Stresses in SCUBA and Breath-Hold Diving
Part V: Near-drowning and Drowning
In the four previous issues of Wound Care and Hyperbaric Medicine, we introduced the subject of stimulus/stress—response/resolution and used this as the basis for discussing the physical, physiological, psychological, and no-panic syndrome stresses of diving.1-4 In this article we will discuss the ultimate and most dreaded stress of all water related activities: suffocation in the water. It is associated with oxygen deprivation to the brain with loss of conscious as well as various degrees of insult to the lungs. Unfortunately, the body’s reactions/responses to these devastating stresses are very limited in the absence of restoration of ventilation. The responses that somewhat mitigate these stresses are observed in the diving reflex and hypothermia, both of which will be discussed. Although 33 different definitions have been ascribed to drowning incidents, we will refer to them as near-drowning and drowning.5 The near-drownings are further subdivided into events with no residual neurological problems and events with neurological residuals (Figure 1). While this article considers the subjects of near-drownings and drownings in general, as much of the information as possible will relate to SCUBA and breath-hold diving activities.
Figure 1: Drowning and the Spectrum of Near-Drownings
Legend: Drownings and near-drownings must always be considered in the context of the event, i.e, loss of consciousness while submerged, and the outcomes. The outcomes range from no residuals to coma. It is suspected that transient LOCs almost always go unreported.
Key: LOC = Loss of consciousness
Whereas drowning deaths throughout the world generate large numbers, it is fortunate that only a small proportion occur in SCUBA divers. Statistics on SCUBA diving related drowning deaths from the Divers Alert Network (DAN) show that approximately 100 deaths (with about a 10 percent variance from year to year) occur in SCUBA divers in the USA, and approximately half are designated as drownings without any established etiologies for the loss of consciousness while submerged.9 The data from drowning deaths in snorkelers and breath-hold divers is less well documented since these incidents tend to be lumped into all deaths where a mortal submersion occurs, and the recording of such deaths, especially for surface swimmers and snorkelers, is even less rigorous. The collection of data on breath-hold diving related drownings is being initiated by DAN, but numbers are not known to us at this time. Furthermore, there is no incentive to report near- drownings, especially those with no residual lung or brain injury. In the USA, near-drownings are estimated to be 500-600 times more common than deaths from drowning.10 Regardless, any loss of consciousness in a water-related activity is a serious concern and especially tragic when the activity is voluntary and done for recreational, fitness, and/or sports-related purposes.
The actual number of drowning deaths throughout the world is unknown, with estimates as high as over 500,000 in 2001 and 372,000 in 2012, according to the WHO. In the USA 40 percent of drownings occur in children younger than four years old.6 Drowning is a leading cause of death worldwide in children five to fourteen years of age. In the USA it is the second leading cause of non-disease, injury-related deaths (secondary to motor vehicle accidents) in children one to four years of age.7 In terms of exposure adjusted person-time estimates, Szpilman et al. note that the chances of drowning is 200 times higher than such estimates from motor vehicle accidents.7
This article describes the precursors/risk factors associated with near-drowning and drowning, the pathophysiological events that occur with submersion injury, factors that influence favorable outcomes, and patient management from first response interventions to definitive management for victims that lose consciousness in the aquatic environment. Special consideration is given to relating these subjects to SCUBA and breath-hold divers. The question of whether or not to use the term “drowned” has some pertinence and is discussed next.
Never Say Drowned
Although death occurring while immersed in water is tantamount to drowning, and is the terminology we advocate, the admonition of “never say drowned” should always be remembered (Figure 2) and is well founded for two reasons. First, never say “drowned” because recoveries, some seemingly miraculous, have occurred after unconscious victims of immersion have been rescued and revived. Some recoveries have occurred after immersions of up to 60 minutes.7,11 Age, absence of panic, the oxygen conserving/diving reflex, and cold water are factors associated with recoveries from prolonged (up to 30 minute) immersions and, in part, reflect the body’s limited responses to the anoxic stress of submersion. A corollary to this admonition of “never say drowned” is the hypothermic victim with a profound bradycardia or asystole immersed for less than 30 minutes. Only after rewarming with no evidence of recovery should the victim be labeled as dead and nonresuscitatable. How these factors associated with the diving reflex affect recovery for the unconscious victim of water immersion will be discussed later in this article.
