Pulmonary Artery Catheter (PAC) Accuracy and Efficacy Compared with Flow Probe and Transcutaneous Doppler (USCOM): An Ovine Cardiac Output Validation

Carotid Doppler ultrasound for non-invasive haemodynamic monitoring: a narrative review

Objective.Accurate haemodynamic monitoring is the cornerstone in the management of critically ill patients. It guides the optimization of tissue and organ perfusion in order to prevent multiple organ failure. In the past decades, carotid Doppler ultrasound (CDU) has been explored as a non-invasive alternative for long-established invasive haemodynamic monitoring techniques. Considering the large heterogeneity in reported studies, we conducted a review of the literature to clarify the current status of CDU as a haemodynamic monitoring tool.Approach.In this article, firstly an overview is given of the equipment and workflow required to perform a CDU exam in clinical practice, the limitations and technical challenges potentially faced by the CDU sonographer, and the cerebrovascular mechanisms that may influence CDU measurement outcomes. The following chapter describes alternative techniques for non-invasive haemodynamic monitoring, detailing advantages and limitations compared to CDU. Next, a comprehensive review of the literature regarding the use of CDU for haemodynamic monitoring is presented. Furthermore, feasibility aspects, training requirements and technical developments of CDU are addressed.Main results.Based on the outcomes of these studies, we assess the applicability of CDU-derived parameters within three clinical domains (cardiac output, volume status, and fluid responsiveness), and amongst different patient groups. Finally, recommendations are provided to improve the quality and standardization of future research and clinical practice in this field.Significance.Although CDU is not yet interchangeable with invasive 'gold standard' cardiac output monitoring, the present work shows that certain CDU-derived parameters prove promising in the context of functional haemodynamic monitoring.

Effects of Performing Applied Muscle Tension during Recovery after Phlebotomy in Young, First-Time Donors: A Pilot Study

Vasovagal reaction (VVR) compromises donor safety and reduces the subsequent return rates. Performing applied muscle tension (AMT) during phlebotomy may reduce the incidence of VVR. However, the effectiveness of performing AMT after phlebotomy to reduce delayed VVR remains unclear. With ethics approval, 12 young, first-time donors (YFTD) were recruited to study the effects on stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) while performing AMT from needle insertion to end of recovery. Measurements from 12 matched control YFTD were used for comparison. Pre-donation anxiety and VVR severity were assessed. Compared to controls, donors who performed AMT had higher SV (Control: 57 mL vs. AMT: 69 mL, p = 0.045), higher CO (Control: 3.7 L·min⁻¹ vs. AMT: 5.2 L·min⁻¹, p = 0.006) and lower SVR (Control: 1962 dyn·s·cm⁻⁵ vs. AMT: 1569 dyn·s·cm⁻⁵, p = 0.032) during mid-phlebotomy. During recovery, the AMT group retained higher SV, higher CO and lower SVR than the control, but not reaching statistical significance. Practicing AMT during recovery resulted in sustained haemodynamic improvements beyond the donation period, despite the reduction in delayed VVR was insignificant compared to the control group. A larger sample size is needed to validate the effectiveness of performing AMT after donation to mitigate delayed VVR.

A performance comparison of the most commonly used minimally invasive monitors of cardiac output

BACKGROUND

Shock is common in critically ill and injured patients. Survival during shock is highly dependent on rapid restoration of tissue oxygenation with therapeutic goals based on cardiac output (CO) optimization. Despite the clinical availability of numerous minimally invasive monitors of CO, limited supporting performance data are available.

METHODS

Following approval of the University of Saskatchewan Animal Research Ethics Board, we assessed the performance and trending ability of PiCCOplus™, FloTrac™, and CardioQ-ODM™ across a range of CO states in pigs. In addition, we assessed the ability of invasive mean arterial blood pressure (iMAP) to follow changes in CO using a periaortic transit-time flow probe as the reference method. Statistical analysis was performed with function-fail, bias and precision, percent error, and linear regression at all flow, low-flow (> 1 standard deviation [SD] below the mean), and high-flow (> 1 SD above the mean) CO conditions.

