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.
Effects of near drowning
The effects of near drowning are variable and depend on a number of factors: the temperature of the water, the length of time immersed and the amount of inhaled water. There is little difference between salt and fresh water.
Initial (primary) effects
Victims progress through:
• Hypoxia
• Confusion
• Lethargy
• Unconsciousness.
Patients frequently report that they experience a ‘high’. Several divers have described this phase as being ‘pleasant’, in that they no longer cared what would happen to them. If the hypoxia continues, then cardiac arrest will occur as a result of hypoxic myocardium. The victim will also suffer the associated problems of hypothermia and the loss of hydrostatic pressure (as described above). In very cold water an asystolic arrest can occur owing to intense vagal stimulation.
Delayed (secondary) effects
Water inhaled into the lungs causes damage; this is multifactorial and includes the development of pulmonary oedema and a reduction in the amount of surfactant. As a result, the subject may initially have few symptoms but may develop marked respiratory problems over several hours (usually 4–8). This problem is known as secondary drowning.
The other secondary problem is infection. Victims will have swallowed and inhaled water that may well contain microorganisms from sewage effluent or rat urine contamination (common in canals). Thus, consideration should be given to the development of infectious illness such as Weil’s disease.
Diagnosis
The diagnosis would seem to be easily deduced from the circumstances; however, the picture is more complex, as the patient is likely to be hypothermic and may have other injuries associated with a fall or dive into water or sustained while in the water. The classic injury to the cervical spine occurs in the person who dives into shallow water thinking that it is deeper than it actually is.
The clinical picture may vary from a cardiac arrest (which may be ventricular fibrillation or asystole) to a conscious patient with few signs or symptoms but who is at risk of secondary drowning.
Airway
Airway findings are variable. The airway may be totally patent, it can be obstructed by the tongue owing to unconsciousness or it may be obstructed by water in the oropharynx.
Breathing
Breathing may be normal, but the chest should be auscultated as the presence of crepitations may indicate that secondary drowning is likely to occur. Breathing may be absent, either with or without cardiac arrest.
Circulation
The pulse is highly variable; many of the changes will be cold related. A profound bradycardia may occur in relation to vagal stimulation.
Treatment
Removal from the water
It is very important that the patient should be kept as horizontal as possible when removed from the water because of the loss of hydrostatic pressure to the body. This is especially important if the patient is hypothermic and it is this combination that has frequently led to deaths in the past.
Airway and breathing
The airway should be checked and cleared with care being taken to maintain the neck in midline immobilisation if cervical spine injury cannot be ruled out. Protecting the neck is difficult while in the water but an inflated life-jacket (not a buoyancy aid) gives some neck protection.
• Suction of the oropharynx may be used to clear the airway, but it must be remembered that in the hypothermic patient, any airway manipulation could cause vagal stimulation or laryngeal spasm
• It is impossible to remove water from the smaller airways because of the capillary attraction between the wall and the water. This water will be absorbed if the patient survives
• The patient should not be put in the head-down position, as this does not help remove water from the lungs and will raise the intracranial pressure, which may already be elevated from the preceding cerebral hypoxia
• Chin lift and jaw thrust should be used but head tilt avoided, if there is a possibility of neck injury. Guedel or nasal airways can be used, but care is needed as vagal stimulation can occur
• In the apnoeic patient, ventilation should be commenced. This is best undertaken via an endotracheal tube or laryngeal mask, as bagging via a mask tends to blow air into the stomach, which usually contains water, and thus increases the risk of regurgitation of stomach contents
• The breathing patient may be placed in the recovery position if spinal injury is excluded, the combination of hypoxia and swallowed water being a good stimulus for vomiting.
Circulation
In the absence of a palpable central pulse, cardiopulmonary resuscitation should be commenced and the appropriate cardiac arrest protocol followed. It should be appreciated that ventricular fibrillation may not be ‘shockable’ if the core temperature is below 30°C. Cardiopulmonary resuscitation on its own can occasionally cure the patient by correcting the hypoxia (this has been recorded a number of times in children).
Bradycardias should be treated with caution. If caused by vagal stimulation their treatment improves the situation, but in the severely hypothermic patient, it is frequently detrimental. A variety of other arrhythmias may be present due to hypothermia. Hypothermia, the loss of hydrostatic pressure and the presence of other injuries all contribute to a relative hypovolaemia. Intravenous access and warmed fluids are therefore required.
Ventricular fibrillation may not be ‘shockable’ if the core temperature is below 30°C.
Hypothermia
The near-drowned patient is frequently hypothermic. Once the patient is out of the water, wet clothes should be taken off as early as possible, otherwise continued heat loss will result from evaporation. First-aid measures must be aimed at preventing further heat loss.
Associated Injuries
The possibility of injuries must be considered and appropriate measures taken. The presence of hypovolaemia from a significant haemorrhage considerably complicates the clinical picture.
Further treatment in hospital
In the patient with cardiac arrest, continued resuscitation will take place until the patient is warm but still not responding. Immersion hypothermia can be treated by rapid rewarming, in which the patient is placed in a bath at 40°C with legs and arms dangling out. This should only be done where the cooling has been rapid. This treatment is only practicable and safe if the patient is conscious and sufficiently alert to cooperate. It should not be used for the unconscious patient. If a bath is unavailable a shower is an alternative, but is less efficient and requires even greater cooperation from the patient.
The patient should be kept under observation owing to the risks of secondary drowning and should not be discharged home unless the blood gases and chest X-ray are normal and the patient is free from any symptoms, with a clear chest on auscultation.
For further information, see Ch. 41 in Emergency Care: A Textbook for Paramedics.
