Noninvasive assessment of cardiac output in critically ill patients by analysis of the finger blood pressure waveform

Non-Invasive Wearable Patch Utilizing Seismocardiography for Peri-Operative Use in Surgical Patients

OBJECTIVE

Optimizing peri-operative fluid management has been shown to improve patient outcomes and the use of stroke volume (SV) measurement has become an accepted tool to guide fluid therapy. The Transesophageal Doppler (TED) is a validated, minimally invasive device that allows clinical assessment of SV. Unfortunately, the use of the TED is restricted to the intra-operative setting in anesthetized patients and requires constant supervision and periodic adjustment for accurate signal quality. However, post-operative fluid management is also vital for improved outcomes. Currently, there is no device regularly used in clinics that can track patient's SV continuously and non-invasively both during and after surgery.

METHODS

In this paper, we propose the use of a wearable patch mounted on the mid-sternum, which captures the seismocardiogram (SCG) and electrocardiogram (ECG) signals continuously to predict SV in patients undergoing major surgery. In a study of 12 patients, hemodynamic data was recorded simultaneously using the TED and wearable patch. Signal processing and regression techniques were used to derive SV from the signals (SCG and ECG) captured by the wearable patch and compare it to values obtained by the TED.

RESULTS

The results showed that the combination of SCG and ECG contains substantial information regarding SV, resulting in a correlation and median absolute error between the predicted and reference SV values of 0.81 and 7.56 mL, respectively.

SIGNIFICANCE

This work shows promise for the proposed wearable-based methodology to be used as an alternative to TED for continuous patient monitoring and guiding peri-operative fluid management.

Hemodialysis Patients Have Impaired Cerebrovascular Reactivity to CO2 Compared to Chronic Kidney Disease Patients and Healthy Controls: A Pilot Study

Introduction

Recurrent hemodialysis (HD)–induced ischemia has emerged as a mechanism responsible for cognitive impairment in HD patients. Impairment of cerebrovascular function in HD patients may render the brain vulnerable to HD-induced ischemic injury. Cerebrovascular reactivity to CO₂ (CVR) is a noninvasive marker of cerebrovascular function. Whether CVR is impaired in HD patients is unknown. In this study, we compared CVR between healthy participants, HD patients, and chronic kidney disease (CKD) patients not yet requiring dialysis.

Methods

This was a single-center prospective observational study carried out at Kidney Clinical Research Unit in London, Canada. We used carefully controlled hypercapnia to interrogate brain vasomotor control. Transcranial Doppler was combined with 10–mm Hg step changes in CO₂ from baseline to hypercapnia (intervention) and back to baseline (recovery) to assess CVR in 8 HD, 10 CKD, and 17 heathy participants.

Results

HD patients had lower CVR than CKD or healthy participants during both intervention and recovery (P < 0.0001). There were no differences in CVR between healthy and CKD participants during either intervention (P = 0.88) or recovery (P = 0.99). The impaired CVR in HD patients was independent of CO₂-induced changes in blood pressure, heart rate, cardiac output, or dialysis vintage. In the CKD group, CVR was not associated with the estimated glomerular filtration rate.

Conclusions

Our study shows that HD patients have impaired CVR relative to CKD and healthy participants. This renders HD patients vulnerable to ischemic injury during circulatory stress of dialysis and may contribute to the pathogenesis of cognitive impairment.

Non-Invasive Monitoring of Cardiac Output in Critical Care Medicine

Critically ill patients require close hemodynamic monitoring to titrate treatment on a regular basis. It allows administering fluid with parsimony and adjusting inotropes and vasoactive drugs when necessary. Although invasive monitoring is considered as the reference method, non-invasive monitoring presents the obvious advantage of being associated with fewer complications, at the expanse of accuracy, precision, and step-response change. A great many methods and devices are now used over the world, and this article focuses on several of them, providing with a brief review of related underlying physical principles and validation articles analysis. Reviewed methods include electrical bioimpedance and bioreactance, respiratory-derived cardiac output (CO) monitoring technique, pulse wave transit time, ultrasound CO monitoring, multimodal algorithmic estimation, and inductance thoracocardiography. Quality criteria with which devices were reviewed included: accuracy (closeness of agreement between a measurement value and a true value of the measured), precision (closeness of agreement between replicate measurements on the same or similar objects under specified conditions), and step response change (delay between physiological change and its indication). Our conclusion is that the offer of non-invasive monitoring has improved in the past few years, even though further developments are needed to provide clinicians with sufficiently accurate devices for routine use, as alternative to invasive monitoring devices.