RESULTS

We made a total of 116,957 paired CO measurements. The non-invasive CO monitors often failed to provide a CO value (CardioQ-ODM: 40.6% failed measurements; 99% confidence interval [CI], 38.5 to 42.6; FloTrac: 9.6% failed measurements; 99% CI, 8.7 to 10.5; PiCCOplus: 4.7% failed measurements; 99% CI, 4.5 to 4.9; all comparisons, P < 0.001). The invasive mean arterial pressure provided zero failures, failing less often than any of the tested CO monitors (all comparisons, P < 0.001). The PiCCOplus was most interchangeable with the flow probe at all flow states: PiCCOplus (20% error; 99% CI, 19 to 22), CardioQ-ODM (25% error; 99% CI, 23 to 27), FloTrac (34% error; 99% CI, 32 to 38) (all comparisons, P < 0.001). At low-flow states, CardioQ-ODM (43% error; 99% CI, 32 to 63) and Flotrac (45% error; 99% CI, 33 to 70) had similar interchangeability (P = 0.07), both superior to PiCCOplus (48% error; 99% CI, 42 to 60) (P < 0.001). Regarding CO trending, the CardioQ-ODM (correlation coefficient, 0.82; 99% CI, 0.81 to 0.83) was statistically superior to other monitors including iMAP, but at low flows iMAP (correlation coefficient, 0.58; 99% CI, 0.58 to 0.60) was superior to all minimally invasive CO monitors (all comparisons P < 0.001).

CONCLUSIONS

None of the minimally invasive monitors of CO performed well at all tested flows. Invasive mean arterial blood pressure most closely tracked CO change at critical flow states.

New Advances in Monitoring Cardiac Output in Circulatory Mechanical Assistance Devices. A Validation Study in a Porcine Model

Cardiac output (CO) measurement by continuous pulmonary artery thermodilution (CO_CTD) has been studied in patients with pulsatile-flow LVADs (left ventricular assist devices), confirming the clinical utility. However, it has not been validated in patients with continuous-flow LVADs. Therefore, the aim of this study was to assess the validity of CO_CTD in continuous-flow LVADs. Continuous-flow LVADs were implanted in six miniature pigs for partial assistance of the left ventricle. Both methods of measuring CO—measurement by CO_CTD and intermittent pulmonary artery thermodilution, standard technique (CO_ITD)—were used in four consecutive moments of the study: before starting the LVAD (basal moment), and with the LVAD started in normovolemia, hypervolemia (fluid overloading), and hypovolemia (shock hemorrhage). At the basal moment, CO_CTD and CO_ITD were closely correlated (r² = 0.97), with a mean bias of −0.13 ± 0.16 L/min and percentage error of 11%. After 15 min of partial support LVAD, CO_CTD and CO_ITD were closely correlated (r² = 0.91), with a mean bias of 0.31 ± 0.35 L/min and percentage error of 20%. After inducing hypervolemia, CO_CTD and CO_ITD were closely correlated (r² = 0.99), with a mean bias of 0.04 ± 0.07 L/min and percentage error of 5%. After inducing hypovolemia, CO_CTD and CO_ITD were closely correlated (r² = 0.74), with a mean bias of 0.08 ± 0.22 L/min and percentage error of 19%. This study shows that continuous pulmonary thermodilution could be an alternative method of monitoring CO in a porcine model with a continuous-flow LVAD.

Stable Automatic Envelope Estimation for Noisy Doppler Ultrasound

Doppler ultrasound technology is widespread in clinical applications and is principally used for blood flow measurements in the heart, arteries, and veins. A commonly extracted parameter is the maximum velocity envelope. However, current methods of extracting it cannot produce stable envelopes in high noise conditions. This can limit clinical and research applications using the technology. In this article, a new method of automatic envelope estimation is presented. The method can handle challenging signals with high levels of noise and variable envelope shapes. Envelopes are extracted from a Doppler spectrogram image generated directly from the Doppler audio signal, making it less device-dependent than existing image-processing methods. The method's performance is assessed using simulated pulsatile flow, a flow phantom, and in vivo ascending aortic flow measurements and is compared with three state-of-the-art methods. The proposed method is the most accurate in noisy conditions, achieving, on average, for phantom data with signal-to-noise ratios (SNRs) below 10 dB, bias and standard deviation of 0.7% and 3.3% lower than the next-best performing method. In addition, a new method for beat segmentation is proposed. When combined, the two proposed methods exhibited the best performance using in vivo data, producing the least number of incorrectly segmented beats and 8.2% more correctly segmented beats than the next best performing method. The ability of the proposed methods to reliably extract timing indices for cardiac cycles across a range of signal quality is of particular significance for research and monitoring applications.

