Accuracy and Efficacy of Impedance Cardiography as a Non-Invasive Cardiac Function Monitor

PURPOSE

The most common method of monitoring cardiac output (CO) is thermodilution using pulmonary artery catheter (PAC), but this method is associated with complications. Impedance cardiography (ICG) is a non-invasive CO monitoring technique. This study compared the accuracy and efficacy of ICG as a non-invasive cardiac function monitoring technique to those of thermodilution and arterial pressure contour.

MATERIALS AND METHODS

Sixteen patients undergoing liver transplantation were included. Cardiac index (CI) was measured by thermodilution using PAC, arterial waveform analysis, and ICG simultaneously in each patient. Statistical analysis was performed using intraclass correlation coefficient (ICC) and Bland-Altman analysis to assess the degree of agreement.

RESULTS

The difference by thermodilution and ICG was 1.13 L/min/m², and the limits of agreement were -0.93 and 3.20 L/min/m². The difference by thermodilution and arterial pressure contour was 0.62 L/min/m², and the limits of agreement were -1.43 and 2.67 L/min/m². The difference by arterial pressure contour and ICG was 0.50 L/min/m², and the limits of agreement were -1.32 and 2.32 L/min/m². All three percentage errors exceeded the 30% limit of acceptance. Substantial agreement was observed between CI of thermodilution with PAC and ICG at preanhepatic and anhepatic phases, as well as between CI of thermodilution and arterial waveform analysis at preanhepatic phase. Others showed moderate agreement.

CONCLUSION

Although neither method was clinically equivalent to thermodilution, ICG showed more substantial correlation with thermodilution method than with arterial waveform analysis. As a non-invasive cardiac function monitor, ICG would likely require further studies in other settings.

Catheter-Based Measurements of Absolute Coronary Blood Flow and Microvascular Resistance: Feasibility, Safety, and Reproducibility in Humans

BACKGROUND

The principle of continuous thermodilution can be used to calculate absolute coronary blood flow and microvascular resistance (R). The aim of the study is to explore the safety, feasibility, and reproducibility of coronary blood flow and R measurements as measured by continuous thermodilution in humans.

METHODS AND RESULTS

Absolute coronary flow and R can be calculated by thermodilution by infusing saline at room temperature through a dedicated monorail catheter. The temperature of saline as it enters the vessel, the temperature of blood and saline mixed in the distal part of the vessel, and the distal coronary pressure were measured by a pressure/temperature sensor-tipped guidewire. The feasibility and safety of the method were tested in 135 patients who were referred for coronary angiography. No significant adverse events were observed; in 11 (8.1%) patients, bradycardia and concomitant atrioventricular block appeared transiently and were reversed immediately on interruption of the infusion. The reproducibility of measurements was tested in a subgroup of 80 patients (129 arteries). Duplicate measurements had a strong correlation both for coronary blood flow (ρ=0.841, P<0.001; intraclass correlation coefficient=0.89, P<0.001) and R (ρ=0.780, P<0.001; intraclass correlation coefficient=0.89, P<0.001). In Bland-Altman plots, there was no significant bias or asymmetry.

CONCLUSIONS

Absolute coronary blood flow (in L/min) and R (in mm Hg/L/min or Wood units) can be safely and reproducibly measured with continuous thermodilution. This approach constitutes a new opportunity for the study of the coronary microcirculation.

Noninvasive cardiac output monitoring in a porcine model using the inspired sinewave technique: a proof-of-concept study

Background

Cardiac output (Q˙) monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current ‘gold standard’—bolus thermodilution (Q˙T)—has the potential to cause life-threatening complications. We present a novel noninvasive and fully automated method that uses the inspired sinewave technique to continuously monitor cardiac output (Q˙IST).

Methods

Over successive breaths the inspired nitrous oxide (N₂O) concentration was forced to oscillate sinusoidally with a fixed mean (4%), amplitude (3%), and period (60 s). Q˙IST was determined in a single-compartment tidal ventilation lung model that used the resulting amplitude/phase of the expired N₂O sinewave. The agreement and trending ability of Q˙IST were compared with Q˙T during pharmacologically induced haemodynamic changes, before and after repeated lung lavages, in eight anaesthetised pigs.

Results

Before lung lavage, changes in Q˙IST and Q˙T from baseline had a mean bias of –0.52 L min⁻¹ (95% confidence interval [CI], –0.41 to –0.63). The concordance between Q˙IST and Q˙T was 92.5% as assessed by four-quadrant analysis, and polar plot analysis revealed a mean angular bias of 5.98° (95% CI, –24.4°–36.3°). After lung lavage, concordance was slightly reduced (89.4%), and the mean angular bias widened to 21.8° (–4.2°, 47.6°). Impaired trending ability correlated with shunt fraction (r=0.79, P<0.05).

Conclusions

The inspired sinewave technique provides continuous and noninvasive monitoring of cardiac output, with a ‘marginal–good’ trending ability compared with cardiac output based on thermodilution. However, the trending ability can be reduced with increasing shunt fraction, such as in acute lung injury.