Hemodynamic monitoring in sepsis

Arterial waveform analysis that does not require continuous calibration, impedance cardiography, electrical cardiometry, velocity-encoded phase contrast magnetic resonance imaging (MRI), pulsed dye densitometry, noninvasive pulse pressure analysis using tonometry, suprasternal Doppler, partial CO2 rebreathing techniques, and transcutaneous Doppler are just some of the other emerging technologies not described in this review that may be used routinely in the management of sepsis and septic shock in the very near future. These innovative approaches may further increase our ability to optimize patients' fluid status and hemodynamics. We also have ability to monitor the microcirculation. This increasingly sophisticated approach to the management of sepsis and septic shock will hopefully translate into better patient outcomes. However, optimal use of any hemodynamic monitoring requires an understanding of its physiologic underpinnings. Accurate interpretation of the hemodynamic information coupled with a protocolized management algorithm is the cornerstone of an effective resuscitation effort. Many forms of hemodynamic monitoring have emerged over the past 20 to 30 years with no convincing evidence for the superiority of any single techniques (Table 2). The goal of hemodynamic monitoring and optimization is to combat the systemic imbalance between tissue oxygen supply and demand ranging from global tissue hypoxia to overt shock and multiorgan failure. It remains unproven that hemodynamic monitoring of disease progression can effectively change patient outcome. However, despite our increased understanding of sepsis pathophysiology, mortality and morbidity from the disease remains high. Therefore, the search for the optimal parameters in resuscitation and the best way they can be monitored will continue.

Methods in pharmacology: measurement of cardiac output

Many methods of cardiac output measurement have been developed, but the number of methods useful for human pharmacological studies is limited. The 'holy grail' for the measurement of cardiac output would be a method that is accurate, precise, operator independent, fast responding, non-invasive, continuous, easy to use, cheap and safe. This method does not exist today. In this review on cardiac output methods used in pharmacology, the Fick principle, indicator dilution techniques, arterial pulse contour analysis, ultrasound and bio-impedance are reviewed.

Hemodynamic monitoring in sepsis

Tissue hypoperfusion is an important factor in the development of multiple organ failure. Therefore, recognition of sepsis-induced tissue hypoperfusion and timely clinical intervention to prevent and correct this are fundamental aspects of managing patients with sepsis and septic shock. Hemodynamic monitoring plays a key role in the management of the critically ill and is used to identify hemodynamic instability and its cause and to monitor response to therapy. However, the utility of many forms of hemodynamic monitoring that are used in management of sepsis and septic shock remain controversial and unproven. This article examines emerging technologies as well as more established techniques used to monitor hemodynamics in sepsis and assesses their potential roles in optimization of sepsis-induced tissue hypoperfusion.

Noninvasive cardiac output determination: broadening the applicability of hemodynamic monitoring

Although cardiac output (CO) monitoring is usually only used in intensive care units (ICUs) and operating rooms, there is increasing evidence that CO should be determined and optimized as early as possible, even before admission to the ICU, in the care of hemodynamically compromised patients. A variety of different minimally or noninvasive CO determination techniques have been developed, but not all of them are suitable for early hemodynamic monitoring outside the ICU. In this review, the different available methods for CO monitoring are presented and their potential for early hemodynamic assessment is discussed.

Noninvasive cardiac output determination using applanation tonometry-derived radial artery pulse contour analysis in critically ill patients

Conventional thermodilution cardiac output (CO) monitoring is limited mainly to intensive care units and operating rooms because it requires the use of invasive techniques. To reduce the potential for complications and to broaden the applicability of hemodynamic monitoring, noninvasive methods for CO determination are being sought. Applanation tonometry allows noninvasive CO estimation through pulse contour analysis, but the method has not been evaluated in critically ill patients. We therefore performed noninvasive radial artery applanation tonometry in 49 critically ill medical intensive care unit patients and compared CO estimates to invasive CO measurements obtained using a pulmonary artery catheter or the PiCCO transpulmonary thermodilution system. One-hundred-sixteen measurements were performed, and patients were receiving vasopressor support during 78 measurements. When the data were analyzed with bias and precision statistics, a large bias of 2.03 L x min(-1) x m(-2) and a high percentage error of 85% were found between the invasive measurements and applanation tonometry-derived CO estimates, with the noninvasive CO results being significantly lower than the invasive ones (P < 0.001). There was no significant difference in bias between the patients who were receiving vasopressor support and those who were not (P = 0.874) or between patients with good and poor applanation tonometry pressure waveform signal quality (P = 0.071). Whereas a significant increase in the invasively determined CO was observed when a fluid bolus was administered (n = 7, P = 0.016), these changes were not reflected by the noninvasive method. We conclude that radial artery applanation tonometry is not suitable to determine CO in critically ill hemodynamically unstable patients.

