A Critical Review of the Ability of Continuous Cardiac Output Monitors to Measure Trends in Cardiac Output

Accuracy, Precision, and Trending of 4 Pulse Wave Analysis Techniques in the Postoperative Period

OBJECTIVE

The aim of this study was to analyze the accuracy, precision, and trending ability of the following 4 pulse wave analysis devices to measure continuous cardiac output: PiCCO₂ ([PCCO]; Pulsion Medical System, Munich, Germany); LiDCO_Rapid ([LCCO]; LiDCO Ltd, London, UK); FloTrac/Vigileo ([FCCO]; Edwards Lifesciences, Irvine, CA); and Nexfin ([NCCO]; BMEYE, Amsterdam, The Netherlands).

DESIGN

Prospective, observational clinical study.

SETTING

Intensive care unit of a single-center, teaching hospital.

PARTICIPANTS

The study comprised 22 adult patients after elective coronary artery bypass surgery.

INTERVENTIONS

Three measurement cycles were performed in all patient durings their immediate postoperative intensive care stay before and after fluid loading. Hemodynamic measurements were performed 5 minutes before and immediately after the administration of 500 mL colloidal fluid over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

PCCO, LCCO, FCCO, and NCCO were assessed and compared with cardiac output derived from intermittent transpulmonary thermodilution (ICO). One hundred thirty-two matched sets of data were available for analysis. Bland-Altman analysis using linear mixed effects models with random effects for patient and trial revealed a mean bias ±2 standard deviation (%error) of -0.86 ± 1.41 L/min (34.9%) for PCCO-ICO, -0.26 ± 2.81 L/min (46.3%) for LCCO-ICO, -0.28 ± 2.39 L/min (43.7%) for FCCO-ICO, and -0.93 ± 2.25 L/min (34.6%) for NCCO-ICO. Bland-Altman plots without adjustment for repeated measurements and replicates yielded considerably larger limits of agreement. Trend analysis for all techniques did not meet criteria for acceptable performance.

CONCLUSIONS

All 4 tested devices using pulse wave analysis for measuring cardiac output failed to meet current criteria for meaningful and adequate accuracy, precision, and trending ability in cardiac output monitoring.

Noninvasive oscillometric cardiac output determination in the intensive care unit - comparison with invasive transpulmonary thermodilution

Assessment of the cardiac output (CO) is usually performed with invasive techniques requiring specialized equipment in the intensive care unit (ICU). With TEL-O-GRAPH (TG), CO can be derived from the oscillometrically obtained brachial pulse wave during the measurement of brachial blood pressure. CO and stroke volume (SV) determinations with TG were compared with transpulmonary thermodilution measurements with the PICCO system (PICCO) in 38 haemodynamically unstable ICU patients with a total of 84 comparison measurements performed. SV (33.3 ± 9.0 ml/m² vs. 44.3 ± 14.4 ml/m², p < 0.001) and CO (2.7 ± 0.5 l/min/m² vs. 3.8 ± 1.2 l/min/m², p < 0.001) were underestimated significantly with TG and oscillometric brachial systolic blood pressure (BP) was significantly lower and diastolic BP significantly higher than invasive femoral artery pressure. A linear correlation was found between CO dimension and CO underestimation with TG. Correct tracking of CO changes with a fluid challenge was possible in 69.5% of measurements. Oscillometric noninvasive CO is possible in the ICU, but accuracy and precision of this new method are lacking. Implementation of a correction factor accounting for the linear increase in CO underestimation observed with increasing CO could improve CO assessment with TG in haemodynamically unstable patients.

Transthoracic echocardiography: an accurate and precise method for estimating cardiac output in the critically ill patient

Background

Cardiac output (CO) monitoring is a valuable tool for the diagnosis and management of critically ill patients. In the critical care setting, few studies have evaluated the level of agreement between CO estimated by transthoracic echocardiography (CO-TTE) and that measured by the reference method, pulmonary artery catheter (CO-PAC). The objective of the present study was to evaluate the precision and accuracy of CO-TTE relative to CO-PAC and the ability of transthoracic echocardiography to track variations in CO, in critically ill mechanically ventilated patients.

Methods

Thirty-eight mechanically ventilated patients fitted with a PAC were included in a prospective observational study performed in a 16-bed university hospital ICU. CO-PAC was measured via intermittent thermodilution. Simultaneously, a second investigator used standard-view TTE to estimate CO-TTE as the product of stroke volume and the heart rate obtained during the measurement of the subaortic velocity time integral.

Results

Sixty-four pairs of CO-PAC and CO-TTE measurements were compared. The two measurements were significantly correlated (r = 0.95; p < 0.0001). The median bias was 0.2 L/min, the limits of agreement (LOAs) were –1.3 and 1.8 L/min, and the percentage error was 25%. The precision was 8% for CO-PAC and 9% for CO-TTE. Twenty-six pairs of ΔCO measurements were compared. There was a significant correlation between ΔCO-PAC and ΔCO-TTE (r = 0.92; p < 0.0001). The median bias was –0.1 L/min and the LOAs were –1.3 and +1.2 L/min. With a 15% exclusion zone, the four-quadrant plot had a concordance rate of 94%. With a 0.5 L/min exclusion zone, the polar plot had a mean polar angle of 1.0° and a percentage error LOAs of –26.8 to 28.8°. The concordance rate was 100% between 30 and –30°. When using CO-TTE to detect an increase in ΔCO-PAC of more than 10%, the area under the receiving operating characteristic curve (95% CI) was 0.82 (0.62–0.94) (p < 0.001). A ΔCO-TTE of more than 8% yielded a sensitivity of 88% and specificity of 66% for detecting a ΔCO-PAC of more than 10%.

Conclusion

In critically ill mechanically ventilated patients, CO-TTE is an accurate and precise method for estimating CO. Furthermore, CO-TTE can accurately track variations in CO.

Agreement of Bioreactance Cardiac Output Monitoring With Thermodilution During Hemorrhagic Shock and Resuscitation in Adult Swine

OBJECTIVE

The study tests the hypothesis that noninvasive cardiac output monitoring based upon bioreactance (Cheetah Medical, Portland, OR) has acceptable agreement with intermittent bolus thermodilution over a wide range of cardiac output in an adult porcine model of hemorrhagic shock and resuscitation.

DESIGN

Prospective laboratory animal investigation.

SETTING

Preclinical university laboratory.

SUBJECTS

Eight ~ 50 kg Yorkshire swine with a femoral artery catheter for blood pressure measurement and a pulmonary artery catheter for bolus thermodilution.

