Drowning

AUTHOR: DR JENNY BAKER

What is drowning?

Drowning is defined as the experience of respiratory impairment secondary to submersion or immersion into water (3). Submersion occurs when the upper airway is beneath the surface of the water, whilst immersion refers to the airway remaining above the water. 

Drowning outcomes are categorised as mortality, morbidity, and non-morbidity (3). The Wilderness Medical Society (WMS) does not recommend the use of other terms to categorise drowning including wet, dry, or secondary.  There is also no distinction between salt and freshwater drownings and their management. This is because, regardless of the situation, the pathophysiology is triggered hypoxia, and this is the target of treatment (3,4).

Why is it important?

Drowning causes over 200,000 deaths a year worldwide, making it the third leading cause of death by accidental injury (5). The World Health Organisation recognised it as a major public health issue in 2012, describing it as ‘one of the most preventable, neglected and pressing public health issues’ (5). It kills two thirds of the number that die from malnutrition and half the number that die from malaria, and disproportionately affects low- and middle-income countries, children and males (5). Furthermore, these numbers are likely to significantly underestimate the problem as many data sources don’t include fatalities associated with intentional drowning (suicide or homicide), natural disasters or migrant boat accidents (5). Read the WHO report on the global impact of drowning here: https://www.who.int/publications/i/item/global-report-on-drowning-preventing-a-leading-killer

In the UK, there are around 600 drowning deaths annually (6). These figures do not report non-fatal drownings or rescues that prevent drowning; for example, the Royal National Lifeboat Institution (RNLI) reported over 3000 rescues and many more preventative actions in 2021 (7). These figures highlight the importance of water safety both on and off expedition.

Although there are some cases in which drowning occurs in warm water, these are usually related to hot tubs or exertional hyperthermia in competitive swimmers (8). This article will focus on the physiological phenomena that occur on entering cold water (<20°C) and how this can result in drowning.

Cold Water Immersion

Breath hold time

A person’s ability to hold their breath contributes to their ability to prevent drowning. It allows them to prevent aspiration whilst submerged, under waves or when struggling to keep their head above water. It is determined by oxygen consumption, carbon dioxide production and respiratory drive (8).  

Cold Shock Response 

Immersion into cold water causes sudden cooling of cutaneous thermal receptors. This triggers a dramatic increase in sympathetic activation, causing an involuntary gasp, followed by hyperventilation, and accompanied by peripheral vasoconstriction, tachycardia and hypertension. This is known as the cold shock response (CSR). This reduces breath holding through an increase in oxygen consumption and a high respiratory drive.  It can also result in drowning through aspiration directly, if the gasp occurs while submerged (9). 

The cold shock response can be reduced by habituation, which occurs after just a few short immersions in 15°C water. However, studies have shown that this habituation is likely to be reduced by anxiety (10), potentially moderating its benefits in accidental immersion. 

Diving Response 

The diving response occurs on submersion of the face in cold water and breath holding. It is characterised by a parasympathetically driven bradycardia. It is increased in diving mammals and children and is thought to be a protective mechanism to reduce oxygen consumption, increasing breath hold time and, subsequently, survival underwater (11). 

Autonomic Conflict

Rapid submersion in cold water can cause simultaneous stimulation of the diving and cold shock responses. This results in opposing autonomic action on the heart: the diving response increases parasympathetic activity, to cause bradycardia, whilst the cold shock response triggers sympathetic activity, stimulating a tachycardia. This conflicting action within the heart can cause arrhythmias. This is known as autonomic conflict.

A further increase in parasympathetic activity when a breath hold is released increases the incidence of arrhythmias at this time. These arrhythmias are normally benign, but if combined with other predisposing factors, such as QT prolongation, coronary vessel disease or ischaemic heart disease they can be fatal (11).  The true extent of autonomic conflict as a cause of death is not known as arrhythmias are undetectable on autopsy and terminal gasps will likely result in aspiration of water, giving the appearance of drowning (11).

Figure 1: The effects of cold-water immersion resulting in arrhythmias (11).

Swim Failure 

The longer a person is immersed, the risk of swim failure increases, making them unable to hold their head above the water or to self-rescue. This may occur through fatigue or hypothermia. 

