Minimally invasive cardiac output technologies in the ICU: putting it all together

New Developments in Continuous Hemodynamic Monitoring of the Critically Ill Patient

Hemodynamic monitoring is a cornerstone in the assessment of patients with circulatory shock. Timely recognition of hemodynamic compromise and proper optimisation is essential to ensure adequate tissue perfusion and maintain renal, hepatic, abdominal, and cerebral functions. Hemodynamic monitoring has significantly evolved since the first inception of the pulmonary artery catheter more than 50 years ago. Bedside echocardiography, when combined with noninvasive and minimally invasive technologies, provides tools to monitor and quantify the cardiac output to promptly react and improve hemodynamic management in an acute care setting. Commonly used technologies include noninvasive pulse-wave analysis, pulse-wave transit time, thoracic bioimpedance and bioreactance, esophageal Doppler, minimally invasive pulse-wave analysis, transpulmonary thermodilution, and pulmonary artery catheter. These monitoring strategies are reviewed here, along with detailed analysis of their operating mode, particularities, and limitations. The use of artificial intelligence to enhance performance and effectiveness of hemodynamic monitoring is reviewed to apprehend future possibilities.

Cardiac output monitoring - invasive and noninvasive

PURPOSE OF REVIEW

The purpose of this article is to review various contemporary cardiac output (CO) measurement technologies available and their utility in critically ill patients.

RECENT FINDINGS

CO measurement devices can be invasive, minimally invasive, or noninvasive depending upon their method of CO measurement. All devices have pros and cons, with pulmonary artery catheter (PAC) being the gold standard. The invasive techniques are more accurate; however, their invasiveness can cause more complications. The noninvasive devices predict CO via mathematical modeling with several assumptions and are thus prone to errors in clinical situations. Recently, PAC has made a comeback into clinical practice especially in cardiac intensive care units (ICUs). Critical care echocardiography (CCE) is an upcoming tool that not only provides CO but also helps in differential diagnosis. Lack of proper training and nonavailability of equipment are the main hindrances to the wide adoption of CCE.

SUMMARY

PAC thermodilution for CO measurement is still gold standard and most suitable in patients with cardiac pathology and with experienced user. CCE offers an alternative to thermodilution and is suitable for all ICUs; however, structural training is required.

Updates in Hemodynamic Monitoring: A Review for Pharmacists

Vital signs are regularly monitored in hospitalized patients. In the intensive care unit (ICU), traditional non-invasive blood pressure monitoring and telemetry may not provide enough information to determine the etiology of hemodynamic instability or guide intervention. Arterial catheters remain the gold-standard for continuous blood pressure monitoring and are commonly used in ICU patients. Pulmonary artery catheters and central venous catheters are beneficial in select patient populations and provide more advanced and specific information about a patient's hemodynamics. However, neither are benign and can increase risk of complications such as infection, arrhythmias, pneumothorax and vascular or valvular damage. In the past 10 years, the development of reliable non-invasive (NICOM), or minimally-invasive (MICOM), cardiac output monitoring devices has accelerated. The MICOM devices require an arterial catheter to obtain hemodynamic values, whereas NICOM devices do not require any arterial or venous access. These devices have emerged to be particularly useful in evaluating and managing patients with suspected mixed shock. As these devices become more prevalent, it is imperative that clinical pharmacists become familiar with interpreting this data as it may have a substantial impact on medication selection and optimization. This review will discuss the basics of NICOM and MICOM devices, limitations with these methods of monitoring, and clinical application for pharmacists.

