Inter-observer variation in reading ambulant venous pressure from invasive venous pressure curves: The need for clear guidelines

Objective: To assess the inter-observer variation between three experts by reading ambulant venous pressure (AVP) from graphs of intravenous pressure measurements. Method: Invasive venous pressure measurement in a dorsal foot vein was performed in 38 legs with and 50 legs without a history of objectively diagnosed proximal deep vein thrombosis during a standardized exercise. Three experts independently estimated AVP from the pressure curves. Presence of post-thrombotic syndrome was determined for each leg according to the criteria of Prandoni. Results: For each observer, the association between the presence of post-thrombotic syndrome and the level of AVP readings was statistically significant (P < 0.001). Median AVP readings by the three experts for all graphs were 51.4, 43.0 and 32.2 mmHg, showing systematic differences in the way AVP was estimated. The random inter-observer variation was expressed as the standard deviation of the differences in readings by a pair of experts. For the three pairs, these standard deviations were 13, 10 and 10 mmHg, respectively. Conclusion: Even though AVP readings from the three experts in this study seemed as correct as those reported in the literature, there is proof of large systematic and random errors in estimating AVP from intravenous pressure measurement graphs. It is likely that other phlebologists would show at least similarly large measurement error. In order to improve the situation, clear reading instructions should be devised, based on consensus between experts in the field of intravenous pressure measurements.

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