Doppler Flow Velocity and Thermodilution to Assess Coronary Flow Reserve: A Head-to-Head Comparison With [15O]H2O PET

OBJECTIVES

This study sought to compare Doppler flow velocity reserve (CFR_Doppl) and thermodilution-derived coronary flow reserve (CFR_thermo) head-to-head with the gold standard for quantification of myocardial perfusion, [¹⁵O]H₂O positron emission tomography (PET).

BACKGROUND

Coronary flow reserve (CFR) is an important parameter for assessing coronary vascular function. To date, 2 techniques are available for invasive assessment of CFR: Doppler flow velocity and thermodilution. Although these techniques have been compared with each other, neither has been compared with [¹⁵O]H₂O PET perfusion imaging.

METHODS

CFR was assessed in 98 vessels of 40 consecutive stable patients with suspected coronary artery disease. Patients underwent [¹⁵O]H₂O PET, followed by invasive angiography in conjunction with simultaneous measurements of fractional flow reserve, CFR_Doppl, and CFR_thermo. Both normal and obstructed arteries were included.

RESULTS

The quality of Doppler flow velocity traces was significantly lower than that of thermodilution curves (p < 0.001). A moderate correlation was observed between CFR_Doppl and CFR_thermo (r = 0.59; p < 0.001). CFR_Doppl correlated well with PET-derived CFR (CFR_PET) (r = 0.82; p < 0.001). In contrast, the correlation between CFR_thermo and CFR_PET was only modest (r = 0.55; p < 0.001). This difference in correlation with CFR_PET was significant (t = 4.9; df = 95; p < 0.001). Bland-Altman analysis revealed a tendency of CFR_thermo to overestimate flow reserve at higher values.

CONCLUSIONS

Coronary flow reserve, determined using Doppler flow velocity, has superior agreement with [¹⁵O]H₂O PET in comparison with CFR_thermo.

Impact of Obesity on Noninvasive Cardiac Hemodynamic Measurement by Electrical Cardiometry in Adults With Aortic Stenosis

OBJECTIVES

There are substantial potential benefits to noninvasive cardiac monitoring methods, such as electrical cardiometry (EC), over more invasive methods, including significantly reduced risk of complications, lower up-front and operational costs, ease of use, and continuous monitoring. To take advantage of these technologies, clinical equivalence to currently established methods must be determined. The authors sought to determine if the noninvasive measurement of cardiac index (CI) by EC was clinically equivalent to thermodilution (TD) in adult patients with aortic stenosis (AS).

DESIGN

This is a cross-sectional study comparing measurement devices in a single patient group.

SETTING

Single-center, university teaching hospital.

PARTICIPANTS

The study included 52 adult patients with aortic stenosis undergoing right heart catheterization.

INTERVENTIONS

Cardiac output (CO) was measured concurrently using EC with an ICON device and TD in 52 participants with AS. CI values were to determine the accuracy and precision of EC in reference to TD. Percentage error (PE) was used to assess their clinical equivalence. The participants were divided further into groups (normal and overweight/obese) based on body mass index and the analysis was repeated.

MEASUREMENTS AND MAIN RESULTS

CO measurement made by EC in adult patients with obesity or overweight was reduced significantly relative to TD. This was not observed in normal-weight adult AS patients. EC provided clinically equivalent measurements to TD for measuring CI in normal-weight adult AS patients (PE = 25.0%), but not for those adult AS patients with overweight or obesity (PE = 42.3%).

CONCLUSION

Overall, the ICON device produced lower CO and index measurements relative to TD in adult patients with AS. Overweight and obesity also significantly affected the relative precision and accuracy of the ICON electrical cardiometric device to measure CI in these patients.

Evaluation of Cardiac Index and Extravascular Lung Water After Single-Lung Transplantation Using the Transpulmonary Thermodilution Technique by the PiCCO2 Device

OBJECTIVES

First evaluation of the transpulmonary thermodilution technique by the PiCCO2 device to assess cardiac index and pulmonary edema during the postoperative course after single-lung transplantation.

DESIGN

Prospective observational study.

SETTINGS

Intensive care unit, university hospital (single center).

PARTICIPANTS

Single-lung transplant patients.

INTERVENTIONS

The authors compared cardiac index measured by PiCCO2 and pulmonary artery catheter and assessed pulmonary edema using extravascular lung water index and pulmonary vascular permeability index measured by PiCCO2.

MEASUREMENTS AND MAIN RESULTS

A Bland-Altman method was used to compare cardiac index measured by PiCCO2 and pulmonary artery catheter. Extravascular lung water index and pulmonary vascular permeability index were compared according to the PaO₂/FiO₂ ratio with a threshold value of 150 mmHg. Ten single-lung transplant patients were included. Cardiac index measured by PiCCO2 and pulmonary artery catheter were 3.3 L/min/m² (2.9-3.6) and 2.5 L/min/m² (2.2-3.0). Bias for cardiac index was 0.71 L/min/m² (-0.03; 1.44) and limit of agreements were -0.03 and 1.44 L/min/m². Extravascular lung water index was 12 mL/kg (11-16) and pulmonary vascular permeability index was 2.3 (2.0-3.1), consistent with pulmonary edema. Extravascular lung water index was higher in the group of PaO₂/FiO₂ ratio ≤150 mmHg compared with the group of PaO₂/FiO₂ ratio >150 mmHg (17 v 12 mL/kg, p = 0.04), whereas pulmonary vascular permeability index only tended to be higher (3.1 v 2.1, p = 0.06).

