Agreement of precordial and subclavian Doppler ultrasound venous gas emboli grades in a large diving data set

Introduction: Doppler ultrasound is used to detect inert gas bubbles in the body following decompression from dives. Two sites may be monitored, the precordial (PC) and subclavian (SC) positions. PC is the predominant site, allowing observation of bubbles returning from the entire body. However, the SC site provides unambiguous signals, whereas the PC site is noisy and difficult to grade. This retrospective study compared agreement of PC and SC Doppler data. Methods: Datasets from the large University of California at San Diego Doppler database were graded on the Kisman Masurel (KM) scale and included: one PC measurement at rest followed by three during movement (n = 4 measurements); this was repeated for the left (n = 4 measurements) and right (n = 4 measurements) SC veins, producing a set of 12 grades. Primary analysis included: agreement between resting PC and SC grades, between movement PC and SC grades, and for unmatched grades, whether the SC grade was higher or lower than PC. Results: Four-hundred and fifty-three datasets were available (5,436 individual recordings). At rest, 281 (62.0%) PC and SC grades matched (weighted kappa agreement 0.33, 95% CI ± 0.04), while only 176 (38.9%) movement grades matched (0.29, ± 0.02). Of the unmatched data, resting SC grades were higher than PC in 70.3% and lower in 29.6%; after movement, SC grades were higher in 45.8% and lower in 54.2%. Conclusions: These data revealed a large discrepancy between PC and SC grades. Overall, this suggests that Doppler observations from both positions will give the most comprehensive representation of bubble load.