Ability of the third-generation FloTrac/Vigileo software to track changes in cardiac output in cardiac surgery patients: a polar plot approach.

OBJECTIVE: To evaluate the ability of the third-generation (3.01) of FloTrac/Vigileo monitor (Edwards Lifesciences, Irvine, CA) to follow variations in cardiac output (∆CO) using the new polar plot approach. DESIGN: Prospective interventional study. SETTING: Single hospital university study. PARTICIPANTS: Twenty-five patients referred for cardiac surgery. INTERVENTIONS: CO was measured simultaneously by 3 to 5 bolus thermodilution (COtd measurements), using a pulmonary artery catheter and by arterial pulse contour analysis, using the FloTrac/Vigileo (COvi). Data were collected at eight time points: before incision, after sternotomy, before and after protamine sulfate infusion, at the start of sternal closure, at the end of surgery, on arrival to intensive care unit, and after a standardized volume expansion with 500 mL of hetastarch 6%. MEASUREMENTS AND MAIN RESULTS: One-hundred thirty-five pairs of CO data were collected; the mean bias of all CO measurements corrected for repeated measures was 0.2 L/min with limits of agreements of -3.3 L/min and +2.9 L/min. The percentage error was 66.5%. The polar plot analysis included 71 significant ∆CO and showed a mean polar angle of -3.4 degrees with 95% polar percentage error equivalent limits of -61 to 55; 69% of analysed data points fell within the 30-degree limits and provided a correct polar concordance rate. CONCLUSIONS: Third-generation FloTrac/Vigileo software still lacks the accuracy to reliably detect changes in cardiac output (∆CO) in cardiac surgery. Improvements to FloTrac/Vigileo CO algorithm and software still are needed in this particular setting.

Combination of continuous pulse pressure variation monitoring and cardiac filling pressure to predict fluid responsiveness.

To assess if combining central venous pressure (CVP) and/or pulmonary capillary wedge pressure (PCWP) information with arterial pulse pressure variation can increase the ability to predict fluid responsiveness in patients under general anesthesia. This study is a retrospective analysis of patients scheduled for coronary artery bypass surgery and monitored with a pulmonary artery catheter who underwent a volume expansion after induction of general anesthesia. Among the 46 patients studied, 31 were responders to volume expansion. CVP similar to PCWP, was a poor predictor of fluid responsiveness, as indicated by low values of areas under the receiver operating characteristic curves [0.585 (95 % CI 0.389-0.780) and 0.563 (95 % CI 0.373-0.753) respectively, p = 0.76]. The area obtained for PPV was 0.897 (95 % CI 0.801-0.992) with a threshold value of 12 %. The sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio was 83.9 %, 86.7 %, 6.29 and 0.19 respectively. Combining information on right and/or left cardiac filling pressures with PPV did not increase the ability to predict whether a patient will be a responder or a non-responder to volume expansion. The ability to identify a potentially fluid responsive patient was no better using PPV plus cardiac filling pressures when compared to using PPV alone. Therefore, if PPV values are being monitored in a patient, CVP and PCWP values do not provide additional information to predict fluid responsiveness.

Bedside assessment of passive leg raising effects on venous return.

OBJECTIVE: Passive leg raising (PLR) provides a reversible fluid-loading challenge and can be used to predict fluid responsiveness. The amount of blood volume recruited by this maneuver called stressed volume (Vs) is unknown. The present study aims to assess the quantitative effects of passive leg raising on venous return at bedside. METHODS: We conducted a prospective interventional study. Nine mechanically ventilated postoperative cardiac surgery patients with preserved left ventricular function were enrolled. Cardiac output (CO) was continuously monitored by PiCCO™ via the pulse contour method. Ten second intervals of inspiratory breath holding at four plateau pressures (5, 15, 25 and 35 cm H(2)O) were performed to measure the relationship between blood flow (CO) and central venous pressure (CVP). These were used to determine mean systemic filling pressure (Pmsf) and Vs. Patients were studied at three successive steps: semirecumbent position, after PLR and back in the semirecumbent position after volume expansion (VE). RESULTS: Similar to VE, PLR significantly increased Pmsf from 19.7 (17.0-22.6) mmHg at baseline to 22.0 (18.5-27.8) mmHg (p <0.05). CO increased 11.1% (9.5-20) with PLR and 14.8% (4.2-19.9) with VE. Venous return resistance was unchanged throughout the three conditions, whereas the the pressure gradient for venous return (Pmsf-CVP) increased during PLR (p = 0.058) and during VE (p < 0.05). Baseline circulatory compliance was 1.14 (0.52-2.65) ml mm Hg(-1) kg(-1). Vs increased to 3.5 (1.1-3.9) ml kg(-1) with PLR. CONCLUSIONS: The effect of transient hemodynamic changes on venous return induced by passive leg raising can be directly measured in intensive care patients using inspiratory-hold procedures. This technique makes quantification of PLR feasible and could be used clinically to assess fluid responsiveness.