Figure 2: Why "Never Say Drowned"
Legend: When a victim is found unconscious in the water, they should not automatically be labeled as dead. About 90% of the victims recover. Furthermore, the caregiver should ascertain the cause of the loss of consciousness so etiology-specific appropriate care is provided.
The second reason for “never say drowned” is that in many victims of water immersion a preceding event leads to the loss of consciousness in the water. If the problem that led to the loss of consciousness is not recognized and appropriate interventions are not initiated, recovery will be hampered. For example, loss of consciousness from a cardiac event while immersed requires markedly different treatment than that from water aspiration associated with a blackout (see reference 4) or from unconsciousness due to an arterial gas embolism. This caveat of ascertaining the reason for the loss of consciousness while immersed is especially true for the near-drowning victim, where appropriate immediate early management is so crucial to achieve good outcomes. Often when a drowning occurs it makes the headlines of the local newspaper; however, follow-up information as to the cause of the loss of consciousness is almost never reported.
|General Risk Factors (see reference 1)|
|1. Exceeding one's capabilities||Diving too deeply (nitrogen narcosis), swimming to/returning from dive sites (exhaustion)|
|2. Lack of awareness of diving conditions||Open water dives (disorientation), cave diving, hull penetrations (panic), diving in currents, rip tides, traversing surf zones (exhaustion and panic)|
|3. Alcohol and illicit drug use||Impairs judgment (panic, disregard for risks, increased susceptibility to nitrogen narcosis) (see reference 2)|
|Special Risks Associated with SCUBA Diving (see reference 2)|
|1. Equipment related||Lack of familiarity (buoyancy control), inoperable or in need of servicing (equipment failures), loss of monitors—flooding, dead battery (disorientation, uncontrolled ascents, decompression obligations)|
|2. Entanglements||Especially with kelp and hull penetrations (panic, exhaustion of air supply)|
|3. Exposure and exhaustion||Hypothermia, surface swimming against currents (exhaustion)|
|4. Sensor failures, wrong gas mixtures||Insufficient oxygen partial pressures (hypoxia) with closed circuit rebreathers|
|Special Risks Associated with Breath-hold Diving (see reference 4)|
|1. Profound hyperventilation||Blackout from hypoxia before CO2, elevation signals the diver to breathe|
|2. Deep dives with hypoxia on ascent||Diffusion at blackout (see reference 4)|
|1. Diving with medical problems||Impaired heart function, uncontrolled diabetes, seizure disorder, stroke residuals|
|2. Diving in dangerous environments||Overhead boats (propeller/head injuries), polluted waters (toxic chemicals), sharks|
|3. Envenomation from marine animals||Usually from carelessness (stonefish) or handling (blue-ringed octopus, sea snakes)|
Causes and Risks Factors for Near- drowning and Drowning
There are multiple reasons why near-drowning and drowning occur. Probably the least frequent is that of forceful immersion as a consequence of homicide, attempted homicide, or torture. Conversely, the most frequent cause for near-drowning and drowning is that of risk-taking, especially with respect to diving (Table 1). Several subcategories of risk-taking exist: first there is risk-taking associated with exceeding one’s diving capabilities. Second there is risk-taking due to unawareness of the diving conditions or challenges. Third there is risk- taking with equipment-related situations. Fourth there is risk-taking associated with alcohol and/ or illicit drug use in association with water-related activities. Alcohol has been reported in about 50 percent of drowning deaths, although the majority of these are in non-diving related water associated activities.15 Other risk factors are those of SCUBA diving without adequate supervision/pre-dive briefings and disregarding the buddy system.