CONCLUSION

PiCCO2 device systematically overestimated cardiac index compared with pulmonary artery catheter. However, it might be useful to assess pulmonary edema in acute respiratory failure after single-lung transplantation.

Right Ventricular Function After Cardiac Surgery Is a Strong Independent Predictor for Long-Term Mortality

OBJECTIVE

To establish the all-cause mortality of right ventricular dysfunction after cardiac surgery in a heterogeneous group of cardiac surgery patients.

DESIGN

Retrospective analysis of a heterogeneous group of 1,109 cardiac surgery patients in a 4-year period.

SETTING

Single-center study in a tertiary teaching hospital.

PARTICIPANTS

One thousand one hundred nine cardiac surgery patients. By protocol, patients were monitored with a pulmonary artery catheter, enabling continuous right ventricular ejection fraction (RVEF) measurements.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed once per minute for the first 24 postoperative hours and expressed as average over the complete period. Primary outcome was 2-year all-cause mortality. RVEF was categorized into 3 subgroups: <20%, 20-30%, and >30%. Median follow-up time was 739 days. Two-year mortality was significantly different across groups: 4.1% for patients with RVEF >30%, 8.2% in the group with RVEF 20-30%, and 16.7% for patients with RVEF <20%, p < 0.001. Additional risk factors for a poor RVEF were age, body weight, New York Heart Association class, chronic obstructive pulmonary disease, poor left ventricular function, and higher risk scores (Acute Physiology and Chronic Health Evaluation and European System for Cardiac Operative Risk Evaluation). In a multivariate analysis, RVEF as a continuous variable was associated independently with the primary outcome (odds ratio 0.95 confidence interval 0.91-0.99, p = 0.011.) Odds ratios for RVEF <20% were 1.88 (confidence interval 1.18-3.00, p = 0.008).

CONCLUSIONS

Right ventricular function is associated independently with 2-year all-cause mortality in a heterogenic cardiac surgery population.

Hemodynamic Assessment of Patients With Septic Shock Using Transpulmonary Thermodilution and Critical Care Echocardiography: A Comparative Study

BACKGROUND

To assess the agreement between transpulmonary thermodilution (TPT) and critical care echocardiography (CCE) in ventilated patients with septic shock.

METHODS

Ventilated patients in sinus rhythm requiring advanced hemodynamic assessment for septic shock were included in this prospective multicenter descriptive study. Patients were assessed successively using TPT and CCE in random order. Data were interpreted independently at bedside by two investigators who proposed therapeutic changes on the basis of predefined algorithms. TPT and CCE hemodynamic assessments were reviewed offline by two independent experts who identified potential sources of discrepant results by consensus. Lactate clearance and outcome were studied.

RESULTS

A total of 137 patients were studied (71 men; age, 61 ± 15 years; Simplified Acute Physiologic Score, 58 ± 18; Sequential Organ Failure Assessment, 10 ± 3). TPT and CCE interpretations at bedside were concordant in 87/132 patients (66%) without acute cor pulmonale (ACP), resulting in a moderate agreement (kappa, 0.48; 95% CI, 0.37-0.60). Experts' adjudications were concordant in 100/129 patients without ACP (77.5%), resulting in a good intertechnique agreement (kappa, 0.66; 95% CI, 0.55-0.77). In addition to ACP (n = 8), CCE depicted a potential source of TPT inaccuracy in 8/29 patients (28%). Lactate clearance at H6 was similar irrespective of the concordance of online interpretations of TPT and CCE (55/84 [65%] vs 32/45 [71%], P = .55). ICU and day 28 mortality rates were similar between patients with concordant and discordant interpretations (29/87 [36%] vs 13/45 [29%], P = .60; and 31/87 [36%] vs 16/45 [36%], P = .99, respectively).

CONCLUSIONS

Agreement between TPT and CCE was moderate when interpreted at bedside and good when adjudicated offline by experts, but without impact on lactate clearance and mortality.

How Useful is Extravascular Lung Water Measurement in Managing Lung Injury in Intensive Care Unit?

Context:

The primary goal of septic shock management is optimization of organ perfusion, often at the risk of overloading the interstitium and causing pulmonary edema. The conventionally used end points of resuscitation do not generally include volumetric parameters such as extravascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI).

Aims:

This study aimed to assess the prognostic value of EVLWI and PVPI by calculating their correlation with the severity of lung injury.

Settings and Design:

This prospective observational study included twenty mechanically ventilated critically ill patients with Acute Physiology and Chronic Health Evaluation score (APACHE II) >20.

