Monitoring Heat Injuries in a Hazmat Environment

A study in 2002 suggested that spending time in an air-conditioned area is the strongest factor in preventing heat-related deaths.¹⁶ The study also recommended prevention measures if heat exposure cannot be avoided: working in the cooler part of the day, plenty of water or nonalcoholic drinks, cool showers, lightweight light-colored clothing, and avoiding direct sunshine.¹⁶

A study in 2013 suggested that heat injuries are a significant threat to the effectiveness of military operations in general and to the youngest (the most inexperienced soldiers) specifically.¹⁷ The study further suggested that it is imperative that leaders be aware of adequate hydration on the one hand and excessive water intake on the other and enforce effective countermeasures against all types of heat injuries.¹⁷

Hyponatremia

Hyponatremia is a possible complication of heat exposure and can be divided into categories according to volume: hypovolemia, euvolemia, and hypervolemia.¹⁸ Hyponatremia is associated with excessive water consumption and excessive sodium losses via sweat during prolonged physical exertion. Symptoms of hyponatremia are related to the severity of sodium deficit and the rate of sodium decline.¹⁸ These symptoms include but are not limited to polydipsia, muscle cramps, headache, altered mental status, coma, and status epilepticus.

Hypovolemic hyponatremia usually will have signs of volume depletion, and sodium levels < 20 mEq/L. Treatment typically consists of volume replenishment with isotonic saline (0.9%), treatment of the underlying condition, and correction of the factors causing hypovolemia.

Euvolemic hyponatremia is typically due to the syndrome of inappropriate antidiuretic hormone (SIADH) and spot urinary sodium is > 20 mEq/L. Correction consists of fluid restriction and correction of the underlying cause.¹⁸

Hypervolemic hyponatremia occurs when the kidneys are overwhelmed and cannot excrete water effectively. It is commonly caused by heart failure, cirrhosis, or renal injury. Treatment consists of correction of the underlying cause, sodium and fluid restriction, and diuretic therapy.¹⁸ In severe cases of hyponatremia, sodium levels usually have decreased rapidly—typically in less than 24 hours.

Hyponatremia is defined as plasma sodium levels < 135 mEq/L, and severe symptoms often occur when the sodium level reaches 120 mEq/L. Treatment must be initiated quickly to avoid cerebral edema, respiratory failure, brain stem herniation, and death. Correction includes hypertonic 3% saline infusion at a rate of 0.5 to 2 mL/kg per hour until symptoms resolve. Two separate studies in 2014 and 2013 suggested that the rate of sodium correction should be 6 to 12 mEq/L in the first 24 hours and 18 mEq/L or less in 48 hours.^19,20

In 2009, Sterns and colleagues suggested that for the treatment of hyponatremia the therapeutic goals for serum sodium concentrations should be 6 to 8 mmol/L in 24 hours, 12 to 14 mmol/L in 48 hours, and 14 to 16 mmol/L in 72 hours.²¹ To exceed these parameters in the correction of hyponatremia risks overcorrection and iatrogenic brain damage.²¹

Care must be taken not to overcorrect sodium levels. In 2013, Sood and colleagues reported that in severe hyponatremia, a combination of 3% saline and 1 to 2 µg of desmopressin every 6 to 8 hours achieved a predictable correction of 3 to 7 mEq/L per hour with no overcorrection.²²

In the spring of 1998, U.S. Army guidelines were revised not only to protect service members from heat injury, but also from hyponatremia caused by excessive sodium loss due to exertion combined with excessive water consumption. There were fewer hospitalizations of soldiers for hyponatremia due to excessive water consumption after the guidelines were implemented.²³ Potential hyponatremia in PPE is even greater due to the strenuous environment. The potential injury due to heat injury on the one hand and hyponatremia on the other demands tailored scrutiny by experienced providers and commanders who can make appropriate changes to the work-rest cycle as needed.

Quick recognition and treatment of exercise-induced hyponatremia is essential to avoid altered mental status, seizures, coma, and death. Current guidelines for the correction of exercise-induced hyponatremia suggest rapid correction of hyponatremia with up to three 100 mL boluses of 3% NaCl in 10-minute intervals. A 2012 case study by Elsaesser and colleagues reported that a severely dehydrated marathon runner with exercise-induced hyponatremic encephalopathy achieved a resolution of symptoms with rapid correction with 100 mL boluses of 3% NaCl spaced in 10-minute intervals. An additional volume of 650 mL of 3% NaCl given over 2 hours for a total volume of 950 mL was needed to resolve the exercise-induced hyponatremia.²⁴ It seems that a 4- to 6-mmol/L increase in serum (Na+) is adequate to reverse most serious clinical manifestations of acute hyponatremia.²¹

When hyponatremia is corrected too rapidly, the brain’s ability to absorb the metabolites is overwhelmed, resulting in osmotic demyelination.²¹ Demyelination was produced in animal models by the rapid induction of hypernatremia and can occur in patients who are overcorrected to a hypernatremic state.²⁰ When individuals with chronic hyponatremia are corrected to normal sodium levels, an initial improvement may occur followed by new and often progressive neurologic deficits.²⁰