Drowning is defined as ‘death due to obstruction of the air passages by any fluid.’ While typically occurring in water, drowning can occur in any fluid. Finding a body in water does not necessarily indicate death due to drowning. Drowning can occur in a few inches of water, and complete knowledge of the circumstances and location of the body should be available to make a proper and accurate determination of the cause of death.
Drowning is a diagnosis of exclusion – a body found in water, with no other significant finding attributing to death will be diagnosed to have died due to drowning. Most deaths due to drowning are accidental or suicidal. Certain clues like presence of ligatures around hands and feet suggest a criminal act.
The investigation of death in a body recovered from water is difficult, given the variety of mechanisms possibly in play. The examination must investigate all these potential mechanisms as well as attempt to answer other questions that may assist in the investigation. Reason for death in a body that retrieved from the water:
- Died of natural causes before entering the water
- Died of natural causes while entering the water
- Died of natural causes after entering the water
- Died from exposure and hypothermia in the water
- Died of injuries sustained before entering the water
- Died of injuries sustained while entering the water
- Died of injuries sustained after entering the water
- Died from submersion, but not drowning
- Died from drowning – respiratory distress caused by aspiration of water into the lungs
Even when the cause of death is drowning, it is important for the investigation to examine the cause for entering the water as well as the reason for failure of survival. These questions are invariably linked to the manner of death and should consider the circumstances as well as all other evidences related to the case. When sufficient evidence is available, it may be reasonable to attempt to answer these questions. Lack of definite signs should be interpreted with caution due to the variety of mechanisms involved and should perhaps be left to the judiciary to perform a complete investigation of all evidences and provide a definitive answer as to the circumstances of death.
Evidence of immersion
Immersion of the body in water brings about a number of changes that are extremely variable. Many factors influence the changes including tidal or non-tidal, water temperature, clothing worn, base of the water body, animal activity etc.
Generally, skin of hands and feet appear wrinkled and macerated, fingertips appear swollen, within a few hours of immersion in cold water. In addition, cutis anserina undergo post-mortem rigidity and so cause the hair on skin to ‘stand’. Soon, layers of skin separate, leading to peeling, ‘degloving’ and ‘destocking’. Loss of epidermal layers due to peeling may cause pigmentation changes, which can mislead as to the ethnic origin of the deceased.
Estimation of post-mortem interval from signs of immersion, and post-mortem changes in a body recovered from water can be extremely erroneous and unreliable. A very generalized and arbitrary ‘rule of thumb’ states that ‘decomposition in water in temperate climates occurs at roughly half the rate of a body left in air.’ Gaseous distension becomes apparent after a few days, after which skin and hair are loosened and detached. Despite the hair being detached from dermal attachments, the skin and hair remain apparently in situ for a few weeks. A few weeks after, gaseous decomposition and bloating causes the body to ‘surface’, leading to its discovery.
Post-mortem artefact and immersion
Bodies recovered from flowing rivers as well as tidal waters may sustain injuries following contact with sand, rocks, and other underwater structures. Collision of a body with propeller blades typically causes deep ‘chop’ wounds and/ or lacerations.
Other post-mortem artifacts typically seen in bodies recovered from water include damage by aquatic life. The decomposition and dissolution of soft tissue from around the joints causes loss of integrity of skeletal structure, especially of the hand and feet. These small bones may be detached and swept away by current.
In addition, ante-mortem injuries may get washed and appear pale on examination, in the absence of histopathological examination, this can lead to misdiagnosis as a post-mortem injury. Bodies recovered from water invariably tend to have some injuries and it becomes imperative for the post-mortem examination to seek histo-pathological investigation to help estimate the time of injury.
Pathophysiology of drowning
Immersion in fluid, results in obstruction to the gaseous exchange by replacement of oxygen by the fluid both in the environment as well as in the alveoli. As a result, there is mechanical obstruction due to replacement of air as well as electrolyte imbalance caused by the fluid. This results respiratory distress due to pulmonary surfactant insufficiency, pulmonary edema, alveolitis, hypoxaemia and metabolic acidosis. In addition, exposure to cold water can lead to hypothermia, causing cognitive impairment, thereby increasing the risks of wrong decisions and aspiration of water.
Signs of drowning
The classical finding associated with drowning are the effects of submersion and could be seen in any death where the body is submerged post-mortem. They are neither diagnostic not sensitive for drowning. As already discussed, drowning is a diagnosis of exclusion and a complete autopsy examination with no other significant findings, in a body recovered from water, will lead to the conclusion of drowning.
Alternative mechanisms of death
Dry drowning is a form of death due to immersion where signs of aspiration are absent at autopsy. Alternative explanations include trauma, intoxication, cardiac arrhythmias etc.
Stimulation of trigeminal nerve in the pharyngeal/laryngeal mucosa causes reflex apnea, bradycardia and peripheral vasoconstriction called the ‘diving response’. This is seen to increase in anxiety/fear, temperature under 20°C and alcohol intoxication.
The cold shock response on contact with water causes respiratory effects including prolonged gasping, hyperventilation, and hypoxia, as well as cardiovascular effects like tachycardia, increased cardiac output, hypertension and cardiac irritability. These changes make the body susceptible to cardiac arrhythmias, especially ventricular fibrillation.
Sudden contact with water, as seen in drowning, causes activation of both diving and cold shock responses, which is thought to precipitate supraventricular tachyarrhythmia.
The role of alcohol in drowning
Alcohol levels are frequently elevated in victims of drowning. While the association has been shown to be significant, a causal relationship has not been established. One hypothesis, that is obvious, is the incapacitation caused by alcohol intoxication and the associated loss of inhibitions resulting in pursuit of dangerous tasks, with loss of co-ordination and fatigue causing submersion and eventual death. Another theory summarises that peripheral vasodilatation associated with intoxication results in hastening of the effects of hypothermia.
The confirmatory diagnosis of drowning as cause of death is extremely difficult. In the past, post-mortem blood electrolyte levels, especially chloride concentration, and specific gravity have been analyzed to separate fresh and seawater drowning. However, such tests are of no utility in the diagnosis of drowning. Recent studies have proposed blood strontium analysis as a marker of drowning, but has not found widespread acceptance.
Diatoms are microscopic organisms ubiquitously present in sea and fresh water. They have a siliceous capsule that survives acid digestion. The presence of diatoms in organs (kidneys and brain) and bone marrow was widely accepted to be confirmatory for diagnosis of drowning.
However, recent studies have found diatom to be ubiquitous in food and the environment. Diatoms have been found in non-drowning deaths and have been absent in document cases of drowning. Some authors have proposed DNA analysis to match the species of diatoms found in the water with those found in the organs. However, this has also been challenged by assertions that diatoms vary at different depths in the same body of water.
Therefore, diatomology, study of diatoms, must be used with caution and only in context with other available evidence(s), where it may prove to be an important piece of corroboration.