Subjects and Methods:

EVLWI and PVPI were measured using transpulmonary thermodilution, and simultaneously, PaO₂:FiO₂ ratio, alveolar-arterial gradient of oxygen (AaDO₂), and chest radiograph scores from two radiologists were obtained.

Statistical Analysis:

The correlation of EVLWI and PVPI with chest radiograph scores, PaO₂:FiO₂ ratio, and AaDO₂ were calculated. The inter-observer agreement between the two radiologists was tested using kappa test.

Results:

EVLWI and PVPI correlated modestly with PaO₂:FiO₂ (r = −0.32, P = 0.0004; r = −0.39, P = 0.0001). There was a better correlation of EVLWI and PVPI with PaO₂:FiO₂ ratio (r = −0.71, P < 0.0001; r = −0.58, P = 0.0001) in the acute respiratory distress syndrome (ARDS) subgroup. The EVLWI values correlated significantly with corresponding chest radiograph scores (r = 0.71, P < 0.0001 for observer 1 and r = 0.68, P < 0.0001 for observer 2).

Conclusions:

EVLWI and PVPI may have a prognostic significance in the assessment of lung injury in septic shock patients with ARDS. Further research is required to reveal the usefulness of EVLWI as an end point of fluid resuscitation in the management of septic shock with ARDS.

Fluid resuscitation management in patients with burns: update

Since 1968, when Baxter and Shires developed the Parkland formula, little progress has been made in the field of fluid therapy for burn resuscitation, despite advances in haemodynamic monitoring, establishment of the 'goal-directed therapy' concept, and the development of new colloid and crystalloid solutions. Burn patients receive a larger amount of fluids in the first hours than any other trauma patients. Initial resuscitation is based on crystalloids because of the increased capillary permeability occurring during the first 24 h. After that time, some colloids, but not all, are accepted. Since the emergence of the Pharmacovigilance Risk Assessment Committee alert from the European Medicines Agency concerning hydroxyethyl starches, solutions containing this component are not recommended for burns. But the question is: what do we really know about fluid resuscitation in burns? To provide an answer, we carried out a non-systematic review to clarify how to quantify the amount of fluids needed, what the current evidence says about the available solutions, and which solution is the most appropriate for burn patients based on the available knowledge.

Evaluation of cardiac output by bioreactance technique in patients undergoing liver transplantation

BACKGROUND

This study compared the cardiac output (CO) obtained from PiCCO with that obtained from the noninvasive NICOM method.

METHODS

Twenty-one cirrhotic patients receiving liver transplantation were enrolled. During the operation, their CO was measured by the PiCCO system via the thermodilution method as the standard and by the NICOM method. Two parameters including cardiac index (CI) and stroke volume index (SVI) were collected simultaneously at three phases during the surgery including the dissection phase (T1), the anhepatic phase (T2), and the reperfusion phase (T3). Correlation, Bland and Altman methods, and linear mixed model were used to evaluate the monitoring ability of both systems.

RESULTS

Poor correlation was noted between the data measured by NICOM and PiCCO; the correlation coefficients for CI and SVI measured between the two systems were 0.32 and 0.39, respectively. Bland and Altman analysis showed the percentage error of CI as 63.7%, and that of SVI as 66.6% for NICOM compared to PiCCO. Using the linear mixed model, the CI and SVI measured using NICOM were significantly higher than those using PiCCO (estimated regression coefficient 0.92 and 10.77, both p < 0.001). Mixed model analysis showed no differences between the trends of CI and SVI measured by the two methods.

CONCLUSIONS

NICOM provided a comparable CI and SVI trend when compared to the gold standard PiCCO, but it raises concerns as an effective CO monitor because of its tendency to overestimate CI and SVI especially during the state of high cardiac output.

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.

Transpulmonary thermodilution (PiCCO) measurements in children without cardiopulmonary dysfunction: large interindividual variation and conflicting reference values

BACKGROUND

The PiCCO system, based on transpulmonary thermodilution, is one of the few tools available for continuous hemodynamic monitoring in children. However, published data for some of the derived variables reveal indexed values that seem questionable.

AIMS

The aim of this study was to collect data from hemodynamically normal children and compare these to existing reference values. Furthermore, we sought to explore if indexing some of the variables differently could improve the clinical application of the obtained values.

METHODS

This is a prospective observational study in a tertiary university hospital including 31 children without cardiopulmonary disease scheduled for major neurosurgery. Measurements were performed after induction of general anesthesia.

RESULTS

Median age was 8 months. PiCCO-derived median Cardiac Index (CI) was 3.8 l · min(-1) · m(-2) (range 2.6-6.6), reference range 3.0-5.0, median Global End-Diastolic Volume Index (GEDVI) was 366 ml · m(-2) (range 269-685), reference range 680-800, whereas median Extravascular Lung Water Index (EVLWI) was 12 ml · kg(-1) (range 7-31), reference range 3-7. All measured variables had a high interindividual variation, especially in children weighing less than 15 kg.

