Knowledge of central venous pressure (CVP) is considered valuable in the assessment and treatment of various states of critical illness and injury.
Objectives: We tested a noninvasive means of determining CVP (NICVP), by monitoring forearm volume changes in response to externally applied circumferential pressure to the upper arm veins.
Methods: Sixteen patients who were undergoing CVP monitoring as a part of their care had NICVP determined and compared with CVP. Volume changes were measured in the forearm with mercury-in-silastic strain gauge plethysmography. A pressure cuff is placed in the upper extremity. The cuff is inflated over 5s to a pressure above CVP but below diastolic arterial pressure (40 mmHg). This allows blood into the forearm but prevents venous return. After 45-60 s the cuff is rapidly deflated. NICVP was determined as the cuff pressure noted at the maximum derivative of the forearm volume decrease during deflation. NICVP was then compared to invasively measured CVP taken during the same period.
Results: A total of 48 trials (three per subject) were performed on 16 patients. The range of CVP recorded was 0-22 mmHg. The correlation between CVP and NICVP was 0.98 (95% CI: 0.95-0.98) (p<0.001). The bias between methods was 0.26 mmHg with the limits of agreement being 3.4 to -2.89 mmHg. When the average of three trials per patients was analysed the bias stayed at 0.26 mmHg but the limits of agreement improved to 2.54 and -2.03 mmHg.
Conclusion: NICVP as determined in this study may be a clinically useful substitute for traditional CVP measurement and may offer a valid tool for early diagnosis and treatment of acute states in which knowledge of CVP would be helpful.