Accuracy of noninvasive continuous arterial pressure monitoring using ClearSight during one-lung ventilation

Noninvasive continuous arterial pressure monitoring may be clinically useful in patients who require continuous blood pressure monitoring in situations where arterial catheter placement is limited. Many previous studies on the accuracy of the noninvasive continuous blood pressure monitoring method reported various results. However, there is no research on the effectiveness of noninvasive arterial pressure monitoring during one-lung ventilation. The purpose of this study was to compare arterial blood pressure obtained through invasive method and noninvasive method by using ClearSight during one-lung ventilation.In this retrospective observational study, a total of 26 patients undergoing one-lung ventilation for thoracic surgery at a single institution between March and July 2019 were recruited. All patients in this study were cannulated on their radial artery to measure continuously invasive blood pressures and applied ClearSight on the ipsilateral side of the cannulated arm. We compared and analyzed the agreement and trendability of blood pressure recorded with invasive and noninvasive methods during one-lung ventilation.Blood pressure and pulse rate showed a narrower limit of agreement with a percentage error value of around 30%. In addition, the tracking ability of each measurement could be determined by the concordance rate, all of which were below acceptable limits (92%).In noninvasive arterial blood pressure monitoring using ClearSight, mean blood pressure and pulse rate show acceptable agreement with the invasive method.

Volume Capnography in the Intensive Care Unit: Potential Clinical Applications

Volume capnography provides a noninvasive, continuous display of the fractional concentration or partial pressure of carbon dioxide (Pco₂) versus exhaled volume. Derived measurements and calculations are influenced by changes in both ventilation and perfusion and are therefore useful for assessing both respiratory and cardiovascular function. This article provides an evidence-based review of several potential uses of volume capnography in the intensive care unit: 1) monitoring the effectiveness of ventilation by using end-tidal Pco₂ as a surrogate for arterial Pco₂, 2) assessing volume responsiveness, 3) measuring cardiac output, 4) determining prognosis in patients with the acute respiratory distress syndrome, 5) optimizing alveolar recruitment, and 6) excluding pulmonary embolism. Studies performed during the past few decades have clearly shown that volume capnography can provide important prognostic information in patients with acute respiratory distress syndrome and that end-tidal Pco₂ should not be used to estimate or even to monitor the direction of change in the arterial Pco₂ in mechanically ventilated intensive care unit patients. Unfortunately, few conclusions can be made from studies evaluating other potential applications. Of these, the most promising are the noninvasive measurement of cardiac output and optimization of alveolar recruitment in patients with acute respiratory distress syndrome and in mechanically ventilated, morbidly obese patients.

Approach and Management of Hypertension After Kidney Transplantation

Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed.

Measuring cardiac output at the bedside

PURPOSE OF REVIEW

Bedside cardiac output (CO) measurement is an important part of routine hemodynamic monitoring in the differential diagnosis of circulatory shock and fluid management. Different choices of CO measurement devices are available. The purpose of this review is to review the importance of CO [or stroke volume (SV)] measurement and to discuss the various methods (devices) used in determination of CO.

RECENT FINDINGS

CO measurement devices can be classified into two types: those use simple physical principles with minimal assumptions, and those predicting CO via mathematical modelling with a number of assumptions. Both have pros and cons, with the former being more accurate but with limited continuous monitoring capability whereas the latter less accurate but usually equipped with continuous monitoring functionality. With frequent updates in mathematical models, research data constantly become outdated in this area. Recent data suggest devices based on mathematical modelling have limited accuracies and poor precisions.

SUMMARY

Measurement of CO or SV is important in critically ill patients. Most devices have accuracy and reliability issues. The choice of device should depend on the purpose of measurement. For diagnostic purposes, devices based on simple physical principles, especially thermodilution and transthoracic echocardiography are more reliable due to accuracy.

Disagreement in cardiac output measurements between fourth-generation FloTrac and critical care ultrasonography in patients with circulatory shock: a prospective observational study

Background

Cardiac output measurements may inform diagnosis and provide guidance of therapeutic interventions in patients with hemodynamic instability. The FloTrac™ algorithm uses uncalibrated arterial pressure waveform analysis to estimate cardiac output. Recently, a new version of the algorithm has been developed. The aim was to assess the agreement between FloTrac™ and routinely performed cardiac output measurements obtained by critical care ultrasonography in patients with circulatory shock.

Methods

A prospective observational study was performed in a tertiary hospital from June 2016 to January 2017. Adult critically ill patients with circulatory shock were eligible for inclusion. Cardiac output was measured simultaneously using FloTrac™ with a fourth-generation algorithm (CO_AP) and critical care ultrasonography (CO_CCUS). The strength of linear correlation of both methods was determined by the Pearson coefficient. Bland-Altman plot and four-quadrant plot were used to track agreement and trending ability.