Cardiac output derived from arterial pressure waveform analysis in patients undergoing cardiac surgery: validity of a second generation device

BACKGROUND

The performance of a recently introduced, arterial waveform-based device for measuring cardiac output (CO) without the need of invasive calibration (FloTrac/Vigileo) has been controversial. We designed the present study to assess the validity of an improved version of this monitoring technique compared with intermittent thermodilution CO measurement using a pulmonary artery catheter in patients undergoing cardiac surgery.

METHODS

Forty ASA III patients scheduled for elective coronary artery bypass grafting with cardiopulmonary bypass (CPB) were studied. Simultaneous CO measurements by bolus thermodilution and the FloTrac/Vigileo device were obtained after induction of anesthesia (T1), before CPB (T2), after CPB (T3), after sternal closure (T4), on arrival in the intensive care unit (T5), 4 h (T6), 8 h (T7), and 24 h after surgery (T8). CO was indexed to the body surface area (cardiac index, CI). A percentage error of 30% or less was established as the criterion for method interchangeability.

RESULTS

Two hundred and eighty-two data pairs were analyzed. Thermodilution CI ranged from 1.2 to 4.1 L x min(-1) x m(-2) (mean 2.5 +/- 0.54 L x min(-1) x m(-2)). Bias and precision (1.96 sd of the bias) were 0.19 L x min(-1) x m(-2) and +/- 0.60 L x min(-1) x m(-2), resulting in an overall percentage error of 24.6%. Subgroup analysis revealed a percentage error of 28.3% for data pairs obtained intraoperatively (T1-4) and 20.7% in intensive care unit (T5-8).

CONCLUSION

CI values obtained by the improved, second generation semiinvasive arterial waveform device showed good intraoperative and postoperative agreement with intermittent pulmonary artery thermodilution CI measurements in patients undergoing coronary artery bypass graft surgery.

Development and validation of a noninvasive method to estimate cardiac output using cuff sphygmomanometry

BACKGROUND

Obtaining cardiac output (CO) measurements noninvasively during routine blood pressure recording can improve hypertension management. A new method has been developed that estimates cardiac output using pulse-waveform analysis (PWA) from a brachial cuff sphygmomanometer. This study evaluates the ability of PWA to track changes in CO as derived by Doppler ultrasound during dobutamine stimulation.

HYPOTHESIS

This study aims to validate the PWA CO estimation over a wide CO range as would be obtained by dobutamine stimulation during Doppler ultrasound evaluation.

METHOD

A total of 48 patients undergoing standard dobutamine stress echocardiography testing for accepted clinical indications were enrolled. Among them, 44 patients (age 36-83, 18 females, 26 males) with good waveform data for analyses provided estimates of CO in this study. Noninvasive measurements of CO were performed using both Doppler ultrasound recordings and PWA techniques simultaneously at each stage of dobutamine infusion.

RESULTS

A total of 207 simultaneous pulse-waveform analyses and Doppler measurements were taken during dobutamine stress on 44 cardiac patients. Linear regression analysis revealed good intra-patient correlation between pulse-waveform analysis and Doppler at different dobutamine-induced CO with coefficients from r = 0.69 to 0.98 (p < 0.05). Analysis of all patients yielded an overall correlation of r = 0.82 (p < 0.001, bias = 0.4 L/min, standard deviation = 1.8 L/min).

CONCLUSION

The CO measured noninvasively from a sphygmomanometer using this PWA method correlates well with those of Doppler through a range of dobutamine-stimulated levels. The CO by PWA should be useful for monitoring hemodynamic changes in hypertensive and cardiac patients during routine blood pressure measurement.

Retracted: Semi-invasive monitoring of cardiac output by a new device using arterial pressure waveform analysis: a comparison with intermittent pulmonary artery thermodilution in patients undergoing cardiac surgery

BACKGROUND

Thermodilution technique using a pulmonary artery catheter (PAC) is a widely used method to determine cardiac output (CO). It is increasingly criticized because of its invasiveness and its unclear risk-benefit ratio. Thus, less invasive techniques for measuring CO are highly desirable. We compared a new, semi-invasive device (FloTrac/Vigileo) using arterial pressure waveform analysis for CO measurement in patients undergoing cardiac surgery with bolus thermodilution measurements.

