Background: A new method using repeated freediving to assist persons trapped in cars under water was previously found to be efficient: victims could be rescued from 5-8 m within 4´16 – 6´22, with average dive times of 28s (14-46s). The present aim was to reveal if this method would expose rescue divers to risk of hypoxic syncope, which may occur at an arterial oxygen saturation (SaO2) of around 50%.
Methods: In order to determine risk of hypoxic syncope, SaO2 was measured ( Nonin Onyx 9500) after swimming dives to 8 m depth and of 30, 35, 40 and 45s duration . Four divers made 2 dives each per duration.
Results: After the dives of 45s duration, mean nadir SaO2 was 90%, and less desaturation resulted in shorter dives. Full recovery was always reached within 50s. Thus, there was an adequate safety margin, allowing assistance from the other diver should problems arise.
Discussion: As the dive durations used in the alternating freediving method resulted in SaO2 levels well above those associated with syncope, with complete recovery between dives, the risk of syncope is very small. For safe operations it is important to follow the alternating freediving guidelines considering diving duration and depth, and to use adequately trained divers.
Conclusions: Repeated freediving is not exposing rescuers to danger of hypoxic syncope, and the metod could be incorporated in the surface rescuers training.