Drowning is a process that causes respiratory impairment due to submersion or immersion in a liquid. It is a serious public health concern, often occurring silently and rapidly. When an individual drowns, the primary threat to life involves the lungs, as their function is disrupted, leading to a lack of oxygen in the body. This deprivation affects all organs, especially the brain and heart. Understanding the specific physiological events within the lungs during and after a drowning incident is crucial for appreciating the severity of this type of injury.
Immediate Airway and Lung Reactions
When water first enters the airway, the body’s immediate protective response is often laryngospasm. This reflex involves the involuntary closure of the vocal cords, sealing the airway to prevent water from entering the lungs. While this mechanism can initially prevent water aspiration, it also obstructs breathing, leading to oxygen deprivation. This initial phase can last for approximately one minute before the spasm fatigues.
In some cases, laryngospasm persists until cardiac arrest, preventing any significant amount of water from entering the lungs. This phenomenon has historically been referred to as “dry drowning” because the lungs remain free of aspirated fluid. Conversely, “wet drowning,” which is more common, occurs when the laryngospasm relaxes due to hypoxia, allowing water to be inhaled into the lungs.
Physiological Changes Within the Lungs
Once water enters the lungs, damaging physiological changes begin. A crucial element affected is pulmonary surfactant, a substance lining the alveoli that reduces surface tension and prevents their collapse. Both fresh and salt water can wash out or inactivate this surfactant, leading to widespread alveolar collapse, a condition known as atelectasis. This collapse significantly reduces the lung’s ability to inflate and exchange gases efficiently.
The impairment of gas exchange is a direct consequence of this damage. When alveoli collapse or fill with fluid, oxygen cannot effectively pass from the air sacs into the bloodstream, and carbon dioxide cannot be removed. This leads to hypoxemia, a dangerously low level of oxygen in the blood, and hypercarbia, an excess of carbon dioxide.
The presence of water in the lungs often triggers pulmonary edema, which is the accumulation of fluid in the lung tissue and air spaces. This occurs due to damage to the fragile alveolar-capillary membrane, increasing its permeability and allowing fluid to leak from blood vessels into the alveoli. This fluid accumulation further impedes gas exchange and reduces lung compliance, making it harder for the lungs to expand, thus exacerbating respiratory distress.
How Water Type Affects the Lungs
The type of water aspirated—freshwater or saltwater—can lead to distinct physiological responses within the lungs, primarily due to osmotic differences. Saltwater is hypertonic, meaning it has a higher concentration of solutes than human blood. When saltwater enters the alveoli, this osmotic gradient causes fluid to be drawn from the bloodstream and surrounding lung tissues into the alveolar spaces. This movement of fluid exacerbates pulmonary edema and can lead to hemoconcentration, where the blood becomes thicker.
Conversely, freshwater is hypotonic, having a lower solute concentration than blood. If a significant amount of freshwater is aspirated, it can be rapidly absorbed from the alveoli into the bloodstream. This influx of fluid can lead to hemodilution, diluting the blood. While these systemic electrolyte disturbances and red blood cell changes were once thought to be major factors in drowning outcomes, studies suggest that in most cases, the volume of aspirated fluid is often too small to cause severe systemic effects.
Post-Drowning Respiratory Complications
Even after a non-fatal drowning event, individuals can experience delayed respiratory complications. One such concern is secondary drowning, where symptoms of respiratory distress develop hours or even up to 48 hours after the initial incident. This occurs when inhaled water irritates the lung lining, leading to inflammation and a gradual buildup of fluid (pulmonary edema) that impairs the lungs’ ability to oxygenate blood.
Acute Respiratory Distress Syndrome (ARDS) is another severe complication that can arise after drowning. ARDS is characterized by widespread inflammation in the lungs, leading to fluid accumulation in the alveoli, further impairing gas exchange. Drowning is a known cause of ARDS.
The aspiration of water, especially from contaminated sources, also carries a risk of pneumonia. Contaminants present in the aspirated water can lead to infection and inflammation within the lung tissue. This aspiration pneumonia can complicate recovery.