with CO monitoring using both CO-FloTrac and CO_cont. Optimal time adjustments between the two measurements were determined based on R-squared values. (3) Results: A total of 134.2 h of data from 30 patients was included in the final analysis. The mean bias was -0.94 (95% CI, -1.35 to -0.52) L/min and the limits of agreements were -3.64 (95% CI, -4.44 to -3.08) L/min and 1.77 (95% CI, 1.21 to 2.57) L/min. The percentage error was 66.1% (95% CI, 52.4 to 85.8%). Depending on the time scale and the size of the exclusion zone, concordance rates ranged from 61.0% to 75.0%. (4) Conclusion: Despite the time adjustments, CO-FloTrac showed non-negligible overestimation, clinically unacceptable precision, and poor trending ability during OPCAB surgery.

Hemodynamic Monitoring Using a Pulmonary Artery Catheter Versus the Vigileo/FloTrac System during Elective Cardiac Surgery Based on Real-world Data in Japan

BACKGROUND

The controversy concerning the benefits of pulmonary artery catheter (PAC)-based hemodynamic monitoring in cardiac surgeries has not been adequately addressed. This study aims to compare the all-cause mortality between the PAC with venous oxygen saturation monitoring and the Vigileo/FloTrac (FloTrac) system with central venous oxygen saturation monitoring in cardiac surgeries.

METHODS

This nationwide retrospective study includes adult patients who underwent elective cardiac surgeries between April 2010 and October 2014, based on the Japanese health insurance claims database. The main outcome was 30-day all-cause mortality. Propensity scores (PS) were used to adjust for the confounding factors. Treatment effects were estimated using multivariable logistic regression analysis, including PS.

RESULTS

A total of 5,838 patients were included in this study. The crude 30-day mortality rates were 2.4% (8/334) and 1.7% (96/5,504) in the FloTrac and PAC groups, respectively. After PS matching, the ORs for 30-day all-cause mortality, in-hospital mortality after PAC placement (vs. FloTrac) were 0.36 (95% CI: 0.05-2.37; p = 0.28) and 0.59 (95% CI: 0.16-2.20; p = 0.43), respectively. The amount of dobutamine was larger in the PAC group (281 ± 31 mg vs 155 ± 19 mg; p < 0.001). There were no significant differences in the amounts of other inotropes, the volume of fluids, or blood transfusions.

CONCLUSIONS

The association between PAC (with venous oxygen saturation monitoring) and mortality in patients who underwent elective cardiac surgeries was unclear compared to FloTrac (with central venous oxygen saturation monitoring). Additional investigation is needed to evaluate the benefits of PAC-specific hemodynamic parameters in this population.

Clinical Application of the Fluid Challenge Approach in Goal-Directed Fluid Therapy: What Can We Learn From Human Studies?

Resuscitative fluid therapy aims to increase stroke volume (SV) and cardiac output (CO) and restore/improve tissue oxygen delivery in patients with circulatory failure. In individualized goal-directed fluid therapy (GDFT), fluids are titrated based on the assessment of responsiveness status (i.e., the ability of an individual to increase SV and CO in response to volume expansion). Fluid administration may increase venous return, SV and CO, but these effects may not be predictable in the clinical setting. The fluid challenge (FC) approach, which consists on the intravenous administration of small aliquots of fluids, over a relatively short period of time, to test if a patient has a preload reserve (i.e., the relative position on the Frank-Starling curve), has been used to guide fluid administration in critically ill humans. In responders to volume expansion (defined as individuals where SV or CO increases ≥10–15% from pre FC values), FC administration is repeated until the individual no longer presents a preload reserve (i.e., until increases in SV or CO are <10–15% from values preceding each FC) or until other signs of shock are resolved (e.g., hypotension). Even with the most recent technological developments, reliable and practical measurement of the response variable (SV or CO changes induced by a FC) has posed a challenge in GDFT. Among the methods used to evaluate fluid responsiveness in the human medical field, measurement of aortic flow velocity time integral by point-of-care echocardiography has been implemented as a surrogate of SV changes induced by a FC and seems a promising non-invasive tool to guide FC administration in animals with signs of circulatory failure. This narrative review discusses the development of GDFT based on the FC approach and the response variables used to assess fluid responsiveness status in humans and animals, aiming to open new perspectives on the application of this concept to the veterinary field.

