Chapter 41. Near drowning
‘Wet’ drowning
The individual aspirates water into the lungs, after an episode of breath holding until the victim cannot hold the breath any longer. On inspiration, much of the water is probably swallowed, but a proportion is inhaled. This inhaled water blocks the airways, only a proportion of it getting as far as the alveoli. The result is hypoxia, which after a short period results in hypoxic cardiac arrest and hence death. It only requires 10 mL of inhaled water per kilogram of body weight to be fatal.
Fresh water in the alveoli is absorbed, resulting in haemolysis of red blood cells and haemodilution. Sea water, being hypertonic, causes withdrawal of water from the blood and no haemolysis.
‘Dry’ drowning
No (or very little) water actually enters the lungs. This may be because of laryngeal spasm but is more likely to be because of primary cardiac arrest due to stimulation of the vagus nerve by cold water. It is this mechanism that causes the death of people who drop into cold water. It is likely that this is the cause of death in ‘spray drowning’ – deaths that occur in people on the surface of rough water. Vagal sensitivity is increased by hypothermia which occurs rapidly in cold-water immersion.
‘Dry’ drowning accounts for between 10% and 25% of drowning deaths.
In the UK, drowning is the fourth leading cause of death in men under the age of 35 years and the second leading cause of death in children, with 40% of all drowning deaths occurring in children under the age of 5 years.
‘Near drowning’ is the term applied to a survivable drowning episode
Effects of immersion in cold water
• Sudden rapid deep breath
• Rapid shallow breathing at maximal lung capacity
• Reduced ability to hold the breath (very low temperatures)
• Peripheral vasoconstriction
• Reduction in circulating volume
• Fluid shifts between compartments
• Sudden fall in BP on removal from the water in a vertical position.
Hypothermia is routine in patients removed from the water
The diving reflex
The diving reflex occurs in many mammals but its significance in adults is doubtful. It does seem to be more developed in children and probably explains why young children can survive prolonged cold-water immersion.
A reflex bradycardia occurs when cold water stimulates areas of the face and neck. This bradycardia, associated with the rapid cooling caused by cold-water immersion, can be protective of the victim by rapidly reducing the oxygen requirements of the brain and other tissues with a high metabolic requirement.
Other effects
The cold water, partly by producing hypothermia and partly by a direct cold effect on the pharynx, causes intense vagal stimulation, which results in a severe bradycardia or asystole. For this reason, manipulation of the airway in a near-drowned person can cause cardiac arrest.
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