METHODS

Forty patients undergoing coronary artery bypass grafting or valve repair were enrolled. A PAC was inserted and routine radial arterial access was used for semi-invasive determination of CO with the Vigileo. CO was measured simultaneously by bolus thermodilution and the Vigileo technique after induction of anaesthesia (T1), before cardiopulmonary bypass (CPB) (T2), after CPB (T3), after sternal closure (T4), on arrival in the intensive care unit (ICU) (T5), and 4 h (T6), 8 h (T7), and 24 h after surgery (T8). CO was indexed to the body surface area (cardiac index, CI).

RESULTS

A total of 244 pairs of CI measurements were analysed. Bias and precision (1.96 sd of the bias) were 0.46 litre min(-1) m(-2) and +/- 1.15 litre min(-1) m(-2) (r = 0.53) resulting in an overall percentage error of 46%. Subgroup analysis revealed a percentage error of 51% for data pairs obtained intraoperatively (T1-T4), 42% in ICU (T5-T8), and 56% for values obtained during low CI (T1-T8).

CONCLUSIONS

In cardiac surgery patients, CO measured by a new semi-invasive arterial pressure waveform analysis device showed only moderate agreement with intermittent pulmonary artery thermodilution measurement.

Analysis of the Ear Pulse Oximeter Waveform

OBJECTIVE

For years researchers have been attempting to understand the relationship between central hemodynamics and the resulting peripheral waveforms. This study is designed to further understanding of the relationship between ear pulse oximeter waveforms, finger pulse oximeter waveforms and cardiac output (CO). It is hoped that with appropriate analysis of the peripheral waveforms, clues can be gained to help to optimize cardiac performance.

METHODS

Part 1: Studying the effect of cold immersion test on plethysmographic waveforms. Part 2: Studying the correlation between ear and finger plethysmographic waveforms and (CO) during CABG surgery. The ear and finger plethysmographic waveforms were analyzed to determine amplitude, width, area, upstroke and downslope. The CO was measured using continuous PA catheter. Using multi-linear regression, ear plethysmographic waveforms, together with heart rate (HR), were used to determine the CO Agreement between the two methods of CO determination was assessed.

RESULTS

Part 1: On contralateral hand immersion, all finger plethysmographic waveforms were reduced, there was no significant change seen in ear plethysmographic waveforms, except an increase in ear plethysmographic width. Part 2: Phase 1: Significant correlation detected between the ear plethysmographic width and other ear and finger plethysmographic waveforms. Phase 2: The ear plethysmographic width had a significant correlation with the HR and CO. The correlation of the other ear plethysmographic waveforms with CO and HR are summarized (Table 5). Multi-linear regression analysis was done and the best fit equation was found to be: CO=8.084 - 14.248 x Ear width + 0.03 x HR+ 92.322 x Ear down slope+0.027 x Ear Area Using Bland & Altman, the bias was (0.05 L) but the precision (2.46) is large to be clinically accepted.

CONCLUSION

The ear is relatively immune to vasoconstrictive challenges which make ear plethysmographic waveforms a suitable monitor for central hemodynamic changes. The ear plethysmographic width has a good correlation with CO.

Hemodynamics and Autonomic Control of Heart Rate Turbulence

INTRODUCTION

Late heart rate deceleration parallels the increase of systolic blood pressure during heart rate turbulence (HRT) after ventricular premature complexes (VPC). This is consistent with the involvement of baroreflex mechanism. Physiological background of systolic blood pressure dynamics is not known. Enhanced sympathetic activation and nonautonomic post-VPC changes of stroke volume have been speculated on.

METHODS AND RESULTS

We studied 28 subjects (aged 56 +/- 11 years; 20 males; 18 normal and 10 abnormal left ventricular (LV) function) with spontaneous occurrence of VPCs. HRT indices and baroreflex sensitivity were analyzed from the ECGs and finger arterial pressure recordings during 30 minutes of spontaneous respiration in supine position. Beat-by-beat stroke volume and peripheral vascular resistance were computed by a nonlinear, self-adaptive model of aortic input impedance (Modelflow, Finapres Medical Systems, Arnhem, The Netherlands). Indices of HRT and baroreflex sensitivity were highly correlated. In patients with preserved LV function, there was no substantial dynamics of stroke volume in the late phase after VPC, while peripheral vascular resistance increased significantly. In patients with impaired LV function, potentiated first sinus beat after VPC triggered transient hemodynamic alternans. Dynamics of peripheral vascular resistance was attenuated and stroke volume was depressed in the late phase after VPC.