An observational feasibility study - does early limb ergometry affect oxygen delivery and uptake in intubated critically ill patients - a comparison of two assessment methods

Background

Early rehabilitation can reduce ventilation duration and improve functional outcomes in critically ill patients. Upper limb strength is associated with ventilator weaning. Passive muscle loading may preserve muscle fibre function, help recover peripheral muscle strength and improve longer term, post-hospital discharge function capacity. The physiological effects of initiating rehabilitation soon after physiological stabilisation of these patients can be concerning for clinicians. This study investigated the feasibility of measuring metabolic demand and the safety and feasibility of early upper limb passive ergometry. An additional comparison of results, achieved from simultaneous application of the methods, is reported.

Methods

This was an observational feasibility study undertaken in an acute teaching hospital’s General Intensive Care Unit in the United Kingdom. Twelve haemodynamically stable, mechanically ventilated patients underwent 30 minutes of arm ergometry. Cardiovascular and respiratory parameters were monitored. A Friedman test identified changes in physiological parameters. A metabolic cart was attached to the ventilator to measure oxygen uptake. Oxygen uptake was concurrently calculated by the reverse Fick method, utilising cardiac output from the LiDCO™ and paired mixed venous and arterial samples. A comparison of the two methods was made. Data collection began 10 minutes before ergometry and continued to recovery. Paired mixed venous and arterial samples were taken every 10 minutes.

Results

Twelve patients were studied; 9 male, median age 55 years, range (27–82), median APACHE score 18.5, range (7–31), median fraction inspired oxygen 42.5%, range (28–60). Eight patients were receiving noradrenaline. Mean dose was 0.07 mcg/kg/min, range (0.01–0.15). Early ergometry was well tolerated. There were no clinically significant changes in respiratory, haemodynamic or metabolic variables pre ergometry to end recovery. There was no significant difference between the two methods of calculating VO₂ (p = 0.70).

Conclusions

We report the feasibility of using the reverse Fick method and indirect calorimetry to measure metabolic demand during early physical rehabilitation of critically ill patients. More research is needed to ascertain the most reliable method. Minimal change in metabolic demand supports the safety and feasibility of upper limb ergometry. These results will inform future study designs for further research into exercise response in critically ill patients.

Trial Registration

Clinicaltrials.gov No. NCT04383171. Registered on 06 May 2020 - Retrospectively registered. http://www.clinicaltrials.gov.

Bioreactance Cardiac Output Trending Ability in Preterm Infants: A Single Centre, Longitudinal Study

INTRODUCTION

It is unknown whether bioreactance (BR) can accurately track cardiac output (CO) changes in preterm neonates.

METHODS

A prospective observational longitudinal study was performed in stable preterm infants (<37 weeks) during the first 72 h of life. Stroke volume (SV) and CO, as measured by BR and transthoracic echocardiography, were compared.

RESULTS

The mean gestational age (GA) was 31.3 weeks and mean birth weight (BW) was 1,563 g. Overall, 690 measurements were analysed for trending ability by 4-quadrant and polar plots. For non-weight-indexed measurements, 377 (54.6%) lay outside the 5% exclusion zone, the concordance rate was poor (77.2%) with a high mean angular bias (28.6°), wide limits of agreement and a poor angular concordance rate (17.4%). Neither GA, BW nor respiratory support mode affected trending data. Patent ductus arteriosus, postnatal age, and CO level had variable effects on trending data. Trending data for 5 and 10% exclusion zones were also compared.

CONCLUSION

The ability of BR to track changes in CO is not interchangeable with CO changes as measured by echocardiography. BR, as a trend monitor for changes in CO or SV to determine clinical decisions around interventions in neonatology, should be used with caution.

