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For several years a subcommittee of the Hawaii Department of Health has sought answers to the remarkable incidence of snorkel-related drownings and near drownings in Hawaii. Statistics over the years have supplied numerical information but available details concerning the clinical nature of these incidents have been lacking.

A number of volunteer members of the subcommittee have, over the past years, initiated a study to address this issue. Hawaii appears to be the focal point of numerous drownings, most of which are ocean-related and the majority of which involve tourists with predilection for ages over 50.

The Medical Examiner’s office has been assiduous in examining postmortem cases, but the nature of this form of demise makes it difficult to retrospectively reconstruct the reason for drowning in many cases.

A study in progress has resulted in our understanding that the usual proposed explanations for these events are not the cause; they include anxiety, panic, fatigue, inexperience, and for years the role of carbon dioxide rebreathing has been repeatedly eliminated as well. It has been demonstrated that some of these mysterious cases (and possibly the majority) are caused by hypoxia (lack of sufficient oxygen in circulation blood to support life). Lack of sufficient oxygen rapidly leads to functional failure of body systems, including and especially the brain.

Confusion, diminished consciousness, weakness, and loss of normal reflex responses are symptoms commonly experienced in this setting. Hypoxia in these cases results from onset of rapid accumulation of fluid flowing from capillaries into the air spaces (alveolae) in the lungs, which blocks entry of oxygen molecules into the capillary blood on its way to the heart.

Fluid in the alveolae is commonly referred to as pulmonary edema. Capillaries and alveolae anatomically and intimately share a common delicate membrane (alveolocapillary membrane) sandwiched between them. This membrane allows for oxygen, nitrogen, and carbon dioxide to transit between air and blood. It is permeable to water, which transits either way as well. The vacuum, or increase in negative pressure, required to maintain adequate volumes of ventilation in the alveolae during immersion promotes rapid onset of pulmonary edema (ROPE) and hypoxia under certain circumstances.

‘For years, this type of negative pressure pulmonary edema has been well known to anesthesiologists, scuba divers, and more recently has been recognized in swimmers. It is known to exist, for example, in mammals capable of high levels of ventilation and cardiac output of blood at high levels of effort. In the case of scuba events, it is referred to as immersion pulmonary edema.

The connection between hypoxia due to this form of ROPE and hypoxia resulting from snorkeling activities has not been well documented or studied in the past. Since initiation of this study there has been a sufficient number of observations in cases of individuals surviving these hypoxic episodes to be certain that this mechanism of death is indeed reality, but the incidence and multifaceted mechanisms involved in its genesis need further exploration and clarification.

The scope of this study is to obtain detailed information from as many drowning and near drowning cases of individuals snorkeling as possible in an attempt to understand demographics and distribution of these events in order to best identify the predisposing factors that increase the risk.

Could Long Airplane Rides Increase The Danger?

In the process of study are several of the obvious potential causes for excessive negative transthoracic pressure which can contribute to or induce ROPE. These include immersion and increased inspiratory resistance induced by various snorkel device designs.

Numerous devices have already been tested on equipment designed and fabricated to analyze snorkel airway resistance. There is no question that snorkels are responsible for increasing transthoracic pressure depending upon the degree of resistance added to other factors.

The study is also addressing the various comorbidities (chronic medical illnesses) which may play a role in increasing the risk of development of ROPE in this setting. A number of subclinical cardiac abnormalities which commonly go unrecognized because they produce little or no symptoms at usual levels of activity, include certain heart disturbances which impair distension of the muscle of the left side of the heart, as well as other congenital or acquired heart and lung abnormalities.

An interesting hypothesis being addressed relates to long-haul air travel which is required to arrive in Hawaii from virtually anywhere in the world. It is intriguing to consider the possibility that long periods of travel of this type in aircraft pressurized to altitudes greater than a given passenger’s habitats may result in subtle unrecognizable impairment of the alveolocapillary membrane and mechanisms that control pulmonary edema formation.

It is well known that mountain climbers may be affected in this fashion. More likely than not it may affect air travelers as well.

It is anticipated that by collating information as cases arise, analysis of the results can direct further study attempts to answer these and other outstanding questions.

It is hoped that additional interest in this subject will entrain the interest of other researchers so as to validate the concept sufficient to propose messages of prevention of adverse events of this type in the interests of ocean safety.