INTERVENTIONS

With the pigs anesthetized and mechanically ventilated, 40 mL/kg of blood was removed yielding marked hypotension and a rise in plasma lactate. After 60 minutes, pigs were resuscitated with shed blood and crystalloid. Noninvasive cardiac output monitoring and intermittent thermodilution cardiac output were simultaneously measured at nine time points spanning baseline, hemorrhage, and resuscitation.

MEASUREMENTS AND MAIN RESULTS

Simultaneous noninvasive cardiac output monitoring and thermodilution measurements of cardiac output were compared by Bland-Altman analysis. A plot was constructed using the difference of each paired measurement expressed as a percentage of the mean of the pair plotted against the mean of the pair. Percent bias was used to scale the differences in the measurements for the magnitude of the cardiac output. Method concordance was assessed from a four-quadrant plot with a 15% zone of exclusion. Overall, noninvasive cardiac output monitoring percent bias was 1.47% (95% CI, -2.5 to 5.4) with limits of agreement of upper equal to 33.4% (95% CI, 26.5-40.2) and lower equal to -30.4% (95% CI, -37.3 to -23.6). Trending analysis demonstrated a 97% concordance between noninvasive cardiac output monitoring and thermodilution cardiac output.

CONCLUSIONS

Over the wide range of cardiac output produced by hemorrhage and resuscitation in large pigs, noninvasive cardiac output monitoring has acceptable agreement with thermodilution cardiac output.

Performance of a capnodynamic method estimating effective pulmonary blood flow during transient and sustained hypercapnia

The capnodynamic method is a minimally invasive method continuously calculating effective pulmonary blood flow (CO_EPBF), equivalent to cardiac output when intra pulmonary shunt flow is low. The capnodynamic equation joined with a ventilator pattern containing cyclic reoccurring expiratory holds, provides breath to breath hemodynamic monitoring in the anesthetized patient. Its performance however, might be affected by changes in the mixed venous content of carbon dioxide (C_vCO₂). The aim of the current study was to evaluate CO_EPBF during rapid measurable changes in mixed venous carbon dioxide partial pressure (P_vCO₂) following ischemia–reperfusion and during sustained hypercapnia in a porcine model. Sixteen pigs were submitted to either ischemia–reperfusion (n = 8) after the release of an aortic balloon inflated during 30 min or to prolonged hypercapnia (n = 8) induced by adding an instrumental dead space. Reference cardiac output (CO) was measured by an ultrasonic flow probe placed around the pulmonary artery trunk (CO_TS). Hemodynamic measurements were obtained at baseline, end of ischemia and during the first 5 min of reperfusion as well as during prolonged hypercapnia at high and low CO states. Ischemia–reperfusion resulted in large changes in P_vCO₂, hemodynamics and lactate. Bias (limits of agreement) was 0.7 (−0.4 to 1.8) L/min with a mean error of 28% at baseline. CO_EPBF was impaired during reperfusion but agreement was restored within 5 min. During prolonged hypercapnia, agreement remained good during changes in CO. The mean polar angle was −4.19° (−8.8° to 0.42°). Capnodynamic CO_EPBF is affected but recovers rapidly after transient large changes in P_vCO₂ and preserves good agreement and trending ability during states of prolonged hypercapnia at different levels of CO.

Comparison of stroke volume measurement between non-invasive bioreactance and esophageal Doppler in patients undergoing major abdominal-pelvic surgery

PURPOSE

Bioreactance is a non-invasive technology for measuring stroke volume (SV) in the operating room and critical care setting. We evaluated how the NICOM^® bioreactance device performed against the CardioQ^® esophageal Doppler monitor in patients undergoing major abdominal-pelvic surgery, focusing on the effect of different hemodynamic interventions.

METHODS

SV_NICOM and SV_ODM were simultaneously measured intraoperatively, including before and after interventions including fluid challenge, vasopressor boluses, peritoneal gas insufflation/removal, and Trendelenburg/reverse Trendelenburg patient positioning.

RESULTS

A total of 768 values were collected from 21 patients. Pre- and post-intervention measures were recorded on 155 occasions. Bland-Altman analysis revealed a bias of 8.6 ml and poor precision with wide limits of agreement (54 and -37 ml) and a percentage error of 50.6%. No improvement in precision was detected after taking into account repeated measurements for each patient (bias: 8 ml; limits of agreement: 74 and -59 ml). Concordance between changes in SV_NICOM and SV_ODM before and after interventions was also poor: 78.7% (all measures), 82.4% (after vasopressor administration), and 74.3% (after fluid challenge). Using Doppler SV as the reference technique, the area under the receiver operating characteristic curve assessing the ability of the NICOM device to predict fluid responsiveness was 0.81 (0.7-0.9).

CONCLUSIONS

In patients undergoing major abdomino-pelvic surgery, SV values obtained by NICOM showed neither clinically or statistically acceptable agreement with those obtained by esophageal Doppler. Although, in the setting of this study, bioreactance technology cannot reliably replace esophageal Doppler monitoring, its accuracy for predicting fluid responsiveness was higher, up to approximately 80%.

TRIAL REGISTRATION

Observational study.

Continuous Non-invasive finger cuff CareTaker® comparable to invasive intra-arterial pressure in patients undergoing major intra-abdominal surgery

Background

Despite increased interest in non-invasive arterial pressure monitoring, the majority of commercially available technologies have failed to satisfy the limits established for the validation of automatic arterial pressure monitoring by the Association for the Advancement of Medical Instrumentation (AAMI). According to the ANSI/AAMI/ISO 81060–2:2013 standards, the group-average accuracy and precision are defined as acceptable if bias is not greater than 5 mmHg and standard deviation is not greater than 8 mmHg. In this study, these standards are used to evaluate the CareTaker® (CT) device, a device measuring continuous non-invasive blood pressure via a pulse contour algorithm called Pulse Decomposition Analysis.

Methods

A convenience sample of 24 patients scheduled for major abdominal surgery were consented to participate in this IRB approved pilot study. Each patient was monitored with a radial arterial catheter and CT using a finger cuff applied to the contralateral thumb. Hemodynamic variables were measured and analyzed from both devices for the first thirty minutes of the surgical procedure including the induction of anesthesia. The mean arterial pressure (MAP), systolic and diastolic blood pressures continuously collected from the arterial catheter and CT were compared. Pearson correlation coefficients were calculated between arterial catheter and CT blood pressure measurements, a Bland-Altman analysis, and polar and 4Q plots were created.

