Recently, several people have contacted me asking for my take on Dr. Pollock’s article, Loss of Consciousness in Breath-Holding Swimmers. Several of these readers read the article as advocating the position that prolonged underwater breath holding activities are safe, provided that they are not preceded by excessive hyperventilation. At The Redwoods Group, we have long advocated for a clear, posted rule prohibiting prolonged underwater breath holding. We stand by that guidance and encourage the research into this issue to continue so that we can develop a robust combination of awareness, education, and appropriate rules and guidelines to keep all swimmers safe.

Dr. Pollock’s article presents a well researched, well written, and valid position—but not a consensus one. There is room for disagreement and respectful skepticism to the conclusions that he draws in the article.

Specifically, I question the conclusion that “blackouts occurring in most swimming pool cases, particularly those in shallow pools, are almost undoubtedly driven by excessive hyperventilation alone…” and that “a normal person cannot voluntarily breath-hold long enough to lose consciousness without hyperventilation” in so far as those statements are not consistent with incidents we have investigated.

Since 2006, Redwoods has investigated over 200 unconscious submersions in lifeguarded facilities. In 16 of these events, breath holding was the most immediate factor that led to unconsciousness—what is commonly referred to as “Shallow Water Blackout.” 2 of these events resulted in fatalities.

In only 5 of the 16 events did our investigations reveal that excessive hyperventilation took place prior to the breath holding activity. In several additional cases we suspect that excessive hyperventilation took place, either intentionally or unintentionally on the part of the victim. Hyperventilation is certainly a high risk factor for Shallow Water Blackout. But we have also investigated cases with no reported hyperventilation, and cases in which the victim and witnesses could clearly state that there was no hyperventilation prior to breath holding, only that the victim only took one or two deep breaths before the breath holding swim.  These cases appear to be inconsistent with Dr. Pollock’s conclusion that two to three deep breaths prior to prolonged breath holding should fall within a safe limit.

I also disagree with Dr. Pollock’s assertion that the prohibition of breath holding “is a fairly irrational response to the problem” if the statement is intended to include recommendations to prohibit long, prolonged, or excessive breath holding as opposed to any and all breath holding. Although it is not a nuanced solution, the clarity of the rule provides a guidepost for lifeguards and swim coaches to observe and correct behavior. Even where hyperventilation does take place prior to breath holding, it may prove to be effectively unobservable by a lifeguard, and therefore impossible to correct. It is true that breath control and limited breath holding is inherent in swimming activity, and it is unclear how much is “long,” “prolonged,” or “excessive.” But the clear posting of this rule also appears to have been effective as the frequency and severity of breath-hold related unconscious events has dropped significantly at our partners’ facilities since we began aggressively advocating for it.

Dr. Pollock’s article stresses the importance of educating swimmers on the dangers and safe limits of breath holding and hyperventilation, and I agree that this is an important component in any strategy to eliminate injury and death due to Shallow Water Blackout. But our investigations convince me that this cannot be sufficient alone, and I don’t think we can state with confidence what the safe limits for hyperventilation and breath holding are yet.

Lifeguards, swim coaches, free divers, academics, military personnel, and the family members of those who have lost loved ones unnecessarily to Shallow Water Blackout will need to continue to work together to study what we know, identify what we need to know, and develop additional rules, guidelines, and best practices to prevent Shallow Water Blackout in all areas of aquatics.

Gareth Hedges

Senior Associate General Counsel

The Redwoods Group