Perioperative non-invasive versus semi-invasive cardiac index monitoring in patients with bariatric surgery - a prospective observational study

Background

In morbidly obese patients undergoing laparoscopic bariatric surgery, the combination of obesity-related comorbidities, pneumoperitoneum and extreme posture changes constitutes a high risk of perioperative hemodynamic complications. Thus, an advanced hemodynamic monitoring including continuous cardiac index (CI) assessment is desirable. While invasive catheterization may bear technical difficulties, transesophageal echocardiography is contraindicated due to the surgical procedure. Evidence on the clinical reliability of alternative semi- or non-invasive cardiac monitoring devices is limited. The aim was to compare the non-invasive vascular unloading to a semi-invasive pulse contour analysis reference technique for continuous CI measurements in bariatric surgical patients.

Methods

This prospective observational study included adult patients scheduled for elective, laparoscopic bariatric surgery after obtained institutional ethics approval and written informed consent. CI measurements were performed using the vascular unloading technique (Nexfin®) and semi-invasive reference method (FloTrac™). At 10 defined measurement time points, the influence of clinically indicated body posture changes, passive leg raising, fluid bolus administration and pneumoperitoneum was evaluated pre- and intraoperatively. Correlation, Bland-Altman and concordance analyses were performed.

Results

Sixty patients (mean BMI 49.2 kg/m²) were enrolled into the study and data from 54 patients could be entered in the final analysis. Baseline CI was 3.2 ± 0.9 and 3.3 ± 0.8 l/min/m², respectively. Pooled absolute CI values showed a positive correlation (r_s = 0.76, P < 0.001) and mean bias of of − 0.16 l/min/m² (limits of agreement: − 1.48 to 1.15 l/min/m²) between the two methods. Pooled percentage error was 56.51%, missing the criteria of interchangeability (< 30%). Preoperatively, bias ranged from − 0.33 to 0.08 l/min/m² with wide limits of agreement. Correlation of CI was best (r_s = 0.82, P < 0.001) and percentage error lowest (46.34%) during anesthesia and after fluid bolus administration. Intraoperatively, bias ranged from − 0.34 to − 0.03 l/min/m² with wide limits of agreement. CI measurements correlated best during pneumoperitoneum and after fluid bolus administration (r_s = 0.77, P < 0.001; percentage error 35.95%). Trending ability for all 10 measurement points showed a concordance rate of 85.12%, not reaching the predefined Critchley criterion (> 92%).

Conclusion

Non-invasive as compared to semi-invasive CI measurements did not reach criteria of interchangeability for monitoring absolute and trending values of CI in morbidly obese patients undergoing bariatric surgery.

Trial registration

The study was registered retrospectively on June 12, 2017 with the registration number NCT03184272.

Comparing the Mutual Interchangeability of ECOM, FloTrac/Vigileo, 3D-TEE, and ITD-PAC Cardiac Output Measuring Systems in Coronary Artery Bypass Grafting

OBJECTIVE

The aim of this study was to compare the mutual interchangeability of 4 cardiac output measuring devices by comparing their accuracy, precision, and trending ability.

DESIGN

A single-center prospective observational study.

DESIGN

Nonuniversity teaching hospital, single center.

PARTICIPANTS

Forty-four consecutive patients scheduled for elective, nonemergent coronary artery bypass grafting (CABG).

INTERVENTIONS

The cardiac output was measured for each participant using 4 methods: intermittent thermodilution via pulmonary artery catheter (ITD-PAC), Endotracheal Cardiac Output Monitor (ECOM), FloTrac/Vigileo System (FLOTRAC), and 3-dimensional transesophageal echocardiography (3D-TEE).

