Validation of cardiac output measurement with the LiDCOTM pulse contour system in patients with impaired left ventricular function after cardiac surgery*

Predicting Fluid Responsiveness Using Carotid Ultrasound in Mechanically Ventilated Patients: A Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies

BACKGROUND

A noninvasive and accurate method of determining fluid responsiveness in ventilated patients would help to mitigate unnecessary fluid administration. Although carotid ultrasound has been previously studied for this purpose, several studies have recently been published. We performed an updated systematic review and meta-analysis to evaluate the accuracy of carotid ultrasound as a tool to predict fluid responsiveness in ventilated patients.

METHODS

Studies eligible for review investigated the accuracy of carotid ultrasound parameters in predicting fluid responsiveness in ventilated patients, using sensitivity and specificity as markers of diagnostic accuracy (International Prospective Register of Systematic Reviews [PROSPERO] CRD42022380284). All included studies had to use an independent method of determining cardiac output and exclude spontaneously ventilated patients. Six bibliographic databases and 2 trial registries were searched. Medline, Embase, Emcare, APA PsycInfo, CINAHL, and the Cochrane Library were searched on November 4, 2022. Clinicaltrials.gov and Australian New Zealand Clinical Trials Registry were searched on February 24, 2023. Results were pooled, meta-analysis was conducted where possible, and hierarchical summary receiver operating characteristic models were used to compare carotid ultrasound parameters. Bias and evidence quality were assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool and the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) guidelines.

RESULTS

Thirteen prospective clinical studies were included (n = 648 patients), representing 677 deliveries of volume expansion, with 378 episodes of fluid responsiveness (58.3%). A meta-analysis of change in carotid Doppler peak velocity (∆CDPV) yielded a sensitivity of 0.79 (95% confidence interval [CI], 0.74-0.84) and a specificity of 0.85 (95% CI, 0.76-0.90). Risk of bias relating to recruitment methodology, the independence of index testing to reference standards and exclusionary clinical criteria were evaluated. Overall quality of evidence was low. Study design heterogeneity, including a lack of clear parameter cutoffs, limited the generalizability of our results.

CONCLUSIONS

In this meta-analysis, we found that existing literature supports the ability of carotid ultrasound to predict fluid responsiveness in mechanically ventilated adults. ∆CDPV may be an accurate carotid parameter in certain contexts. Further high-quality studies with more homogenous designs are needed to further validate this technology.

Reliability of bioreactance and pulse power analysis in measuring cardiac index during cytoreductive abdominal surgery with hyperthermic intraperitoneal chemotherapy (HIPEC)

PURPOSE

Various malignancies with peritoneal carcinomatosis are treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (HIPEC). The hemodynamic instability resulting from fluid balance alterations during the procedure necessitates reliable hemodynamic monitoring. The aim of the study was to compare the accuracy, precision and trending ability of two less invasive hemodynamic monitors, bioreactance-based Starling SV and pulse power device LiDCOrapid with bolus thermodilution technique with pulmonary artery catheter in the setting of cytoreductive surgery with HIPEC.

METHODS

Thirty-one patients scheduled for cytoreductive surgery were recruited. Twenty-three of them proceeded to HIPEC and were included to the study. Altogether 439 and 430 intraoperative bolus thermodilution injections were compared to simultaneous cardiac index readings obtained with Starling SV and LiDCOrapid, respectively. Bland-Altman method, four-quadrant plots and error grids were used to assess the agreement of the devices.

RESULTS

Comparing Starling SV with bolus thermodilution, the bias was acceptable (0.13 l min^- 1 m^- 2, 95% CI 0.05 to 0.20), but the limits of agreement were wide (- 1.55 to 1.71 l min^- 1 m^- 2) and the percentage error was high (60.0%). Comparing LiDCOrapid with bolus thermodilution, the bias was acceptable (- 0.26 l min^- 1 m^- 2, 95% CI - 0.34 to - 0.18), but the limits of agreement were wide (- 1.99 to 1.39 l min^- 1 m^- 2) and the percentage error was high (57.1%). Trending ability was inadequate with both devices.

CONCLUSION

Starling SV and LiDCOrapid were not interchangeable with bolus thermodilution technique limiting their usefulness in the setting of cytoreductive surgery with HIPEC.

