Hiking To Hyperpyrexia
Heat Illness In The High Desert
by Jonathan Edwards, RN
Summer has arrived in the high desert with temperatures above 100 degrees by mid-day. The "black flag" is raised at the Marine Corps Base in Twenty-nine Palms when it gets too hot for extended fieldwork, however in this time of war, training must continue. Marines are instructed to drink plenty of water and eat their sodium-rich MREs (Meals Ready-to-Eat). Still,
many "fall-out" of training and report to their Navy Hospital Corpsmen at Battalion Aid Stations in the field. Most suffer only mild symptoms and are kept in the field. Others require Humvee or helicopter transport to Robert E. Bush Naval Hospital for treatment.
Marines treated at the hospital ER for heat illness usually do not require invasive cooling measures. Evaporation is the method of choice as each 1.7ml of water evaporating on the skin removes 1 kcal of heat energy. Most suffer minor illnesses such as cramps, syncope and exhaustion and completely recover in the ER. Hyponatremia (serum sodium levels below 130 mmol/L) and fluid volume depletion from profuse sweating cause the cramping. The most common muscle contractions occur in the legs and resolve with rest, removal from heat, oral hydration and stretching.
Many of the heat syncope cases occur while standing watch or inspection in the heat. The stress of the heat aggravates peripheral pooling of blood by dilating cutaneous vessels. Most cases spontaneously resolve. Treatment leans towards the syncopal episode unless core body temperature indicates otherwise.
Core body temperature (done rectally: sorry, Marines!) determines treatment for the final classes of heat illness. The difference between heat exhaustion and heat stoke is not so much temperature but rather the presence of clinically significant tissue injury. In both cases, core temperature must be reduced below 102.2 degrees first by increasing evaporation with fans, removal of clothing and moving to a cool environment, then as needed by cool saline bags to the groin and axilla, cold water enemas, nasogastric lavage and finally peritoneal lavage. Brain damage may occur at 107 degrees.
Most cases of heat exhaustion occur below 102.2 and require external cooling and gradual rehydration. Labs should include serum electrolytes. If hyponatremic, rehydration should include sodium to prevent complications. A study of hikers suffering from exertional heat illness in the Grand Canyon National Park has shown that the hyponatremic patients were hyper-hydrated. Water intoxication occurs when cerebral edema starts. Nausea and vomiting seen in all of hyponatremic hikers just makes the situation worse. Recently the Army has reported its first known death of a trainee as a result of acute water intoxication.
The rise in the use of metabolic-enhancing herbal products has been noted in many of the heat illness cases at Robert E. Bush Naval Hospital. Controlled studies for the relationship between ephedra-containing herbs and heat illness are not readily available. All Marines are advised not to use these herbal products during the training periods. Nurses play a key role
in the education of the Marines who do use ephedra and report to the ER for heat illnesses.
Heat stroke occurs in two classes: those that have a preexisting condition that impairs their thermoregulation and those active individuals that experience endogenous heat loads. The second class, which is complicated by acute rhabdomyolysis, will be the focus here. Classically, the skin is flushed, warm and dry, but prehospital interventions may have masked those findings. The brain, liver, kidneys and muscle groups are all affected. DIC may occur secondary to the rhabdomyolosis. Encephalopathy in these patients may cause anything from confusion to coma. Intubation may also be required for pulmonary edema. So much is going on with a true heat stroke patient that it requires an article itself. The key point to remember is not to delay cooling for the diagnostic evaluation, and both should occur simultaneously.
As always, prevention is the best cure for heat illness. As nurses, we have an excellent opportunity to educate our patients on the dangers of extreme summer heat. Remind them to drink plenty of fluid (2 - 4 glasses an hour) while active in the heat unless they have a fluid restricted medical condition. For most patients a balanced diet will suffice, however, additional salt in the diet may be required for summer-time athletes, and acclimatized outdoor workers. Wear lightweight clothing and protect the skin from the sun as sunburn impairs the cooling ability of the skin. Finally, get the word out to restrict activity in the middle of the day when the stress of the heat and sun are worst, it'll cool off . . . eventually.