Results

The correlation of systolic, diastolic, and mean arterial pressures were 0.92, 0.86, 0.91, respectively (p < 0.0001 for all the comparisons). The Bland-Altman comparison yielded a bias (as measured by overall mean difference) of −0.57, −2.52, 1.01 mmHg for systolic, diastolic, and mean arterial pressures, respectively with a standard deviation of 7.34, 6.47, 5.33 mmHg for systolic, diastolic, and mean arterial pressures, respectively (p < 0.001 for all comparisons). The polar plot indicates little bias between the two methods (90%/95% CI at 31.5°/52°, respectively, overall bias = 1.5°) with only a small percentage of points outside these lines. The 4Q plot indicates good concordance and no bias between the methods.

Conclusions

In this study, blood pressure measured using the non-invasive CT device was shown to correlate well with the arterial catheter measurements. Larger studies are needed to confirm these results in more varied settings. Most patients exhibited very good agreement between methods. Results were well within the limits established for the validation of automatic arterial pressure monitoring by the AAMI.

The value of arterial pressure waveform cardiac output measurements in the radial and femoral artery in major cardiac surgery patients

Background

A relatively new uncalibrated arterial pressure waveform cardiac output (CO) measurement technique is the Pulsioflex-ProAQT® system. Aim of this study was to validate this system in cardiac surgery patients with a specific focus on the evaluation of a difference in the radial versus the femoral arterial access, the value of the auto-calibration modus and the ability to show fluid-induced changes.

Methods

In twenty-five patients scheduled for ascending aorta, aortic arch replacement, or both we measured CO simultaneously by transpulmonary thermodilution (COtd) and by using the ProAQT® system connected to the radial (COpR), as well as the femoral artery catheter (COpF). Hemodynamic data were assessed at predefined time points; from incision until 16 h after ICU admission.

Results

In total 175 (radial) and 179 (femoral) pairs of CO measurement were collected. The accuracy of COpR/COpF was evaluated showing a mean bias of −0.31 L/min (±2.9 L/min) and -0.57 L/min (± 2.8 L/min) with percentage errors of 49 and 46% respectively. Trending ability of the ProAQT® device was evaluated; the four quadrant concordance rates in the radial and femoral artery were 74 and 75% and improved to 77 and 85% after auto-calibration. The mean angular biases in the radial and femoral artery were 6.4° and 6.0° and improved to 5° and 3.3° after auto-calibration. The polar concordance rates in the radial and femoral artery were 65 and 70% and improved to 76 and 84% after auto-calibration. Considering the fluid-induced changes in stroke volume(SV), the coefficient of correlation between the changes in SVtd and SVp was 0.57 (p < 0.01) in the radial artery and 0.60 (p < 0.01) in the femoral artery.

Conclusions

The ProAQT® system can be of additional value if the clinician wants to determine fluid responsiveness in cardiac surgery patients. However, the ProAQT® system provided inaccurate CO measurements compared to transpulmonary thermodilution. The trending ability was poor for COpR but moderate for COpF. Auto-calibration of the system did not improve accuracy of CO measurements nor did it improve the prediction of fluid responsiveness. However, the trending ability was improved by auto-calibration, possibly by correcting a drift over a longer time period.

Comparison of bedside assessed arm and leg fluid filtration determined by venous congestion plethysmography in perioperative cancer patients: An observational study investigating agreement

In recent years, pathophysiology and clinical impact of microvascular fluid filtration has regained interest. As the latest data in surgical patients have been published almost 20 years ago, there is need for further research to better understand fluid filtration during the perioperative period. Venous congestion plethysmography (VCP) provides a rapid and noninvasive method, which has been shown suitable for the assessment of fluid filtration in limbs. Fluid filtration assessed by VCP can be obtained from forearm and calf measurement sites, while in many clinical situations a reduced access to the patient often restricts the measurements to patient's forearm. We aimed to investigate if fluid filtration obtained from forearm and calf measurement site is interchangeable in nonsedated perioperative patients.Fluid filtration by VCP was obtained simultaneously from forearm and calf in patients with ovarian cancer at 4 time points during the perioperative course and assessed by the difference of volume changes of the limb between third and sixth minutes (VC6-3min) during venous congestion. VC6-3min obtained from forearm and calf measurement sites was compared with respect to agreement and evaluated regarding the association with the presence of leg edema.A total of 74 paired measurements were analyzed in 29 patients. Forearm VC6-3min was significantly higher than calf VC6-3min (median [25th; 75th quartile], 0.6 (0.4; 0.9) vs 0.4 [0.3; 0.6] %, P = 0.008). Bland-Altman and Polar analysis revealed a poor agreement between forearm and calf VC6-3min at predefined time points and changes of VC6-3min during the perioperative course (bias +0.23%, limits of agreement [LOA] -1.1% to 1.6%; angular bias -2.5°, radial LOA -82° to +77°). Forearm VC6-3min was significantly increased in patients with presence of leg edema (0.7 (0.5; 1.0) vs 0.5 (0.4; 0.6) %, P < 0.001) while calf VC6-3min did not differ in patients with and without edema.This study indicates that forearm and calf measurement sites are not interchangeable when bedside assessing fluid filtration by VCP in nonsedated perioperative patients. Considering that only forearm fluid filtration was related to the presence of edema, forearm measurement site should be chosen as a primary site for assessing fluid filtration.

Determination of renal function and injury using near-infrared fluorimetry in experimental cardiorenal syndrome

Cardiorenal syndrome type 1 causes acute kidney injury but is poorly understood; animal models and diagnostic aids are lacking. Robust noninvasive measurements of glomerular filtration rate are required for injury models and clinical use. Several have been described but are untested in translational models and suffer from biologic interference. We developed a mouse model of cardiorenal syndrome and tested the novel near-infrared fluorophore ZW800-1 to assess renal and cardiac function. We performed murine cardiac arrest and cardiopulmonary resuscitation followed by transthoracic echocardiography, 2 and 24 h later. Transcutaneous fluorescence of ZW800-1 bolus dispersion and clearance was assessed with whole animal imaging and compared with glomerular filtration rate (GFR; inulin clearance), tubular cell death (using unbiased stereology), and serum creatinine. Correlation, Bland-Altman, and polar analyses were used to compare GFR with ZW800-1 clearance. Cardiac arrest and cardiopulmonary resuscitation caused reversible cardiac failure, halving fractional shortening of the left ventricle (n = 12, P = 0.03). Acute kidney injury resulted with near-zero GFR and sixfold increase in serum creatinine 24 h later (n = 16, P < 0.01). ZW800-1 biodistribution and clearance were exclusively renal. ZW800-1 t_1/2 and clearance correlated with GFR (r = 0.92, n = 31, P < 0.0001). ZW800-1 fluorescence was reduced in cardiac arrest, and cardiopulmonary resuscitation-treated mice compared with sham animals 810 s after injection (P < 0.01) and bolus time-dispersion curves demonstrated that ZW800-1 fluorescence dispersion correlated with left ventricular function (r = 0.74, P < 0.01). Cardiac arrest and cardiopulmonary resuscitation lead to experimental cardiorenal syndrome type 1. ZW800-1, a small near-infrared fluorophore being developed for clinical intraoperative imaging, is favorable for evaluating cardiac and renal function noninvasively.

