Teaching Self-Assessment of Doppler Ultrasound for Bubble Grading in Divers: Learning Curve, Reliability, and Surveying Precision.

BackgroundObserving modern decompression protocols alone cannot fully prevent Diving Accidents especially in repetitive diving. Audio Doppler bubble measurements to estimate supersaturation are done in special professional settings only, being not available for the broad community of sports SCUBA divers. In case SCUBA divers without medical and ultrasound training could learn audio Doppler self-assessment for reliable bubble grading on a stable skill level and with an efficient single teaching intervention, this skill could add significantly to diving safety. MethodsWe taught audio Doppler self-assessment of the subclavian vein and cardiac precordial probe position to 41 divers in a 45-minute standardized training session. Assessment was made of 684 audio Doppler measurements by both the trained divers and a medical professional plus additional 2D-echocardiography as reference. ResultsAll air dives were within normal sports diving limits and decompression bubbles were observable via echocardiography in 32.3% of all measurements. The specificity of audio bubble detection was 96.1% but the sensitivity was low for lower bubble grades, increasing to 25%, 35% and 67% for higher echo-detected bubble grades 3, 4 and 5. The number of attempts to achieve a reliable venous signal within 30 seconds was 13 at the subclavian position and 18 at the precordial position. More bubble positive measurements could be detected at the precordial position for both self and medical professional assessment. The performance level of the taught skill remained stable over six months without further practice.ConclusionAudio Doppler self-assessment can be learned by people without medical and ultrasound training and a reliable venous signal can be achieved after a comparably steep learning curve. However, accurate bubble grading is not possible using audio Doppler as only higher bubble grades can be detected. Nevertheless, this qualitative finding can be important in self-evaluating decompression stress and potentially help the diver to judge on measures for avoiding decompression accidents.