In addition, several factors are associated particularly with breath-hold diving. Profound hyperventilation before submersion is a significant risk factor for loss of consciousness during underwater swimming and breath-holding diving activities.4 Another risk factor in this category is the breath-hold dive with resulting diffusional blackout.4 Finally, there are serious risks for those who attempt to set world unlimited and free dive breath-hold depth records (now greater than 500 feet).
In SCUBA diving excess risks are associated with inadequate training, lack of familiarity with equipment, and/or poor fitness.1,16As mentioned earlier, drowning deaths in SCUBA divers are rare with reported deaths in the USA consistently remaining around 100 (±10%) per year.9 Especially significant risks to SCUBA divers include diving too deeply with air, resulting in nitrogen narcosis; panic, which is frequently caused by entanglement; and depletion of air supply. Drowning deaths from decompression sickness and arterial gas embolism are exceedingly rare because the victims are usually on the surface when symptoms manifest themselves and a buddy diver is usually in attendance. Other SCUBA diving causes/risk factors associated with loss of consciousness in the water include hypothermia and exhaustion. With closed circuit rebreather diving, drowning deaths most often occur due to hypoxia from insufficient oxygen partial pressures caused by human error or equipment malfunctions.3,17There are also medical conditions that can cause loss of consciousness in water such as myocardial infarction, heart arrhythmias, stroke, seizure and hypoglycemia.4 Trauma from boating accidents and shark bites (with acute blood loss) can be another cause of loss of consciousness in the water. Finally, there is the potential (possibly non-existent) for loss of consciousness in divers from venomous marine animal bites and stings, such as from the sea snake and the blue-ringed octopus.
Related Near-drowning and Drowning Terminology
A number of other terms associated with drowning are eschewed by the WCOD in favor of the simple outcome terminology of morbidity, no morbidity, or mortality after water immersion, as previously mentioned. The problem with this simplified terminology is that additional descriptions are required in order to define and/or explain the morbidity. Nonetheless, it is important to be aware of other terminology associated with near-drowning and drowning. Sudden (instantaneous) drowning was described by Keatinge in 1977.18 He postulated that the immediate loss of consciousness and drowning deaths in aviators whose planes were shot down over the cold North Sea waters was due to uncontrollable gasps in the near freezing water. If the head were submerged, water would be aspirated and consciousness almost immediately lost due to brain hypoxia. Wet and dry drowning refers to whether or not enough water is aspirated to cause electrolyte imbalances in the body. Further discussion of this will occur later in this article. Secondary drowning refers to the delayed onset of pulmonary edema after a near-drowning episode19 and is most frequently reported in near- drownings of children. It is believed to be due to a hypoxic insult to the alveolar capillaries, which gradually lose their integrity so that diffusion of serum into the alveoli occurs and causes the victim to become progressively hypoxic with dyspnea, tachypnea, confusion, agitation, and eventually lose consciousness. Treatment requires all measures necessary to manage pulmonary edema including breathing enriched oxygen mixtures, diuretics, intubation, and positive end-expiratory pressure ventilation.
Another variant of “delayed” drowning was associated in a breath-holding thoracic squeeze episode.21 Three hours following an apparent full recovery after loss of consciousness and retrieval during ascent of a breath-hold dive (i.e., diffusional blackout—see reference 4), the victim became progressively hypoxic and failed to respond to treatment measures. Autopsy demonstrated serum and blood in the alveoli. The three-hour latency period represented the time it took for serum and blood to accumulate in the alveoli and reflected the characteristics of a delayed drowning.
Figure 3: Swann's Dog Studies from the 1940s
Legend: During the first author's time in medical school, this was the prevailing information on what happened (in humans) in near-drownings and drownings from which test questions were derived.
Evolution of the Understanding of the Pathophysiology and Management of Near-drowning
The understanding of what happens in near- drowning has evolved from total misinformation to a sound physiological basis today. Based on dog studies by Swann in the late 1940s, distinction was made between what occurs in fresh- and saltwater drownings (Figure 3).22 Therapy was consequently directed at maintaining electrolyte balance because of hemodilution with freshwater drownings and hypernatremia with saltwater drownings.