The Mechanoreflex and Hemodynamic Response to Passive Leg Movement in Heart Failure

BACKGROUND

Sensitization of mechanosensitive afferents, which contribute to the exercise pressor reflex, has been recognized as a characteristic of patients with heart failure (HF); however, the hemodynamic implications of this hypersensitivity are unclear.

OBJECTIVES

The present study used passive leg movement (PLM) and intrathecal injection of fentanyl to blunt the afferent portion of this reflex arc to better understand the role of the mechanoreflex on central and peripheral hemodynamics in HF.

METHODS

Femoral blood flow (FBF), mean arterial pressure, femoral vascular conductance, HR, stroke volume, cardiac output, ventilation, and muscle oxygenation of the vastus lateralis were assessed in 10 patients with New York Heart Association class II HF at baseline and during 3 min of PLM both with fentanyl and without (control).

RESULTS

Fentanyl had no effect on baseline measures but increased (control vs fentanyl, P < 0.05) the peak PLM-induced change in FBF (493 ± 155 vs 804 ± 198 ΔmL·min(-1)) and femoral vascular conductance (4.7 ± 2 vs 8.5 ± 3 ΔmL·min(-1)·mm Hg)(-1) while norepinephrine spillover (103% ± 19% vs 58% ± 17%Δ) and retrograde FBF (371 ± 115 vs 260 ± 68 ΔmL·min(-1)) tended to be reduced (P < 0.10). In addition, fentanyl administration resulted in greater PLM-induced increases in muscle oxygenation, suggestive of increased microvascular perfusion. Fentanyl had no effect on the ventilation, mean arterial pressure, HR, stroke volume, or cardiac output response to PLM.

CONCLUSIONS

Although movement-induced central hemodynamics were unchanged by afferent blockade, peripheral hemodynamic responses were significantly enhanced. Thus, in patients with HF, a heightened mechanoreflex seems to augment peripheral sympathetic vasoconstriction in response to movement, a phenomenon that may contribute to exercise intolerance in this population.

Pilot Study: Estimation of Stroke Volume and Cardiac Output from Pulse Wave Velocity

Background

Transesophageal echocardiography (TEE) is increasingly replacing thermodilution pulmonary artery catheters to assess hemodynamics in patients at high risk for cardiovascular morbidity. However, one of the drawbacks of TEE compared to pulmonary artery catheters is the inability to measure real time stroke volume (SV) and cardiac output (CO) continuously. The aim of the present proof of concept study was to validate a novel method of SV estimation, based on pulse wave velocity (PWV) in patients undergoing cardiac surgery.

Methods

This is a retrospective observational study. We measured pulse transit time by superimposing the radial arterial waveform onto the continuous wave Doppler waveform of the left ventricular outflow tract, and calculated SV (SV_PWV) using the transformed Bramwell-Hill equation. The SV measured by TEE (SV_TEE) was used as a reference.

Results

A total of 190 paired SV were measured from 28 patients. A strong correlation was observed between SV_PWV and SV_TEE with the coefficient of determination (R²) of 0.71. A mean difference between the two (bias) was 3.70 ml with the limits of agreement ranging from -20.33 to 27.73 ml and a percentage error of 27.4% based on a Bland-Altman analysis. The concordance rate of two methods was 85.0% based on a four-quadrant plot. The angular concordance rate was 85.9% with radial limits of agreement (the radial sector that contained 95% of the data points) of ± 41.5 degrees based on a polar plot.

Conclusions

PWV based SV estimation yields reasonable agreement with SV measured by TEE. Further studies are required to assess its utility in different clinical situations.

Cardiac Output Assessed by the Fourth-Generation Arterial Waveform Analysis System Is Unreliable in Liver Transplant Recipients

BACKGROUND

Liver transplant recipients often have violent hemodynamic fluctuation during surgery that may be related to perioperative and postoperative morbidity. Because there are some considerations for the risk of the pulmonary arterial catheter (PAC), the conventional invasive device for cardiac output (CO) measurement, a reliable and minimally invasive alternative is required. We validated the reliability of CO measurements with the use of a minimally invasive FloTrac system with the latest fourth-generation algorithm in liver transplant recipients.

METHODS

Forty liver transplant recipients without atrial fibrillation, valvular pathology, or intracardiac shunt were recruited in this prospective, observational study. CO values measured by use of PAC with continuous thermodilution method (COTh) and FloTrac devices (COFT) were collected simultaneously throughout the operation for reliability validation.

RESULTS

Four hundred pairs of CO data points were collected in total. The linear regression analysis showed a high correlation coefficient (73%, P < .001). However, the percent error between COTh and COFT was 42.2%, which is worse than the established interchangeability criterion of 30%. The concordance rates were calculated at 89% and 59% by 4-quadrant plot and polar plot analysis, respectively. Neither met the preset validation criteria (>92% for the 4-quadrant plot and >90% for polar plot analyses).

CONCLUSIONS

Our study demonstrates that the CO measurements in liver transplant recipients by the latest FloTrac system and the PAC do not meet the recognized interchangeability criterion. Although the result showed improvement in linear regression analysis, it failed to display a qualified trending ability.

Cardiac output assessment in pregnancy: comparison of two automated monitors with echocardiography

OBJECTIVE

To compare non-invasive hemodynamic measurements obtained in pregnant and postpartum women using two automated cardiac output monitors against those obtained by two-dimensional (2D) transthoracic echocardiography (TTE).

METHODS

This was a cross-comparison study into which we recruited 114 healthy women, either with normal singleton pregnancy (across all three trimesters) or within 72 hours following delivery. Cardiac output estimations were obtained non-invasively using two different monitors, Ultrasound Cardiac Output Monitor (USCOM®, which uses continuous-wave Doppler analysis of transaortic blood flow) and Non-Invasive Cardiac Output Monitor (NICOM®, which uses thoracic bioreactance), and 2D-TTE. The performance of each monitor was assessed relative to that of TTE by calculating bias, precision, 95% limits of agreement and mean percentage difference (MPD). Intraobserver repeatability was assessed for both monitors and interobserver reproducibility was assessed for USCOM, NICOM being operator-independent.

