Focused rapid echocardiographic evaluation versus vascular cather-based assessment of cardiac output and function in critically ill trauma patients

Use of Ultrasound to Assess Hemodynamics in Acutely Ill Patients

Early diagnosis of AKI and preventive measures can likely decrease the severity of the injury and improve patient outcomes. Current hemodynamic monitoring variables, including BP, heart and respiratory rates, temperature, and oxygenation status, have been used to identify patients at high risk for AKI. Despite the widespread use of such variables, their ability to accurately and timely detect patients who are high risk has been questioned. Therefore, there is a critical need to develop and validate tools that can measure new and more kidney-specific hemodynamic and laboratory variables, potentially assisting with AKI risk stratification, implementing appropriate and timely preventive measures, and hopefully improved outcomes. The new ultrasonography techniques provide novel insights into kidney hemodynamics and potential management and/or therapeutic targets. Contrast-enhanced ultrasonography; Doppler flow patterns of hepatic veins, portal vein, and intrakidney veins; and ultrasound elastography are among approaches that may provide such information, particularly related to vascular changes in AKI, venous volume excess or congestion, and fluid tolerance. This review summarizes the current state of these techniques and their relevance to kidney hemodynamic management.

A novel method of calculating stroke volume using point-of-care echocardiography

Background

Point-of-care transthoracic echocardiography (POC-TTE) is essential in shock management, allowing for stroke volume (SV) and cardiac output (CO) estimation using left ventricular outflow tract diameter (LVOTD) and left ventricular velocity time integral (VTI). Since LVOTD is difficult to obtain and error-prone, the body surface area (BSA) or a modified BSA (mBSA) is sometimes used as a surrogate (LVOTD^BSA, LVOTD^mBSA). Currently, no models of LVOTD based on patient characteristics exist nor have BSA-based alternatives been validated.

Methods

Focused rapid echocardiographic evaluations (FREEs) performed in intensive care unit patients over a 3-year period were reviewed. The age, sex, height, and weight were recorded. Human expert measurement of LVOTD (LVOTD^HEM) was performed. An epsilon-support vector regression was used to derive a computer model of the predicted LVOTD (LVOTD^CM). Training, testing, and validation were completed. Pearson coefficient and Bland-Altman were used to assess correlation and agreement.

Results

Two hundred eighty-seven TTEs with ideal images of the LVOT were identified. LVOTD^CM was the best method of SV measurement, with a correlation of 0.87. LVOTD^mBSA and LVOTD^BSA had correlations of 0.71 and 0.49 respectively. Root mean square error for LVOTD^CM, LVOTD^mBSA, and LVOTD^BSA respectively were 13.3, 37.0, and 26.4. Bland-Altman for LVOTD^CM demonstrated a bias of 5.2. LVOTD^CM model was used in a separate validation set of 116 ideal images yielding a linear correlation of 0.83 between SV^HEM and SV^CM. Bland Altman analysis for SV^CM had a bias of 2.3 with limits of agreement (LOAs) of − 24 and 29, a percent error (PE) of 34% and a root mean square error (RMSE) of 13.9.

Conclusions

A computer model may allow for SV and CO measurement when the LVOTD cannot be assessed. Further study is needed to assess the accuracy of the model in various patient populations and in comparison to the gold standard pulmonary artery catheter. The LVOTD^CM is more accurate with less error compared to BSA-based methods, however there is still a percentage error of 33%. BSA should not be used as a surrogate measure of LVOTD. Once validated and improved this model may improve feasibility and allow hemodynamic monitoring via POC-TTE once it is validated.

Echo is a good, not perfect, measure of cardiac output in critically ill surgical patients

BACKGROUND

Compared with a pulmonary artery catheter (PAC), transthoracic echocardiography (TTE) has been shown to have good agreement in cardiac output (CO) measurement in nonsurgical populations. Our hypothesis is that the feasibility and accuracy of CO measured by TTE (CO-TTE), relative to CO measured by PAC thermodilution (CO-PAC), is different in surgical intensive care unit patients (SP) and nonsurgical patients (NSP).

METHODS

Surgical patients with PAC for hemodynamic monitoring and NSP undergoing right heart catheterization were prospectively enrolled. Cardiac output was measured by CO-PAC and CO-TTE. Pearson coefficients were used to assess correlation. Bland-Altman analysis was used to determine agreement.

RESULTS

Over 18 months, 84 patients were enrolled (51 SP, 33 NSP). Cardiac output TTE could be measured in 65% (33/51) of SP versus 79% (26/33) of NSP; p = 0.17. Inability to measure the left ventricular outflow tract diameter was the primary reason for failure in both groups; 94% (17/18) in SP versus 86% (6/7) NSP; p = 0.47. Velocity time integral could be measured in all patients. In both groups, correlation between PAC and TTE measurement was strong; SP (r = 0.76; p < 0.0001), NSP (r = 0.86; p < 0.0001). Bland-Altman analysis demonstrated bias of -0.1 L/min, limits of agreement of -2.5 and +2.3 L/min, percentage error (PE) of 40% for SP, and bias of +0.4 L/min, limits of agreement of -1.8 and +2.5 L/min, and PE of 40% for NSP.