CONCLUSIONS

Values obtained by the PiCCO system in children have a wide range, and should therefore be interpreted with caution. Current reference values published for GEDVI and EVLWI are not applicable in children; the former is too high and the latter too low, and should not guide clinical practice. Indexing by other physiological indices may reduce this problem. Using current variables, we find GEDVI 280-590 ml · m(-2) and ELWI 7-27 ml · kg(-1) to be typical ranges for children.

Transesophageal Echocardiographic Measurement of Cardiac Index by the Prosthetic Mitral Valve Method Is Not Similar to the Continuous Thermodilution Method Via a Pulmonary Artery Catheter

OBJECTIVE

To compare the agreement of cardiac index measurements between transesophageal echocardiography across the prosthetic mitral valve and the continuous thermodilution method through a pulmonary artery catheter (PAC-TD) in patients undergoing double-valve replacement.

DESIGN

Observational prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty-five patients undergoing double-valve replacement (12 men and 13 women, age 25-78 years, ASA III-IV, NYHA II-III, LVEF≥45%). Patients were grouped according to their prosthesis (mechanical prosthesis v bioprosthesis).

INTERVENTIONS

All patients underwent cardiac index assessment during double-valve replacement.

MEASUREMENTS AND MAIN RESULTS

Cardiac index across the prosthetic mitral valve was measured simultaneously using transesophageal echocardiography (CI(MV)) and PAC-TD (CI(PAC)) at 15, 30, 45, and 60 minutes after weaning from cardiopulmonary bypass, and at 0, 15, and 30 minutes after incision closure. A correlation was present between CI(MV) and CI(PAC) in both groups (mechanical prosthesis: r = 0.47, p<0.01; bioprosthesis: r = 0.60, p<0.01). In the mechanical prosthesis group, the bias between techniques (CI(PAC) v CI(MV)) was-0.5 L/min/m(2) (95% CI:-1.97 to 0.97), and error was 55%. In the bioprosthesis group, the bias between both techniques was-1.3 L/min/m(2) (95% CI:-3.1 to 0.5), and error was 56%.

CONCLUSIONS

A relatively weak correlation and lack of agreement between values of CI(PAC) and CI(MV) were observed in patients undergoing double-valve replacement. Therefore, transesophageal echocardiography might not be interchangeable with PAC-TD for measuring cardiac output or cardiac index. A regression equation is needed to correct the probable value of CI(PAC). CI(MV) might be useful as a quantitative or semi-quantitative cardiac output measurement.

Comparison of cardiac output measurements using transpulmonary thermodilution and conventional thermodilution techniques in anaesthetized dogs with fluid overload

OBJECTIVE

To evaluate the agreement between cardiac output (CO) values obtained using a transpulmonary thermodilution technique (TPTDCO) and conventional thermodilution technique (TDCO) in anaesthetized dogs with fluid overload.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six healthy Beagle dogs aged 7-8 years.

METHODS

Dogs were anaesthetized with sevoflurane in oxygen, and catheters were inserted for TPTDCO and TDCO measurement. After instrumentation, baseline CO was measured using each technique at a central venous pressure (CVP) of 3-7 mmHg. Dogs were subsequently administered lactated Ringer's solution and 6% hydroxyethyl starch to induce fluid overload. CO measurements were obtained using each technique at CVP values of 8-12 mmHg, 13-17 mmHg, 18-22 mmHg and 23-27 mmHg. Agreements between CO measurements obtained with the respective techniques were analysed using Dunnett's test, Pearson's correlation coefficient and Bland-Altman analysis.

RESULTS

Thirty pairs of CO values were obtained, ranging from 1.45 L minute(-1) to 4.69 L minute(-1) for TPTDCO and from 1.30 L minute(-1) to 4.61 L minute(-1) for TDCO. TPTDCO and TDCO values correlated strongly (r(2)  = 0.915, p < 0.001). The bias and mean relative bias between TPTDCO and TDCO were 0.26 ± 0.30 L minute(-1) (limits of agreement - 0.29 to 0.81 L minute(-1) ) and 9.7%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

TPTDCO and TDCO measurements obtained in anaesthetized dogs during fluid overload exhibited good agreement. Accordingly, transpulmonary thermodilution provides an accurate measurement of CO in dogs with fluid overload.