Orthostatic intolerance after fast-track knee arthroplasty: Incidence and hemodynamic pathophysiology

BACKGROUND

Early postoperative mobilization can be hindered by orthostatic intolerance (OI) due to failed orthostatic cardiovascular regulation. The underlying mechanisms are not fully understood and specific data after total knee arthroplasty (TKA) are lacking. Therefore, we evaluated the incidence of OI and the cardiovascular response to mobilization in fast-track TKA.

METHODS

This prospective observational cohort study included 45 patients scheduled for primary TKA in spinal anesthesia with a multimodal opioid-sparing analgesic regime. OI and the cardiovascular response to sitting and standing were evaluated with a standardized mobilization procedure preoperatively, and at 6h and 24h postoperatively. Hemodynamic variables were measured non-invasively (LiDCO™ Rapid). Perioperative bleeding, fluid balance, surgery duration, postoperative hemoglobin, opioid use and pain during mobilization were recorded.

RESULTS

Eighteen (44%) and 8 (22%) patients demonstrated OI at 6 and 24h after surgery respectively. Four (10%) and 2 (5%) patients experienced severe OI and terminated the mobilization procedure prematurely. Dizziness was the most common OI symptom during mobilization at 6h. OI was associated with decreased orthostatic responses in systolic, diastolic, mean arterial pressures and heart rate (all p<0.05), while severe OI patients demonstrated impaired diastolic, mean arterial pressures, heart rate and cardiac output responses (all p<0.05). No statistically significant differences in perioperative bleeding, fluid balance, surgery duration, postoperative hemoglobin, pain or opioid use were observed between orthostatic tolerant and intolerant patients.

CONCLUSION

Early postoperative OI is common following fast-track TKA. Pathophysiologic mechanisms include impaired orthostatic cardiovascular responses. The progression to severe OI symptoms appears to be primarily due to inadequate heart rate response.

Reliability of Bioreactance and Pulse-Power Analysis in Measuring Cardiac Index in Patients Undergoing Cardiac Surgery With Cardiopulmonary Bypass

OBJECTIVES

Less-invasive and continuous cardiac output monitors recently have been developed to monitor patient hemodynamics. The aim of this study was to compare the accuracy, precision, and trending ability of noninvasive bioreactance-based Starling SV and miniinvasive pulse-power device LiDCOrapid to bolus thermodilution technique with a pulmonary artery catheter (TDCO) when measuring cardiac index in the setting of cardiac surgery with cardiopulmonary bypass (CPB).

DESIGN

A prospective method-comparison study.

SETTING

Oulu University Hospital, Finland.

PARTICIPANTS

Twenty patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Cardiac index measurements were obtained simultaneously with TDCO intraoperatively and postoperatively, resulting in 498 measurements with Starling SV and 444 with LiDCOrapid.

MEASUREMENTS AND MAIN RESULTS

The authors used the Bland-Altman method to investigate the agreement between the devices and four-quadrant plots with error grids to assess the trending ability. The agreement between TDCO and Starling SV was qualified with a bias of 0.43 L/min/m² (95% confidence interval [CI], 0.37-0.50), wide limits of agreement (LOA, -1.07 to 1.94 L/min/m²), and a percentage error (PE) of 66.3%. The agreement between TDCO and LiDCOrapid was qualified, with a bias of 0.22 L/min/m² (95% CI 0.16-0.27), wide LOA (-0.93 to 1.43), and a PE of 53.2%. With both devices, trending ability was insufficient.

CONCLUSION

The reliability of bioreactance-based Starling SV and pulse-power analyzer LiDCOrapid was not interchangeable with TDCO, thus limiting their usefulness in cardiac surgery with CPB.

Peri-operative oxygen consumption revisited: An observational study in elderly patients undergoing major abdominal surgery

BACKGROUND

Monitoring oxygen consumption (VO2) is neither recommended nor included in peri-operative haemodynamic algorithms aiming at optimising oxygen delivery (DO2) in major abdominal surgery. Estimates of peri-operative VO2 changes are uncertain in earlier publications and have limited generalisability in the current high-risk surgical population. In a prospective non-interventional observational study in elderly patients undergoing major abdominal procedures, we investigated the change of VO2 after induction of anaesthesia and secondarily, the further changes during and after surgery in relation to DO2 and estimated oxygen extraction ratio (O2ER) by routine monitoring.

