Cardiac index measurements during rapid preload changes: a comparison of pulmonary artery thermodilution with arterial pulse contour analysis.

STUDY OBJECTIVE: To compare cardiac index (CI) values obtained by pulmonary artery thermodilution (CIPA), arterial thermodilution (CITD), and arterial pulse contour analysis (CIPC) during rapid fluid administration, as accurate and rapid detection of CI changes is critical during acute preload changes for guiding volume and vasopressor therapy in critically ill patients, and the accuracy of CIPC during acute changes in loading condition is currently unknown. DESIGN: Prospective clinical study. SETTING: Cardiac surgical intensive care unit of a university hospital. PATIENTS: Seventeen American Society of Anesthesiologists (ASA) physical status II and III patients, aged 32 to 76 years, with normal left ventricular function during the early postoperative period after elective coronary artery bypass graft surgery. MEASUREMENTS: After baseline determinations of CIPA, CIPC, and CITD were made, fluid loading was performed using 10 mL times body mass index of hydroxyethyl starch 6%. CIPA, CIPC, and CITD were determined, and changes in CI (DeltaCI) were calculated. Fluid load was repeated until no increase in stroke volume index (DeltaSVI <10%) was achieved. MAIN RESULTS: Regression analysis between CIPA/CIPC, CIPA/CITD, and CIPC/CITD revealed r2 = 0.92, r2 = 0.92, and r2 = 0.98. Regression analysis between DeltaCIPA/DeltaCIPC, DeltaCIPA/DeltaCITD, and DeltaCIPC/DeltaCITD revealed r2 = 0.57, r2 = 0.67, and r2 = 0.74, respectively. Bland-Altman analysis was used to determine accuracy and precision of the 3 methods compared. The mean differences (m) and SD between DeltaCIPA/DeltaCIPC, DeltaCIPA/DeltaCITD, and DeltaCIPC/DeltaCITD resulted in m = -1.01%, SD = 6.51%; m = -0.83%, SD = 5.80%; and m = -0.33%, SD = 4.65%, respectively. CONCLUSION: Compared with pulmonary artery thermodilution, arterial pulse contour analysis reflects relative changes in CI during rapid changes of preload with clinically acceptable accuracy.

Influence of tidal volume on left ventricular stroke volume variation measured by pulse contour analysis in mechanically ventilated patients.

OBJECTIVE: Real-time measurement of stroke volume variation by arterial pulse contour analysis (SVV) is useful in predicting volume responsiveness and monitoring volume therapy in mechanically ventilated patients. This study investigated the influence of the depth of tidal volume (V(t)) on SVV both during the state of fluid responsiveness and after fluid loading in mechanically ventilated patients. DESIGN AND SETTING: Prospective study in a university hospital, adult cardiac surgery intensive care unit. PATIENTS AND PARTICIPANTS: 20 hemodynamically stable patients immediately after cardiac surgery. INTERVENTIONS: Stepwise fluid loading using colloids until stroke volume index (SVI) did not increase by more than 10%. Before and after fluid loading V(t) was varied (5, 10, and 15 ml/kg body weight) in random order. MEASUREMENTS AND RESULTS: Pulse contour SVV was measured before and after volume loading at the respective V(t) values. Thirteen patients responded to fluid loading with an increase in SVI greater than 10%, which confirmed volume responsiveness at baseline measurements. These were included in further analysis. During volume responsiveness SVV at V(t) of 5 ml/kg (7+/-0.7%) and SVV at V(t) of 15 ml/kg (21+/-2.5%) differed significantly from that at V(t) of 10 ml/kg (15+/-2.1%). SVV was correlated significantly with the magnitude of V(t). After volume resuscitation SVV at the respective V(t) was significantly reduced; further, SVV at V(t) of 5 ml/kg(-1) (5.3+/-0.6%) and 15 ml/kg (16.2+/-2.0%) differed significantly from that at V(t) of 10 ml/kg (10.2+/-1.0%). SVV and depth of V(t) were significantly related. CONCLUSIONS: In addition to intravascular volume status SVV is affected by the depth of tidal volume under mechanical ventilation. This influence must be regarded when using SVV for functional preload monitoring.