When to recalibrate the PiCCO? From a physiological point of view, the answer is simple

Excess pressure as an analogue of blood flow velocity

INTRODUCTION

Derivation of blood flow velocity from a blood pressure waveform is a novel technique, which could have potential clinical importance. Excess pressure, calculated from the blood pressure waveform via the reservoir-excess pressure model, is purported to be an analogue of blood flow velocity but this has never been examined in detail, which was the aim of this study.

METHODS

Intra-arterial blood pressure was measured sequentially at the brachial and radial arteries via fluid-filled catheter simultaneously with blood flow velocity waveforms recorded via Doppler ultrasound on the contralateral arm (n = 98, aged 61 ± 10 years, 72% men). Excess pressure was derived from intra-arterial blood pressure waveforms using pressure-only reservoir-excess pressure analysis.

RESULTS

Brachial and radial blood flow velocity waveform morphology were closely approximated by excess pressure derived from their respective sites of measurement (median cross-correlation coefficient r = 0.96 and r = 0.95 for brachial and radial comparisons, respectively). In frequency analyses, coherence between blood flow velocity and excess pressure was similar for brachial and radial artery comparisons (brachial and radial median coherence = 0.93 and 0.92, respectively). Brachial and radial blood flow velocity pulse heights were correlated with their respective excess pressure pulse heights (r = 0.53, P < 0.001 and r = 0.43, P < 0.001, respectively).

CONCLUSION

Excess pressure is an analogue of blood flow velocity, thus affording the opportunity to derive potentially important information related to arterial blood flow using only the blood pressure waveform.

Are management decisions in critical patients changed with use of hemodynamic parameters from transpulmonary thermodilution technique?

Background

The assessment of hemodynamic variables is a mainstay in the management of critically ill patients. Hemodynamic variables may help physicians to choose among use of a vasopressor, an inotropic agent, or discontinuation of drugs. In this study, we aimed to investigate the usefulness of advanced hemodynamic variables in clinical decision-making.

Methods

Surveys regarding the case were administered to 25 surgeons working in nationally designated trauma centers or on trauma teams, using a voting system at a medical conference. The patient was a 67-year-old male with a crush injury of the left leg after a pedestrian traffic accident, who had aggravated pulmonary edema after leg amputation. Three clinical situations were given and the decision choices were: immediately after amputation, in 8 hours, and on the second day after amputation. Three kinds of variables from hemodynamic monitoring systems were provided for each clinical situation: conventional hemodynamic variables, including central venous pressure; variables from pulse contour analysis (PCA) [cardiac output (CO), stroke volume index, stroke volume variation (SVV), and systemic vascular resistance index); and variables from transpulmonary thermodilution (TPTD) technique (global ejection fraction and extravascular lung water index). The changes in decisions according to each provided hemodynamic variable were investigated and analyzed.

Results

The advanced hemodynamic parameters were considered to have a decisive effect on choosing vasopressors and inotropic agents. The decision was changed in 88% (22/25) of physicians using variables from the advanced monitoring systems. Among them, 82% (18/22) of physicians chose hemodynamic variables from the TPTD technique as their reason for change regarding management of a patient with severe pulmonary edema.

Conclusions

Advanced monitoring systems might be helpful in decision-making for critically ill patients. Multiple parameters and trends in change could be more important than a single value. Clinicians should select the system most appropriate according to its advantages and limitations, and interpret the variables obtained correctly.

Application of pulse index continuous cardiac output system in elderly patients with acute myocardial infarction complicated by cardiogenic shock: A prospective randomized study

BACKGROUND

Cardiogenic shock (CS) secondary to acute myocardial infarction (AMI) complicates management of the condition, and often leads to poor prognosis. Prompt and accurate monitoring of cardiovascular and accompanying hemodynamic changes is crucial in achieving adequate management of the condition. Advances in technology has availed procedures such as pulse index continuous cardiac output (PiCCO), which can offer precise monitoring of cardiovascular functions and hemodynamic parameters. In this study, PiCCO is evaluated for its potential utility in improving management and clinical outcomes among elderly patients with AMI complicated by CS.

AIM

To assess whether use of the PiCCO system can improve clinical outcomes in elderly patients with AMI complicated by CS.

METHODS

Patients from emergency intensive care units (EICU) or coronary care units (CCU) were randomized to receive PiCCO monitoring or not. The APACHE II score, SOFA score, hs-TnI, NT-proBNP, PaO₂/FiO₂ ratio and lactate levels on day 1, 3 and 7 after treatment were compared. The infusion and urine volume at 0-24 h, 24-48 h and 48-72 h were recorded, as were the cardiac index (CI), extravascular lung water index (EVLWI), intrathoracic blood volume index (ITBVI) and global end diastolic volume index (GEDVI) at similar time intervals.

RESULTS

Sixty patients with AMI complicated by CS were included in the study. The PiCCO group had a significantly lower APACHE II score, SOFA score, hs-TnI and NT-proBNP levels on day 1, 3 and 7 after treatment. The infusion and urine volume during 0-24 h in the PiCCO group were significantly greater, and this group also showed significantly higher ADL scores. Furthermore, the PiCCO group spent lesser days on vasoactive agents, mechanical ventilation, and had a reduced length of stay in EICU/CCU. Additionally, the CI was significantly higher at 48 h and 72 h in the PiCCO group compared with that at 24 h, and the EVLWI, ITBVI and GEDVI were significantly decreased at 48 h and 72 h.