METHODS

VO2 was determined by indirect calorimetry (QuarkRMR) in 20 patients more than 65 years (ASA II to IV), scheduled for elective open upper abdominal surgery with combined epidural and general anaesthesia. Data were collected during 20-minute periods pre-operatively and after anaesthesia induction, with subsequent measurements during surgery and postoperatively. Simultaneously, DO2 was monitored using LiDCOplus. The O2ER was estimated from arterial-central venous oxygen content calculation. Mixed models were used to analyse the peri-operative changes.

RESULTS

VO2 decreased after induction of anaesthesia by a mean of 34% (95% CI, 28 to 39). After 2 h of surgery, VO2 was reduced by 24% (95% CI, 20 to 27) compared with the awake baseline measurements. Pre-operative mean DO2 was 440 (95% CI, 396 to 483) ml min m and decreased by a mean of 37% (95% CI, 30 to 43) during anaesthesia. The estimated O2ER did not change intra-operatively 0.24 (95% CI, 0.21 to 0.26) but increased postoperatively to 0.31 (95% CI, 0.27 to 0.36). The changes of VO2 were parallel with changes of DO2 and O2ER in the intra-operative period.

CONCLUSION

General anaesthesia reduced VO2 by approximately a third in elderly patients undergoing major abdominal surgery. Parallel changes of intra-operative VO2 and delivery were demonstrated while oxygen extraction was low. The relevance of these changes needs further assessment in relation to outcomes and haemodynamic interventions.

TRIAL REGISTRATION

Clinicaltrials.gov NCT03355118.

To Swan or Not to Swan: Indications, Alternatives, and Future Directions

The pulmonary artery catheter (PAC) has revolutionized bedside assessment of preload, afterload, and contractility using measured pulmonary capillary wedge pressure, calculated systemic vascular resistance, and estimated cardiac output. It is placed percutaneously by a flow-directed balloon-tipped technique through the venous system and the right heart to the pulmonary artery. Interest in the hemodynamic variables obtained from PACs paved the way for the development of numerous less-invasive hemodynamic monitors over the past 3 decades. These devices estimate cardiac output using concepts such as pulse contour and pressure analysis, transpulmonary thermodilution, carbon dioxide rebreathing, impedance plethysmography, Doppler ultrasonography, and echocardiography. Herein, the authors review the conception, technologic advancements, and modern use of PACs, as well as the criticisms regarding the clinical utility, reliability, and safety of PACs. The authors comment on the current understanding of the benefits and limitations of alternative hemodynamic monitors, which is important for providers caring for critically ill patients. The authors also briefly discuss the use of hemodynamic monitoring in goal-directed fluid therapy algorithms in Enhanced Recovery After Surgery programs.

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.

Validation of electrical velocimetry in resuscitation of patients undergoing liver transplantation. Observational study

Major hemodynamic changes are frequently noted during liver transplantation (LT). We evaluated the performance of electrical velocimetry (EV) as compared to that of TEE in SV optimization during liver transplantation. This was an observational study in 32 patients undergoing LT. We compared SV values measured simultaneously by EV (SV_EV) and TEE (SV_TEE) at baseline 30 min after induction, at the end of dissection phase, 30 min after anhepatic phase, 30 min after reperfusion. We also evaluated the reliability of EV to track changes In SV before and after 49 fluid challenges. Finally, the SV variation (SVV) and pulse pressure variation (PPV) were tested as predictors for volume responsiveness, defined as an increase in SV ≥ 10% after 250 ml of colloid. For 112 paired SV data, the overall correlation was 0.76 and bias (limits of agreement) 0.3 (- 29 to 29) ml percentage error 62%. The EV was able to track changes in SV with a concordance rate of 97%, and a sensitivity and specificity of 93% to detect a positive fluid challenge. The AUC values (with 95% confidence intervals) for SVV and PPV were 0.68 (0.52-0.83) and 0.72 (0.57-0.86), respectively, indicating low predictive capacity in these setting. The absolute values of SV derived from EV did not agree with SV derived from TEE. However, EV was able to track the direction of changes in SV during hemodynamic management of patients undergoing liver transplantation.Clinical trial registration: Clinicaltrials.gov Identifier: NCT03228329 prospectively Registered on 13-July-2017.