CONCLUSION

There was strong correlation and moderate agreement between TTE and PAC in both SP and NSP. In both patient populations, inability to measure the left ventricular outflow tract diameter was a limiting factor.

LEVEL OF EVIDENCE

Diagnostic tests or criteria, level III.

Cardiac Ultrasound in the Intensive Care Unit: A Review

Transthoracic echocardiography (TTE) is an incredibly valuable tool in today’s emergency rooms and intensive care units (ICUs). It has the ability to provide a complete evaluation of the structure and function of the heart, the valves, stroke volume, ejection fraction, and much more. Previous academic studies have also determined that point-of-care TTE done by non-cardiologist physicians can also provide higher accuracy in patient assessment and management, with potential prognostic impact by assessing the severity of cardiac dysfunction and response to treatment. The aim of this review article is to examine further these point-of-care evaluations, what they entail, their benefits, and where further research would better our own understanding.

Assessment of left ventricular ejection fraction in critically ill patients at the time of speckle tracking echocardiography: intensivists in training for echocardiography versus experienced operators

BACKGROUND

The biplane Simpson's method is considered the gold standard to assess and monitor left ventricular (LV) ejection fraction (EF) in critically ill patients. Recently, a new semi-automatic technique based on speckle tracking echocardiography called "Auto-EF" has been introduced. We compared LVEF values obtained with biplane Simpson's method and Auto-EF by two groups of operators: trainee echocardiography intensivists and experienced echocardiographers.

METHODS

A standard transthoracic echocardiography was performed on 37 patients. According to image quality 29 patients were selected. Each inexperienced and experienced operator executed an off-line analysis using both Simpson's method and Auto-EF. LVEF obtained by the two groups of operators were then compared.

RESULTS

EF values assessed with Simpson's method showed a moderate correlation (r=0.70, P<0.01) between inexperienced and experienced operators. The Bland-Altman analysis showed a mean bias of 0.3% with limits of agreement (LoA) from -24.4 to +25.1%. Values obtained with Auto-EF showed a good correlation (r=0.94, P<0.01) with a mean bias of 0.2% and LoA from -10.1 to +10.4%.

CONCLUSIONS

Due to its semiautomatic nature, for inexpert operators Auto-EF seems more reproducible than the traditional Simpson's method for monitoring left ventricular function in critically ill patients.

Evaluation of the utility of cardiac ultrasonography of patients in a surgical intensive care unit

Background

Ultrasonography is being more commonly used by intensivists to assess the hemodynamic status of patients in intensive care units (ICUs) and for other purposes.

Objective

To review the indications for and evaluate the impact of cardiac ultrasonography (CUS) on the management of patients in a surgical ICU (SICU).

Method

We conducted a retrospective observational cohort study of patients in the SICU who underwent CUS performed by intensivists at King Chulalongkorn Memorial Hospital from January 2011 to March 2013. CUS was used to determine (1) preload (using inferior vena cava (IVC) diameter and collapsibility index), (2) cardiac contractility (using subjective assessment and fractional shortening), and (3) other miscellaneous findings.

Result

We included data from 157 patients (96 male and 61 female) whose age ranged from 15 to 99 years (mean 63.5 years) in the study. CUS was performed 190 times in these 157 patients. The most common indication for CUS was hemodynamic status assessment (78), followed by shock (69), oliguria (35), and other (8). CUS results led to 71 changes in management (37% of cases) ; namely, fluid challenge (38), inotropic drug management (7), drainage of pleural/abdominal fluid (12), and other changes (14). A weakly-positive correlation between the IVC diameter and CVP (Pearson’s r = 0.45) was demonstrated. The overall mortality rate was 14.6%.

Conclusion

CUS performed by intensivists can be used to assess the hemodynamic status of patients in the SICU, especially those with shock or oliguria, and lead to changes in the management of these patients.

Ultrasonic evaluation of the heart

PURPOSE OF REVIEW

To discuss the role of echocardiography for the hemodynamic evaluation of critically ill patients.

RECENT FINDINGS

In addition to its crucial role in evaluating heart abnormalities as in the classical cardiological approach, echocardiography is now frequently used by intensivists for noninvasive hemodynamic evaluation of the critically ill patient. Using echocardiography, it is possible to measure cardiac output, intravascular pressures and volumes, systolic and diastolic function of both ventricles, and preload responsiveness. This not only allows characterization of the precise nature of hemodynamic alterations in patients with circulatory and respiratory failure, but also provides guidance for hemodynamic optimization and optimization of ventilatory settings. There are now many data showing how echocardiography can be useful in detecting otherwise unrecognized myocardial depression in sepsis and right ventricular dysfunction in mechanically ventilated patients. The main limitation of echocardiography for hemodynamic monitoring is its intermittent nature. Hence, echocardiography is often combined with other monitoring devices, allowing continuous measurement of flow and triggering new echocardiographic evaluations.