Modell in the late 1970s found that fluid and electrolyte imbalances were not the reason morbidity was associated with near-drownings.23 Rather, it was due to hypoxia. With the newly acquired avail- ability of arterial blood gas measurements, Mod- ell showed that blood oxygen tensions fell precipitously with asphyxia in water, approaching nearly zero within 10 minutes (Figure 4).
Figure 4: Modell's Blood Gas Studies in Drownings
Legend: Modell demonstrated that hypoxia was the pathophysiological event that initially occurred in drownings.
Table 2: Modell's Method for Pulmonary Management of Drownings
>25 cm H2O
<25 cm H2O
Key: CAP = capacity, cc = cubic centimeters, cmH2O = centimeters of water, CPAP = continuous positive airway pressure, Insp = inspiratory, IPPB = intermediate positive pressure breathing, PaO2 = partial pressure of arterial oxygen (mmHg), PEEP = positive end-expiratory pressure, PT = physical therapy, WNL = within normal limits
He advocated using advanced pulmonary life support measures to achieve adequate blood oxygenation to protect the brain, and his approach utilized three categories of severity using blood gasses and respiratory parameters (Table 2). For the more severe presentations continuous positive airway pressure (CPAP) was used, and in the most severe situations positive end-expiratory pressure (PEEP) was initiated. Modell observed that if the near-drowning victim arrived in the emergency department alert, 100 percent recovery was observed. If the sensorium was blunted, 90 percent recovery occurred. However, if the victim was comatose at the time of arrival full recovery with his techniques only occurred in 50 percent of the near-drowning victims.
Subsequently, Conn amended Modell’s recommendation to stress cerebral resuscitation in comatose patients after near-drowning.24 He advocated “HYPER” therapy, which was an acronym for interventions to modify hydration, ventilation, body temperature, excitability, and rigidity (Table 3). With use of his “HYPER” therapy in 18 patients who arrived comatose, he observed that 61 percent had full recovery and only 5.5 percent had residual brain damage. He contrasted this in 21 patients using Modell’s approach where 28 percent had full recovery and 38 percent had residual brain damage.
Table 3: The Five Components of Conn's "HYPER" Therapy
Note: With Conn's "HYPER" therapy, 61% of his 18 patients who arrived comatose demonstrated full recovery and only 5.5% had residual brain damage. He contrasted this with experiences where 28% of patients had full recovery and 38% had residual brain damage.
Current management for near-drownings is based on improved understanding of the pathophysiology of water immersion and optimization of management. In 85-90 percent of human drownings, water is aspirated and consequently the event could be considered a “wet” near-drowning, drowning event. This is confirmed at autopsy by the findings of diatoms from the aspirated water in the alveoli. The other small percentages of drownings are “dry” types where water does not enter the alveoli secondary to laryngospasm.
Drowning victims are too busy struggling (unless blackout has occurred) and too “air hungry” to yell for help. Once water enters the alveoli, four pathophysiological events occur (Figure 5). These include 1) decreased lung compliance, 2) ventilation-perfusion mismatching, 3) intrapulmonary shunting, and 4) surfactant washout. The common final denominators are hypoxemia and acidosis that lead to secondary problems of encephalopathy, acute respiratory distress syndrome, cardiac problems (ischemia, infarction, and/or arrhythmias), and renal shutdown.
All therapy is directed at maintaining adequate arterial blood saturations (above 90 percent) and acid-base balance including CPAP, PEEP, vasopressors, fluids, diuretics, acid buffers, intubation with barbiturates for sedation, etc. If aspiration of contaminated water is suspected, antibiotics are given. Finally, the use of steroids for reducing cerebral edema is controversial and apparently neither Modell nor Conn used them in their resuscitation protocols. An excellent algorithm for the evaluation and management of drowning victims has been generated by Szpilman et al.7 They grade the victim from “Dead” to “Rescue” with six intermediate grades (1 to 6) based on the duration of immersion and the physical examination findings at the time of presentation to the emergency department. Management is specified for each grade with accompanying survival rates. Hyperbaric oxygen would seem a logical adjunct for mitigating the brain pathophysiology of hypoxia and cerebral edema (see text box below). Unfortunately, we are not aware of any reports of using HBO for such.
