Contrary to how it is often depicted in movies, the act of drowning often goes unnoticed. There appear to be three separate actions or body positions people adopt when confronted with the possibility of drowning. Depending on their swimming ability, injuries, or illnesses, some will progress through all three of these stages, while others will not.
In a drowning, the victim is submerged under or immersed in water and requires rescue or assistance; not all drowning victims are unresponsive during their rescue and upon recovery, some are awake, voice responsive, or pain responsive. Drowning is a process with three possible outcomes: 1. Death, 2. survival with brain damage, and 3. survival without brain damage. Water in the lungs may cause an inflammatory response that leads to pulmonary edema (PE); the more particulates in suspension or chemicals in solution, the greater the likelihood of PE. In most cases, the S/Sx of PE will appear within 4-6 hours; decreased water quality increases the likelihood of pulmonary edema and subsequent respiratory infections.
Upon submersion in water, 85% of drowning victims involuntarily inhale, partially flooding their lungs and stomach with water; 15% will experience an immediate spasm of their larynx that prevents water from entering their lungs. In both cases, due to a systemic loss of oxygen, the victim will quickly become unresponsive, after a few minutes their heart will stop, and, in most cases, after roughly five more minutes they will suffer permanent brain damage. If not rescued, all unresponsive drowning victims will die. If rescued, the unresponsive patient who still has a pulse (but is not breathing) has a reasonable chance for recovery if rescue breathing is begun immediately. A patient who has no pulse and no respirations may, with immediate CPR, also recover completely, however, mortality is high.
Most unresponsive drowning victims aspirate greater than four ml/kg; aspiration of one to three ml/kg of fluid leads to significantly impaired gas exchange. During resuscitation aspirated water is absorbed into the microvascular bed surrounding the alveoli where it may wash out the surfactant and stimulate mast cell degranulation. If mast cells degranulate, inflammation will occur and plasma will leak into the alveoli, causing pulmonary edema. Listening with a stethoscope—and occasionally with an ear to the patient's bare chest—will reveal rales, crackling noises that indicate fluid is accumulating in the patient's lungs.
In rare cases, usually associated with cold water and young children, a few pulseless and apneic victims may also have a complete recovery if rescued within 30-90 minutes—depending on water temperature—and CPR started immediately. These fortunate few will have experienced both a laryngospasm and an immediate shell/core response known as the "Mammalian Diving Response" or MDR. An MDR immediately slows their metabolic processes while preventing water from entering their lungs, thus providing protection for up to 90 minutes. Given the potential for an MDR, start CPR on all pulseless and apneic drowning victims who have been submerged for less than 30 minutes in water warmer than 43ºF (6ºC) or less than 90 minutes in colder water. If a recovery occurs during CPR, it will usually happen within the first few minutes. If pulse and respirations are not forthcoming, continue resuscitation efforts for a full 30 minutes. A Mammalian Diving Response:
The amount of central nervous system damage (due to lack of oxygen and corresponding acidosis) will determine the patient's ultimate outcome. If the period of ischemia is limited or the victim rapidly develops core hypothermia (or an MDR) the damage may be limited and the patient may recover with only minor neurologic sequelae. The incidence of pulmonary edema increases with the amount of particulate matter dissolved or suspended in the water (e.g., salt, dirt, sand, chemicals, etc.). If CPR or rescue breathing is successful, a patient, even awake patients, may still die from pulmonary edema; if S/Sx of respiratory distress are present they may decompensate within the following 4-6 hours and death may follow within 72 hours. Delayed infection is also a potential respiratory complication that may eventually cause an pneumonia due to bacteria in the aspirated water.
Post-Resuscitation Assessment & Treatment
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Download the Wilderness Medical Society's 2016 Practice Guidelines for Drowning