Postoperative management of patients undergoing cardiac surgery in Austria : A national survey on current clinical practice in hemodynamic monitoring and postoperative management

Background

No data are currently available regarding the current clinical practice in postoperative care of cardiac surgical patients in Austria.

Objective

The study investigated the current intensive care management concerning hemodynamic monitoring and strategies to treat common perioperative disorders of patients after cardiac surgery in Austria.

Methods

A survey consisting of 31 questions was sent to intensivists at all 9 hospitals offering cardiac surgery in Austria.

Results

The response rate was 100%. The mean number of procedures on cardiopulmonary bypass per centre was 722 ± 223. In the majority of cases postoperative critical care is performed by anesthesiologists. Blood gas analysis, pulse oximetry, electrocardiogram, temperature, central venous pressure, arterial pressure and hourly urine output are de facto standard monitoring in all centers. Transesophageal echocardiography is available in all centers and is frequently used. Crystalloids are the first choice for volume replacement, whereas levosimendan and adrenaline are employed for the treatment of low cardiac output syndrome.

Conclusions

This study provides insights into the current state of postoperative management of cardiac surgical patients in Austria. Standard monitoring as proposed by international guidelines is well established in Austrian intensive care units. Echocardiography is widely seen as a very important tool in the postoperative care of cardiac surgical patients. Knowledge about the status quo of postoperative intensive care management of cardiac surgical patients enables further development of patient care.

Electronic supplementary material

The online version of this article (10.1007/s00508-018-1403-3) contains supplementary material, which is available to authorized users.

Predictive values of pulse pressure variation and stroke volume variation for fluid responsiveness in patients with pneumoperitoneum

Animal studies suggest that dynamic predictors remain useful in patients with pneumoperitoneum, but human data is conflicting. Our aim was to determine predictive values of pulse pressure variation (PPV) and stroke volume variation (SVV) in patients with pneumoperitoneum using LiDCORapid™ haemodynamic monitor. Standardised fluid challenges of colloid were administered to patients undergoing laparoscopic procedures, one fluid challenge per patient. Intra-abdominal pressure was automatically held at 12 mmHg. Fluid responsiveness was defined as an increase in nominal stroke index (nSI) ≥ 10%. Linear regression was used to assess the ability of PPV and SVV to track the changes of nSI and logistic regression and area under the receiver operating curve (AUROC) to assess the predictive value of PPV and SVV for fluid responsiveness. Threshold values for PPV and SVV were obtained using the "gray zone" approach. A p < 0.05 was considered as statistically significant. 56 patients were included in analysis. 41 patients (73%) responded to fluids. Both PPV and SVV tracked changes in nSI (Spearman correlation coefficients 0.34 for PPV and 0.53 for SVV). Odds ratio for fluid responsiveness for PPV was 1.163 (95% CI 1.01-1.34) and for SVV 1.341 (95% CI 1.10-1.63). PPV achieved an AUROC of 0.674 (95% CI 0.518-0.830) and SVV 0.80 (95% CI 0.668-0.932). The gray zone of PPV ranged between 6.5 and 20.5% and that of SVV between 7.5 and 13%. During pneumoperitoneum, as measured by LiDCORapid™, PPV and SVV can predict fluid responsiveness, however their sensitivity is lower than the one reported in conditions without pneumoperitoneum. Trial registry number: (with the Australian New Zealand Clinical Trials Registry): ACTRN12612000456853.

Impact of hemodynamic goal-directed resuscitation on mortality in adult critically ill patients: a systematic review and meta-analysis

