Comparison of superior vena caval and femoroiliac venous pressure measurements during normal and inverse ratio ventilation

Objective: The aim of this study was to estimate the agreement between superior vena caval pressure (SVCP) and femoroiliac venous pressure (FIVP) measurements by using short (<20 cm) femoral catheters commonly used in an adult intensive care unit. In addition, the effects of two modes of Ventilation on agreement were assessed. Design: Measurements of central venous pressure were recorded from both sites by using the same pressure transducer connected to the catheters via a three-way stopcock. SVCP and FIVP were recorded at 5-min intervals for 40 mins with the patient in the supine position. Recordings were taken from ventilated patients during a randomized crossover sequence of normal and inverse ratio Ventilation (IRV). Analyses included Pearson's correlation (r), intraclass correlation (r(l)), Bland-Altman plots, and repeated measures analysis of variance with crossover tests for period and period-treatment interactions. Setting: Adult intensive care unit. Patients: Adult intensive care patients. Measurements: Central venous pressure. Results: Twenty-two patients were enrolled in the study, giving 162 paired measurements; r was .97 (p < .0001), and r(i) was .96. The bias for SVCP-FIVP measurements was -0.75 mm Hg (95% confidence interval = -1.31 to -0.18), with 95% limits of agreement of -3.30 to 1.81 mm Hg. Seventeen patients were suitable for randomization to normal ratio ventilation and IRV. IRV significantly increased SVCP and FIVP (p < .002). Tests for the effect of mode of ventilation on agreement (p = .36), for period (p = .26), and for period-treatment interaction (p = .84) were not significant. Conclusion: The study showed excellent overall agreement with acceptable clinical agreement for SVCP and FIVP measurements that was not affected by changing the mode of ventilation. IRV significantly increased central venous pressure measurements from both catheter sites but had no effect on agreement.