A multicenter prospective cohort study of volume management after subarachnoid hemorrhage: circulatory characteristics of pulmonary edema after subarachnoid hemorrhage

OBJECT Subarachnoid hemorrhage (SAH) is often accompanied by pulmonary complications, which may lead to poor outcomes and death. This study investigated the incidence and cause of pulmonary edema in patients with SAH by using hemodynamic monitoring with PiCCO-plus pulse contour analysis. METHODS A total of 204 patients with SAH were included in a multicenter prospective cohort study to investigate hemodynamic changes after surgical clipping or coil embolization of ruptured cerebral aneurysms by using a PiCCO-plus device. Changes in various hemodynamic parameters after SAH were analyzed statistically. RESULTS Fifty-two patients (25.5%) developed pulmonary edema. Patients with pulmonary edema (PE group) were significantly older than those without pulmonary edema (non-PE group) (p = 0.017). The mean extravascular lung water index was significantly higher in the PE group than in the non-PE group throughout the study period. The pulmonary vascular permeability index (PVPI) was significantly higher in the PE group than in the non-PE group on Day 6 (p = 0.029) and Day 10 (p = 0.011). The cardiac index of the PE group was significantly decreased biphasically on Days 2 and 10 compared with that of the non-PE group. In the early phase (Days 1-5 after SAH), the daily water balance of the PE group was slightly positive. In the delayed phase (Days 6-14 after SAH), the serum C-reactive protein level and the global end-diastolic volume index were significantly higher in the PE group than in the non-PE group, whereas the PVPI tended to be higher in the PE group. CONCLUSIONS Pulmonary edema that occurs in the early and delayed phases after SAH is caused by cardiac failure and inflammatory (i.e., noncardiogenic) conditions, respectively. Measurement of the extravascular lung water index, cardiac index, and PVPI by PiCCO-plus monitoring is useful for identifying pulmonary edema in patients with SAH.

Hemodynamic monitoring: To calibrate or not to calibrate? Part 2--Non-calibrated techniques

There is much evidence that fluid overload leads to adverse outcomes in perioperative and critically ill patients. Cardiac output monitoring can help us guiding initial and ongoing fluid resuscitation and can help us to assess whether a patient will be responsive to fluids when hypotensive. In recent years, many sophisticated devices that measure a variety of hemodynamic parameters have evolved on the market. We wanted to provide an overview of the different techniques available today, including their validation in different patient populations. In this second part of the review, we focus on non-calibrated techniques, both invasive and non-invasive. For each technique a short overview of the working principle, together with the advantages, disadvantages and the available validation literature is listed. Many promising minimal invasive monitoring devices can help us to further optimize our hemodynamic treatment in both the perioperative and critical care setting. However, the validation data are scarce for many of these techniques, especially in complex circumstances with changing hemodynamics (preload, afterload and contractility), as with the use of fluids and vasoactive medication. The measurements made by these devices, therefore, need to be interpreted with caution. Further improvements and more validation data are needed before these techniques can be implemented in common day practice. Moreover, in severely shocked hemodynamic unstable patients, calibrated techniques are to be preferred over those which are uncalibrated. Hence, the new techniques not only need to be accurate, but also need to be precise in order to keep track of changes.

Hemodynamic monitoring: To calibrate or not to calibrate? Part 1--Calibrated techniques

Over recent decades, hemodynamic monitoring has evolved from basic cardiac output monitoring techniques to a broad variety of sophisticated monitoring devices with extra parameters. In order to reduce morbidity and mortality and optimize therapeutic strategies, different monitoring techniques can be used to guide fluid resuscitation and other medical management. Generally, they can be divided in calibrated and non-calibrated techniques. In the first part of this review, the available calibrated techniques, ranging from invasive to non-invasive, will be discussed. We performed a review of the literature in order to give an overview of the current hemodynamic monitoring devices. For each monitoring system, a short overview of the physical principles, the advantages and disadvantages and the available literature with regard to validation is given. Currently, many promising hemodynamic monitoring devices are readily available in order to optimize therapeutic management in both perioperative and ICU settings. Although several of these calibrated techniques have been validated in the literature, not all techniques have been shown to reduce morbidity and mortality. Many new techniques, especially some non-calibrated devices, lack good validation data in different clinical settings (sepsis, trauma, burns, etc.). The cardiac output values obtained with these techniques need therefore to be interpreted with caution as will be discussed in the second part of this concise review. Transthoracic echocardiography forms a good initial choice to assess hemodynamics in critically ill patients after initial stabilisation. However in complex situations or in patients not responding to fluid resuscitation alone, advanced hemodynamic monitoring is recommended with the use of calibrated techniques like transpulmonary thermodilution. Calibrated techniques are preferred in patients with severe shock and changing conditions of preload, afterload and contractility. The use of the pulmonary artery catheter should be reserved for patients with right ventricular failure in order to assess the effect of medical treatment.

Impact of Positive End-Expiratory Pressure on Thermodilution-Derived Right Ventricular Parameters in Mechanically Ventilated Critically Ill Patients

OBJECTIVES

To examine the effect of positive end-expiratory pressure (PEEP) on right ventricular stroke volume variation (SVV), with possible implications for the number and timing of pulmonary artery catheter thermodilution measurements.

DESIGN

Prospective, clinical pilot study.

SETTING

Academic medical center.

PARTICIPANTS

Patients who underwent volume-controlled mechanical ventilation and had a pulmonary artery catheter.

INTERVENTION

PEEP was increased from 5-to-10 cmH2O and from 10-to-15 cmH2O with 10-minute intervals, with similar decreases in PEEP, from 15-to-10 cmH2O and 10-to-5 cmH2O.

