Immersion Pulmonary Oedema (IPO) is the accumulation of fluid in the lungs whilst immersed in water. In the United States it is referred to as Immersion Pulmonary Edema (IPE).
When we enter water, the hydrostatic pressure acts on the veins in our limbs resulting in an increase in the volume of blood returning to the heart.
When a diver is cold, peripheral vessels constrict to preserve heat pushing more blood to the heart. The increased volume can overwhelm the ability of the heart to pump blood from the lungs to the body, and the backpressure exerted allows fluid to leak into the airways.
Risk Factors
| Cardiovascular disease
(high blood pressure, irregular heart rhythms, previous heart attacks and heart valve abnormalities) |
Affects the hearts ability to cope with the increased blood return |
| Cold-water or stress | Causes an exaggerated blood pressure response. Can occur even in physically fit athletes. |
| Over-hydration | Increases total blood volume |
| Tight wetsuits/drysuits | Compresses veins increasing volume of blood returning to the heart. |
| Use of rebreathers | Creates a negative inspiratory pressure drawing fluid into the lungs |
| Exercise or exertion in water | Higher respiratory rate and effort of breathing creates a negative inspiratory pressure drawing fluid into the lungs. |
Symptoms
The symptoms of IPO include:
- shortness of breath
- difficulty breathing (often feeling as if you have run out of gas, or regulator failure)
- a cough with or without frothy/ blood stained sputum
- dizziness
If this happens at depth, divers need to ascend to the surface, which will drop their inspired partial pressure of oxygen (pp02). This higher pp02 may have been protective by keeping oxygen levels in the blood high enough to perfuse the brain, as the levels drop hypoxia results and the diver may lose consciousness.
If you think you or someone you are with has IPO the most important thing to do is to get out of the water, remove any tight clothing and call 999 as you may need supplemental oxygen.
Can I Dive Again?
If you have suffered from Immersion Pulmonary Oedema once, then you are at higher risk of this happening again. Divers or swimmers who have survived IPO describe it as a terrifying experience and are often hesitant to enter the water again. Certainly, we will encourage divers to think about giving up the sport due to the risk of fatality.
For some, giving up diving is not an option that they are willing to consider and they will want to continue, despite the risk involved. In these cases, we will discuss reducing any contributing risk factors and will refer them on to a dive cardiologist for further input. The cardiologist will assess their cardiovascular health and look at what changes could reduce risk. This may be a case of improving blood pressure control, altering the type of diving they do and avoiding cold water or exertion. Although these factors may reduce risk, there will always be a chance of IPO re-occurring so it is important that the diver fully comprehends this risk.
To learn more:
- Watch Dr Peter Wilmshurst, the worldwide expert on IPO, speak at the BSAC conference 2017.
- Read the December 2024 SPUMS/UKDMC Joint Position Statement.