MEASUREMENTS AND MAIN RESULTS

Measurements were performed simultaneously at 5 time points: presternotomy, poststernotomy, before cardiopulmonary bypass, after cardiopulmonary bypass, and after sternal closure. A series of statistical and comparison analyses including ANOVA, Pearson correlation, Bland-Altman plots, quadrant plots, and polar plots were performed, and inherent precision for each method and percent errors for mutual interchangeability were calculated. For the 6 two-by-two comparisons of the methods, the Pearson correlation coefficients (r), the percentage errors (% error), and concordance ratios (CR) were as follows: ECOM_versus_ITD-PAC (r = 0.611, % error = 53%, CR = 75%); FLOTRAC_versus_ITD-PAC (r = 0.676, % error = 49%, CR = 77%); 3D-TEE versus ITD-PAC (r = 0.538, % error = 64%, CR = 67%); FLOTRAC_versus_ECOM (r = 0.627, % error = 51%, CR = 75%); 3D-TEE_versus ECOM (r = 0.423, % error = 70%, CR = 60%), and 3D-TEE_versus_FLOTRAC (r = 0.602, % error = 59%, CR = 61%).

CONCLUSIONS

Based on the recommended statistical measures of interchangeability, ECOM, FLOTRAC, and 3D-TEE are not interchangeable with each other or to the reference standard invasive ITD-PAC method in patients undergoing nonemergent cardiac bypass surgery. Despite the negative result in this study and the majority of previous studies, these less-invasive methods of CO have continued to be used in the hemodynamic management of patients. Each device has its own distinct technical features and inherent limitations; it is clear that no single device can be used universally for all patients. Therefore, different methods or devices should be chosen based on individual patient conditions, including the degree of invasiveness, measurement performance, and the ability to provide real-time, continuous CO readings.

Efficacy of minimal invasive cardiac output and ScVO2 monitoring during controlled hypotension for double-jaw surgery

Background

Controlled hypotension (CH) provides a better surgical environment and reduces operative time. However, there are some risks related to organ hypoperfusion. The EV1000/FloTrac system can provide continuous cardiac output monitoring without the insertion of pulmonary arterial catheter. The present study investigated the efficacy of this device in double jaw surgery under CH.

Methods

We retrospectively reviewed the medical records of patients who underwent double jaw surgery between 2010 and 2015. Patients were administered conventional general anesthesia with desflurane; CH was performed with remifentanil infusion and monitored with an invasive radial arterial pressure monitor or the EV1000/FloTrac system. We allocated the patients into two groups, namely an A-line group and an EV1000 group, according to the monitoring methods used, and the study variables were compared.

Results

Eighty-five patients were reviewed. The A-line group reported a higher number of failed CH (P = 0.005). A significant correlation was found between preoperative hemoglobin and intraoperative packed red blood cell transfusion (r = 0.525; P < 0.001). In the EV1000 group, the mean arterial pressure (MAP) was significantly lower 2 h after CH (P = 0.014), and the cardiac index significantly decreased 1 h after CH (P = 0.001) and 2 h after CH (P = 0.007). Moreover, venous oxygen saturation (ScVO₂) decreased significantly at both 1 h (P = 0.002) and 2 h after CH (P = 0.029); however, these values were within normal limits.

Conclusion

The EV1000 group reported a lower failure rate of CH than the A-line group. However, EV1000/FloTrac monitoring did not present with any specific advantage over the conventional arterial line monitoring when CH was performed with the same protocol and same mean blood pressure. Preoperative anemia treatment will be helpful to decrease intraoperative transfusion. Furthermore, ScVO₂ monitoring did not present with sufficient benefits over the risk and cost.

Accuracy of non-invasive and minimally invasive hemodynamic monitoring: where do we stand?

One of the most important variables in assessing hemodynamic status in the intensive care unit (ICU) is the cardiac function and blood pressure. Invasive methods such as pulmonary artery catheter and arterial line allow monitoring of blood pressure and cardiac function accurately and reliably. However, their use is not without drawbacks, especially when the invasive nature of these procedures and complications associated with them are considered. There are several newer methods of noninvasive and minimally invasive hemodynamic monitoring available. In this manuscript, we will review these different methods of minimally invasive and non-invasive hemodynamic monitoring and will discuss their advantages, drawbacks and limitations.