Comparison of different techniques of central venous pressure measurement in mechanically ventilated critically ill patients

Background. Several techniques exist for measuring central venous pressure (CVP) but little information is available about the accuracy of each method. The aim of this study was to compare different methods of CVP measurements in mechanically ventilated patients. Methods. CVP was measured in mechanically ventilated patients without spontaneous breathing using four different techniques: 1) end expiratory CVP measurement at the base of the "c" wave (CVPMEASURED), chosen as the reference method; 2) CVP measurement from the monitor averaging CVP over the cardiac and respiratory cycles (CVPMONITOR); 3) CVP measurement after a transient withdrawing of mechanical ventilation (CVPNADIR); 4) CVP measurement corrected for the transmitted respiratory pressure induced by intrinsic PEEP (calculated CVP: CVPCALCULATED). Bias, precision, limits of agreement, and proportions of outliers (difference > 2 mm Hg) were determined. Results. Among 61 included patients, 103 CVP assessments were performed. CVPMONITOR bias [-0.87 ( 1.06) mm Hg] was significantly different from those of CVPCALCULATED [1.42 (1.07), P < 0.001 and CVPNADIR (1.04 (1.29), P< 0.001]. The limits of agreement of CVPMONITOR [< 2.96 to 1.21 mm Hg] were not significantly different to those of CVPNADIR (-1.49 to 3.57 mm Hg, P-0.39) and CVPCALCULATED (-0.68 to 3.53 mm Hg, P = 0.31). The proportion of outliers was not significantly different between CVPMONITOR (n = 5, 5%) and CVPNADIR ( n = 9, 9%, P = 0.27) but was greater with CVPCALCULATED (n = 16, 15%, P = 0.01). Conclusions. In mechanically ventilated patients, CVPMONITOR is a reliable method for assessing CVPMEASURED. Taking into account transmitted respiratory pressures, CVPCALCULATED had a higher proportion of outliers and precision than CVPNADIR.