Performance evaluation of a portable bioimpedance cardiac output monitor for measuring hemodynamic changes in athletes during a head-up tilt test

The use of impedance cardiography to monitor physiological changes in sports is rarely reported. Using head-up tilt test, we evaluated a portable noninvasive impedance cardiography device (PhysioFlow) by comparing it with a reference Doppler monitor (USCOM). Accuracy in tracking hemodynamic changes deteriorated with higher tilt, implying a gravitational influence on its performance. Stroke volume measurements were overestimated, but the changes were underestimated. Despite its convenient physical features, the suitability of PhysioFlow for sports use is questionable.

Utilization of echocardiography during septic shock was associated with a decreased 28-day mortality: a propensity score-matched analysis of the MIMIC-III database

Background

Hemodynamic management is of paramount importance in patients with septic shock. Echocardiography has been increasingly used in assessing volume status and cardiac function. However, whether the utilization of echocardiography has an impact on prognosis is unknown. Thus, we intended to explore its effect on the outcomes of patients with septic shock.

Methods

The study was based on the Medical Information Mart for Intensive Care (MIMIC) III database. Septic shock patients were divided into two groups according to the usage of echocardiography during the onset of septic shock. The primary outcome was 28-day mortality. Secondary outcomes included the usage of inotropes, ventilation-free and norepinephrine-free time, and fluids input. Propensity-score matching was used to reduce the imbalance.

Results

Among 3,291 eligible patients, 1,289 patients who underwent echocardiography (Echo), and 1,289 who did not receive the Echo, had similar propensity scores and were included in the analyses. After matching, the Echo group had a significantly lower 28-day mortality (33.2% vs. 37.7%, P=0.019). More patients in the Echo group received pulmonary artery catheter (PAC) (4.2% vs. 0.2%, P<0.001) and inotropes (17.8% vs. 7.1%, P<0.001). In the survival analysis, Echo utilization was associated with improved 28-day mortality [hazard ratio (HR): 0.83; 95% confidence interval (CI), 0.73-0.95, P=0.005]. A reduced likelihood of 28-day mortality in patients with Echo vs. those without Echo was maintained either when excluding patients receiving multiple echocardiography scans (HR, 0.82; 95% CI, 0.72-0.94; P=0.004) or when excluding patients undergoing PAC or pulse index continuous cardiac output (PiCCO) (HR, 0.87; 95% CI, 0.76-0.99; P=0.034).

Conclusions

Utilization of echocardiography was associated with improved 28-day outcomes in patients with septic shock.

Comparison of Cardiac Output of Both 2-Dimensional and 3-Dimensional Transesophageal Echocardiography With Transpulmonary Thermodilution During Cardiac Surgery

OBJECTIVES

To compare agreement and variability of cardiac output measurement of 2-dimensional (2D) and 3D transesophageal echocardiography (TEE) with thermodilution before and after bypass.

DESIGN

Prospective observational study.

SETTING

Two tertiary hospitals.

INTERVENTIONS

Cardiac output (CO) was measured simultaneously with thermodilution and TEE by multiplying either the left ventricular outflow tract area (LVOTA) or aortic valve area (AVA), the velocity-time integral (VTI) of flow at the same site, and heart rate. The LVOTA was calculated using diameter for 2D TEE. Planimetry was used for 3D TEE. The AVA was measured using planimetry.

PARTICIPANTS

The study comprised 82 adult patients undergoing coronary or valve surgery.