The effect of hemodynamic optimization in critically ill patients has been challenged in recent years. The aim of the meta-analysis was to evaluate if a protocolized intervention based on the result of hemodynamic monitoring reduces mortality in critically ill patients. We performed a systematic review and meta-analysis according to the Cochrane Handbook for Systematic Reviews of Interventions. The study was registered in the PROSPERO database (CRD42015019539). Randomized controlled trials published in English, reporting studies on adult patients treated in an intensive care unit, emergency department or equivalent level of care were included. Interventions had to be protocolized and based on results from hemodynamic measurements, defined as cardiac output, stroke volume, stroke volume variation, oxygen delivery, and central venous-or mixed venous oxygenation. The control group had to be treated without any structured intervention based on the parameters mentioned above, however, monitoring by central venous pressure measurements was allowed. Out of 998 screened papers, thirteen met the inclusion criteria. A total of 3323 patients were enrolled in the six trials with low risk of bias (ROB). The mortality was 22.4% (374/1671 patients) in the intervention group and 22.9% (378/1652 patients) in the control group, OR 0.94 with a 95% CI of 0.73–1.22. We found no statistically significant reduction in mortality from hemodynamic optimization using hemodynamic monitoring in combination with a structured algorithm. The number of high quality trials evaluating the effect of protocolized hemodynamic management directed towards a meaningful treatment goal in critically ill patients in comparison to standard of care treatment is too low to prove or exclude a reduction in mortality.

Unreliable Tracking Ability of the Third-Generation FloTrac/Vigileo™ System for Changes in Stroke Volume after Fluid Administration in Patients with High Systemic Vascular Resistance during Laparoscopic Surgery

BACKGROUND

The FloTrac/Vigileo™ system does not thoroughly reflect variable arterial tones, due to a lack of external calibration. The ability of this system to measure stroke volume and track its changes after fluid administration has not been fully evaluated in patients with the high systemic vascular resistance that can develop during laparoscopic surgery.

METHODS

In 42 patients undergoing laparoscopic prostatectomy, the stroke volume derived by the third-generation FloTrac/Vigileo™ system (SV-Vigileo), the stroke volume measured using transesophageal echocardiography (SV-TEE) as a reference method, and total systemic vascular resistance were evaluated before and after 500 ml fluid administration during pneumoperitoneum combined with the Trendelenburg position.

RESULTS

Total systemic vascular resistance was 2159.4 ± 523.5 dyn·s/cm5 before fluid administration. The SV-Vigileo was significantly higher than the SV-TEE both before (68.8 ± 15.9 vs. 57.0 ± 11.0 ml, P < 0.001) and after (73.0 ± 14.8 vs. 64.9 ± 12.2 ml, P = 0.003) fluid administration. During pneumoperitoneum combined with the Trendelenburg position, Bland-Altman analysis for repeated measures showed a 53.8% of percentage error between the SV-Vigileo and the SV-TEE. Four-quadrant plot (69.2% of a concordance rate) and polar plot analysis (20.6° of a mean polar angle, 16.4° of the SD of a polar angle, and ±51.5° of a radial sector containing 95% of the data points) did not indicate a good trending ability of the FloTrac/Vigileo™ system.

CONCLUSIONS

The third-generation FloTrac/Vigileo™ system may not be useful in patients undergoing laparoscopic surgery, based on unreliable performance in measuring the stroke volume and in tracking changes in the stroke volume after fluid administration during pneumoperitoneum combined with the Trendelenburg position.

Accuracy of Continuous Cardiac Output Measurement With the LiDCOplus System During Intra-Aortic Counterpulsation After Cardiac Surgery

OBJECTIVE

To evaluate the effect of intra-aortic counterpulsation on precision, accuracy, and concordance of continuous pulse contour cardiac output determined using LiDCOplus (LiDCO Group, London).

DESIGN

Prospective trial.

SETTING

University hospital critical care unit.

PARTICIPANTS

Patients with intra-aortic balloon pump support in the 1:1 mode after elective or urgent cardiac surgery.

INTERVENTIONS

Lithium dilution calibrated pulse contour cardiac output was compared with pulmonary artery bolus thermodilution cardiac output during hemodynamically stable conditions in the course of standardized postoperative management.

MEASUREMENTS AND MAIN RESULTS

Fifty-one paired measurements demonstrated good correlation between the 2 methods (r = 0.88, p<0.001). Mean bias was -0.14±0.81 L/min, limits of agreement 1.48 to -1.77 L/min, and percentage error 28%. Concordance between the 2 techniques regarding directional changes>±10% cardiac output was 100% (p = 0.008). Trending ability was moderate when paired cardiac output changes were assessed using linear regression, 4-quadrant table, and polar plots. When changes <±10% of the reference cardiac output were excluded, 90% of the data pairs still lay within the 30° radial limits. Optimal timing of the balloon pump was indispensable for proper determination of pulse contour cardiac output.