Water is thermoneutral at 32°C; below this environmental heat loss exceeds heat production through thermogenesis. Below 25°C, swimming, or treading water to float, becomes detrimental to thermal control, as the increase in thermogenesis is not sufficient to outweigh the increase in conduction as limbs move through cold water (12). As nerves and muscles cool, lack of coordinated muscle contraction can make swimming impossible. In colder water, or longer immersion, reduction in core body temperature can directly cause loss of consciousness through hypothermia. Both can result in submersion and drowning (8). In view of this, the HELP (Heat Escape Lessening Posture) position (3) is recommended for those with a buoyancy aid to maintain body temperature (See figure 2). This involves drawing knees into the chest, crossing ankles and bringing arms in; this reduces heat loss and conserves energy. For more about hypothermia, check out Dr Lucy Longbottom’s post here!

Figure 2: The HELP (Heat Escape Lessening Posture) https://rnli.org/safety

The drowning process

Figure 3 explains the processes that lead to a person being unable to prevent submersion and aspirating or inhaling water, resulting in the respiratory impairment that characterises drowning. 

Tipton and Montgomery described the drowning process in 6 steps (13); the first of which is the struggle to maintain the airway above the water. This begins at the point that ‘swimming becomes struggling’ and is characterised by the ‘Instinctive Drowning Response’; a lack of waving or calling for help, horizontal arm movements and repeated submersion of the airway. It lasts up to a minute, which likely relates to the length of anaerobic activity possible before exhaustion. As a rescuer, it is vital to recognise this response and the urgency of this presentation. 

Following this, a person will become submerged and begin breath holding, causing hypoxaemia and hypercapnia to develop, increasing the respiratory drive, and, eventually, causing resumption of breathing. An adult is not normally able to breath hold to the point of loss of consciousness (13). This resumption of breathing will lead to aspiration. 

Aspirated water enters the lungs and disrupts surfactant function, in turn disturbing membrane integrity and allowing shifts in fluid, plasma and electrolytes. There is also an increase in surface tension and reduction of lung compliance. These combine to result in acute pulmonary oedema, ventilation-perfusion mismatch, and reduced gas exchange. This occurs from around 2.5ml/kg of aspirated water (8). Loss of efficient gas exchange causes further hypoxia and hypercapnia, resulting in loss of consciousness and, eventually, cardiac arrest. 

Submersion into, and aspiration of, ‘icy’ (<6°C) water, may be protective. The entrance of ice-cold water into the lungs causes rapid cooling of blood, and subsequently of the heart, lungs and brain. This rapidly induced hypothermia can dramatically reduce oxygen consumption and extend submersion time without sequelae (8). The most extreme example of this follows a young woman who fell into an icy river while skiing (14). She was submerged for over an hour and had a core temperature of 13.7°C on arrival to hospital and no spontaneous circulation for two hours. Five months after the event she had some residual neurological deficit but had already returned to working, hiking and skiing. It’s thought that the rapid onset of hypothermia reduced her oxygen requirement so much that her body’s oxygen stores were sufficient for survival.

Figure 3: The Physiological Pathways to Drowning. This diagram shows how the above phenomena lead to drowning. Adapted from (13)

Figure 4: Classification of the grades of drowning as assessable in the field with associated mortality. (3)

How to manage a drowning situation

The highest predictor of outcome following drowning is submersion time (15). Thus, removing people from the water is vital, but so is keeping yourself safe. The WMS only recommends that rescuers enter the water to rescue a drowning person if they are trained to do so and confident with the environment. The mantra ‘Reach, throw, row, don’t go’ emphasises the use of throwing flotation devices or going by boat, if possible, rather than entering a body of water (3).

Once on land, a full assessment can be made to inform management. Drowning is described by 6 grades of severity: dependent on oxygen saturations, pulmonary auscultation, and signs of shock (9). Figure 4 shows the associated mortality with each of these stages in a way that can be assessed and defined on expedition, while figure 5 summarises the management of these grades.

Figure 5: The grades of severity of drowning and management of each, adapted from (15). 

The mainstay of treatment is the reversal of any hypoxia (15). Those who are asymptomatic can be discharged at the scene and continue with activity. Those with added sounds on auscultation should be observed for signs of deterioration for 6 hours, following which they may also continue as normal, if they remain asymptomatic. WMS suggests that, if evacuation from an expedition may be lengthy or difficult, it should be arranged for anyone with abnormal auscultation following submersion and can be stepped down if there is no deterioration throughout the observation period (3). Any respiratory distress, shock or reduction in mental state requires evacuation and further medical treatment. 