Management of metformin-associated lactic acidosis by continuous renal replacement therapy.

BACKGROUND: Metformin-associated lactic acidosis (MALA) is a severe metabolic failure with high related mortality. Although its use is controversial, intermittent hemodialysis is reported to be the most frequently used treatment in conjunction with nonspecific supportive measures. Our aim was to report the evolution and outcome of cases managed by continuous renal replacement therapy (CRRT). METHODOLOGY AND PRINCIPAL FINDINGS: Over a 3-year period, we retrospectively identified patients admitted to the intensive care unit for severe lactic acidosis caused by metformin. We included patients in our study who were treated with CRRT because of shock. We describe their clinical and biological features at admission and during renal support, as well as their evolution. We enrolled six patients with severe lactic acidosis; the mean pH and mean lactate was 6.92±0.20 and 14.4±5.1 mmol/l, respectively. Patients had high illness severity scores, including the Simplified Acute Physiology Score II (SAPS II) (average score 63±12 points). Early CRRT comprised either venovenous hemofiltration (n = 3) or hemodiafiltration (n = 3) with a mean effluent flow rate of 34±6 ml/kg/h. Metabolic acidosis control and metformin elimination was rapid and there was no rebound. Outcome was favorable in all cases. CONCLUSIONS AND SIGNIFICANCE: Standard use of CRRT efficiently treated MALA in association with symptomatic organ supportive therapies.

Transpulmonary thermodilution in a pediatric patient with an intracardiac left-to-right shunt.

Monitoring of cardiac output (CO) in the perioperative period and in seriously ill pediatric patients is of major importance for medical management. Hemodynamic monitoring, using transpulmonary thermodilution (TPTD) via a single thermal indicator injection, allows for measurements of CO, volumetric variables and extravascular lung water (EVLW). We describe and explain the influence of a left-to-right shunt on TPTD curve characteristics and EVLW measurements in a young child undergoing a surgical atrial septal defect repair. We suggest that these specific changes in the TPTD curve and the overestimation of EVLW detected by current device, in absence of gas exchange abnormalities, could be indicators of existing circulatory shunts in pediatric patients.

Relations between respiratory changes in R-wave amplitude and arterial pulse pressure in mechanically ventilated patients.

INTRODUCTION: R-wave obtained from the electrocardiogram depends on ventricular stroke volume. We assessed the relationship between respiratory variations in R-wave (DeltaRDII) and in pulse pressure (DeltaPP) during general anesthesia. METHOD: R-wave amplitude was measured from standard lead II (RDII). Maximal RDII (RDIImax) and minimal RDII (RDIImin) were determined over one respiratory cycle. DeltaRDII was calculated as 100 x [RDIImax-RDIImin]/([RDIImax + RDIImin]/2. DeltaRDII and DeltaPP were simultaneously recorded. RESULTS: There was a significant relationship (r = 0.79; P < 0.001) between DeltaRDII and DeltaPP. A DeltaRDII > 13% detected patients with a DeltaPP > 13% with an 89% sensitivity, and an 88% specificity. CONCLUSION: DeltaRDII and DeltaPP are related in this setting.

Ability of pleth variability index to detect hemodynamic changes induced by passive leg raising in spontaneously breathing volunteers.

INTRODUCTION: Pleth Variability Index (PVI) is a new algorithm that allows continuous and automatic estimation of respiratory variations in the pulse oximeter waveform amplitude. Our aim was to test its ability to detect changes in preload induced by passive leg raising (PLR) in spontaneously breathing volunteers. METHODS: We conducted a prospective observational study. Twenty-five spontaneously breathing volunteers were enrolled. PVI, heart rate and noninvasive arterial pressure were recorded. Cardiac output was assessed using transthoracic echocardiography. Volunteers were studied in three successive positions: baseline (semirecumbent position); after PLR of 45 degrees with the trunk lowered in the supine position; and back in the semirecubent position. RESULTS: We observed significant changes in cardiac output and PVI during changes in body position. In particular, PVI decreased significantly from baseline to PLR (from 21.5 +/- 8.0% to 18.3 +/- 9.4%; P < 0.05) and increased significantly from PLR to the semirecumbent position (from 18.3 +/- 9.4% to 25.4 +/- 10.6 %; P < 0.05). A threshold PVI value above 19% was a weak but significant predictor of response to PLR (sensitivity 82%, specificity 57%, area under the receiver operating characteristic curve 0.734 +/- 0.101). CONCLUSION: PVI can detect haemodynamic changes induced by PLR in spontaneously breathing volunteers. However, we found that PVI was a weak predictor of fluid responsiveness in this setting.