CONCLUSION

Applying the PiCCO system could improve the clinical outcomes of elderly patients with AMI complicated by CS.

Improved pressure contour analysis for estimating cardiac stroke volume using pulse wave velocity measurement

BACKGROUND

Pressure contour analysis is commonly used to estimate cardiac performance for patients suffering from cardiovascular dysfunction in the intensive care unit. However, the existing techniques for continuous estimation of stroke volume (SV) from pressure measurement can be unreliable during hemodynamic instability, which is inevitable for patients requiring significant treatment. For this reason, pressure contour methods must be improved to capture changes in vascular properties and thus provide accurate conversion from pressure to flow.

METHODS

This paper presents a novel pressure contour method utilizing pulse wave velocity (PWV) measurement to capture vascular properties. A three-element Windkessel model combined with the reservoir-wave concept are used to decompose the pressure contour into components related to storage and flow. The model parameters are identified beat-to-beat from the water-hammer equation using measured PWV, wave component of the pressure, and an estimate of subject-specific aortic dimension. SV is then calculated by converting pressure to flow using identified model parameters. The accuracy of this novel method is investigated using data from porcine experiments (N = 4 Pietrain pigs, 20-24.5 kg), where hemodynamic properties were significantly altered using dobutamine, fluid administration, and mechanical ventilation. In the experiment, left ventricular volume was measured using admittance catheter, and aortic pressure waveforms were measured at two locations, the aortic arch and abdominal aorta.

RESULTS

Bland-Altman analysis comparing gold-standard SV measured by the admittance catheter and estimated SV from the novel method showed average limits of agreement of ±26% across significant hemodynamic alterations. This result shows the method is capable of estimating clinically acceptable absolute SV values according to Critchely and Critchely.

CONCLUSION

The novel pressure contour method presented can accurately estimate and track SV even when hemodynamic properties are significantly altered. Integrating PWV measurements into pressure contour analysis improves identification of beat-to-beat changes in Windkessel model parameters, and thus, provides accurate estimate of blood flow from measured pressure contour. The method has great potential for overcoming weaknesses associated with current pressure contour methods for estimating SV.

Impact of arterial load on the agreement between pulse pressure analysis and esophageal Doppler

Introduction

The reliability of pulse pressure analysis to estimate cardiac output is known to be affected by arterial load changes. However, the contribution of each aspect of arterial load could be substantially different. In this study, we evaluated the agreement of eight non-commercial algorithms of pulse pressure analysis for estimating cardiac output (PPCO) with esophageal Doppler cardiac output (EDCO) during acute changes of arterial load. In addition, we aimed to determine the optimal arterial load parameter that could detect a clinically significant difference between PPCO and the EDCO.

Methods

We included mechanically ventilated patients monitored with a prototype esophageal Doppler (CardioQ-Combi™, Deltex Medical, Chichester, UK) and an indwelling arterial catheter who received a fluid challenge or in whom the vasoactive medication was introduced or modified. Initial calibration of PPCO was made with the baseline value of EDCO. We evaluated several aspects of arterial load: total systemic vascular resistance (TSVR = mean arterial pressure [MAP]/EDCO * 80), net arterial compliance (C = EDCO-derived stroke volume/pulse pressure), and effective arterial elastance (Ea = 0.9 * systolic blood pressure/EDCO-derived stroke volume). We compared CO values with Bland-Altman analysis, four-quadrant plot and a modified polar plot (with least significant change analysis).

Results

A total of 16,964-paired measurements in 53 patients were performed (median 271; interquartile range: 180-415). Agreement of all PPCO algorithms with EDCO was significantly affected by changes in arterial load, although the impact was more pronounced during changes in vasopressor therapy. When looking at different parameters of arterial load, the predictive abilities of Ea and C were superior to TSVR and MAP changes to detect a PPCO-EDCO discrepancy ≥ 10% in all PPCO algorithms. An absolute Ea change > 8.9 ± 1.7% was associated with a PPCO-EDCO discrepancy ≥ 10% in most algorithms.

Conclusions

Changes in arterial load profoundly affected the agreement of PPCO and EDCO, although the contribution of each aspect of arterial load to the PPCO-EDCO discrepancies was significantly different. Changes in Ea and C mainly determined PPCO-EDCO discrepancy.

Clinical review: Does it matter which hemodynamic monitoring system is used?

Hemodynamic monitoring and management has greatly improved during the past decade. Technologies have evolved from very invasive to non-invasive, and the philosophy has shifted from a static approach to a functional approach. However, despite these major changes, the critical care community still has potential to improve its ability to adopt the most modern standards of research methodology in order to more effectively evaluate new monitoring systems and their impact on patient outcome. Today, despite the huge enthusiasm raised by new hemodynamic monitoring systems, there is still a big gap between clinical research studies evaluating these monitors and clinical practice. A few studies, especially in the perioperative period, have shown that hemodynamic monitoring systems coupled with treatment protocols can improve patient outcome. These trials are small and, overall, the corpus of science related to this topic does not yet fit the standard of clinical research methodology encountered in other specialties such as cardiology and oncology. Larger randomized trials or quality improvement processes will probably answer questions related to the real impact of these systems.