RESULTS

Following exclusions due to poor-quality results of a monitor or TTE, or for medical reasons, our analysis included 98 women (29 in the first trimester, 25 in the second and 21 in the third, and 23 postpartum). For cardiac output estimation, when compared with TTE, USCOM had a bias ranging from 0.4 to 0.9 L/min. The MPD of USCOM was 29% in the third-trimester cohort. NICOM had a bias ranging from -1.0 to 0.6 L/min, with a MPD of 32% in the third-trimester group. There was limited agreement between the cardiac output monitors and TTE in the first and second trimesters, with a MPD of 38% for USCOM in both first and second trimesters, and 71% and 61% for NICOM in first and second trimesters, respectively. For cardiac output estimation using USCOM, we found excellent intraobserver repeatability (intraclass correlation coefficient (ICC), 0.97; 95% CI, 0.95-0.98) and interobserver reproducibility (ICC, 0.90; 95% CI, 0.81-0.94), and the repeatability for NICOM was comparable (ICC, 0.95; 95% CI, 0.93-0.97).

CONCLUSIONS

We found good agreement of both USCOM and NICOM when compared with 2D-TTE, specifically in the third trimester of pregnancy. Both devices had good intraobserver repeatability and either had good interobserver reproducibility or were operator-independent. Future studies should take into account the significant differences in the precise maternal hemodynamic values obtained by these devices, and consider developing device-specific reference ranges in pregnancy and the postpartum period. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Accuracy of Cardiac Output by Nine Different Pulse Contour Algorithms in Cardiac Surgery Patients: A Comparison with Transpulmonary Thermodilution

Objective. Today, there exist several different pulse contour algorithms for calculation of cardiac output (CO). The aim of the present study was to compare the accuracy of nine different pulse contour algorithms with transpulmonary thermodilution before and after cardiopulmonary bypass (CPB). Methods. Thirty patients scheduled for elective coronary surgery were studied before and after CPB. A passive leg raising maneuver was also performed. Measurements included CO obtained by transpulmonary thermodilution (CO_TPTD) and by nine pulse contour algorithms (CO_X1–9). Calibration of pulse contour algorithms was performed by esophageal Doppler ultrasound after induction of anesthesia and 15 min after CPB. Correlations, Bland-Altman analysis, four-quadrant, and polar analysis were also calculated. Results. There was only a poor correlation between CO_TPTD and CO_X1–9 during passive leg raising and in the period before and after CPB. Percentage error exceeded the required 30% limit. Four-quadrant and polar analysis revealed poor trending ability for most algorithms before and after CPB. The Liljestrand-Zander algorithm revealed the best reliability. Conclusions. Estimation of CO by nine different pulse contour algorithms revealed poor accuracy compared with transpulmonary thermodilution. Furthermore, the less-invasive algorithms showed an insufficient capability for trending hemodynamic changes before and after CPB. The Liljestrand-Zander algorithm demonstrated the highest reliability. This trial is registered with NCT02438228 (ClinicalTrials.gov).

Evaluation of New Calibrated Pulse-Wave Analysis (VolumeViewTM/EV1000TM) for Cardiac Output Monitoring Undergoing Living Donor Liver Transplantation

Background

Intrapulmonary thermodilution technique using a pulmonary artery catheter is widely used for measuring cardiac output (CO) in patients undergoing liver transplantation. However, its invasiveness and associated complications have led to an interest in less invasive modalities. Thus, we aimed to evaluate whether the new calibrated pulse-wave analysis method monitoring (VolumeView^TM/EV1000^TM) is interchangeable with intrapulmonary thermodilution technique.

Methods

Twenty-eight patients undergoing living donor liver transplantation were enrolled in this prospective observational study. COs were recorded automatically by the two devices and compared simultaneously at 10-minute intervals. The agreement of absolute CO values and the tracking ability of CO changes trends were compared. A Bland-Altman analysis with percentage errors and concordance rate for trend analysis using both a 4-quadrant plot and a polar plot were performed on the data.

Results

A total of 375 paired datasets from 25 patients were included in analysis. COs measured by intrapulmonary thermodilution ranged from 3.8–13.7 L/min. The mean CO difference between the two techniques was 0.57 L/min, and the 95% limits of agreement were -0.98 L/min to 2.12 L/min with a percentage error of 42.3%. The percentage errors in the dissection, anhepatic, and reperfusion phase were 30.5%, 31.7%, and 27.4%, respectively. The concordance rate between the two techniques was 78.4%.

Conclusion

The calibrated pulse-wave analysis and intrapulmonary thermodilution failed to show acceptable interchangeability in terms of both estimating CO and tracking CO changes during living donor liver transplantation.

Comparison of PulsioFlex® uncalibrated pulse contour method and a modified Fick principle with transpulmonary thermodilution measurements in critically ill patients

Monitoring of cardiac index (CI) by uncalibrated pulse contour (PC) methods has been shown to be inaccurate in critically ill patients. We tested accuracy and trending of a new pulse contour method and a modified Fick method using central venous oxygen saturation. We studied 21 critically ill and mechanically ventilated patients (age 20-86 years) monitored by PC (PulsioFlex®) and transpulmonary thermodilution (TPTD, PiCCO2®) as reference. At baseline, reference and PC-derived CI (CIPC) were recorded and CI obtained by Fick's method (FM, CIFICK). After four hours, measurements were performed analogously for trending analysis. CI are given in l/min/m2 as mean±standard deviation. At baseline CITPTD was 3.7±0.7, CIPC 3.8±0.7 and CIFICK 5.2±1.8. After 4 hours, CITPTD was 3.5±0.6, CIPC 3.8±1.2 and CIFICK 4.8±1.7. Mean bias for PC at baseline was -0.1 (limits of agreement [LOA] -1.4 to 1.2) and -0.4 (LOA -2.6 to 1.9) after four hours. Percentage errors (PE) were 34% and 60% respectively. FM revealed a bias of -1.5 (LOA -4.8 to 1.8, PE 74%) at baseline and -1.5 (LOA -4.5 to 1.4, PE 68%) at four hours. With an exclusion window of 10% of mean cardiac index, trending analysis by polar plots showed an angular bias of 5° (radial LOA±57°) for PC and 16° (radial LOA±51°) for FM. Although PC values at baseline were marginally acceptable, both methods fail to yield clinically acceptable absolute values. Likewise, trending ability is not adequate for both methods to be used in critically ill patients.