The Diving Reflex
Near-drownings, and the seemingly miraculous recoveries that have been observed after rescues, require a discussion of the diving reflex. The diving reflex is a series of innate responses that are associated with immersion in water (Figure 7). The reflex is highly developed in diving mammals and other aquatic animals, allowing them to remain submerged from six minutes (porpoises) to two hours (blue whales).30 This series of physiological responses conserve oxygen and direct blood flow exclusively to the two most vital organs needed to safely continue the breath-hold dive; namely, the heart and the brain. The diving reflex has three components: 1) bradycardia, 2) vasoconstriction with shunting of blood to all body systems (except the heart and brain), and 3) anaerobic metabolism. Absence of panic, minimizing moments of the extremities, immersion in cold water, and young age (especially the fetus) facilitate the effectiveness of the diving reflex.
Figure 5: Sequence of Events in Diving-related Near-drownings and Drownings
Legend: Modell demonstrated that hypoxia was the pathophysiological event that initially occurred in drownings.
Figure 6: The Role of the Acute Use of Hyperbaric Oxygen for Near Drownings
Legend: The mechanisms of hyperbaric oxygen (HBO) have applications for the pathophysiology of near drowning, especially with respect to the brain injury.
First-response Interventions for Near-drowning victims
The first step in any near-drowning event is retrieval of the victim from the water. If on the surface, the Red Cross water safety adage of “throw, tow, row and only then go” is sound advice. Certainly, the rescuer should not be put in jeopardy. What is worse than a drowning is a double drowning with the rescuer as the second victim. The next steps in the first response interventions are 1) getting the victim to a stable platform like a boat if in open water or the shore if nearby and 2) activating the Emergency Response System (best initiated by dialing 911 if in the USA). After this, basic life support (BLS) measures, which continue to evolve, should be initiated (Table 4). While performing BLS, the hypothermic victim should not be rewarmed. The reason for this is the hypothermic victim may be in asystole, and during the rewarming the initial cardiac response is likely to be ventricular fibrillation, which is rapidly fatal if not immediately corrected. Once advanced support with an automated external defibrillator is available and intravenous (IV) access established, rewarming while continuing resuscitation should be done.
Rewarming techniques include removal of wet garments to prevent evaporative heat loss, shielding from wind, covering with warm blankets or clothing, application of warm water bottles to axillary and groin areas, instillation of warm IV fluids, and inhalation of warm, humidified air. Usually multiple techniques are used for additive warming effects. Heimlich “hugs” (abdominal thrusts) are not recommended for drowning victims as the maneuver is not effective in expelling water from the lungs and may precipitate vomiting that can lead to lung aspiration.
Figure 7: Components of the Oxygen Conserving/ Diving Reflex
Legend: The diving/O2 conserving reflex is initiated by water coming in contact with the terminal branches of the trigeminal nerve. Andersen's classic experiment with the duck shows how profound it is in prolonging survival with immersion apnea.31 It has been observed in a variety of animals, but best appreciated in the diving mammals. Components of the diving reflex can be observed in humans. The reflex is obliterated by struggling and panic.
Table 4: Highlights in the History of Cardiopulmonary Resuscitation
1. In the beginning...He (God) breathed the breath of life into Adam's nostrils and the man became a living creature. (Genesis 2:7)
2. There are anecdotal commentaries throughout the ages for recovery of drowning victims
3. 1740 Paris Academy of Science: Mouth-to-mouth resuscitation recommended for drowning victims
4. 1767 Amsterdam Society for Recovery of Drowned Victims
5. 1903 George Crille, a surgeon, introduced the technique of external cardiac compression
6. 1950-1973 Various techniques for artificial resuscitation
7. 1954 James Elam reported that expired air was adequate to maintain adequate oxygenation
8. 1964-1963 cardiopulmonary resuscitation was developed under the auspices of the American Heart Association headed by Leonard Scheris
9. 1973 to present National Conferences on CPR and ECC approximately every four years with refinement of techniques and simplification of applications. Items such as rhythms, exchanges of rescuers, ABCs (airway, breathing, cardiac compressions), activation of the ERS ( Emergency Response System), advanced life support and pediatric advanced life support qualifications, and use of the AED ( Automated Electrical Defibrillator). Heimlich maneuver for expelling foreign objects reported in 1974
10. 2010 American Heart Association Guidelines with CAB (chest compressions, airway, and breathing) management, nearly uniform rates, simplified exchanges of rescuers, improved AEDs, and higher quality training manikins.
