The need for optimisation of post-dive ultrasound monitoring to properly evaluate the evolution of venous gas emboli.

Abstract

Audio Doppler ultrasound and echocardiographic techniques are useful tools for investigating the formation of inert gas bubbles after hyperbaric exposure and can help to assess the risk of occurrence of decompression sickness. However, techniques, measurement period and regularity of measurements must be standardised for results to be comparable across research groups and to be of any benefit. There now appears to be a trend for fewer measurements to be made than recommended, which means that the onset, peak and cessation of bubbling may be overlooked and misreported. This review summarises comprehensive Doppler data collected over 15 years across many dive profiles and then assesses the effectiveness of measurements made between 30 and 60 minutes (min) post-dive (commonly measured time points made in recent studies) in characterising the evolution and peak of venous gas emboli (VGE). VGE evolution in this dive series varied enormously both intra- and inter-individually and across dive profiles. Median, rather than mean values are best reported when describing data which have a non-linear relation to the underlying number of bubbles, as are median peak grades, rather than maximum, which may reflect only one individual's data. With regard to monitoring, it is apparent that the evolution of VGE cannot be described across multiple dive profiles using measurements made at only 30 to 60 min, or even 90 min post-dive. Earlier and more prolonged measurement is recommended, while the frequency of measurements should also be increased; in doing so, the accuracy and value of studies dependent on bubble evolution will be improved.