Environment-Related Conditions




Heat-Realted Illness



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Definitions and Epidemiology



Heat illnesses exist on a spectrum of seriousness. An athlete need not experience symptoms of mild then moderate then severe heat illness to have heat stroke. The exact epidemiology is poorly defined and varies widely dependent on the study population and environmental conditions.



Definitions, pathogenesis, clinical presentations, and key principles of treatment of heat-related illnesses are summarized in Table 38-1.1–8




Table 38-1. Heat-Related Illnesses




Pathogenesis



Pathogenesis is summarized in Table 38-1.1–8 Risk factors are summarized in Table 38-2. Core body temperature is determined by the balance of heat generation and dissipation. A major contribution to the total thermal load is the generation of heat from exercising muscle. At maximal effort, skeletal muscle generates as much as 20 times the energy at rest. However, muscle energy generation is inefficient and as much as 75% is converted to heat, providing a major thermal load to the body systems. Additional thermal load is provided by the environment itself through radiant heat and convection in the environment. Dissipation of heat from the body to the environment is a combination of convection, radiation, and evaporative loss. But as the ambient temperature and humidity increase, the body becomes dependent on evaporative loss. At 23°C (74°F), 71% of heat dissipation is dependent on evaporative loss versus 100% dependence on evaporative loss at 35°C (95°F).9 Logic dictates that ambient temperatures approaching 35°C, and high relative humidity, will decrease the efficacy of evaporative heat loss. It is noted that although core temperature above 40°C (104°F) is the definition for exertional heat stroke, higher core temperatures have been recorded in asymptomatic elite athletes. Therefore, the elevation of core temperature alone does not indicate heat illness.




Table 38-2. Risk Factor for Heat-Related Illnesses



The body’s response to increasing core temperature is vasodilatation of the skin capillaries to dissipate heat. At the same time, there is vasodilatation of the skeletal muscle to provide oxygen and nutrients to the working muscle. As the skin temperature increases, neural regulation increases sweat loss. This sweat loss is hypotonic or isotonic. Thus, initially there may be no significant electrolyte loss. However, as exercise and sweating continues over longer endurance activities, continued loss of sweat can influence the loss of electrolytes.



Clinical presentation, diagnosis, and treatment are summarized in Table 38-1.




Prevention



Prevention of heat-related illnesses includes providing for a period of acclimatization, modification of activities based on the heat index, and access to electrolyte sports beverages. The process of acclimatization includes physiological adaptations that allow for increased peripheral blood flow, earlier onset of sweating, and greater volume of sweat. Acclimatization occurs over a period of 7 to 14 days where the athlete is gradually introduced to increasing levels and duration of physical activity.



Although weather forecasts may provide some information regarding the ambient temperature, relative humidity, and heat index, it is advisable to perform measurements at the site on a regular basis. Instruments for measurement of environmental conditions vary from the sling psychrometer to more expensive heat stress monitors. Figure 38-1 provides a table for determination of the heat index using temperature and relative humidity. Physical activities for children in hot climate should be modified based on the wet bulb globe temperatures (Table 38-3).3 Similar guidelines for adults can be accessed from American College of Sports Medicine at www.acsm.org.




Figure 38-1



Heat index calculation. (National weather service: www.crh.noaa.gov/jkl/?n=heatindexcalculator)





Table 38-3. American Academy of Pediatrics Recommendations for Restraints on Activities at Different Levels of Heat Stress3



Maintenance of proper hydration before, during, and after physical activities is paramount to preventing dehydration and associated exertional heat illnesses. Loss of 2% of the total body weight to fluid losses increases physiologic strain and has a negative effect on physical and cognitive performance. Detailed information regarding fluid replacement is available through the position statements of American College of Sports Medicine (ACSM) and the National Athletic Trainers’ Association (NATA).4,5



Athletes should be euhydrated prior to beginning practice or competition. First morning urine osmolarity or specific gravity and morning body weight monitoring can be used to evaluate individual hydration status. This information can be used by the athlete during training along with the fluids consumed to develop an individual hydration plan. Urine should not be dark and generally should have a specific gravity lower than 1.020. Four hours prior to competition, the athlete should slowly consume fluids to ensure urine production. The use of hyperhydration has not been shown to prevent dehydration and may increase the need to void during competition.



The quantity of fluid needed during exercise is highly variable between athletes as sweating rates have been reported between 400 mL/h and 1800 mL/h. General starting quantities recommended are 400 to 800 mL per hour, or 200 to 300 mL every 20 minutes, with regular monitoring of body weight and urine color or specific gravity so that the athletes may customize their fluid intake to individual needs.4–8 Larger volumes may be required depending on sport-specific demands. For example, American football players in full gear have been shown to have losses of 8 L per day.



The major loss to sweat is water; however, there are losses of sodium, potassium, and chloride. Carbohydrate intake of 30 to 60 g during longer competition, more than 90 minutes may be beneficial to maintain blood glucose levels as well as promoting absorption and retention of fluids. Beverages should be chilled and flavored to encourage consumption. Commercial sports drinks generally provide approximately 20–30 meq/L of sodium chloride, 2–5 meq/L of potassium chloride, and 60–80 g/L of carbohydrate. It would be appropriate for these nutrients to be supplied in other sources besides a sport drink as well.



Rehydration following exercise is best accomplished with normal meals and beverages. The general guideline is that 1.5 L of fluid are consumed for every 1 kg of body weight loss. If it is impractical to consume a full meal, sodium containing snacks and carbohydrates are beneficial in promoting fluid absorption and retention.




Lightening Injuries



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Definitions and Epidemiology



Lightening causes a vast array of injuries and is one of the top causes of weather-related fatalities. In the US, over 100 fatalities and many more injuries are related to lightening strikes annually.9 Athletes are at risk of lightening injuries because of the fact that many athletic events take place in the afternoons during thunderstorm seasons. Additionally, the flat cleared fields used for practice and competition afford no protection.




Pathogenesis



The electrical current from lightening preferentially travels through the human body because of the high electrolyte-rich medium (i.e., serum, extracellular fluid) that composes the human body. There are five major mechanisms of lightening injury as listed in Table 38-4. Because lightening strike victims do not remain in contact with the electrical source, the body does not remain energized, and therefore can be approached and touched.9




Table 38-4. Mechanisms of Lightening Injury9




Clinical Presentation



After a lightening strike, victims may present with a wide range of injuries dependent on the mechanism of the contact with lightening. Victims in cardiopulmonary arrest may be found unresponsive, apneic, pulseless, and with dilated and fixed pupils. Many of these findings are secondary to the charge of energy in the body, and despite these findings, victims can still be revived. Other injuries include burns, fractures, blast injuries, and tympanic membrane perforations.



The diagnosis is based on the history.




Treatment



Initial on-field treatment begins with ensuring a safe environment for the rescuer. In many circumstances the victim may need to be emergently moved from the site of injury to a safe area for the rescuer, followed by management based on the standard principles of basic and advanced life support by appropriately trained personnel. Data shows that recovery from cardiopulmonary arrest secondary to lightening strikes is favorable, therefore the general triage principles are modified, and the pulseless, apneic patient should be treated first. Table 38-5 lists the steps for prehospital treatment of lightening injuries.




Table 38-5. Pre-Hospital Care for Lightening Strike Victims
Jan 21, 2019 | Posted by in SPORT MEDICINE | Comments Off on Environment-Related Conditions
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