Abstract P88: Noninvasive Measurement of Central Venous Pressure
Introduction: Early goal directed therapy is considered to be valuable in the resuscitation of critically ill and injured patients including those with trauma, sepsis, and post resuscitation period of cardiac arrest. Central venous pressure (CVP) is often used as a parameter in optimizing fluid therapy in goal directed therapy, however, it is invasive. We tested a noninvasive means of determining CVP (NICVP), by monitoring upper arm blood flow changes in response to externally applied circumferential pressure to the upper arm veins.
Methods: Forty critically ill subjects who were undergoing CVP monitoring as a part of their care had NICVP determined and compared with CVP. Volume changes were measured in the upper arm using tetrapolar impedance plethysmography underneath a blood pressure cuff. The cuff was inflated over 5 seconds to a pressure above CVP but below diastolic arterial pressure. After 45 seconds the cuff was rapidly deflated. NICVP was determined as the cuff pressure noted at the maximum derivative of the volume increase under the cuff during deflation. NICVP was then compared by Bland-Altman analysis to invasively measured CVP taken during the same period.
Results: A total of 120 trials were performed on 40 subjects (3/subject). Recorded CVP values ranged from 2.7 to 20.7 mmHg. The mean difference between CVP and NICVP values was −0.04±1.4 mm Hg (95% CI: −0.29 to 0.21 mmHg). Limits of agreement determined by Bland-Altman analysis were −2.7 mmHg and 2.7 mmHg (95% CI: −3.24 to −2.25 mmHg for the lower limit and 2.18 to 3.14 mmHg for the upper limit). Correlation between CVP and NICVP was 0.94 (95% CI: 0.92 to 0.96; p<0.0001). Twenty-one subjects were mechanically ventilated. NICVP in these subjects demonstrated no degradation in performance due to mechanical ventilation.
Conclusion: NICVP as determined in this study may be a clinically useful substitute for invasive CVP measurement and may offer a tool for noninvasive execution of early goal directed therapy where knowledge of CVP would be helpful.