CONCLUSIONS

Delayed sympathetically mediated vasomotor response to VPC produces systolic blood pressure overshoot. This subsequently induces vagally mediated late heart rate deceleration. Under physiologic conditions, there is no evidence of other hemodynamic and/or mechanical effect outside the autonomic reflex arch. In patients with LV dysfunction, both depressed vagal and sympathetic modulation and, indirectly, enhanced postextrasystolic potentiation account for attenuated HRT.

Use of lithium dilution and pulse contour analysis cardiac output determination in anaesthetized horses: a clinical evaluation

OBJECTIVE

To assess the suitability of a human algorithm for calculation of continuous cardiac output from the arterial pulse waveform, in anaesthetized horses.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Twenty-four clinical cases undergoing anaesthesia for various conditions.

MATERIALS AND METHODS

Cardiac output (Qt), measured by lithium dilution (QtLiDCO), was compared with a preceding, calibrated Qt measured from the pulse waveform (QtPulse). These comparisons were repeated every 20-30 minutes. Positive inotropes or vasopressors were administered when clinically indicated. Cardiac indices from 30.7 to 114.9 mL kg(-1) minute(-1) were recorded. Unusually shaped QtLiDCO curves were rejected and the measurement was repeated immediately.

RESULTS

Eighty-nine comparisons were made between QtLiDCO and QtPulse. The bias between the mean (+/-SD) of the two methods (QtLiDCO - QtPulse) was -0.07 L minute(-1)(+/-3.08) (0.24 +/- 6.48 mL kg(-1) minute(-1)). The limits of agreement were -12.72 and 13.2 mL kg(-1) minute(-1) (Bland & Altman 1986; Mantha et al. 2000). Linear regression analysis demonstrated a correlation coefficient (r2) of 0.89. Cardiac output in individual patients varied from 49.1 to 183% of the initial measurement at the time of calibration. Linear regression of log-transformed Qt variation for each method found a mean difference of 9% with limits of agreement of -4.1 to 22.1%.

CONCLUSIONS AND CLINICAL RELEVANCE

This method of pulse contour analysis is a relatively noninvasive and reliable way of monitoring continuous Qt in the horse under anaesthesia. The ability to easily monitor Qt might decrease morbidity and mortality in the anaesthetized horse.

Equipment review: the success of early goal-directed therapy for septic shock prompts evaluation of current approaches for monitoring the adequacy of resuscitation

A recent trial utilizing central venous oxygen saturation (SCVO₂) as a resuscitation marker in patients with sepsis has resulted in its inclusion in the Surviving Sepsis Campaign guidelines. We review the evidence behind SCVO₂ and its relationship to previous trials of goal-directed therapy. We compare SCVO₂ to other tools for assessing the adequacy of resuscitation including physical examination, biochemical markers, pulmonary artery catheterization, esophageal Doppler, pulse contour analysis, echocardiography, pulse pressure variation, and tissue capnometry. It is unlikely that any single technology can improve outcome if isolated from an organized pattern of early recognition, algorithmic resuscitation, and frequent reassessment. This article includes a response to the journal's Health Technology Assessment questionnaire by the manufacturer of the SCVO₂ catheter.

Non-invasive estimation of cardiac output in critical care patients

OBJECTIVE

This study was carried out to compare cardiac output measurements determined by thermodilution and by Portapres, a non-invasive system.

DESIGN, PATIENTS AND SETTING

Eighty-seven non-invasive blood pressure measurements were performed in 46 patients in our critical care unit utilising the new, non-invasive Portapres system. Cardiac output values were obtained from these blood pressure values using an aortic impedance model and compared to cardiac output values estimated by the thermodilution technique.

MEASUREMENTS AND MAIN RESULTS

Statistically significant (p < 0.01) differences (2.3 l/min; limits of agreement +/-5 l/min) were noted between invasive and non-invasive cardiac output measurements. Differences in measured cardiac outputs increased for patients receiving catecholamine therapy, in patients with hemodynamic instability (e.g., sepsis and cardiac insufficiency), in patients with artificial ventilation, in patients with long duration of intensive care, in younger (<60 yr) patients and in women. We found no influence of the body mass index (BMI) on the accuracy of Portapres results. In only one single subgroup, 10 patients with pulmonary diseases, Portapres measurements were not statistically significant different from reference results.

