Another wave smacks the weather bow, sending spray rattling onto the coach roof and over the dodger. A second later, you poke your head out of the companionway hatch to check with the on-watch crew. “How’s it going, Sandy?” you shout toward the huddled figure sitting in the cold moonlight.
“Murmph” comes the reply with a slight nod of the sou’wester.
“Great!” you agree and slam the hatch just in time to avoid the next shot of spray. Aside from a little seasickness she’s been a fine crewmember. Besides, who could complain about the wet ride when you’re making 9 knots on a beam reach?
Unfortunately, by dawn your fine crewmember has been reduced to a shivering mass, mumbling incoherently into the open collar of her foul-weather gear. She noticed, but did not react to, the fast-moving ferry that passed 80 yards off your stern an hour ago. She did not care that the wind had backed a bit, carrying you 20° off course. She had been unable to perform even the simple task of opening the snap hook on her harness, which would have allowed her to move into the shelter of the dodger.
The term for Sandy’s problem is mild sub-acute hypothermia, the type that quietly creeps up on you because you allow yourself or someone else to be just a little cold for a long time. The effort to stay warm over hours or days progressively depletes the body’s available energy stores. The shell/core effect, a normal response to being cold, shunts blood from the skin and extremities into the body core. As much as three liters of blood can be displaced in this manner. Over time, the kidneys react to the increased blood volume in the core by removing fluid from circulation. The result is hypothermia and dehydration. The body runs out of fuel and loses the ability to generate and distribute heat. Mild hypothermia
As core temperature drops below 96° F, the first effects are subtle mental status changes and a loss of judgment and common sense as the brain is deprived of oxygen and energy and cools below the level of normal function. In the very early stages, a normally happy and cooperative person may become grumpy and irritable. A vociferous and contrary crewmember may become quiet and complacent (which is particularly dangerous since you may be tempted to leave him that way). A hypothermic person doesn’t complain much, even about being cold. Unless you’re really paying attention, it’s easy for the problem to go unnoticed until you have a major medical emergency on your hands.
What Sandy needs immediately is shelter, food and fluids while she is still awake enough to swallow safely and cooperate with treatment. Her shivering is the most efficient method of body-core rewarming, generating up to six times the heat production of her resting metabolic rate. The process just needs to be adequately fueled, and the heat generated needs to be trapped near her body. It may seem natural to want to add external heat, but putting heat packs inside her clothing, or using the ever-popular skin to skin contact can actually inhibit shivering and delay rewarming.
The most important food is simple sugar, which is easily absorbed by the gut and quickly available for metabolism and heat production. Rehydration is equally critical. As Sandy’s body rewarms, blood will return to the skin, resulting in lower blood volume in the body core — a form of shock.
The temperature of the food is much less important than the sugar content. Imagine pouring a half a pound of warm tea into 130 pounds of cold body. You will not transfer much heat energy. However, the three tablespoons of honey you put into the tea may save the crewmember’s life by fueling internal heat production. Trying to warm Sandy by getting her up onto her feet and exercising without first feeding and hydrating her could be disastrous. She could suffer what is sometimes termed circum-rescue collapse, due to shock, depleted energy stores or cardiac arrhythmia. Severe hypothermia
In field use, the term severe hypothermia defines a patient who can no longer cooperate with treatment. This is where Sandy will be headed if you don’t warm her up right now! Body-core temperature will dropy´below 90° F, and the patient will exhibit a reduced level of consciousness. Giving anything by mouth will risk choking or aspiration of the food or fluid into the lungs. Attempting to hoist the patient vertically onto a boat or helicopter can result in a precipitous drop in blood pressure, resulting in sudden death. Severe hypothermia is a complex medical problem best managed in a well-equipped hospital ashore. People have been successfully resuscitated from body-core temperatures in the low 70s.
