Accuracy of impedance cardiography for evaluating trends in cardiac output: a comparison with oesophageal Doppler.

BACKGROUND: Impedance cardiography (ICG) enables continuous, beat-by-beat, non-invasive, operator-independent, and inexpensive cardiac output (CO) monitoring. We compared CO values and variations obtained by ICG (Niccomo™, Medis) and oesophageal Doppler monitoring (ODM) (CardioQ™, Deltex Medical) in surgical patients. METHODS: This prospective, observational, single-centre study included 32 subjects undergoing surgery with general anaesthesia. CO was measured simultaneously with ICG and ODM before and after events likely to modify CO (vasopressor administration and volume expansion). One hundred and twenty pairs of CO measurements and 94 pairs of CO variation measurements were recorded. RESULTS: The CO variations measured by ICG correlated with those measured by ODM [r=0.88 (0.82-0.94), P<0.001]. Trending ability was good for a four-quadrant plot analysis with exclusion of the central zone (<10%) [95% confidence interval (CI) for concordance (0.86; 1.00)]. Moderate to good trending ability was observed with a polar plot analysis (angular bias: -7.2°; 95% CI -12.3°; -2.5°; with radial limits of agreement -38°; 24°). After excluding subjects with chronic obstructive pulmonary disease, a Bland-Altman plot showed a mean bias of 0.47 litre min(-1), limits of agreements between -1.24 and 2.11 litre min(-1), and a percentage error of 35%. CONCLUSION: ICG appears to be a reliable method for the non-invasive monitoring of CO in patients undergoing general surgery.

[Influence of open chest conditions on pulse pressure variations]. / Influence de l'ouverture du thorax par sternotomie sur les variations respiratoires de la pression pulsée.

OBJECTIVES: Pulse pressure variations are used to assess fluid responsiveness in mechanically ventilated patients. The accuracy of this index in open chest conditions remained unclear. The aim of the study was to evaluate the effect of open chest conditions on pulse pressure variations. STUDY DESIGN: Non-interventional prospective study. METHODS AND PATIENTS: Twenty-eight mechanically ventilated patients scheduled for open-heart surgery were included. Pulse pressure variations, peak aortic velocity, and stroke volume were measured before and after thoracotomy with pericardotomy. Measurements were made at each step and compared. RESULTS: Neither pulse pressure variation nor peak aortic velocity and nor stroke volume variation were modified by open chest conditions (median=5% [interquartile range=6] vs 4% [6], p=NS), (20% [11] vs 17% [12], p=NS and 11% [7] vs 10% [3], p=NS) respectively. Pulse pressure variations were correlated to stroke volume before thoracotomy (r'=-0.432; p=0.02) and after thorocatomy (r'=-0.433, p=0.02). CONCLUSION: In these studied patients, preload dependancy indices were not modified by open chest conditions. Pulse pressure variations remained correlated to stroke volume even after thoracotomy.