MEASUREMENTS AND MAIN RESULTS

One hundred fifty-four complete sets of measurements were obtained (82 prebypass and 72 postbypass). All TEE methods had acceptable correlation and absence of proportional or fixed bias except for the left ventricular outflow tract (LVOT) VTI modal trace method, which had poor correlation and proportional but not fixed bias (regression coefficient [95% confidence interval], bias [percentage of mean CO]): 2D LVOT VTI modal trace 0.67 (0.54-0.80), -36.4%; 2D LVOT VTI outer edge trace 0.96 (0.80-1.12), -15.3%; 2D AVA planimetry 0.96 (0.75-1.18), +4.9%; 3D LVOT area planimetry 1.18 (0.96-1.41), +0.8%; 3D AVA planimetry 1.20 (0.93-1.46), +0.4%. All TEE methods had wide levels of agreement compared with thermodilution (-3.94 to +0.23 L/min, -2.83 to +1.28 L/min, -2.23 to +2.73 L/min, -2.35 to +2.42 L/min, and -2.57 to +2.61 L/min, respectively). Measurement variability was superior for all TEE methods compared with thermodilution before but not after bypass.

CONCLUSIONS

Although limits of agreement of CO measurement with 3D TEE and thermodilution are wide, 2D planimetry of the AVA and continuous wave Doppler may be substituted for thermodilution before and after bypass.

The utility of limited trans-thoracic echocardiography in the stratification of pulse pressure variation: A feasibility study in major open abdominal surgery

Background and Aim:

Limitation in use of pulse pressure variation (PPV) in predicting fluid responsiveness (FR) in hypotensive patients is encountered when values are in the “gray zone” (8–13%). Dynamic arterial elastance (E_adyn= PPV/SVV) can be used in such situations to predict arterial pressure response to volume expansion (VE). In our study, we used respiratory variation of ascending aorta velocity time integral (AoVTI) calculated from suprasternal window as a surrogate of stroke volume variation (SVV). Fluids/vasopressors were administered to hypotensive patients intraoperatively based on value of E_adyn. Aim was to assess feasibility and utility of suprasternal echocardiography in the above-mentioned subset of patients.

Materials and Methods:

Hemodynamic data were monitored and respiratory variation in AoVTI was recorded using suprasternal echocardiography at all time points when patients developed hypotension (systolic blood pressure <90 mm Hg/<20% of baseline for 5 min) and at randomly selected time intervals when hemodynamic stability was maintained. VE with 250 ml of Ringer lactate (RL) was done in hypotensive patients with PPV value of 8–13% and E_adyn>0.9. Increase of >15% in AoVTI after VE defined “fluid responsiveness.”

Results:

Twenty-eight patients were enrolled, but three were excluded in view of left ventricular systolic dysfunction detected during preinduction echocardiography. Hemodynamic and echocardiographic data were recorded at 538 observation points in 25 adults. Hypotension occurred in 247 data sets, and in 168 data sets, value of PPV was 8–13%. VE was carried out in only those 131 data sets in which the value of E_adyn was >0.9. Area under the curve (AUC) for VE as an intervention in the indeterminate (PPV 8–13%) group was 0.574 (0.49–0.68, 95% CI, P < 0.049), and in the observation set with PPV >13, the AUC value was 0.7 (0.59–0.98, 95% CI, P < 0.01).

Conclusions:

Echocardiography using the suprasternal window in the operating room during abdominal surgery is feasible, but the utility of E_adyn in stratification of patients with PPV 8–13% is inconclusive.

Understanding the Haemodynamics of Hypertension

PURPOSE OF REVIEW

This article introduces the haemodynamic principles that underpin the pathophysiology of hypertension and introduces a rational physiological approach to appropriate pharmacologic treatment.

