When a shallow dive becomes dangerous: a barotrauma and its consequences

You don't always need to dive deep to have an unforgettable experience. Often, the full beauty of the underwater world is revealed just a few metres below the surface. However, these seemingly harmless ‘easy dives’ harbour risks that are easily underestimated. A case clearly shows how even a shallow dive can lead to a medical emergency.

"This will be your easiest nightdive." Kona, Hawaii.

The dive

An experienced recreational diver planned a shallow water dive with his group. The planned depth was around 10 metres, and the dive time was to be approximately 40 minutes. Initially, everything went according to plan. However, about halfway through the dive, the diver suddenly lost control of his buoyancy. Despite attempting to release air via the inflator, he ascended uncontrollably and at high speed to the surface. His diving partners ended the dive in a controlled manner and rushed to his aid.

At the surface, the accident victim was immediately rescued by his diving colleagues and passers-by. He was conscious, responsive and alert at all times. However, neurological symptoms appeared immediately after the ascent: complete paralysis and sensory disturbances in his left leg, and later also in his left arm. The group reacted in an outstanding manner: 100% oxygen was immediately administered via a diving regulator and the emergency services were alerted. At the same time, hyperbaric chamber treatment was organised and the patient was transported there by rescue helicopter.

Treatment

Upon arrival at the emergency room, the paralysis had subsided. The patient reported no persistent neurological deficits. Nevertheless, hyperbaric oxygen therapy was performed according to US Navy Table 6 – without complications. A neurological examination the next day showed no further paralysis, but slight sensory disturbances of varying degrees in the legs and slight unsteadiness when walking (ataxia).

Medical assessment

The clinical picture, with initial hemiparesis (one-sided paralysis of arm and leg) and spinal irritation phenomena (dissociated sensory disturbances) in conjunction with the uncontrolled emergency ascent, strongly suggests pulmonary barotrauma with subsequent arterial gas embolism – involving the brain and spinal cord. Decompression sickness was unlikely based on the depth and dive time. From a diving medicine perspective, the accident victim was recommended to take a break from diving for at least three months. Any return to diving should only be approved by experienced diving medicine specialists.

Conclusion: Shallow depth, high risk

This case illustrates that serious diving incidents with neurological symptoms can also occur at shallow depths. The immediate administration of 100% oxygen, the rapid alerting of the emergency services and the prompt hyperbaric oxygen treatment were decisive factors in the favourable outcome.

The incident underscores the enormous importance of proper buoyancy control, especially in shallow water. Boyle's law explains why: the closer you get to the water's surface, the greater the effect of volume changes. An ascent of just five metres from a depth of ten metres causes the BCD to increase in volume by around a third – at a depth of 40 metres, the increase would only be around 11%. This has a proportional effect on buoyancy – immediately. This means that a small mistake at shallow depths can quickly lead to an uncontrollable ascent.

Combined with the reflexive holding of breath in panic, this creates a dangerous mix. Failure to exhale causes the lungs to overinflate during ascent. This can lead to rupture of the alveolar-capillary membrane and direct entry of air into the arterial bloodstream – with potentially life-threatening consequences.

Prevention: weight, control, calm

Correct weighting is essential. In fact, excessive amounts of weight rarely lead to incidents – the opposite is much more common. Many divers experience buddies ascending uncontrollably at the end of a dive because they are carrying too little weight and the increased buoyancy resulting from their almost empty tank can no longer be sufficiently compensated.

In this specific case, the victim's equipment was thoroughly examined. No technical defects were found – especially not on the BCD or inflator. The cause of the uncontrolled ascent remains unclear, but human error in a particularly critical area – shallow water – is likely.