Result

Eighty-nine paired cardiac output measurements were performed in 17 patients during their first 24 h of admittance. CO_AP and CO_CCUS had strong positive linear correlation (r² = 0.60, p < 0.001). Bias of CO_AP and CO_CCUS was 0.2 L min⁻¹ (95% CI − 0.2 to 0.6) with limits of agreement of − 3.6 L min⁻¹ (95% CI − 4.3 to − 2.9) to 4.0 L min⁻¹ (95% CI 3.3 to 4.7). The percentage error was 65.6% (95% CI 53.2 to 77.3). Concordance rate was 64.4%.

Conclusions

In critically ill patients with circulatory shock, there was disagreement and clinically unacceptable trending ability between values of cardiac output obtained by uncalibrated arterial pressure waveform analysis and critical care ultrasonography.

Trial registration

Clinicaltrials.gov, NCT02912624, registered on September 23, 2016

Electronic supplementary material

The online version of this article (10.1186/s40560-019-0373-5) contains supplementary material, which is available to authorized users.

A Novel Fluorescent Clinical Method to Rapidly Quantify Plasma Volume

OBJECTIVES

To determine the performance of a rapid fluorescent indicator technique for measuring plasma volume (PV).

METHODS

This was an open-label, observational evaluation of a two-component intravenous visible fluorescent dye technique to rapidly measure PV in 16 healthy subjects and 16 subjects with chronic kidney disease (8 stage 3 and 8 stage 4 CKD), at 2 clinical research sites. The method consisted of a single intravenous injection of 12 mg of a large 150-kDa carboxy-methyl dextran conjugated to a fluorescent rhodamine-derived dye as the PV marker (PVM), and 35 mg of a small 5-kDa carboxy-methyl dextran conjugated to fluorescein, the renal clearance marker. Dye concentrations were quantified 15 min after the injections for initial PV measurements using the indicator-dilution principle. Additional samples were taken over 8 h to evaluate the stability of the PVM as a determinant of PV. Blood volumes (BV) were calculated based on PV and the subject's hematocrit. Pharmacokinetic parameters were calculated from the plasma concentration data taken over several days using noncompartmental methods (Phoenix WinNonlin®). Linear correlation and Bland-Altman plots were used to compare visible fluorescent injectate-measured PV compared to Nadler's formula for estimating PV. Finally, 8 healthy subjects received 350 mL infusion of a 5% albumin solution in normal saline over 30 min and a repeat PV determination was then carried out.

RESULTS

PV and BV varied according to weight and body surface area, with PV ranging from 2,115 to 6,234 mL and 28.6 to 41.9 mL/kg when weight adjusted. Both parameters were stable for > 6 h with repeated plasma measurements of the PVM. There was no difference between healthy subjects and CKD subjects. Overall, there was general agreement with Nadler's estimation formula for the mean PV in subjects. A 24-h repeat dose measurement in 8 healthy subjects showed PV variability of 98 ± 121 mL (mean = 3.8%). Additionally, following an intravenous bolus of 350 mL of a 5% albumin solution in normal saline in 8 healthy subjects, the mean (SD) measured increase in PV was 356 (±50.0) mL post-infusion. There were no serious adverse events reported during the study.

CONCLUSIONS

This minimally invasive fluorescent dye approach safely allowed for rapid, accurate, and reproducible determination of PV, BV, and dynamic monitoring of changes following fluid administration.

Comparison of two continuous non-invasive haemodynamic monitoring techniques in the perioperative setting

BACKGROUND

The aim of the study was to identify the accuracy of and agreement between two non-invasive haemodynamic monitoring techniques in the perioperative setting - thoracic electrical bioimpedance (TEB) and Edwards Lifesciences ClearSight system (CS).