RECENT FINDINGS

Outdated understanding of haemodynamics based on previous measurement systems can no longer be applied to our understanding of the circulation. We question the current view of hypertension as defined by a predominantly systolic blood pressure and introduce the concept of vasogenic, cardiogenic and mixed-origin hypertension. We postulate that failure to identify the individual's haemodynamic pattern may lead to the use of inappropriate medication, which in turn may be a major factor in patient non-compliance with therapeutic strategies. A population-based approach to treatment of hypertension may lead to suboptimal functional dynamics in the individual patient. Finally, we question the validity of current guidelines and published evidence relating morbidity and mortality to the future treatment of hypertension. The importance of individual haemodynamic profiles may be pivotal in the understanding, diagnosis and treatment of hypertension if optimal control with minimal adverse effects is to be achieved. Research based on individual haemodynamic patterns is overdue.

The normal ranges of cardiovascular parameters measured using the ultrasonic cardiac output monitor

The ultrasonic cardiac output monitor (USCOM) is a noninvasive transcutaneous continuous wave Doppler method for assessing hemodynamics. There are no published reference ranges for normal values in adults (aged 18-60 years) for this device. This study aimed to (1) measure cardiovascular indices using USCOM in healthy adults aged 18-60 years; (2) combine these data with those for healthy children (aged 0-12), adolescents (aged 12-18), and the elderly (aged over 60) from our previously published studies in order to present normal ranges for all ages, and (3) establish normal ranges of USCOM-derived variables according to both weight and age. This was a population-based cross-sectional observational study of healthy Chinese subjects aged 0.5-89 years in Hong Kong. USCOM scans were performed on all subjects, to produce measurements including stroke volume, cardiac output, and systemic vascular resistance. Data from previously published studies (children, adolescents, and the elderly) were included. Normal ranges were defined as lying between the 2.5th and 97.5th percentiles. A total of 2218 subjects were studied (mean age = 16.4, range = 0.5-89; 52% male). From previous studies, 1197 children (aged 0-12, 55% male), 590 adolescents (aged 12-18, 49% male), and 77 elderly (aged 60-89, 55% male) were included. New data were collected from 354 adults aged 18-60 (47% male). Normal ranges are presented according to age and weight. We present comprehensive normal ranges for hemodynamic parameters obtained with USCOM in healthy subjects of all ages from infancy to the elderly.

Stroke Volume Monitoring: Novel Continuous Wave Doppler Parameters, Algorithms and Advanced Noninvasive Haemodynamic Concepts

PURPOSE OF REVIEW

Adequate oxygen delivery is essential for life, with hypoxia resulting in dysfunction, and ultimately death, of the cells, organs and organism. Blood flow delivers the oxygen bound in the blood, while haemodynamics is the science of blood flow. Stroke volume (SV) is the fundamental unit of blood flow, and reflects the interdependent performance of the heart, the vessels and the autonomic nervous system. However, haemodynamic management remains generally poor and predominantly guided by simple blood pressure observations alone.

RECENT FINDINGS

Doppler ultrasound measures SV with unequalled clinical precision when operated by trained personnel. Combining SV with BP measurements allows calculation of flow-pressure based measures which better reflect cardiovascular performance and allows personalised physiologic and pathophysiologic modelling consistent with Frank's and Starling's observations.

SUMMARY

Doppler SV monitoring and novel flow-pressure parameters may improve our understanding of the cardiovascular system and lead to improved diagnosis and therapy. This review examines the physics and practice of Doppler SV monitoring and its application in advanced haemodynamics.

A System for Continuous Estimating and Monitoring Cardiac Output via Arterial Waveform Analysis

BACKGROUND

Cardiac output (CO) is the total volume of blood pumped by the heart per minute and is a function of heart rate and stroke volume. CO is one of the most important parameters for monitoring cardiac function, estimating global oxygen delivery and understanding the causes of high blood pressure. Hence, measuring CO has always been a matter of interest to researchers and clinicians. Several methods have been developed for this purpose, but a majority of them are either invasive, too expensive or need special expertise and experience. Besides, they are not usually risk free and have consequences.

OBJECTIVE

Here, a semi-invasive system was designed and developed for continuous CO measurement via analyzing and processing arterial pulse waves.

RESULTS

Quantitative evaluation of developed CO estimation system was performed using 7 signals. It showed that it has an acceptable average error of (6.5%) in estimating CO. In addition, this system has the ability to consistently estimate this parameter and to provide a CO versus time curve that assists in tracking changes of CO. Moreover, the system provides such curve for systolic blood pressure, diastolic blood pressure, average blood pressure, heart rate and stroke volume.

