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Drowning | Risk factors, pathogenesis and pre-hospital management

“Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid. Drowning outcomes are classified as death, morbidity and no morbidity”
Drowning is the process of experiencing respiratory impairment from submersion



In 2004 an estimated 388 000 people died worldwide as a result of drowning. This total, taken from Global Burden of Disease figures, makes drowning the third leading cause of death from unintentional injury (after road traffic accidents and falls). It is a significant underestimate, as it includes only deaths from ‘accidental drowning and submersion’, excluding drowning due to cataclysms (floods), assaults, suicides, and transport accidents. Drowning is a global public health concern which results in significant morbidity and mortality.




Risk factors for drowning include

Sex
Males are more likely to die or be hospitalized due to drowning than females. Overall the male rate of drowning is more than twice that of females. Studies suggest this is due to increased exposure to water and riskier behaviour such as swimming alone, drinking alcohol before swimming alone and boating.
Age
Children under 5 have the highest drowning mortality rates of any age group worldwide.
Socioeconomic status
Ethnic minority groups have higher rates of drowning mortality rates, possibly due to differences in opportunities to learn to swim.
Occupation
The occupational mortality amongst Alaskan fisherman is 116 per 100 000, with an estimated 90% of deaths due to drowning

Prevention
The interventions which follow are based on research evidence (where availa­ble) and expert opinion.

Remove the hazard
• Drain unnecessary accumulations of water (e.g. baths, ponds, buckets, etc.).

Create barriers
• Build flood control embankments in flood-prone areas.
• Implement and enforce mandatory isolation fencing for swimming pools.
• Where possible, fence around rural fish ponds, construction ditches (where filled with rainwater) and other bodies of water around houses and in the community.
• Encourage fencing around rural homes in proximity to water (e.g. farmhouses).
• Encourage the use of grills over water wells.

Protect those at risk

• Promote “learn to swim” programs for primary school children, especially in low- and middle-income countries.
• Increase access to public swimming pools to promote learning to swim.
• Swimming and water-safety skills are associated with significant reductions in drowning fatalities.
• Increase awareness of the need to supervise children both in and outside the home, and establish parent groups or other childcare mechanisms in rural communities, especially around harvest times.
• Instruct children to avoid entering fast-flowing streams, and not to swim alone.
• Train lifeguards for regular deployment in supervised swimming locations.
• Harmonize internationally the flags and symbols used for beach safety.
• Educate and/or legislate against consuming alcohol while boating or around large bodies of water.
• Increase education in boat safety regulations as well as of the need for per­sonal floatation devices when boating.
• All boats and larger vessels should be checked regularly for safety, includ­ing safety equipment, and never exceed the maximum passenger capacity for which they were designed.

Counter the damage
• Train the general community in resuscitation. Timely resuscitation initiated by layperson bystanders increases the survival prospects of paediatric drowning victims.

Pathogenesis

The physiologic consequences of drowning are due primarily to hypoxic-ischemic and reperfusion injuries. The devastating long-term neurologic consequences of drowning occur almost exclusively among patients who have drowning-associated asphyxial cardiac arrests. Patients who do not experience cardiac arrest rarely have significant sequelae.

Drowning-associated asphyxia is caused by laryngospasm, apnea, or pulmonary aspiration of water. Furthermore, when the victim loses consciousness, he or she may vomit and aspirate swallowed water. The resultant hypoxia, hypercarbia, and acidosis can decrease myocardial contractility, elevate pulmonary artery and systemic vascular resistance, and produce cardiac arrhythmias (bradycardia, asystole, ventricular fibrillation). With sufficient duration of submersion, the asphyxial insult inevitably results in cardiac arrest.

Lung injury in drowning patients is characterized by abnormal surfactant function and increased capillary endothelial permeability. This injury leads to increased intrapulmonary shunting, ventilation/perfusion mismatch, atelectasis, and poor lung compliance, which cause further hypoxemia and hypercarbia. When severe enough, this process may lead to acute respiratory distress syndrome (ARDS). Contrary to earlier beliefs, pulmonary injuries from fresh water and saltwater drowning typically do not differ substantially.

The most devastating consequence of drowning and the most frequent cause of death is hypoxic-ischemic injury to the brain. The degree of central nervous system injury is related to the duration of untreated cardiac arrest, the effectiveness of initial cardiopulmonary resuscitation (CPR), and secondary cerebral injuries after resuscitation (eg, further hypoxic episodes, inadequate cerebral blood flow, cerebral edema, and hyperthermia).

Pre-hospital care

Early resuscitation has been shown to play a significant role in increasing survival. Rescuers may find an individual at any stage of the drowning process and consequently a drowning victim may require anything from simple observation to rapid and continued resuscitation. As with all emergencies, management should be aimed at ensuring adequate Airway, Breathing and Circulation, with cervical spine stabilisation if the patient is unresponsive or there is any possibility of trauma.

In the event of cardiac arrest cardiopulmonary resuscitation (CPR) should be commenced in all patients and continued during transfer to hospital, as hypothermia may make the detection of vital signs difficult in the pre-hospital setting. The adage that hypothermic patients are not dead until they are ‘warm and dead’ has good foundation – recovery from prolonged submergence is well documented in children and, although it is less common in adults, there are some remarkable case reports of survival.

Rescue breaths can be given whilst the patient is still in the water however chest compressions are often ineffective due to problems with buoyancy. The patient should be removed from the water at the earliest opportunity, in a supine or foetal position where possible. There is a recognised risk of circulatory collapse during or following rescue from immersion in water.

Use of the Heimlich manoeuvre to expel water from the lungs has been shown to be ineffective and should not be attempted, as it may cause the patient to vomit and aspirate. Where available, supplemental high-flow oxygen should be given as soon as possible. Ventilation via any method may require higher pressures than expected, due to poor compliance, however, if the pre-hospital team are unable to ventilate the patient, airway obstruction should be suspected.

Traditionally, rescuers have been advised to begin re-warming as soon as possible, by removing the victim from wet clothing, before wrapping them in blankets and administrating warmed fluid (where facilities allow). However, there is now good evidence that therapeutic cooling improves neurological outcome in out-of-hospital ventricular fibrillation cardiac arrest. Further research is required to determine whether this evidence can be extended to victims of drowning.




Reference
https://www.who.int/news-room/fact-sheets/detail/drowning
https://emedicine.medscape.com/article/772753-overview
https://www.cdc.gov/homeandrecreationalsafety/water-safety/waterinjuries-factsheet.html
https://www.msdmanuals.com/professional/injuries-poisoning/drowning/drowning
https://bestpractice.bmj.com/topics/en-us/657
https://www.healthline.com/health/how-long-does-it-take-to-drown

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