MATERIALS AND METHODS

The study included ten patients. Parametric quantitative data were expressed as mean ± SD. The Shapiro-Wilk test was used to test the normality of the distributions. A linear regression model was used to measure the strength of the linear relationship between TEB and CS. Bland-Altman analysis was performed to assess the mean difference, precision, and the limits of agreements (LOA). The Critchley and Critchley method was used to calculate the percentage error (PE), and if <30%, it was considered clinically acceptable.

RESULTS

Ten patients were involved in our study. The mean cardiac output (CO) with TEB was 6.15 ± 1.14 L/min vs. 4.78 ± 1.40 L/min with CS (p < 0.01). The relationship was significant (n = 144; r 2 = 0.7; p < 0.01). The mean bias, LOA, and PE were 1.37 ± 1.01 L/min, 3.35 L/min and -0.61 L/min and 36.22%, respectively. The mean stroke volume index (SVI) with TEB was 48.64 ± 9.8 ml/beat/m2 vs. 37.12 ± 9.14 ml/beat/m2 with CS (p < 0.01). The relationship was significant (n = 144; r 2 = 0.65; p < 0.01). The mean bias, LOA, and PE were 11.52 ± 7.92 ml/beat/m2, 27.04 ml/beat/m2 and -4 ml/beat/m2 and 36.19%.

CONCLUSIONS

The two methods of non-invasive haemodynamic monitoring are not compatible in the perioperative setting. However, the CS system has more advantages in terms of continuity and simplicity of monitoring, while measurements of TEB are interrupted by electrocautery.

Accuracy and reliability of noninvasive stroke volume monitoring via ECG-gated 3D electrical impedance tomography in healthy volunteers

Cardiac output (CO) and stroke volume (SV) are parameters of key clinical interest. Many techniques exist to measure CO and SV, but are either invasive or insufficiently accurate in clinical settings. Electrical impedance tomography (EIT) has been suggested as a noninvasive measure of SV, but inconsistent results have been reported. Our goal is to determine the accuracy and reliability of EIT-based SV measurements, and whether advanced image reconstruction approaches can help to improve the estimates. Data were collected on ten healthy volunteers undergoing postural changes and exercise. To overcome the sensitivity to heart displacement and thorax morphology reported in previous work, we used a 3D EIT configuration with 2 planes of 16 electrodes and subject-specific reconstruction models. Various EIT-derived SV estimates were compared to reference measurements derived from the oxygen uptake. Results revealed a dramatic impact of posture on the EIT images. Therefore, the analysis was restricted to measurements in supine position under controlled conditions (low noise and stable heart and lung regions). In these measurements, amplitudes of impedance changes in the heart and lung regions could successfully be derived from EIT using ECG gating. However, despite a subject-specific calibration the heart-related estimates showed an error of 0.0 ± 15.2 mL for absolute SV estimation. For trending of relative SV changes, a concordance rate of 80.9% and an angular error of -1.0 ± 23.0° were obtained. These performances are insufficient for most clinical uses. Similar conclusions were derived from lung-related estimates. Our findings indicate that the key difficulty in EIT-based SV monitoring is that purely amplitude-based features are strongly influenced by other factors (such as posture, electrode contact impedance and lung or heart conductivity). All the data of the present study are made publicly available for further investigations.

Perioperative fluid management in kidney transplantation: a black box

The incidence of delayed graft function in patients undergoing kidney transplantation remains significant. Optimal fluid therapy has been shown to decrease delayed graft function after renal transplantation. Traditionally, the perioperative volume infusion regimen in this patient population has been guided by central venous pressure as an estimation of the patient’s volume status and mean arterial pressure, but this is based on sparse evidence from mostly retrospective observational studies. Excessive volume infusion to the point of no further fluid responsiveness can damage the endothelial glycocalyx and is no longer considered to be the best approach. However, achievement of adequate flow to maintain sufficient tissue perfusion without maximization of cardiac filling remains a challenge. Novel minimally invasive technologies seem to reliably assess volume responsiveness, heart function and perfusion adequacy. Prospective comparative clinical studies are required to better understand the use of dynamic analyses of flow parameters for adequate fluid management in kidney transplant recipients. We review perioperative fluid assessment techniques and discuss conventional and novel monitoring strategies in the kidney transplant recipient.