Reliability of cardiac output measurements using LiDCOrapid™ and FloTrac/Vigileo™ across broad ranges of cardiac output values

Knowing a patient's cardiac output (CO) could contribute to a safe, optimized hemodynamic control during surgery. Precise CO measurements can serve as a guide for resuscitation therapy, catecholamine use, differential diagnosis, and intervention during a hemodynamic crisis. Despite its invasiveness and intermittent nature, the thermodilution technique via a pulmonary artery catheter (PAC) remains the clinical gold standard for CO measurements. LiDCOrapid™ (LiDCO, London, UK) and FloTrac/Vigileo™ (Edwards Lifesciences, Irvine, CA) are less invasive continuous CO monitors that use arterial waveform analysis. Their calculations are based on arterial waveform characteristics and do not require calibration. Here, we evaluated LiDCOrapid™ and FloTrac/Vigileo™ during off-pump coronary artery bypass graft (OPCAB) and living-donor liver transplantation (LDLT) surgery. This observational, single-center study included 21 patients (11 OPCAB and 10 LDLT). We performed simultaneous measurements of CO at fixed sampling points during surgery using both devices (LiDCOrapid™ version 1.04-b222 and FloTrac/Vigileo™ version 3.02). The thermodilution technique via a PAC was used to obtain the benchmark data. LiDCOrapid™ and FloTrac/Vigileo™ were used in an uncalibrated fashion. We analyzed the measured cardiac index using a Bland-Altman analysis (the method of variance estimates recovery), a polar plot method (half-moon method), a 4-quadrant plot and compared the widths of the limits of agreement (LOA) using an F test. One OPCAB patient was excluded because of the use of an intra-aortic balloon pumping during surgery, and 20 patients (10 OPCAB and 10 LDLT) were ultimately analyzed. We obtained 149 triplet measurements with a wide range of cardiac index. For the FloTrac/Vigileo™, the bias and percentage error were -0.44 L/min/m² and 74.4 %. For the LiDCOrapid™, the bias and percentage error were -0.38 L/min/m² and 53.5 %. The polar plot method showed an angular bias (FloTrac/Vigileo™ vs. LiDCOrapid™: 6.6° vs. 5.8°, respectively) and radial limits of agreement (-63.9 to 77.1 vs. -41.6 to 53.1). A 4-quadrant plot was used to obtain concordance rates (FloTrac/Vigileo™ vs. PAC and LiDCOrapid™ vs. PAC: 84.0 and 92.4 %, respectively). We could compare CO measurement devices across broad ranges of CO and SVR using LDLT and OPCAB surgical patients. An F test revealed no significant difference in the widths of the LoA for both devices when sample sizes capable of detecting a more than two-fold difference were used. We found that both devices tended to underestimate the calculated CIs when the CIs were relatively high. These proportional bias produced large percentage errors in the present study.

Comparison between pressure-recording analytical method (PRAM) and femoral arterial thermodilution method (FATD) cardiac output monitoring in an infant animal model of cardiac arrest

Background

The pressure-recording analytical method is a new semi-invasive method for cardiac output measurement (PRAM). There are no studies comparing this technique with femoral artery thermodilution (FATD) in an infant animal model.

Methods

A prospective study was performed using 25 immature Maryland pigs weighing 9.5 kg. Fifty-eight simultaneous measurements of cardiac index (CI) were made by FATD and PRAM at baseline and after return of spontaneous circulation. Differences, correlation, and concordance between both methods were analyzed. The ability of PRAM to track changes in CI was explored with a polar plot.

Results

Mean CI measurements were 4.5 L/min/m² (95 % CI, 4.2–4.8 L/min/m²; coefficient of variation, 27 %) by FATD and 4.0 L/min/m² (95 % CI, 3.6–4.3 L/min/m²; coefficient for variation, 37 %) by PRAM (difference, 0.5 L/min/m²; 95 % CI for the difference, 0.1–1.0 L/min/m²; p = 0.003; n = 58). No correlation between both methods was observed (r = 0.170, p = 0.20). Limits of agreement were −2.9 to 4.0 L/min/m² (−69.9 to 84.9 %). Percentage error was 80.6 %. Only 26.1 % of data points lied within an absolute deviation of ±30° from the polar axis.

Conclusions

No correlation nor concordance between both methods was observed. Limits of agreement and percentage of error were high and clinically not acceptable. No concurrence between both methods in CI changes was observed. PRAM is not a useful method for measurement of the CI in this pediatric model of cardiac arrest.

Evaluation of cardiac output by 5 arterial pulse contour techniques using trend interchangeability method

Cardiac output measurement with pulse contour analysis is a continuous, mini-invasive, operator-independent, widely used, and cost-effective technique, which could be helpful to assess changes in cardiac output. The 4-quadrant plot and the polar plot have been described to compare the changes between 2 measurements performed under different conditions, and the direction of change by using different methods of measurements. However, the 4-quadrant plot and the polar plot present a number of limitations, with a risk of misinterpretation in routine clinical practice. We describe a new trend interchangeability method designed to objectively define the interchangeability of each change of a variable. Using the repeatability of the reference method, we classified each change as either uninterpretable or interpretable and then as either noninterchangeable, in the gray zone or interchangeable. An interchangeability rate can then be calculated by the number of interchangeable changes divided by the total number of interpretable changes. In this observational study, we used this objective method to assess cardiac output changes with 5 arterial pulse contour techniques (Wesseling's method, LiDCO, PiCCO, Hemac method, and Modelflow) in comparison with bolus thermodilution technique as reference method in 24 cardiac surgery patients. A total of 172 cardiac output variations were available from the 199 data points: 88 (51%) were uninterpretable, according to the first step of the method. The second step of the method, based on the 84 (49%) interpretable variations, showed that only 18 (21%) to 30 (36%) variations were interchangeable regardless of the technique used. None of pulse contour cardiac output technique could be interchangeable with bolus thermodilution to assess changes in cardiac output using the trend interchangeability method in cardiac surgery patients. Future studies may consider using this method to assess interchangeability of changes between different methods of measurements.

