Cardiac output monitoring: Technology and choice

The accurate quantification of cardiac output (CO) is given vital importance in modern medical practice, especially in high-risk surgical and critically ill patients. CO monitoring together with perioperative protocols to guide intravenous fluid therapy and inotropic support with the aim of improving CO and oxygen delivery has shown to improve perioperative outcomes in high-risk surgical patients. Understanding of the underlying principles of CO measuring devices helps in knowing the limitations of their use and allows more effective and safer utilization. At present, no single CO monitoring device can meet all the clinical requirements considering the limitations of diverse CO monitoring techniques. The evidence for the minimally invasive CO monitoring is conflicting; however, different CO monitoring devices may be used during the clinical course of patients as an integrated approach based on their invasiveness and the need for additional hemodynamic data. These devices add numerical trend information for anesthesiologists and intensivists to use in determining the most appropriate management of their patients and at present, do not completely prohibit but do increasingly limit the use of the pulmonary artery catheter.

Heart rate, pulse pressure and mortality in patients with myocardial infarction complicated by heart failure

OBJECTIVE

To assess the relationship between heart rate (HR), pulse pressure (PP), and their association with mortality in a population of high-risk patients following acute myocardial infarction (MI).

METHODS

We performed an analysis in 22,398 patients included in "The High-Risk Myocardial Infarction Database Initiative", a database of clinical trials evaluating pharmacologic interventions in patients with MI complicated by signs of heart failure (HF) or left ventricular dysfunction. We found an interaction between HR and PP. Based on median HR and median PP, patients were divided in four categories: (1) HR < 75 bpm and PP ≥ 50 mm Hg (reference), (2) HR < 75 bpm and PP < 50 mm Hg, (3) HR ≥ 75 bpm and PP ≥ 50 mm Hg, and (4) HR ≥ 75 bpm and PP < 50 mm Hg. The association between these categories and outcomes was studied using a Cox proportional hazard model.

RESULTS

After a median follow-up of 24 (18-33) months, 3561 (16%) patients died of all-causes and 3048 (14%) patients of cardiovascular (CV) causes. In multivariate analysis, patients from the fourth category had the highest risk of all-cause mortality (hazard ratio of 1.69; 95% CI: 1.53-1.86) and CV mortality (hazard ratio of 1.78; 95% CI: 1.60-1.97).

CONCLUSIONS

There is an interaction between HR and PP in patients with HF following MI, with the highest risk being conferred by a clinical status with both an elevated HR and a lower PP. These findings identify a high-risk population likely to require an aggressive diagnostic and management strategy.

The Compensatory Reserve For Early and Accurate Prediction Of Hemodynamic Compromise: A Review of the Underlying Physiology

Shock is deadly and unpredictable if it is not recognized and treated in early stages of hemorrhage. Unfortunately, measurements of standard vital signs that are displayed on current medical monitors fail to provide accurate or early indicators of shock because of physiological mechanisms that effectively compensate for blood loss. As a result of new insights provided by the latest research on the physiology of shock using human experimental models of controlled hemorrhage, it is now recognized that measurement of the body's reserve to compensate for reduced circulating blood volume is the single most important indicator for early and accurate assessment of shock. We have called this function the "compensatory reserve," which can be accurately assessed by real-time measurements of changes in the features of the arterial waveform. In this paper, the physiology underlying the development and evaluation of a new noninvasive technology that allows for real-time measurement of the compensatory reserve will be reviewed, with its clinical implications for earlier and more accurate prediction of shock.

LiDCO-based fluid management in patients undergoing hip fracture surgery under spinal anaesthesia: a randomized trial and systematic review

BACKGROUND

Hip fracture is a condition with high mortality and morbidity in elderly frail patients. Intraoperative fluid optimization may be associated with benefit in this population. We investigated whether intraoperative fluid management using pulse-contour analysis cardiac monitoring, compared with standard care in patients undergoing spinal anaesthesia, would provide benefits in terms of reduced time until medically fit for discharge and postoperative complications.

METHODS

Patients undergoing surgical repair of fractured neck of femur, aged >60 yr, receiving spinal anaesthesia were enrolled in this single-centre, blinded, randomized, parallel group trial. Patients were allocated to either anaesthetist-directed fluid therapy or a pulse-contour-guided fluid optimization strategy using colloid (Gelofusine) boluses to optimize stroke volume. The primary outcome was time until medically fit for discharge. Secondary outcomes included postoperative complications, mobility, and mortality. We updated a systematic review to include relevant trials to 2014.

RESULTS

We recruited 130 patients. Time until medically fit for discharge was similar in both groups, mean [95% confidence interval (CI)] 12.2 (11.1-13.5) vs 13.1 (11.9-14.5) days (P=0.31), as was total length of stay 14.2 (12.9-15.8) vs 15.3 (13.8-17.2) days (P=0.32). There were no significant differences in complications, function, or mortality. An updated meta-analysis (four studies, 355 patients) found non-significant reduction in early mortality [relative risk 0.66 (0.24-1.79)] and in-hospital complications [relative risk 0.80 (0.61-1.05)].

CONCLUSIONS

Goal-directed fluid therapy during hip fracture repair under spinal anaesthesia does not result in a significant reduction in length of stay or postoperative complications. There is insufficient evidence to either support or discount its routine use.

CLINICAL TRIAL REGISTRATION

ISRCTN88284896.

Semi-invasive measurement of cardiac output based on pulse contour: a review and analysis

PURPOSE

The aim of this review was to provide a meta-analysis of all five of the most popular systems for arterial pulse contour analysis compared with pulmonary artery thermodilution, the established reference method for measuring cardiac output (CO). The five investigated systems are FloTrac/Vigileo(®), PiCCO(®), LiDCO/PulseCO(®), PRAM/MostCare(®), and Modelflow.