SUMMARY

Echocardiography has now become an important tool for hemodynamic evaluation of the critically ill patient. Echocardiography should be performed in most patients with circulatory and respiratory failure.

Trauma-Related Critical Care

BACKGROUND

Post-trauma resuscitation has evolved based on civilian and wartime experiences over the last decade. Similarly, data from large multicenter randomized trials have changed the management of critically ill trauma patients in the intensive care unit.

METHODS

This is a review of the literature focusing on areas relevant to the management of trauma patients in the intensive care unit.

RESULTS

The following topics are included: (1) ventilator management, (2) trauma sepsis, (3) use of vasopressors in hemorrhage, (4) glucose control, (5) nutrition, and (6) hemodynamic monitoring.

CONCLUSION

This review demonstrated the most recent data of trauma-related critical care. Further studies will be needed to settle growing controversies in the management of critically injured patients.

Making the financial case for a surgeon-directed critical care ultrasound program

BACKGROUND

We sought to demonstrate that a well-staffed, surgeon-directed, critical care ultrasound program (CCUP) is financially sustainable and provides administrative and educational support for point-of-care ultrasound.

METHODS

The CCUP provides a clinical service and training as well as conducts research. Initial costs, annual costs (C), revenue (R), and savings (S) were prospectively recorded. Using data from the first 3 years, we calculated the projected C, R, and S at 5 years. We determined CCUP sustainability by C < R and C < R + S at 3 years and 5 years.

RESULTS

During 36 months, the CCUP covered four surgical intensive care units (55 beds). Start-up costs included one basic and one cardiovascular device per 25 beds and a data storage system linking reports and images to the electronic medical record ($203,650). Billing increased threefold from Years 1 to 3, with a 21% increase between Years 2 to 3. Yearly costs included 0.5 full-time equivalent (FTE) sonographer and 0.2 FTE surgeon ($106,025); this was increased to 1 FTE and 0.25 FTE, respectively, for Years 4 and 5. The total 3-year cost was $521,725 and projected to be $863,325 by Year 5. The total 3-year revenue was $290,775 and projected to be $891,600 at 5 years. The total 3-year savings associated with the CCUP was $600,035 and is projected to be $1,194,220. With the use of the C < R, the CCUP meets operating expenses at Year 3 and covers overall cost at 5 years. If savings are included, then the CCUP is sustainable by its third year and is potentially profitable by Year 5.

CONCLUSION

A surgeon-directed CCUP is financially sustainable, addresses administrative issues, and provides valuable training in point-of-care ultrasound.

The role of invasive techniques in cardiopulmonary evaluation

PURPOSE OF REVIEW

To discuss the role of the invasive monitoring techniques pulmonary artery catheter (PAC) and transpulmonary thermodilution (TPD) for cardiopulmonary monitoring in the critically ill patient.

RECENT FINDINGS

Characterization of the nature of hemodynamic alterations and hemodynamic optimization can be achieved both with PAC and TPD. Some recent trials suggest that volumetric measurements may be preferred in conditions with preserved left ventricular systolic function, whereas pressure measurements should be preferred in patients with altered left ventricular systolic function. Extravascular lung water is strongly associated with outcome and may be used to reflect the impact of fluid management strategies. The time response of this measurement needs still to be better defined.

SUMMARY

This review highlights that PAC and TPD have an important role in cardiopulmonary monitoring of critically ill patients. Both techniques can be used efficiently to diagnose the nature of circulatory or respiratory failure and to monitor the effects of therapies. The choice of the technique should be guided by the patient's condition and the need for additional measurements rather than based on physician's preferences.

Systematic review of uncalibrated arterial pressure waveform analysis to determine cardiac output and stroke volume variation

The FloTrac/Vigileo™, introduced in 2005, uses arterial pressure waveform analysis to calculate cardiac output (CO) and stroke volume variation (SVV) without external calibration. The aim of this systematic review is to evaluate the performance of the system. Sixty-five full manuscripts on validation of CO measurements in humans, published in English, were retrieved; these included 2234 patients and 44,592 observations.

RESULTS

have been analysed according to underlying patient conditions, that is, general critical illness and surgery as normodynamic conditions, cardiac and (post)cardiac surgery as hypodynamic conditions, and liver surgery and sepsis as hyperdynamic conditions, and subsequently released software versions. Eight studies compared SVV with other dynamic indices. CO, bias, precision, %error, correlation, and concordance differed among underlying conditions, subsequent software versions, and their interactions, suggesting increasing accuracy and precision, particularly in hypo- and normodynamic conditions. The bias and the trending capacity remain dependent on (changes in) vascular tone with most recent software. The SVV only moderately agreed with other dynamic indices, although it was helpful in predicting fluid responsiveness in 85% of studies addressing this. Since its introduction, the performance of uncalibrated FloTrac/Vigileo™ has improved particularly in hypo- and normodynamic conditions. A %error at or below 30% with most recent software allows sufficiently accurate and precise CO measurements and trending for routine clinical use in normo- and hypodynamic conditions, in the absence of large changes in vascular tone. The SVV may usefully supplement these measurements.