Drowning

Published on 14/03/2015 by admin

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Chapter 29 Drowning

Paul M. Middleton

EPIDEMIOLOGY

In Australia 39 children died from drowning in 2000/1, and the 5-year average was 35, a figure again reached in 2006/7. In 2006/7 277 people overall drowned, an increase of 13% on the 5-year average. Males of all ages, except those aged 0–4 years, were almost three times as likely as females to drown and, while the number of drowning deaths in lagoons and lakes dropped by 53% compared to the 5-year average, drownings at the beach increased by 39%. Deaths in over 55s remained stable at the average. The most common location of drowning among children was in domestic swimming pools, with the second commonest location being in the bath. Indigenous Australians are four times more likely to drown than other Australians, and alcohol or drug use was implicated in 14% of accidental drownings in Australia, of whom 79% were males.

PATHOPHYSIOLOGY

The concepts of ‘wet’ and ‘dry’ drowning, based on the presumption that a variable degree of laryngospasm occurs which, in some patients, prevents any aspiration of water or other substances into the airway, bronchial tree and lungs, were discarded at the World Congress on Drowning.

The International Liaison Committee on Resuscitation (ILCOR) advisory statement on drowning describes an involuntary period of laryngospasm secondary to the presence of liquid in the oropharynx or larynx. It has been described that most patients aspirate less than 4 mL kg^–1 of fluid and that approximately 10–20% of individuals maintain tight laryngospasm until cardiac arrest occurs and inspiratory efforts have ceased. This has been confirmed by autopsy studies, with 10% of patients showing no aspiration and approximately 20% of patients presenting with normal chest radiographs. Other sources suggest that drowning probably never occurs without aspiration to some degree.

What appears clear is that initial voluntary breath holding precedes a variable degree of aspiration of water, followed eventually by apnoea, with the common pathway in all drowning being profound hypoxia associated with acidosis and hypercapnoeia. This hypoxia not only leads to unconsciousness, loss of airway reflexes and aspiration, but also leads to the cardiovascular effects of drowning. These include extreme bradycardia, ventricular fibrillation and asystole, which are often exacerbated by hypothermia in cold waters. Hypothermia is common in child victims of drowning due to their large surface area:body mass ratio and, although hypothermia has been associated with a poor prognosis after drowning as it is related to the duration of submersion, it has also been associated with a better prognosis, particularly in children, presumably due to a protective effect on cerebral organ function with the rapid onset of low temperatures. There have been several cases reported of survival of both children and adults following submersion in cold water for up to 66 minutes.

Following early survival, lethal hypoxia may still develop. However, in these later instances it is due to the effects of surfactant disruption and abnormal function, atelectasis and intrapulmonary shunting. This profound secondary hypoxia may itself lead to respiratory failure and cardiac arrest.

In some groups of patients, aspiration of sand, silt, stagnant water, sewage and vomitus may result in bronchial occlusion, bronchospasm, inflammatory damage to alveolar capillary membranes, abscess formation and pneumonia. Late, atypical pneumonias may be caused by less common pathogens such as Aeromonas, Pseudallescheria and Burkholderia.

PRECIPITATING EVENTS

Drowning is sometimes precipitated by an injury or medical condition. Loss of consciousness for whatever reason may result in drowning, particularly concussion, stroke or cardiac arrhythmia; this last cause may be underestimated in older adults with ischaemic heart disease, but also in younger patients with unrecognised prolonged QT syndromes. Concussion may be associated with motor vehicle accidents or diving, as are serious trauma including cervical spine injuries. It is also important to recognise the role of intentional injury, homicide, suicide and child abuse.

OUTCOME

The commonest cause of death in hospitalised drowning patients is post-hypoxic encephalopathy. Other common causes of death are acute respiratory distress syndrome (ARDS), multi-organ dysfunction syndrome (MODS) or sepsis syndrome.

Generally speaking, judging prognosis after a drowning incident is difficult, but there are recognised associations with particular outcomes. Pointers towards poor prognosis include:

• prolonged submersion

• delayed or no basic life support

• requirement for basic life support (BLS)/advanced life support (ALS) in the emergency department

• unreactive pupils

• acute resuscitation efforts lasting over 25 minutes.

Individuals with any of these features have been reported to survive without disability, although the chances of successful resuscitation to a favourable neurological outcome are usually slim. Importantly, age has no independent association with outcome.

Examination

Examination should follow a systematic course as described by ABCDE. Treatment should follow the same schema and should be delivered in systems when any abnormality is identified.

Drowning victims may be classified into one of four groups based on presenting physical examination:

• asymptomatic

• symptomatic

• airway compromise—partial or complete requiring prior intervention

• breathing—hypoxia, dyspnoeic, tachypnoeic, decreased oxygen saturation

• circulation—bradycardia, tachycardia, hypotension

• dysfunction—decreased level of consciousness, localising signs, other neurological deficit, anxiety

• exposure and environment—hypothermia, metabolic acidosis

• cardiopulmonary arrest

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