A modified breathing pattern improves the performance of a continuous capnodynamic method for estimation of effective pulmonary blood flow

In a previous study a new capnodynamic method for estimation of effective pulmonary blood flow (CO_EPBF) presented a good trending ability but a poor agreement with a reference cardiac output (CO) measurement at high levels of PEEP. In this study we aimed at evaluating the agreement and trending ability of a modified CO_EPBF algorithm that uses expiratory instead of inspiratory holds during CO and ventilatory manipulations. CO_EPBF was evaluated in a porcine model at different PEEP levels, tidal volumes and CO manipulations (N = 8). An ultrasonic flow probe placed around the pulmonary trunk was used for CO measurement. We tested the CO_EPBF algorithm using a modified breathing pattern that introduces cyclic end-expiratory time pauses. The subsequent changes in mean alveolar fraction of carbon dioxide were integrated into a capnodynamic equation and effective pulmonary blood flow, i.e. non-shunted CO, was calculated continuously breath by breath. The overall agreement between CO_EPBF and the reference method during all interventions was good with bias (limits of agreement) 0.05 (-1.1 to 1.2) L/min and percentage error of 36 %. The overall trending ability as assessed by the four-quadrant and the polar plot methodology was high with a concordance rate of 93 and 94 % respectively. The mean polar angle was 0.4 (95 % CI -3.7 to 4.5)°. A ventilatory pattern recurrently introducing end-expiratory pauses maintains a good agreement between CO_EPBF and the reference CO method while preserving its trending ability during CO and ventilatory alterations.

Comparison of Transpulmonary Thermodilution and Calibrated Pulse Contour Analysis with Pulmonary Artery Thermodilution Cardiac Output Measurements in Anesthetized Dogs

Background

Transpulmonary thermodilution (TPTD_CO) and calibrated pulse contour analysis (PCA_CO) are alternatives to pulmonary artery thermodilution cardiac output (PATD_CO) measurement.

Hypothesis

Ten mL of ice‐cold thermal indicator (TI₁₀) would improve the agreement and trending ability between TPTD_CO and PATD_CO compared to 5 mL of indicator (TI₅) (Phase‐1). The agreement and TA between PCA_CO and PATD_CO would be poor during changes in systemic vascular resistance (SVR) (Phase‐2).

Animals

Eight clinically normal dogs (20.8–31.5 kg).

Methods

Prospective, experimental study. Simultaneous TPTD_CO and PATD_CO (averaged from 3 repetitions) using TI₅ and TI₁₀ were obtained during isoflurane anesthesia combined or not with remifentanil or dobutamine (Phase‐1). Triplicate PCA_CO and PATD_CO measurements were recorded during phenylephrine‐induced vasoconstriction and nitroprusside‐induced vasodilation (Phase‐2).

Results

Mean bias (limits of agreement: LOA) (L/min), percentage bias (PB), and percentage error (PE) were 0.62 (−0.11 to 1.35), 16%, and 19% for TI₅; and 0.33 (−0.25 to 0.91), 9%, and 16% for TI₁₀. Mean bias (LOA), PB, and PE were 0.22 (−0.63 to 1.07), 6%, and 23% during phenylephrine; and 2.12 (0.70–3.55), 43%, and 29% during nitroprusside. Mean angular bias (radial LOA) values were 2° (−10° to 14°) and −1° (−9° to 6°) for TI₅ and TI₁₀, respectively (Phase‐1), and 38° (5°–71°) (Phase‐2).

Conclusions and Clinical Importance

Although TI₁₀ slightly improves the agreement and trending ability between TPTD_CO and PATD_CO in comparison to TI₅, both volumes can be used for TPTD_CO in replacement of PATD_CO. Vasodilation worsens the agreement between PCA_CO and PATD_CO. Because of PCA_CO's poor agreement and trending ability with PATD_CO during SVR changes, this method has limited clinical application.

A comparison of the non-invasive ultrasonic cardiac output monitor (USCOM) with the oesophageal Doppler monitor during major abdominal surgery

BACKGROUND

Perioperative interventions, targeted to increase global blood flow defined by explicit measured goals, reduce postoperative complications. Consequently, reliable non-invasive estimation of the cardiac output could have far-reaching benefit.

METHODS

This study compared a non-invasive Doppler device - the ultrasonic cardiac output monitor (USCOM) - with the oesophageal Doppler monitor (ODM), on 25 patients during major abdominal surgery. Stroke volume was determined by USCOM (SV_USCOM) and ODM (SV_ODM) pre and post fluid challenges.

RESULTS

A ≥ 10% change (Δ) SV_USCOM had a sensitivity of 94% and specificity of 88% to detect a ≥ 10% Δ SV_ODM; the area under the receiver operating curve was 0.94 (95% CI 0.90-0.99). Concordance was 98%, using an exclusion zone of <10% Δ SV_ODM. 135 measurements gave median SV_USCOM 80 ml (interquartile range 65-93 ml) and SV_ODM 86 ml (69-100 ml); mean bias was 5.9 ml (limits of agreement -20 to +30 ml) and percentage error 30%.

CONCLUSIONS

Following fluid challenges SV_USCOM showed good concordance and accurately discriminated a change ≥10% in SV_ODM.

Minimally Invasive Cardiac Output Monitoring: Agreement of Oesophageal Doppler, LiDCOrapid™ and Vigileo FloTrac™ Monitors in Non-Cardiac Surgery

There is lack of data about the agreement of minimally invasive cardiac output monitors, which make it impossible to determine if they are interchangeable or differ objectively in tracking physiological trends. We studied three commonly used devices: the oesophageal Doppler and two arterial pressure–based devices, the Vigileo FloTrac™ and LiDCOrapid™. The aim of this study was to compare the agreement of these three monitors in adult patients undergoing elective non-cardiac surgery. Measurements were taken at baseline and after predefined clinical interventions of fluid, metaraminol or ephedrine bolus. From 24 patients, 131 events, averaging 5.2 events per patient, were analysed. The cardiac index of LiDCOrapid versus FloTrac had a mean bias of −6.0% (limits of agreement from −51% to 39%) and concordance of over 80% to the three clinical interventions. The cardiac index of Doppler versus LiDCOrapid and Doppler versus FloTrac, had an increasing negative bias at higher mean cardiac outputs and there was significantly poorer concordance to all interventions. Of the preload-responsive parameters, Doppler stroke volume index, Doppler systolic flow time and FloTrac stroke volume variation were fair at predicting fluid responsiveness while other parameters were poor. While there is reasonable agreement between the two arterial pressure–derived cardiac output devices (LiDCOrapid and Vigileo FloTrac), these two devices differ significantly to the oesophageal Doppler technology in response to common clinical intraoperative interventions, representing a limitation to how interchangeable these technologies are in measuring cardiac output.