Respiratory assistance should be given as required and will range from high flow oxygen to mechanical ventilation in those with respiratory arrest (15). Prior to arrival at a hospital, supplemental oxygen should be given in whatever form is available to reduce hypoxia (3).

Cardiac Arrest 

Cardiac arrest in drowning occurs due to hypoxia and is rarely a shockable cardiac rhythm (9). Consequently, compression-only CPR is not recommended in drowning victims, and 5 ‘rescue breaths’ should be given before the first round of chest compressions (3). Rescuers that are trained to do so can give these peri-rescue prior to extraction from the water (9). Furthermore, WMS recommend that application of AED pads should not be a priority and should not take precedence over chest compressions due to the high likelihood of pulseless electrical activity or asystole (3). Despite this, Brayne et al. found good outcomes from cardiac arrest secondary to drowning with 25% survival from out of hospital cardiac arrest in a study of drowning admissions to hospitals in the southwest (16). 

CPR should continue until the patient is has been in asystole for more than 25 minutes, although WMS highlight awareness of the likelihood of unfavourable outcomes in those that have been submerged more than 30 minutes in >6°C water, or 90 minutes in water below 6°C. Consideration should also be given to the role of concomitant hypothermia, and CPR should continue during attempts at rewarming (3). Read more about the management of hypothermia. WMS also highlights the importance of ceasing resuscitation efforts if, at any point, the rescue team is at risk (3).

Complications of drowning

The major complication arising from drowning is hypoxic brain injury. The risk of severe neurological sequelae and death is almost exclusively determined by length of submersion, with likelihood of survival with good neurological function being almost 0% following submersion of more than 25 minutes (15). Early extraction from the water and administration of supplemental oxygen aids to reduce this. As discussed above, this risk often informs decision making on management in the drowned patient. 

Whilst water entering the lungs can introduce pathogens, most patients do not require antibiotic treatment and empirical therapy has not been shown to improve outcomes (15). Pneumonia is most likely to develop in the days following a drowning event and the risk increases in those who require mechanical ventilation (15). Due to the high prevalence of atypical organisms, sputum and blood cultures should direct antibiotic choice where possible (3). 

Cervical spine injuries and other trauma is uncommon in drowning situations. Unless there is a clear mechanism suggesting that C-spine trauma may have occurred, immobilisation should not take precedence over necessary airway management in a hypoxic drowning patient (3). 

Prevention of drowning

In recognition of the high numbers of deaths from drowning worldwide, the World Health Organisation released a public health prevention guide in 2017 in an attempt to address the ‘preventable and neglected public health issue’ (17). They highlighted important community measures to reduce drowning including raising awareness of the dangers of being around water, erecting barriers around bodies of water and promoting swimming lessons in all children (17).

Closer to home, the RNLI provide a lifeguard service at many of the UK’s beaches. They perform thousands of preventative actions a year (7) to stop people getting into trouble in the water. As well as educating those on the beach, they highlight safer areas for swimming on the beach and alert people that may be straying out of these areas. They also provide rescues for many who get into trouble before they submerge. All these actions prevent thousands of fatal and non-fatal drownings yearly in the UK (7). 

Whilst the above examples are wider, community-based approaches, a lot can be learnt from them when going on expedition. Team members can be educated on safety around water prior to the expedition, including the recommendation to avoid alcohol when around open water; a significant risk factor for drowning (3). For water-based expeditions, WMS suggest that the ability to swim 25m, tread water and hold a floating position is preferable for participation (3). Wearing a lifejacket if taking part in a water-based activity also helps to prevent submersion. During pre-participation screening, those at higher risk of drowning (coronary artery disease, QT prolongation or seizure disorders) should be counselled about this risk and methods of mitigating it (3).

Take home messages

• Prevention is better than cure – educate team members before departure and wear floatation devices if undertaking water-based activities.
• If someone does enter the water unexpectedly, or gets into difficulty in the water, extraction from the water as soon as possible is vital. 
• Rescuer safety is the most important – ‘Reach, Throw, Row, Don’t Go!’
• Hypoxia is the cause of drowning related mortality and morbidity – give supplemental oxygen as soon as possible. 
• Consider the effects of hypothermia, especially in individuals who were in the water for a prolonged period. 
• Give 5 rescue breaths prior to starting CPR if there is no pulse.

Are you interested in learning more about drowning and other water related conditions?

If so, why not check out our Marine Medicine course? Whilst you’re there, why don’t you take a look at our other courses too?