Near Drowning and Drowning Pathophysiology, Etiology, and Management Notes

Definitions and Classifications of Drowning

Near Drowning
- Defined as a situation where a victim survives a liquid submersion incident, at least on a temporary basis.
- The term is specifically implied when victims are successfully resuscitated and maintain survival for at least $24\,\text{hours}$ .
Dry Drowning
- Affects approximately 10\text{%} to 15\text{%} of drowning victims.
- In these cases, victims do not actually aspirate fluid into their lungs.
- Death occurs due to acute asphyxia brought on by a laryngospasm or prolonged breath-holding.
- The glottis undergoes intense spasms that prevent water from passing into the lungs, but simultaneously block the passage of air.
Wet Drowning
- Drowning: Defined generally as death by suffocation resulting from submersion.
- Submersion in fresh water is the most frequent occurrence.
- Wet Drowning Characterization: Occurs in 85\text{%} to 90\text{%} of drowning victims where fluid is successfully aspirated into the lungs.
- The volume of fluid aspirated is typically less than $22\,\text{ml/kg}$ .
- In these instances, the glottis relaxes, allowing fluid to enter the respiratory system.

Physiology and Pathologic Changes

Initial Physiological Response
- When fluid is initially inhaled, the bronchial walls constrict as part of a parasympathetic reflex.
- Non-cardiogenic Pulmonary Edema: Fluid moves from the pulmonary capillaries into the bronchioles and alveoli.
- The alveolar walls and the interstitium undergo swelling (interstitial edema).
- Surfactant Alteration: There is a decrease in pulmonary surfactant, which leads to a corresponding increase in alveolar surface tension.
Pathologic & Structural Changes
- Laryngospasm: The initial reflexive closure of the airway.
- Interstitial Edema: Includes significant engorgement of the perivascular and peribronchial spaces, alveolar walls, and interstitial spaces.
- Surfactant Depletion: Decreased pulmonary surfactant leading to increased surface tension of the alveolar fluid.
- Secretions: The tracheobronchial tree becomes filled with frothy, white, and pink secretions.
- Alveolar Collapse: Alveolar shrinkage and atelectasis (partial or complete collapse of the lung).
- Consolidation: Alveolar consolidation occurs.
- Bronchospasm: Sudden constriction of the muscles in the walls of the bronchioles.

Etiology and Epidemiology of Drowning

Substance Involvement
- 50% of all adult drowning victims are shown to have utilized alcohol prior to the incident.
Demographic Statistics
- Gender: Nearly 80% of drowning victims are male. There is a particularly high incidence among males between the ages of $10$ and $19$ .
- Race and Location:
  - African-American children: Drown at a rate of $4.5$ per $100,000$ annually, most commonly in freshwater lakes and ponds.
  - Caucasian children: Drown at a rate of $2.5$ per $100,000$ annually, most commonly in home swimming pools.
General Mortality and Prevalence in the United States
- Between $6,000$ and $8,000$ people drown each year in the U.S.
- Drowning is the third leading cause of accidental death overall in the United States.
- Drowning is the second leading cause of accidental death for individuals between $5$ and $44$ years of age.
- Age-Specific Data:
  - Drowning is most common in teenagers and children less than $4$ years of age.
  - More than 40% of all drownings occur in the under-4 age group.
  - About 15% of children have experienced a near-drowning incident by middle-school age.
  - Up to 33% of adults have experienced a near-drowning event at some point in their lives.
- Common Sites: Swimming pools with poor adult supervision are the most frequent sites for drownings.

The Drowning Sequence

Panic and Violent Struggle: The victim attempts to return to the water's surface.
Calmness and Apnea: A temporary period of calm followed by the cessation of breathing.
Swallowing of Fluid: Large amounts of fluid are swallowed, which often leads to vomiting.
Gasping and Aspiration: Gasping inspirations occur, resulting in fluid being aspirated into the lungs.
Convulsions: Seizure-like activity may occur.
Coma: The victim loses consciousness completely.
Death: Total cessation of life functions.

Prognostic Factors in Cold-Water Near Drowning

Age: The younger the victim, the better the prognosis.
Submersion Time: The shorter the duration of submersion, the better. $60\,\text{minutes}$ appears to be the upper limit for survivability in cold-water submersions.
Water Temperature: Colder water is better for prognosis. The favorable range is between $27^\circ\text{F}$ and $70^\circ\text{F}$ .
Water Quality: Cleaner water is associated with better outcomes than contaminated water.
Other Injuries: The absence of serious traumatic injuries improves prognosis.
Amount of Struggle: Less struggling by the victim is associated with better survival rates.
CPR Quality: High-quality CPR technique significantly increases the survival rate.
Suicidal Intent: Victims who attempted suicide have a lower survival rate compared to victims of accidental submersion.

Clinical Manifestations and Bedside Data

Fresh Water Pathophysiology
- Fresh water is hypotonic relative to the blood. Consequently, it is rapidly absorbed into the bloodstream.
- Fresh water destroys pulmonary surfactant, leading to surfactant washout and atelectasis.
- Manifestations include alveolar consolidation, increased thickness of the alveolar-capillary membrane, bronchospasm, and excessive bronchial secretions.
Physical Examination and Vital Signs
- Respiratory Rate: Tachypnea (increased rate).
- Heart Rate: Increased pulse.
- Blood Pressure: Increased.
- Temperature: Hypothermia is common.
- Cyanosis: Bluish discoloration of the skin.
- Cough and Sputum: Frothy, pink, stable bubbles are frequently produced. Sputum may contain bacteria or emesis (vomit) from aspirated fluid.
- Chest Assessment: Crackles, rhonchi, and wheezes (if bronchospasm or foreign body aspiration is present).

Laboratory Tests and Radiologic Findings

Arterial Blood Gases (ABGs)
- During early and advanced stages of near drowning, the typical profile includes:
  - $pH$ : Decreased.
  - $PaCO_2$ : Increased.
  - $HCO_3^-$ : Decreased.
  - $PaO_2$ : Decreased.
Metabolic and Systemic Information
- Lactate: A build-up of lactate leads to a decrease in $pH$ (metabolic acidosis), which is usually related to tissue hypoxia.
- Enzyme Function: Altered enzyme function may lead to cell death if oxygenation and perfusion are not restored.
- Dilution Effects: Massive aspiration of fresh water can lead to a decrease in hemoglobin, hematocrit, and electrolyte concentrations due to hemodilution.
Radiologic Findings
- Chest Radiograph (CXR): Typically shows fluffy infiltrates.
- ARDS: Acute Respiratory Distress Syndrome is very common in near-drowning victims due to fluid aspiration and the resulting inflammatory response.
- Radiographs often display a pulmonary edema pattern shortly after the episode.

General Management of Near Wet Drowning

Field Management
- First Responder Actions: Perform a rapid and direct assessment of the Level of Consciousness (LOC) using the Glasgow Coma Scale (GCS), checking pupils, and identifying impaired sensorium.
- History (Hx): Determine the length of submersion time, whether alcohol was involved, and if there are specific circumstances like diving (risk of spinal injury).
- Intervention: Immediate CPR and stabilization during transport.
Hospital Management
- Continuous monitoring of ventilation and oxygenation via ABGs.
- Chest Radiographs (CXR) to monitor lung status.
- Rewarming: Active or passive rewarming of the hypothermic patient.
- Respiratory Support: Intubation and mechanical ventilation using Positive End-Expiratory Pressure (PEEP). Most wet drowning victims require this level of support to manage pulmonary edema and atelectasis.