Cardiac output monitoring: an integrative perspective

Hemodynamic monitoring

Hemodynamic assessment is a key component of the evaluation of the critically ill patients and has both diagnostic and prognostic utility. This review outlines a general approach to assessment of hemodynamics and perfusion, and then discusses various hemodynamic parameters: heart rate, BP, intravascular (central venous and pulmonary artery) pressures, cardiac output, and myocardial performance, within the context not only of how they are best measured but also how they should be used in a clinical context. Hemodynamics are best assessed using a combination of not only different hemodynamic parameters but also those with the inclusion of clinical indices of perfusion. The benefits of these techniques, as with all medical testing and interventions, must be weighed against any potential risks. Although what to measure and how to measure it is important, what is most important is how to use the information. Evaluating the response to therapeutic interventions is frequently the most useful way to employ hemodynamic monitoring techniques. For the practitioner, learning how to select from a robust set of hemodynamic tools and how to tailor their use to individual clinical settings will allow for optimal patient care.

Performance of a new pulse contour method for continuous cardiac output monitoring: validation in critically ill patients

BACKGROUND

A new calibrated pulse wave analysis method (VolumeView™/EV1000™, Edwards Lifesciences, Irvine, CA, USA) has been developed to continuously monitor cardiac output (CO). The aim of this study was to compare the performance of the VolumeView method, and of the PiCCO2™ pulse contour method (Pulsion Medical Systems, Munich, Germany), with reference transpulmonary thermodilution (TPTD) CO measurements.

METHODS

This was a prospective, multicentre observational study performed in the surgical and interdisciplinary intensive care units of four tertiary hospitals. Seventy-two critically ill patients were monitored with a central venous catheter, and a thermistor-tipped femoral arterial VolumeView™ catheter connected to the EV1000™ monitor. After initial calibration by TPTD CO was continuously assessed using the VolumeView-CCO software (CCO(VolumeView)) during a 72 h period. TPTD was performed in order to obtain reference CO values (COREF). TPTD and arterial wave signals were transmitted to a PiCCO2™ monitor in order to obtain CCO(PiCCO) values. CCO(VolumeView) and CCO(PiCCO) were recorded over a 5 min interval before assessment of CO(TPTD). Bland-Altman analysis, %(errors), and concordance (trend analysis) were calculated.

RESULTS

A total of 338 matched sets of data were available for comparison. Bias for CCO(VolumeView)-CO(REF) was -0.07 litre min(-1) and for CCO(PiCCO)-CO(REF) +0.03 litre min(-1). Corresponding limits of agreement were 2.00 and 2.48 litre min(-1) (P<0.01), %(errors) 29 and 37%, respectively. Trending capabilities were comparable for both techniques.

CONCLUSIONS

The performance of the new VolumeView™-CCO method is as reliable as the PiCCO2™-CCO pulse wave analysis in critically ill patients. However, an improved precision was observed with the VolumeView™ technique. CLINICALTRIALS.GOV IDENTIFIER: NCT01405040.

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.

From macrohemodynamic to the microcirculation

ICU patients need a prompt normalization of macrohemodynamic parameters. Unfortunately, this optimization sometimes does not protect patients from organ failure development. Prevention or treatment of organ failure needs another target to be pursued: the microcirculatory restoration. Microcirculation is the ensemble of vessels of maximum 100 μm in diameter. Nowadays the Sidestream Dark Field (SDF) imaging technique allows its bedside investigation and a recent round-table conference established the criteria for its evaluation. First, microcirculatory derangements have been studied in sepsis: they are mainly characterized by a reduction of vessel density, an alteration of flow, and a heterogeneous distribution of perfusion. Endothelial malfunction and glycocalyx rupture were proved to be the main reasons for the observed microthrombi, capillary leakage, leukocyte rolling, and rouleaux phenomenon, even if further studies are necessary for a better explanation. Therapeutic approaches targeting microcirculation are under investigation. Microcirculatory alterations have been recently demonstrated in other diseases such as hypovolemia and cardiac failure but this issue still needs to be explored. The aim of this paper is to gather the already known information, focus the reader's attention on the importance of microvascular physiopathology in critical illness, and prompt him to actively participate to achieve a more comprehensive understanding of the issue.

Less-invasive approaches to perioperative haemodynamic optimization

PURPOSE OF REVIEW

A number of less-invasive haemodynamic monitoring devices have been introduced in recent years, largely replacing the pulmonary artery catheter (PAC) as a standard monitoring tool. Apart from tracking cardiac output (CO), these monitors provide additional haemodynamic parameters. The aim of this article is to review the most widely used less-invasive monitoring modalities, their technical characteristics and limitations regarding their clinical performance.

RECENT FINDINGS

The utilization of CO monitoring in the perioperative setting has been shown to be associated with improved outcomes if integrated into a haemodynamic optimization strategy. These findings provide the basis of recent recommendations for perioperative monitoring.