CONCLUSIONS

Because of the LiDCOplus-specific algorithm in determining stroke volume from the arterial pulse waveform, which differs from other devices, accuracy and precision of continuous pulse contour cardiac output only are affected insignificantly by intra-aortic counterpulsation. The authors nevertheless caution that the device should be recalibrated after major hemodynamic alterations or otherwise inexplicable changes of the pulse contour cardiac output to improve trending.

Assessment of cardiac output with transpulmonary thermodilution during exercise in humans

The accuracy and reproducibility of transpulmonary thermodilution (TPTd) to assess cardiac output (Q̇) in exercising men was determined using indocyanine green (ICG) dilution as a reference method. TPTd has been utilized for the assessment of Q̇ and preload indexes of global end-diastolic volume and intrathoracic blood volume, as well as extravascular lung water (EVLW) in resting humans. It remains unknown if this technique is also accurate and reproducible during exercise. Sixteen healthy men underwent catheterization of the right femoral vein (for iced saline injection), an antecubital vein (ICG injection), and femoral artery (thermistor) to determine their Q̇ by TPTd and ICG concentration during incremental one- and two-legged pedaling on a cycle ergometer and combined arm cranking with leg pedaling to exhaustion. There was a close relationship between TPTd-Q̇ and ICG-Q̇ ( r = 0.95, n = 151, standard error of the estimate: 1.452 l/min, P < 0.001; mean difference of 0.06 l/min; limits of agreement −2.98 to 2.86 l/min), and TPTd-Q̇ and ICG-Q̇ increased linearly with oxygen uptake with similar intercepts and slopes. Both methods had mean coefficients of variation close to 5% for Q̇, global end-diastolic volume, and intrathoracic blood volume. The mean coefficient of variation of EVLW, assessed with both indicators (ICG and thermal) was 17% and was sensitive enough to detect a reduction in EVLW of 107 ml when changing from resting supine to upright exercise. In summary, TPTd with bolus injection into the femoral vein is an accurate and reproducible method to assess Q̇ during exercise in humans.

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.

Haemodynamic monitoring using arterial waveform analysis

PURPOSE OF REVIEW

To describe the theory behind arterial waveform analysis, the different variables that may be obtained using this method, reliability of measurements and their clinical relevance. Areas for future research are identified.

RECENT FINDINGS

The precision of cardiac output (CO) measurements varies considerably and deteriorates during haemodynamic instability. Significant device-to-device differences exist. Nevertheless, most are sufficiently accurate for tracking changes in CO. Targeted intervention guided by haemodynamic monitoring reduces mortality and morbidity in high-risk surgical patients. Dynamic changes in variables such as systolic pulse variation, pulse pressure variation (PPV) and stroke volume variation (SVV) may be useful for evaluating fluid responsiveness, although important caveats exist. Newer indices such as PPV : SVV ratio may be useful in identifying preload and vasopressor-dependent patients. Peripheral arterial dP/dt has not been validated in critically ill patients and requires further investigation.

SUMMARY

Despite significant limitations in measurement accuracy and inter-device differences, arterial waveform analysis is a potentially useful tool for monitoring the central circulation in critically ill patients. Future studies investigating the effects of haemodynamic management guided by arterial waveform variables in critically ill patients are urgently needed. The evaluation of cardiopulmonary interactions and usefulness of dP/dt are other areas that require further investigation.

Less invasive methods of advanced hemodynamic monitoring: principles, devices, and their role in the perioperative hemodynamic optimization

The monitoring of the cardiac output (CO) and other hemodynamic parameters, traditionally performed with the thermodilution method via a pulmonary artery catheter (PAC), is now increasingly done with the aid of less invasive and much easier to use devices. When used within the context of a hemodynamic optimization protocol, they can positively influence the outcome in both surgical and non-surgical patient populations. While these monitoring tools have simplified the hemodynamic calculations, they are subject to limitations and can lead to erroneous results if not used properly. In this article we will review the commercially available minimally invasive CO monitoring devices, explore their technical characteristics and describe the limitations that should be taken into consideration when clinical decisions are made.