MEASUREMENTS AND MAIN RESULTS

In 15 patients, right ventricular parameters were measured using thermodilution at 10% intervals of the ventilatory cycle at each PEEP level with a rapid-response thermistor. Mean right ventricular stroke volume and end-diastolic volume declined during incremental PEEP and normalized on return to 5 cmH2O PEEP (p = 0.01 and p = 0.001, respectively). Right ventricular SVV remained unaltered by changes in PEEP (p = 0.26), regardless of incremental PEEP (p = 0.15) or decreased PEEP (p = 0.12). The coefficients of variation in the ventilatory cycle of all other thermodilution-derived right ventricular parameters also were unaffected by changes in PEEP.

CONCLUSIONS

This study showed that increases in PEEP did not affect right ventricular SVV in critically ill patients undergoing mechanical ventilation despite reductions in mean right ventricular stroke volume and end-diastolic volume. This could be explained by cyclic counteracting changes in right ventricular preloading and afterloading during the ventilatory cycle, independent of PEEP. Changes in PEEP did not affect the number and timing of pulmonary artery catheter thermodilution measurements.

Constant infusion transpulmonary thermodilution for the assessment of cardiac output in exercising humans

To determine the accuracy and precision of constant infusion transpulmonary thermodilution cardiac output (CITT-Q) assessment during exercise in humans, using indocyanine green (ICG) dilution and bolus transpulmonary thermodilution (BTD) as reference methods, cardiac output (Q) was determined at rest and during incremental one- and two-legged pedaling on a cycle ergometer, and combined arm cranking with leg pedaling to exhaustion in 15 healthy men. Continuous infusions of iced saline in the femoral vein (n = 41) or simultaneously in the femoral and axillary (n = 66) veins with determination of temperature in the femoral artery were used for CITT-Q assessment. CITT-Q was linearly related to ICG-Q (r = 0.82, CITT-Q = 0.876 × ICG-Q + 3.638, P < 0.001; limits of agreement ranging from -1.43 to 3.07 L/min) and BTD-Q (r = 0.91, CITT-Q = 0.822 × BTD + 4.481 L/min, P < 0.001; limits of agreement ranging from -1.01 to 2.63 L/min). Compared with ICG-Q and BTD-Q, CITT-Q overestimated cardiac output by 1.6 L/min (≈ 10% of the mean ICG and BTD-Q values, P < 0.05). For Q between 20 and 28 L/min, we estimated an overestimation < 5%. The coefficient of variation of 23 repeated CITT-Q measurements was 6.0% (CI: 6.1-11.1%). In conclusion, cardiac output can be precisely and accurately determined with constant infusion transpulmonary thermodilution in exercising humans.

Evolving concepts of hemodynamic monitoring for critically ill patients

The last decades have been characterized by a continuous evolution of hemodynamic monitoring techniques from intermittent toward continuous and real-time measurements and from an invasive towards a less invasive approach. The latter approach uses ultrasounds and pulse contour analysis techniques that have been developed over the last 15 years. During the same period, the concept of prediction of fluid responsiveness has also been developed and dynamic indices such as pulse pressure variation, stroke volume variation, and the real-time response of cardiac output to passive leg raising or to end-expiration occlusion, can be easily obtained and displayed with the minimally invasive techniques. In this article, we review the main hemodynamic monitoring devices currently available with their respective advantages and drawbacks. We also present the current viewpoint on how to choose a hemodynamic monitoring device in the most severely ill patients and especially in patients with circulatory shock.

Comparison of the accuracy of transpulmonary thermodilution measurement using indicators of different temperatures

Transpulmonary thermodilution measurement is a convenient method for hemodynamic monitoring. However, the previously reported indicator temperature was not consistent. This study aimed to compare the accuracy of Pulse index Continuous Cardiac Output (PiCCO) monitoring using indicators of different temperatures. A total of 104 critically ill patients received PiCCO monitoring using indicators of either 0°C or 8°C. The PiCCO measurements, including general ejection fraction, global end-diastolic index, and cardiac index, were compared between the two temperatures, and were also correlated with that of transesophageal echocardiography (TEE). The two indicator temperatures differed significantly in hemodynamic measurements (P<0.01). PiCCO measurements with either indicator temperatures showed positive correlation with TEE results (P<0.05). The 0°C indicator had universally higher correlation coefficients than the 8°C indicator. So, PiCCO monitoring with the 0°C indicator might have better accuracy than the 8°C indicator.

The Precision of Pulmonary Artery Catheter Bolus Thermodilution Cardiac Output Measurements Varies With the Clinical Situation

OBJECTIVE

To investigate the effects of ventilatory mode, injectate temperature, and clinical situation on the precision of cardiac output measurements.

DESIGN

Randomized, prospective observational study.

SETTING

Single university hospital.

PARTICIPANTS

Forty patients undergoing planned cardiac surgery, receiving a pulmonary artery catheter according to institutional routine.

INTERVENTIONS

Cardiac output was measured at 4 predefined time points during the perioperative patient course, twice during controlled and twice during spontaneous ventilation, using 2 blocks of 8 measurement replications with cold and tepid injectate in random order.