The ideal field treatment for severe hypothermia is careful packaging to prevent further heat loss, gentle handling in the horizontal position, and expeditious evacuation to a major medical facility. The use of rescue breathing is safe and may help, but the application of cardiopulmonary resuscitation (CPR) may be harmful. The patient’s heart may still be functioning, although too slowly or softly for you to detect. Chest compressions or rough handling can throw the cold heart into ventricular fibrillation, from which the patient is unlikely to recover. In hypothermia, CPR is not indicated unless you are absolutely certain that the heart has stopped. Rewarming
Offshore, ideal treatments and rapid evacuation are seldom possible. You may find that your only option is to attempt the controlled rewarming of a severe hypothermic onboard. It has been done successfully in far from ideal circumstances but too infrequently to have any trained experts on the subject.
Picture a man overboard at dusk. You spend all night searching, finally locating him at dawn, floating head-up but apparently lifeless in his PFD. You haul him gently aboard, remembering to keep him horizontal. His body-core temperature measures 88° F. This man is probably alive and salvageable, but you are 800 miles from the nearest hospital. Now what?
A review of recent studies suggests that the best treatment would involve removal of wet clothing, packaging in dry insulation and a vapor barrier (plastic tarp) to prevent evaporative heat loss. Gradual external rewarming with heat packs and hot water bottles should be initiated at the rate of 2° to 3° per hour. A low-reading clinical thermometer is helpful in this process.
Rescue breathing, in addition to increasing oxygen in the blood, will add some heat to the area of the brain-stem, possibly improving the patient’s own thermo-regulation. If the patient warms enough to begin to shiver, give sugar and fluids liberally if the patient can swallow without aspirating. Sugar and warm saline can also be instilled rectally with an enema or by way of a warmed IV if you have that capability (D5NS warmed to 108° in the bag).
Several studies have highlighted the technique of warming only the extremities with warm water or heat packs. This allows blood circulating through the extremity to be warmed and returned to the core circulation. It avoids the dramatic vasodilatation and shock that would occur if the whole patient were immersed in warm water at once. Aquarius Medical Corporation of Scottsdale, Ariz., has developed a device that enhances this technique by applying a small vacuum chamber to the hand and forearm. This engorges blood vessels in the extremity for more efficient heat transfer from the integral heat pack to the blood. It shows considerable promise as a method of safe rewarming, and if tests continue to be successful, it may someday be a field treatment option for rescue services, such as the Coast Guard.
As always, however, prevention is preferable to expensive devices and heroic resuscitation. If you stay cold long enough, you will become hypothermic. The normal cold response of shell/core effect and shivering may be no problem while running between buildings in town. But at sea, feeling cold is a problem that should be corrected immediately. Make the extra effort to stay well-insulated and dry. Don’t be afraid of a diet higher in sugar, carbohydrates and fat, which will provide both the fast-burning glucose that you need when chilled and the longer-burning energy from more complex foods. It can require up to 6,000 calories a day to stay warm in cold weather. Cold-water drowning
The treatment of severe hypothermia differs considerably from the recommended field treatment for cold-water drowning. A victim who has been under the water for more than a few minutes will be in cardiac arrest due to suffocation. The incidental and rapid onset of hypothermia due to cold-water immersion reduces the oxygen demand of body tissues, providing a brief period of protection from brain death. If you rescue someone who has been under cold water for less than an hour, aggressive resuscitation with CPR, external rewarming and emergency evacuation is recommended. Depletion of energy stores and dehydration are not an immediate concern of field treatment.
You should be aware that the chances for survival of a drowning victim in cardiac arrest are near zero without immediate access to advanced life support and hospital care. Offshore, such a resuscitation should be attempted only if it does not place the boat and surviving crew at risk. If a viable pulse has not been restored within one hour, there is no chance of success and the effort should be discontinued.
Jeff Isaac is a practicing physician’s assistant, licensed mariner and an instructor of wilderness and marine medicine with Wilderness Medical Associates and The Ocean Navigator School of Seamanship.