The unconscious SCUBA diver imposes additional challenges.If the diver is unconscious on the surface, measures as just described are appropriate. Inflating the buoyancy compensator (BC) and ditching gear in the water will lessen the exertion required by the rescuer to bring the victim to shore or the diving platform. More controversial is the management of the SCUBA diver who is found unconscious on the bottom. Three different “schools of thought” exist for handling this challenge:
First Option: Replace the regulator in the victim’s mouth, gain control of the head with the head carry (as has been taught in Red Cross lifesaving and water safety courses), cradle the head on the rescuer’s chest while extending the victim’s neck, then perform a slow swimming ascent aided, possibly, by improving buoyancy through judicious inflation of the rescuer’s BC. Once on the surface, the measures described for the near-drowning victim found on the surface are employed.
Second Option: Swim the victim to the surface with or without ditching the SCUBA tanks and regulator by grasping the victim’s BC straps with or without improving buoyancy with the rescuer’s BC. A variation of this is placing the rescuer’s second stage octopus regulator into the victim’s mouth before ascending.
Third Option: Swim the victim to the surface with or without ditching the victim’s gear by grasping the victim’s fins and letting the head dangle in the downward position during the ascent. Again, inflation of the rescuer’s BC can be used to improve buoyancy.
We advocate the head control option for several reasons. With head control and neck extension of the unconscious victim, there is less chance of an arterial gas embolism occurring during ascent from retained air in the lungs whose egress is blocked by the flexed neck. Should the unconscious victim still execute agonal respiratory efforts, the regulator in the mouth may prevent aspiration of water. Finally, should spontaneous breathing resume during the ascent process, the regulator will provide an air supply and allow resumption of oxygen delivery to the brain and other tissues.
Unconscious SCUBA divers using closed circuit re- breathers (CCR) present additional challenges.33 Should water enter the breathing circuit, its reaction with the soda lime in the carbon dioxide scrubber will cause the breathing mixture to become caustic, which could cause severe respiratory system injury if breathing is resumed. Because of the special techniques utilized for CCR SCUBA, additional hazards must be considered.2 These include seizure from oxygen toxicity and loss of consciousness from hypoxia. If the patient is seizing, is it recommended that ascent not be initiated until the seizure has ended.33 With blackout from hypoxia breathing efforts may continue, so it is important that an air supply be maintained for the victim during ascent. The supply would preferably be from the open circuit pony bottle that CCR divers are recommended to carry. Finally, because of the ability for long, deep dives with CCR, it is likely that a decompression obligation or manifested decompression sickness will occur once the victim is brought to the surface. This possibility must be considered in the definitive management of the victim, as will be discussed in the next section.
Definitive Management of near-drownings
After the unconscious diver is at a medical center advanced life-support measures are initiated, or if already started, continued with intubation, artificial ventilation, and intravenous fluids. If no spontaneous heartbeat or breathing is present on arrival at the emergency department, the prognosis for recovery is bleak. A decision to pronounce the victim dead may be made by a physician at that time. However, if the period of immersion was relatively short, that is to say 60 minutes or less, and the victim is markedly hypothermic, rewarming while continuing advanced life support should be considered.7 When normothermic, a decision to continue life support measures should then be made. Medications as indicated are administered, e.g., anti-arrhythmic medications for irregular heart- beat, steroids if aspiration is apparent on chest x-ray, antibiotics if lung infection is a concern (the victim was in polluted water), and sedatives/paralyzing agents if the victim is resisting the ventilator. Blood tests and x-rays will help in decision making for management at this stage.