SUMMARY

An array of monitoring modalities have been introduced that can reliably track CO in the perioperative setting and make the PAC dispensable in most clinical situations. In order to be used safely and efficiently, knowledge regarding the inherent monitoring techniques and their limitations, their clinical validity and the utility of the parameters provided is crucial.

Noninvasive continuous hemodynamic monitoring

Monitoring of continuous blood pressure and cardiac output is important to prevent hypoperfusion and to guide fluid administration, but only few patients receive such monitoring due to the invasive nature of most of the methods presently available. Noninvasive blood pressure can be determined continuously using finger cuff technology and cardiac output is easily obtained using a pulse contour method. In this way completely noninvasive continuous blood pressure and cardiac output are available for clinical use in all patients that would otherwise not be monitored. Developments and state of art in hemodynamic monitoring are reviewed here, with a focus on noninvasive continuous hemodynamic monitoring form the finger.

Residents and ICU nurses get reliable static and dynamic haemodynamic assessments with aortic oesophageal Doppler

BACKGROUND

Aortic oesophageal Doppler (ODM) allows continuous non-invasive haemodynamic monitoring. We tested to confirm if residents and nurses were able to reposition oesophageal probe (OP), obtain aortic blood flow of good quality and so perform reliable static and dynamic haemodynamic assessments.

METHODS

Prospective observational study assessing ODM measurements were obtained by six residents and three nurses after they have participated in training. Measured (aortic diameter) and calculated haemodynamic data [indexed stroke volume (SVI), cardiac index] were directly obtained from ODM, after residents and nurses repositioned the OP. In a second group of patients, we tested the ability of residents and nurses to detect rapid haemodynamic changes after a passive leg raising. SVI comparison was the primary end point. Statistical analysis was performed using the method of Bland and Altman.

RESULTS

Sixty-six haemodynamic measurements were performed on 42 patients. Mean bias for SVI between the skilled physician and residents, and between the skilled physician and nurses were -0.9 ± 5.2 ml/m(2) (P = 0.15), with a percentage error of 31%, and 0.9 ± 5.1 ml/m(2) (P = 0.14), with a percentage error of 33%, respectively. There was an excellent correlation for SVI between the physician and residents (r = 0.9; P < 0.0001) and between the physician and nurses (r = 0.9; P < 0.0001). Induced changes in SVI measured by residents and nurses strongly followed those of our skilled physician.

CONCLUSION

Residents and nurses get reliable static and dynamic haemodynamic assessments with ODM compared to our skilled physician.

Resuscitation and monitoring in gastrointestinal bleeding

INTRODUCTION

Gastrointestinal bleeding is a common life-threatening problem, causing significant mortality, costs and resource allocation. Its management requires a dynamic multidisciplinary approach that directs diagnostic and therapeutic priorities appropriately.

MATERIALS AND METHODS

Articles published within the past 15 years, related to gastrointestinal bleeding, were reviewed through MEDLINE search, in addition to current guidelines and standards.

RESULTS

Decisions of ICU admission and blood transfusion must be individualized based on the extent of bleeding, hemodynamic profile and comorbidities of the patient and the risk of rebleeding. A secure airway may be required to optimize oxygenation and to prevent aspiration. Doses of induction agents must be reduced due to the changes in volume of distribution. Volume replacement is the cornerstone of resuscitation in profuse bleeding, but nontargeted aggressive fluid resuscitation must be avoided to allow clot formation and to prevent increased bleeding. Decision to give blood transfusion must be based on physiologic triggers rather than a fixed level of hemoglobin. Coagulopathy must be corrected and hypothermia avoided. Need for massive transfusion must be recognized as early as possible, and a 1:1:1 ratio of packed red blood cells, fresh frozen plasma and platelets is recommended to prevent dilutional coagulopathy. Tromboelastography can be used to direct hemostatic resuscitation. Transfusion related lung injury (TRALI) is a significant problem with a mortality rate approaching 40%. Prevention of TRALI is important in patients with gastrointestinal bleeding, especially among patients having end-stage liver disease. Preventive strategies include prestorage leukoreduction, use of male-only or never-pregnant donors and avoidance of long storage times. Management of gastrointestinal bleeding requires delicately tailoring resuscitation to patient needs to avoid nonspecific aggressive resuscitation. "Functional hemodynamic monitoring" requires recognition of indications and limitations of hemodynamic measurements. Dynamic indices like systolic pressure variation are more reliable predictors of volume responsiveness. Noninvasive methods of hemodynamic monitoring and cardiac output measurement need further verification in patients with gastrointestinal bleeding.

CONCLUSIONS

Management of gastrointestinal bleeding requires a dynamic multidisciplinary approach. The mentioned advances in management of hemorrhagic shock must be considered in resuscitation and monitoring of patients with GI bleeding.