Page 83 - JSOM Summer 2022

Sodium cognizant of the dangers posed by overcorrection. Correction
Sodium (Na ), most commonly found in table salt (NaCl) and of hyponatremia aims to prevent cerebral edema and brain her-
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seawater, is also the primary electrolyte found in most routinely niation. However, rapid overcorrection of hyponatremia risks
used resuscitative fluids, such as normal saline (0.9% NaCl) osmotic demyelination syndrome (ODS), with myelin sheath
and lactated Ringer’s (LR). It is also used as the diluent for ad- destruction resulting in severe and sometimes irreversible brain
ministration of medications, e.g., tranexamic acid via “piggy- damage. 16–20 ODS is commonly manifested by gait disturbances,
back.” Normal range for sodium is generally 135–145mEq/L, seizures, and paresis. Although ODS is more common in over-
with hyponatremia defined as below 135mEq/L and hyperna- correction of chronic hyponatremia, it has been documented
tremia as above 145mEq/L. 6 to occur in treatment of acute hyponatremia. 6,18–20 Even most
severe hyponatremia symptoms, to include seizure, may resolve
Hyponatremia (Low Sodium) after a 4–6mEq/L rise within the first 24 hours of treatment. 1,5,6
Hyponatremia (Na <135mEq/L) is the most common electro- The 24-hour correction targets range from 6–12mEq/L, with
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lyte disorder, found in up to 30% of acutely ill patients and of- caution for smaller and slower rates for chronic hyponatre-
ten related to the intense physical nature of military training. 6–11 mia. In mildly hyponatremic patients, values can be rechecked
1,5
Hyponatremia can be classified as hyperosmolar (increased every 6–12 hours, while more severe patients should be tested
fluid volume from ICF to ECF without enough commensurate every 2–4 hours to reevaluate interventions.
increase in sodium), iso-smolar (a displacement of ECF fluid by
high protein or lipid levels), or hypoosmolar (impaired water Hypernatremia (Excess Sodium)
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excretion and increased reabsorption with significant intersti- Hypernatremia (Na > 145mEq/L) describes a hyper-osmolar
tial space redistribution). In most active-duty persons in ex- state with excess sodium in the ECF. Hypernatremia can be
treme environmental conditions, hyperosmolar hyponatremia classified as hypervolemic (excessive sodium retention without
will be the most common presentation, resulting from im- commensurate water retention), isovolemic (loss of free wa-
proper hydration with electrolyte-poor fluids (instead of sports ter), or hypovolemic (decreased fluid volume from ICF to ECF
drinks or oral rehydration salts) during intense physical activ- without excretion of sodium). In military patients, hypernatre-
ity. 6,8,9,12,13 This is commonly referred to as “water intoxication” mia could stem from excessive water loss in acute illness (fever,
or “exercise-associated hyponatremia.” 6,8,9,12,13 In addition to diarrhea), or low free water intake (due to nonavailability or
vague symptoms common to electrolyte imbalances, presenta- poor hydration). 2–4,21,22 Isolated high sodium intake occurs less
tions specifically concerning for severe hyponatremia include frequently. Additionally, environmental heat can trigger ex-
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seizures, presenting initially or in the course of management. cessive water loss relative to sodium, to include thermal burn
6,8
Conversely, some patients may be asymptomatic. Monitoring injuries. 14,23
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for hyponatremia should be considered in burn patients due to
loss of extracellular sodium caused by increased cellular per- Hypernatremia symptoms may present vaguely, but more
meability. This should be managed as per Joint Trauma System suggestive symptoms include excessive thirst and/or excessive
(JTS) clinical practice guidelines (CPG), however they are not urination (polyuria). 2,22 Neurologic symptoms occur as brain
mentioned in JTS CPGs for prolonged care. 14 cells shrink secondary to intracellular fluid shifts, which can
trigger cerebral vascular rupture and intracranial hemorrhage,
Severity may be labeled as mild (130–134mEq/L), moderate resulting in severe headache syndromes. Hypovolemic hy-
2,5
(120–129mEq/L) or severe (<120mEq/L), but these cut-offs pernatremia present with extreme thirst complaints and an
are not universal, and some equate symptomatic hyponatre- overall “dry” appearance, including abnormal skin turgor. 3,24
mia as severe hyponatremia. Others propose hyponatremia is Conversely, patients may be completely asymptomatic. 3,25
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only clinically significant below 130mEq/L, and these patients
constitute only about 10% of all hyponatremia cases. 1,5,6,15 Severity classifications are not universal, although concentra-
Once established, initial hyponatremia treatment balances tions greater than 160mEq/L generally establishes a “severe”
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acuity, laboratory values and clinical findings. Acute hypona- diagnosis. Treatment of hypernatremia balances symptom se-
tremia is defined as known or suspected onset less than 48 verity with laboratory values and rates of correction. While
hours prior to presentation, likely in military cases of water overall volume replacement is generally the goal of treatment,
intoxication. 6,16 Less likely cases of chronic hyponatremia correction should be pursued over a 24- to 48-hour period
present 48 hours after onset. 17,18 to avoid cerebral edema from rapid water movement into de-
3,5
hydrated brain cells. Despite variation in correction rates,
Acute hyponatremia should be suspected in most military set- most agree serum sodium should not be lowered more than
tings, with a treatment focus on free water restriction and so- 8–12mEq/L within a 24-hour period. 2,3,5,22,26 Alert patients can
dium replacement. Hyponatremia in the alert patient can be be encouraged to drink free water, while those unable to take
treated with oral replacement therapy in the form of rehydra- oral fluids can be treated with hypotonic IV fluids such as dex-
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tion salts or commercial sports drinks, although intravenous trose 5% (containing 0mEq/L of Na ), 0.45% NaCl (77mEq/L
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(IV) fluid replacement can be concurrently utilized if avail- Na ), or LR (130mEq/L Na ) for likely hypovolemia. 2,5,22 Free
able. 1,5,6 If the patient cannot tolerate oral fluids, IV therapy – water via nasogastric tube may be considered in the uncon-
normally in the form of saline – should be used. scious or intubated patient. Correction rates should be deliber-
ate and controlled with serial lab draws, but no consensus on
There is broad support for the use of hypertonic saline (3% frequency exists, requiring telemedicine consult in prolonged
NaCl) given over 10 minutes when hyponatremia manifests field care.
with seizures. 1,5,6,13 This is generally recommended as a one-time
IV treatment of 100cc, although some argue for repeat dosing Potassium
up to three times if seizures persist. 5,6,13 While correcting se- Potassium (K ) is the most abundant intracellular cation,
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rum sodium should be aggressively pursued, medics must be with over 75% of body stores found within skeletal muscle
Prehospital Electrolyte Care | 81