Once advanced life-support measures are established, it is necessary to decide whether hyperbaric oxygen (HBO) recompression is needed. If decompression was omitted or arterial gas embolism is likely, HBO recompression should be started as soon as possible. Another consideration (which is controversial) is whether to use HBO for brain resuscitation for the anoxic brain insult. If HBO is to be used as an adjunct for acute ischemic brain in- jury, the decision must be made jointly by the family, the attending physician, and hyperbaric medicine specialist.
As soon as the near-drowning victim has stabilized, decisions for subsequent management are required. If the person is recovering well, rehabilitation is started for residuals of the neurological injury. If the victim remains in a persistent vegetative state, typical interventions in preparation for transfer to a long-term care facility include tracheotomy, percutaneous endoscopic gastrostomy tube placement, management of contractures, and prevention of pressure ulcers. The prognosis for recovery depends almost entirely on the severity of the anoxic brain injury, and the electroencephalogram may be helpful for determining long-term prognosis. Usually critical care management can resolve the lung injury regardless of the severity of the brain injury. The off-label use of HBO for victims of near-drowning who have serious residuals, but have plateaued with their rehabilitation, remains controversial.
Favorable Prognostic Signs in Victims of Near-drowning
A number of favorable prognostic signs have been associated with near-drownings. First, the shorter the period of immersion, the better the victim’s prognosis. Szpilman et al. reported that the risk of severe neurological impairment after hospital discharge was 10 percent if the period of immersion were zero to five minutes, 56 percent if six to ten minutes, 88 percent if eleven to twenty-five minutes and nearly 100 percent if greater than twenty- five minutes.7 Other favorable prognostic indicators include immersion in water temperatures less than 50°F, a core temperature of less than 95° F, young age, and time to effective BLS less than 10 minutes.6 Victims of near-drownings who arrive in the emergency department with a spontaneous heartbeat have better than a 50 percent chance of survival, whereas those without spontaneous cardiac activity have less than a 12 percent chance of survival.7 Factors that complement the diving reflex, such as absence of panic, young age, hypothermia, and avoidance of extremity movements, also favor survival. If the victim is alert at the time of the arrival to the emergency department, the chance of survival without neurological residuals approaches 100 percent.23 Other factors that favor a good prognosis at the time of arrival at the emergency department include the female gender, absence of aspiration, time to basic life support of less than 10 minutes, blood pH greater than 7.1, blood glucose greater 112 mg percent, Glasgow Coma Score greater than 6, and the presence of the pupillary response.6
Myths and Unresolved Questions about Near-drownings and Drownings
1. Precise definitions that are established by experts should always be used for a victim who has experienced a loss of consciousness in the water.
Comment: We advocate simplicity; “drowning” if the victim is dead and “near-drowning” if alive after recovery and resuscitation efforts. However, the severity of residual neurological injury in near-drowning ranges on a continuum from none to persistent vegetative state (Figure 1).
2. Drowning, is a sufficient diagnosis for anyone who has lost consciousness in the water.
Comment: As mentioned before, “never say drowned.” It sounds like a paradox to acknowledge this adage, but then use the term drowning. The message is that the underlying cause of the loss of consciousness in water needs to be ascertained, be it from decompression illness, breathhold blackout, cardiac arrest, seizure, trauma, etc. The cause dictates the optimal management for the near-drowning treatment.
3. Usually near-drownings and drownings occur in the absence of risk factors.
Comment: An analysis of the circumstances surrounding the drowning will usually identify underlying risk factors that lead to the loss of consciousness such as a heart attack from coronary artery disease, excessive hyperventilation leading to blackout, viola- tion of decompression practices, etc. (Table 1).
4. All victims of near-drowning, even if asymptomatic, need to be observed for 24 hours before discharge from the medical center where initially evaluated.