CONCLUSIONS

To date, Portapres measurements cannot replace thermodilution cardiac output estimations. Fluctuations of finger arterial perfusion due to hemodynamic instability, hypothermia and catecholamines may be responsible for problems of Portapres use in critically ill patients.

Minimally invasive hemodynamic monitoring for the intensivist: current and emerging technology

OBJECTIVE

To review minimally invasive cardiac output monitoring devices currently available for use in the intensive care unit.

DATA SOURCES

Medline search from 1966 to present plus cited reference studies and abstracts from available product literature.

STUDY SELECTION

Selection criteria included published reports and abstracts comparing the accuracy of minimally invasive cardiac output monitors to a "gold standard."

DATA SYNTHESIS

Many reports have been published on the accuracy of individual minimally invasive cardiac output monitors, but cumulative data reviewing each type of monitor have not been synthesized and made available to the clinician.

CONCLUSIONS

Emerging noninvasive or minimally invasive means of cardiac output monitoring are based on varied physiologic principles and can be used for following hemodynamic trends. Each of these methods has advantages and disadvantages; it is important for the clinician to understand the strengths and limitations of each device to effectively use the information derived.

In vivo interaction of endotoxin and recombinant bactericidal/permeability-increasing protein (rBPI23): hemodynamic effects in a human endotoxemia model

The cardiovascular derangement that results from the administration of endotoxin in healthy subjects is qualitatively similar to what is observed in patients in septic shock. The biological response to endotoxin is attributed in part to cytokine release. In experimental endotoxemia, recombinant bactericidal/permeability increasing protein (rBPI(23)) has shown a protective effect by binding endotoxin with the subsequent inhibition of the endotoxin-induced cytokine release and of neutrophil activation. In a controlled, blinded crossover study the early cardiovascular effects of rBPI(23) were investigated in an experimental endotoxemia model in humans. The beat-to-beat changes in arterial pressure and cardiac output following infusion of endotoxin (40 EU/kg body weight) and rBPI(23) (1 mg/kg) or placebo (human serum albumin, 0.2 mg/kg) were studied for 2 hours in 8 healthy male adults. Endotoxin or rBPI(23) alone did not induce significant cardiovascular changes. Endotoxin following rBPI(23) infusion elicited a fall in total peripheral resistance with its nadir after 4 minutes to 40% (range 16-53; P <.001) of control level. Mean arterial pressure showed little change, and the fall in total peripheral resistance was associated with a reflex increase in heart rate and cardiac output (32%; range 43-106). Changes in cardiovascular variables in the subsequent 2 hours were not significant. In vitro activation of the contact system by, respectively, rBPI(23), LPS, and LPS-rBPI(23) complexes was assessed. Following incubation with rBPI(23), LPS, and LPS-rBPI(23) complexes, complex levels were generated at levels comparable to those observed in the buffer control. The rapid vasodilatation by endotoxin administered concomitantly with rBPI(23) is not mediated by complement or contact system activation. The early vasodilatation is compensated by an increase in cardiac output, which therefore does not result in arterial hypotension. The monitoring of continuous cardiac output allows for the detection of rapid effects on systemic flow and conductance that go unnoticed in a recording of arterial pressure.

A comparison of cardiac output derived from the arterial pressure wave against thermodilution in cardiac surgery patients

In three clinical centres, we compared a new method for measuring cardiac output with conventional thermodilution. The new method computes beat-to-beat cardiac output from radial artery pressure by simulating a three-element model of aortic input impedance, and includes non-linear aortic mechanical properties and a self-adapting systemic vascular resistance. We compared cardiac output by continuous model simulation (MF) with thermodilution cardiac output (TD) in 54 patients (18 female, 36 male) undergoing coronary artery bypass surgery. We made three or four conventional thermodilution estimates spread equally over the ventilatory cycle. In 490 series of measurements, thermodilution cardiac output ranged from 2.1 to 9.3, mean 5.0 litre min(-1). MF differed +0.32 (1.0) litre min(-1) on average with limits of agreement of -1.68 and +2.32 litre min(-1). Differences decreased when the first series of measurements in a patient was used to calibrate the model. In 436 remaining series, the mean difference became -0.13 (0.47) litre min(-1) with limits of agreement of -1.05 and +0.79 litre min(-1). When consecutive measurements were made, the change was greater than 0.5 litre min(-1), on 204 occasions. The direction of change was the same with both methods in 199. The difference between the methods remained near zero during surgery suggesting that a single calibration per patient was adequate. Aortic model simulation with radial artery pressure as input reliably monitors changes in cardiac output in cardiac surgery patients. Before calibration, the model cannot replace thermodilution, but after calibration the model method can quantitatively replace further thermodilution estimates.

