FRCA Notes

Drowning

Written exam questions on "near-drowning" having appeared twice in the past decade, and the topic brings a personal tinge of PTSD having been one of my Final Viva short cases.

The 2016 SAQ gave marks for knowing the relevant history, investigations and initial management in a case of near-drowning.

Examiners for the 2018 SAQ (62% pass rate) bemoaned a lack of knowledge of management beyond mere intubation and ventilation.

Resources

  • Drowning is defined as: "respiratory impairment arising from submersion or immersion in liquid"

  • Immersion = liquid splashed across a person's face e.g. water-boarding
  • Submersion = airway goes below the level of the surface of the liquid

Classification

  1. No evidence of inhalation
  2. Evidence of water inhalation but adequate ventilation
  3. Evidence of water inhalation but inadequate ventilation
  4. Cardiac arrest

  • Drowning is the second leading cause of unnatural death after RTCs
  • The majority of drowning incidents occur in fresh water e.g. swimming pools, lakes and rivers, often only a few metres from safety
  • Young males are the commonest demographic group, but a significant proportion occur in children
  • The single most common factor in drowning accidents is alcohol; it is present in 75% of adult cases

Risk factors

Patient factors Environmental factors Event-related factors
Toddlers (inadequate supervision) Working on or near water Alcohol or drug intoxication
Adolescents (risk-taking behaviour) Rural areas Trauma
Males Hot weather Suicide
Existing cardiac disease inc. MI, long QT syn. Area prone to flooding NAI, abuse or assault
Existing neurological disease inc. seizure


  • The key mediator of morbidity and mortality following drowning is hypoxia

Physiological stages of drowning

  1. Panic - as the victim attempts to keep their head above water; elevated HR and RR
  2. Breath holding - the victim tires and frequent submersion occurs
  3. Terminal gasp (gasp reflex) - usually results in either laryngospasm or pulmonary aspiration
  4. Unsresponsiveness - cerebral hypoxia leads to unresponsiveness within a minute of the terminal gasp

The diving reflex

  • A protective reflex present in infants but less so in adults
  • Triggered by cold-water stimulus (<21°C) to the ophthalmic division of the trigeminal nerve
  • It is a trigemino-vagal reflex causing:
    • Apnoea
    • Vasoconstriction of non-vital capillary beds → redistribution of blood flow to brain and heart
    • Bradycardia → reduced myocardial oxygen consumption
  • It may, overall, improve outcome by reducing oxygen supply/demand mismatch

Acute lung injury

  • Breath holding, laryngospasm and pulmonary aspiration contribute to the key underlying pathophysiological sequelae; hypoxia, hypercarbia and acidosis
  • Laryngospasm may reduce pulmonary water load and therefore improve outcome in the absence of cerebral injury
  • Submersion also causes hypothermia, which although theoretically provides a degree of protection against hypoxic brain injury often arises after significant hypoxia has already occurred

  • Fluid aspiration causes an acute lung injury (ALI)
    • Washes out surfactant → alveolar collapse and atelectasis
    • There is V/Q mismatch owing to impaired alveolar ventilation → shunt
    • The filling of the lungs with water impairs inflation/relaxation → reduced lung compliance
    • Alveolar oedema arises due to:
      • Fresh water: hypotonic fluid causes direct toxicity to alveoli and vascular endothelium, which also causes interstitial oedema
      • Salt water: generation of an osmotic gradient across the alveolar membrane

  • Other contributors to ALI include:
    • Bronchospasm
    • Attempted respiration against a closed glottis ± alveolar rupture
    • Inhaled toxins e.g. chlorine, pollutants, particulate material

  • In time there is:
    • ARDS
    • Pulmonary infection
      • Aerobic Gram-negative bacteria e.g. Pseudomonas, Aeromonas
      • Funghi e.g.Pseudoallescheria boydii
      • Worse following freshwater drowning owing to higher bacterial burden
    • MODS

Other pathophysiological events

  • Cardiovascular: dysrhythmia, cardiac failure and cardiac collapse due to hypoxia, acidosis, hypothermia and catecholamine stress
  • Neurological: global neurological injury from trauma, hypoxia and subsequent cerebral oedema
  • Renal: AKI & rhabdomyolysis from myoglobinuria or haemoglobinuria
  • Metabolic: profound metabolic acidosis

  • NB salt vs. fresh water drowning does not lead to differing degrees of lung injury nor different electrolyte issues (despite seawater's 1000mosm/kg osmolality)

  • A spectrum of features may present
  • The principle problems are:
    • Respiratory failure from surfactant depletion/dysfunction, aspiration of particular matter and latterly pneumonia/ARDS
    • Hypoxic brain injury
    • Cardiovascular compromise

  • Cold-water shock may occur:
    • Gasp reflex (which increases pulmonary aspiration)
    • Tachypnoea
    • Tachycardia

Pre-hospital

  • Remove the patient from the body of water
  • Cut off wet clothing
  • Start re-warming process

  • Aim to restore adequate tissue oxygen delivery, as hypoxia is the major cause of death, using an A-E approach
  • Cardiac arrest is typically non-shockable, and one should follow the BLS/ALS algorithm with modifications i.e. 5 rescue breaths prior to starting CPR

In-hospital

  • Patients should be managed as per ATLS guidelines using a C-ABCDE approach
  1. Intubation and ventilation is often required in the presence of agitation, low GCS or hypoxaemia
    • C-spine injuries may be present and adequate precautions should be instigated

  2. Apply 100% oxygen via non-rebreathe mask
    • If no improvement in oxygenation, prepare for RSI
    • Lung - protective, open-lung (high PEEP) ventilation as in ARDS
    • Take sputum/tracheal aspirates for microbiology
    • Consider bronchoscopy and suction

  3. A fairly standard approach to the trauma patient:
    • Wide-bore IV access
    • Bloods: FBC, U&E, clotting, LFT, toxicology, ABG, glucose
    • Arterial line
    • Fluid resuscitation with warmed crystalloid

  4. Neuroprotective measures as standard
    • Trauma CT

  5. Management of hypothermia e.g. passive/active re-warming to at least 34°C

    6. Passive Active (external) Active (internal)
    Warm environment >30°C Forced air blankets Warm IV fluids
    Remove wet clothing Radiant heaters Humidified, warm inspired gases
    Insulating blankets Body cavity lavage
    Coolguard catheter
    Extracorporeal methods e.g. CPB, ECMO

  6. Antibiotics if grossly contaminated water but prophylactic antibiotics or anti-fungals are not routinely recommended

Predictors of poor outcome

  • Warm water drowning (some protective effect from cold water)
  • Submersion >10mins
  • Delay to onset of CPR >10mins
  • Severe acidosis (pH <7)
  • Abnormal neurology, such as:
    • Low GCS or absent brainstem function
    • GCS 3 + fixed, dilated pupils on admission

Prognosis

  • Mortality from drowning correlates with class:
    • Class 2: <1%
    • Class 3: 12%
    • Class 4: 23%
  • Paediatric mortality may be higher (30 - 50%)

  • In those who experience cardiac arrest and survive, the incidence of neurological deficit is up to 30%