MEASUREMENTS AND MAIN RESULTS

The data were analyzed using a hierarchical linear mixed model. Clinical precision was determined as half the width of the 95% confidence interval for the underlying true value. The single-measurement precision measured in 2 different clinical situations for each temperature/ventilation combination was 8% to 10%, 11% to 13%, 13% to 15%, and 23% to 24% in controlled ventilation with cold injectate, controlled ventilation with tepid injectate, spontaneous breathing with cold injectate, and spontaneous breathing with tepid injectate, respectively. Tables are provided for the number of replications needed to achieve a certain precision and for how to identify significant changes in cardiac output.

CONCLUSIONS

Clinical precision of cardiac output measurements is reduced significantly during spontaneous relative to controlled ventilation. The differences in precision between repeated measurement series within the temperature/ventilation combinations indicate influence of other situation-specific factors not related to ventilatory mode. Compared with tepid injectate in patients breathing spontaneously, the precision is 3-fold better with cold injectate and controlled ventilation.

Comparison of thermodilution, lithium dilution, and pulse contour analysis for the measurement of cardiac output in 3 different hemodynamic states in dogs

OBJECTIVE

To (1) evaluate lithium dilution (LiDCO) and transpulmonary thermodilution (PiCCOTD ) in relation to traditional thermodilution (PAC-TD) for determining cardiac output (CO) in 3 different hemodynamic states in dogs and to (2) compare the continuous CO values obtained using power analysis (PulseCO) with continuous PiCCO (PiCCOc).

DESIGN

Prospective randomized study.

SETTING

University research laboratory.

ANIMALS

Fourteen healthy Beagles.

INTERVENTIONS

CO was measured using PAC-TD, LiDCO, and PiCCOTD in 3 different hemodynamic states induced in random order and defined on the basis of the mean arterial pressure (MAP). Normodynamic state was defined as the baseline MAP and 1 MAC sevoflurane. The hypodynamic state was induced with a deep level of sevoflurane anesthesia. The hyperdynamic state was induced with noradrenaline. After these measurements were obtained in each hemodynamic state, CO was monitored continuously for 30 min using PulseCO and PiCCOc. Agreement was assessed using Bland-Altman analysis and intraclass correlation coefficients, and a trend score was determined for the continuous CO measurements.

MEASUREMENTS AND MAIN RESULTS

There was good agreement among the 3 modalities of CO measurement in each hemodynamic state. The mean CIPAC-TD /CIPICCOTD bias was -0.04 ± 1.19 L/min/m(2) (limits of agreement, -2.37/1.93 L/min/m(2) ), and the mean CIPAC-TD /CILiDCO bias was -0.11 ± 1.55 L/min/m(2) (limits of agreement, -3.04/2.93 L/min/m(2) ). The mean CIPulseCO -CIPiCCOc bias was -0.04 ± 1.91 L/min/m(2) (limits of agreement, -1.95/1.87 L/min/m(2) ), which suggested good agreement. The CIPulseCO -CIPiCCOc trend score, calculated from 252 paired comparisons, was 93.3% positive after zone exclusion (∆CI < 15%).

CONCLUSIONS

Both LiDCO and PiCCOTD agreed well with PAC-TD for the measurement of CO under different hemodynamic conditions. Moreover, PiCCOc appears to be an accurate method for monitoring continuous CO in dogs as its performance for measurement was similar to that of PulseCO.

Hybrid measurement to achieve satisfactory precision in perioperative cardiac output monitoring

Advanced haemodynamic monitoring employing minimally invasive cardiac output measurement may lead to significant improvements in patient outcomes in major surgery. However, the precision (scatter) of measurement of available generic technologies has been shown to be unsatisfactory with percentage error of agreement with bolus thermodilution (% error) of 40% to 50%. Simultaneous measurement and averaging by two or more technologies may reduce random measurement scatter and improve precision. This concept, called the hybrid method, was tested by comparing accuracy and precision of measurement relative to bolus thermodilution using combinations of three component methods. Thirty patients scheduled for either elective cardiac surgery or liver transplantation were studied. Agreement with simultaneous bolus thermodilution of hybrid combinations of continuous thermodilution (QtCCO) or Vigeleo™/FloTrac™ pulse contour measurement (QtFT) with pulmonary Capnotracking (QtCO2) was assessed pre- and post-cardiopulmonary bypass or pre- and post-reperfusion of the donor liver and compared with that of the component methods alone. Hybridisation of QtCO2 (% error 42.2) and QtCCO (% error 51.3) achieved significantly better precision (% error 31.3) than the component methods (P=0.0004) and (P=0.0195). Due to poor inherent precision of QtFT (% error 82.8), hybrid combination of QtFT with QtCO2 did not result in better precision than QtCO2 alone. Hybrid measurement can approach a 30% error, which is recommended as the upper limit for acceptability. This is a practical option where at least one component method, such as Capnotracking, is automated and does not increase the cost or complexity of the measurement process.