Can stroke volume and cardiac output be determined reliably in a tilt-table test using the pulse contour method?

The applicability of the finger pressure-derived pulse contour (PC) technique was evaluated in the measurement of stroke volume (SV), cardiac output (CO) and their changes in different phases of the tilt-table test. The reference method was whole-body impedance cardiography (ICG). A total number of 40 physically active patients, aged 41 +/- 19 years, were randomly chosen from a pool of 230. Specifically speaking, 20 of the patients experienced (pre)syncope (tilt+ patients) during the head-up tilt (HUT), and 20 did not (tilt-). A total number of three measurement periods, 30-60 s each, were analysed: supine position, 5 min after the commencement of HUT, and 1 min before set down. SV and CO values measured by PC underestimated significantly those measured by ICG (biases +/- SD 19 +/- 14 ml and 1.55 +/- 1.14 l min-1, respectively) in agreement with earlier reports. The bias between the methods was almost the same in the different phases of the test. However, the SD of the bias was bigger for tilt+ (P < 0.05). When the bias between the methods was eliminated by scaling the first measurement to 100%, the agreement between the methods in the second and third measurements was clearly better than without scaling. Both methods showed a physiological drop in SV after the commencement of HUT. These results indicate that PC suffices in tracking the changes in CO and SV, but for absolute values it is not reliable.

The future of bedside monitoring

Today's intensivists are provided with more information than ever before, yet current monitors present data from multiple sources in a relatively raw form with virtually no intelligent data integration and processing. In the next century, technological advances in miniaturization, biosensors and computer processing, coupled with an improved understanding of critical illnesses at the molecular level, will lead to the development of a new generation of monitors. Monitoring will move from the traditional macroscopic invasive approach to a noninvasive, molecular analysis of evolving critical disease processes. It is likely that disturbances in homeostasis will become known immediately or before they would otherwise be manifest clinically. Nanotechnology will permit monitoring of critical changes in the intracellular environment or the by-products of cellular metabolism and signal messaging. This article discusses monitoring technologies that hold promise for further development in the next century and point out techniques likely to be abandoned.

Simultaneous comparison of thoracic bioimpedance and arterial pulse waveform-derived cardiac output with thermodilution measurement

OBJECTIVE

To compare the accuracy and reliability of thoracic electrical bioimpedance (TEB) and the arterial pulse waveform analysis with simultaneous measurement of thermodilution cardiac output (TD-CO) in critically ill patients.

DESIGN

Prospective data collection.

SETTING

Emergency department and critical care unit in a 2,000-bed inner-city hospital.

PATIENTS

A total of 29 critically ill patients requiring invasive hemodynamic monitoring for clinical management were prospectively studied.

INTERVENTIONS

Noninvasive cardiac output was simultaneously measured by a TEB device and by analysis of the arterial pulse waveform derived from the finger artery. Invasive cardiac output was determined by the thermodilution technique.

MEASUREMENTS AND MAIN RESULTS

A total of 175 corresponding TD-CO and noninvasive hemodynamic measurements were collected in 30-min intervals. They revealed an overall bias of 0.34 L/min/m2 (95% confidence interval, 0.24-0.44 L/min/m2; p < .001) for the arterial pulse waveform analysis and of 0.61 L/min/m2 (95% confidence interval, 0.50-0.72 L/min/m2; p < .001) for the TEB. In 39.4% (n = 69) of all measurements, the discrepancy between arterial pulse waveform analysis and TD-CO was >0.50 L/min/m2. The discrepancies of the arterial pulse waveform analysis correlated positively with the magnitude of the cardiac index (r2 = 0.29; p < .001). In 56.6% (n = 99) of all measurements, the discrepancy between TEB and TD-CO was >0.50 L/min/m2. The magnitude of the discrepancies of the TEB was significantly correlated with age (r2 = 0.17; p = .02). Measurements were in phase in 93.2% of all arterial pulse waveform analysis and in 84.9% of all TEB readings (p < .001).

CONCLUSIONS

The arterial pulse waveform analysis exhibits a greater accuracy and reliability as compared with the TEB with regard to overall bias, number of inaccurate readings, and phase lags. The arterial pulse waveform analysis may be useful for the monitoring of hemodynamic changes. However, both methods fail to be a substitute for the TD-CO because of a substantial percentage of inaccurate readings.

