Immersion pulmonary edema (IPE) continues to be a central focus of dive medicine researchers and clinicians. Late last week, at the 2017 EUBS Annual Meeting, four scientists presented five different studies on the subject.
It appears that IPE is significantly more common than previously reported. In a two year period (2014-16) one hyperbaric facility in Cozumel diagnosed 40 cases of IPE among recreational scuba divers1. On the other side of the world, there were 21 cases of IPE reported among French military rebreather divers in a six year period2.
In the Cozumel study, an analysis of risk factors was attempted. For each case of IPE, there were two non-IPE recreational diving cases admitted to the same facility. Patients involved in the IPE cases in this series were found to be older than patients in the corresponding non-IPE cases. The non-IPE cases did more multi-day, repetitive, deeper and longer dives than IPE cases, and had a history of regular exercise more often. This could be interpreted as showing that IPE occurs more frequently in less fit divers, but more evidence is required to come to a definitive conclusion. Data from this study was presented in poster form, and we can only hope that this will be published as a full length paper at some point, with more details and data analysis.
Military divers involved in the French rebreather study were categorically both young and fit. The main factor that triggered the IPE in these cases was negative pressure breathing, which is present in back mounted rebreathers with lung centroid deeper than the breathing bag. In 30% of cases the situation was exaggerated by improper rebreather adjustment.
A third study report presented a case of pulmonary edema associated with Takotsubo syndrome in a 75-year old woman3. The woman had previously performed 100 dives. On the day of incident she performed a rapid ascent after 23 minutes at 84 feet. The reason for the ascent was not reported. Twenty minutes after surfacing, she started feeling the chest pain, pain in the bottom of the lungs, and difficulty breathing. Within an hour the patient reported further increased difficulty breathing was admitted to the emergency department. Initial evaluation with echocardiography revealed pulmonary edema, and further test found signs of pneumomediastinum with signs of acute coronary syndrome and dysfunction of the heart with characteristics of Takotsubo syndrome. The patient also underwent a coronarography which showed normal coronary arteries. Takotsubo syndrome is known as a stress induced cardiomyopathy and patients typically recover well, unless in case of aquatic activities, they drown. This patient probably decided to end the dive due to symptoms caused by this condition and associated pulmonary edema. During the ascent, she also experience a lung over-pressurization which resulted in the pneumomediastinum.
A fourth presentation showed that IPE may occur more often as the disabling condition preceding the drowning4. While at the surface in a vertical position, swimmers lungs are at a greater pressure than surface air, and they must breathe against negative pressure caused by their immersion. While this is occurring, their heart is additionally stressed due to a shift of blood from the extremities, to their chest cavity, also caused by immersion. It is expected that some water will seep into the lungs from the bloodstream in this situation, but in divers who are struggling due to panic or lack of buoyancy, this could develop into full pulmonary edema, flooding the alveoli completely and disabling a diver, who would then drown.
The final presentation on IPE covered risks involved in breath hold diving. While all activities that involve immersion in water have some risk of IPE, the risk involved in breath hold diving may be greater than previously understood. According to this presentation, 25% of elite breath hold divers have experienced IPE. The study used underwater echocardiography to study the mechanisms of IPE during breath hold diving, and preliminary reports indicate that IPE in breath hold diving is associated with hypoxia, pulmonary capillary congestion, and left ventricular dysfunction.
Garcia-Magna E. Risk factors for scuba diving pulmonary edema in recreational divers. p. 78
Gemp E et al. Immersion pulmonary edema with rebreather among French military divers from 2009 to 2015: role of hydrostatic imbalance. p 74.
GArcia-Magna E. Takotsubo syndrome associated with scuba diving pulmonary edema (SDPE). p 79
Castagna O, MacIver D. Is cardiogenic pulmonary edema a critical step in the pathophysiological mechanism of drowning? p. 20.
Marabotti C. Breath hold diving-induced acute pulmonary edema. New pathophysiological insight from underwater Doppler echocardiography. p. 76