Use of the PiCCO system in critically ill patients with septic shock and acute respiratory distress syndrome: a study protocol for a randomized controlled trial

BACKGROUND

Hemodynamic monitoring is very important in critically ill patients with shock or acute respiratory distress syndrome(ARDS). The PiCCO (Pulse index Contour Continuous Cardiac Output, Pulsion Medical Systems, Germany) system has been developed and used in critical care settings for several years. However, its impact on clinical outcomes remains unknown.

METHODS/DESIGN

The study is a randomized controlled multi-center trial. A total of 708 patients with ARDS, septic shock or both will be included from January 2012 to January 2014. Subjects will be randomized to receive PiCCO monitoring or not. Our primary end point is 30-day mortality, and secondary outcome measures include ICU length of stay, days on mechanical ventilation, days of vasoactive agent support, ICU-free survival days during a 30-day period, mechanical-ventilation-free survival days during a 30-day period, and maximum SOFA score during the first 7 days.

DISCUSSION

We investigate whether the use of PiCCO monitoring will improve patient outcomes in critically ill patients with ARDS or septic shock. This will provide additional data on hemodynamic monitoring and help clinicians to make decisions on the use of PiCCO.

TRIAL REGISTRATION

http://www.clinicaltrials.gov NCT01526382.

The PiCCO Monitor: A Review

Advanced haemodynamic monitoring remains a cornerstone in the management of the critically ill. While rates of pulmonary artery catheter use have been declining, there has been an increase in the number of alternatives for monitoring cardiac output as well as greater understanding of the methods and criteria with which to compare devices. The PiCCO (Pulse index Continuous Cardiac Output) device is one such alternative, integrating a wide array of both static and dynamic haemodynamic data through a combination of trans-cardiopulmonary thermodilution and pulse contour analysis. The requirement for intra-arterial and central venous catheterisation limits the use of PiCCO to those with evolving critical illness or at high risk of complex and severe haemodynamic derangement. While the accuracy of trans-cardiopulmonary thermodilution as a measure of cardiac output is well established, several other PiCCO measurements require further validation within the context of their intended clinical use. As with all advanced haemodynamic monitoring systems, efficacy in improving patient-centred outcomes has yet to be conclusively demonstrated. The challenge with PiCCO is in improving the understanding of the many variables that can be measured and integrating those that are clinically relevant and adequately validated with appropriate therapeutic interventions.

Arterial waveform analysis in anesthesia and critical care

PURPOSE OF REVIEW

In this review, we describe the basic principles of arterial waveform analysis (AWA) to assess cardiac output (CO) and cardiac preload. The validity of commercially based hemodynamic monitoring systems is discussed, together with their clinical applications and limitations.

RECENT FINDINGS

Currently, three devices (the FloTrac system, PiCCO monitor, and LiDCO system) are available for measurement of AWA-based CO. In addition, dynamic preload parameters such as stroke volume variation (SVV) and pulse pressure variation (PPV) are determined, which may be useful to predict fluid responsiveness in mechanically ventilated patients.

SUMMARY

AWA provides a less invasive and easy-to-use alternative for CO measurement. The validity of AWA devices has been verified in a variety of patients and circumstances, but their performance is compromised in the presence of hemodynamic instability, cardiac arrhythmias, or other factors disturbing the arterial pressure waveform. The definitive role of dynamic preload parameters like SVV and PPV is a matter of research. Large trials in which the value of early goal-directed therapy using this technology is studied in relation to outcome are urgently needed.

Cardiac output derived from arterial pressure waveform

PURPOSE OF REVIEW

Cardiac output (CO) and other flow-based hemodynamic variables have become increasingly important to guide treatment of patients undergoing major surgery with expected fluid shifts in the operating room as well as critically ill ICU patients. Established techniques such as pulmonary artery thermodilution, however, might not be justified in all of these patients. As arterial access is commonly available, less-invasive arterial pressure waveform-based CO devices are becoming more and more popular.

RECENT FINDINGS

Many studies dealing with arterial pressure waveform-based CO have emerged in recent years providing additional information with regard to accuracy of the different commercially available devices. Furthermore, methods of comparative CO studies have been recently brought into question.

SUMMARY

Although there are differences in invasiveness and the need for external calibration, all available devices provide parameters for enhanced hemodynamic monitoring. Initial validation studies of the more established techniques such as the pulse contour cardiac output (PiCCO) or LiDCO were recently met with less enthusiasm, whereas the initially disappointing validation studies of the FloTrac/Vigileo device had encouraging results after software updates. The pressure recording analytical method (PRAM) technique has not so far been sufficiently evaluated to be able to come to a conclusion. Further investigation is required with regard to the ability of the arterial pressure waveform-based methods to guide goal-directed therapy.