CONCLUSION

Evaluation of the results showed that the developed system is capable of accurately estimating CO. The curves which the system provides for important parameters may be valuable in monitoring hemodynamic status of high-risk surgical patients and critically ill patients in Intensive Care Units (ICU). Therefore, it could be a suitable system for monitoring hemodynamic status of critically ill patients.

Refractory Vasoplegic Syndrome in an Adult Patient with Infective Endocarditis: A Case Report and Literature Review

Postoperative vasoplegic syndrome (VS) is characterized by low systemic vascular resistance, normal or elevated cardiac output, and poor response to volume expansion. The incidence of VS after cardiac surgery requiring cardiopulmonary bypass is about 20%. Sometimes, VS becomes refractory and initial treatments do not work, rendering treatment a great challenge. In this study, we describe a young male patient with endocarditis undergoing tricuspid valve replacement. When being weaned off cardiopulmonary bypass, the patient experienced VS. The patient's blood pressure did not increase after the administration of a high dose of epinephrine and norepinephrine. Therefore, he was commenced on a low dose of vasopressin and gradually his blood pressure reached the normal range. Although the standard management of VS is a high dose of vasopressors, this patient was refractory to a combination of epinephrine and norepinephrine; only a vasopressin infusion was able to treat the patient. Eventually, he was weaned from bypass and the operation was terminated satisfactorily. Thereafter, the patient passed the recovery period in the cardiac intensive care unit and was discharged. It seems that vasopressin is an excellent option in refractory vasoplegia with minimal response to other vasopressors.

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.

Measuring the cardiac output in acute emergency admissions: use of the non-invasive ultrasonic cardiac output monitor (USCOM) with determination of the learning curve and inter-rater reliability

Traditionally, assessment of the cardiac output has been limited to theatre or the intensive care unit. However, non-invasive cardiac output estimation is now readily available, and its application may have wider benefit in the emergency setting. The non-invasive ultrasonic cardiac output monitor (USCOM) was investigated to determine its learning curve and inter-rater reliability. Four trainee operators each performed stroke volume measurements on 25 volunteers, compared to an experienced operator pre- and post-passive leg raise. Inter-rater reliability was then assessed on 24 acute emergency in-patients. Mean percentage difference in stroke volume decreased from 19% (95% confidence intervals 14-23) across volunteers 1-5, to 6% (4-8) for the last 5 volunteers scanned. Consequently, on acute emergency in-patients, excellent inter-rater reliability (Lin's concordance correlation coefficient (ρ_c) 0.96 (0.92-0.98)) and agreement of a change ≥10% in stroke volume following passive leg raise on 23/24 cases were found. Following a training period of less than 5 h, USCOM stroke volume measurements demonstrated excellent inter-rater reliability.

Does using two Doppler cardiac output monitors in tandem provide a reliable trend line of changes for validation studies?

The demise of the pulmonary artery catheter as a gold standard in cardiac output measurement has created the need for new standard. Doppler cardiac output can be measured suprasternally (USCOM) and via the oesophagus (CardioQ). Use in tandem they may provide a reliable trend line of cardiac output changes against which new technologies can be assessed. Data from three similar clinical studies was pooled. Simultaneous USCOM and CardioQ readings, 13 (7-27), were performed every 15-30 min intraoperatively. Within individual patient regression analysis was performed. Data was normalized, CardioQ against USCOM, to eliminate the systematic error component following calibration. Bland-Altman and trend, concordance and polar analysis, were performed on the grouped data. Cardiac output was indexed (CI) to BSA. Data from 53 patients, aged 59 (26-81) years, scheduled for major surgery were included. Within-individual mean (SD) CI was 3.4 (0.6) L min(-1) m(-2). Correlation was good to excellent in 83 % of cases, R(2) > 0.80, and reasonable in 96 %, R(2) > 0.60. Percentage error was 38 %, and decreased to 14 % with normalization. The estimated 95 % precision for a single Doppler reading was ±10 %. Concordance rate was 96.6 % (confidence intervals 94.7-99.5 %) and above the >92 % threshold for good trending ability. Polar analysis also confirmed good trending ability. The regression line between Doppler methods was offset with a slope of 0.9, thus CardioQ CI readings increased relative to USCOM. Both Doppler methods trended cardiac output reliably. Used in tandem they provide a new standard to assess cardiac output trending.