Trending, Accuracy, and Precision of Noninvasive Hemoglobin Monitoring During Human Hemorrhage and Fixed Crystalloid Bolus

Automated critical care systems for en route care will rely heavily on noninvasive continuous monitoring. It has been reported that noninvasive assessment of blood hemoglobin via CO-oximetry (SpHb) assessed by spot measurements lacks sufficient accuracy for clinical decision making in trauma patients. However, the precision and utility of trending of continuous hemoglobin have not been evaluated in hemorrhaging humans. This study measured the trending and concordance of SpHb changes during dynamic variations resulting from controlled hemorrhage with concomitant fluid infusion. With institutional review board approval and informed consent, 12 healthy volunteers under general anesthesia were subjected to hemorrhage (10 mL/kg for 15 min) accompanied by Ringer's lactate solution infusion (30 mL/kg for 20 min). The SpHb was measured continuously by the Masimo Radical-7, whereas total blood hemoglobin was measured by arterial blood sampling. Trend analysis, assessed by plots of SpHb against time of 12 subjects, shows consistent falls in SpHb during hemodilution without exception. Four-quadrant concordance analysis was 95.4% with an exclusion zone of 1 g/dL. Spot comparisons of 106 data pairs (SpHb and total blood hemoglobin) showed that 50% exhibited an error of more than 1 g/dL with bias of 1.08 ± 0.82 g/dL and 95% limits of agreement of -0.5 to 2.6. Both trend analysis and concordance analysis suggest high precision of pulse CO-oximetry during hemodilution by hemorrhage and fluid bolus in human volunteers. However, accuracy was similar to other studies and therefore the use of pulse CO-oximetry alone is likely insufficient to make transfusion decisions.

Comparing cardiac output monitors and defining agreement: A systematic review and meta-analysis

BACKGROUND

Measuring cardiac output is common in critical care and perioperative medicine. Different monitoring systems are often judged against others in comparative studies. There is no agreed standard or definition on which to base the conclusions of such studies.

OBJECTIVES

To review comparative studies of cardiac output monitors using an agreement:tolerability index (ATI) as a measure of monitor precision. To compare the ATI of a monitor with the conclusions of authors regarding agreement and clinical utility.

DESIGN

Systematic review of comparative studies of cardiac output monitoring systems. The precision of each monitor was standardised against an ATI using a tolerability interval based on the normal range for cardiac index. The conclusions of each study were described as positive, neutral or negative, depending on whether authors reported the monitor to be acceptably precise and/or clinically useful. Comparison was made between the precision of a monitor and the likelihood of it being favoured by authors.

DATA SOURCES

PubMed was searched up to March 2012.

ELIGIBILITY CRITERIA

Studies published in English that compared two or more methods for measuring cardiac output in adult humans.

RESULTS

A total of 213 papers documenting 409 separate comparisons of two methods of measuring cardiac output were included. ATIs for the different comparisons varied from 0.07 to 6.84 (where an ATI < 1 indicates acceptable agreement, 1-2 marginal and >2 unacceptable agreement). Thirty-one percent of authors defined their own terms for acceptable agreement. ATI was only moderately correlated with the conclusions of the authors (Spearman rho = 0.47, P < 0.0001).

CONCLUSIONS

Authors should define what constitutes acceptable agreement a priori when reporting comparative studies of cardiac output monitors. The ATI and the tolerability interval may be a useful basis for helping define acceptable precision.

Assessment of changes in cardiac index with calibrated pulse contour analysis in cardiac surgery: A prospective observational study

OBJECTIVES

To assess the trending ability of calibrated pulse contour cardiac index (CIPC) monitoring during haemodynamic changes (passive leg raising [PLR] and fluid loading) compared with transpulmonary thermodilution CI (CITD).

METHOD

Seventy-eight mechanically-ventilated patients admitted to intensive care with calibrated pulse contour following cardiac surgery were prospectively included and investigated during PLR, and after fluid loading. Fluid responsiveness was defined as a≥15% CITD increase after a 500ml bolus. Areas under the empiric receiver operating characteristic curves (ROCAUC) for changes in CIPC (ΔCIPC) during PLR to predict fluid responsiveness and after fluid challenge to predict an increase at least 15% in CITD after fluid loading were calculated.

RESULTS

Fifty-five patients (71%) were classified as responders, 23 (29%) as non-responders. ROCAUC for ΔCIPC during PLR in predicting fluid responsiveness, its sensitivity, specificity, and percentage of patients within the inconclusive class of response were 0.67 (95% CI=0.55-0.77), 0.76 (95% CI=0.63-0.87), 0.57 (95% CI=0.34-0.77) and 68%, respectively. Bias, precision and limits of agreements and percentage error between CIPC and CITD after fluid challenge were 0.14 (95% CI: 0.08-0.20), 0.26, -0.37 to 0.64 l min(-1)m(-2), and 20%, respectively. The concordance rate was 97% and the polar concordance at 30° was 91%. ROCAUC for ΔCIPC in predicting an increase of at least 15% in CITD after fluid loading was 0.85 (95% CI: 0.76-0.92).

CONCLUSION

Although ΔCIPC after fluid loading could track the direction of changes of CITD and was interchangeable with bolus transpulmonary thermodilution, PLR could not predict fluid responsiveness in cardiac surgery patients.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

Estimated continuous cardiac output based on pulse wave transit time in off-pump coronary artery bypass grafting: a comparison with transpulmonary thermodilution

To evaluate the accuracy of estimated continuous cardiac output (esCCO) based on pulse wave transit time in comparison with cardiac output (CO) assessed by transpulmonary thermodilution (TPTD) in off-pump coronary artery bypass grafting (OPCAB). We calibrated the esCCO system with non-invasive (Part 1) and invasive (Part 2) blood pressure and compared with TPTD measurements. We performed parallel measurements of CO with both techniques and assessed the accuracy and precision of individual CO values and agreement of trends of changes perioperatively (Part 1) and postoperatively (Part 2). A Bland-Altman analysis revealed a bias between non-invasive esCCO and TPTD of 0.9 L/min and limits of agreement of ±2.8 L/min. Intraoperative bias was 1.2 L/min with limits of agreement of ±2.9 L/min and percentage error (PE) of 64 %. Postoperatively, bias was 0.4 L/min, limits of agreement of ±2.3 L/min and PE of 41 %. A Bland-Altman analysis of invasive esCCO and TPTD after OPCAB found bias of 0.3 L/min with limits of agreement of ±2.1 L/min and PE of 40 %. A 4-quadrant plot analysis of non-invasive esCCO versus TPTD revealed overall, intraoperative and postoperative concordance rate of 76, 65, and 89 %, respectively. The analysis of trending ability of invasive esCCO after OPCAB revealed concordance rate of 73 %. During OPCAB, esCCO demonstrated poor accuracy, precision and trending ability compared to TPTD. Postoperatively, non-invasive esCCO showed better agreement with TPTD. However, invasive calibration of esCCO did not improve the accuracy and precision and the trending ability of method.