Treatment at the scene of an accident is sometimes of little ultimate consequence with many disorders, but in drowning it often determines whether the victim lives or dies. The standard of first aid and resuscitation training of the rescuers therefore influences outcome.
In human drowning, deterioration after initial resuscitation is frequently recorded, and this influences management (see Chapter 23).
The temperature of the water and thus the degree of hypothermia may also be factors. Poorer results are achieved in warm water drowning.
In what was previously referred to as ‘dry’ drowning (in which the distal airway remains relatively dry because of early laryngospasm), the patient is hypoxic and, if rescued in time, may– make a rapid recovery. However, when laryngospasm relaxes and fluid aspiration occurs as it eventually does if the victim remains immersed, the result is drowning.
Other factors that influence outcome include the following: the presence of chlorine, other chemicals and foreign bodies; the aspiration of stomach contents; and the subsequent development of pneumonitis, respiratory infection and multi-organ failure.
One likely cause for delayed death is progressive lung injury2. ARDS develops in a significant proportion of drowning cases; usually hours or days after the aspiration. Other causes of death in the days after the event include cerebral hypoxia, secondary infections (usually of the lungs), renal failure and iatrogenic events.
Factors that negatively influence survival have been well documented by Modell:
- Prolonged immersion.
- Delay in effective cardiopulmonary resuscitation.
- Severe metabolic acidosis (pH <7.1).
- Asystole on admission to hospital.
- Fixed dilated pupils.
- Low Glasgow Coma Scale score (<5).
Nevertheless, none of these predictors is infallible, and survival with normal cerebral function has been reported with all the foregoing factors.
Claims of survival after extended duration underwater without ventilation of the lungs have been used to encourage rescuers to persevere with resuscitation efforts. There have been cases reported in victims who have been submerged for between 15 and 45 minutes4–7 and who have survived without neurological sequelae. The explanations given for such prolonged durations of survival are as follows:
1. Hypothermia is protective and develops very rapidly with aspiration of water. In swimmers and divers, hypothermia may be present before the incident.
2. The ‘diving reflex’ is a possible, but contentious, explanation. Within seconds of submersion, the diving reflex may be triggered by sensory stimulation of the trigeminal nerve and by reflex or voluntary inhibition of the respiratory centre in the medulla. This produces bradycardia and shunting of the blood to the areas more sensitive to hypoxia – the brain and coronary circulations. It is independent of baroreceptor or chemoreceptor inputs. The diving reflex is more intense in the frightened or startled animal, compared with animals which dive or submerge voluntarily, but it is not known whether this finding is applicable to humans. Water temperatures higher than 20°C do not inhibit the diving reflex, but progressively lower temperatures augment it.
3. Gas exchange in the lungs can continue after submersion. With or without the effects of laryngospasm, there may be several litres of air remaining within the lungs, thus allowing for continued exchange of respiratory gases. Increased pressure (depth) transiently enhances oxygen uptake by increasing the PO2 in compressed lungs. In an unconscious state, with low oxygen use and the effects of hypothermia, a retained respiratory gas volume could add considerably to the survival time, although it is not often considered in the literature on drowning.
Whether fluid enters the lungs in an unconscious victim depends on many factors, including the spatial orientation of the body. For example, a dependent position of the nose and mouth, facing downward, is not conducive to fluid replacement of the air in the lungs.
Even though spectacular and successful rescue can be achieved after prolonged submersion, it is more frequent that this is not so. Many victims lose consciousness and die after only a few minutes of submersion.