SOURCE

In a comprehensive literature search through MEDLINE(®), Web of Knowledge (v.5.11), and Google Scholar, we identified prospective studies and reviews that compared the pulse contour approach with the reference method (n = 316). Data extracted from the 93 selected studies included range and mean cardiac output, bias, percentage error, software versions, and study population. We performed a pooled weighted analysis of their precision in determining CO in various patient groups and clinical settings.

PRINCIPAL FINDINGS

Results of the majority of studies indicate that the five investigated systems show acceptable accuracy during hemodynamically stable conditions. Forty-three studies provided adequate data for a pooled weighted analysis and resulted in a mean (SD) total pooled bias of -0.28 (1.25) L·min(-1), percentage error of 40%, and a correlation coefficient of r = 0.71. In hemodynamically unstable patients (n = 8), we found a higher percentage error (45%) and bias of -0.54 (1.64) L·min(-1).

CONCLUSION

During hemodynamic instability, CO measurement based on continuous arterial pulse contour analysis shows only limited agreement with intermittent bolus thermodilution. The calibrated systems seem to deliver more accurate measurements than the auto-calibrated or the non-calibrated systems. For reliable use of these semi-invasive systems, especially for critical therapeutic decisions during hemodynamic disorders, both a strategy for hemodynamic optimization and further technological improvements are necessary.

Pulmonary carbon dioxide elimination for cardiac output monitoring in peri-operative and critical care patients: history and current status

Minimally invasive measurement of cardiac output as a central component of advanced haemodynamic monitoring has been increasingly recognised as a potential means of improving perioperative outcomes in patients undergoing major surgery. Methods based upon pulmonary carbon dioxide elimination are among the oldest techniques in this field, with comparable accuracy and precision to other techniques. Modern adaptations of these techniques suitable for use in the perioperative and critical are environment are based on the differential Fick approach, and include the partial carbon dioxide rebreathing method. The accuracy and precision of this approach to cardiac output measurement has been shown to be similar to other minimally invasive techniques. This paper reviews the underlying principles and evolution of the method, and future directions including recent adaptations designed to deliver continuous breath-by-breath monitoring of cardiac output.

Comparison of esCCO and transthoracic echocardiography for non-invasive measurement of cardiac output intensive care

BACKGROUND

The esCCO monitor (ECG- estimated Continuous Cardiac Output, Nihon Kohden(®)) is a new non-invasive tool for estimating cardiac output (CO). It derives CO from the pulse wave transit time (PWTT) estimated by the ECG and the plethysmographic wave. An initial calibration is needed to refine the relation linking pulse pressure (measured by arterial pressure cuff) to PWTT. To assess the accuracy and reliability of the esCCO system, we performed an analysis of agreement of CO values obtained by transthoracic echocardiography (TTE).

METHODS

Thirty-eight intensive care unit patients were prospectively included. CO was determined simultaneously using esCCO (CO(esCCO)) and TTE (CO(TTE)) as our reference method.

RESULTS

A total of 103 paired readings from 38 patients were collected. The correlation coefficient between CO(esCCO) and CO(TTE) was 0.61 (P<0.001). The Bland and Altman analysis corrected for repeated measures showed a bias of -1.6 litre min(-1) and limits of agreement from -4.7 to +1.5 litre min(-1), with a percentage error (2 sd/mean CO) of 49%. The correlation for CO changes was significant (R=0.63, P<0.001), but the concordance rate was poor (73%). Polar plot analysis showed an angular bias of -9° with radial limits of agreement from -54° to +36°. The bias appeared to correlate with systemic vascular resistance (R=-0.45, P<0.001).

CONCLUSIONS

In critically ill patients, the performance of the esCCO monitor was not clinically acceptable, and this monitor cannot be recommended in this setting. Moreover, the esCCO failed to trend CO data reliably.

Continuous and minimally invasive cardiac output monitoring by long time interval analysis of a radial arterial pressure waveform: assessment using a large, public intensive care unit patient database

BACKGROUND

A potential practical approach for continuous and minimally invasive cardiac output (CO) monitoring in intensive care unit (ICU) patients is to mathematically analyse an arterial pressure (AP) waveform using an existing radial artery line ('pulse contour analysis'). We recently proposed a technique to estimate the relative CO change by unique long time interval analysis (LTIA) of an AP waveform. We aimed to test this technique in an ICU patient population and compare its accuracy relative to other techniques.

METHODS

We studied a public, electronic ICU patient database. We extracted 1482 pairs of radial AP waveforms and thermodilution CO measurements (via single bolus injections) from 169 patients. We applied the LTIA and previous pulse contour analysis techniques to the AP waveforms. We assessed the calibrated CO estimates against the thermodilution measurements.

RESULTS

The overall root-mean-squared-error of the LTIA technique was 18.8%. This total level of accuracy was not better than the previous techniques. However, the average magnitude of the thermodilution changes was only 12.3% (9.9 sd). When the magnitude of the thermodilution change exceeded 30%, 50%, and 70%, the median squared-error differences between the LTIA technique and the most accurate previous technique were -45 (-322:69 quartiles) (P=0.005), -128 (-704:23) (P=0.006), and -862 (-2871:306)%(2) (P=0.055), respectively. The LTIA technique was therefore superior in detecting clinically important CO changes.

CONCLUSIONS

The LTIA technique attained an overall accuracy that may be considered clinically acceptable after taking into account the known thermodilution error and became progressively more accurate than previous techniques with increasing CO changes.