Using bispectral index and cerebral oximetry to guide hemodynamic therapy in high-risk surgical patients

High-risk surgery represents 12.5% of cases but contributes 80% of deaths in the elderly population. Reduction in morbidity and mortality by the use of intervention strategies could result in thousands of lives being saved and savings of up to £400m per annum in the UK. This has resulted in the drive towards goal-directed therapy and intraoperative flow optimization of high-risk surgical patients being advocated by authorities such as the National Institute of Health and Care Excellence and the Association of Anaesthetists of Great Britain and Ireland.Conventional intraoperative monitoring gives little insight into the profound physiological changes occurring as a result of anesthesia and surgery. The build-up of an oxygen debt is associated with a poor outcome and strategies have been developed in the postoperative period to improve outcomes by repayment of this debt. New monitoring technologies such as minimally invasive cardiac output, depth of anesthesia and cerebral oximetry can minimize oxygen debt build-up. This has the potential to reduce complications and lessen the need for postoperative optimization in high-dependency areas.Flow monitoring has thus emerged as essential during intraoperative monitoring in high-risk surgery. However, evidence suggests that current optimization strategies of deliberately increasing flow to meet predefined targets may not reduce mortality.Could the addition of depth of anesthesia and cerebral and tissue oximetry monitoring produce a further improvement in outcomes?Retrospective studies indicate a combination of excessive depth of anesthesia hypotension and low anesthesia requirement results in increased mortality and length of hospital stay.Near infrared technology allows assessment and maintenance of cerebral and tissue oxygenation, a strategy, which has been associated with improved outcomes. The suggestion that the brain is an index organ for tissue oxygenation, especially in the elderly, indicates a role for this technology in the intraoperative period to assess the adequacy of oxygen delivery and reduce the build-up of an oxygen debt.The aim of this article is to make the case for depth of anesthesia and cerebral oximetry alongside flow monitoring as a strategy for reducing oxygen debt during high-risk surgery and further improve outcomes in high-risk surgical patients.

The maintenance and monitoring of perioperative blood volume

The assessment and maintenance of perioperative blood volume is important because fluid therapy is a routine part of intraoperative care. In the past, patients undergoing major surgery were given large amounts of fluids because health-care providers were concerned about preoperative dehydration and intraoperative losses to a third space. In the last decade it has become clear that fluid therapy has to be more individualized. Because the exact determination of blood volume is not clinically possible at every timepoint, there have been different approaches to assess fluid requirements, such as goal-directed protocols guided by invasive and less invasive devices.

This article focuses on laboratory volume determination, capillary dynamics, aspects of different fluids and how to clinically assess and monitor perioperative blood volume.

Measurement of cardiac output during exercise in healthy, trained humans using lithium dilution and pulse contour analysis

The aim of this study was to evaluate the use of pulse contour analysis calibrated with lithium dilution in a single device (LiDCO) for measurement of cardiac output (Q) during exercise in healthy volunteers. We sought to; (a) compare pulse contour analysis (PulseCO) and lithium indicator dilution (LiDCO) for the measurement of Q during exercise, and (b) assess the requirement for recalibration of PulseCO with LiDCO during exercise. Ten trained males performed multi-stage cycling exercise at intensities below and above ventilatory threshold before constant load maximal exercise to exhaustion. Uncalibrated PulseCO Q (Qraw) was compared to that calibrated with lithium dilution at baseline Qbaseline, during submaximal exercise below (Qlow) and above (Qhigh) ventilatory threshold, and at each exercise stage individually (Qexercise). There was a significant difference between Qbaseline and all other calibration methods during exercise, but not at rest. No significant differences were observed between other methods. Closest agreement with Qexercise was observed for Qhigh (bias ± limits of agreement: 4.8 ± 30.0%). The difference between Qexercise and both Qlow and Qraw was characterized by low bias (4-7%) and wide limits of agreement (> ± 40%). Calibration of pulse contour analysis with lithium dilution prior to exercise leads to a systematic overestimation of exercising cardiac output. A single calibration performed during exercise above the ventilatory threshold provided acceptable limits of agreement with an approach incorporating multiple calibrations throughout exercise. Pulse contour analysis may be used for Q measurement during exercise providing the system is calibrated during exercise.

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.