In vitro evaluation of an ultrasonic cardiac output monitoring (USCOM) device

Non-invasive cardiac output monitoring techniques provide high yield, low risk mechanisms to identify and individually treat shock in the emergency setting. The non-invasive ultrasonic cardiac output monitoring (USCOM) device uses an ultrasound probe applied externally to the chest; however limitations exist with previous validation strategies. This study presents the in vitro validation of the USCOM device against calibrated flow sensors and compares user variability in simulated healthy and septic conditions. A validated mock circulation loop was used to simulate each condition with a range of cardiac outputs (2-10 l/min) and heart rates (50-95 bpm). Three users with varying degrees of experience using the USCOM device measured cardiac output and heart rate by placing the ultrasound probe on the mock aorta. Users were blinded to the condition, heart rate and cardiac output which were randomly generated. Results were reported as linear regression slope (β). All users estimated heart rate in both conditions with reasonable accuracy (β = 0.86-1.01), while cardiac output in the sepsis condition was estimated with great precision (β = 1.03-1.04). Users generally overestimated the cardiac output in the healthy simulation (β = 1.07-1.26) and reported greater difficulty estimating reduced cardiac output compared with higher values. Although there was some variability between users, particularly in the healthy condition (P < 0.01), all estimations were within a clinically acceptable range. In this study the USCOM provided a suitable measurement of cardiac output and heart rate when compared with our in vitro system. It is a promising technique to assist with the identification and treatment of shock.

Fluid responsiveness is about stroke volume, and not pulse pressure Yogi: the power of Doppler fluid management and cardiovascular monitoring

Fluid infusion is one of the most common critical care interventions, yet approximately 50% of all fluid interventions are unnecessary and potentially harmful. An improved approach to identification of fluid responsiveness is of clinical importance. Currently fluid responsiveness is most frequently identified by blood pressure (BP) measurements or a surrogate. However fluid responsiveness is simply the increase in stroke volume (SV) associated with volume expansion, and may not be reflected in BP or BP surrogates. Guyton demonstrated that BP=COxSVR, and it is know that baroreceptor mediated autonomic nervous system regulation of SV and SVR to preserve BP may mask significant and critical changes in haemodynamics. Dr Pinsky in his recent J Clin Monit Comput Editorial evaluated the relative merits of pulse pressure variability (PPV) methods, a variant on BP measurement, for assessment of fluid responsiveness and promoted the use of physiologic challenges to augment the applicability of PPV. However this guidance is only half right. This letter reminds clinicians of the physiologic limitations of PPV as a measure of fluid responsiveness, even when combined with physiologic challenges, and recommends the replacement of BP with SV measurements. The combination of accurate Doppler measurement of SV and physiologic challenges, as Dr Pinsky recommends, is a physiologically rational and effective approach to identification of fluid responsiveness with established evidence. The direct monitoring of SV and SV changes has the potential to improve a long standing critical care and anaesthetic conundrum; when to give fluid and when to stop.

Age-specific non-invasive transcutaneous Doppler ultrasound derived haemodynamic reference ranges in elderly Chinese adults

Background

Whilst there is a presumption in medicine that ageing adversely affects cardiovascular function, it is unknown if resting haemodynamics are compromised in the elderly, and if so, to what degree. This study was intended to answer several questions; whether age-related changes in haemodynamics occur; whether there was a difference between the haemodynamics of ageing subjects with and without mild chronic disease; whether there was a difference in haemodynamics as measured from either the aortic or the pulmonary valve; and to establish reference ranges for this population.

Methods

Chinese adults aged over 60 years were divided into three age bands of 61–70, 71–80 and over 80 years. The haemodynamic parameters were measured using a non-invasive Doppler ultrasound-based instrument, the Ultrasonic Cardiac Output Monitor (USCOM).