Estimation of beat-to-beat changes in stroke volume from arterial pressure: a comparison of two pressure wave analysis techniques during head-up tilt testing in young, healthy men

OBJECTIVE

The aim of this study was to compare beat-to-beat changes in stroke volume (SV) estimated by two different pressure wave analysis techniques during orthostatic stress testing: pulse contour analysis and Modelflow, i.e., simulation of a three-element model of aortic input impedance.

METHODS

A reduction in SV was introduced in eight healthy young men (mean age, 25; range, 19-32 y) by a 30-minute head-up tilt maneuver. Intrabrachial and noninvasive finger pressure were monitored simultaneously. Beat-to-beat changes in SV were estimated from intrabrachial pressure by pulse contour analysis and Modelflow. In addition, the relative differences in Modelflow SV obtained from intrabrachial pressure and noninvasive finger pressure were assessed.

RESULTS

Beat-to-beat changes in Modelflow SV from intrabrachial pressure were comparable with pulse contour measures. The relative difference between the two methods amounted to 0.1+/-1% (mean +/- SEM) and was not dependent on the duration of tilt. The difference between Modelflow applied to intrabrachial pressure and finger pressure amounted to -2.7+/-1.3% (p = 0.04). This difference was not dependent on the duration of tilt or level of arterial pressure.

CONCLUSIONS

Based on different mathematical models of the human arterial system, pulse contour and Modelflow compute similar changes in SV from intrabrachial pressure during orthostatic stress testing in young healthy men. The magnitude of the difference in SV derived from intrabrachial and finger pressure may vary among subjects; Modelflow SV from noninvasive finger pressure tracks fast and brisk changes in SV derived from intrabrachial pressure.

Monitoring cardiac function without the use of a pulmonary artery catheter

Investigators have been trying to develop ways to measure cardiac function that are less invasive and more cost-effective than a pulmonary artery catheter. None of the technologies currently available are yet ready for routine use in assessing cardiac function in the operating room and in the intensive cardiac unit.

Non-invasive cardiac output determination: state of the art

This review deals with recent developments in non-invasive cardiac output measurement. In the past few years significant progress has been made with semi-invasive transoesophageal echocardiography; the method now provides advanced facilities to measure cardiac output and other important characteristics of cardiac function. The method is, however, operator-dependent and the equipment used is expensive, which means that large-scale use on intensive care patients is not feasible. Whole-body impedance cardiography has recently shown good accuracy and flexibility in use, and seems to be the most promising method for the non-invasive measurement of cardiac output.

Use of pulse oximetry to recognize severity of airflow obstruction in obstructive airway disease: correlation with pulsus paradoxus

STUDY OBJECTIVES

The purpose of this cross-sectional study was to confirm the observation that pulse oximetry tracing correlates with pulsus paradoxus, and is therefore a measure of the severity of air trapping in obstructive airway disease.

DESIGN

Cross-sectional survey.

SETTING

The ICU in a tertiary care academic hospital.

PATIENTS

Twenty-six patients consecutively admitted to the ICU with obstructive airway disease, either asthma or COPD.

MEASUREMENTS AND RESULTS

Forty-six percent of the study patients required mechanical ventilation, and 69% had an elevated pulsus paradoxus. We defined the altered pulse oximetry baseline tracing as the respiratory waveform variation (RWV). The RWV was measured in numerical form as the change in millimeters from the baseline. Pulsus paradoxus was significantly correlated with the RWV of the pulse oximetry tracing (p < 0.0001). An analysis of the respiratory variations in the pulse oximetry waveforms in obstructive lung disease patients reflects the presence and degree of auto-positive end-expiratory pressure (auto-PEEP; p < 0.0001).

CONCLUSIONS

We describe the characteristic alterations in the pulse oximetry tracings that occur in the presence of pulsus paradoxus and auto-PEEP. Since pulse oximetry is available universally in ICUs and emergency departments, it may be a useful noninvasive means of continually assessing pulsus paradoxus and air trapping severity in obstructive airway disease patients.

Benefits, risks and alternatives of pulmonary artery catheterization

Twenty-five years after the introduction of the pulmonary artery catheter in clinical practice, its effectiveness in improving patient outcome is seriously questioned. Experts still recommend to use pulmonary artery catheters in selected critically ill patients, although evidence supporting these recommendations is lacking. The risks and the unclear benefits associated with this procedure should prompt the search for alternative, noninvasive monitoring techniques.