Comment: Although delayed onset of pulmonary edema may occur within the first 24-48 hours after the near-drowning event, if the patient is asymptomatic with normal ventilatory functions observation in the hospital setting is not necessary. However, at discharge the patient and/or family should be aware of delayed onset of pulmonary edema associated with near-drowning and instructed to return the patient to the medical facility immediately if shortness of breath, cough, or other respiratory symptoms occur.
5. The primary concern in near-drownings is the management of the respiratory insult.
Comment: Although adequate ventilation is essential for recovering the victim, management of the possible anoxic brain insult must not be over- looked. Whereas respiratory function will inevitably recover, the neurological injury is more likely to be irreversible.
6. If the period of loss of consciousness while immersed is greater than four minutes, resuscitation efforts should not be initiated.
Comment: Although death of brain neurons occurs after four minutes of anoxia, with intact heart function oxygen physically dissolved in the blood is still being delivered to the brain. This is complemented by the diving reflex, which is initiated by immersion. This prolongs survival and promotes full recovery after immersion exceeding four minutes. In addition, hypothermia can slow metabolism and reduce brain oxygen demands.
7. In the USA children's near-drownings are usually in open waters such as lakes and oceans.
Comment: In the USA, the most common cause of near-drownings and drownings in children occurs when they fall, unwitnessed, into a backyard swimming pool, which is an event typically associated with families affluent enough to have swimming pools. “Water safe” in a child does not guarantee that with clothes, shoes, and possibly restrictive garments on, he/she can swim to safety. Pediatricians have said that the only safe thing to fill a backyard pool with is sand! In third world countries, drownings are usually from play activities in (usually polluted) rivers.
8. In most near-drownings and drownings no water enters the lungs due to the laryngospasm reflex.
Comment: Although the laryngospasm reflex is very profound, and one of the last to be lost with impending death, in 85-90 percent of near-drownings and drownings water is aspirated. This qualifies the drowning as a “wet” type. Even small amounts of aspirated water can alter pulmonary functions and require critical care management.
9. Autopsies of drowning victims always have pathognomonic findings.
Comment: Often autopsies of drowning victims demonstrate no specific findings for the cause of death. Aspiration of sea water may show diatoms in the lung tissues. Heart disease can be confirmed by atherosclerosis of coronary arteries, but deaths from arrhythmias are usually undiagnosable. Thoracic squeeze injury can show edema and blood in the alveoli.
10. Near-drownings and drownings associated with SCUBA diving need not be managed any differently than the problems from other causes.
Comment: Special training and techniques are needed to manage SCUBA divers found unconscious on the bottom. Once at a medical center, a decision needs to be made as to whether hyperbaric oxygen recompression is needed for omitted decompression and/or arterial gas embolism in addition to the usual advanced life support measures.
The management of near-drowning has made note- worthy advancement in both basic life support as well as advanced life support. Unfortunately, the human only has limited reflexes/responses to the hypoxic insult associated with immersion in contrast to almost all of the other stresses associated with diving. The diving reflex and induced hypothermia by the surrounding water environment are the limited responses the body has to deal with the anoxic immersion stress. Although lung function is usually recoverable with advanced life support interventions, neurological injury is often not recoverable. Consequently, attention to rescue and management must always be directed to preventing anoxic brain injury. Usually, underlying causes lead to unconsciousness in the water, hence, “never say drowned” as the cause. Rather, seek the underlying cause and remember that seemingly miraculous recoveries have occurred after recovering a victim from a presumed drowning. This directs treatment interventions from heart attack management to recompression treatments and from observation only for delayed effects of the immersion to physical therapy. Finally, the best measure for near-drownings and drownings is prevention through water safety and diving knowledge. In no water activities is this truer than in SCUBA and breath-hold diving.
- Strauss MB, Miller SS. Stresses in SCUBA and breath- hold diving. Part I: Introduction and physical stresses. Wound Care & Hyperbaric Medicine. 2014; 5(1):16- 28 Available from: http://www.bestpub.com/periodi- cals-and-subscriptions/wchm.html
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