Results

One hundred and sixty-five subjects (48.5% males) were recruited. 78 (47.3%) had no known disease whilst 87 (52.7%) had mild chronic illness. A total of 21 individual haemodynamic parameters were measured or calculated for each subject. There were no significant differences in stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR) or in body surface area (BSA)-indexed parameters, SV index (SVI), cardiac index (CI) and SVR index (SVRI) across age groups, or in other indexed haemodynamic parameters. No significant differences in indexed haemodynamics were found between those subjects with and those without mild chronic disease. Small, statistically significant, but clinically insignificant, differences (< 5%) were found between the aortic and pulmonary valve measurements for SV, SVI and heart rate.

Conclusions

Ageing does not have any significant effect on resting haemodynamics in the elderly population studied. Mild chronic disease does not adversely affect resting haemodynamics in this population.

General Significance

Reference ranges were established for 21 haemodynamic parameters, as measured by USCOM, for an elderly Chinese population but not for non-Chinese populations.

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Ageing has no significant effect on resting haemodynamics in the population studied.

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Mild chronic disease does not adversely affect resting haemodynamics in this population.

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Reference ranges were established for 21 haemodynamic parameters in Chinese elderly.

Obituary: pulmonary artery catheter 1970 to 2013

The birth of the intermittent injectate-based conventional pulmonary artery catheter (fondly nicknamed PAC) was proudly announced in the New England Journal of Medicine in 1970 by his parents HJ Swan and William Ganz. PAC grew rapidly, reaching manhood in 1986 where, in the US, he was shown to influence the management of over 40% of all ICU patients. His reputation, however, was tarnished in 1996 when Connors and colleagues suggested that he harmed patients. This was followed by randomized controlled trials demonstrating he was of little use. Furthermore, reports surfaced suggesting that he was unreliable and inaccurate. It also became clear that he was poorly understood and misinterpreted. Pretty soon after that, a posse of rivals (bedside echocardiography, pulse contour technology) moved into the neighborhood and claimed they could assess cardiac output more easily, less invasively and no less reliably. To make matter worse, dynamic assessment of fluid responsiveness (pulse pressure variation, stroke volume variation and leg raising) made a mockery of his ‘wedge’ pressure. While a handful of die-hard followers continued to promote his mission, the last few years of his existence were spent as a castaway until his death in 2013. His cousin (the continuous cardiac output PAC) continues to eke a living mostly in cardiac surgery patients who need central access anyway. This paper reviews the rise and fall of the conventional PAC.

USCOM-window to the circulation: utility of supra-sternal Doppler in an elderly anaesthetized patient for a robotic cystectomy

Supra-sternal Doppler (USCOM Ltd., Sydney, Australia) can be used during anaesthesia to measure cardiac output (CO) and related flow parameters. However, before the USCOM can be used routinely, its utility and limitations need to be fully understood and critical information about its use disseminated. In "Window to the Circulation" we use the example of an elderly man undergoing major urological robotic surgery to highlight the utility and limitations of intra-operative USCOM use. USCOM readings were verified against oesophageal Doppler. Despite the lack of major blood loss (<500 ml in 8-h), significant changes in haemodynamics were recorded. CO ranged from 3.2 to 8.3 l/min. The quality of USCOM scans and reliability of data was initially poor, but improved as CO increased as surgery progressed. When USCOM scans became acceptable the correlation with oesophageal Doppler was R(2) = 8.0 (p < 0.001). Several characteristic features of the supra-sternal Doppler scans were identified: Aortic and pulmonary flow waves, valve closure, E and A waves, false A-wave and aberrant arterial flow patterns. Their identification helped with identifying the main flow signal across the aortic valve. The USCOM has the potential to monitor changes in CO and related flow parameters intra-operatively and thus help the anaesthetist to more fully understand the patient's haemodynamics. However, achieving a good quality scan is important as it improves the reliability of USCOM data. The supra-sternal route is rich in flow signals and identifying the aortic valve signal is paramount. Recognizing the other characteristic waveforms in the signal helps greatly.